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Abstract
Activated sludge is widely used in wastewater treatment plants (WWTPs) to treat municipal and industrial wastewater. The formation of activated sludge flocculates underpins the separation of biomass from nutrient depleted wastewater through gravity. Although research has been conducted to understand and improve activated sludge treatment, there remains a lack of knowledge on underlying mechanisms in activated sludge floc formation. Consequently, the knowledge base for preventing activated sludge malfunctions such as pin flocs or bulking is lacking.
This project is based on the hypothesis that activated sludge flocs are nucleated by particulate organic matter (POM) that passes through primary screening and sedimentation and enters secondary biological treatment units. Colonization of particulate organic matter by activated sludge bacteria was compared with colonization of glass beads. The types of organic matter tested includes chitin, keratin, lignocellulose, lignin and cellulose. Bacterial community profiles were generated from DNA extracted from these biopolymers after incubation in aerated activated sludge over two weeks in the presence and absence of regular nutrient amendment regimes (reduced carbon and nitrogen). Scanning electron microscopy images of colonized surfaces were generated.
Keratin showed poor attachment ability for bacterial colonization on its surface in activated sludge. Bacterial colonization and biofilm formation processed fastest on chitin among tested POM and chitin-biofilms have higher diversity bacterial communities which could potentially withstand environmental disturbance. The addition of reduced C, N resources in activated sludge promote the dominance of Proteobacteria in activated sludge and bacteria capable of decomposing POM tend to occupy more on corresponding POM over time. The abundance of key bacteria involved in nitrification and denitrification on specific POM was explored and provided useful information for adjusting engineered biofilms to a high efficiency for nitrogen pollutants removal.
Furthermore, this study successfully isolated five strains performing ammonium, nitrite, nitrate transformation and identified them as: Pseudomonas guangdongensis, Acinetobacter tandoii, Pseudomonas pseudoalcaligenes, Pseudomonas stutzeri, Rhizobium borbori. N-pollutant degradation was observed with chitin colonized by N processing bacteria in artificial wastewater with 50 mg/L NH4+, NO2- and NO3-. Potential exists for constructing synthetic activated sludge flocs through using chitin as a surface substratum to be deployed in WWTPs for N-pollutant degradation. Taken together, this research proved the feasibility of constructed biofilm deployed in the wastewater treatment in future and gave some credence to the notion of a development strategy in WWTPs.