On-site Wastewater Treatment Systems Research Articles

Option of last resort or pragmatic solution? Social perspectives on onsite wastewater treatment systems in northern Argentina

ABSTRACT The unplanned and rapid expansion of metropolitan areas reduces accessibility to existing and often outdated centralized water and wastewater systems. In this context, sanitation policies that focus exclusively on centralized systems become expensive and unfeasible. Using Q methodology, we identified three different social perspectives on onsite wastewater treatment systems (OWTS) in the metropolitan area of the Lerma Valley in northern Argentina. We focused our analysis on the legal, environmental, and technical aspects of onsite sanitation. The perspectives found were: ‘OWTS have advantages’, ‘Hard path for sewerage’, and ‘Process before technology’. We describe the perspectives identified and we provide an analysis of their differences and similarities to discuss their possible policy implications for our study area and comparable regions in the country and beyond.

Pepper mild mottle virus as an effective tool in microbial source tracking for deficient domestic on-site water treatment systems

Pollution from domestic on-site wastewater treatment systems (OWTS) is a significant contaminant pressure in many rural catchments. However, due to their design, and dispersed proliferation, it is difficult to assess their impact. Water testing methodologies employ bacterial culturing methods and chemical analysis which may lose resolution and/or specificity being confounded by diffuse agricultural sources within a rural environment. In this study, we successfully assessed the applicability of Pepper Mild Mottle Virus (PMMoV) as a human faecal source tracker for deficient on-site wastewater treatment systems. The transport of PMMoV was first studied in the effluent of a 30 cm deep soil column which was dosed for 510 days with primary influent from a conventional septic system. The removal of PMMoV through the 30 cm deep soil column was quantified with a 5-day seeding trial employing primary influent mixed with PMMoV sourced from Tabasco pepper product ®. The trial was then carried out at field scale with the seeding solution dosed into an operational percolation trench receiving septic tank effluent which had been instrumented for porewater sampling. Samples were taken at depths of 10 cm, 30 cm, and 50 cm across the length of the trench at distances of 1 m, 7.5 m, and 17.5 m from the inlet of the trench. PMMoV was detected on all days of the trial, with a peak concentration of 1 × 106 found at the rear of the trench on day 2 of the seeding trial. Finally, to assess the effectiveness of PPMoV as a microbial source tracking tool from a water receptor perspective, three rural catchments with high densities of OWTSs were sampled and analysed for hourly variations in biological parameters which included total coliforms, Escherichia coli, PMMoV, and chemical parameters total organic carbon, total nitrogen, and total carbon. PMMoV was detected in all river samples over a 24-hour period, thereby indicating its suitability as a tracer of human wastewater effluent in such environments with multiple diffuse sources.

Battle of the Bites: The Effect of Sewage Effluent Exposure on Mosquitofish Biocontrol of Mosquitoes in Residential Louisiana.

Mosquitofish, Gambusia affinis, are eponymous larval mosquito predators. Their ability to colonize and survive in habitats that are uninhabitable by other potential predators allows them to naturally manage larval mosquito populations in most ground pools they are present in. However, effluent from residential onsite wastewater treatment systems (OWTSs) appears to limit the presence of fish predators. This is especially problematic in Louisiana, where regulations allow the discharge of OWTS effluent into open drainage conveyances. To determine the effect of effluent on the capacity of mosquitofish for biocontrol in contaminated areas, we assessed the body condition metrics of populations from two effluent-exposed sites and two sites not exposed to effluent, determined the lethal effect of effluent-contaminated drainage water on fish, and measured the prey consumption rates in the presence of effluent. Female fish collected from effluent-impacted sites had a reduced somatic body condition and most females examined displayed masculinized anal fins resembling the male gonopodium structure. This trait was not seen in fish collected from the control sites and has not yet been documented in association with OWTSs or in the state of Louisiana. Fish from the control sites survived at effluent-contaminated water levels < 70%, and the prey clearance rates increased with dilution. Onsite wastewater treatment system effluent has significant effects on both the short- and long-term persistence of mosquitofish, their body composition, reproductive health, and larval mosquito consumption. These effects likely release mosquito larvae from suppression and may increase the threat of mosquito-transmitted pathogens in effluent-contaminated locations.

Occurrence and concentrations of traditional and emerging contaminants in onsite wastewater systems and water supply wells in eastern North Carolina, USA.

Onsite wastewater treatment systems (OWTSs) and private wells are commonly used in Eastern North Carolina, USA. Water from private wells is not required to be tested after the initial startup, and thus persons using these wells may experience negative health outcomes if their water is contaminated with waste-related pollutants including bacteria, nitrate or synthetic chemicals such as hexafluoropropylne oxide dimer acid and its ammonium salt (GenX). Water samples from 18 sites with OWTSs and groundwater wells were collected for nitrate, Escherichia coli (E. coli), total coliform, and GenX concentration analyses. Results showed that none of the 18 water supplies were positive for E. coli, nitrate concentrations were all below the maximum contaminant level of 10 mg L-1, and one well had 1 MPN 100 mL-1 of total coliform. However, GenX was detected in wastewater collected from all 18 septic tanks and 22% of the water supplies tested had concentrations that exceeded the health advisory levels for GenX. Water supplies with low concentrations of traditionally tested for pollutants (nitrate, E. coli) may still pose health risks due to elevated concentrations of emerging contaminants like GenX and thus more comprehensive and routine water testing is suggested for this and similar persistent compounds.

A Critical Review of Green Approach on Wastewater Treatment Strategies

Green approach on wastewater treatment strategies aims to promote sustainable and environmentally friendly methods for treating wastewater while also reducing the environmental impact of traditional wastewater treatment processes. Hence, the objective of this paper was to undertake a critical review of green approach on wastewater treatment strategies using standard techniques of harvesting data from secondary sources from 2015 to 2023. Information obtained reveals that energy-efficient treatment technologies, such as anaerobic digestion and membrane bioreactors, use less energy than traditional treatment technologies. Treating wastewater for reuse can reduce the demand for freshwater resources and the energy required for water treatment. Onsite wastewater treatment systems, such as septic systems and composting toilets, can reduce the amount of wastewater that needs to be transported and treated at centralized facilities. Incorporating green infrastructure, such as rain gardens and permeable pavement, into urban areas can help reduce the amount of stormwater runoff that enters the wastewater treatment system. Extracting nutrients, such as nitrogen and phosphorus, from wastewater can be used as a fertilizer for crops, reducing the need for synthetic fertilizers. Overall, these green wastewater treatment strategies aim to reduce the energy consumption, chemical usage, and environmental impact of traditional wastewater treatment processes, while promoting sustainable and efficient use of resources.

Onsite wastewater treatment systems are a major source of pharmaceutical products in surface water of peri-urban/rural areas

Most of the published studies on pharmaceutical products (PhPs) focus on their occurrence in the influent/effluent at wastewater treatment plants (WWTPs) in urban areas with high population density. In peri-urban/rural areas not collected to any WWTP, despite the lack of sewage collection, and often (poor) on-site treatment, data on PhPs occurrence in surface water bodies is scarce. In this study, we investigated the impact of onsite wastewater treatment systems on the occurrence of six PhPs, along with hydrological and hydrochemical data, in the drainage network of a peri-urban/rural area in Italy.Our results, along with data from other studies, show onsite treatment systems are a major source of PhPs. In the drainage water 76% of the analyses positively quantified the presence of PhPs, with carbamazepine and clarithromycin always quantifiable, even in scarcely inhabited areas, at generally higher concentrations of PhPs than those reported in previous studies. As a result, onsite treatment systems may cause ubiquitous, even if at low concentrations, PhPs occurrence in the aquatic systems.In order to allow data comparison, studies reporting PhPs environmental concentration values should clearly detail the urban /environmental setting (population density, presence of WWTPs) and the hydrological/hydrochemical conditions. Furthermore, the joint use of hydrochemical parameters and PhPs data may provide useful proxies for the occurrence of PhPs or to identify nitrate sources of urban origin. Discharge, T, EC and ORP values may help understanding relevance of mixing and, then, the importance of dilution processes in reducing PhPs concentration.The occurrence of PhPs in surface water has to be duly considered in order to protect the aquatic ecosystems and groundwater, and the use of such water for safe irrigation purposes. Further treatment trains based on the concept of nature-based solutions (i.e, vegetated channels, artificial wetlands) could constitute a valuable solution exploiting the soil–water-plant continuum around main residential areas in order to enhance degradation processes.

The use of sterol profiles, supported with other faecal source tracking methods, to apportion septic tanks contamination in rural catchments

Identifying the origin of faecal pollution in water is needed for effective water management decisions to protect both human health and aquatic ecosystems. Traditionally used indicators of faecal contamination, such as E. coli, only indicate pollution from warm-blooded animals and not the specific source of contamination; hence, more source specific tracers are required. The study has focussed on separating the two main sources of contaminants within rural catchments in Ireland, agriculture and on-site wastewater treatment systems (predominantly septic tanks). While human-specific effluent tracers may assist in identifying potential pathways from individual septic tanks to surface waters, it is difficult to quantify the cumulative impact of such systems at a catchment scale. This study has investigated faecal sterols as a method to quantify such an impact on four small catchments in areas of low subsoil permeability with high densities of septic tanks. The results demonstrate the usefulness of faecal sterols which provide a quantitative evaluation of the respective impact between agricultural pasture inputs and on-site effluent showing differences between the four catchments. The study also highlights the need to derive more specific local reference sterol profile databases for specific countries or regions, using local source material of animal faeces and effluent. Two intensive sampling campaigns on the four catchments then used faecal sterols in parallel to fluorescent whitening compounds (FWCs), caffeine, artificial sweeteners and selected pharmaceuticals to gain further insights and confirmation about contamination hotspots as well as providing comparison between the different parameters. The combination of sterols, FWCs, caffeine, acesulfame and cyclamate has proven suitable to provide an estimate of the extent of human contamination in these rural catchments and has yielded additional information about potential pollution pathways and proximity of contamination. Overall, this methodology can help to facilitate a targeted and effective water management in such catchments.

Investigating the Relationship between Surface Water Pollution and Onsite Wastewater Treatment Systems.

Onsite wastewater treatment systems (OWTSs) are important nonpoint sources (NPSs) of pollution to consider in watershed management. However, limited OWTS data availability makes it challenging to account for them as an NPS of water pollution. In this study, we succeeded in obtaining OWTS permits and integrated them with environmental data to model the pollution potential from OWTSs at the watershed scale using GIS-based multicriteria decision analysis. Then, in situ water quality parameters─Escherichia coli (E. coli), total nitrogen, total phosphorus, temperature, and pH─were measured along the main tributary at base-flow conditions. Three general linear models were developed to relate E. coli to water quality parameters and OWTS pollution indicators. It was found that the model with the OWTS pollution potential had the lowest corrected Akaike information criterion (AICc) value (35.01) compared to the models that included classified OWTS pollution potential input criteria (AICc = 36.76) and land cover (AICc = 36.74). These results demonstrate that OWTSs are a significant contributor to surface water pollution, and future efforts should be made to improve access to OWTS data (i.e., location and age) to account for these systems as an NPS of water pollution.

Modeling the effect of improved sewage disposal rates on ecological status for aquatic organisms in Japan

Improving sewage disposal rates is an important policy for maintaining the health of aquatic organisms in river environments. In Japan, the rate is not yet 100 %. Two measures are necessary to eliminate the discharge of untreated greywater: (1) increase the number of households connected to sewage lines in areas with sewage systems, and (2) replace single-type household onsite wastewater treatment systems (OWTSs) with combined-type systems. To estimate the effect of improving the disposal rate on river water quality, we developed a hydrology-based organic pollution assessment model with a gridded spatial resolution of 250 m to estimate the biochemical oxygen demand (BOD) in rivers in Gunma Prefecture, Japan. We considered three scenarios based on the sewage disposal rate of 70.5 % in 2015. In Scenario A, the disposal rate is increased to 75.2 % in 2030 by increasing the connection rate to sewage lines. In Scenario B, the rate is increased to 88.2 % in 2030 through additional progress in converting from single-to combined-type OWTSs. In Scenario C, the rate reaches 100 % by 2040. The ecological status of rivers was evaluated using taxon richness of Ephemeroptera, Plecoptera, and Trichoptera estimated from its reported relationship to BOD. The number of sites in Gunma Prefecture polluted by organic waste classified as III (poor) and IV (very poor) was estimated to be 1610 under the present state (2015) and decreased to 1212 (25 % reduction) in Scenario A, 619 (62 % reduction) in Scenario B, and 50 (97 % reduction) in Scenario C, with the improvements mainly in small branch rivers. The effects of improved disposal rates were mainly evident in areas with relative high population densities using single-type OWTSs outside of areas with a sewage system, and measures taken in these areas were shown to be effective.

Household level wastewater management and disposal data collection in the U.S.: the history, shortcomings, and future policy implications

Abstract Country-level sanitation access is monitored globally by the Joint Monitoring Programme (JMP). However, recent reports on sanitation access in high-income countries indicate that the JMP data may underestimate the prevalence of unsafely managed sanitation in these settings. This study explains the surveys that collect household-level wastewater management data in the U.S. and analyzes the accuracy and reliability of these data sets. From 1940 to 1990, sewage disposal data were collected comprehensively through the U.S. Decennial Census. These data are currently collected through the American Housing Survey (AHS) which appears to greatly underestimate the usage of onsite wastewater treatment systems (OWTS). In addition to these surveys, we highlight current efforts to introduce a sewage disposal question to the American Community Survey (ACS), localized efforts to collect wastewater data, and the Point-in-Time count of people experiencing homelessness. Using estimates of OWTS usage in new housing, this study provides the first defensible national estimate of OWTS usage since 1990. We estimate that 25.03% of U.S. households use OWTS which exceeds the AHS estimate (15.7%) by over 12 million households. This study discusses the potential for better wastewater data collection to inform future wastewater policy and improve the quality of life for U.S. residents.

Illuminated septic tank – A microalgae assisted onsite wastewater treatment system

To reduce the anthropogenic nutrient loading into natural waterways, onsite wastewater treatment is essential for households without access to municipal sewer systems. However, many conventional septic tanks significantly underperform the centralized wastewater treatment. In the present study, a novel illuminated septic tank inoculated with the consortium of microalga Chlorella vulgaris and aerobic bacteria was developed by modifying the conventional configuration. The inclusion of microalgae facilitated aeration inside the septic tank through photosynthetic oxygen evolution, and the microalgae-bacteria consortium enhanced the wastewater treatment performance. With the operation at 15 ℃ and a hydraulic retention time of 2.5 days, the lab-scale algae-assisted septic tank significantly decreased the concentrations of ammonium-nitrogen (NH4+-N), soluble phosphorus (P), total P, and total chemical oxygen demand by 54%, 65.2%, 78.5%, and 90.7% in the discharged effluent, respectively (p < 0.05), whereas the conventional septic tank without microalgae did not exhibit any treatment of NH4+-N or soluble P and the total P removal efficiency was lower by 50%. Meanwhile, the photosynthetic activity of microalgae altered the gas composition in the tank headspace by consuming carbon dioxide, emitting oxygen, and inhibiting the evolution of methane, which further benefited the aeration requirement and contributed to the mitigation of greenhouse gas emissions from septic systems.

Hierarchical prioritization of on-site wastewater treatment systems using combined decision analysis and Microsoft Visual Basic

Decision makers are increasingly considering environmental sustainability and social impacts when choosing a wastewater treatment unit, along with the system's costs and technical capabilities. Number of factors must be taken into consideration when making this decision, including specific site constraints as well as the preferences of the client. Furthermore, while the literature acknowledges the value of scenario-based analysis, it does not provide decision-makers with the means to perform a tailored analysis specific to their project. Consequently, the aim of this research is to develop a user-friendly program for conducting sustainability assessments that can be used by decision-makers to conduct their own individual assessments. Additionally, the paper prioritizes 21 on-site wastewater treatment units for two different scenarios based on the availability of units in New Zealand.Microsoft Visual Basic for Applications (VBA) was used to develop a multi-criteria decision analysis program in Excel. The main novelty of our research is the incorporation of VBA with a decision-making process to create a user-friendly and efficient decision aid tool, simplifying the process and improving its efficiency and usability. The results of the analysis for Scenario A (a rural Iwi school wanting an environmentally-friendly, locally-produced system) indicated that the Advanced Wastewater System, a bed reactor aerated wastewater treatment system, was the most sustainable unit. Eco Sewage System was found to be the most sustainable option for Scenario B (a residential house in a recently developed rural area), due to its ability to treat wastewater solids aerobically without the need for separate primary treatment.

Operationalizing resilience: A deductive fault-driven resilience index for enabling adaptation

The impact of climate change and the dynamic nature of environmental conditions underscore the critical need to enhance resilience of systems and process safety considerations. The efficacy of such efforts primarily depends on how resilience is measured. Among the myriad efforts to quantify resilience, composite indicators have emerged as promising tools. However, these indicators typically employ statistical methods to derive weights for aggregation and rely on statistical homogeneity among indicators which can limit their scope and fidelity. In this study, we propose an alternative novel resilience index derived from a system’s structure and the essential conditions for safe operation during and after disruptions. The proposed measure reflects the systems’ ability to resist and respond to failures by addressing possibilities of impact propagation to other infrastructure systems. Moreover, it eliminates the need for weights and allows for compensability among its leading indicators. Using a case study based on the on-site wastewater treatment and disposal systems (OSTDS) in South Florida that faces increasing risks due to rising sea levels, we investigate the validity of the proposed index and perform a comparative analysis with statistically-driven measures. Furthermore, we demonstrate the adaptation of the proposed index for decision making within a generalized optimization framework.

Impact of maintenance on domestic wastewater treatment systems

AbstractWastewater treatment systems are important sources of contaminants of emerging substances, including pharmaceuticals, and personal care products. Onsite wastewater treatment systems provide alternative solutions to centralized systems; although they are becoming increasingly popular, little is known about the effect of maintenance on their performance. In the current study, chemical and microbiological parameters in the effluents from two identical on-site wastewater treatment systems were analyzed, one being properly maintained while the other not maintained at all. Taxonomic profiles vastly differed from each other, and organic micropollutants are present at higher concentrations in the effluent of the non-maintained unit. The results highlight the importance of proper maintenance.

Development of a Soft Sensor Using Machine Learning Algorithms for Predicting the Water Quality of an Onsite Wastewater Treatment System.

Developing advanced onsite wastewater treatment systems (OWTS) requires accurate and consistent water quality monitoring to evaluate treatment efficiency and ensure regulatory compliance. However, off-line parameters such as chemical oxygen demand (COD), total suspended solids (TSS), and Escherichia coli (E. coli) require sample collection and time-consuming laboratory analyses that do not provide real-time information of system performance or component failure. While real-time COD analyzers have emerged in recent years, they are not economically viable for onsite systems due to cost and chemical consumables. This study aimed to design and implement a real-time remote monitoring system for OWTS by developing several multi-input and single-output soft sensors. The soft sensor integrates data that can be obtained from well-established in-line sensors to accurately predict key water quality parameters, including COD, TSS, and E. coli concentrations. The temporal and spatial water quality data of an existing field-tested OWTS operated for almost two years (n = 56 data points) were used to evaluate the prediction performance of four machine learning algorithms. These algorithms, namely, partial least square regression (PLS), support vector regression (SVR), cubist regression (CUB), and quantile regression neural network (QRNN), were chosen as candidate algorithms for their prior application and effectiveness in wastewater treatment predictions. Water quality parameters that can be measured in-line, including turbidity, color, pH, NH4+, NO3-, and electrical conductivity, were selected as model inputs for predicting COD, TSS, and E. coli. The results revealed that the trained SVR model provided a statistically significant prediction for COD with a mean absolute percentage error (MAPE) of 14.5% and R2 of 0.96. The CUB model provided the optimal predictive performance for TSS, with a MAPE of 24.8% and R2 of 0.99. None of the models were able to achieve optimal prediction results for E. coli; however, the CUB model performed the best with a MAPE of 71.4% and R2 of 0.22. Given the large fluctuation in the concentrations of COD, TSS, and E. coli within the OWTS wastewater dataset, the proposed soft sensor models adequately predicted COD and TSS, while E. coli prediction was comparatively less accurate and requires further improvement. These results indicate that although water quality datasets for the OWTS are relatively small, machine learning-based soft sensors can provide useful predictive estimates of off-line parameters and provide real-time monitoring capabilities that can be used to make adjustments to OWTS operations.

Environmental assessment of on-site source-separated wastewater treatment and reuse systems for resource recovery in a sustainable sanitation view

Sustainable sanitation solutions are necessary for promoting public health and environmental security. In this study, on-site domestic wastewater treatment (WWT) systems used for households in rural and peri-urban areas of Brazil were compared in different scenarios from a life cycle assessment (LCA) perspective. The evaluated scenarios represented different practices in wastewater management, such as direct discharge into the soil, rudimentary treatment, septic tank, public sewerage system, and source separation of wastewater streams for water, nutrient, and organic matter recovery. The WWT technologies considered in the proposed scenarios of source-separated wastewater streams were as follows: an evapotranspiration tank (TEvap) and composting toilet for blackwater, a modified constructed wetland (EvaTAC) for greywater, and a storage tank for urine. LCA was performed in this study according to the ISO standards to assess the environmental impacts at both midpoint and endpoint levels. The results show that on-site source-separated wastewater treatment systems with resource recovery result in significant reductions in environmental impacts compared to scenarios with precarious conditions or ‘end-of-pipe’ solutions. For example, regarding the human health damage category, the scenarios involving resource recovery, including systems such as EvaTAC, TEvap, composting toilet, and urine storage tank, demonstrate significantly lower values (−0.0117 to −0.0115 DALY) compared to scenarios with rudimentary cesspits and septic tanks (0.0003 to 0.001 DALY). We conclude that the focus should be beyond mere pollution aspects and instead concentrate on the benefits of the co-products, which are: avoiding the extraction and consumption of valuable and increasingly scarce raw materials, such as potable water, and production of synthetic fertilizer. Furthermore, it is highly recommended that an LCA of sanitation systems synergistically integrates the WWT process, the constructive aspects, and the resource recovery potential.

Hydraulic conductivity assessment of falling head percolation tests used for the design of on-site wastewater treatment systems

The suitability of a location for an on-site wastewater treatment process (for areas which lack access to centralised wastewater treatment systems) requires an assessment of the permeability of the soil into which the effluent will be discharged. In many jurisdictions this is determined using some type of in-situ percolation test. Falling head percolation tests, which give a value of percolation time (PT) that is empirically related to the notion of hydraulic conductivity, are widely used as they are relatively simple to carry out, but the test does not have a sound theoretical framework and test methods are not standardised internationally. In comparison, the saturated hydraulic conductivity of a soil obtained from a constant head well permeameter test is independent of test conditions, and so is a more suitable metric for design. A database of over 900 falling head tests carried out across a range of different subsoil types in Ireland has been collated, all with the inherent limitations of the existing regulative framework regarding the percolation test and soil texture assessment. These tests were then modelled using Hydrus 2-D numerical modelling simulations to determine equivalent field saturated hydraulic conductivity (Kfs) values and thereby provide a correlation with PT values across the range of subsoil conditions. In addition, falling head tests have been carried out in parallel to constant head permeameter tests in the field and compared against the relationship derived from the broad dataset of simulated results. This revealed an optimal solution by which to determine Kfs from the field permeameter test (using parameters recommended for most structured soils from clays to loams). The trendline based on Irish data was also compared against more generic formulations of the relationship between PT, and Kfs and shown to match closely, particularly the Reynolds (2016) ‘unified’ methodology. Finally, the Irish threshold PT limits for on-site wastewater treatment have been converted to Kfs values and compared against other international standards.

Existing evidence related to soil retention of phosphorus from on-site wastewater treatment systems in boreal and temperate climate zones: a systematic map

BackgroundIn Sweden there are nearly one million soil-based on-site wastewater treatment systems (OWTSs). OWTSs may contribute to eutrophication of surface waters, due to the discharge of phosphorus (P). Hence, in certain cases, a high P removal rate (up to 90%) of OWTSs is required by Swedish authorities. Since these requirements may have costly consequences to property owners, it is debated whether they are too strict. In this debate, it is often claimed that the soil retention of P occurring in the natural environments may be underestimated by authorities. Soil retention is the inhibition of the transport of P through the ground, due to different chemical, physical and biological processes occurring there. These processes make the P transport slower, which may reduce the unwanted impact on receiving water bodies. However, the efficiency of soil retention of P remains unclear. The objective of this systematic map was to collect, code, organise and elucidate the relevant evidence related to the topic, to be able to guide stakeholders through the evidence base, and to support future research synthesising, commissioning, and funding. The systematic map was carried out in response to needs declared by the Swedish Agency for Marine and Water Management but the conclusions should be valid for a wider range of countries across boreo-temperate regions.MethodsSearches were made for peer-reviewed and grey literature using bibliographic databases, search engines, specialist websites, and stakeholder contacts. The references were screened for relevance according to a predefined set of eligibility criteria. A detailed database of the relevant studies was compiled. Data and metadata that enable evaluation and discussion of the character and quality of the evidence base were extracted and coded. Special focus was placed on assessing if existing evidence could contribute to policy and practice decision making. Descriptive information about the evidence base was presented in tables and figures. An interactive evidence atlas and a choropleth were created, displaying the locations of all studies.Review findings234 articles out of 10,797 screened records fulfilled the eligibility criteria. These articles contain 256 studies, performed in the field or in the laboratory. Six different study types were identified, based on where the measurements were conducted. Most studies, including laboratory studies, lack replicates. Most field studies are observational case studies.ConclusionsIt is not possible to derive valid generic measures of the efficiency of soil retention of P occurring in the natural soil environment from available research. Neither does the evidence base allow for answering the question of the magnitude of the potential impact of OWTSs on the P concentration in recipients on a general basis, or under what conditions OWTSs generally have such an impact. A compilation of groundwater studies may provide examples of how far the P may reach in x years, but the number of groundwater studies is insufficient to draw any general conclusions, given the complexity and variability of the systems. Future research should strive for replicated study designs, more elaborate reporting, and the establishment of a reporting standard.

Aerosol partitioning potential of bacteria presenting antimicrobial resistance from different stages of a small decentralized septic treatment system

The release of airborne pathogens with antimicrobial resistance is a growing global public health threat. The potential spread of antimicrobial resistant bacteria and antimicrobial resistance genes (ARB/ARGs) from wastewater effluents through aerosolization is not fully understood. Septic tanks are on-site wastewater treatment systems (OWTS) used in about 25% of households in the United States (US). The system in this study consists of four tanks connected by two different treatment types, with wastewater moving from the most contaminated, Tank 1, to the most purified holding, Tank 4. Aerosol samples at each tank were collected in the summer and winter with open and closed lids to observe their effect on bioaerosol emissions. The water inside each tank was also sampled to compare the bacteria concentration and composition. Results from microbial and molecular analysis indicate lower concentrations of bacteria in the aerosols compared to the water samples. The antibiotic testing indicates that aerosolized bacteria from the winter were more resistant to the antibiotics used compared to the aerosolized bacteria from the summer. The occurrence of aerosolized bacteria likely depends on operational conditions and discharge methods, on changes in humidity, temperature, and air velocity, while the effluent resistance can be influenced by quorum sensing. Further assessment of the water and bioaerosol microbiome should include the genomic analysis of antimicrobial resistance of bacterial isolates from both sources and thus provide an important link regarding human exposure to ARBs/ARGs near wastewater treatment systems.Copyright © 2023 American Association for Aerosol Research

Factors affecting effluent quality in on-site wastewater treatment systems in the cold climates of Finland and Sweden

Decentralized sanitation facilities serving single households to small communities can offer a more flexible way of improving global sanitation. In Nordic countries, on-site wastewater treatment systems (OWTS) are mostly used in sparsely populated areas and are regulated for the removal of phosphorus (Tot-P), organic matter (biological oxygen demand, (BOD7)) and total nitrogen (Tot-N). However, available reports, albeit commonly using small data sets, call attention to often low and variable treatment performance. In this work, a statistical analysis of 1301 samples from 395 units reported in 10 studies from Finland and Sweden was conducted. The objective was to increase knowledge regarding the effluent water quality of OWTS and their compliance with regulations. In addition, the goal was to identify possible factors affecting contaminant concentrations. Overall, compliance with base-level BOD7 removal requirements was met by most units while 10% of units exceeded Tot-N and >25% exceeded Tot-P limits. Non-compliance rates were high, especially for Tot-P, considering the studied data set was composed mostly of semi-new units (median 3.8 years). Neither weather (air temperature, precipitation, and snowmelt), age or load factors were found to strongly explain the data variability in either soil-based systems (SBS) or package plants (PP). Tot-N and Tot-P effluent concentrations of the two systems were not significantly different. Effluent BOD7 concentrations were lower in SBS (median 3.0 mg/L) when compared to PP (median 7.7 mg/L). Units with P-sorbing filters (median 0.69 mg/L) and chemical precipitation (median 1.54 mg/L), presented lower Tot-P effluent concentrations in contrast to traditional sand filters (median 4.0 mg/L). The biological process used in PP had a measurable effect on effluent BOD7 concentrations, with attached growth units presenting higher values (median 8.1 mg/L) than suspended growth units (median 7.1 mg/L). Although the data set utilized was large, its analysis revealed intrinsic bias in data collection, especially regarding system types and sampling seasonality with colder winter periods sampling underrepresented. There is a need for data collection to improve to allow conclusive treatment efficiency assessment including possible effects of climate and process-related factors.