Role of Ca-bentonite to improve the humification, enzymatic activities, nutrient transformation and end product quality during sewage sludge composting

This study was aimed to examine the response of Ca-bentonite (CB) amendment to improve the sewage sludge (SS) composting along with wheat straw (WS) as bulking agent. Five treatments (SS+WS) were mixed with or without blending of discrepant concentration of CB (2%, 4%, 6%, and 10%), respectively, and without CB added treatment applied as the control. The results showed that compared to control and 2% CB blended treatments, while the 6-10% CB-amended treatment indicated maximum enzymatic activities with the composting progress and highest organic matter degradation and loss. The amendment of 6-10% CB increased the humic acid, HA/FA ratio, DON, NH4+-N, NO3 and DOC but reduced the fulvic acids content and the maturity period by 2 weeks as compared to control. In addition, maturity parameters also confirmed that the highest seed germination was observed with the 10% CB applied compost followed by 6% CB, 4% CB and 2% CB applied treatments, respectively.