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Rice straw was added to a sewage sludge digester and its effects on methane production, dewatering characteristics, and microbial communities in the digested sludge were examined by a continuous digestion experiment under mesophilic conditions (35 °C). Stable gas generation was monitored in all digestion experiments. Methane yield from raw sludge, chopped rice straw and softened rice straw were estimated to be 0.27, 0.18 and 0.26 NL/g total solids load, respectively. The capillary suction time of digested sludge was decreased by the addition of rice straw. Archaeal and bacterial communities in the sludge were elucidated by PCR-DGGE (polymerase chain reaction--denaturing gradient gel electrophoresis) targeting 16S rRNA genes. The Shannon index of DGGE profiles indicated that bacterial diversity increased with the addition of softened rice straw. DNA sequences of significant bands of the digested sludge were most closely related to Methanosaeta concilii (97.4% identity) and Methanoculleus bourgensis (100% identity). Meanwhile, those in the co-digested sludge with rice straw were most closely related to Methanosarcina barkeri (98.4% identity) and Methanoculleus bourgensis (99.3% identity). Although both Methanosaeta spp. and Methanosarcina spp. metabolize acetate to methane, Methanosarcina spp. have a competitive advantage at acetate concentrations of >70 mg/L. Results suggested that the quantity of acetate produced during rice straw degradation may change the archaeal community.

Treatment of eutrophic lake water was investigated, when alum sludge and/or wood were used as the media for laboratory-scale filtration. Process 1 consisted of Column 1 with wood and Column 2 with alum sludge in series, and Process 2 of Column 3 with alum sludge. The filtration velocity was 0.45 and 0.91 m/d for 49 days each. Both processes removed suspended solids and total phosphorus well with about 98% and 92% removal efficiency, respectively. Total nitrogen removal efficiency was higher in Process 1 (64-72%) than Process 2 (18-19%), because of biological denitrification using organics supplied from wood. The dissolution of organics and aluminium from wood and alum sludge, respectively, was not significant in the effluent. An alkaline extraction method was able to extract two-thirds of phosphorus in the alum sludge. Thus, alum sludge was excellent at removing and recovering phosphorus and the filtration combining wood and alum sludge enabled the concomitant removal of nitrogen and phosphorus.

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