Septic tanks and cesspools are the main onsite wastewater treatment systems in Suffolk County, Long Island New York, and they are the major source of excess nitrogen loading to the coastal environment. When upgrading these systems with advanced treatment unit (ATU), considerations should be taken upon the impact of legacy nitrogen that remained surrounding the cesspools. In this study, we investigated the legacy nitrogen quantity and composition in two existing cesspools. Core samples were taken every 6’’ beneath the bottom of the cesspool with a total of 8 samples from two sites. Total nitrogen (TN) and carbon (TC) maintained in the core samples were analyzed. Nitrogen species composition and quantity were measured by standard soil extraction method. The quantity of pathogen in the sediments was measured by EPA method 1680.<br/>Highest nitrogen concentrations were observed at top 6’’ of the sediment, and organic nitrogen comprises more than 95% of the TN. Ammonium was the major inorganic nitrogen form and accounts for 0.32 and 3.17 % of TN present in the sediment samples from two sites. An average of 0.01and 0.12 mg inorganic nitrogen/g soil, and 3.0 and 4.1 mg TN/g soil were observed in sediment samples from two sites, respectively. The amount of TN decreased as the depth increased at both sites. A linear correlation (R<sup>2</sup>= 0.86 and 0.93) was observed on TOC and TN of the sediment samples indicating the amount of legacy nitrogen depends on the quantity of TC present. The pathogen test showed a low concentration of fecal coliform (600 MPN/g dry soil) in the sediment samples. The quantitative analysis of microbial composition is underway. In this study, we will be able to estimate the quantity of legacy nitrogen as a nitrogen sink in current cesspools, and evaluate its impact on nitrogen releasing when current systems are upgraded.

Impact of legacy nitrogen in conventional septic system on nitrogen removal for onsite wastewater treatment

255th National Meeting (2018)

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