The upflow anaerobic sludge blanket (UASB) process is an anaerobic treatment system wherein the organic matter is digested, absorbed and metabolized into bacterial cell mass and bio gas. Anaerobic digestion is the degradation of organic material without the aid of oxygen.

The UASB process is a combination of physical and biological processes. The main feature of physical process is separation of solids and gases from the liquid and that of biological process is degradation of decomposable organic material under anaerobic conditions.

In the UASB treatment concept, the treatment tank consists of an upflow reactor with feed inter distribution system at the bottom of the reactor with 3 phases gas, liquid, solid, separator (glss) at the top. the waste water is evenly distributed over the reactor bottom through feed inlet pipes and flows upwards through a bed of anaerobic sludge in the lower part of reactor called the digestion compartment. During passage through the sludge bed particulate matter is entrapped and the degradable matter is completely or partially digested. Dissolved organic matter is removed from the solution by the anaerobic bacteria and converted into bio gas and a small fraction into new bacterial bio mass. The bio gas provides a gentle mixing in the sludge bed. In the upper part of the reactor, 3 phase glss is installed.

The bio gas produced is collected in a gas collector (gas holder) from where it is withdrawn. The remaining water sludge mixture enters a setling compartment where the sludge can settle and flow back into the digestion compartment. After setling, the water is collected in the effluent gutters and discharged out of the reactor to the final polishing unit (FPU) to meet discharge standards.

The domestic waste water treated in a UASB reactor is suitable for discharge in river water or for irrigation after polishing in a high rate pond. The bio gas generated can be utilised for generating electricity. Sludge cakes after de-watering and drying on sludge dry beds is suitable for use as manure.

1. The cost of UASB plant is significantly lower than that of aerobic plant
2. This has a negligible number of electrical and mechanical components, thus requiring low degree of maintenance and saves operational and maintenance cost. Thus also eliminates possibilities of problem that may arise in case of brake down of highly maintained intensive process.
3. The energy requirement in the UASB reactor is very low.
4. UASB system generates energy in the form of bio gas which can be used for the production of electricity and which can make UASB plants self sustaining for power reqirement.
5. This system reduces the space requirement, which is a big advantage for developing cities.
6. The production of excess sludge in a UASB reactor is very low. This reduces the load on the sludge treatment system. However, the sludge from UASB plant is very stabliized and can be used as manure.
7. Final polishing pond can be used for fish culture, which can be source of revenue.

1. 45 mld sewage treatment plant at Faridabad, ( Haryana )
2. 30 mld sewage treatment plant at Sonipat, ( Haryana ).
3. construction of 70 mld sewage treatment plant at Ghaziabad ( Uttar Pradesh ).
4. constructionof 78 mld sewage treatment plant at Agra ( Uttar Pradesh ).
5. construction of 19.35 mld sewage treatment plant at Shimla ( Himanchal Pradesh ).