Septic Treatment

With increasing frequency, people are asking how to use NSF-listed home plants for office, restaurant, or other non-residential applications. Based on the last several years of experience, I now have come to the opinion that at no time should any NSF-listed home plant be used on anything other than residential strength wastewater.

There are two basic reasons for this opinion. The first reason is that non-residential applications usually generate wastewater of higher strength and higher solids content than residential wastewater. The treatment capacity of these home plants is not tested nor intended to handle higher strength wastewater. Further, the pretreatment and treatment capacity of these home plants is not intended to handle the higher solids content of high strength wastewater.

The second reason is that many non-residential applications have other wastewater strength parameters that are also outside the treatment capacities of these home plants. Restaurants, for example, have high levels of fats, oils and grease (FOG), high levels of undigested foods, high levels of toxic products, as well as often having high temperature wastewater. I do not currently believe that any home plant is designed or intended to treat this type of wastewater.

It is my opinion that the only way a home plant can be used correctly on a non-residential strength wastewater application is if the wastewater is first pretreated by a product or process specifically designed for the high strength constituent(s). If the wastewater is pretreated to reduce the strength to a residential strength, then and only then can a home plant be used correctly.

The following is a listing of quotes that appear to support this opinion for only using home plants for residential applications.

NSF Standard 40:
Title: "Residential Wastewater Treatment Systems"
"1.1 Purpose The purpose of this Standard is to establish minimum materials, design and construction, and performance requirements for residential wastewater treatment
"1.2 Scope This standard contains minimum requirements for residential wastewater treatment systems having simple, defined discharge points and rated treatment capacities between 1514 L/day (400 gal/day) and 5678 L/day (1500 gal/day)."
"3.6 residential wastewater (wastewater): Human body waste and liquid waste generated by the occupants of an individual residence."
"3.7 residential wastewater treatment system: An organized and coordinated system of components that functions to treat wastewater generated by individual residences."

TCEQ rules, 30TAC285:
Since the promulgation of these rules in 1997, 30TAC285.91, Table III has stated, "Commercial/institutional facilities must pretreat their wastewater to 140 BOD5."

Texas' First High Strength Workshop:
"Home plant ATUs are not designed for high strength, and should not be used for high strength wastewater."
"Wastewater is considered high strength if it possesses anything outside the parameters of residential strength wastewater", which are considered to be:
BOD < 300 (many say 200) mg/l
TSS < 300 (many say 200) mg/l
FOG < no visible film
pH about 7.4

My recommended solution, therefore, is as follows:
1. Immediately stop using inappropriate treatment products. NSF-listed units are only certified for residential strength wastewater. Instead use a high-strength treatment product or process to pretreat the wastewater,
bringing the wastewater strength down to residential strength. Then, and only
then, can you use 30TAC285 for the design of the balance of the OSSF.
2. For all non-residential strength applications, use the design approach presented by Texas' first high strength wastewater workshop as follows:
1st: quantify Q by determining maximum flow, minimum flow, and average flow - hourly, daily, weekly, monthly, even annually (schools).
2nd: quantify influent wastewater strength parameters for BOD, CBOD, TSS, pH, FOG, & temperature.
3rd: determine effluent wastewater strength parameter limits.
4th: select a treatment and disposal process appropriate for the above conditions and for the site-specific conditions.
3. The Designer must state in writing the assumed influent Q, BOD/CBOD, TSS, pH, FOG, temperature, and any other criteria, such as nutrients if applicable, and must state, in writing, the effluent values that the design is intended to achieve.
4. The Regulatory Agency must condition the permit on achieving the effluent values required by the rules or permit. For restaurants, the renewal of the food license should be conditioned on continual compliance with the OSSF permit.
5. Since the wastewater from this type of project is higher risk than residential strength wastewater, additional management activities should be required in the permit to ensure proper treatment and disposal, thereby protecting the public from this increased health risk.

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