Feasibility Study of Recycling and Reusing Coagulants in Taiwan's Water Treatment Plants Using Sludge Acidification Technique

摘要

As sludge produced from drinking water plants contains large amount of aluminum hydroxide, sludge treated with acid will result in the dissolution of aluminum hydroxide, decreasing of total suspended solid, and hence, the volume of sludge cake. In addition, the supernatant after acid treatment contains high concentration of aluminum ions, making it to be reusable as coagulants. The aluminum concentration in the supernatant after acidification decreases with pH. The optimal pH value for acid treatment of sludge is 2.5 after testing sludge samples from 2 water treatment plants in Taiwan. The performance of recycled coagulants is comparable to new PAC, and chemical changes after acidification need to be considered when using recycled coagulants. The method presented in this study could be a cost effective pretreatment of sludge because it has the potential to reduce the volume of sludge and reduce the usage of coagulant by recycling the supernatant.