Co-Treatment of Water Softening and Wastewater Sludges

摘要

Water softening and wastewater treatment processes both produce large quantities of sludge. It was hypothesized that mixing the softening sludge and wastewater sludge would produce a sludge of intermediate quality more suitable for thickening and dewatering than either sludge treated separately. The study revealed that mixing the sludges reduced final sludge volumes in the range of 4 to 52%. The ratios of softening sludge to wastewater sludge solids was the key factor influencing volume reductions. Total solid balance indicates that negligible dissolution and precipitation occurred upon mixing of the sludges. Slight increases in alkalinity and total hardness were observed in the supernate. Co-treatment of the softening sludge with the wastewater sludge reduced BOD5 and suspended solids in the supernate in the range of 20 to 87%. The improvement was due to improved solids capture. A hypothetical economic analysis for the city of Lafayette, Louisiana (population 80,000), indicated a 16% daily hauling savings by transporting the water softening sludge to the wastewater treatment plant for gravity thickening and final disposal rather than separate gravity thickening sludge disposal.