On‐Site Waste Treatment and Disposal by Sequencing Batch Reactor‐Drip Irrigation: Effluent Distribution and Solute Transport

Abstract

On‐site wastewater systems (OWS) are used in areas not served by municipal treatment systems for biological and chemical renovation of wastewater prior to its entrance into surface or groundwaters. A traditional OWS (septic‐tank effluent with gravity dispersal) may not function properly in soils with low hydraulic conductivity horizons or other restrictive features. Uniform dispersal of highly treated effluent (HTE) in conjunction with controlled dosing offered by subsurface drip irrigation systems (SDIS) can play an important role in overcoming these limitations. An OWS consisting of a sequential batch reactor (SBR) for production of HTE and a SDIS to control dosing and dispersal of the SBR effluent (SBRE) was used in this study. The OWS is designed to treat 18,925 L of SBRE d−1. Efficiency of wastewater treatment by the OWS was evaluated by analyzing the SBRE and soil solution collected beneath the SDIS for several water‐quality parameters. Measuring soil‐water potentials monitored the effectiveness of the SDIS to disperse effluent. The SBR produced HTE with fecal coliform counts averaging less than 4,000 CFU 100 mL−1, and more than 95% of the N was present as nitrate. Soil‐water potentials ranged between −5.1 and −56.5 KPa beneath the SDIS. None of the soil solution samples was positive for fecal coliforms. Nitrate concentration in soil solution was lower beneath the SDIS than in the SBRE. This decrease was attributed to plant uptake and denitrification. Phosphorus (P) concentration was reduced by 99% beneath the SDIS when compared with P concentration present in the SBRE.