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Treatment performance of advanced onsite wastewater treatment system

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Treatment performance of advanced onsite wastewater treatment systems in the Otsego Lake watershed, 2008 results Holly Waterfield1 and Sarah Kessler2 INTRODUCTION This report serves to document the treatment performance monitored for two of the systems installed as a part of a NYS DEC grant to demonstrate the use of advanced onsite wastewater treatment systems, and one additional system that was installed on BFS property to serve the Upland Interpretive Center (UIC). Treatment performance was assessed based on the following analyses: biochemical oxygen demand (BOD or CBOD), total suspended solids (TSS), nitrate, ammonia, and total phosphorus (TP). An historical overview of Otsego Lake’s nutrient loading and onsite wastewater treatment is provided below. Otsego Lake is located in northern Otsego County, New York. According to the historical overview by Harman, et al. (1997), the monitoring of Otsego Lake’s water quality dates back to a 1935 NYS Department of Environmental Conservation (DEC) study. Routine water quality monitoring efforts began subsequent to the establishment of the Biological Field Station (BFS) in 1968 (Harman, et al. 1997). Comparisons to these and other historical datasets had shown overall decreasing water quality conditions, noting in particular increased phosphorous concentrations likely tied to loading from watershed activities (agriculture, road maintenance, onsite wastewater treatment, etc.). Onsite wastewater treatment (septic) systems are estimated to contribute only 7% of the total phosphorus load (Albright 1996), though the combination of the bio-available form and time of greatest loading at the height of the growing season is likely to lead to stimulation of algal production (Harman, et al. 1997). The cascading effects of such nutrient loading on the lake’s ecosystem are far-reaching, and began to concern lake users and the Village of Cooperstown, which uses Otsego Lake as its source of drinking water. In 1985, the Village implemented public Health Law 1100 in order to give them legal grounds to protect the lake as their source of drinking water (Harman, et al. 1997). Additional actions to curb further water quality degradation in the lake culminated in the formation of a watershed management plan in 1998, which identified nutrient loading as the greatest threat to the health of Otsego Lake. Wastewater treatment via onsite treatment systems were listed second on a prioritized list of action areas (Anonymous 1998), and efforts to manage the effectiveness of these treatment systems began with a 2004 inventory of all systems in the established Lake Shore Protection District followed by the inception of the inspection program in 2005 (Anonymous 2007). Under this program, any system found to be in failing condition is to be replaced within one calendar year. Such replacement systems generally make use of advanced or enhanced treatment technologies due to conditions that constrain the use of conventional designs, such as setback to the lake or a tributary, soil depth to bedrock or groundwater, percolation rate, etc. Many of these enhanced treatment technologies are new the region, and thus are unfamiliar to industry professionals, regulators, and residents. For this reason, a DEC grant sought and obtained to fund a demonstration project to install and monitor  Research Support Specialist, Biological Field Station. 2 BFS Intern funded by OCCA, summer 2007. Present affiliation: Ithaca College. the treatment performance of six shared advanced treatment systems. The scope of the grant has since been amended, changing the total number of treatment systems to three, with the last installed in December of 2008. Biochemical oxygen demand (BOD or CBOD) and total suspended solids (TSS) are typical metrics used to characterize the strength of residential wastewater (Crites and Tchobanoglous 1998). BOD is an analysis used to determine the relative oxygen requirements of wastewater, effluents, and polluted waters, by measuring the oxygen utilized during a given incubation period (APHA 1989). It is expected that organic material is broken down as wastewater progresses through a treatment system, thus decreasing the oxygen requirements of highly-treated wastewater and in turn resulting in lower BOD concentrations over the course of the treatment system. TSS analysis measures the total amount of suspended or dissolved solids in wastewater. Solids may negatively affect water quality for drinking or bathing and potentially clog a drain field. As with BOD, the amount of solids in treated effluent should be lower than that of raw wastewater. Nitrate and ammonia concentrations provide insight into the physio-chemical conditions along the treatment train, as the transformations between various nitrogen forms are dependent on oxygen availability, alkalinity, temperature, and the presence of specific bacterial populations. Nitrogen is a dynamic component of wastewater treatment systems, which are often designed to facilitate specific transformations of nitrogen species. Advanced treatment systems most often incorporate a secondary treatment step that involves aerating the wastewater in order to create favorable conditions for the bacterial transformation of ammonia to nitrate, called nitrification. Nitrogen can be completely removed from the waste stream through the process of denitrification, during which nitrate is converted to nitrogen gas (N2), which is released to the atmosphere. Nitrification is generally considered the most limiting step of this overall nitrogen removal process, as it supplies the nitrate that is converted to N2 gas. Phosphorus, as previously mentioned, is the nutrient of greatest concern with regards to vulnerable freshwater bodies. The removal of phosphorus from the waste stream prior to subsurface disposal will be of great benefit to lake management efforts should the technologies installed prove to be successful. METHODS AND MATERIALS Three onsite wastewater treatment systems (OWTS) were monitored in this study and are displayed in Figure 1; these include the system serving the SUNY Oneonta BFS Thayer Farm Upland Interpretive Center (UIC) and two homeowner systems, which for the purpose of this study will be called OWTS 1 and


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