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TECHNICAL REPORT

Waste Management

Recirculating Sand Filters for Treatment of Synthetic Dairy Parlor Washings

Department of Civil Engineering, National University of Ireland, Galway, Ireland

^* Corresponding author (Mark{at}marcon.ie).

Received for publication January 10, 2003. Land-spreading and spray irrigation are the most widely used practices for the disposal of dairy wastewaters in Ireland but in some cases there can be problems due to contamination of surface and ground water. The use of intermittent sand filtration has been suggested as an alternative treatment process. However, a single pass through a sand filter limits denitrification because of the absence of reducing conditions following nitrification and the lack of an available carbon source. This leads to poor total nitrogen (TN) reduction and an effluent that is high in nitrate nitrogen (NO₃–N). This paper follows a previous paper in which two instrumented stratified sand filter columns (0.9 and 0.425 m deep, and both 0.3 m in diameter) were intermittently loaded with synthetic dairy parlor washings at a number of hydraulic loading rates, leading to a TN reduction of 27 to 41%. In the present study, under a chemical oxygen demand (COD) of 23.4 g m^–2 d^–1, the TN was reduced by 83.2% when three-quarters of the sand filter effluent was recirculated through an anoxic zone. This produced an effluent NO₃–N concentration of 60 mg L^–1. With recirculation, the improvement in the removal of organic matter and ammonia N (NH₄–N) is minimal. Recirculating sand filters appear to offer a mechanically simple and effective method for the removal of nitrogen from dairy parlor effluents and are a significant improvement over a single-pass sand filter.

Abbreviations: COD, chemical oxygen demand • SS, suspended solids • TN, total nitrogen

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This Issue in Journal of Environmental Quality

JEQ 2004 33: 413-418. [Full Text]  

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