Technical Paper

The study compared the performance of upflow anaerobic sludge blanket (UASB) reactors and anaerobic filters (AF) for the treatment of wheat straw washwater (WSW) which has a high concentration of Potassium ions. The trial was conducted at mesophilic temperatures (37 o C). The digesters were started up over a 48-day period using a synthetic wastewater feed and reached an organic loading rate (OLR) of 6 g COD L -1 day -1 with a specific methane production (SMP) of 0.333 L CH4 g -1 COD. When the feed was switched to WSW, it was not possible to maintain the same loading rate; the SMP in all reactors fell sharply to less than 0.1 L CH4 g -1 COD, with the AF affected more than the UASB. On reducing the OLR to 3 g COD L -1 day -1 the reactors recovered to produce 0.21 L CH4 g -1 CODadded and exhibited 82% COD removal. A discrepancy between the COD consumed and the methane produced could be accounted for through increased maintenance energy requirement of the microbial community for osmo-regulation as K + was found to accumulate in the sludge and in the UASB reached a concentration of 4.5 mg K g -1 wet weight of granules. Overall, anaerobic digestion of WSW was found to be one of the promising techniques in generating clean energy as one tonne of wheat straw would approximately generates 4148 L of CH4.