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Recirculating Sand Filters for Treatment of Synthetic Dairy Parlor Washings
Author(s) -
Healy M. G.,
Rodgers M.,
Mulqueen J.
Publication year - 2004
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq2004.7130
Subject(s) - effluent , sand filter , filtration (mathematics) , anoxic waters , environmental science , denitrification , environmental engineering , filter (signal processing) , chemical oxygen demand , nitrification , nitrate , pulp and paper industry , organic matter , slow sand filter , nitrogen , environmental chemistry , chemistry , water treatment , wastewater , engineering , statistics , mathematics , organic chemistry , electrical engineering
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 (NO 3 –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 NO 3 –N concentration of 60 mg L −1 With recirculation, the improvement in the removal of organic matter and ammonia N (NH 4 –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.