Advances in Wastewater Treatment Pond Performance Using High Rate Ponds
Ponds are probably the most common technology used for treatment of municipal, agricultural, and aquacultural wastewaters in the US. Compared to mechanical treatment technologies, ponds remove oxygen demand and suspended solids with low cost and energy consumption. However, nutrient removal is an increasingly common regulatory requirement, and conventional ponds are not well suited for nitrogen and phosphorus removal. Newer pond technologies (e.g., paddle wheel-mixed high rate ponds and newer variants of aerated lagoons) have advanced the reliability, effectiveness, and geographical range of pond treatment. This paper reports on results of pilot studies that have the goal of developing operational methods for high rate ponds (HRPs) that will allow them to consistently meet typical total suspended solids (TSS) secondary treatment discharge limits through bioflocculation, without chemical coagulants, and to allow them to remove nutrients to meet concentration or mass load discharge limits. The research was conducted in model 5-m2 (50-ft2) HRP tanks fed municipal wastewater. Unlike other Cal Poly HRP studies in which the ponds are operated at a 30-cm depth (1 ft) to optimize solar exposure of the algal cells and sparged with CO2 to balance carbon:nutrient ratios, the present studies were conducted in 68-cm deep ponds without CO2 addition, to better mimic existing full-scale wastewater treatment HRPs. Hydraulic residence times of 3 to 5 days were tested, and nighttime aeration was provided to some ponds. The studies demonstrated the ability to maintain bioflocculated algal cultures, with settling of algal biomass to achieve typical effluent discharge limits for pond suspended solids (40-60 mg/L). Total ammonia nitrogen removal during summer was >90%, and during winter it averaged 73%. Soluble carbonaceous BOD5 was <10 mg/L, and total BOD5 after effluent settling was <50 mg/L. These results are promising steps towards developing a low-cost, energy-efficient pond technology that, in suitable climates, can meet modern discharge standards.
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Document Type: Research Article
Publication date: 2011-01-01
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