Activated-sludge yield reduction using chemical uncouplers

To determine whether chemical additions can be used to reduce sludge production in biological wastewater treatment, uncouplers of respiratory adenosine triphosphate production were added to activated-sludge cultures. Effects of 12 uncoupling chemicals on cell yields in batch cultures were compared. The most effective of these chemicals, 2,4,5-trichlorophenol (TCP), was tested in a continuous-flow, bench-scale, completely mixed activated-sludge system treating simulated municipal wastewater. Initially, TCP addition reduced average yield by approximately 50%. After 80 days, sludge yield increased as TCP levels in the reactor decreased. Specific oxygen use rates were good indicators of sludge yields, increasing from 8 g O2/g volatile suspended solids (VSS)·d without TCP addition to approximately 20 g O2/g VSS·d, when sludge yield was lowest. These results suggest that addition of chemical uncouplers to biological wastewater treatment systems can significantly reduce sludge production, but long-term bioacclimation can eventually negate the effects of uncoupler addition.