Nutrient Removal by Effluent Spraying

by Herbert B. Foster, Jr.,
Paul C. Ward,
Arnold A. Prucha,

Serial Information: Journal of the Sanitary Engineering Division, 1965, Vol. 91, Issue 6, Pg. 1-12

Document Type: Journal Paper


The South Tahoe Public Utility District, which provides sewage collection and disposal for the south shore area of Lake Tahoe, Calif. and Nev., operates an activated sludge plant whose effluent is first ponded and then sprayed on a forested hillside. The area available for spraying is limited and is therefore saturated, and the water that escapes from the soil mantle is either collected in an intercepting ditch and recycled back to the oxidation pond or it reaches the small creeks which eventually enter Lake Tahoe. The nutrient load carried by the water that reaches the Lake was of principal concern. Extensive measurements were made of the volumes and nature of the applied effluent and the runoff waters. It was found that when the hillside was intermittently sprayed during dry weather periods at rates averaging approximately 38,000 gpad, approximately 90% of the applied phosphate and 60% of the applied nitrogen were removed. During the periods when the soil mantle was soaked with rainfall or snow melt, removal efficiencies dropped. The poorest performance occurred when the hillside was frozen and one area was sprayed without rest. Synthetic detergent, coliform, fecal coli, and fecal streptococcus removals were also found to be substantial.

Subject Headings: Lakes | Slopes | Nutrients | Effluents | Saturated soils | Snowmelt | Lifeline systems | Sewage

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