Onsite Wastewater Systems Research Articles

Development and Application of Methods for Prioritizing and Managing Onsite Wastewater Systems to Meet Environmental and Public Health Needs

Development and Application of Methods for Prioritizing and Managing Onsite Wastewater Systems to Meet Environmental and Public Health Needs

Nitrogen Treatment Efficiency of a Large Onsite Wastewater System in Relation to Water Table Dynamics

The objective of this study is to determine if the nitrogen treatment efficiency of a large onsite wastewater system (OSW) in the coastal plain of North Carolina is influenced by changes in the elevation of the water table. Groundwater readings including depth to water, pH, temperature, specific conductance, and dissolved oxygen are recorded eight times over a 15‐month period (May 2013–August 2014) encompassing typically “wet” (two sampling events) and “dry” (three sampling events) seasons, and a water table fluctuation of 1.7 m. Groundwater from piezometers (n = 7) near the OSW and septic tank effluent samples are collected for analyses of total dissolved nitrogen (TDN) during each field visit to determine if the TDN treatment efficiency is influenced by the water table elevation. The treatment efficiency of the OSW is directly correlated with wastewater strength (r = 0.882; p = 0.004) and inversely correlated to water table elevation (r = −0.754; p = 0.031). The TDN treatment efficiency at this site decreases with increases in water table elevation, and groundwater TDN concentrations beneath the OSW are typically higher when wastewater concentrations of TDN are higher. Sea level rise and climate change are projected to increase groundwater levels and therefore may have negative effects on water quality adjacent to OSW. Ensuring that OSW are installed with the maximum practical vertical separation to groundwater and setback distances to surface waters, designed with long trenches and oriented perpendicular to the dominant groundwater flow direction will help to maximize TDN treatment.

Exurban housing development, onsite wastewater disposal, and groundwater vulnerability within a changing policy context

On-site wastewater treatment systems (OWTS) are designed to collect, filter, and release treated wastewater effluent back into the natural environment. If these decentralized systems are not properly installed or regularly maintained, or are spatially distributed at densities that exceed the landscape’s ability to safely treat wastewater effluent, groundwater can become contaminated. We examine in this paper the evolution of state-level policies regulating on-site wastewater management in the State of Wisconsin (USA). We also present a spatiotemporal analysis of on-site wastewater systems installed in a metropolitan county within southeastern Wisconsin. Findings show: 1) advances in OWTS technologies, coupled with regulatory policy changes, have reduced the influence of physiographic constraints on exurban housing development, 2) over 7,000 on-site wastewater systems are unevenly distributed across the county’s landscapes, and 3) several OWTS clusters are at high enough densities to threaten groundwater quality, potentially posing public health risks from polluted private well-water. Groundwater contamination risk was assessed, county-wide, by using GIS overlay analysis to compare septic system density (greater than 2.0 systems per acre) with groundwater vulnerability. Our spatial analysis identified several “hot spots” that may warrant groundwater monitoring and OWTS inspections to limit potential health impacts. This method of analysis can help public sector planners design context-sensitive policies to manage unsewered housing development within the rural landscape.

On-Site Wastewater Systems: Investigating Dynamics and Diurnal Patterns Impacting on the Performance of Mound Systems

Many dynamics and diurnal patterns impact upon the performance of effluent disposal areas. The timing of household water use and conveyance to a septic tank impacts on the available volume for application to an effluent disposal area. The timing and method of effluent application will impact on the performance of the effluent disposal area in assimilating nutrients and maintaining adequate infiltration rates. Rainfall patterns will impact on soil saturation at different times during the year; and threshold rainfall events may increase groundwater levels that will impact on the performance of the effluent disposal area. However, the dynamics and diurnal patterns comprising the “whole-of-on-site wastewater- system” are rarely discussed in the literature. This paper uses data obtained from a study of two allotments in a non-sewered subdivision at Salt Ash (NSW) to highlight these dynamics and diurnal patterns in order to improve the performance evaluation of on-site wastewater systems, in particular Mound systems. Results indicate that under existing septic tank-collection well design criteria the variability in average daily indoor water use and average diurnal water use patterns will impact on the temporal comparative performance of effluent disposal areas (Mound systems) at similar sites.

Phosphate treatment by onsite wastewater systems in nutrient-sensitive watersheds of North Carolina's Piedmont.

The goal of this study was to gain a better understanding of the PO4-P treatment efficiency of onsite wastewater systems (OWS) installed in nutrient-sensitive watersheds of the North Carolina Piedmont. Four OWS including two conventional and two single-pass sand filter (SF) systems were evaluated at sites with clay-rich soils. Piezometers were installed near all of the OWS, and down-gradient from the conventional OWS for groundwater collection and characterization. Septic tanks, groundwater, SF effluent, and surface waters were sampled each season during 2015 (five times) and analyzed for PO4-P and Cl concentrations and for various environmental parameters. The conventional and SF OWS reduced PO4-P concentrations by an average of 99% and 90%, respectively, before discharge to surface waters. Mass-load reductions of PO4-P were also greater for the conventional OWS (mean 95%), relative to SF (83%) systems. The effluents discharged by SF OWS were influencing surface water quality. Additional treatment of the effluent from single-pass SF with reactive media is suggested, along with monitoring of the final effluent for PO4-P concentrations. This research provides important information that is absent from the published literature concerning PO4-P contributions to water resources from OWS in clay soils.

Field Evaluation of Nitrogen Treatment by Conventional and Single-Pass Sand Filter Onsite Wastewater Systems in the North Carolina Piedmont

Excess nitrogen loading has contributed to the impairment of major watersheds across North Carolina. Onsite wastewater systems (OWS) are a potential source of nitrogen to water resources, but more research is needed to determine their actual contributions, especially in the Piedmont region of the state. The objective of this study was to determine the total dissolved nitrogen (TDN) treatment efficiency of four OWS in clayey soils of the North Carolina Piedmont. Two OWS were conventional style, and two were single-pass sand filters. The four volunteered sites with OWS were instrumented with piezometers (27 total) for groundwater collection and analyses. Piezometers were installed within 1.5 m of each OWS and downgradient from the conventional OWS. Septic tank effluent, groundwater from the piezometers, sand filter effluent, and adjacent surface waters were sampled bimonthly (five times) during 2015. Samples were analyzed for TDN, NO3 −-N, NH4 +-N, chloride, dissolved organic carbon, and physical and chemical parameters on each sampling event. Groundwater samples collected 35 m downgradient from the two conventional OWSs had TDN concentrations and masses, on average, of 98 and 70 %, respectively, lower than septic tank effluent. Isotopic analysis of the natural abundance of δ15N and δ18O in NO3 − in groundwater collected at the conventional OWS sites suggests that denitrification was a mass removal mechanism. The sand filter OWS reduced TDN concentrations by an average of 80 % and mass loading by 50 % prior to discharge to surface waters. Nitrogen management regulations in nutrient-sensitive watersheds should consider the contributions from OWS, especially direct discharge systems like sand filters. Improvements in the TDN treatment efficiency of direct discharge OWS would result in immediate surface water quality improvements.

Modeling Impacts of Residential and Agricultural Development and Beneficial Management Practice Scenarios on Phosphorus Dynamics in a Small Watershed

<abstract> <b><sc>Abstract.</sc></b> Both agricultural land uses and residential on-site wastewater systems (OWS) have the potential to be nonpoint sources of phosphorus (P) in rural watersheds. Watershed-scale computer models are a commonly used tool for evaluating the impacts of increased human development on P dynamics and for evaluating how beneficial management practices (BMPs) can reduce P loading. Many agricultural field BMPs have been evaluated using watershed-scale models; however, no studies have compared their efficacy to OWS BMPs in a mixed land use watershed. The objectives of this research were to (1) use the P on-site wastewater simulator (POWSIM) and the Soil and Water Assessment Tool (SWAT) to simulate different agricultural and residential development scenarios in the Thomas Brook watershed in Nova Scotia, Canada, and evaluate their impacts on sediment and total P (TP) loads and TP concentrations and (2) simulate and evaluate different individual and combinations of select agricultural and OWS BMPs. A 50-year simulation period was used for both the development and BMP scenarios. The development scenarios evaluated included increasing the residential population and conversion of hay fields or pastures to corn-based cropping regimes. The agricultural BMPs evaluated were (1) corn and rotational crop replacement with no-till agricultural land uses and (2) no-till corn. Decreased failure rates, increased watercourse setbacks, disposal field replacement, and the use of high P sorption filter media were the OWS BMPs evaluated. The agricultural development scenarios increased cumulative sediment and P loads at the watershed outlet, while the residential scenarios increased the frequency of hyper-eutrophic conditions in the stream during the last 20 simulated years. Agricultural crop replacement BMPs produced the highest reductions in cumulative sediment (13% to 46%) and TP loads (26% to 34%) but had no observable change on the in-stream trophic status. The OWS BMPs produced small reductions in TP loading (2% to 15%), no sediment load reductions, but had a positive effect on the trophic status. The best ranked combination of agricultural and OWS BMPs resulted in a cumulative TP load reduction of 58%, and the dominant trophic state at the end of the 50-year period was mesotrophic, as compared to eutrophic for the reference simulation. The best combination BMP scenario included replacing corn and rotational crops with pastures, using high P sorption filter media (5000 mg P kg^-1 media), and lowering of the OWS failure rate to 5%. The results of these modeling scenarios showed that agricultural BMPs were most effective in reducing cumulative P loads, while OWS BMPs were effective in mitigating in-stream eutrophication impacts. This study highlights the importance of identifying specific water quality issues that need to be targeted prior to implementing a watershed BMP strategy. Further model refinement and testing are required with improved field measurements to improve model confidence before the model should be used for planning and design purposes.

Factors Affecting the Performance of Primary Treatment in Onsite Systems

Approximately 23 percent of the estimated 115 million occupied homes in the United States are served by onsite wastewater systems. The vast majority of onsite wastewater treatment systems include a septic tank, grease trap, or both for primary treatment. These units are efficient, simple, low-energy treatment units whose performance is critically important to the overall functioning of onsite wastewater systems. Regulations, industry standards, guidance materials and engineering texts vary widely and are often incomplete in their consideration of the factors that may influence primary unit performance in onsite systems. The objective of this research was therefore to identify, compile, analyze, and report on the existing body of work addressing the performance of primary treatment units in onsite wastewater systems and the factors impacting performance. Design, construction/installation, and maintenance issues were considered, with a goal of establishing what is known, what is not known and what future research is needed in this area. Over 700 sources of information were collected, with most reviewed and presented in this document - the white paper. A bibliographic database, which can continue to be updated into the future, was developed as a companion piece to the white paper, as a tool for researchers and practitioners. This title belongs to WERF Research Report Series ISBN: 9781780403700 (eBook) ISBN: 9781843397816 (Print)

Influent Constituent Characteristics of the Modern Waste Stream from Single Sources: Literature Review

A literature review was conducted to assess the current status of knowledge on the composition of raw wastewater and primary treated effluent (i.e., septic tank effluent) from single source onsite wastewater systems. The overall goal of this research project is to characterize the extent of conventional constituents, microbial constituents, and organic wastewater contaminants in single source onsite raw wastewater and primary treated effluent to aid onsite wastewater system design and management. Information obtained was evaluated using cumulative frequency distributions to compare individual constituent concentrations in various waste streams and by using data qualifiers to enable assessment of parameters that might affect single source waste stream composition. To supplement information on the single source raw wastewater and primary treated effluent composition, state agencies responsible for onsite wastewater regulation were contacted to assess the prevalence of different system types installed and in operation. Selected demographics that capture differences in lifestyle habits that could affect raw wastewater composition were also assessed. A large amount of data was captured by this literature review, however information gaps were identified. The information presented here will be used to guide future project monitoring and assessment of modern raw wastewater waste streams. This title belongs to WERF Research Report Series ISBN: 9781843397731 (eBook)

Hydrogen Production in the Anaerobic Treatment of Domestic-Grade Synthetic Wastewater

The aim of this study was to evaluate the potential of domestic wastewater for anaerobic hydrogen production. High-strength and ordinary-strength organic loadings of synthetic wastewater, i.e., real-time domestic wastewater with and without a mixture of food waste, were tested. During operation at a high strength loading, the initial pH was maintained at 7 and then gradually decreased, and a pH of 5–5.5 was observed as the best experimental condition. A pH of 5–5.5 was controlled during the operation at an ordinary-strength loading. Maximum hydrogen yields of 1.125 mol H2/mol glucose and 1.01 mol H2/mol glucose were observed during operation at high (48 g COD/L·day) and ordinary (3 g COD/L·day) strength loadings in terms of chemical oxygen demand (COD), respectively, with hydrogen contents of 42%–53%. The operating environment of the hydrogen production system was found to be very crucial because the metabolic pathway of the microorganism and production of intermediates were found to be dynamic with the controlled environment. Smaller COD removals of 30% and 26% were observed in high-strength and ordinarystrength loadings, respectively. Organic mass balance in terms of COD described the distribution of organics in the system via reactor byproducts. The findings of this study can be applied during the design of onsite domestic wastewater and energy recovery systems.

Fecal Contamination in the Surface Waters of a Rural- and an Urban-Source Watershed.

Surface waters are commonly used as source water for drinking water and irrigation. Knowledge of sources of fecal pollution in source watersheds benefits the design of effective source water protection plans. This study analyzed the relationships between enteric pathogens ( O157:H7, spp., and spp. [, and ]), water quality (turbidity, temperature, and ), and human and ruminant-cow and mitochondrial DNA (mtDNA)-based fecal source tracking (FST) markers in two source watersheds. Water samples ( = 329) were collected at 10 sites (five in each watershed) over 18 mo. The human marker (HF183) occurred in 9 to 10% of the water samples at nine sampling sites; while a forested site in the urban watershed tested negative. Ruminant-cow markers (BacR and CowM2) only appeared in the rural watershed (6%). The mtDNA markers (HcytB and AcytB) showed the same pattern but were less sensitive due to lower fecal concentrations. Higher prevalences ( < 0.05) of spp. (41 vs. 16% for the rural and urban watershed, respectively) and O157:H7 (12 vs. 3%) were observed in the rural watershed, while spp. levels were comparable (23-28%). Densities of ≥100 colony-forming units (CFU) 100 mL increased the odds ( < 0.05) of detecting the enteric bacterial pathogens. The water turbidity levels (nephelometric turbidity units [NTU] ≥ 1.0) similarly predicted ( < 0.05) pathogen presence. Storm events increased ( < 0.01) pathogen and fecal marker concentrations in the waterways. The employment of multiple FST methods suggested failing onsite wastewater systems contribute to human fecal pollution in both watersheds.

Feasibility analysis of wastewater and solid waste systems for application in Indonesia

Indonesia is one of many developing countries with a backlog in achieving targets for the implementation of wastewater and solid waste collection, treatment and recovery systems. Therefore a technical and financial feasibility analysis of these systems was performed using Indonesia as an example. COD, BOD, nitrogen, phosphorus and pathogen removal efficiencies, energy requirements, sludge production, land use and resource recovery potential (phosphorus, energy, duckweed, compost, water) for on-site, community based and off-site wastewater systems were determined. Solid waste systems (conventional, centralized and decentralized resource recovery) were analyzed according to land requirement, compost and energy production and recovery of plastic and paper. In the financial analysis, investments, operational costs & benefits and Total Lifecycle Costs (TLC) of all investigated options were compared. Technical performance and TLC were used to guide system selection for implementation in different residential settings. An analysis was undertaken to determine the effect of price variations of recoverable resources and land prices on TLC. A 10-fold increase in land prices for land intensive wastewater systems resulted in a 5 times higher TLC, whereas a 4-fold increase in the recovered resource selling price resulted in maximum 1.3 times higher TLC. For solid waste, these impacts were reversed — land price and resource selling price variations resulted in a maximum difference in TLC of 1.8 and 4 respectively. Technical and financial performance analysis can support decision makers in system selection and anticipate the impact of price variations on long-term operation. The technical analysis was based on published results of international research and the approach can be applied for other tropical, developing countries. All costs were converted to per capita unit costs and can be updated to assess other countries' estimated costs and benefits. Consequently, the approach can be used to guide wastewater and solid waste system planning in developing countries.

Reevaluating onsite wastewater systems: expert recommendations and municipal decision-making

Onsite wastewater treatment systems (OWTS) serve 20–25% of the households in the USA, and large parts of rural Canada, Australia, and Europe. Urbanization and newer environmental standards are leading many communities that currently rely on OWTS to think of alternatives. We study this decision-making in 19 municipalities across the USA through the unique lens of feasibility reports commissioned by the respective municipalities and authored by engineering/design consulting firms. The reports omitted certain essential information relevant to the decision-making process, and were not of high quality due to a lack of specificity on various parameters. However, the reports evaluated a balanced mix of decentralized and centralized treatment options, and the final recommendations were not biased in any particular direction. Most municipalities failed to take any follow-up action on the report recommendations, calling into question the motive behind commissioning these reports. Although not representative of the entire USA, the small sample of feasibility reports evaluated here is indicative in nature and provided significant insights about the inputs that help municipalities make decisions on complex issues.

Preliminary Evaluation of a Permeable Reactive Barrier for Reducing Groundwater Nitrate Transport from a Large Onsite Wastewater System

A permeable reactive barrier was installed between a large Onsite Wastewater System (OWS) and a monitoring well located down-gradient from the OWS. Groundwater samples from the well had shown elevated and increasing concentrations of NO3--N (>20 mg L-1 for 2 years). The barrier was constructed using woodchips from various tree species that were placed in a trench excavated to approximately the same depth as the well which was experiencing elevated NO3--N concentrations. Groundwater samples (5) were collected from the well between two weeks and four months after the barrier was installed. Groundwater NO3--N concentrations dropped by an average of 5 mg L-1, while Dissolved Organic Carbon (DOC) concentrations increased by 11 mg L-1 and Cl concentrations stayed relatively stable (<2 mg L-1 increase). The data suggest that denitrification fueled by the DOC from the barrier may be contributing to the lower NO3--N concentrations. Monitoring will continue at the site to determine the longer-term water quality trends. More research should be conducted to evaluate the applicability of permeable barriers as a best management practice for non-point sources of pollution in nutrient sensitive areas.

Septic Systems as a ‘Green’ Technology

ity. On-site treatment systems are now an integral part of our wastewater infrastructure and are collectively referred to as decentralized wastewater systems. Decentralized wastewater technology and management refers to wastewater treatment and dispersal systems from the individual on-site treatment system (septic systems) to small community collection and treatment systems (cluster systems) and includes the process involved in siting, installing, operating and maintaining the systems. These systems rely upon land application by surface or subsurface dispersal and proper treatment of the wastewater. They allow the treated wastewater to re-enter the hydrologic cycle close to where the potable water was removed. Often, as in the case of an individual system, this is less than a few hundred feet. They are considered to be non-point source discharges by federal and state standards. Often septic systems are portrayed in a negative light but they are now an integral part of our wastewater infrastructure. Photo by David Lindbo and courtesy of Soil Science @ NC State's Flickr photostream.

Evaluation of Onsite Wastewater System Performance and Nutrient Trading Policy in Support of Falls Lake Nutrient Strategy Development

Evaluation of Onsite Wastewater System Performance and Nutrient Trading Policy in Support of Falls Lake Nutrient Strategy Development

A Watershed Modeling Framework for Phosphorus Loading from Residential and Agricultural Sources

Phosphorus (P) loading from residential onsite wastewater systems (OWSs) into neighboring surface waters is a poorly understood process in rural watersheds; this can be further challenged when rural residential dwellings are intermixed with agricultural land use. The objectives of this research were (i) to design a P onsite wastewater simulator (POWSIM) to assess P loads from individual or clusters of residential OWSs typically used in Nova Scotia, Canada; and (ii) to simulate OWS P loads in a mixed agricultural watershed (Thomas Brook Watershed [TBW], NS) using the Soil and Water Assessment Tool (SWAT) model in conjunction with POWSIM, to predict and compare P loading from agricultural and residential sources. The POWSIM loading tool has three computational components: (i) disposal field selection and treatment media mass calculation, (ii) disposal field P treatment dynamics, and (iii) soil subsurface plume P treatment dynamics. The combination TBW POWSIM and SWAT modeling approach produced a better simulation of baseflow total P (TP) loads in both a predominantly residential subcatchment and one dominated by agriculture than the SWAT model without POWSIM. The residential subcatchment had 48% of its average annual land use TP load (simulated) contributed by OWSs, whereas the agricultural subcatchment had 39%. Watershed-scale sensitivity analyses of POWSIM input parameters for 18- and 50-yr OWS operation periods found the P loading rate into the disposal field, long-term P removal rates in the disposal field and soil systems, soil maximum P sorption capacity, and mass of native soil involved in P treatment to be most sensitive.

On Your Time

The need for competency-based training for the public health workforce is well documented. However, human and financial resource limitations within public health agencies often make it difficult for public health practitioners to attend classroom-based training programs. The Internet is an increasingly popular way of extending training beyond the workforce. Although research describes attributes of effective online learning modules, much of the available training delivered via the Internet does not incorporate such attributes. The authors describe the On Your Time training series, an effective distance education program and training model for public health practitioners, which includes a standardized process for development, review, evaluation, and continuous quality improvement. On Your Time is a series of awareness-level (i.e., addressing what practitioners should know), competency-based training modules that address topics related to regulatory responsibilities of public health practitioners (e.g., assuring compliance with codes and regulations governing housing, retail food safety, private water supplies, hazardous and solid waste, on-site wastewater systems, etc.), public health surveillance, case investigation, disease prevention, health promotion, and emergency preparedness. The replicable model incorporates what is known about best practices for online training and maximizes available resources in the interests of sustainability.

Fe(III) reduction-mediated phosphate removal as vivianite (Fe3(PO4)2⋅8H2O) in septic system wastewater

Phosphate is a water contaminant from fertilizers, soaps, and detergents that enters municipal and onsite wastewater from households, businesses, and other commercial operations. Phosphate is a limiting nutrient for algae, and is one of the molecules that promotes eutrophication of water bodies. Phosphate is especially problematic in onsite wastewater because there are few removal mechanisms under normal operating conditions; a system must be amended specifically with compounds to bond to or adsorb phosphate in the septic tank or within the leach field. Vivianite (Fe3(PO4)2⋅8H2O) is a stable mineral formed from ferrous iron and phosphate, often as the result of Fe(III) reducing microbial activity. What was unknown was the concentration of phosphate that could be removed by this process, and whether it was relevant to mixed microbial systems like septic tank wastewater. Data presented here demonstrate that significant concentrations of phosphate (12–14mM) were removed as vivianite in growing cultures of Geobacter metallireducens strain GS-15. Vivianite precipitates were identified on the cell surfaces and within multi cell clusters using TEM–EDX; the mineral phases were directly characterized using XRD. Phosphate was also removed in dilute and raw (undiluted) septic wastewater amended with different forms of Fe(III) including solid phase and soluble Fe(III). Vivianite precipitates were recovered and identified using XRD, along with siderite (ferrous carbonate), which was expected given that the systems were likely bicarbonate buffered. These data demonstrate that ferric iron amendments in septic wastewater increase phosphate removal as the mineral vivianite, and this may be a good strategy for phosphate attenuation in the septic tank portion of onsite wastewater systems.

Cryptosporidium infection, onsite wastewater systems and private wells in the arid Southwest

Few prior studies have examined the potential health risks from transmission of enteric parasites via aquifers contaminated by wastewater from onsite systems. A cross-sectional study of 600 residents in households served with either onsite wastewater systems and private wells or city sewer/water systems in three different sites in central New Mexico compared serological responses to Cryptosporidium, a common waterborne infections agent. Study participants completed a short self-administered questionnaire with questions on demographic characteristics, characteristics of the onsite wastewater system and private well, and common risk factors associated with cryptosporidiosis. A sample of household tap water was collected, as well as a blood sample from each study participant to measure IgG responses to antigen groups for Cryptosporidium. Logistic regression analysis showed a significant association between having an onsite wastewater system and private well and the 27-kDa marker for Cryptosporidium in the River Valley site after adjusting for covariates (OR = 1.98; 95% CI = 1.11-3.55). This study, together with one prior study, suggests that the presence of onsite wastewater systems and private wells might be associated with an increased risk of Cryptosporidium infection.