Recipient Organization
UNIV OF MINNESOTA
(N/A)
ST PAUL,MN 55108
Performing Department
Water Resources Center
Non Technical Summary
Onsite wastewater treatment systems (OWTS) serve approximately 25% of households in the United States, corresponding to over 25 million households (Amador and Loomis, 2018), and are the technology of choice in rural and suburban areas where population density and cost preclude the use of centralized sewer collection and treatment systems. In unsewered watersheds they are the sole means of wastewater treatment, even for non-residential wastewater applications. Onsite wastewater treatment systems are an integral part of the water infrastructure throughout the country and are expected to protect ground and surface waters from inputs of carbon, nutrients, pathogens, and pharmaceutical and personal care compounds. These systems are expected to function under a wide range of environmental conditions with little intervention. Properly-functioning OWTS help protect public health without which ground and surface waters used as drinking water supplies would become contaminated with pathogens, nutrients and other compounds, making them unsuitable for human consumption (Ahmed et al., 2005; O'Reilly et al., 2007; Borchardt et al., 2011; Wallender et al., 2014).To design OWTS that function effectively under a wide variety of conditions, and meet our performance expectations, we must have a thorough understanding of the processes on which these systems rely to treat wastewater. This is particularly challenging for OWTS, which rely on complex interactions of hydraulic, hydrologic, physical, chemical and biological processes to treat wastewater. Despite their ubiquity and importance as part of the nation's water infrastructure, our understanding of these processes at work in OWTS lags behind that for centralized sewage treatment systems.The systematic study of OWTS has evolved considerably over the past half century, leading to improvements in understanding of how contaminant removal takes place within components in the treatment train and the receiving soil. This has led to more effective contaminant removal from changes in system design, improved understanding of the biogeochemical processes that remove contaminants, biomimicry of natural ecological systems, improved selection of soils receiving wastewater, and better placement of systems both within the soil profile and within watersheds to maximize treatment and minimize impact. These improvements have come about, in large measure, from the efforts of scientists, engineers and outreach professionals in Land Grant and private universities across the U.S., funded by federal, state and local agencies, and through collaborations with regulators and private industry. However, few options still exist for regions with challenging soil conditions (e.g. shallow soils on steeply sloping landscapes, soils with shallow depth to a limiting layer or soils with unpredictable water movement, such as regions with high clay content or karst topography), where conventional OWTS designs are difficult to accommodate. More work is needed to identify low-cost solutions for effective decentralized wastewater treatment in rural communities with challenging soil conditions, to improve residents' quality of life and protect human and environmental health in these regions.In addition, several new challenges have developed in different parts of the country, such as more stringent nutrient and pathogen reduction regulations, removal of chemicals of emerging concern (CECs; such as pharmaceuticals, personal care products, nanoparticles, flame retardants, etc.) present in wastewater, and high strength commercial wastewater. In addition, a changing climate presents a continental-scale challenge to OWTS. Soil-based wastewater treatment systems are regulated, designed, and built based on assumptions about the volume of wastewater applied, the magnitude and distribution of past precipitation events, the historical range of variations in depth to water table, and soil temperature over the long-term (decades). These assumptions are no longer valid in many parts of the country because of climate change related variability in precipitation, temperature, and weather patterns.As climate change continues to alter the temporal and spatial patterns of precipitation and temperature, we must expect attendant consequences as sea levels rise and changes in groundwater levels develop. These changes will affect treatment dynamics in OWTS, through changes in soil moisture dynamics, surface and groundwater hydrology, water use patterns and associated changes in wastewater composition and volume within soil-based treatment technologies (Mihaly, 2017). Changes in precipitation (e.g. more frequent and intense events) and long-term gradual sea level and/or groundwater table rise represent poorly understood threats to OWTS. Short-term catastrophic flooding brought on by intense storm or precipitation events may present challenges to proper OWTS function and longevity. The short-term excess water infiltrating from above during floods, and the long-term upward creeping of the water table (from sea level rise or changes in groundwater table elevation) from below the drainfield reduces the unsaturated soil required for adequate wastewater renovation. The treatment performance of different types of OWTS in response to these different types of flood events has been poorly characterized, despite the substantial risks improperly treated wastewater presents to human and environmental health.In contrast to wet conditions in some regions, climate change may produce even drier conditions in arid regions. This is likely to produce a more concentrated wastewater as more stringent water conservation measures are used to save scarce potable water, placing a greater burden on soil treatment areas to effectively renovate wastewater. New innovative OWTS designs will need to be developed in these regions to reach treatment standards that enable wastewater reuse and recycling to save precious potable supplies and still be protective of public and environmental health.Regulatory decision-makers that set codes and policies and other stakeholders need to understand the consequences of these changes and the options available to mitigate, adapt, and plan for climate change and its effects on OWTS. As in the past, they rely on scientists, engineers and outreach professionals to carry out the research and provide them the necessary information in an effective and timely manner.
Animal Health Component
60%
Research Effort Categories
Basic
10%
Applied
60%
Developmental
30%
Goals / Objectives
Improve our understanding of the interactions among wastewater, soils, biogeochemical cycles and processes and treatment performance (contaminant removal) of existing and novel wastewater treatment technologies in different geographic regions and landscapes over time and considering climate change.
Examine watershed-level impacts of septic systems on water quality and other environmental parameters in suburban, rural and coastal areas.
Develop educational materials and tools to acquaint the public and practitioners about management, operation, maintenance and health issues related to OWTS in light of system performance, and the need for adaptation to climate change.
Project Methods
The two main functions of the STA are (i) to allow for infiltration of wastewater in the subsurface, and (ii) to remove contaminants from wastewater. The main objective of the proposed work is to further our understanding about how soil characteristics, system design, microbial community dynamics, and climate change affect the hydrologic and biogeochemical processes that govern the functioning of the STA. This will be based on data gathered from experimental, observational and modeling efforts at a variety of spatial (microcosm to watershed) and temporal (hours to decades) scales from different geographic regions and landscapes in the US.We recognize that hydrologic and biogeochemical processes do not take place in isolation from each other, but often interact in ways that can enhance or interfere with the functioning of OWTS. For example, removal of dissolved and particulate organic C by microorganisms in the STA can reduce the development of a biomat - a low-permeability layer of organic polymers, microorganisms and inert particles that forms at the STA-native soil interface that restricts the infiltration of wastewater and can result in hydraulic failure. In coarse-textured soils or soils with well-developed structure, the development of a biomat may be beneficial in removal of pathogenic organisms due to increasing hydraulic retention time needed for effective removal processes to occur. On the other hand, the effectiveness of bacteria and virus removal in the STA is affected by soil type and is sensitive to water saturation in the soil, with less removal observed as the soil moisture content increases. The combination of biomat formation, soil permeability, and soil moisture content (wastewater loading rate, rainfall infiltration, and water table dependent) all must produce the "Goldilocks" point where both soil water movement and effective wastewater treatment are optimized. Thus, the proposed work will address these interactions within the context of both regional differences in soil type and climate.We are also aware of the practical limitations presented by short-term experimental and observational studies in terms of predicting climate impacts on STA functions, particularly with respect to long-term effects of climate variables. To this end, we will include a modeling component that incorporates climate variability and change in their influences on hydrologic and biogeochemical processes in the STA.Effective wastewater treatment in regions with suboptimal soil types require not only that we understand how existing systems work and interact with soil type and climate, but also how these may be modified or replaced to improve their effectiveness, to provide innovative and cost-effective solutions in regions with challenging soils, as well as adaptation to new climate regimes. To this end, the proposed research will be conducted on both natural and engineered soils and treatment media, and on conventional and innovative STAs.Specific methods by objective:Objective 1. Improve our understanding of the interactions among wastewater, soils, biogeochemical cycles and processes and treatment performance (contaminant removal) of existing and novel wastewater treatment technologies in different geographic regions and landscapesover time and considering climate variability.We will examine relationships among soil properties, system design, climate variables and movement of water in the STA and underlying vadose zone, with attention to the following scenarios:Impact of (i) increased water inputs to surface soils and (ii) reduced wastewater inputs to the STA on (i) vadose zone hydraulic processes and (ii) surface and subsurface transport of contaminants.Impact of rising water tables on water movement at the individual system and watershed scales.Interactions among changes in water inputs, depth to water table and rising temperature in the context of water movement and contaminant transport.Changes in system performance over time as systems become established after installation and begin to age and eventually approach the end of their design lives.Objective 2. Examine watershed-level impacts of septic systems on water quality and other environmental parameters in suburban, rural, and coastal areas.Both simulation models and monitoring methods will be used to accomplish our objectives. Results of modeling efforts will be used to inform decisions on system siting and design.Using simulation models, we will optimize the OWTS design by adjusting the design parameters and looking at the model output in terms of discharge capacity, chemical discharge, and pathogen fate. Once we have identified one or two optimal design criteria through simulation, we will test those designs in field-based pilot studies and collect data to show the workability of the new design criteria.Objective 3. Develop educational materials and tools to acquaint the public and practitioners about management, operation, maintenance and health issues related to OWTS in light of system performance, and the need for adaptation to climate change.Utilizing research knowledge gained from project Objectives 1 and 2, we will synthesize data, develop, and deliver stakeholder-appropriate education and outreach materials related to soil type and/or climate change and: (i) interactions of soils, water, and wastewater relative to soil and site suitability for OWTS; (ii) wastewater biogeochemistry in advanced treatment OWTS, in soil treatment areas and underlying soils; and, (iii) modeling of wastewater movement and contaminant migration in soils underlying OWTS soil treatment areas.To help OWTS practitioners, we will continue the outreach work started under NE 1045 and NE 1545 by:Utilizing a technology matrix table that helps public and private decision makers to determine what OWTS technologies are best suited for nutrient and pathogen sensitive watersheds and addresses various on-lot site constraints such as shallow groundwater tables, shallow bedrock, slowly and rapidly permeable soils and size restricted lots.Working with industry and regulatory stakeholders to develop and improve materials for design, operation, maintenance, installation, economics, planning, management, and analyzing and diagnosing malfunctions of conventional and advanced OWTS as it relates to adaptation to and mitigation site constraints and of climate change.Enhancing existing and developing new training modules for regulatory agencies to inform them of the latest research findings to help influence their policy, regulations, and decision-making capabilities.Using the education materials described above, we propose to train OWTS practitioners, decision makers and the public. Delivery of materials will be at outreach workshops conducted within the existing network of Land Grant and private institution OWTS training centers and programs across the United States. In addition, training materials will also be delivered at state, regional and national professional conferences and trade shows. Delivery methods may include lectures, online content, distance learning venues and hands-on field exercises, fact sheets, demonstration systems and props, Power Point slides, videos and DVDs.