Analysis of aquatic worms in flocculated digested sludge and extraction of extracellular polymeric substances in wastewater treatment plants

Abstract

Activated sludge process in wastewater treatment plant (WWTP) produces large amount of excess sludge. The disposal of sludge in Netherlands is costly (500 EUR/ton wet solids), and therefore reduction techniques of digested sludge are of great interest to improve the costs of wastewater treatment. First part of this study focused on one of the biological approaches to reduce the excess sludge that can be achieved by aquatic worms in short period of time. Worms are efficient degraders to extra mineralization of sludge into biomass, water and CO2. In optimal condition the total biomass production is low. The investigation on worm predation shows high concentration of ammonia in sludge is toxic and it inhibits the growth of worms, so flocculation was done to separate ammonia from solid. The hypothesis is that flocculated digested sludge (FDS) can be degraded by aquatic worms. In this study, we evaluated the degradation rate, temperature effect, ammonia concentration and worm growth rate. The obtained results from worm experiment showed, in long test (12 days), with the worm biomass of (21.2 g/ww), the degradation of sludge in worm reactor is (15.75 %), while it is (6.65 %) in aerated reactor. Temperature is not conclusive and it could be between (18 to 22C) n the second part of the experiment, the extraction of extracellular polymeric substances (EPS) method in flocculated digested sludge to compare with non-flocculated digested sludge was evaluated. The results indicated concentration of EPS in digested sludge and flocculated digested sludge is not the same by applying extraction method named cation exchange resin. Although sonication is an applicable technique to destroy the size of flocs in flocculated digested sludge, the result does not show any balance in amount of extracted EPS in both types of sludge.