Influence of inoculum selection on the utilisation of volatile fatty acid and glucose in sulfate reducing reactors.

The capacity of three inocula (sewer biofilm, mangrove and estuary sediment) to utilise typical fermentation products of municipal solid waste for biological sulfate reduction was investigated. Each inoculum was used in two reactors, one fed a mixture of volatile fatty acids and another fed glucose to provide a suite of fermentation products via naturally occurring fermentation. Following 228 days of reactor operation, reactors inoculated with mangrove and estuary sediments exhibited higher sulfate reducing efficiencies (80-88%) compared to the biofilm-inoculated reactors (32-49%). Minimal use of acetate and its accumulation in the biofilm-inoculated reactors pointed to the high abundance of incomplete-oxidising sulfate reducing bacteria (SRB), Desulfovibrio and Desulfobulbus (90-96% of the sulfate reducing population). Although Desulfovibrio was also prominent in reactors inoculated with mangrove and estuary sediments, Desulfobacter, a known acetoclastic sulfate reducer, emerged from trace levels in these sediment (0.01% abundance in the estuary sediments and below detection in the mangrove sediments) to comprise 14%-70% of the sulfate reducing population at the end of reactor operation.

Rapid digestion of shredded MSW by sequentially flooding and draining small landfill cells.

This paper compares the digestion of a packed bed of shredded municipal waste using a flood and drain regime against a control digestion of similarly prepared material using a trickle flow regime. All trials were performed on shallow (2m) beds of the sub-8cm fraction of shredded mixed MSW, encapsulated in a polyethylene bladder. The control cell (Cell 1) was loaded with 1974 tonnes shredded municipal waste and produced 76±9m(3) CH4dryt(-1) (45±2m(3) CH4 'as received't(-1)) over 200days in response to a daily recirculation of the leachate inventory which was maintained at 60m(3). The flood and drain operation was performed on two co-located cells (Cell 2 and Cell 3) that were loaded simultaneously with 1026 and 915 tonnes of the sub-8cm fraction of shredded mixed MSW, with a third empty cell used as a reservoir for 275m(3) of mature landfill leachate. Cell 2 was first digested in isolation by flooding and draining once per week to avoid excessive souring. Gas production from Cell 2 peaked and declined to a steady residual level in 150days. Cell 3 was flooded and drained for the first time 186days after the commencement of Cell 2, using the same inventory of leachate which was now exchanged between the cells, such that each cell was flooded and drained twice per week. Biogas production from Cell 3 commenced immediately with flooding, peaking and reducing to a residual level within 100days. The average CH4 yield from Cells 2 and 3 was 123±15m(3)dryt(-1) (92±2m(3) 'as received't(-1), equal to 95% of the long term (2month) BMP yield.