Waste to resource - beneficial use of water treatment residuals as a stormwater control measure amendment for phosphorus removal

Abstract

2020 Fall.Includes bibliographical references.The increase in nutrient pollution is an alarming issue, and innovative and cost-effective measures need to be taken. This study addressed two issues: removing dissolved phosphorus introduced through stormwater runoff using water treatment residuals (WTRs) and the economic value of diverting this waste material from landfills to be used as an amendment in stormwater best management practices for treating stormwater runoff. The City of Fort Collins has monitored a bioretention rain garden located at a municipal facility for several years and has consistently seen a slight decrease and, at times, even an increase in the total mass of phosphorous in stormwater effluent leaving these facilities. The increase in mass was primarily due to higher dissolved phosphorous concentrations in the rain garden's effluent. Based on prior research at Colorado State University, the use of water treatment residuals (WTRs) was selected for laboratory-scale analysis and field-scale evaluation. This research aimed to evaluate whether this waste material generated during drinking water treatment operations could be diverted from landfills and instead, used as an amendment in stormwater best management practices (BMPs) for treating stormwater runoff. Simultaneously, it is hoped that this waste product's beneficial use can result in a safe and significant reduction in dissolved phosphorous input into water bodies. WTRs from the local water treatment plant were evaluated and found to have a very high adsorptive capacity for phosphorus with a phosphorus sorption capacity (PSC) of 21.56 lbs. dissolved phosphorus per ton WTRs, making it a strong candidate as an amendment to current BMPs. A column test was conducted to demonstrate a proof of concept for how WTRs can reduce phosphorus loads leaving BMPs. Column tests revealed that exposure time and application location (top, mixed, or bottom) of WTRs within the BMP media were the critical factors of phosphorus removal. A study was also conducted to determine how much phosphorus load could be reduced if WTRs were applied to BMPs throughout Fort Collins. The citywide analysis displayed a significant reduction, if not an elimination, of the need to send this current waste product to local landfill facilities, thereby reducing disposal costs and increasing the useful life of local landfill operations. The current operation by the City of Fort Collins disposes WTRs into the county's landfill. This study estimated the cost of current operations, the cost of using WTRs in stormwater BMPs, and an additional potential scenario in where the landfill was moved twice as far. Transportation, tipping/application, and staff time were the main cost components and were estimated for the different scenarios. It was found that using WTRs as an amendment in stormwater BMPs would save the City around $5,000 annually compared to the current operation and$13,000 compared to the disposing of WTRs to the new landfill. The outcome of such an approach was shown to be not only economical, but it also provided environmental and social benefits as it would reduce dissolved phosphorus significantly from stormwater runoff, which results in improved water quality and elimination of a current product