Enhancement of flocculation and dewaterability of a highly stable activated sludge using a hybrid system of organic coagulants and polyelectrolytes

Abstract

This study investigates the influence of hybrid coagulation-flocculation system on the flocculation and dewaterability efficiency of a real highly stable activated sludge obtained from the membrane bioreactor tank of a petroleum industry. Two organic coagulants, polyDADMAC (FL 4440) and polyamine (FL 2949), coupled with differently structured polyacrylamides (PAMs) are used. Residual turbidity, Zeta potential (ζ), flocs size, and capillary suction time (CST) are used to assess the impact of the hybrid system on the degree of flocculation and dewaterability of MBR sludge. The study reveals that electrical double layer compression, which lowers the electrostatic repulsion between the particles, contributes to the improvement in flocculation behavior. Addition of FL 4440 and FL 2949 prior to PAM has greatly reduced the turbidity and ζ of the sludge suspension by decreasing the required doses of PAMs from 67 % to 80 % depending on the type of the PAMs used. Addition of FL 2949 and FL 4440 has strong influence on the linear structured PAMs with 71 and 80 % reduction in the required PAM’s dose for the 40 % Charge density (CD) (FO 4490 SSH) and 60 % CD (FO 4690 SSH), respectively followed by slightly and highly branched structured PAMs. Similar observations have been noted for flocs size and dewaterability (CST) measurements of the flocculated MBR sludge. Overall, this study has successfully determined the effect of hybrid coagulation-flocculation on the flocculation performance of MBR sludge.