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: 9781843393511 (Print)ISBN: 9781780403519 (eBook)

A typical onsite wastewater treatment system consists of a septic tank and a soil treatment unit to treat wastewater before it is discharged through the vadose zone to an aquifer. A tool was developed for the purpose of predicting the fate and transport of nitrogen in soil treatment units (STUMOD or Soil Treatment Unit Model). STUMOD calculates nitrogen species concentrations and the fraction of total nitrogen reaching the aquifer or a specified soil depth. Input data include parameters for hydraulics and nutrient transport and transformation. An analytical solution is used to calculate the profile of pressure based on Darcy’s equation and the relationships between suction head, unsaturated hydraulic conductivity, and soil moisture. Chemical transport is based on simplification of the advection–dispersion equation. STUMOD is relatively simple to use but accounts for important processes such as ammonium sorption, nitrification, and denitrification. STUMOD accounts for the effect of soil moisture content (a surrogate for redox conditions) on nitrification and denitrification reactions. The model has provisions to handle the influence of temperature and organic carbon content on nitrogen transformation. Model outputs, generated based on input parameters obtained from extensive literature review, were compared to a numerical model and data from laboratory tests and field sites. Both measured data and STUMOD outputs show a relatively higher removal in clayey soils compared to sandy soils. Consistent with literature data for most soils, STUMOD predicted ammonium conversion to nitrate within the first foot below the trench infiltrative surface.

Drip dispersal of partially treated wastewater was investigated as an approach for onsite water reclamation and beneficial reuse of water and nutrients in a semi-arid climate. At the Mines Park Test Site in Golden, Colorado, a drip dispersal system (DDS) was installed at 20- to 30-cm depth in an Ascalon sandy loam soil profile. Two zones with the same layout were established to enable study of two different hydraulic loading rates. Zones 1 and 2 each had one half of the landscape surface with native vegetation and the other with Kentucky bluegrass sod. After startup activities, domestic septic tank effluent was dispersed five times a day at footprint loading rates of 5 L/m(2)/d for Zone 1 and 10 L/m(2)/d for Zone 2. Over a two-year period, monitoring included the frequency and volume of effluent dispersed and its absorption by the landscape. After the first year of operation in October a N-15 tracer test was completed in the sodded portion of Zone 1 and samples of vegetation and soil materials were collected and analyzed for water content, pH, nitrogen, 15N, and bacteria. Research revealed that both zones were capable of absorbing the effluent water applied at 5 or 10 L/m2/d. Effluent water dispersed from an emitter infiltrates at the emitter and along the drip tubing and water movement is influenced by hydrologic conditions. Based on precipitation and evapotranspiration at the Test Site, only a portion of the effluent water dispersed migrated downward in the soil (approx. 34% or 64% for Zone 1 or 2, respectively). Sampling within Zone 1 revealed water filled porosities were high throughout the soil profile (>85%) and water content was most elevated along the drip tubing (17-22% dry wt.), which is also where soil pH was most depressed (pH 4.5) due to nitrification reactions. NH4+ and NO3- retention occurred near the dispersal location for several days and approximately 51% of the N applied was estimated to be removed by plant uptake and denitrification. Heterotrophic bacteria levels were elevated (up to 1 log) in the subsurface within the DDS but there was effective elimination of effluent fecal coliform and Escherichia coli bacteria. (C) 2013 Elsevier Ltd. All rights reserved.

Onsite wastewater treatment systems are commonly used in the United States to reclaim domestic wastewater. A distinct biomat forms at the infiltrative surface, causing resistance to flow and decreasing soil moisture below the biomat. To simulate these conditions, previous modeling studies have used a two-layer approach: a thin biomat layer (1-5 cm thick) and the native soil layer below the biomat. However, the effect of wastewater application extends below the biomat layer. We used numerical modeling supported by experimental data to justify a new conceptual model that includes an intermediate zone (IZ) below the biomat. The conceptual model was set up using Hydrus 2D and calibrated against soil moisture and water flux measurements. The estimated hydraulic conductivity value for the IZ was between biomat and the native soil. The IZ has important implications for wastewater treatment. When the IZ was not considered, a loading rate of 5 cm d resulted in an 8.5-cm ponding. With the IZ, the same loading rate resulted in a 9.5-cm ponding. Without the IZ, up to 3.1 cm d of wastewater could be applied without ponding; with the IZ, only up to 2.8 cm d could be applied without ponding. The IZ also plays a significant role in soil moisture distribution. Without the IZ, near-saturation conditions were observed only within the biomat, whereas near-saturation conditions extended below the biomat with the IZ. Accurate prediction of ponding is important to prevent surfacing of wastewater. The degree of water and air saturation influences pollutant treatment efficiency through residence time, volatility, and biochemical reactions.

Methods were modified and tested to monitor the occurrence of 20 pharmaceuticals and consumer product chemicals in raw wastewater and septic tank effluent (STE) from six single-family homes (two each located in Florida, Colorado, and Minnesota) each utilizing an onsite wastewater treatment system. Ten compounds were detected, including the stimulant caffeine, the metal-chelating agent ethylenediaminetetraacetic acid, the surfactant metabolite 4-nonylphenolmonoethoxylate, and the antimicrobial triclosan, which were present in all wastewater samples. Pharmaceutical occurrence and levels were more variable than consumer product chemicals; nonprescription anti-inflammatory drugs were the most frequently detected pharmaceuticals. Concentrations ranged from <1 mu g/L to > 1,000 mu g/L and varied by compound, site, and sampling event. No clear relationship between raw wastewater and STE composition existed. Raw wastewater composition, which previously has not been reported, reflected the per-capita water consumption and chemical-consuming activities at the source during the 24 h of sample collection. STE composition was likely affected by all consumptive activities during the tank hydraulic residence time (similar to 1 to 2 weeks) as well as differences in conditions between sites and at a single site over time (e. g., residence time, temperature, and load of organic compounds). Knowledge of source activities regarding the types, frequencies, and levels of pharmaceuticals and consumer product chemicals present in onsite wastewaters can aid in efforts to minimize potential risk to ecological and human health.

Decentralized systems are responsible for treating approximately 25% of the wastewater generated in the United States. The most common decentralized system involves onsite treatment using a septic tank unit followed by dispersal to a subsurface soil infiltration unit where percolation to groundwater occurs. To evaluate the hydraulic and purification processes occurring during soil treatment of septic tank effluent (STE), a field experiment was initiated in the Spring of 2003 with continued operation and monitoring for 2 years. A replicated factorial design (2 2) was employed to evaluate three infiltrative surface architectures (ISAs) (open, stone, and synthetic) and two daily hydraulic loading rates (HLRs) (4 and 8 cm/day). Pilot-scale test cells were established in native sandy loam soils at the Mines Park Test Site located on the Colorado School of Mines campus in Golden, Colo. STE was obtained from a nearby multifamily apartment building and applied to the test cells daily. Field monitoring included baseline characterization of soil and site properties, routine characterization of the STE applied, observations of STE ponding on the infiltrative surface, periodic measurement of constant-head infiltration rates, and periodic sampling and analyses of the soil pore water at 60- or 120-cm depths below the infiltrative surface. Monitoring revealed that the ISA and HLR influenced the rate and extent of hydraulic capacity loss during soil treatment. For example, an open horizontal infiltrative surface maintained an infiltration capacity that was 40-80% higher than one covered with either washed stones or synthetic aggregate. Purification of STE during infiltration and percolation through the sandy loam soil was very high. The cumulative mass removed during 2 years of operation for dissolved organic carbon, total nitrogen, and total phosphorus averaged 94, 42, and 99%, respectively. While there was no significant difference in the purification performance based on ISA or HLR, an increase in the vadose zone depth slightly increased purification.

A conventional on-site wastewater system (OWS) is traditionally comprised of one or more septic tanks for treatment of raw wastewater followed by percolation through natural soil to achieve purification prior to groundwater recharge. Other types of engineered treatment units (e.g., sand filters, textile media filters) may be implemented where site conditions are not suitable for conventional systems or in sensitive areas, such as those with nitrogen loading concerns. The research presented here is part of a large field study conducted to evaluate the purification performance of OWS employing three different engineered treatment units: a septic tank, a septic tank with a textile filter unit (TFU), and a septic tank with a membrane bioreactor (MBR). The TFU or MBR employ treatment processes that are designed to achieve higher purification compared to a septic tank so that soil treatment can be accomplished at higher hydraulic loading rates and/or with less unsaturated soil depth. This paper describes the installation, operation, and monitoring of the effluent generated from three engineered treatment units operated for a period of 16-28 months. The three treatment units, as expected, achieved different purification efficiencies for organic matter, total suspended solids, nutrients, and bacteria with the relative removal efficiency of MBR>TFU> septic tank. The relative degree of operational complexity, operation and maintenance requirements, energy use, and cost followed the same ranking.

Treatment units, such as sand filters, textile media filters, and membrane bioreactors, are designed to enable higher or equivalent performance to a septic tank so that soil treatment can be accomplished at higher hydraulic loading rates and/or with less unsaturated soil depth. A field study was conducted to evaluate the performance of an overall treatment train with the soil treatment unit receiving effluent from three treatment units (septic tank [ST], ST with textile filter unit [TFU], and ST with membrane bioreactor [MBR]). The effluents from the three treatment units were applied to 18 in situ test cells at two hydraulic loading rates (2 or 8 cm/d). Each effluent was characterized and the effects of the effluent quality on the hydraulic and purification performance during soil treatment were studied. The treatment units achieved very different treatment efficiencies for organic matter, solids, nutrients, and bacteria (relative efficiency of ST < TFU < MBR). Addition of a treatment unit to produce effluent of higher quality than typical septic tank effluent can retard soil clogging development and enable application of higher hydraulic loading rates to soil, however, the increase in hydraulic loading rate is likely limited by the hydraulic properties of the natural soil. After 32 months of operation, the treatment and purification was >99% removal for total phosphorus and >87% removal of dissolved organic carbon after 60 cm of soil for each effluent quality. Nitrogen removal rates were ~60% in the TFU test cells and ~35% in the ST test cells. The treatment trains including a TFU or MBR, generally performed better with respect to purification and were less affected by HLR than the treatment train based on only a ST and soil treatment.

An experimental study was completed to assess the impact of sampling methods, contaminant levels, and subsurface temperatures on the quantification of tetrachloroethylene (PCE) and trichloroethylene (TCE) in source zones contaminated by dense non–aqueous phase liquids (DNAPLs). Intact cores of clean aquifer solids (fine‐grained uniform sand with low foc) from a DNAPL site in Florida were spiked with neat PCE and TCE to yield concentrations such that DNAPL‐phase contamination would be absent or present. Three methods characterized by different levels of media disaggregation and atmospheric exposure (MDE) were used to obtain samples from intact cores, which were at temperatures of 2°C, 20°C, and 38°C. The results of this study demonstrated that sampling of intact cores can yield negative bias, ranging from 0% to 98% or more, in the concentrations of PCE and TCE measured. Larger negative bias was correlated with higher MDE methods, presumably due to elevated volatilization losses during sample collection and containerization. Larger negative bias was also correlated with higher temperatures but only during sampling using higher MDE methods. The results of this study suggest that intact core sampling procedures may or may not lead to erroneous conclusions about a DNAPL source zone. For example, sampling data may lead to a conclusion that a potential source zone has no DNAPL‐phase contamination present when in fact it is present, or that remediation has achieved source zone cleanup to a residual concentration goal, when in fact the goal was not met. Conversely, if a remediation goal is to achieve a specified mass depletion level (e.g., 90%), measurement bias may not result in an erroneous conclusion. Further research is planned to examine a wider range of aquifer properties and sampling conditions and to assess the impacts of measurement errors on DNAPL source zone characterization and assessment of remediation performance.

Porous media biofilters (PMBs) are commonly used to treat domestic wastewater. Biomats develop at the infiltrative surface of PMBs due to continued wastewater application and create an impedance to flow. The goal of this research is to quantify the temporal evolution of normalized biomat hydraulic conductivity (Kbm/bbm) and effective hydraulic conductivity (Ke). Ke is the overall hydraulic conductivity of the infiltrative zone, including biomat and unsaturated media below the biomat. Research was conducted using eight one-dimensional (1D) sand columns with gravel-free and gravel-laden infiltrative surfaces. The columns were loaded at design rates of 100–200 cm/d for 20 weeks of column operation. The Ke values for these continuously loaded columns were determined from analyses of bromide-tracer tests, falling-head permeability tests, and volumetric water content measurements during biomat development. The reduction in the Ke due to biomat formation is due to two factors: reduced hydraulic conductivity of the thin biomat, and a reduced hydraulic conductivity of the subsoil due to development of a biomat-induced unsaturated flow regime. Unsaturated hydraulic conductivities of the subsoil below the biomat (Kss) were estimated from capillary curves and water content measurements. For observed final biomat thicknesses (less than 1 cm), the biomat hydraulic conductivity, Kbm, is three orders of magnitude smaller than the unsaturated hydraulic conductivity (Kss). However, the relatively large thickness of the vadose zone causes the Kss to be an important contributor to the overall Ke value. For these columns, the final Ke values were approximately two orders of magnitude smaller than the original value. Because the exact thickness of the biomat (bbm) is unknown during the flow experiments, the hydraulic conductance of the biomat zone is presented using a normalized hydraulic conductivity function (Kbm/bbm). A similar Kbm/bbm is reached regardless of wastewater loading rate. An exponential relationship exists between the volume of wastewater applied to the column and both Ke and Kbm/bbm.

Soil treatment of wastewater has the potential to achieve high purification efficiency, yet the understanding and predictability of purification with respect to removal of viruses and other pathogens is limited. Research has been completed to quantify the removal of virus and bacteria through the use of microbial surrogates and conservative tracers during controlled experiments with three-dimensional pilot-scale soil treatment systems in the laboratory and during the testing of full-scale systems under field conditions. The surrogates and tracers employed included two viruses (MS-2 and PRD-1 bacteriophages), one bacterium (ice-nucleating active Pseudomonas), and one conservative tracer (bromide ion). Efforts have also been made to determine the relationship between viruses and fecal coliform bacteria in soil samples below the wastewater infiltrative surface, and the correlation between Escherichia coli concentrations measured in percolating soil solution as compared with those estimated from analyses of soil solids. The results suggest episodic breakthrough of virus and bacteria during soil treatment of wastewater and a 2 to 3 log (99-99.9%) removal of virus and near complete removal of fecal coliform bacteria during unsaturated flow through 60 to 90 cm of sandy medium. Results also suggest that the fate of fecal coliform bacteria may be indicative of that of viruses in soil media near the infiltrative surface receiving wastewater effluent. Concentrations of fecal coliform in percolating soil solution may be conservatively estimated from analysis of extracted soil solids.

The majority of onsite and decentralized wastewater facilities rely on the infiltration of wastewater effluents into subsurface soils where percolation results in the recharge of local groundwater (Siegrist et al., 2001). In these systems, a critical design element involves estimating the design infiltration rate for a particular type of wastewater effluent into a specific soil and environmental setting. The infiltration of wastewater effluents into soils and estimation of design application rates for a given system design and environmental setting are extremely complex and often poorly understood and oversimplified. Below is a short overview of infiltration rate (IR) theory as applicable to wastewater effluents, followed by a synopsis of recent and ongoing research at the Colorado School of Mines (CSM). The goal at CSM has been to advance the quantitative understanding of the dynamics of infiltration rate behavior during treatment of wastewater effluents in soil and account for the effects of infiltrative surface architecture (ISA) and other elements during wastewater soil absorption system (WSAS) design. Wastewater Infiltration into Soil and the Effects of Infiltrative Surface Architecture

A research effort was undertaken to investigate the genesis of particles produced during in situ chemical oxidation (ISCO) of trichloroethene (TCE) with permanganate (MnO4-) and to explore the effects of those particles on system permeability and metal mobility. The experimental approach included characterization of soil and groundwater samples from an ISCO field site, batch experiments with a replicated 2(5) factorial design, and flow-through column experiments. Analyses of intact soil cores from an ISCO field site-revealed that MnO2 solids were present in the subsurface near an injection well for NaMnO4 but at low levels (2.3-2.5 mg/g dry wt media) calculated to fill <1% v/v of the aquifer porosity. Batch tests revealed that the mass of filterable solids (>0.45 mum) produced during chemical oxidation with MnO4- was increased at higher TCE concentrations (54 versus 7 mg/L) and in the presence of ambient silt/clay-sized particles in the groundwater (750 versus 7.5 mg/L). Under otherwise comparable conditions, increasing the MnO4- dose markedly increases the oxidant consumption and also increases the solids production. The oxidant form (NaMnO4 versus KMnO4) or reaction time (15 versus 300 min) had little effect on oxidant consumption or filterable solids production. During MnO4- oxidation of higher levels of TCE in a groundwater with ambient silt/clay particles present, there can be substantial increases in filterable solids generated, which are <1 mum in size and consist of MnO2, Commingled with other mineral matter. Conceivably, low volumetric fillings of these solids could cause permeability loss. Flow-through column experiments revealed that permeability loss was possible during ISCO but only under conditions with very high MnO2 solids production. On the positive side, the MnO2 solids produced can increase the sorption potential for metals such as cadmium and can represent a mode of immobilization. This research demonstrated that ISCO with permanganate has the potential to yield system permeability loss under some conditions as well as to affect metal mobility. The magnitude of these effects is related to the subsurface conditions, target organic chemical mass, and permanganate dose and delivery method. The production of solids during ISCO needs to be carefully considered during process design and operation to avoid solids-related performance problems while exploiting potential benefits.

A field pilot test was conducted at a U. S. Department of Energy site to evaluate in situ chemical oxidation of trichloroethene (TCE) in a silty‐sandy gravel aquifer located at 26 to 30 feet (8 to 9 m) below ground surface. A vertical well‐to‐well recirculation system was designed and implemented by placing four corner extraction wells in a square grid, with each well 45 feet (13.7 m) from a center injection well. Ground water was extracted from the four perimeter wells, combined aboveground in a piping network, and then amended inline with sodium permanganate (NaMnO4) before reinjection into the aquifer through a center injection well. During the pilot test, oxidant amended ground water (250 mg/L NaMnO4) was injected at 18 gpm (68.1 L/m) for 10 days, during which time‐354 pounds (160.6 kg) of NaMnO4 were delivered and approximately 240,660 gallons (911 kL) of ground water were recirculated and treated. NaMnO4 injection using vertical wells in a five‐spot pattern was capable of providing sufficient hydraulic control to deliver oxidant throughout the permeable zones of the 4100 ft2 (380 m2) test area within three days. TCE concentrations were reduced, from 2,000 μg/L to <10 μg/L, throughout all but the lower permeable eastern edge of the test region, indicating an apparent reduction in contaminant levels of 92% within three days and 97% within 10 days (two hours after the end of active recirculation). One month after system shut down, residual oxidant concentrations in the ground water had declined to <1 mg/L, while a gradual increase in TCE concentrations was observed. Oxidant consumption over time is expected due to a combination of factors, including oxidation of the natural organic material present, oxidation of TCE that diffused out from the finer‐grained and less permeable zones, and advection of TCE into the test area from the upgradient plume. No adverse effects to system toxicity, generation of reaction intermediates and products (e.g., chlorinated organic acids or partially degraded chlorocarbons), or reduction in formation permeability were observed.