Six Best Practices for High Strength Waste Designs
Posted on by Dennis Hallahan, P.E.
The fun in designing decentralized onsite wastewater treatment systems is that they’re all unique. For example, an onsite wastewater treatment system for one restaurant may vary significantly from the next. This is due to the fact that facilities like restaurants can vary due to location in terms of traffic exposure, popularity, the habits inside of the facility and other factors. These can present challenges for treating high strength waste (HSW). HSW is not limited to restaurants; just about any commercial facility can generate some form of HSW. This presents unique challenges to system designers and engineers. Fortunately, Infiltrator has experience in wastewater treatment system designs for HSW facilities and can provide assistance.
What is High Strength Waste?
The exact definition of high strength waste (HSW) varies depending on local code. Some localities define HSW based on the Biochemical Oxygen (BOD) or Total Suspended Solids (TSS) levels. But in general, the industry has loosely defined HSW as anything greater than residential waste strength.
Best Practices for High Strength Waste Designs:
Code Conformance: Local or state code will set minimum parameters for design based on desired treatment levels for the facility. It’s recommended that each design element be slightly above the minimum code requirements to ensure sufficient treatment.
Research: It’s very important to understand the day-to-day operations of the facility which will help identify the wastewater characteristics. If this is an existing facility this can be as simple as reviewing historical records. For new facilities you’ll want to conduct research on similar businesses. Part of your research should also include collecting and testing wastewater samples.
System Sizing: As mentioned earlier it is recommended to size up your system beyond the minimum code requirements to ensure optimal treatment. For example, you may consider to double the tank sizes to increase retention time. Also, soil loading rates in codes are often based on residential strength waste, it’s recommended to spread effluent over a larger footprint to provide better long-term performance.
Flow Equalization: The incorporation of flow equalization into a system is crucial if you are working with a facility where use spikes during certain times of the day or week. Flow equalization allows dosing of the system to be spread out over an extended amount of time instead of overloading the system at once.
Pretreatment: Incorporating an ATU or remediator into the system can reduce the strength of the effluent before it reaches the drainfield for treatment.
Ongoing Maintenance: The system should be designed to ensure the ease of access for ongoing maintenance. For example, septic tanks should be equipped with risers installed to grade allowing easy access to open the lids.
This is a condensed list that was pulled from this white paper on HSW design recommendations. There is no one solution that will fit all cases requiring HSW. This information is meant to serve as a guide to get you started in the process to identify the appropriate solution.
Feel free to contact us if you would like us to help with your next HSW design.
About the Author:
Dennis Hallahan, P.E.
Dennis F. Hallahan, P.E., is the Technical Director of Infiltrator Water Technologies. Dennis has over twenty-eight years of experience with the design and construction of on-site wastewater treatment systems. He has authored several articles for on-site industry magazines and has given numerous presentations nationally on the science and fundamentals of on-site wastewater treatment systems. Dennis also oversees a department that is responsible for product research and testing for both Universities and private consultants. The department develops system sizing charts for national and international approvals and assists customers and field representatives in the planning and review of large decentralized systems. He received his MS in civil engineering from the University of Connecticut and his BS in civil engineering from the University of Vermont. Dennis is a registered professional engineer in Connecticut. He has been with Infiltrator for over 16 years and in his current position as Technical Director, he is responsible for the technology transfer between Infiltrator and the regulatory and design communities. Dennis also holds several patents for on-site wastewater products. Member ASCE, WEF, serves on the NOWRA Technical Practice and Educational Committees, also on the New England Water Environment Federation’s Small Community Committee.