Harold Keener
The Ohio State University
Studies to evaluate runoff volume and nutrient concentration from compost windrows were conducted at the OARDC in Wooster composting pad. The 29,750 square foot pad has a slope of 1-2% with windrows parallel to the slope and a wood chip filter at the base and perpendicular to the slope to trap larger particles. Runoff from the pad drains to a series of three wetland treatment cells designed to retain a 25-year rain event. The 2003 study simulated rainfall for 100-, 25- and 5-year storms and measured total suspended solids, total dissolved solids, ammonia-N, nitrate-N, phosphorus, potassium and micronutrients. The study concluded that the greater the rainfall, the larger the volume of runoff and the higher the concentration of nutrients. A follow up study in 2004 assessed the effect of compost age on runoff volume and nutrient concentration. The results indicated that the volume of runoff increased with the age of the compost, probably due to a crusting over of the surface of the windrow resulting in a hydrophobic effect. While the concentration of most nutrients decreased with age of the compost, the total amount of nutrients lost showed no definite trends. Additional research is needed to evaluate biological oxygen demand of the runoff and the effect of biofilters as well as to develop a model for predicting runoff parameters for different compost mixes.
The PowerPoint presentation can be accessed online via the link at www.oardc.ohio-state.edu/ocamm.
Discussion:
Lynn Willett (OSU) asked if the wetland treatment cells are lined and, if not, is seepage through the soil a problem. Keener noted that the cells are not lined but were designed to be impermeable. There may be approximately 5% loss to the subsurface.
Willett asked if any adjustment for the wetland is needed to account for the time of year. Keener noted that the there are two key issues involved. It is assumed that the wetland does not function as well in the winter because there is not as much uptake from plants. Also, management of water levels in the cells is critical as more water may need to be held in the winter whereas in the summer it may be pumped out and used to water windrows or irrigate crops. The goal is to minimize discharge from the cells.
Diane Borger asked if there was replication of the 2003 data in the 2004 study. Keener replied that the fourth windrow that was needed to do so was not available. Both studies indicated the need for good housekeeping on the pads as material between the windrows can have a significant impact. Runoff studies from covered windrows result in relatively high concentrations of nutrients, probably from the uncovered edges.
Willett questioned the dry matter percentage when the windrow is first formed and the percentage of dry matter in a mature compost. Keener replied that the goal is 60-65% moisture when the windrow is formed with a reduction to about 45% moisture for a mature compost.
Borger asked if there was any odor from the runoff. Keener noted that it was not noticeable, although those working with the samples may have noticed some.
Willett asked if the windrows were aerated using forced air or by turning only. Keener responded that turning was the only method of aeration. Data indicated that penetration of water is shallow at the top of the windrow but the base becomes more saturated as the compost matures.
Tom Zimmerman (ATI) asked why the base of the windrow has more moisture if the top is hydrophobic. Keener noted that the data is still being analyzed and that more research is needed. As more research is done, it will become clearer as to how a site should be designed and managed to minimize runoff.
Willett noted that most compost sites are not as clean as the OARDC site and asked how it is maintained. Gerald Reid (OSU) responded that after turning the edges of the windrow are cleaned up. However, some fine particles are left when a windrow is removed.
Notes by Mary Wicks
The OCAMM (Ohio Composting and Manure Management) Program is funded by OARDC/OSU.