Research on waste stabilisation ponds in the United Kingdom--initial results from pilot-scale facultative ponds.

Three pilot-scale facultative ponds were constructed at Esholt wastewater treatment works in Bradford, West Yorkshire, UK. The ponds were operated in parallel to test the effect of surface BOD loading on performance and the maintenance of facultative conditions. The performance criteria adopted were BOD, SS and ammonia removal. The criterion for facultative conditions was the presence of an algal population maintaining aerobic conditions at the pond surface. Filtered BOD removal was found to be more than 90%, non-seasonal, and related to areal BOD loading. SS removal was also found to be non-seasonal, at around 95% but not related to areal BOD load. Ammonia removal was seasonal (32-48% October to March; 60-81% March to July) and related to areal BOD load. At the test loadings (60, 110 and 169 kg/ha.d) an algal population was not maintained in winter. The initial results indicate that a much lower loading is required to maintain facultative conditions than to optimise BOD and SS removal.