| Abstract: | Cassava tubers produced under hot, dry and monsoon governed climate in the Salem region, Tamil Nadu, South India, consume together with the about 1000 starch extracting industries daily, 9 millions of litres of groundwater which have to be pumped from a depth of 80 m below ground level. Because of water shortage, adjacent fields are irrigated with organically highly enriched sago factories wastewater and the land becomes unproductive. One-third of the wastewater is presently channelled through a few installed biogas plants with a purification efficiency, biological oxygen demand, of only around 30%. Microbiologically and chemically analysed in- and effluents of biogas plants exhibited nutrient contents sufficient to maintain a rice crop and significantly higher population densities of fermenting bacteria and methanogenic archaea, despite C/N ratio of about 250. CO2 and CH4 emissions from aerobic and anaerobic incubated sago factory biogas plants in- and effluents indicated that the present purification efficiency of 30% can be further enhanced. This investigation has given clues for designing a purification system that connects the already installed biogas plants with a well-aerated, hydro-cultured, constructed wetland and a Stirling motor device for electric power gains and heat distillation, for enabling reuse of process water and saving groundwater. |
