Sludge predation by aquatic worms: Physicochemical characteristics of sewage sludge and implications for dewaterability

Abstract

Worm predation is an eco-friendly and low energy cost means of sludge reduction that has shown great promise. The worm predation process consists of inoculating specific species of aquatic worms into the sludge system to build a suitable biotope. After predation, the residual sludge needs to be discharged and disposed. This study investigates the potential effects of worm predation on sludge dewatering focusing on the mechanisms, characteristics of sedimentation, filtration and dewatering for the sludge from the predation process. It also describes the changes in extracellular polymeric substance and bound water, and discusses options to improve sludge dewatering. The results suggested that worm predation restrained the viscosity and surface charge of residual sludge and helped prevent sludge bulking. However, sludge filterability deteriorated when predation occurred. The residual sludge experienced a significant reduction in the contents of loosely bound and tightly bound extracellular polymeric substances and a decreased ratio of protein to polysaccharides content during the five days of predation. Extending the sludge retention time of predation to five days contributed to a release of bound water and synergistically improved centrifugal dewatering of the residual sludge with ferric chloride added as conditioner.