Comparative performance of anaerobic reactors for treatment of sago industry wastewater

For a country like India where energy continues to be precious, with oil prices continuing to rise unlike in the West, anaerobic digestion has far greater relevance than it has to many other regions of the world. The cassava starch production in our country is mainly concentrated in small to medium scale factories, which generates 30,000–40,000 l of effluent per ton of sago produced. The effluent is acidic and highly organic in nature having chemical oxygen demand (COD) of 5,000–7,000 mg l⁻¹ during the season and 1,000–5,000 during the off-season. These effluents pose a serious threat to the environment and quality of life in the rural area. Since the treatment of cassava starch factory effluents through the normal biogas plants with 30–55 days retention period is very costly, attempts have been made to treat them through high-rate hybrid reactor with several hours of retention period. In Random-Packed Anaerobic Filter, the maximum COD reduction was observed (84.4 %) at 10 h hydraulic retention time (HRT). At 4 h HRT only 46.3 % COD was removed. Even though higher COD removal was achieved at 20 h, the better HRT was at 10 h as the difference between the 20 and 10 h HRT in only 0.2 %. In Up-flow Anaerobic Sludge Blanket reactor, the maximum COD removal (90 %) and total solid (TS) removal (82 %) were observed in a HRT of 30 h, whereas low COD (67 %) and TSs (64 %) removal was observed at 5 h HRT. The treatment of sago industry effluent in a hybrid reactor was studied and the HRT employed was 10, 24, 32, and 40 h. The COD removal rates were 86, 93, 94, and 95 %, and the TSs removal was 79, 85, 86, and 89 %. When the results of all these three reactors were compared, the hybrid reactor seems to be better with an optimum HRT range of 10–20 h. Hence, the anaerobic digestion has proved to be an effective method of treating the sago industry wastewater with simultaneous production of energy in the form of methane.