Comparison of Nitrogen Treatment by Four Onsite Wastewater Systems in Nutrient-Sensitive Watersheds of the North Carolina Coastal Plain

Abstract

Wastewater may be a source of nitrogen (N) to groundwater and surface waters if not effectively treated. In North Carolina, onsite wastewater systems (OWSs) are used by 50% of the population for wastewater treatment, but most OWSs are not routinely monitored. There is a lack of information regarding the N contributions from OWSs to water resources. Four sites with OWSs were instrumented with groundwater wells near their drainfield trenches to compare N concentrations in groundwater to concentrations in wastewater and to determine the N treatment efficiency of the systems. Two OWSs (Site 200 and 300) were less than 1 year old, and two (Site 100 and 400) were more than 10 years old at the start of the study. Two OWSs (Site 100 and 200) used pressure dosing, while two OWSs (Site 300 and 400) used gravity distribution. The mean N treatment efficiency of the four OWSs was 77%. The new OWSs were more efficient (92%) relative to the older OWSs (62%) at reducing N concentrations. Similar N treatment efficiencies were observed when pooling data for the pressure dosed (77%) and gravity (79%) OWSs. Each OWS influenced groundwater by causing increases in N concentrations. It is important that new OWSs are installed at a shallow depth and with sufficient separation to groundwater to promote the aerobic treatment of wastewater. Remediation strategies including the installation of permeable reactive barriers or the use of media filters may be needed in some areas to reduce N transport from existing OWS.

Evaluating the use of chemically modified clinoptilolite zeolite for the simultaneous recovery of ammonium and phosphate from blackwater

“…The Mg-PT and Na-PT bulk liquid equilibrium pH increased to 7.02 and 7.28, respectively, indicating that the extent of pH increase was due to the removal of NH 4 from solution, raising the pH accordingly. The pHs of the effluent were well within the range desired for discharge (6)(7)(8)(9), indicating that in practice no pH adjustments may be needed. Other P sorption materials, such as Polonite, has a high sorption capacity for phosphorus but effluent wastewater can have pHs of near 12 as hydroxides are released.…”

“…In several New England coastal counties considered critical resource areas, studies have shown than advanced secondary OWTS targeted to meet the local standard of 19 mg N L −1 do so 0-78% of the time, with their treatment effectiveness heavily dependent on the treatment train of the applied commercial technology and the daily nitrogen loading rates. [6][7][8] Meanwhile, achieving phosphorus reductions is left to natural attenuation in drainfields or requires an additional secondary or tertiary treatment step. 9 Drainfields with high clay content soils do well at removing phosphorus due to their high iron and aluminum content while sandy soils with limited metal oxides do poorly.…”