Purdue News

October 20, 2000 Experimental system could solve Indiana's septic tank problem WEST LAFAYETTE, Ind. – Purdue University agricultural engineers are evaluating an alternative wastewater treatment process they believe may make septic tanks in Indiana more efficient and environmentally friendly. The process removes nitrogen and harmful organic matter as the wastewater travels through a special filtering system and into an irrigation area. Existing septic tank systems could be retrofitted with the recirculating sand filter and drip irrigation field, engineers say. The system also appears to work well in many soils considered unsuitable for traditional septic systems. "A conventional septic system gets rid of only 10 percent to 20 percent of the nitrogen. This system is in the 80 percent to 85 percent area," says Don Jones, a Purdue Cooperative Extension Service agricultural engineer. This past spring, a sand filter-drip irrigation system was constructed at Throckmorton-Purdue Agricultural Center, a Purdue ag research farm in Tippecanoe County. The system is equipped to treat 2,100 gallons of wastewater per day, equal to about five three-bedroom homes. Engineers will monitor the system for up to four years and post information on the Purdue Department of Agricultural and Biological Engineering Internet site. The Throckmorton-Purdue research could offer a safe, affordable solution to rural homeowners dealing with aging septic systems. According to officials at the Indiana State Board of Health, more than 200,000 of Indiana's 800,000 septic tanks are inadequate, and may be creating a serious health risk. Many septic tanks are overflowing or backing up, spreading bacteria into lawns and homes, polluting the groundwater and breeding insects. A sand filter-drip irrigation process takes the septic concept a few steps further. With a conventional septic system, effluent flows into a septic tank, where solids settle on the bottom while liquids continue to a distribution box to be released in a drain field. A sand filter-drip irrigation system begins with a septic tank, then effluent flows through a sand filter – a below-ground bed of grain-sized gravel. The wastewater collects in drainpipes below the filter and is recirculated through the system. After a second trip through the filter, the wastewater is discharged through a series of half-inch-diameter tubes, or drip irrigation. The irrigation tubes are located about 6 inches under ground, allowing the filtered wastewater to readily reach the root systems of vegetation. Few sand filter-drip irrigation septic systems exist in Indiana, Jones says. The systems are more common along the west coast, where soils are less compatible with conventional septic systems. Because of its unique construction and wastewater treatment process, the sand filter-drip irrigation system may work well for Indiana, he says. "Only 20 percent of the soils in Indiana are suitable for a traditional 24-inch-deep trench septic," Jones says. "Some counties are actually rated 100 percent unsuitable by the Natural Resources Conservation Service." Cost to install a sand filter-drip irrigation system runs between $8,000 and $12,000, Jones says. Installing a traditional septic system is about $3,000, with municipal sewer hook-up anywhere from $16,000 to $24,000. The large Throckmorton-Purdue sand filter-drip irrigation system cost $30,000. Yearly maintenance on a residential sand filter-drip irrigation system is about $100 to $150. "What's good about this system is it's quick to put in, there's minimal soil disturbance and it's easy to repair," says Steve Hawkins, assistant director of Purdue Agricultural Centers. "And the on-site wastewater treatment is, in some ways, like what you have at a city treatment plant." The Throckmorton-Purdue project is a joint effort of Purdue and the state Board of Health. The sand filter-drip irrigation system was designed by Earthtek Environmental Systems Inc. of Batesville, Ind., and constructed by Hack Excavating of Lafayette. Other Indiana companies supplying parts or services included Goff Electric of Crawfordsville, Hartford City Concrete and IPM Associates of Fishers. Sources: Don Jones, (765) 494-1178; jonesd@ecn.purdue.edu Steve Hawkins, (765) 494-8367; seh@aes.purdue.edu Writer: Steve Leer, (765) 494-8415; sleer@aes.purdue.edu Purdue News Service: (765) 494-2096; purduenews@purdue.edu Related Web sites: Purdue Residential Onsite Wastewater Disposal Purdue Department of Agricultural and Biological Engineering To the Purdue News and Photos Page