NUTRIENT AND BACTERIA DYNAMICS OF PACKAGE TREATMENT PLANTS IN COASTAL CARTERET COUNTY, NORTH CAROLINA

Abstract

Nutrient and bacteria enrichment problems are well documented in the waterways along North Carolina's coast. Surface and subsurface wastewater inputs have been documented as a source of these pollutants in a variety of coastal settings. While many studies have been conducted on the effects of municipal wastewater treatment plants and septic tank systems on water quality, relatively few have focused on package treatment plants. These facilities are common in certain coastal settings where connection to sanitary sewer collection systems is not available and wastewater flows are greater than what is typically processed by septic systems. Package treatment plants discharge treated wastewater effluent onsite either at the surface or in the subsurface. The potential for the migration of wastewater constituents is high in these settings due to shallow water tables and sandy soils. This study monitored and assessed the effectiveness of seven package treatment plants located on Bogue Banks on the North Carolina coast. Influent and effluent samples were collected monthly for one year (February 2014 -- January 2015) and analyzed for nitrogen, phosphorus, fecal indicator bacteria, and other water quality parameters. Annual average concentrations of total nitrogen in effluent ranged from 7.0 -- 24.7 mg/l with exports of 12.6 -- 47.5 kg/ha/yr. Annual average concentrations of total phosphorus in effluent ranged from 2.2 -- 6.4 mg/l with exports of 4.0 -- 29.0 kg/ha/yr. Six out of seven package treatment plants exceeded a state permitted maximum daily value for E. coli (43 CFU/100 ml) at least for 25 % of the sampling events. This variability could be the result of seasonal changes in temperature, wastewater strength, wastewater quantity, and/or microbial activity. These elevated nutrient exports suggest that additional advanced nutrient treatment should be considered to help reduce exports to the ground/surface waters.