Widespread access to clean water and sanitation supports the dual goals of improving public health and protecting environmental health globally. Onsite wastewater treatment systems (OWTS, i.e., septic systems) are an integral part of the water infrastructure that contributes to these goals in the United States and around the world. There is increasing demand for environmental scientists and engineers that are well versed in these systems, but college‐level courses on the subject are lacking. To address this gap, we developed and taught a senior‐level course that covers the siting, design, troubleshooting, and regulatory aspects of OWTS. We use a problem‐based learning approach in which students work in permanent groups to solve a sequence of problems, in the process of which they engage with the course content. Students’ understanding of the material is assessed at the group and individual levels through presentations, annotated slides, personal reflections, and science communication exercises. Formal and informal feedback from students has been overwhelmingly favorable, especially with regard to the use of problem‐based learning and the use of specifications grading, which allows students to revise their work until they achieve the level of mastery they desire. Overall, our course succeeded in providing students with an opportunity to grapple with the practical aspects of OWTS design and regulation, to develop their research and communication skills, and to work in groups effectively.

Nitrate (NO3-) pollution from onsite wastewater treatment systems (OWTS) is a concern in coastal communities that rely on groundwater for drinking water because of health risks associated with high levels of NO3- and the potential for eutrophication in areas where ground and surface water are connected. We examined the relationship between OWTS density and groundwater NO3- concentration in glacial soils with different parent material in a coastal watershed in the town of Charlestown, Rhode Island (USA). The area is underlain by glacial till and fluvial deposits, with groundwater as the only source of potable water and OWTS as the only means of treatment. The density of OWTS/ha was not significantly different between glacial fluvial (median=1.0; range, 0.04-4.8; n=207) and till (median=1.3; range, 0.012-3.81; n=160) soil parent material. Nitrate levels (mg N/L) in shallow well samples taken from 2013 to 2022 were significantly higher in till (median=3.7; range 0-15; n=160) than in glacial fluvial (median=2.7, range 0-9.7; n=207) parent material. Groundwater NO3- levels increased linearly with density of OWTS, and the slope (mg N ha/L OWTS) and intercept (mg N/L) values for the regression were significantly higher for till (0.99; 2.28) than glacial fluvial (0.66; 1.95) parent material. Regression intercept values >0.5 mg N/L, corresponding to a density of 0 OWTS/ha, point to widespread mixing of contaminated groundwater. Cumulative probability analysis showed that the proportion of samples with NO3- levels corresponding to Extreme pollution risk (>5 mg N/L) was much higher in till than in glacial fluvial parent material at the same OWTS densities. Fewer than 10% of the NO3- values were in the Low risk category (<0.5 mg N/L) regardless of OWTS density or parent material. Our results suggest that OWTS density and soil parent material should be part of the criteria for water management and land use decisions to protect public and environmental health.

Removal of manganese (Mn) and iron (Fe) oxide coatings from indicators of reduction in soil (IRIS) is considered a function of microbial reduction of these elements under sufficiently reducing conditions, but there may be situations where removal is abiotic. We examined whether abiotic removal of Mn and Fe oxide coatings may be facilitated by organic acids and whether loss of Mn can take place via chemical reduction by ferrous iron (Fe2+) in vitro. Loss of color from Mn-IRIS in citric acid solution was highest at 1 and 10 mM regardless of pH, with no loss observed at lower concentrations. Effects of citric acid on Fe-IRIS were also limited to 1 and 10 mM, but color loss only occurred at pH 4.5 and the rate and extent of loss were lower than for Mn-IRIS. Color loss from Mn-IRIS in oxalic acid was highest at 1 and 10 mM and increased with decreasing pH. Effects of oxalic acid on loss of color from Fe-IRIS were limited to 1 and 10 mM. Loss of color from Mn-IRIS was limited to 10 mM salicylic acid and pH 4.5, with no effect on Fe-IRIS regardless of concentration and pH. Only the two highest concentrations of Fe2+ (50 and 100 mM) resulted in reduction of the Mn-IRIS coating and subsequent deposition of an Fe oxide coating. Organic acids and pH have a differential effect on color loss from Mn- and Fe-IRIS, with only high concentrations of organic acids at low pH possibly interfering with interpretation.

Tracking changes in the quantity and variability of soil organic carbon (SOC) stocks associated with different land uses over time is a critical step in understanding decadal-scale impacts of soils on climate change, and can be an important reality check for more complex modeling efforts. In this study, we used a Bayesian statistical framework to quantify and compare SOC stocks among common southern New England land use types (sod farms, silage corn, forest, and turfgrass), including sod fields in continuous production for different periods of time (approximately 10, 20, and 30 years). Further, we modeled the export of SOC associated with sod har-vesting, propagating uncertainty from observations to export estimates. Despite unsustainable annual rates of soil removal (74 to 114 Mg ha-1), SOC stocks for sod fields in production for different time periods were not credibly lower than those of the other land uses examined. Mean exported SOC from sod harvest ranged from 1.67 to 3.23 Mg ha-1, which was enough to entirely deplete the 0-30 cm SOC stock in approximately 30 years. These results suggest that organic C inputs to the upper 30 cm of sod farm soils, from subsoil incorporation during post-harvest tillage and belowground net primary production, may have been maintaining SOC by offsetting loses over several decades. This is unlikely to continue, however, if the eolian mantle that characterizes these soils is depleted due to the cumulative impact of sod harvest on soil removal.

Manganese (Mn) and Fe indicator of reduction in soils (IRIS) devices are low-cost, convenient tools for identifying reducing conditions in soils. Because Mn is reduced at similar redox potentials as nitrate, there is considerable interest in using Mn IRIS tools for understanding microbial reduction of Mn as a surrogate for processes such as denitrification. However, the sensitivity of these devices to differences in Mn-reducing capacity has not been empirically investigated. Here we have found that the rate of birnessite paint removal from Mn IRIS films exposed to a twofold dilution series of the Mn-reducing bacterium Shewanella oneidensis is directly proportional to the number of S. oneidensis cells added. Thus, regularly monitored birnessite IRIS sensors are capable of indicating twofold differences in Mn reduction in soil and can be used to measure relative Mn reduction rates over time in a single location or compare and contrast Mn reduction rates across soil types.

Indicator of Reduction in Soils (IRIS) films are visual sensors used to document weakly or moderately reducing conditions in soils based on the reduction and removal of brown manganese (Mn) oxide or orange iron (Fe) oxide paints, respectively, from underlying white polyvinyl chloride (PVC) films. Paint removal is largely assumed to result from anaerobic microbial reduction using metal oxides on the PVC films as electron acceptors. If true, IRIS films could indicate conditions favorable to other biogeochemical processes that occur at similar redox potentials to those facilitating paint removal. Our objective here was to assess the effects of selected abiotic soil properties on IRIS film paint removal to determine whether removal can accurately be attributed to biotic processes alone. Through field deployments and laboratory incubation experiments using IRIS films, we investigated relative sulfide concentration and dissolved organic matter as two abiotic factors potentially capable of removing paint from Mn IRIS films. Our results showed that abundance of reactive soluble sulfides cause rapid and extensive abiotic paint removal from Mn films, whereas ambient concentrations of dissolved organic matter in freshwater wetland porewater does not drive abiotic removal. Furthermore, we found that the visible formation of black iron monosulfides on Fe films can be used to detect sulfide concentrations that will remove paint from Mn films. This study suggests that whereas some abiotic soil properties (e.g., sulfide concentration) can cause paint removal, IRIS films may be a viable tool to approximate biotic process rates where abiotic paint removal can be ruled out.

Soil fauna includes earthworms, collembolans, mites, nematodes, and protozoa. These are eukaryotic, heterotrophic, motile organisms that require oxygen for metabolism. Their physical range, habitats, and food resources are constrained by their respective sizes and the availability of pores of appropriate size within the soil. This chapter describes both invertebrate animals that live in the soil and their habitat and additionally examines their activities in the context of the soil foodweb. We focus on the role of soil animals in controlling microbial pathogens, mineralizing nutrients, changing microbial community composition, and enhancing primary production. Like aboveground fauna, the physical structure of the ecosystem places constraints on the activities of the soil fauna, especially in relation to the microflora. As a result of their feeding, burrowing, and movement, the soil fauna also engineer the habitat for the soil microflora, transport beneficial and pathogenic microorganisms, and affect the production of detrital resources from plants.

Non-proprietary N-removal onsite wastewater treatment systems are less costly than proprietary systems, increasing the likelihood of adoption to lower N inputs to receiving waters. We assessed the capacity of non-proprietary lignocellulose-amended soil treatment areas (LCSTAs)—a 45-cm-deep layer of sand above a 45-cm-deep layer of sand and sawdust—to lower the concentration of total N (TN) in septic tank effluent (STE) at mesocosm and field scales. The mesocosm received wastewater for two years and had a median effluent TN concentration of 3.1 mg/L and TN removal of 60–100%, meeting regulatory standards of 19 mg/L or 50% removal. Removal varied inversely with temperature, and was lower below 10 °C. Removal was higher in the mesocosm than in five field sites monitored for 12–42 months. Median effluent TN concentration and removal met the standard in three continuously-occupied homes but not for two seasonally-occupied homes. Sites differed in temporal pattern of TN removal, and in four of five sites TN removal was greater—and effluent TN concentration lower—in the LCSTA than in a control STA containing only sand. The performance of non-proprietary LCSTAs was comparable to that for proprietary systems, suggesting that these may be a viable, more affordable alternative for lowering N inputs to receiving waters.

Wastewater is a major source of nitrogen (N) to groundwater and coastal waterbodies, threatening both environmental and public health. Advanced N-removal onsite wastewater treatment systems (OWTS) are used to reduce effluent N concentration; however, few studies have assessed their effectiveness. We evaluated the total N (TN) concentration of effluent from 50 advanced N-removal OWTS in Charlestown, Rhode Island, USA for 3 years. We quantified differences in effectiveness as a function of N-removal technology and home occupancy pattern (seasonal vs. year-round use), and examined the relationship between wastewater properties and TN concentration. RX30 systems produced the lowest median TN concentration (mg N/L) (13.2), followed by FAST (13.4), AX20 (14.9), and Norweco (33.8). Compliance with the state's regulatory standard for effluent TN concentration (19 mg N/L) was highest for RX30 systems (78%), followed by AX20 (73%), FAST (67%), and Norweco (0%). Occupancy pattern did not affect effluent TN concentration. Variation in TN concentration was driven by ammonium and nitrate for all technologies, and also by temperature for FAST and pH for Norweco. Median daily (g N/day) and annual (kg N/yr) N loads were significantly higher for year-round (5.3 and 2.3) than for seasonal (3.7 and 0.41) systems, likely due to differences in volume of wastewater treated. Our results suggest that advanced N-removal OWTS vary in their compliance with the state regulatory standard for effluent TN and can withstand long periods of non-use without compromising effectiveness. Nevertheless, systems used year-round do produce a higher daily and annual N load than seasonally-used systems.

Lignocellulose-amended, layered soil treatment areas (STAs) remove nitrogen (N) passively from wastewater by sequential nitrification and denitrification. As wastewater percolates through the STA, the top sand layer promotes nitrification, and the lower, lignocellulos-amended sand layer promotes heterotrophic denitrification. Layered STAs can remove large amounts of N from wastewater, which may increase their emissions of CO2, N2O, and CH4 to the atmosphere. We measured greenhouse gas (GHG) flux from sawdust-amended (Experimental) and sand-only (Control) STAs installed in three homes in southeastern Massachusetts, USA. The Experimental STAs did not emit significantly more GHGs to the atmosphere than Control STAs receiving the same wastewater inputs, and both Control and Experimental STAs emitted more CO2 and N2O - but not CH4 - than soil not treating wastewater. Median (range) flux (mu mol m(-2) s(-1)) for all homes for the Control STAs was 7.6 (0.8-23.0), 0.0001 (-0.0004-0.004), and 0.0008 (0-0.02) for CO2, CH4 and N2O, respectively, whereas values for the Experimental STAs were 6.6 (0.3-243), 0 (-0.0005-0.005), and 0.0004 (0-0.02) for CO2, CH4 and N2O, respectively. Despite the absence of differences in flux between Control and Experimental STAs, the Experimental STA had significantly higher subsurface GHG levels than the Control STA, suggesting microbial consumption of excess gas levels near the ground surface in the Experimental STA. The flux of GHGs from Experimental and Control STAs was controlled chiefly by temperature, soil moisture, and subsurface GHG concentrations. Total emissions (gCO(2)e capita(-1) day(-1)) were higher than those reported by others for conventional STAs, with mean values ranging from 0 to 1835 for septic tanks, and from 30 to 1938 for STAs. Our results suggest that, despite a higher capacity to remove N from wastewater, layered STAs may have limited impact on air quality compared to conventional STAs. (C) 2020 Elsevier B.V. All rights reserved.

Many coastal communities rely on individual onsite wastewater treatment (i.e., septic) systems to treat and disperse wastewater. Proper wastewater treatment in these systems depends on sufficient volume of unsaturated soil below the drainfield’s infiltrative surface. This is governed by the vertical separation distance—the distance between the groundwater table and the drainfield infiltrative surface—which is specified in (regulatory jurisdictions’ onsite wastewater system) regulations. Groundwater tables along the southern New England coast are rising due to sea-level rise, as well as changes in precipitation and water use patterns, which may compromise the functioning of existing septic systems. We used long-term shallow groundwater monitoring wells and ground-penetrating radar surveys of 10 drainfields in the southern Rhode Island coastal zone to determine whether septic system drainfields have adequate separation distance from the water table. Our results indicate that only 20% of tested systems are not impaired by elevated groundwater tables, while 40% of systems experience compromised separation distance at least 50% of the time. Surprisingly, 30% of systems in this study do not meet separation distance requirements at any time of the year. Neither age of system nor a system’s geographical relationship to a tidal water body was correlated with compromised separation distance. The observed compromised separation distances may be a result of inaccurate methods, specified by the regulations, to determine the height of the seasonal high water table. Our preliminary results suggest that enacting changes in the regulatory permitting process for coastal zone systems may help protect coastal drinking and surface water resources.

Advanced onsite wastewater treatment systems (OWTS) use biological nitrogen removal (BNR) to mitigate the threat that N-rich wastewater poses to coastal waterbodies and groundwater. These systems lower the N concentration of effluent via sequential microbial nitrification and denitrification. We used high-throughput sequencing to evaluate the structure and composition of nitrifying and denitrifying bacterial communities in advanced N-removal OWTS, targeting the genes encoding ammonia monooxygenase (amoA) and nitrous oxide reductase (nosZ) present in effluent from 44 advanced systems. We used QIIME2 and the phyloseq package in R to examine differences in taxonomy and alpha and beta diversity as a function of advanced OWTS technology, occupancy pattern (seasonal vs. year-round use), and season (June vs. September). Richness and Shannon’s diversity index for amoA were significantly influenced by season, whereas technology influenced nosZ diversity significantly. Season also had a strong influence on differences in beta diversity among amoA communities, and had less influence on nosZ communities, whereas technology had a stronger influence on nosZ communities. Nitrosospira and Nitrosomonas were the main genera of nitrifiers in advanced N-removal OWTS, and the predominant genera of denitrifiers included Zoogloea, Thauera, and Acidovorax. Differences in taxonomy for each gene generally mirrored those observed in diversity patterns, highlighting the possible importance of season and technology in shaping communities of amoA and nosZ, respectively. Knowledge gained from this study may be useful in understanding the connections between microbial communities and OWTS performance and may help manage systems in a way that maximizes N removal.

Septic systems represent a source of greenhouse gases generated by microbial processes as wastewater constituents are degraded. Both aerobic and anerobic wastewater transformation processes can generate nitrous oxide and methane, both of which are potent greenhouse gases (GHGs). To understand how microbial communities in the surface soils above shallow drainfields contribute to methane and nitrous oxide consumption, we measured greenhouse gas surface flux and below-ground concentrations and compared them to the microbial communities present using functional genes pmoA and nosZ. These genes encode portions of particulate methane monooxygenase and nitrous oxide reductase, respectively, serving as a potential sink for the respective greenhouse gases. We assessed the surface soils above three drainfields served by a single household: an experimental layered passive N-reducing drainfield, a control conventional drainfield, and a reserve drainfield not in use but otherwise identical to the control. We found that neither GHG flux, below-ground concentration or soil properties varied among drainfield types, nor did methane oxidizing and nitrous oxide reducing communities vary by drainfield type. We found differences in pmoA and nosZ communities based on depth from the soil surface, and differences in nosZ communities based on whether the sample came from the rhizosphere or surrounding bulk soils. Type I methanotrophs (Gammaproteobacteria) were more abundant in the upper and middle portions of the soil above the drainfield. In general, we found no relationship in community composition for either gene based on GHG flux or below-ground concentration or soil properties (bulk density, organic matter, above-ground biomass). This is the first study to assess these communities in the surface soils above an experimental working drainfield, and more research is needed to understand the dynamics of greenhouse gas production and consumption in these systems.

Coastal communities preparing for climate change and sea-level rise need to consider the impact large storms will have on belowground infrastructure. Although these communities often rely on on-site wastewater treatment systems (OWTSs) to treat wastewater, there is little research describing how these systems might be impaired after a large storm. A geographic information system (GIS)-based model was used to examine the potential impact of storms (1 in 25 to 1 in 500 years events, Category 1-4 hurricanes) on OWTSs along the southern Rhode Island shore. Based on geographic location, coastal geologic setting, and proximity to coastal features, the number of OWTSs threatened by wave inundation and storm surge ranges from similar to 2,000 in a Category 1 hurricane to similar to 3,000-3,800 in major flood events, to more than 4,600 from a Category 4 hurricane. The number of affected OWTSs increases by similar to 200 if 0.3 m of sea-level rise expected over the next 30 years is considered. Damages incurred can cost homeowners from $1,000 to more than $30,000. Compromised systems will also threaten human and environmental health as untreated wastewater enters groundwater and coastal waters. Methods from this study can be applied to improve coastal communities' resilience planning globally. (c) 2020 American Society of Civil Engineers.

Biological nitrogen removal (BNR) in centralized and decentralized wastewater treatment systems is assumed to be driven by the same microbial processes and to have communities with a similar composition and structure. There is, however, little information to support these assumptions, which may impact the effectiveness of decentralized systems. We used high-throughput sequencing to compare the structure and composition of the nitrifying and denitrifying bacterial communities of nine onsite wastewater treatment systems (OWTS) and one wastewater treatment plant (WTP) by targeting the genes coding for ammonia monooxygenase (amoA) and nitrous oxide reductase (nosZ). TheamoAdiversity was similar between the WTP and OWTS, butnosZdiversity was generally higher for the WTP. Beta diversity analyses showed the WTP and OWTS promoted distinctamoAandnosZcommunities, although there is a core group of N-transforming bacteria common across scales of BNR treatment. Our results suggest that advanced N-removal OWTS have microbial communities that are sufficiently distinct from those of WTP with BNR, which may warrant different management approaches.

Advanced onsite wastewater treatment systems (OWTS) designed to remove nitrogen from residential wastewater play an important role in protecting environmental and public health. Nevertheless, the microbial processes involved in treatment produce greenhouse gases (GHGs) that contribute to global climate change, including CO2, CH4, N2O. We measured GHG emissions from 27 advanced N-removal OWTS in the towns of Jamestown and Charlestown, Rhode Island, USA, and assessed differences in flux based on OWTS technology, home occupancy (year-round vs. seasonal), and zone within the system (oxic vs. anoxic/hypoxic). We also investigated the relationship between flux and wastewater properties. Flux values for CO2, CH4, and N2O ranged from -0.44 to 61.8, -0.0029 to 25.3, and -0.02 to 0.23 mu mol GHG m(-2) s(-1), respectively. CO2 and N2O flux varied among technologies, whereas occupancy pattern did not significantly impact any GHG fluxes. CO2 and CH4 - but not N2O flux was significantly higher in the anoxic/hypoxic zone than in the oxic zone. Greenhouse gas fluxes in the oxic zone were not related to any wastewater properties. CO2 and CH4 flux from the anoxic/hypoxic zone peaked at -22-23 degrees C, and was negatively correlated with dissolved oxygen levels, the latter suggesting that CO2 and CH4 flux result primarily from anaerobic respiration. Ammonium concentration and CH4 flux were positively correlated, likely clue to inhibition of CH4 oxidation by NH4+. N2O flux in the anoxic/hypoxic zone was not correlated to any wastewater property. We estimate that advanced N-removal OWTS contribute 262 g CO2 equivalents capita(-1) day(-1), slightly lower than emissions from conventional OWTS. Our results suggest that technology influences CO2 and N2O flux and zone influences CO2 and CH4 flux, while occupancy pattern does not appear to impact GHG flux. Manipulating wastewater properties, such as temperature and dissolved oxygen, may help mitigate GHG emissions from these systems. (C) 2020 Elsevier B.V. All lights reserved.