WERF Research Report
3 total works
Modeling Onsite Wastewater Systems at the Watershed Scale
by John McCray, Mengistu Geza, Eileen P Poeter, Kyle E. Murray, and David S Morgan
Published 13 September 2009
The purpose of this User's Guide is to provide guidance on modeling watershed-scale problems associated with decentralized wastewater-treatment systems (DWTS), with a particular focus on onsite wastewater systems (OWS). The guide focuses on modeling transport and fate of the nutrients nitrogen (N) and phosphorus (P) because these are the most common OWS constituents of concern, and because these pollutants are regulated in surface waters (N and P) and in ground water (N). However, limited but useful information is also provided regarding the modeling of organic wastewater contaminants, such as pharmaceuticals, pesticides, and other household products. It provides some general information on modeling bacterial pollutants.
The guide can be used by decision makers to determine whether relatively simple screening models (presented in Appendix A) are sufficient for use in the decision-making process, or if sophisticated models (presented in Appendix B) are more appropriate. The document provides guidance about the type of model that should be used for particular scenarios, and the data requirements for model implementation. The guide is also useful to modeling experts by providing guidance on important issues such as conceptual-model development, mathematical-model selection, modelsensitivity analyses, model uniqueness, and calibration. Finally, the guide provides some real-world and hypothetical case studies that can demonstrate the usefulness of using watershed-scale models, and provide templates for certain common scenarios relevant to the decentralized wastewater treatment community.
The guide can be used by decision makers to determine whether relatively simple screening models (presented in Appendix A) are sufficient for use in the decision-making process, or if sophisticated models (presented in Appendix B) are more appropriate. The document provides guidance about the type of model that should be used for particular scenarios, and the data requirements for model implementation. The guide is also useful to modeling experts by providing guidance on important issues such as conceptual-model development, mathematical-model selection, modelsensitivity analyses, model uniqueness, and calibration. Finally, the guide provides some real-world and hypothetical case studies that can demonstrate the usefulness of using watershed-scale models, and provide templates for certain common scenarios relevant to the decentralized wastewater treatment community.
Available online as an eBook only.
DEC1R06a: Development of Quantitative Tools to Determine the Expected Performance of Unit Process in Wastewater Treatment Units
Onsite wastewater treatment system (OWTS) systems are an important part of the wastewater treatment and water management infrastructure in the U.S. Thus, proper OWTS selection, design, installation, operation and management are essential. While OWTS vary widely in their design and implementation, most systems are conventional OWTS that on the soil treatment unit (STU) for wastewater constituent treatment, hydraulic capacity, and eventual recharge to water resources. While there is considerable concern about potential water quality degradation associated with OWTS, current permitting and design focus mainly on ensuring that the hydraulic loading is not excessive. The STU provides an effective and sustainable means for wastewater reclamation, but occasional water quality degradation has been experienced. The likely cause for this is an incomplete understanding of treatment processes in various STUs, and the lack of available tools for assessing the performance of the STU.
The overall goal of the project was to provide a toolkit to assess STU performance to enable evaluation and design of expected STU performance for important wastewater constituents over a relevant range of OWTS operating conditions. The toolkit is appropriate for a wide range of users, and includes an implementation protocol for different tools of varying complexity. Specific project objectives were to: identify the best practices, available data, data gaps, and promising tools and techniques utilized in STU design and performance, develop and test tools for performance-based STU design, develop a protocol for using the tools, refine the tools and protocol using data from laboratory studies, field sites, and numerical modeling, and provide a final tool-kit and protocol to aid system designers and decision makers assess the expected STU performance.
DEC1R06b: Quantitative Tools to Determine the Expected Performance of Unit Process in Wastewater Treatment Units: Toolkit Users Guide
Onsite wastewater treatment systems (OWTS) are an important part of water management infrastructure in the United States. Thus, proper OWTS selection, design, installation, operation and management are essential. To aid this life-cycle, a toolkit was developed to enable evaluation and design of expected STU performance. The toolkit is comprised of this Guidance Manual, a companion Toolkit User's Guide, individual tools, and supplemental information. This framework provides detailed information to less experienced user's while enabling more experienced users to start directly with STUMOD or other tool implementation referring to limited sections of the Guidance Manual or User's Guide. The toolkit was developed for a wide range of users faced with different needs of varying complexity when evaluating treatment of nitrogen, microbial pollutants (bacteria and virus), and organic wastewater contaminants (OWCs). Progressing through simple to more complex tools ultimately guides the user to the simplest tool that is appropriate, but discourages using a tool that is too simple for the decision at hand. The simplest tools include look-up tables and cumulative frequency distributions to direct the user to available pertinent information. Nomographs enable initial screening and quick insight into expected nitrogen removal based on the predicted output from STUMOD. Cumulative probability graphs illustrate modeling results in a risk-based framework while numerical model simulations demonstrate the usefulness of complex tools. Finally, two spreadsheet tools were developed for nitrogen transport, N-CALC and STUMOD, allowing the user to evaluate a range of STU operating conditions, soil hydraulics, and/or treatment parameters, as well as the relative influence of these factors on performance.
DEC1R06c: Quantitative Tools to Determine the Expected Performance of Unit Process in Wastewater Treatment Units: Visual-Graphics Tools
This file includes the visual-graphic tools: nomographs, cumulative probability graphs, and scenario illustrations. Chapter 1.0 includes nomographs illustrating the fraction of total-nitrogen remaining with depth. Chapter 2.0 includes cumulative probability graphs that illustrate the likely range of treatment outcomes. Chapter 3.0 includes HYDRUS simulation outputs that illustrate various operational scenarios. Finally, a list of visual-graphic tools is provided to aid in locating the visual-graphic tool of interest. This is a separate document that must be used in conjunction with the Guidance Manual and User's Guide.
The companion Guidance Manual is organized into four chapters describing the toolkit and providing guidance for tool selection and use. The fundamental assumptions that were incorporated and a detailed description of the tool development for these visual-graphic tools are provided in the companion User's Guide. Additional tools provided as separate files include STUMOD and N-CALC as MicrosoftTM Xcel files. In both the nomograph and the cumulative probability graphs, treatment information provided by these tools is based on data generated by numerical models that can incorporate complex and robust treatment and operating conditions. The parameters used for nomograph development are summarized in Table VG-1. Table VG-2 provides a definition for each parameter. Because the choices for representative OWTS conditions are limited, the user must decide how their OWTS system fits within the limited treatment estimations displayed by the graphics.
Nomographs and cumulative probability graphs were developed for the following fixed operating conditions:
DEC1R06a: Development of Quantitative Tools to Determine the Expected Performance of Unit Process in Wastewater Treatment Units
Onsite wastewater treatment system (OWTS) systems are an important part of the wastewater treatment and water management infrastructure in the U.S. Thus, proper OWTS selection, design, installation, operation and management are essential. While OWTS vary widely in their design and implementation, most systems are conventional OWTS that on the soil treatment unit (STU) for wastewater constituent treatment, hydraulic capacity, and eventual recharge to water resources. While there is considerable concern about potential water quality degradation associated with OWTS, current permitting and design focus mainly on ensuring that the hydraulic loading is not excessive. The STU provides an effective and sustainable means for wastewater reclamation, but occasional water quality degradation has been experienced. The likely cause for this is an incomplete understanding of treatment processes in various STUs, and the lack of available tools for assessing the performance of the STU.
The overall goal of the project was to provide a toolkit to assess STU performance to enable evaluation and design of expected STU performance for important wastewater constituents over a relevant range of OWTS operating conditions. The toolkit is appropriate for a wide range of users, and includes an implementation protocol for different tools of varying complexity. Specific project objectives were to: identify the best practices, available data, data gaps, and promising tools and techniques utilized in STU design and performance, develop and test tools for performance-based STU design, develop a protocol for using the tools, refine the tools and protocol using data from laboratory studies, field sites, and numerical modeling, and provide a final tool-kit and protocol to aid system designers and decision makers assess the expected STU performance.
DEC1R06b: Quantitative Tools to Determine the Expected Performance of Unit Process in Wastewater Treatment Units: Toolkit Users Guide
Onsite wastewater treatment systems (OWTS) are an important part of water management infrastructure in the United States. Thus, proper OWTS selection, design, installation, operation and management are essential. To aid this life-cycle, a toolkit was developed to enable evaluation and design of expected STU performance. The toolkit is comprised of this Guidance Manual, a companion Toolkit User's Guide, individual tools, and supplemental information. This framework provides detailed information to less experienced user's while enabling more experienced users to start directly with STUMOD or other tool implementation referring to limited sections of the Guidance Manual or User's Guide. The toolkit was developed for a wide range of users faced with different needs of varying complexity when evaluating treatment of nitrogen, microbial pollutants (bacteria and virus), and organic wastewater contaminants (OWCs). Progressing through simple to more complex tools ultimately guides the user to the simplest tool that is appropriate, but discourages using a tool that is too simple for the decision at hand. The simplest tools include look-up tables and cumulative frequency distributions to direct the user to available pertinent information. Nomographs enable initial screening and quick insight into expected nitrogen removal based on the predicted output from STUMOD. Cumulative probability graphs illustrate modeling results in a risk-based framework while numerical model simulations demonstrate the usefulness of complex tools. Finally, two spreadsheet tools were developed for nitrogen transport, N-CALC and STUMOD, allowing the user to evaluate a range of STU operating conditions, soil hydraulics, and/or treatment parameters, as well as the relative influence of these factors on performance.
DEC1R06c: Quantitative Tools to Determine the Expected Performance of Unit Process in Wastewater Treatment Units: Visual-Graphics Tools
This file includes the visual-graphic tools: nomographs, cumulative probability graphs, and scenario illustrations. Chapter 1.0 includes nomographs illustrating the fraction of total-nitrogen remaining with depth. Chapter 2.0 includes cumulative probability graphs that illustrate the likely range of treatment outcomes. Chapter 3.0 includes HYDRUS simulation outputs that illustrate various operational scenarios. Finally, a list of visual-graphic tools is provided to aid in locating the visual-graphic tool of interest. This is a separate document that must be used in conjunction with the Guidance Manual and User's Guide.
The companion Guidance Manual is organized into four chapters describing the toolkit and providing guidance for tool selection and use. The fundamental assumptions that were incorporated and a detailed description of the tool development for these visual-graphic tools are provided in the companion User's Guide. Additional tools provided as separate files include STUMOD and N-CALC as MicrosoftTM Xcel files. In both the nomograph and the cumulative probability graphs, treatment information provided by these tools is based on data generated by numerical models that can incorporate complex and robust treatment and operating conditions. The parameters used for nomograph development are summarized in Table VG-1. Table VG-2 provides a definition for each parameter. Because the choices for representative OWTS conditions are limited, the user must decide how their OWTS system fits within the limited treatment estimations displayed by the graphics.
Nomographs and cumulative probability graphs were developed for the following fixed operating conditions:
- Effluent Quality
- Standard Effluent = representative of septic tank effluent (STE) as 60 mg-N L-1 as ammonium-nitrogen plus 1 mg-N L-1 as nitrate-nitrogen
- Nitrified Effluent = representative of aerobically treated STE to achieve nitrogen reduction and transformation as 15 mg-N L-1 as nitrate-nitrogen
- Hydraulic Loading Rate (HLR)
- 2 cm d-1
- 5% Ksat
- Regional Temperature Range
- Frigid/Cryic = Average Range 0 to 8oC, Annual Mean 4.5oC
- Mesic = Average Range 8 to 15oC, Annual Mean 11.5oC
- Thermic = Average Range 15 to 22oC, Annual Mean 18.5oC
- Hyperthermic = Average Range 22 to 29oC, Annual Mean 25.5oC
The literature review described in this report is part of a larger research project to assess STU performance with respect to treatment of important wastewater constituents. The overall goal of the project is to provide a toolkit and tool-use protocol that is easy to implement and available to a wide range of users to assess STU performance. This literature review is not a preview of tools that we will develop and propose, but rather an analysis of the information and data and the literature, to help guide our tool development. All tools developed will be based on rigorous experimental data and quantitative models verified with field data from operating systems. In some cases, more sophisticated tools (e.g., complex mathematical models) may be warranted depending on the relative complexity of the problem and the relative risk associated with a poor design.
This literature review focused on STU performance, key conditions or factors potentially affecting STU performance, and the current best practices for using models and other available tools to predict expected STU performance. The information gained during this literature review will guide the future direction of the project. Constituents of interest include nitrogen (N), phosphorus (P), microbial pollutants, and emerging organic wastewater contaminants (OWCs). Based on this literature review, it is clear that due to the variability of data collected at field sites, simple binary relationships (e.g., C/Co versus depth for various soil types) for statistical predictions of the attenuation of N, P, microorganisms or OWCs cannot be justified. Specific to N, hydraulic loading rate appears to be more important than soil texture or soil depth within the first 30-60 cm, although both soil depth and texture remain important variables.
Most of the reported results related to the interaction of P with soil appear to be from laboratory batch tests. Similarly, field-scale evaluations of pathogen removal are limited. Finally, most of the existing OWC work has focused on the occurrence and concentrations of selected compounds in streams, lakes, and groundwater impacted by wastewater treatment plant effluents. Currently very few models have been developed for movement and treatment processes of N or P in OWTS. However, adapting the CW2D model for STUs that will predict the effect of different soil types (texture, structure, and drainage class) appears promising. CW2D is a module of the well known HYDRUS model designed to simulate nitrogen treatment in a sand filter. This model incorporates most of the features one might consider, including a comprehensive treatment of microbial growth, the impact of oxygen mass transfer on nitrogen transformation, and variable rates of denitrification due to changes in dissolved oxygen concentrations, dissolved organic matter, and microbial growth. The review of existing models demonstrates that simulation of microbial characteristics in OWTS is still largely uncharted territory.
This literature review focused on STU performance, key conditions or factors potentially affecting STU performance, and the current best practices for using models and other available tools to predict expected STU performance. The information gained during this literature review will guide the future direction of the project. Constituents of interest include nitrogen (N), phosphorus (P), microbial pollutants, and emerging organic wastewater contaminants (OWCs). Based on this literature review, it is clear that due to the variability of data collected at field sites, simple binary relationships (e.g., C/Co versus depth for various soil types) for statistical predictions of the attenuation of N, P, microorganisms or OWCs cannot be justified. Specific to N, hydraulic loading rate appears to be more important than soil texture or soil depth within the first 30-60 cm, although both soil depth and texture remain important variables.
Most of the reported results related to the interaction of P with soil appear to be from laboratory batch tests. Similarly, field-scale evaluations of pathogen removal are limited. Finally, most of the existing OWC work has focused on the occurrence and concentrations of selected compounds in streams, lakes, and groundwater impacted by wastewater treatment plant effluents. Currently very few models have been developed for movement and treatment processes of N or P in OWTS. However, adapting the CW2D model for STUs that will predict the effect of different soil types (texture, structure, and drainage class) appears promising. CW2D is a module of the well known HYDRUS model designed to simulate nitrogen treatment in a sand filter. This model incorporates most of the features one might consider, including a comprehensive treatment of microbial growth, the impact of oxygen mass transfer on nitrogen transformation, and variable rates of denitrification due to changes in dissolved oxygen concentrations, dissolved organic matter, and microbial growth. The review of existing models demonstrates that simulation of microbial characteristics in OWTS is still largely uncharted territory.