The Methods for Minimization of Excess Sludge Production

Abstract

Municipal and industrial wastewater treatment plants produce large amounts of sludge. The treatment and disposal of sludge compulsory depend on the environmental and legal obligations. Moreover, the cost of sludge treatment and disposal is more than 50 % of total cost of wastewater treatment. The reasons such as legal restriction, increasing cost and sensitivity of sludge disposal accelerated the researches related to the investigation and developing of strategies for the minimization of sludge production.

The reasonable way of tackling problems related to sludge-management is to reduce sludge production in the wastewater treatment itself, rather than relying on post treatment. Alternative technologies for on-site reduction of sludge production have been studied since 1990s. The approaches related to sludge reduction of excess sludge production are based on cryptic growth with cell lysis, uncoupling metabolism, endogenous metabolism and microbial predation.

The most widely adopted techniques in sludge reduction such as ozonation, chlorination, mechanical treatment, ultrasonic treatment, thermal, chemical and thermo-chemical treatment and their combination  are based on lysis cryptic-growth. The techniques based on uncoupled metabolism are the addition of chemical metabolic uncouplers and addition of side-stream reactor (Oxic-Settling Anaerobic (OSA) Process). Sludge reduction techniques based on endogenous metabolism are basically extended aeration activated sludge processes and membrane biological reactors (MBR). The process based on microbial predation by organisms such as metazoan and protozoa is also applicable for sludge minimization.

This study summarized the state-of-the-art of the current sludge minimization technologies based on different metabolisms for during biological treatment. These different methods can be utilized for sludge minimization considering capital, operation and environmental cost. The feasibility of methods should be investigated in full-scale treatment plants in a long term operation for the comparison and interpretation of minimization methods.