sewage treatment through USAB technology expectations and reality
dr.vinod tare and asit nema
with experience of over a decade and half of USAB for sewage treatment in the country, a number of inherent limitations of the technology in particular and that of anaerobic processes in general have been realized. Fundamentally attempting to generate energy or achieve improvement in wastewater quality without commensurate energy inputs is in violation of the second law of thermodynamics. Municipal sewage being a high ertropy material with low organic loads, it is not suitable as a feedstock for an apparent ‘liquid bioreactor’ promising reliable output of energy. The ‘initial oxygen demand’ of effluent from a USAB reactor has potential to sweep the dissolved oxygen of receiving water bodies in a very short period of time. Post treatment requirement prima facie negate the smaller footprint advantage often claimed by its proponents. The energy generation feature which was considered to be its unique selling proposition is not found to be a sustainable avenue either, because of low and inconsistent biogas yield-high microbial sensitivity to temperature variations which disrupts anaerobic process in winter when virtually biogas generation stops; requirement of supplementary fuel in indigenous duel fuel systems (which define the state of art in the country ); inability to adopt cogeneration route for waste heat utilization etc. on top of this, its environmental footprint is also not desirable-the corrosive ambience created by release of hydrogen sulphide and other gases causes damage to plant, equipment and adjoining public and private buildings and also creates odour nuisance for the adjacent community. This paper attempts to bring out all the limitations of the USAB technology and advocates for alternative aerobic realistic technology solutions.