Analysis of nutrient removal at the Drake Water Reclamation Facility
Date
2016
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Abstract
Since the 1960’s, the Federal Government through the United States Environmental Protection Agency (USEPA) has been working to create and enforce regulations to protect and counteract the degradation experienced in the nation’s waterways due to increased nutrient loading (primarily phosphorus and nitrogen). The eutrophication caused by excess levels of these nutrients is not only an aesthetic issue, but is toxic to aquatic life and can also create issues detrimental to human health. In 2007, the Colorado Department of Public Health and Environment began working on new nutrient regulations for state dischargers, particularly larger Publicly Owned Treatment Works (POTWs) like the City of Fort Collins and its two wastewater treatment plants, Mulberry Water Reclamation Facility (MWRF) and Drake Water Reclamation Facility (DWRF). Since 2008, The City of Fort Collins has been upgrading its secondary treatment systems to Biological Nutrient Removal (BNR) in preparation for National Pollutant Discharge Elimination System (NPDES) permit compliance in 2020. Early in the design process, it was determined that DWRF suffered from a limitation in influent carbon for adequate nutrient removal and carbon addition would need to be considered. The City analyzed various local carbon sources and has been working to determine the viability of beer waste from local breweries as a viable carbon source. The overarching goal of this work is to evaluate the current nutrient removal efforts at DWRF to help determine if adjustments are required to the wastewater treatment Master Plan to consistently meet Colorado’s Regulation 85 nutrient discharge limits. This study included monitoring of nutrient water quality values at specific points in the treatment system while adding beer waste at varying flow rates and durations to determine its effect on the system. Different automated control strategies were tested using several dosage schemes including Oxidation Reduction Potential (ORP) values. Finally, water quality data was analyzed and compared alongside historical nitrogen and phosphorus values to evaluate the effects of the beer waste addition to effluent quality and plant removal performance. The initial values for effluent total inorganic nitrogen showed promise, averaging 9.79 mg/L in comparison to 12.05 mg/L when beer waste was not added. However, a mass balance comparison with influent nitrogen values showed no significant difference in BNR process performance for nitrogen with the beer addition. Effluent phosphorus values averaged 2.24 mg/L-P which was slightly lower than without beer waste addition (2.42 mg/L), but not considered a statistically significant decrease. During the study, an observation was made that adjusting time-of-day and flowrate of the dewatering centrate return significantly decreased effluent phosphorus concentrations down to 1.1 mg/L, significantly lower than P concentrations without beer addition (p < 0.05). An analysis of phosphorus removal at DWRF also highlighted the historical improvement of phosphorus removal as BNR improvements are brought on-line, even though the required effluent limits required by Regulation 85 have not been achieved yet. Overall, carbon addition via beer waste has shown to have positive impact on DWRF’s ability to remove nutrients. Lower effluent concentrations of nitrogen were achieved when beer waste was added to DWRF and lower effluent P concentrations were also achieved as long as centrate return flow was controlled. Additional study is required for long-term control of centrate return flows which may include the analysis of side-stream treatment solutions. Additional analysis to determine the role of beer waste addition independent of centrate flow returns is also recommended.
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Subject
nutrients
wastewater
phosphorus removal
nitrogen removal