Upgrading Aerated Lagoon Effluent with Intermittent Sand Filtration

Intermittent sand filtration was evaluated as a means of upgrading the quality of aerated lagoon effluents to satisfy the requirements of PL 92-500. The aerated lagoon in question treats the wastes from a milk and cheese factory located in northern Utah. The treatment system consists of two diffused air aeration ponds followed by a facultative settling pond, were applied to pilot scale intermittent sand filters with 0.17 mm and 0.40 mm effective size sands. The filters were loaded hydraulically from 0.25 million gallons per acre per day to 1.0 million gallons per acre per day. It was found that sand size has a profound effect on the quality of effluent produced by filtration. Also, sand size was related to the time of operation before plugging occurred. At the levels of application studied, hydraulic loading rate was found to affect BOD removal regardless of influent concentration. However, effluent suspended and volatile suspended solids concentrations reflected changes in influent concentrations regardless of hydraulic loading rate. It was found that filtration of facultative settling pond effluent provided better removals than direct filtration of aerated lagoon effluent using equivalent sand sixes and hydraulic loading rates. It was concluded that intermittent sand filtration was capable of upgrading the effluent from aerated lagoons to meet present and future discharge requirements when effluent from the facultative settling pond was applied to 0.17 mm effective size sand.