Wastewater Management Through Effective Water Reclamation and Discharge Allocation

Abstract

Based on this study’s analysis of the Oxford, North Carolina, wastewater treatment plant (WWTP) water quality data available for the years 2012-2014, the water quality of Oxford’s WWTP effluent was excellent compared to the National Pollutant Discharge Elimination System (NPDES) permit standards. However, despite a high frequency of compliance with the NPDES permit standards over a three year period, zinc and oxygen concentrations in the WWTP effluent may be of concern for the Fishing Creek ecosystem downstream of the WWTP outfall especially during summer or dry periods. Without accurate Fishing Creek discharge data, the degree of dilution and therefore compliance with North Carolina Department of Environmental and Natural Resources (NC DENR) freshwater aquatic life standards for dissolved oxygen and zinc is unknown. Based on the model results and subsequent analysis contained in this report, if the City of Oxford, North Carolina, builds a reclaimed water system, we recommend a wastewater discharge management plan which maximizes the amount of reclaimed water used for beneficial purposes from the City WWTP effluent discharge, with the remainder entering Fishing Creek. The projected amount of water to be reclaimed is estimated through four scenarios which are the inputs to two different models: the amount of reclaimed water is evaluated in economic terms through an incremental cash flow model; the in-stream environmental impacts of the allocation between reclaimed water and creek discharge are also evaluated using a Bayesian network model related to in-stream zinc and dissolved oxygen concentrations. Maximizing the amount of reclaimed water used increases the economic benefit and probability of the Fishing Creek ecosystem being in a ‘good’ state as defined by the NC DENR metrics of the North Carolina Index of Biotic Integrity (fish assessment) and the bioclassification of macroinvertebrates in both wet and dry periods based on WWTP effluent discharge, zinc, and dissolved oxygen concentrations. Before a reclaimed water system is constructed, we recommend the City of Oxford and Granville County conduct a more in depth market study of potential reclaimed water users and demand. A more in depth study would make for better estimations of reclaimed water demand and in turn the economic and environmental benefits.