ENHANCEMENT OF BIOLOGICAL PHOSPHOROUS REMOVAL FROM WASTEWATER

Abstract

Minimizing the anthropogenic nutrient input such as phosphorous (P) to aquatic ecosystems is necessary to prevent eutrophication. Conventional chemical precipitation of P in wastewater using alum is an efficient approach but a large amount of biosolids is produced and the use of chemicals is costly. Enhanced biological phosphorous removal (EBPR), driven by polyphosphate accumulating organisms (PAOs), offers a promising alternative. However, PAOs require an external carbon (C) source for optimal P removal, and competition from other microorganisms, along with low influent carbon availability, can limit EBPR efficiency. This dissertation investigates strategies to improve biological P removal by evaluating the role of PAOs in activated sludge and exploring efficient C sources.First, the contribution of microorganisms to remove P evaluated and different C sources that have been used in EBPR discussed. Among various organic compounds, acetate and propionate emerge as the most favorable options for achieving stable and efficient P removal by PAOs. However, if these organic compounds are manufactured using fossil fuel-derived materials, their addition will reduce the economic and environmental benefits of EBPR. In comparison, in-line fermentation and side-stream EBPR (S2EBPR) are more advantageous in generating C sources for PAOs. Then, to connect the previous studies to real-world applications, a full-scale wastewater treatment has been studied. Batch tests were performed to assess the facility's performance under different conditions, incorporating data from both the facility and activity tests. Batch experiments revealed a strong positive correlation (r = 0.91) between temperature and C consumption rate (3.56-8.18 mg-COD/g-VSS/h) in the system, with temperature ranging from 14 to 18 °C. The anaerobic P-release to COD-uptake ratio decreased from 0.93 to 0.25 mg-P/mg-COD as the temperature increased, suggesting competition between PAOs and other C-consumers, such as heterotrophic microorganisms, to uptake bioavailable C. Lastly, to evaluate the potential of crude glycerol (CG) as a waste-derived C source in enhancement of PAOs activity batch experiments were conducted and kinetic parameters were measured to evaluate the direct and indirect application of CG. Promising results were observed to use CG for supporting PAO activity. The results indicated that CG addition to waste activated sludge (WAS) fermentation increased soluble COD (sCOD) of the fermenter effluent by 64.6 ± 5.7% after 5 days compared to WAS alone. WAS and CG co-fermented sludge improved PAO activity, increasing P release and uptake rates by 61.0 ± 11.8 and 22.2 ± 3.3%, respectively, compared to WAS-alone fermented sludge.