عنوان مقاله [English]
In the first stage of this study, the compound effects of sludge dry solid content and residual bulking agent type (paper, saw dust, straw) mixed with activated sludge (10, 15, and 20% dry solids) on volatile solids (V.S.) reduction were investigated using Eisenia foetida in pilot scale experiments with batches of fifty earthworms in each of the 10 experimental treatments over a period of 10 weeks. The maximum V.S. reduction was attained in the mixture of sludge and paper, with a D.S. of 15% (0.42 ± 0.03 % day-1) while the minimum V.S. reduction was achieved in the mixture of sludge and straw, with a D.S. of 10% (0.26 ± 0.01 % day-1). In the second stage, the survival of Eisenia foetida in the anaerobic sewage sludge was investigated. In the unmixed raw anaerobic sludge, all the earthworms died during the first 9 weeks of the study period due to acute toxicity. From week 10, however, their survival rate improved so that by week 12 when toxicity reduced to 25.40%, they completely survived. This is while in the mixture of anaerobic sludge with paper (D.S. 15%), 100% of the earthworms survived from week 8 after the volatile solids reduced to 20.42% and 17.40%.
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