Sewer sludge for the yard?
UNR Cooperative Extension
Treated sewage sludge is sometimes sold as a fertilizer product. Sounds yucky right? Cornell University defines sewage sludge as a “semi-solid residue of organic matter generated as a byproduct of wastewater treatment.” Products are generated for use on lawns, shrubs, flowers, trees, and gardens. Nitrogen, phosphorus, and organic matter come from the wastewater. However, treatment doesn’t always remove all the contaminants or pathogens that enter the wastewater treatment plant from businesses, homes, or industry.
So, the treated sludge is then made into a fertilizer by first squeezing all the water out through a filter. Then, it is heated to kill viruses and pathogens. Finally, it is dried and turned into granules.
Is it safe? The United States Environmental Protection Agency (EPA) has developed criteria that sewage sludge has to meet in order to be sold. Some people are concerned about pharmaceuticals and other toxic organic chemicals that can be in the sludge that are not regulated or monitored by the EPA. Although it is made from organic materials, it is not allowed for use in certified organic gardens, but otherwise, it can be used in nonorganic gardens. In New York, food crops cannot be planted until 38 months after using sewer sludge.
Metals are of concern in sludge, but of the nine metals regulated by the EPA, all are below EPA standards. However, metals do not degrade and could build up over time. Iron is high, which supposedly will green up lawns, but I’m not sure that the form of iron present in sludge is a form usable by plants. Levels of PCBs and dioxins (highly toxic organic chemicals) vary from one sludge product to another.
Dogs and people (children) could be contaminated by eating sludge. Hand-to-mouth or paw-to-mouth contact should be avoided. Crops might be contaminated, either from absorption through roots or as particles on plant surfaces. Thoroughly washing crops and avoiding use on vegetables may decrease risks. Washing hands after applying sludge is also a good idea.
Golf courses and parks would be good areas for sludge use, along with other areas where pets and children don’t play. As populations grow, recycling waste becomes more and more important. Sewage sludge, when properly treated, could be a good way to reduce waste.
For more information, e-mail firstname.lastname@example.org or call me at 887-2252. You can “Ask a Master Gardener” by e-mailing email@example.com or call your local University of Nevada Cooperative Extension office. Check out many useful horticulture publications at http://www.unce.unr.edu.
• JoAnne Skelly is the Carson City/Storey County Extension educator for University of Nevada Cooperative Extension.