Impact of worm predation on pseudo-steady-state of the circulating fluidized bed biofilm reactor

This paper studies integrated simultaneous carbon and nitrogen removal as well as worm predation, in a circulating fluidized bed biofilm reactor (CFBBR) operated with an anoxic-aerobic bioparticle recirculation. A lab-scale CFBBR with a 8.5-liter reaction zone comprising 2L anoxic and 6.5L aerobic compartments was designed to evaluate the aquatic Oligochaete worm effect. Long-term (200days) performance showed that stable and high-rate chemical oxygen demand (COD) with sodium acetate as the carbon source and total nitrogen (NH₄Cl as nitrogen source) conversions were achieved simultaneously, with low sludge production of 0.082g VSS (volatile suspended solids) g COD^-1 at pseudo-steady-state. Worm predation, which causes considerable sludge reduction of the bioparticle process, was studied. The results proved that the worm predation has a significant impact on the pseudo-steady-state performance of the CFBBR, decreasing biomass yield, decreasing oxygen concentration and increasing expanded bed height.