Advanced pond system: performance with high rate ponds of different depths and areas.

Many domestic Wastewater Stabilisation Ponds (WSPs) or oxidation ponds in New Zealand require upgrading to reduce pollution of receiving waters. Advanced Pond Systems (APS) consisting of an Advanced Facultative Pond, High Rate Pond, Algae Settling Pond and Maturation Pond may provide a cost effective upgrade option. This paper presents the results of a 2-year study of the performance of two pilot APS systems with High Rate Ponds of different depths and areas. The HRPs of the APS systems both had the same flow rate (5 m3 d(-1)), volume (37.5 m3) and thus hydraulic retention time (7.5 d). However, the East HRP had an operating depth of 0.30 m and a surface area of 128 m2, and the West HRP had an operating depth of 0.45 m and a surface area of 85 m2. APS system performance was compared in terms of improvement of water quality. For nearly all parameters measured, there was little difference in performance between the two systems suggesting that the system with the smaller area could be used without affecting treatment. Comparison of final effluent with typical effluent of New Zealand WSPs showed that APS effluent was of higher quality and much less variable over time.