Quantitative Tools to Determine the Expected Performance of Unit Process in Wastewater Treatment Units

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. 

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. 

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 8^oC, Annual Mean 4.5^oC 
  • Mesic = Average Range 8 to 15^oC, Annual Mean 11.5^oC 
  • Thermic = Average Range 15 to 22^oC, Annual Mean 18.5^oC 
  • Hyperthermic = Average Range 22 to 29^oC, Annual Mean 25.5^oC