Abstract
Onsite wastewater systems dispose of primary treated effluent by utilizing the soil for final recycling and renovation of wastewater into the environment. Soil and site limitations have become a challenge to design a wastewater system and dispose of onsite wastewater using a conventional pipe and gravel design. Using secondary-treated effluent from an advanced treatment unit applied to a reduced disposal area offers an additional alternative when developing an onsite wastewater system. The objective of this study was to determine the feasibility of hydraulically loading limiting soils with secondary-treated effluent in a reduced disposal area. A reduced disposal area was constructed at six existing residences within the same subdivision that had shallow redoximorphic features that precluded using a conventional pipe and gravel wastewater design. Each residence had an existing advanced treatment unit with a surface discharge of secondary-treated effluent. Flows were diverted from the surface discharge to the reduced disposal area. Wastewater flows were recorded at regular intervals, along with ponding depths in the disposal area and fluctuations in the seasonal water table over a 12-month period (March 2017 to March 2018). The disposal areas were hydraulically loaded at 2 to 3.8 times the rate recommended for secondary-treated effluent. Wastewater effluent was sampled throughout the study and resulted in a mean of -1 total suspended solids, -1 biochemical oxygen demand, and >6.3 mg·L-1 dissolved oxygen, all of which met or exceeded the minimum water quality criteria for surface discharges of secondary-treated effluent. Three of the six sites showed ponding depths between 0 and 4 cm in the trenches during the study period. The remaining three sites showed ponding between 0 and 35 cm in the trenches during the study period. Based on the results of this study, a reduced disposal area utilizing secondary-treated effluent appears to be a feasible option to surface discharging.
Highlights
Managing household wastewater by onsite disposal is critical to keeping rural areas and water sources free from disease and unsanitary living conditions
The basic premise of using secondary-treated effluent in the study was to minimize the formation of a biomat by managing effluent with low biological oxygen demand (BOD) and total suspended solids (TSS) and large enough dissolved oxygen (DO) and, if surface ponding occurred, the environmental impact would be negligible
Samples collected among the research sites from April 2017 through April 2018 had a mean of 5.3 mg∙L−1 BOD, 8.5 mg∙L−1 TSS, 6.3 mg∙L−1 DO, and 7.4 pH
Summary
Managing household wastewater (i.e. effluent) by onsite disposal is critical to keeping rural areas and water sources free from disease and unsanitary living conditions. Rural dwellings in Arkansas that are not connected to a public sewer system must utilize an onsite wastewater system that relies on the soil to renovate household wastewater before the effluent is returned to the hydrologic cycle. Following Act 402, the Arkansas Department of Health adopted Rules and Regulations regarding onsite wastewater disposal [2]. Wastewater from rural Arkansas homes and businesses is discharged into the soil where the effluent is renovated by filtering through the soil and recycled back into the environment using conventional onsite wastewater systems. As Arkansans continue to develop more rural areas that require an onsite wastewater system, locating suitable soil to safely renovate wastewater has become a challenge due to limiting soils (i.e. shallow depth to bedrock, a shallow seasonal water table, or >35% clay textures) or a limited suitable disposal area available on the property
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