STUDIES ON MAKING A SEWAGE TREATMENT PLANT SELF ENERGIZING IN BOMBAY REGION

Abstract

In the era of energy crisis all possible efforts are. being made to exploit all known energy sources. Gas from .sludge digestion at sewage treatment plant-is known to have' promising energy potential, interms of its multifarious uses. The gas contains 65- percent methane and 35 percent carbondio-xide,. having ' collorific value 6.00 BTU/Cuft.. The gas can be used as domestic fuel in 'kitchen, fuel for lorry propulsion and driving the duel fuel pumps etc. Besides these, the gas can also be utilized to fulfill a part of power requirement at sewage treatment plant by generating electric power. The, thesis presents work on this aspect on the basis of experimental study :carried out. at Dadar Sewage Treatment Plant on Bombay sewage. The main object of the study hay been to determine the • gas -consumption required per KWH for generating electrical energy. Total gas production at the plant is closely linked... with the working efficiencies of sludge digester and primary settling tank. Therefore, an assessment, of performance of these units has also been experimentally carried out for Bombay sewage being received at Dadar. plant. The experimental study brings out the fact that . primary settler provides about 60 percent suspended solids removal effi-ciency with only I hi', detention time, Digester performance was analysed using standard methods. The parameters analysed were moisture content, percent dry volatile and fixed matter, vola-tile acids, alkalinity chlorides, pH, Phosphorous, total nitro-gen, COD, GODS and gas generation. The percent reduction of volatile acids, phosphorous, total nitrogen versus gas produc-tion have been plotted. Variations of all parameters versus time have also been plotted. The analysis reveals that variabi-lity inth-e parameters is..JgLifiarLt, . The data was also used • to design a diphasic digester theoretically. The reduction in detention. time for diphase system is astonishing as it requires only35 days detention time, reducing the capital cost to great • extent, and the gas yield is also increased by 15 percent. Efficiency studies on gas engine involved a complete set up of installing a 6.25 HP duel fuel engine, 3.5 KVA generator and well equipped electrical_ control panel board, with a gas meter. The diesel tank was calibrated. Complete system was run first on diesel and sewage gas was then introduced with various proportions of gas and diesel, fob getting maximum efficiency. .71 percent of gas and 29 percent of diesel combination gave maximum efficiency of about 21 percent and corresponding: per KWH gas consumption for power generation was about 20 Cuft per .KWH while with diesel alone a maximum overall efficiency of 22 per-cent was reported. • Detailed cost analysis has been made and it has been found that about.70 percent of power requirement of plant can be met through electric power generated out of sewage gas with gas engine. Further this proposal was compared with conventional primary treatment without digester, which .concluded that diphasic system with gas engine can save Rs. 20 .lakhs per year in the span of +0 years for a flow of 780 mid, considering the 1982 price level....