Effect of oligochaete worm body fluids on biological phosphorus removal in a bench-scale EBPR system

Abstract

During waste sludge reduction by oligochaetes, phosphorus (P) concentrations in the effluent have been noticed to increase. In the current study, batch experiments were carried out in order to provide explanations for this phosphorus release. The results indicated that increase in effluent phosphorus concentration might not be directly linked to the phosphorus in worm body fluids, as the phosphorus concentration in the system at the start of each operational period did not change significantly. However, the phosphorus removal efficiency rapidly dropped from 93.9%±1.9% to 62.2%±1.3% with increasing addition of oligochaete worm body fluids. Furthermore, an increase in worm body fluids induced a remarkable enhancement of anaerobic phosphorus release rate as well as anaerobic storage of poly-β-hydroxyalkanoate (PHA). At a worm density (wet weight) of 14.4 g/L, the anaerobic phosphorus release rate was elevated by 31.1%±2.8% and 57.3%±4.6% at 2.5% and 5.0% worm death rate, respectively, compared with the control. The contribution of worm body fluids to PHA production was 39.3–67.7 mg/g of dead worm (wet weight), which was mainly attributed to the extra synthesis of poly-β-hydroxyvalerate (PHV). Unfortunately, in the concomitant aerobic stage, inhibition of 3-hydroxybutyric acid (PHB) oxidation and ammonia utilization was observed along with the increasing addition of worm body fluids. Meanwhile, nitrite elevation was found at the beginning of the aerobic stage, which might be negative to the aerobic metabolic processes performed by phosphate-accumulating organisms (PAOs), namely PHB oxidation, phosphate uptake and ammonia utilization for biomass growth.