Abstract
Abstract
Two pilot plant units, a membrane bioreactor (MBR) and a sequencing bioreactor (SBR), were operated in parallel during 2 years on municipal wastewater after primary sedimentation. Biosolids were characterized by measurements of total and volatile suspended solids, settling velocity, cake filtration, water distribution, and polymer demand. Higher volatile suspended solids/total suspended solids (VSS/TSS) ratios characterized the MBR biosolids obtained in solid residence time conditions of 25 days. Settling tests indicated a poor settling and significantly higher sludge volume index to MBR biosolids. Cake filtration and specific resistance reflected low dewatering characteristics of MBR biosolids. Over 90% of the water in the MBR biosolids mixture was entrapped in the biofloc structure and could be released by much higher amounts of chemical conditioner than SBR biosolids. Higher concentrations of carbohydrates and protein have been detected in the mixed liquor of MBR, and this could explain the different biosolids characteristics compared to SBR. Characteristics of MBR biosolids, as determined in this comparative study, should raise important engineering issues in the design and the operation of biosolids treatment of wastewater treatment plants.