One or the economic and effective anaerobic treatment method is the UASB (Upflow Anerobic Sludge Blanket) process. In a UASB Reactor wastewater is fed from the bottom. As it flows upward through the reactor, organic matter in the waste is degraded anaerobically by micro organisms resident in the sludge blanket. Besides converting organics to cell mass, biogas rich in methane is produced as a by product. A Gas Liquid Solid separator(GLSS) provided near the top of the reactor, enables sludge to settle into the blanket, biogas to escape into the dome at the top of the reactor, and treated supernatant to flow out of the reactor. High sludge concentration in sludge blanket and low concentration of suspended solids in the reactor over flow are characteristic features of a good UASBR.

UASB Technology

The basic advantages of a UASBR over aerobic treatment units are :

* UASBR in a compact unit, ideal for economic space utilization.
* UASB treatment process requires no external input of energy. Even the required mixing is achieve by upflowing waste water and rising gas bubbles.
* Nutrient requirement (i.e. N&P) is muc less than (about half that needed ) for aerobic treatment.
* Residuals (i.e.sludge) generated by UASB treatmet are much less in amount and well digested, requiring reduced sludge hanldling and causing much less odour problems.

The UASBR comprises no mechanical or moving part involving wear and tear. Thus it is virtually maintenance free and involves few operational problems. When properly designed and made, a UASBR provides trouble-free service for many years.

* Biogas, rich in methane, is generated as a valuable by product. Methane produced is about 0.15 to 0.35 Nm3/kg COD destroyed.
* Owing to the compactness of UASBR , absence of mechanical/moving components, energy efficiency of the process, and reduced post- treatment and sludge handling requirements, both the capital cost and running cost of a UASBR based treatment plant are significantly less than for a fully aerobic teratment plant.
* Once a UASBR has been put in operation, acclimatised bacteria can survive without food in the reactor for long durations. This enables easy strartup of the UASBR after prolonged periods of being out of operation.
* UASBR is a noiseless, closed and covered unit that is aesthetically very satisfying.

UASBR APPLICATIONS:
UASB Technology has found applications worldwide, in treating various types of wastewater. Among industries, some popular applications are in the food processing and producing industries, dairies and milk-processing units, sugar mills, pulp and paper, breweries, distilleries, potato, vegetable and fruit processing plants, soft drink plants, tanneries and slaughterhouses. For complex industrial wastes or adverse environmental conditions, however, a pilot study or treatability assessment is desirable. For municipal waste waters (Sewage) BOD removal of 60% to 80% is normal under favourable conditions (influent BOD >=140 mg/l. BOD/COD => 0.4, temperature 15-42 ºC, etc.) Suspended solids may be also reduced in the process, but some post-treatment (aerated lagoon or stablization/polishing pond) is generally needed for BOD removal to the desired degree.

Effluent

TANNERY EFFLUENT STANDARD (AFTER PRIMARY TREATMENT) : DISPOSAL CHANNEL/CONDUIT CARRYING WASTEWATER TO SECONDARY TREATMENT PLANT

*Note: The above standards will apply to those tannery units which have made full contribution to a Common Effluent Treatment (CETP) comprising secondary treatment. Those who have not contributed will be governed by earlier Notification No. S.O. 64 (E) dated January 18, 1988.

Source: EPA Notification

[G.S.R 742(E) dt. 30th Aug; 1990]

Tanneries : Effluent Standards

* For effluent discharged into inland surface waters BOD limit shall be made stricter to 30 mg/l by the concerned State Pollution Control Board.

Source: EPA Notification

[G.S.R. 415(E), 5th May 1992]

ACTION POINTS UNDER CREP FOR TANNERY SECTOR

Chrome Recovery

• All the chrome-tanning units in the country will have the Chrome Recovery Plant either on individual basis or on collective basis in the form of Common Chrome Recovery Plant and use the recovered chrome in the tanning process.
• Common Chrome Recovery Plant is to be installed and commissioned at Kanpur, for which the Feasibility Report has already been prepared.
• Recovered Chromium is to be utilized in tanning process

Waste Minimization Measures

• Waste minimization circles will be formed in all the clusters of tanneries in the country to implement waste minimization measures and for adoption of clean technologies.
• Efforts should be taken to implement the waste minimization measures in all the tanneries in the country and gradually made obligatory with time to the tannery units.

Reduction of Water Consumption in Tannery Units

• All the tanneries should install water meters and flow meters to measure actual consumption and waste water discharge.
• Water consumption rates will be brought down to 28 m 3 /tonne of hides by taking waste minimization measures.

Compliance of standards

All CETPs and ETPs should take the following measures:

• Employ qualified and well trained staff for O & M of the ETPs/CETPs.
• Installation of automatic monitoring instruments.
• Interlocking of manufacturing processes with ETP operation
• Separate Energy meters for ETPs/CETPs by December 2003.
• Open anaerobic lagoons should be converted into closed systems with gas recovery
• For health & safety of worker in the industry & ETP/ CETP the guidelines developed by CPCB should be implemented.
• All major tannery units should take-up environmental auditing on annual basis.
• Major tannery units & CETPs should attempt to obtain ISO-14000 certification
• Tannery units &CETP management should take-up modification/up-gradation of the CETPs/ETPs wherever necessary

Management of Total Dissolved Solids (TDS)

All tannery units to adopt the following

• Manual/mechanical desalting.
• Use of cleaner technology for less use of salt.
• Refrigerated transportation of hides
• High Rate Transpiration system for effluent treatment
• Treated wastewater will be mixed with the sewage & the treated effluent be used on land for irrigation.

Solid Waste Management

All the tannery units to adopt the following:

• Utilization of Process sludge for by-product recovery.
• Resource Recovery from process sludge and ETP sludge in the form of Biogas.
• Chromium recovery from tanned leather shavings.
• Safe disposal of hazardous sludge and non-hazardous solid wastes.

Salts from Solar Evaporation

All the tannery units to adopt the following:

• Reuse of recovered salt.
• Quality improvement of recovered salts for reuse
• Safe land disposal
• Sea disposal

Use of Boron bearing compounds will be dispensed with. By: December 2003

Ground water quality monitoring to be strengthened.

Sulphur recovery from sulphide bearing effluents to be explored.

The implementation of recommendations of the Task Force on leather tannery units constituted by the Ministry of Environment & Forests, Govt. of India in a phased manner.