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Simultaneous nitrification-denitrification and clarification in a pseudoliquified activated sludge system.
George F Nakhla1, Andrew Lugowski, Anatoly Sverdlikov
1Department of Chemical and Biochemical Engineering, University of Western Ontario, London, Canada. gnakhla@eng.uwo.ca
Summary
This novel wastewater treatment technology integrates nutrient removal and solids separation, achieving high reductions in biochemical oxygen demand and total suspended solids. The system demonstrated reliable performance across various conditions, offering a promising solution for efficient wastewater management.
Area of Science:
- Environmental Engineering
- Water Treatment Technologies
- Biotechnology
Background:
- Conventional wastewater treatment involves multiple stages for nutrient removal and solids separation.
- There is a need for integrated processes that enhance efficiency and reduce operational costs.
- Pilot studies are crucial for validating novel wastewater treatment technologies.
Purpose of the Study:
- To evaluate a novel pseudoliquified activated sludge process for simultaneous nutrient removal and solids separation.
- To assess the system's performance under varying operational conditions, including flow rates, solid residence times (SRT), and temperatures.
- To model the process using Activated Sludge Model No. 2 and compare predictions with experimental data.
Main Methods:
- A pilot-scale pseudoliquified activated sludge system was operated on grit removal effluent.
- Experiments were conducted at flow rates of 29.4 to 54.7 m3/d, SRTs of 15, 37, and 57 days, and temperatures from 12 to 28°C.
- The process was modeled as a two-stage system (aerobic followed by anoxic) using Activated Sludge Model No. 2.
Main Results:
- Achieved >96% biochemical oxygen demand (BOD) and ~90% total suspended solids (TSS) reduction, with effluent concentrations as low as 3 mg/L.
- Demonstrated high denitrification efficiencies (90-91%) and total nitrogen removal, achieving tertiary effluent quality.
- Reported sludge yields over 50% lower than typical activated sludge plants due to high biomass concentrations and long SRTs.
- Nitrification efficiency was impacted at temperatures below 15°C, but overall system performance was reliable despite influent fluctuations.
- Effluent phosphorus concentrations of 0.5-0.8 mg/L were achieved with ferric chloride addition.
- Model predictions for soluble BOD, ammonia, nitrates, and orthophosphates showed good agreement with experimental data.
Conclusions:
- The novel pseudoliquified activated sludge process effectively integrates nutrient removal and solids separation in a single step.
- The system demonstrates robust performance, achieving high effluent quality for BOD, TSS, nitrogen, and phosphorus.
- Lower sludge yields present a significant operational advantage compared to conventional activated sludge processes.
- The process is amenable to modeling, providing a basis for further optimization and scale-up.