Mesophilic (37℃) performance of attached-film anaerobic digesters fed with dairymanure that had been subjected to low temperature (10℃) stress was evaluated. Two digesterspacked with limestone gravel, two with pieces cut from non-woven polyester matting, and two withno packing were subjected to a temperature cycle between 37℃ and 10℃. Two control reactorswithout packing were maintained continuously at 37℃. All reactors were operated in the upflowmode, and the reactors without packing operated similarly to upflow anaerobic sludge blanketsystems. None of the reactors regained their original performance in terms of biogas and methaneproduction characteristics or pollution abatement after the temperature cycle; however, the controlreactors also showed a similar decline in performance during the period of study. The reactors withpolyester packing and those with no packing had similar values for biogas productivity and yield,while those with limestone packing had significantly lower values. It was concluded that the lack ofcomplete recovery of reactor performance could not be attributed to the temperature cycle.Variability in the feed composition or uniform decline in microbial activity over the prolonged periodof time for which the reactors were operational most likely contributed to this effect.
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