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Thursday, December 16, 2010

flood mgmt

http://wrmin.nic.in/writereaddata/linkimages/minutes716122035.pdf

BIHAR URBAN DEV

BIHAR WRD CONTACTS

Sl Office Address/VPN No. Name of Officer Code Telephone No. Mobile No.
􀀀


1 Hon'ble Minister, WRD
9473197001
Sri Vijay Kumar
Choudhary
0612 2217696
2217331
i Private Secretary to
Minister
9473197002
Sri
ii OSD to Minister
9473197002
Sri Md. Abdul
Mannan
0612 2217696
2217331
943146096
1 Principal Secretary
9473197003
Sri Ajay Nayak 0612 2217377
2217948
2217948 (Fax)
2545003 (Res)
2213825 (Res)
9431016121
i Private Secretary to
Principal Secretary,
W.R.D.
Sri Nandlal
Chaudhury
0612 2217377 9905409726
1 Engineer-in-Chief (North)
9473197005
Sri Rajeshwar
Dayal
0612 2217040
2660750(Res)
9431480416
9430518554
2 Engineer-in-Chief
(Middle)
9473197004
Sri Devi Rajak 0612 2217183 9431877570
3 Special Secretary Sri 0612 2217143
4 Joint Secretary Sri Vijay Narayan
Jha
0612 2217797 9431456523
5 Joint Secretary Sri Harihar Prasad
Singh
0612 2217727
2296032 (Res)
9430085883
6 Joint Secretary
(Management)
Sri Ashok Kumar
Prasad
0612 2217382 9430061279
7 Joint Secretary (Budget) Sri Ajit Kumar
Samaiyar
0612 2215212 9431453768
Sl Office Address/VPN No. Name of Officer Code Telephone No. Mobile No.
8 Law Officer Sri Surendra Prasad
Sinha
9331410967
9 Dy. Secretary (Vigilance) Sri Krishna Kumar
Prasad
0612 2221727 9431462249
10 Dy. Secretary Sri Shashi Bhushan
Tiwary
9430567359
11 Dy. Secretary-2
(Management)
Sri Arjun Prasad
Sinha
0612 2217383
2283983 (Res)
9431427316
12 Dy. Secretary-1
(Management)
Sri Jiwaneshwar
Rajak
9431030543
13 Director Land Acquisition
& Rehabilitation
Sri Arun Kumar
Verma
0612 2217604 9304976969
14 Under Secretary
(Management)
Sri Ashok Kumar
Ranjan
9431645622
15 Under Secretary
(Management)
Sri Ravindra Kumar
Shanker
0612 2217241
3121806 (Res)
9430954667
16 Under Secretary
(Management)
Sri Anjani Kumar
Singh
0612 2295154 (Res) 9431074263
17 Under Secretary
(Management)
Sri Satish Kumar 9905092215
18 Under Secretary (CADA) Sri Md. Sohail 0612 2217887 9334035370
19 Under Secretary
(Accounts)
Sri Vinod Kumar
Verma
9934003904
20 Under Secretary
(Headquarter)
Sri Shivnandan
Prasad
0612 225468 (Res) 9973904524
21 Director, Purchase Store
& Material Management
9473197010
Sri Vimalesh
Kumar Jha
0612 2223712 9955604085
22 Public Relation Officer Sri Shubh Chandra
Jha
9431647284
  - !#" $$&% $(' " $*) + ,-$&%/.0,-1&%2$('&-3 " .4$ "
Sl Office Address/VPN No. Name of Officer Code Telephone No. Mobile No.
1 C.E., Planning And
Monitoring Patna
9473197006
Sri Hari Narayan 0612 2215345
2217649 (Fax)
9470833026
9431364301
2 S.E., Planning And
Monitoring Cir-1 Patna
Sri Indu
Kumar
0612 2217258
2217649 (Fax)
9431449143
Bhushan
i E.E., Planning And
Monitoring Div-1 Patna
(Computer Cell)
Sri Bipin Bihari
Mishra
0612 2235241
2217649 (Fax)
9430033143
ii E.E., Planning And
Monitoring Div-2 Patna
Sri
iii E.E., Planning And
Monitoring Div-3 Patna
(M.I.S. Cell)
Sri Bipin Bihari
Mishra
9430061277
iv E.E., Planning And
Monitoring Div-4 Patna
(Computer Cell)
Sri Awadhesh
Kumar Jha
9973937384
v Liaison Engineer, New
Delhi
Sri Padma Kant Jha 011
26850296 (Fax)
26169450
9868631245
vi Liaison Officer,
Kathmandu, Nepal
Sri A.K. Sinha 00977 9721345001
14411278
14415792 (Fax)
9822404547
3 S.E., Planning And
Monitoring Cir-2 Patna
9473197007
Sri Birendra
Kumar Sinha
0612 2217826 9431649623
i E.E., Planning And
Monitoring Div-5 Patna
Sri Prem Prakash
Singh
9470833063
ii E.E., Planning And
Monitoring Div-6 Patna
Sri Vijay Kr.
Shrivastava
9431642469
iii E.E., Planning And
Monitoring Div-7 Patna
Sri Birendra Kumar
Sinha
9431649623
Sl Office Address/VPN No. Name of Officer Code Telephone No. Mobile No.
iv E.E., Planning And
Monitoring Div-8 Patna
Sri Vijay Kumar 9934704436
4
Monitoring Cir-3 Patna
9473197008
Sri Hari Narayan 0612 2217910 9431364301
9470833026
S.E., Planning And
i E.E., Planning And
Monitoring Div-13 Patna
Sri Anil Kumar 9470005087
ii E.E., Planning And
Monitoring Div-14 Patna
Sri Ram Padarath
Prasad Sharma
9430051966
iii E.E., Planning And
Monitoring Div-15 Patna
Sri Kumar Birendra 9835046264
iv E.E., Planning And
Monitoring Div-16 Patna
Sri Ram Yash Singh 9430213057
5 S.E., Planning And
Monitoring Circle-4
Patna
Sri B.K. Verma 0612 2217210 9234912426
i E.E., Planning & Project
Preparation Division,
Anishabad
Sri Surendra 9430888997
ii E.E., Planning & Project
Preparation Division-18,
Patna
iii E.E., Planning & Project
Preparation Division-20,
Patna
Sri Rajbansh
Chaudhury
943222223
6 S.E, Flood Control
Planning & Monitoring
Circle Patna
9473197012
Sri Indu
Kumar
0612 2217309
2215850 (Fax)
9431449143
Bhushan
Sl Office Address/VPN No. Name of Officer Code Telephone No. Mobile No.
i E.E, Flood Control Plan.
& Monitoring Div-1 Patna
9473197014
Sri Randhir Kumar
Sinha
0612 9431619567
ii E.E, Flood Control Plan.
& Monitoring Div-2 Patna
9473197015
Sri Baiju Prasad
Singh
0612 2206669 (Res) 9430001590
iii E.E, Flood Control Plan.
& Monitoring Div-3 Patna
9473197016
Sri Vijay Kumar
Sinha
iv E.E, Flood Control Plan.
& Monitoring Div-4 Patna
9473197017
Sri Prakash
Chandra
0612 2217146 (Res) 9431001230
7 S.E. Flying Squad Circle
Patna
9473197011
Sri Uday Shankar
Prasad
0612 2217250 9431435726
i T.A. Flying Squad Circle
Patna
Sri M. Hasan 9471048638
ii E.E. Flying Squad Div-1
Patna
Sri Din Bandhu Pd.
Verma
9431646892
iii E.E. Flying Squad Div-2
Patna
Sri Jawahar Singh 9431877892
iv E.E. Flying Squad Div-7
Patna
Sri Ram Nandan
Prasad Chaudhary
9430293408
v E.E. Flying Squad Div-8
Patna
Sri Bir Bahadur
Singh
9431621546
8 S.E, Irrigation
Monitoring Circle Patna
Sri Ashok Kumar
Prasad
0612 2204114 9430061279
9 S.E., F.M.I.S.
9473197009
Sri A. K.
Samaiyar
0612 2256999
2243691 (Res)
9431453768

interlinking of rivers in bihar

i.        Kosi-Mechi Link Canal :

The 112.55 km. long canal will mainly pass through the "Terai" area in Nepal. It will start from the left side of Chatra barrage and fall into Mechi river after crossing over three small rivers Bakra, Ratuwa and Kankai through syphon aqueduct. The canal's receiving capacity will be 1407.80 cubic metre per second (cumec) and discharge rate will be 97.64 cumec. The canal would provide irrigational facility to 4.74 lakh hectares of land. Out of this, 1.75 lakh hectares shall be irrigated in Nepal and 2.99 lakh hectares in Bihar. Besides this, provision of 24 MCM water has been made for domestic and industrial requirements of the towns falling in between. As proposed, it would divert 883 MCM water at the rate of 28 cumec to Mechi river for increasing the water in Mahananda river. The canal would also provide navigational facility from Chatra to Ganga via Mechi and Mahananda rivers.

ii.      Kosi-Ghaghara Link Canal :

The 428.76 km long canal, which will start from the right side of the Chatra barrage, will fall in Gaura river, a tributary of Chaghara river, in Uttar Pradesh after crossing over Tiljuga, Khanro, Bagmati and Lalbakkeya rivers in Nepal and Gandak river in Bihar. The canal's receiving capacity will be 1021 cumecs while it will discharge 67 cumec in Gaura river. The total benefited area through this link canals is 10.58 lakh hectares. Out of this, 1.74 lakh hectare area shall be of Udaipur, Saptari, Mahoitari, Sarlahi and Bara districts in Nepal and 8.17 lakh hectare and 0.67 lakh hectare area of North Bihar and Uttar Pradesh, respectively. The canal would also provide 48 MCM water for domestic and industrial requirements of the towns on its way.

iii.    Sone dam-Southern tributaries of Ganga Link Canal :

The 339 km long canal will begin from the right side of the proposed dam across Sone river near Kadwan in Jharkhand. The canal would fall into Badua river after crossing over Morhar, Lilajan, Dharmajayi, Sakri and Kiul rivers. Two hydal projects of 3.5 MW and 1.5 MW capacities would be finalised near the junction of Sakri river. The total benefited area through this canal will be 3.07 lakh hectares in the districts of Patna, Nalanda, Gaya, Jehanabad, Munger, Bhagalpur, Nawada, Jamui and Aurangabad of Bihar and Palamu district of Jharkhand.

iv.    Chunar-Sone Barrage Link Canal :

The 149.10 km long canal will start from the right side of Ganga river near Chunar Tehsil of Mirzapur district in UP. It will fall into Sone river near Indrapuri barrage in Rohtas district. There would be a lift of 38.8 meters, 16.10 meters and 4.4 meters at three different places on route. In addition to taking over substantial command areas of Western Sone High Level and low level canals, this link canal will provide irrigation in 66,793 hectares of new area in Mirzapur, Varanasi and Gazipur districts of UP and Bhabhua, Rohtas, Buxar and Bhojpur districts of Bihar.

v.      Brahmaputra - Ganga (Manas- Sankosh- Teesta- Ganga Link Canal :

It envisages Construction of 457 km long link canal and a dam on river Manas and a dam and a barrage on river Sankosh in Bhutan. There would be 7 numbers of falls on the canal, out of which 4 nos. of falls are located in Bihar. A total hydro power to the tune of 718 MW will be generated on these falls, out of which 393 MW will be generated on falls located in Bihar. The link canal will provide irrigation benefits to an area of 6.53 lack ha. out of which 2.64 lack ha. are in Bihar.

vi.    Gandak-Ganga Canal :


The 639 km long canal, which would start from the right side of the proposed dam across Gandak river in Nepal, will fall in Ganga river near Mustafabad in Rai Bareli district of Uttar Pradesh. It will run through Nepal and various districts of Uttar Pradesh. Though this canal would not cross through Bihar it would make a big impact on the State by taming the flood waters of Gandak. There will be no irrigational facility in Bihar from this canal.

Tuesday, November 30, 2010

buidco projects

Projects
Projects in Hand :

S.NoLocationProjectFund SourceApproved Cost (Rs. In Lakh)
01PhulwarishariffPhulwarishariff Water SupplyUIG2,470.26
02KhagaulKhagaul Water SupplyUIG1,315.43
03DanapurDanapur Water SupplyUIG6,896.45
04PatnaDevelopement of 3 Parks in PatnaGovt.of Bihar220.00
05RajgirRajgir SewerageUIG7,767.00
06HajipurHajipur SewerageNGRBA11,362.00
07BuxarBuxar sewerageNGRBA6,411.00
08Bodh GayaBodh Gaya SewerageUIG9,594.34
09MungerMunger sewerageNGRBA18,789.00
10BakhtiyarpurRoad & Drainage WorkUIDSSMT511.00
11BegusaraiBegusarai sewerageNGRBA6,933.00
12Bodh GayaBodh-Gaya Water SupplyUIG3,355.72
13Khagaul,Danapur,PhulwarishariffSolid Waste ManagementUIG1,155.81
14AraAra Solid Waste ManagementUIDSSMT983.99
15MuzaffarpurMuzaffarpur Water SupplyUIDSSMT9,872.25
16MurliganjRoad With DrainsUIDSSMT1,144.00

Thursday, November 18, 2010

BSHPC PROJECTS

http://www.bshpcltd.com/ps.HTM

MEIL news

Megha Engineering & Infrastructure has bagged an order worth Rs. 239 million from Maharashtra State Power Generation Company for a 2 MW grid connected solar PV power project based on thin film technology. The scope of work includes design, engineering, manufacturing, supply and erection of the unit at Chandrapur Super Thermal Power campus. The project is expected to be completed within 9 months.

Tuesday, November 16, 2010

Design Characteristics for a Municipal Wastewater Treatment Plant Calculation

Design Characteristics for a Municipal Wastewater Treatment Plant Calculation

STP TECHNOLOGIES

TECHNOLOGICAL OPTIONS FOR TREATMENT OF MUNICIPAL WASTEWATER
There are a large variety of treatment techniques designed to remove pollutants from wastewater. The objective of wastewater treatment is to separate wastes from water. In one sense, all wastewater treatment processes can be considered separation processes. There are physical, chemical and biological separation processes. Sedimentation and screening are examples of physical processes. Coagulation, ion exchange and pH adjustment are typical chemical processes, while various forms of biological digestion belong to the category of biological processes. In the biological processes living organisms, while in the physical and chemical processes physical and chemical properties are utilized for waste separation metabolizes organic wastes.
Major Elements of Wastewater Management Systems and Associated Tasks
Elements of Wastewater Management
Associated Tasks
Source of generation
Quantification of wastewater, evaluation of techniques of wastewater reduction and determination of wastewater characteristics
Source control
Design of onsite systems to provide partial treatment of the wastewater
Collection
Design of sewers used to remove wastewater from the various sources of generation
Transmission and pumping
Design of large sewers used to transport wastewater to treatment facilities
Treatment
Selection, analysis and design of treatment operations and processes to meet specified treatment objectives related to the removal of wastewater contaminants of concern
Disposal and reuse
Design of facilities used for the disposal and reuse of treated effluent in the aquatic and land environment, and the disposal and reuse of sludge on land

Treatment of sewage is accomplished by adopting various treatment schemes, each incorporating one or several different treatment units such as Screens, Grit chambers, Plain Sedimentation, Chemical Precipitation, Trickling Filter, Activated Sludge, Anaerobic digestion, Up flow Anaerobic Sludge Blanket (UASB) reactor, Waste Stabilization Pond and Maturation Pond.
CPCB has carried out a series of studies on performance of Sewage Treatment Plants (STPs) in different parts of the country to evaluate their performance. The findings revealed that a majority of the treatment plants are based on Primary Settling followed by Activated Sludge Process (PS+ASP) technology (with anaerobic digesters for sludge), Oxidation Pond or Waste Stabilization Pond (OP or WSP) technology and UASB followed by Polishing Pond (UASB+PP) technology. Findings have also revealed that most of the STPs are not being utilized to the full capacity due to various reasons.
It has been found that low capital and low operational cost sewage treatment method such as Waste Stabilization Ponds (OP or WSP) technology and low operational cost sewage treatment method such as (UASB+PP) technology are quite effective in BOD removal as well as Fecal Coliform (FC) removal. Overall efficiency of STPs based on these low cost technologies in terms of BOD and FC removal can be further improved if effluent suspended solids (SS) are controlled by improvement in final outlet structures. These technologies are best suited for towns and small cities.
In such situations where sewage of a large city is discharged into a receiving water body having insufficient dilution and/or requires to be maintained at high bacteriological quality, the conventional sewage treatment schemes based on (PS+ASP) technology need augmentation with tertiary treatment units for further removal of BOD and FC . Low cost tertiary treatment method such as series of Polishing Ponds is the best option for tertiary treatment. However if land availability is a constraint then other tertiary treatment options such as coagulant aided flocculation+tertiary sedimentation (TS), TS+Filtration, TS+Chlorination may be adopted.
Conventional wastewater treatment
Conventional wastewater treatment consists of pretreatment, primary sedimentation, secondary biological treatment, secondary sedimentation and chlorination before being discharge. Historically, biological techniques have been widely utilized since they are generally economical to build and operate as composed to physico-chemical techniques. Moreover, they are more efficient as natural means of treatment are utilized in optimized conditions.
Treatment systems could be classified according to the degree of pollutant removal into pretreatment, primary, secondary, tertiary and ultimate treatment. They could be classified according to the means of pollutant removal into biological or physico-chemical treatment. Essentially, pretreatment and primary treatment involves screening and grit removal, equalization and the removal of high concentration of solids that might decrease the efficiency of subsequent treatment processes. The term secondary treatment is commonly used to describe any of the following biological processes: activated sludge, extended aeration, trickling filters, aerobic and anaerobic lagoons and anaerobic and facultative (mixed) ponds. In the typical aerobic process the removal of oxygen-demanding dissolved organics through microorganisms takes place.
http://www.cpcb.nic.in/oldwebsite/News%20Letters/Latest/image/pic-page24-0205.jpg

In an activated sludge process, the incoming waste effluent is continuously fed into biological reactor (aeration tank) in which bacterial mass, in a desired concentration, is maintained in suspension. Organic matter in the incoming effluent is partially oxidized by the bacterial mass and partially converted to excess sludge. The sludge in the out-flow of aeration tank is then separated in a clarifier. This sludge is continuously recycled back to the aeration tanks, however, a portion of sludge (excess sludge) is sent to the sludge beds for drying and in this way a desired concentration is maintained. The conventional type activated sludge process could remove as much as 85% of the BOD load.
The extended aeration is essentially similar to the activated sludge process, but yields less sludge for disposal. Through sufficient retention time, biological solids are oxidized, thus minimizing resultant sludge.
In aerobic lagoons, oxygen is usually supplied through surface aerators that keep solids in suspension, allowing for about 50 to 60 percent BOD removal.
Trickling filters are packed with rocks, on the surface of which bacteria are allowed to grow, while wastewater is trickled over through nozzles, allowing for consumption of dissolved organics by bacteria. The relative effectiveness in BOD removal of trickling filters is relatively low compared to other secondary treatment systems.
Tertiary treatment aims at further removal of BOD, suspended solids etc., as well as colour, nitrates, phosphates and other pollutants not adequately removed by secondary treatment processes. Tertiary treatment could involve carbon adsorption, coagulation and sedimentation, ion exchange, membrane filtration, and other processes.
Treatment Processes and Purpose of each Process in a Treatment System
Principal purposes of Unit Processes
Unit Processes
Grit Removal
Grit Chambers
Removal or grinding of coarse solids
Bar Screens
Odour control
Perchlorination, Ozonation
Gross solids-liquid suspension, BOD reduction
Plain primary settling
Gross removal of soluble BOD and COD from raw wastewater
Biological treatment
Removal of oxidized particulates and biological solids
Plain secondary settling
Decomposition or stabilization of organic solids, conditioning of sludge for dewatering
Anaerobic sludge digestion
Ultimate sludge disposal
Sludge drying beds, land disposal, land reclamation
Removal of colloidal solids and turbidity from wastewater
Chemical treatment, sedimentation, mixed-media filtration
Phosphates removal
Chemical coagulation, flocculation and settling
Nitrate removal
Ammonia stripping
Removal of suspended and colloidal materials
Mixed-media filtration
Disinfections
Chlorination, UV treatment


















CLICK  THE ICON FOR VIDEO



It is the process of removing contaminants from wastewater and household sewage, both runoff (effluents) and domestic. It includes physical, chemical, and biological processes to remove physical, chemical and biological contaminants. Its objective is to produce an environmentally-safe fluid waste stream (or treated effluent) and a solid waste (or treated sludge) suitable for disposal or reuse (usually as farm fertilizer). Using advanced technology it is now possible to re-use sewage effluent for drinking water, although Singapore is the only country to implement such technology on a production scale in its production of NEWater[2].

Contents

[edit] Origins of sewage

Sewage is created by residential, institutional, and commercial and industrial establishments and includes household waste liquid from toilets, baths, showers, kitchens, sinks and so forth that is disposed of via sewers. In many areas, sewage also includes liquid waste from industry and commerce.
The separation and draining of household waste into greywater and blackwater is becoming more common in the developed world, with greywater being permitted to be used for watering plants or recycled for flushing toilets. Most sewage also includes some surface water from roofs or hard-standing areas and may include stormwater runoff.
Sewerage systems capable of handling stormwater are known as combined systems or combined sewers. Such systems are usually avoided now since they complicate and thereby reduce the efficiency of sewage treatment plants owing to their seasonality. The wide variability in flow, affected by precipitation, also leads to a need to construct much larger, more expensive, treatment facilities than would otherwise be required. In addition, heavy storms that contribute greater excess flow than the treatment plant can handle may overwhelm the sewage treatment system, causing a spill or overflow. Modern sewered developments tend to be provided with separate storm drain systems for rainwater.[3]
As rainfall travels over roofs and the ground, it may pick up various contaminants including soil particles and other sediment, heavy metals, organic compounds, animal waste, and oil and grease. (See urban runoff.)[4] Some jurisdictions require stormwater to receive some level of treatment before being discharged directly into waterways. Examples of treatment processes used for stormwater include retention basins, wetlands, buried vaults with various kinds of media filters, and vortex separators (to remove coarse solids). Sanitary sewers are typically much smaller than storm sewers, and they are not designed to transport stormwater. In areas with basements, backups of raw sewage can occur if excessive stormwater is allowed into a sanitary sewer system.

[edit] Process overview

Sewage can be treated close to where it is created, a decentralised system, (in septic tanks, biofilters or aerobic treatment systems), or be collected and transported via a network of pipes and pump stations to a municipal treatment plant, a centralised system, (see sewerage and pipes and infrastructure). Sewage collection and treatment is typically subject to local, state and federal regulations and standards. Industrial sources of wastewater often require specialized treatment processes (see Industrial wastewater treatment).
Sewage treatment generally involves three stages, called primary, secondary and tertiary treatment.
  • Primary treatment consists of temporarily holding the sewage in a quiescent basin where heavy solids can settle to the bottom while oil, grease and lighter solids float to the surface. The settled and floating materials are removed and the remaining liquid may be discharged or subjected to secondary treatment.
  • Secondary treatment removes dissolved and suspended biological matter. Secondary treatment is typically performed by indigenous, water-borne micro-organisms in a managed habitat. Secondary treatment may require a separation process to remove the micro-organisms from the treated water prior to discharge or tertiary treatment.
  • Tertiary treatment is sometimes defined as anything more than primary and secondary treatment in order to allow rejection into a highly sensitive or fragile ecosystem (estuaries, low-flow rivers, coral reefs,...). Treated water is sometimes disinfected chemically or physically (for example, by lagoons and microfiltration) prior to discharge into a stream, river, bay, lagoon or wetland, or it can be used for the irrigation of a golf course, green way or park. If it is sufficiently clean, it can also be used for groundwater recharge or agricultural purposes.
Process Flow Diagram for a typical large-scale treatment plant
ESQUEMPEQUE-EN.jpg


Process Flow Diagram for a typical treatment plant via Subsurface Flow Constructed Wetlands (SFCW)
SchemConstructedWetlandSewage.jpg



[edit] Pre-treatment

Pre-treatment removes materials that can be easily collected from the raw wastewater before they damage or clog the pumps and skimmers of primary treatment clarifiers (trash, tree limbs, leaves, etc.).

[edit] Screening

The influent sewage water is screened to remove all large objects carried in the sewage stream.[5] This is most commonly done with an automated mechanically raked bar screen in modern plants serving large populations, whilst in smaller or less modern plants a manually cleaned screen may be used. The raking action of a mechanical bar screen is typically paced according to the accumulation on the bar screens and/or flow rate. The solids are collected and later disposed in a landfill or incinerated. Bar screens or mesh screens of varying sizes may be used to optimise solids removal. If gross solids are not removed they become entrained in pipes and moving parts of the treatment plant and can cause substantial damage and inefficiency in the process.[6]:9

[edit] Grit removal

Pre-treatment may include a sand or grit channel or chamber where the velocity of the incoming wastewater is adjusted to allow the settlement of sand, grit, stones, and broken glass. These particles are removed because they may damage pumps and other equipment. For small sanitary sewer systems, the grit chambers may not be necessary, but grit removal is desirable at larger plants.[6]:10
http://upload.wikimedia.org/wikipedia/commons/thumb/4/46/Sedimentation_tank.jpg/313px-Sedimentation_tank.jpg
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An empty sedimentation tank at the treatment plant in Merchtem, Belgium.

[edit] Fat and grease removal

In some larger plants, fat and grease is removed by passing the sewage through a small tank where skimmers collect the fat floating on the surface. Air blowers in the base of the tank may also be used to help recover the fat as a froth. In most plants however, fat and grease removal takes place in the primary settlement tank using mechanical surface skimmers.

[edit] Primary treatment

In the primary sedimentation stage, sewage flows through large tanks, commonly called "primary clarifiers" or "primary sedimentation tanks." The tanks are used to settle sludge while grease and oils rise to the surface and are skimmed off. Primary settling tanks are usually equipped with mechanically driven scrapers that continually drive the collected sludge towards a hopper in the base of the tank where it is pumped to sludge treatment facilities.[6]:9-11 Grease and oil from the floating material can sometimes be recovered for saponification.
The dimensions of the tank should be designed to effect removal of a high percentage of the floatables and sludge. A typical sedimentation tank may remove from 60 to 65 percent of suspended solids, and from 30 to 35 percent of biochemical oxygen demand (BOD) from the sewage.

[edit] Secondary treatment

Secondary treatment is designed to substantially degrade the biological content of the sewage which are derived from human waste, food waste, soaps and detergent. The majority of municipal plants treat the settled sewage liquor using aerobic biological processes. To be effective, the biota require both oxygen and food to live. The bacteria and protozoa consume biodegradable soluble organic contaminants (e.g. sugars, fats, organic short-chain carbon molecules, etc.) and bind much of the less soluble fractions into floc. Secondary treatment systems are classified as fixed-film or suspended-growth systems.
  • Fixed-film or attached growth systems include trickling filters and rotating biological contactors, where the biomass grows on media and the sewage passes over its surface.
  • Suspended-growth systems include activated sludge, where the biomass is mixed with the sewage and can be operated in a smaller space than fixed-film systems that treat the same amount of water. However, fixed-film systems are more able to cope with drastic changes in the amount of biological material and can provide higher removal rates for organic material and suspended solids than suspended growth systems.[6]:11-13
Roughing filters are intended to treat particularly strong or variable organic loads, typically industrial, to allow them to then be treated by conventional secondary treatment processes. Characteristics include filters filled with media to which wastewater is applied. They are designed to allow high hydraulic loading and a high level of aeration. On larger installations, air is forced through the media using blowers. The resultant wastewater is usually within the normal range for conventional treatment processes.
http://upload.wikimedia.org/wikipedia/commons/3/35/Activated_Sludge_1.png
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A generalized, schematic diagram of an activated sludge process.
A filter removes a small percentage of the suspended organic matter, while the majority of the organic matter undergoes a change of character, only due to the biological oxidation and nitrification taking place in the filter. With this aerobic oxidation and nitrification, the organic solids are converted into coagulated suspended mass, which is heavier and bulkier, and can settle to the bottom of a tank. The effluent of the filter is therefore passed through a sedimentation tank, called a secondary clarifier, secondary settling tank or humus tank.

[edit] Activated sludge

Main article: Activated sludge
In general, activated sludge plants encompass a variety of mechanisms and processes that use dissolved oxygen to promote the growth of biological floc that substantially removes organic material.[6]:12-13
The process traps particulate material and can, under ideal conditions, convert ammonia to nitrite and nitrate and ultimately to nitrogen gas. (See also denitrification).
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A Typical Surface-Aerated Basin (using motor-driven floating aerators)

[edit] Surface-aerated basins (Lagoons)

Many small municipal sewage systems in the United States (1 million gal./day or less) use aerated lagoons.[7]
Most biological oxidation processes for treating industrial wastewaters have in common the use of oxygen (or air) and microbial action. Surface-aerated basins achieve 80 to 90 percent removal of BOD with retention times of 1 to 10 days.[8] The basins may range in depth from 1.5 to 5.0 metres and use motor-driven aerators floating on the surface of the wastewater.[8]
In an aerated basin system, the aerators provide two functions: they transfer air into the basins required by the biological oxidation reactions, and they provide the mixing required for dispersing the air and for contacting the reactants (that is, oxygen, wastewater and microbes). Typically, the floating surface aerators are rated to deliver the amount of air equivalent to 1.8 to 2.7 kg O2/kW·h. However, they do not provide as good mixing as is normally achieved in activated sludge systems and therefore aerated basins do not achieve the same performance level as activated sludge units.[8]
Biological oxidation processes are sensitive to temperature and, between 0 °C and 40 °C, the rate of biological reactions increase with temperature. Most surface aerated vessels operate at between 4 °C and 32 °C.[8]

[edit] Constructed wetlands

Constructed wetlands (can either be surface flow or subsurface flow, horizontal or vertical flow), include engineered reedbeds and belong to the family of phytorestoration and ecotechnologies; they provide a high degree of biological improvement and depending on design, act as a primary, secondary and sometimes tertiary treatment, also see phytoremediation. One example is a small reedbed used to clean the drainage from the elephants' enclosure at Chester Zoo in England; numerous CWs are used to recycle the water of the city of Honfleur in France and numerous other towns in Europe, the US, Asia and Australia. They are known to be highly productive systems as they copy natural wetlands, called the "Kidneys of the earth" for their fundamental recycling capacity of the hydrological cycle in the biosphere. Robust and reliable, their treatment capacities improve as time go by, at the opposite of conventional treatment plants whose machinery age with time. They are being increasingly used, although adequate and experienced design are more fundamental than for other systems and space limitation may impede their use.

[edit] Filter beds (oxidizing beds)

Main article: Trickling filter
In older plants and those receiving variable loadings, trickling filter beds are used where the settled sewage liquor is spread onto the surface of a bed made up of coke (carbonized coal), limestone chips or specially fabricated plastic media. Such media must have large surface areas to support the biofilms that form. The liquor is typically distributed through perforated spray arms. The distributed liquor trickles through the bed and is collected in drains at the base. These drains also provide a source of air which percolates up through the bed, keeping it aerobic. Biological films of bacteria, protozoa and fungi form on the media’s surfaces and eat or otherwise reduce the organic content.[6]:12 This biofilm is often grazed by insect larvae, snails, and worms which help maintain an optimal thickness. Overloading of beds increases the thickness of the film leading to clogging of the filter media and ponding on the surface. Recent advances in media and process micro-biology design overcome many issues with Trickling filter designs.

[edit] Soil Bio-Technology

Main article: Soil Bio-Technology
A new process called Soil Bio-Technology (SBT) developed at IIT Bombay has shown tremendous improvements in process efficiency enabling total water reuse, due to extremely low operating power requirements of less than 50 joules per kg of treated water.[9] Typically SBT systems can achieve chemical oxygen demand (COD) levels less than 10 mg/L from sewage input of COD 400 mg/L.[10] SBT plants exhibit high reductions in COD values and bacterial counts as a result of the very high microbial densities available in the media. Unlike conventional treatment plants, SBT plants produce insignificant amounts of sludge, precluding the need for sludge disposal areas that are required by other technologies.[11]
In the Indian context, conventional sewage treatment plants fall into systemic disrepair due to 1) high operating costs, 2) equipment corrosion due to methanogenesis and hydrogen sulphide, 3) non-reusability of treated water due to high COD (>30 mg/L) and high fecal coliform (>3000 NFU) counts, 4) lack of skilled operating personnel and 5) equipment replacement issues. Examples of such systemic failures has been documented by Sankat Mochan Foundation at the Ganges basin after a massive cleanup effort by the Indian government in 1986 by setting up sewage treatment plants under the Ganga Action Plan failed to improve river water quality.

[edit] Biological aerated filters

Biological Aerated (or Anoxic) Filter (BAF) or Biofilters combine filtration with biological carbon reduction, nitrification or denitrification. BAF usually includes a reactor filled with a filter media. The media is either in suspension or supported by a gravel layer at the foot of the filter. The dual purpose of this media is to support highly active biomass that is attached to it and to filter suspended solids. Carbon reduction and ammonia conversion occurs in aerobic mode and sometime achieved in a single reactor while nitrate conversion occurs in anoxic mode. BAF is operated either in upflow or downflow configuration depending on design specified by manufacturer.
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Schematic diagram of a typical rotating biological contactor (RBC). The treated effluent clarifier/settler is not included in the diagram.

[edit] Rotating biological contactors

Rotating biological contactors (RBCs) are mechanical secondary treatment systems, which are robust and capable of withstanding surges in organic load. RBCs were first installed in Germany in 1960 and have since been developed and refined into a reliable operating unit. The rotating disks support the growth of bacteria and micro-organisms present in the sewage, which break down and stabilise organic pollutants. To be successful, micro-organisms need both oxygen to live and food to grow. Oxygen is obtained from the atmosphere as the disks rotate. As the micro-organisms grow, they build up on the media until they are sloughed off due to shear forces provided by the rotating discs in the sewage. Effluent from the RBC is then passed through final clarifiers where the micro-organisms in suspension settle as a sludge. The sludge is withdrawn from the clarifier for further treatment.
A functionally similar biological filtering system has become popular as part of home aquarium filtration and purification. The aquarium water is drawn up out of the tank and then cascaded over a freely spinning corrugated fiber-mesh wheel before passing through a media filter and back into the aquarium. The spinning mesh wheel develops a biofilm coating of microorganisms that feed on the suspended wastes in the aquarium water and are also exposed to the atmosphere as the wheel rotates. This is especially good at removing waste urea and ammonia urinated into the aquarium water by the fish and other animals.

[edit] Membrane bioreactors

Membrane bioreactors (MBR) combine activated sludge treatment with a membrane liquid-solid separation process. The membrane component uses low pressure microfiltration or ultra filtration membranes and eliminates the need for clarification and tertiary filtration. The membranes are typically immersed in the aeration tank; however, some applications utilize a separate membrane tank. One of the key benefits of an MBR system is that it effectively overcomes the limitations associated with poor settling of sludge in conventional activated sludge (CAS) processes. The technology permits bioreactor operation with considerably higher mixed liquor suspended solids (MLSS) concentration than CAS systems, which are limited by sludge settling. The process is typically operated at MLSS in the range of 8,000–12,000 mg/L, while CAS are operated in the range of 2,000–3,000 mg/L. The elevated biomass concentration in the MBR process allows for very effective removal of both soluble and particulate biodegradable materials at higher loading rates. Thus increased sludge retention times, usually exceeding 15 days, ensure complete nitrification even in extremely cold weather.
The cost of building and operating an MBR is usually higher than conventional wastewater treatment. Membrane filters can be blinded with grease or abraded by suspended grit and lack a clarifier's flexibility to pass peak flows. The technology has become increasingly popular for reliably pretreated waste streams and has gained wider acceptance where infiltration and inflow have been controlled, however, and the life-cycle costs have been steadily decreasing. The small footprint of MBR systems, and the high quality effluent produced, make them particularly useful for water reuse applications.[12]

[edit] Secondary sedimentation

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Secondary Sedimentation tank at a rural treatment plant.
The final step in the secondary treatment stage is to settle out the biological floc or filter material through a secondary clarifier and to produce sewage water containing low levels of organic material and suspended matter.

[edit] Tertiary treatment

The purpose of tertiary treatment is to provide a final treatment stage to raise the effluent quality before it is discharged to the receiving environment (sea, river, lake, ground, etc.). More than one tertiary treatment process may be used at any treatment plant. If disinfection is practiced, it is always the final process. It is also called "effluent polishing."

[edit] Filtration

Sand filtration removes much of the residual suspended matter.[6]:22-23 Filtration over activated carbon, also called carbon adsorption, removes residual toxins.[6]:19

[edit] Lagooning

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A sewage treatment plant and lagoon in Everett, Washington, United States.
Lagooning provides settlement and further biological improvement through storage in large man-made ponds or lagoons. These lagoons are highly aerobic and colonization by native macrophytes, especially reeds, is often encouraged. Small filter feeding invertebrates such as Daphnia and species of Rotifera greatly assist in treatment by removing fine particulates.

[edit] Nutrient removal

Wastewater may contain high levels of the nutrients nitrogen and phosphorus. Excessive release to the environment can lead to a build up of nutrients, called eutrophication, which can in turn encourage the overgrowth of weeds, algae, and cyanobacteria (blue-green algae). This may cause an algal bloom, a rapid growth in the population of algae. The algae numbers are unsustainable and eventually most of them die. The decomposition of the algae by bacteria uses up so much of oxygen in the water that most or all of the animals die, which creates more organic matter for the bacteria to decompose. In addition to causing deoxygenation, some algal species produce toxins that contaminate drinking water supplies. Different treatment processes are required to remove nitrogen and phosphorus.
[edit] Nitrogen removal
The removal of nitrogen is effected through the biological oxidation of nitrogen from ammonia to nitrate (nitrification), followed by denitrification, the reduction of nitrate to nitrogen gas. Nitrogen gas is released to the atmosphere and thus removed from the water.
Nitrification itself is a two-step aerobic process, each step facilitated by a different type of bacteria. The oxidation of ammonia (NH3) to nitrite (NO2) is most often facilitated by Nitrosomonas spp. (nitroso referring to the formation of a nitroso functional group). Nitrite oxidation to nitrate (NO3), though traditionally believed to be facilitated by Nitrobacter spp. (nitro referring the formation of a nitro functional group), is now known to be facilitated in the environment almost exclusively by Nitrospira spp.
Denitrification requires anoxic conditions to encourage the appropriate biological communities to form. It is facilitated by a wide diversity of bacteria. Sand filters, lagooning and reed beds can all be used to reduce nitrogen, but the activated sludge process (if designed well) can do the job the most easily.[6]:17-18 Since denitrification is the reduction of nitrate to dinitrogen gas, an electron donor is needed. This can be, depending on the wastewater, organic matter (from faeces), sulfide, or an added donor like methanol.
Sometimes the conversion of toxic ammonia to nitrate alone is referred to as tertiary treatment.
Many sewage treatment plants use axial flow pumps to transfer the nitrified mixed liquor from the aeration zone to the anoxic zone for denitrification. These pumps are often referred to as Internal Mixed Liquor Recycle (IMLR) pumps.
[edit] Phosphorus removal
Phosphorus removal is important as it is a limiting nutrient for algae growth in many fresh water systems. (For a description of the negative effects of algae, see Sewage treatment#Nutrient removal). It is also particularly important for water reuse systems where high phosphorus concentrations may lead to fouling of downstream equipment such as reverse osmosis.
Phosphorus can be removed biologically in a process called enhanced biological phosphorus removal. In this process, specific bacteria, called polyphosphate accumulating organisms (PAOs), are selectively enriched and accumulate large quantities of phosphorus within their cells (up to 20 percent of their mass). When the biomass enriched in these bacteria is separated from the treated water, these biosolids have a high fertilizer value.
Phosphorus removal can also be achieved by chemical precipitation, usually with salts of iron (e.g. ferric chloride), aluminum (e.g. alum), or lime.[6]:18 This may lead to excessive sludge production as hydroxides precipitates and the added chemicals can be expensive. Chemical phosphorus removal requires significantly smaller equipment footprint than biological removal, is easier to operate and is often more reliable than biological phosphorus removal . Another method for phosphorus removal is to use granular laterite.
Once removed, phosphorus, in the form of a phosphate-rich sludge, may be stored in a land fill or resold for use in fertilizer.

[edit] Disinfection

The purpose of disinfection in the treatment of wastewater is to substantially reduce the number of microorganisms in the water to be discharged back into the environment. The effectiveness of disinfection depends on the quality of the water being treated (e.g., cloudiness, pH, etc.), the type of disinfection being used, the disinfectant dosage (concentration and time), and other environmental variables. Cloudy water will be treated less successfully, since solid matter can shield organisms, especially from ultraviolet light or if contact times are low. Generally, short contact times, low doses and high flows all militate against effective disinfection. Common methods of disinfection include ozone, chlorine, ultraviolet light, or sodium hypochlorite.[6]:16 Chloramine, which is used for drinking water, is not used in wastewater treatment because of its persistence.
Chlorination remains the most common form of wastewater disinfection in North America due to its low cost and long-term history of effectiveness. One disadvantage is that chlorination of residual organic material can generate chlorinated-organic compounds that may be carcinogenic or harmful to the environment. Residual chlorine or chloramines may also be capable of chlorinating organic material in the natural aquatic environment. Further, because residual chlorine is toxic to aquatic species, the treated effluent must also be chemically dechlorinated, adding to the complexity and cost of treatment.
Ultraviolet (UV) light can be used instead of chlorine, iodine, or other chemicals. Because no chemicals are used, the treated water has no adverse effect on organisms that later consume it, as may be the case with other methods. UV radiation causes damage to the genetic structure of bacteria, viruses, and other pathogens, making them incapable of reproduction. The key disadvantages of UV disinfection are the need for frequent lamp maintenance and replacement and the need for a highly treated effluent to ensure that the target microorganisms are not shielded from the UV radiation (i.e., any solids present in the treated effluent may protect microorganisms from the UV light). In the United Kingdom, UV light is becoming the most common means of disinfection because of the concerns about the impacts of chlorine in chlorinating residual organics in the wastewater and in chlorinating organics in the receiving water. Some sewage treatment systems in Canada and the US also use UV light for their effluent water disinfection.[13][14]
Ozone (O3) is generated by passing oxygen (O2) through a high voltage potential resulting in a third oxygen atom becoming attached and forming O3. Ozone is very unstable and reactive and oxidizes most organic material it comes in contact with, thereby destroying many pathogenic microorganisms. Ozone is considered to be safer than chlorine because, unlike chlorine which has to be stored on site (highly poisonous in the event of an accidental release), ozone is generated onsite as needed. Ozonation also produces fewer disinfection by-products than chlorination. A disadvantage of ozone disinfection is the high cost of the ozone generation equipment and the requirements for special operators.

[edit] Odour Control

Odours emitted by sewage treatment are typically an indication of an anaerobic or "septic" condition.[15] Early stages of processing will tend to produce smelly gases, with hydrogen sulfide being most common in generating complaints. Large process plants in urban areas will often treat the odours with carbon reactors, a contact media with bio-slimes, small doses of chlorine, or circulating fluids to biologically capture and metabolize the obnoxious gases.[16] Other methods of odour control exist, including addition of iron salts, hydrogen peroxide, calcium nitrate, etc. to manage hydrogen sulfide levels.

[edit] Package plants and batch reactors

To use less space, treat difficult waste and intermittent flows, a number of designs of hybrid treatment plants have been produced. Such plants often combine at least two stages of the three main treatment stages into one combined stage. In the UK, where a large number of wastewater treatment plants serve small populations, package plants are a viable alternative to building a large structure for each process stage. In the US, package plants are typically used in rural areas, highway rest stops and trailer parks.[17]
One type of system that combines secondary treatment and settlement is the sequencing batch reactor (SBR). Typically, activated sludge is mixed with raw incoming sewage, and then mixed and aerated. The settled sludge is run off and re-aerated before a proportion is returned to the headworks.[18] SBR plants are now being deployed in many parts of the world.
The disadvantage of the SBR process is that it requires a precise control of timing, mixing and aeration. This precision is typically achieved with computer controls linked to sensors. Such a complex, fragile system is unsuited to places where controls may be unreliable, poorly maintained, or where the power supply may be intermittent.
Package plants may be referred to as high charged or low charged. This refers to the way the biological load is processed. In high charged systems, the biological stage is presented with a high organic load and the combined floc and organic material is then oxygenated for a few hours before being charged again with a new load. In the low charged system the biological stage contains a low organic load and is combined with flocculate for longer times.

[edit] Sludge treatment and disposal

The sludges accumulated in a wastewater treatment process must be treated and disposed of in a safe and effective manner. The purpose of digestion is to reduce the amount of organic matter and the number of disease-causing microorganisms present in the solids. The most common treatment options include anaerobic digestion, aerobic digestion, and composting. Incineration is also used albeit to a much lesser degree.[6]:19-21
Sludge treatment depends on the amount of solids generated and other site-specific conditions. Composting is most often applied to small-scale plants with aerobic digestion for mid sized operations, and anaerobic digestion for the larger-scale operations.

[edit] Anaerobic digestion

Main article: Anaerobic digestion
Anaerobic digestion is a bacterial process that is carried out in the absence of oxygen. The process can either be thermophilic digestion, in which sludge is fermented in tanks at a temperature of 55°C, or mesophilic, at a temperature of around 36°C. Though allowing shorter retention time (and thus smaller tanks), thermophilic digestion is more expensive in terms of energy consumption for heating the sludge.
Anaerobic digestion is the most common (mesophilic) treatment of domestic sewage in septic tanks, which normally retain the sewage from one day to two days, reducing the BOD by about 35 to 40 percent. This reduction can be increased with a combination of anaerobic and aerobic treatment by installing Aerobic Treatment Units (ATUs) in the septic tank.
One major feature of anaerobic digestion is the production of biogas (with the most useful component being methane), which can be used in generators for electricity production and/or in boilers for heating purposes.

[edit] Aerobic digestion

Aerobic digestion is a bacterial process occurring in the presence of oxygen. Under aerobic conditions, bacteria rapidly consume organic matter and convert it into carbon dioxide. The operating costs used to be characteristically much greater for aerobic digestion because of the energy used by the blowers, pumps and motors needed to add oxygen to the process.
Aerobic digestion can also be achieved by using diffuser systems or jet aerators to oxidize the sludge.

[edit] Composting

Composting is also an aerobic process that involves mixing the sludge with sources of carbon such as sawdust, straw or wood chips. In the presence of oxygen, bacteria digest both the wastewater solids and the added carbon source and, in doing so, produce a large amount of heat.[6]:20

[edit] Incineration

Incineration of sludge is less common because of air emissions concerns and the supplemental fuel (typically natural gases or fuel oil) required to burn the low calorific value sludge and vaporize residual water. Stepped multiple hearth incinerators with high residence time and fluidized bed incinerators are the most common systems used to combust wastewater sludge. Co-firing in municipal waste-to-energy plants is occasionally done, this option being less expensive assuming the facilities already exist for solid waste and there is no need for auxiliary fuel.[6]:20-21

[edit] Sludge disposal

When a liquid sludge is produced, further treatment may be required to make it suitable for final disposal. Typically, sludges are thickened (dewatered) to reduce the volumes transported off-site for disposal. There is no process which completely eliminates the need to dispose of biosolids. There is, however, an additional step some cities are taking to superheat sludge and convert it into small pelletized granules that are high in nitrogen and other organic materials. In New York City, for example, several sewage treatment plants have dewatering facilities that use large centrifuges along with the addition of chemicals such as polymer to further remove liquid from the sludge. The removed fluid, called centrate, is typically reintroduced into the wastewater process. The product which is left is called "cake" and that is picked up by companies which turn it into fertilizer pellets. This product is then sold to local farmers and turf farms as a soil amendment or fertilizer, reducing the amount of space required to dispose of sludge in landfills. Much sludge originating from commercial or industrial areas is contaminated with toxic materials that are released into the sewers from the industrial processes.[19] Elevated concentrations of such materials may make the sludge unsuitable for agricultural use and it may then have to be incinerated or disposed of to landfill.

[edit] Treatment in the receiving environment

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The outlet of a wastewater treating plant flows into a small river
Many processes in a wastewater treatment plant are designed to mimic the natural treatment processes that occur in the environment, whether that environment is a natural water body or the ground. If not overloaded, bacteria in the environment will consume organic contaminants, although this will reduce the levels of oxygen in the water and may significantly change the overall ecology of the receiving water. Native bacterial populations feed on the organic contaminants, and the numbers of disease-causing microorganisms are reduced by natural environmental conditions such as predation or exposure to ultraviolet radiation. Consequently, in cases where the receiving environment provides a high level of dilution, a high degree of wastewater treatment may not be required. However, recent evidence has demonstrated that very low levels of specific contaminants in wastewater, including hormones (from animal husbandry and residue from human hormonal contraception methods) and synthetic materials such as phthalates that mimic hormones in their action, can have an unpredictable adverse impact on the natural biota and potentially on humans if the water is re-used for drinking water.[20] In the US and EU, uncontrolled discharges of wastewater to the environment are not permitted under law, and strict water quality requirements are to be met. (For requirements in the US, see Clean Water Act.) A significant threat in the coming decades will be the increasing uncontrolled discharges of wastewater within rapidly developing countries.

[edit] Effects on Biology

Sewage treatment plants can have multiple effects on nutrient levels in the water that the treated sewage flows into. These effects on nutrients can have large effects on the biological life in the water in contact with the effluent. Treatment ponds can include any of the following:
  • Oxidation ponds, which are aerobic bodies of water usually 1-2 meters in depth that receive effluent from sedimentation tanks or other forms of primary treatment.
* Dominated by algae
  • Polishing ponds are similar to oxidation ponds but receive effluent from an oxidation pond or from a plant with an extended mechanical treatment.
* Dominated by zooplankton
  • Raw sewage lagoons or sewage lagoons are aerobic ponds where sewage is added with no primary treatment other than coarse screening.
  • Anaerobic lagoons are heavily loaded ponds.
* Dominated by bacteria
  • Sludge lagoons are aerobic ponds, usually 2-5 meters in depth, that receive anaerobically digested primary sludge, or activated secondary sludge under water.
* Upper layers are dominated by algae
[21]
Phosphorous limitation is a possible result from sewage treatment and results in flagellate-dominated plankton, particularly in summer and fall.[22]
At the same time a different study found high nutrient concentrations linked to sewage effluents. High nutrient concentration leads to high chlorophyll a concentrations, which is a proxy for primary production in marine environments. High primary production means high phytoplankton populations and most likely high zooplankton populations because zooplankton feed on phytoplankton. However, effluent released into marine systems also leads to greater population instability.[23]
A study done in Britain found that the quality of effluent effected the planktonic life in the water in direct contact with the wastewater effluent. Turbid, low-quality effluents either did not contain ciliated protozoa or contained only a few species in small numbers. On the other hand, high-quality effluents contained a wide variety of ciliated protozoa in large numbers. Due to these findings, it seems unlikely that any particular component of the industrial effluent has, by itself, any harmful effects on the protozoan populations of activated sludge plants.[24]
The planktonic trends of high populations close to input of treated sewage is contrasted by the bacterial trend. In a study of Aeromonas spp. in increasing distance from a wastewater source, greater change in seasonal cycles was found the furthest from the effluent. This trend is so strong that the furthest location studied actually had an inversion of the Aeromonas spp. cycle in comparison to that of fecal coliforms. Since there is a main pattern in the cycles that occurred simultaneously at all stations it indicates seasonal factors (temperature, solar radiation, phytoplankton) control of the bacterial population. The effluent dominant species changes from Aeromonas caviae in winter to Aeromonas sobria in the spring and fall while the inflow dominant species is Aeromonas caviae, which is constant throughout the seasons.[25]

[edit] Sewage treatment in developing countries

Few reliable figures on the share of the wastewater collected in sewers that is being treated in the world exist. In many developing countries the bulk of domestic and industrial wastewater is discharged without any treatment or after primary treatment only. In Latin America about 15% of collected wastewater passes through treatment plants (with varying levels of actual treatment). In Venezuela, a below average country in South America with respect to wastewater treatment, 97 percent of the country’s sewage is discharged raw into the environment.[26] In a relatively developed Middle Eastern country such as Iran, Tehran's majority of population has totally untreated sewage injected to the city’s groundwater.[27]
In Israel, about 50 percent of agricultural water usage (total use was 1 billion cubic metres in 2008) is provided through reclaimed sewer water. Future plans call for increased use of treated sewer water as well as more desalination plants.[28]
Most of sub-Saharan Africa is without wastewater treatment.

[edit] See also







































Moving Bed Biofilm Reactor
MBBR - Moving Bed Biofilm Reactor
With the Moving bed Bioreactor (MBBR) an economically solution is offered for wastewater treatment if the "bulk" of the pollution load must be disposed of (as means of cost reduction) or if applicable discharge regulations are not as strict.
With this application we offer advanced wastewater treatment solutions for the industrial and municipal markets. These solutions significantly increase the capacity and efficiency of existing wastewater treatment plants, while minimizing the size of new plant deployments.
This method makes it possible to attain good efficiency results of disposal with low energy consumption. This process is used for the removal of organic substances, nitrification and denitrification.
The MBBR system consists of an activated sludge aeration system where the sludge is collected on recycled plastic carriers. These carriers have an internal large surface for optimal contact water, air and bacteria.
MBBR carriers
The carrier material used inside a MBBR system
The bacteria/activated sludge grow on the internal surface of the carriers. The bacteria break down the organic matter from the waste water. The aeration system keeps the carriers with activated sludge in motion. Only the extra amount of bacteria growth, the excess sludge will come separate from the carriers and will flow with the treated water towards the final separator.
The system can consist of a one stage or more stage system (see underneath schedule), depending on the specific demands. The  specific bacteria remain in their own duty tank because of the fact that the carriers remain in only 1 tank, protected by screens.
mbbr scheme
The MBBR process can be used for a variety of different applications to attain the desired results, depending on the quality of the wastewater and the discharge regulations.

Industrial applications
•    Capacity increase
•    Quality Improvement – BOD & Nitrogen Removal
•    Fast recovery from Process Upsets
•    Limited Footprint
•    Future Expansion
•    Minimize Process Complexity and Operator Attention

Benefits
•    Economical very attractive
•    Compact (saves space)
•    Maintenance-friendly
•    Strong
•    High volume load
•    Simply to extend
•    Financial savings on discharge costs




















Membrane Bioreactor
Membrane bioreactors
The Membrane Bioreactor or MBR is based on the conventional wastewater process, but the separation of micro-organisms is performed by filtration with membranes.

3d MBR skid
3D drawing of a crossflow membrane skid

The MBR has some distinctive advantages compared with the conventional treatment systems:

•    Very stable process
The conventional biological system is sensitive to the wastewater composition. Due to variations in wastewater composition and/or presence of complex or toxic substances, high salt concentrations or low oxygen concentrations, the biomass floc formation is poor and the settling process will not perform well. This results in discharge of the micro-organisms and poor effluent quality.
The membranes will however withhold all biomass and other suspended solids, ensuring a high effluent quality.

•    Very compact design
Due to the membrane separation the active micro-organism population in the bioreactor can be maintained at a concentration 4-5 times higher than in conventional systems. This results in bioreactor tank volumes of only 20-25% of the size of conventional systems. A clarifier, being a space-consuming tank, is not required.

•    High effluent quality
The ultra filtration membranes withhold all micro-organisms and most suspended solids, resulting in a clear and highly purified effluent. The effluent may be reused as low-grade process water or for irrigation purposes.

•    Low sludge production
The MBR can operate at a low F/M ratio, being the Feed of organic substance per amount of Micro-organisms per time unit. This results in a high mineralisation of sludge. In conventional systems 1 kg COD will result in about 0,3 -0,4 kg of biomass. With MBR systems 1 kg COD is converted to 0 - 0,2 kg biomass (zero biomass production can be obtained when operating at high temperatures). The discharge of biomass can have significant impact on the operational costs of the system.
•    Treatment wastewater up to 60 °C is possible
•    Treatment of wastewater with chlorine concentrations up to 120 g/l
•    Insentive to shock and vibration (on board of ships)
Field of Application:
•    Poorly degradable water (lightly sludge-sensitive) 
•    In limited space 
•    Stringent discharge regulations 
•    Reuse
50M3 submerged mbrTwo versions of the MBR process are offered, the MemTriq® and the SubTriq®. The MemTriq® is based on a cross-flow filtration process. The biomass is filtered in a filtration unit besides the bioreactor. The SubTriq® is based on filtration with submerged membranes that are submerged in the biomass either in the bioreactor it self or in a separate tank.
50 m3/d submerged MBR system, reusing black water for toilet flushing in an office building

For publications of succesfull MBR applications see below links

Submerged MBR
Submerged Membrane Bioreactor

The SubTriq® is based on a filtration procedure with membranes that are submerged in the biomass, either inside the bioreactor itself or in a separate tank. The membranes are submerged directly in the bioreactor or in a separate tank and filtration takes place by applying vacuum to the inside of the membrane. Membrane fouling is prevented by the flow of coarse air bubbles along the membrane surface or periodic backflushing.
submerged mbr scheme
Prerequisites for the application of submerged Membrane Bioreactors:
•    Wastewater should not be highly concentrated (i.e. household wastewater) 
•    Wastewater that is well biodegradable 
•    Higher flows (> 20m3/h)
One of the distinct advantages of submerged Membrane Bioreactors is their low energy consumption.
submerged membrane tank
Submerged membrane tank, part of a system treating leachate from a landfill.
The System
•    High biomass concentration   
•    Low excess sludge production
•    Minimum space and weight
•    Low operating intervals
•    Stand alone system

Advantages
•    Economically attractive    
•    Compact
•    Trouble-free operation
•    Options for water reuse
•    Fast delivery time
•    Certified by DNV (RMRS at request)

Special Applications
•    Reuse for technical applications (deck wash etc.)
•    Reuse for toilet flushing
•    Use of “extended” system for operating in zero-emission areas
•    Tailor-made executions
•    Also for Retro-fit

Crossflow MBR
Cross flow membrane systems
The MemTriq® is based on a cross-flow filtration process.
The biomass is filtered in a filter installation next to the bioreactor. The membrane modules are placed in a pressurized circulation loop located outside the bioreactor. Membrane fouling is prevented by the use of the shear forces created by the cross-flow operation of the membranes.

crossflow scheme
Prerequisites for the application of cross-flow Membrane Bioreactors:
•    Concentrated wastewater 
•    Waste water that is not easily biodegradable 
•    Small pore sizes 
•    Lower flows (< 20m3/h)
membrane street
Typical membrane street used in a containerized offshore application


Sequencing Batch Reactors:
An Efficient Alternative to Wastewater Treatment

By

Luis H. Abreu and Saribel Estrada


Introduction

The Sequencing Batch Reactor (SBR) is an activated sludge process designed to operate under non-steady state conditions. An SBR operates in a true batch mode with aeration and sludge settlement both occurring in the same tank. The major differences between SBR and conventional continuous-flow, activated sludge system is that the SBR tank carries out the functions of equalization aeration and sedimentation in a time sequence rather than in the conventional space sequence of continuous-flow systems. In addition, the SBR system can be designed with the ability to treat a wide range of influent volumes whereas the continuous system is based upon a fixed influent flowrate. Thus, there is a degree of flexibility associated with working in a time rather than in a space sequence [1].
SBRs produce sludges with good settling properties providing the influent wastewater is admitted into the aeration in a controlled manner. Controls range from a simplified float and timer based system with a PLC to a PC based SCADA system with color graphics using either flow proportional aeration or dissolved oxygen controlled aeration to reduce aeration to reduce energy consumption and enhance the selective pressures for BOD, nutrient removal, and control of filaments [1]. An appropriately designed SBR process is a unique combination of equipment and software. Working with automated control reduces the number of operator skill and attention requirement.
The majority of the aeration equipment of sequencing batch reactors consist of jet, fine bubble, and coarse bubble aeration systems. The main focus of this report is a jet aerated sequencing batch reactor activated sludge system.

Sequencing Batch Reactor Process Cycles

The operating principles of a batch activated sludge process, or SBR, are characterized in six discrete periods:


Anoxic Fill

The influent wastewater is distributed throughout the settled sludge through the influent distribution manifold to provide good contact between the microorganisms and the substrate [1]. The influent can be either pumped in allowed to flow in by gravity. Most of this period occurs without aeration to create an environment that favors the procreation of microorganisms with good settling characteristics. Aeration begins at the beginning of this period.
http://www.rpi.edu/dept/chem-eng/Biotech-Environ/Environmental/Steps/anoxic.gif
Figure 1

Aerated Fill

Mixed liquor is drawn through the manifold, mixed with the influent flow in the motive liquid pump, and discharged, as motive liquid, to the jet aerator [1]. This initiates the feast period. Feast is when the microorganisms have been in contact with the substrate and a large amount of oxygen is provided to facilitate the substrate consumption. Nitrification and denitrification occurs at the beginning of this stage. This period ends when the tank is either full or when a maximum time for filling is reached.
http://www.rpi.edu/dept/chem-eng/Biotech-Environ/Environmental/Steps/aerated.gif
Figure 2

React

During this period aeration continues until complete biodegradation of BOD and nitrogen is achieved. After the substrate is consumed famine stage starts. During this stage some microorganisms will die because of the lack of food and will help reduce the volume of the settling sludge. The length of the aeration period determines the degree of BOD consumption [1], [2].
http://www.rpi.edu/dept/chem-eng/Biotech-Environ/Environmental/Steps/reaction.gif
Figure 3
http://www.rpi.edu/dept/chem-eng/Biotech-Environ/Environmental/Steps/reactor.gif
Figure 4

Settle

Aeration is discontinued at this stage and solids separation takes place leaving clear, treated effluent above the sludge blanket. During this clarifying period no liquids should enter or leave the tank to avoid turbulence in the supernatant.
http://www.rpi.edu/dept/chem-eng/Biotech-Environ/Environmental/Steps/settle.gif
Figure 5
http://www.rpi.edu/dept/chem-eng/Biotech-Environ/Environmental/Steps/sedimen&.gif
Figure 6

Decant

This period is characterized by the withdrawal of treated effluent from approximately two feet below the surface of the mixed liquor by the floating solids excluding decanter [1]. This removal must be done without disturbing the settled sludge.
http://www.rpi.edu/dept/chem-eng/Biotech-Environ/Environmental/Steps/decant.gif
Figure 7

Idle

The time in this stage can be used to waste sludge or perform backwashing of the jet aerator. The wasted sludge is pumped to an anaerobic digester to reduce the volume of the sludge to be discarded. The frequency of sludge wasting ranges between once each cycle to once every two to three months depending upon system design.
http://www.rpi.edu/dept/chem-eng/Biotech-Environ/Environmental/Steps/wasting.gif 
Figure 8

Aeration Equipment

A. Jet Aeration Header
Jet aeration offers significant advantages in the SBR process due to its flexibility, good contact between substrate and microorganisms, and efficient oxygen transfer. One of its main features is that it can mix without aerating.Therefore it can provide for aerated and anoxic mix periods. The header in conjunction with a computer controlling for flow proportional aeration makes more oxygen available at higher flows than at lower flows by measuring the rate of change in the flow level in reactor.
http://www.rpi.edu/dept/chem-eng/Biotech-Environ/Environmental/Steps/aerator.gif
Figure 9
B. Decanter
Decanting is best achieved through solids excluding decanters. The floating decanter is one of the most efficient and contains a spring loaded plug valve operated by hydraulic differential [1]. This decanter is sustained about sixteen inches below the scum by a float therefore avoiding the decanting of floating matter.
http://www.rpi.edu/dept/chem-eng/Biotech-Environ/Environmental/Steps/decanter.gif
Figure 10

Conclusion

Wastewater treatment has been a challenge throughout the years due to varying influent chemical and physical characteristics and stringent effluent regulations. Treatment systems using activated sludge have been able to handle many of these difficulties. Given the lack of on-line computer controls, continuous flow systems have been mostly used for these purposes versus sequencing batch processes. The availability of artificial intelligence has now made the option of a SBR process more attractive thus providing better controls and results in wastewater treatment. This is coupled by the flexibility of a SBR in the treatment of variable flows, minimum operator interaction required, option for anoxic or anaerobic conditions in the same tank, good oxygen contact with microorganisms and substrate, small floor space, and good removal efficiency.
Sequencing batch reactors operate by a cycle of periods consisting of fill, react, settle, decant, and idle. The duration, oxygen concentration, and mixing in these periods could be altered according to the needs of the particular treatment plant. Appropriate aeration and decanting is essential for the correct operations of these plants. The aerator should make the oxygen readily available to the microorganisms. The decanter should avoid the intake of floating matter from the tank. The many advantages offered by the SBR process justifies the recent increase in the implementation of this process in industrial and municipal wastewater treatment.










Going Green: Wastewater



This is what most people envision of a wastewater treatment plant, but there's a more low-tech system called constructed wetlands.
The Village of Minoa treats 130,000 gallons of wastewater each day using these constructed wetlands. There are three cells that are two feet deep, two hundred feet by one hundred feet, built at a one percent pitch to move the wastewater by gravity and planted in these cells are phragmites to help clean the water.

“This is 14 years old. It's working great. We're getting ninety nine percent removals. The biosolids are contained right here. We never have to handle biosolids. As the organisms die off they have their own anaerobic digester at the bottom,” said Steve Giarusso, Minoa Wastewater Treatment Supervisor.
Primary water from Minoa enters the plant where solids are settled out. The remaining water and solids are gravity fed into the cells.
“Think about it now, third world country, no electricity, and no chemicals. The challenge was to use the materials that you only have around you and build a system that works,” said Giarusso.
We just have some raw data; it's got to be reproduced yet. We decided we finally got a break, we've got instruments to look at it and we've cracked certain pharmaceuticals that have never been cracked and we did it with this constructed wetland.
Waste is most often treated using expensive and energy intensive equipment. In a constructed wetland, the gravity and microorganisms do all the work naturally.
“What's the draw back on a constructed wetland, ok? Look at the footage, ok? Its big it takes a large area. We're only using one hundred and thirty thousand gallons,” said Giarusso. “We're finding out how the hydraulics work that 130,000 is adequate.
Officials from the United Nations have been looking at this system for possible applications in third world countries.