This paper investigated the influence of organic loading on BOD and COD removal in primary facultative ponds. The study was based on six full-scale pond plants in which average removals of unfiltered biochemical oxygen demand (BOD) and chemical oxygen demand (COD) were 72 and 50%, respectively. For filtered samples, the removals were 89 and 83%, respectively. First-order removal rates assuming ideal hydraulic patterns (completely mixed and plug-flow) decreased with increments in the mean hydraulic retention time (HRT). Reduction in organic loading also caused a decrease in removal rates. The results emphasized that HRT and surface organic loading are more reliable to estimate first-order removal rates than traditional Arrhenius-style equations. Thus, HRT and surface organic loading can be used to compute more realistic first-order removal rates and surface removal rates. An alternative design procedure based on HRT and surface organic loading was proposed and demonstrated.
Primary facultative ponds; Removal of organic material; Design model
