Effect and optimization of acid-base method in pretreating sludge with low organic content

Effect of acidic and alkaline pretreatment on the disintegration of high solid sludge with low organic content was studied. The pretreatment condition was also optimized based on the economy of chemical reagent addition and the performance of anaerobic biochemical methane potential experiment. Experimental results showed that the solubilizations of COD, protein, carbohydrate and DNA were almost the same, i.e. the related concentrations increased with pH under alkaline conditions, but decreased under acidic conditions, and the performance of alkaline pretreatment was superior to that of acidic pretreatment. The solubilization rate of COD at pH 9, 10, 11, 12 and 13 was 6.5%, 18.0%, 36.7%, 65.5% and 83.5%, respectively. It was also observed that the solubilizations of ammonia and phosphorus were different from those of organic matters, i.e. the related performances under acidic conditions were better than those under alkaline conditions. In addition, the consumption of chemical reagents increased with alkaline pHs and the reaction ratio of OH- decreased sharply when pH was higher than 12. However, alkaline treatment at low pHs (such as 9) showed limited enhancement of methane productivity and volatile solids (VS) removal performance. Therefore, the optimal condition of acidic and alkaline pretreatment on high solid sludge with low organic content was determined as pH 10 or 11, considering the treatment performance and consumption of alkaline reagent.