Slaughterhouse wastewater is not covered under Minnesota Rules Chapter 7080. Septic system sizing in 7080 is based on research of typical flows and wastewater characteristics from domestic residences. If human waste is being combined with processing water all the requirements of 7080 apply along with any other applicable regulations.
A septic system receiving slaughterhouse waste is considered by EPA to be a Class V injection well system. No rules in Minnesota or from the EPA specifically deal with slaughterhouse facilities although EPA does require that a Class V inventory form be completed and mailed to appropriate agencies. Local ordinances administered by counties, cities and townships may have provisions regarding these facilities and must be consulted.
All waste could go into a holding tank and subsequently land applied or taken to a wastewater treatment plant.
Use an onsite septic system to treat the wastewater.
- A flow meter must be installed to track water use. Flow data should be collected at representative times (trying to target busy days) and over several months. If no facility exists or an expansion is planned, estimates should be made which include a safety factor (1.5 x the highest weekly average). A flow meter should be installed to verify estimates.
- It is critical that no hazardous waste enter an onsite septic system as they are not designed to treat such waste.
- Use of cleaning chemicals should be limited. Onsite septic systems can deal with small amount of cleaning chemicals, but if the amount is above typical domestic usage system performance may be impacted.
- If animals are killed in the facility all blood should be caught separately and either used, rendered or taken to a treatment facility.
- All solid material should be dealt with as a solid waste. Fine grates should be put on all floor and sink drains to catch any small particles and hair.
- A commercial size effluent filter (designed for high strength waste) should be placed on the outlet of the last septic tank. A manhole should be located over this filter as there is will be the need for frequent maintenance and cleaning.
- If existing septic tanks are in place, samples should be taken to determine the quality of the effluent. These samples should be taken from either the outlet baffle of the last septic tank or a pump tank if one exists. This effluent should be sampled for BOD5, TSS and FOG. If these levels come back higher than typical [normal levels] a pretreatment unit(s) should be designed to lower the levels to normal domestic strength levels. Normal levels in 7080 for human sewage leaving a septic tank are:
- BOD < 220 mg/l
- TSS < 65 mg/l
- FOG < 30 mg/l
- If no septic tanks exist or if it is a new facility, the wastewater characteristics must be estimated. Wastewater characteristics are hard to predict and should be sampled once the facility has been in operation for three months and pretreatment designed to deal with known levels.
- A maintenance contract should be in place with a licensed onsite professional to assure the proper operation and maintenance of the treatment system.