WCMA Notes: Advancing Wastewater Solutions
Challenges abound in the management of wastewater nutrients from dairy processing, but advances in technology and ongoing dialogue with regulators offer opportunities to keep dairy growing sustainably.
For more than a year, Wisconsin Cheese Maker Association (WCMA) and members have maintained a dialogue with Wisconsin Department of Natural Resources (DNR) regarding land application of dairy plant wastewater – characterized as “industrial sludge” by the state agency. These talks have revealed opportunities for alignment.
This current discussion with regulators began when dairy manufacturers in Wisconsin obtained commercial fertilizer licenses from the Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP), reflecting the nutrient value in treated, land-applied sludge.
Last October, Wisconsin DNR reacted to this growing movement to amend soils with phosphorus, nitrogen and minerals from dairy wastewater sludge. A letter, sent to several dairy processors, stated that “while [your plant] may have a DATCP fertilizer license, this facility is still required to follow its WPDES permit and [DNR] ch. NR 214.” Wisconsin DNR was effectively holding onto regulatory control of what it considers “sludge.”
Site Evaluation
Recent talks with land application staff at Wisconsin DNR have revealed the agency’s belief that state regulations allow flexibility when landspreading dairy plant wastewater sludge. Onsite investigation of new or existing land application sites, rather than reliance on data such as NRCS soil survey maps, has the potential to increase approved land application acreage. Onsite soil investigations for depth to groundwater, depth to bedrock, and soil textures may determine better soil conditions than soil mapping and open the potential for reduced restrictions and greater application.
Cake Sludge
Wisconsin regulators are upbeat about evolving technology to remove moisture and increase solids in wastewater sludge. So called “cake sludge,” with solids content of 12 percent or greater, can seek reduced restrictions and opportunities to cover a larger percentage of acres on land application sites. But first, Wisconsin DNR would seek these favorable characteristics in a cake sludge:
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High percent solids content (i.e., ~>12%)
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Low chloride concentration (i.e., load is nitrogen-limited)
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Favorable carbon to nitrogen (N) ratio (i.e., elevated carbon content in waste will consume N during breakdown of the carbonous material)
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Limited ammonia-N concentrations (i.e., ammonia-N is readily available unlike organic-N)
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Defined and consistent available N content
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Consistent and nontoxic material characteristics
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Limited odor
Regulators agreed with a memo released by WCMA this week noting that dairy processors who execute professional, onsite evaluation of soil conditions at land application sites, or process cake sludge with favorable characteristics, could seek fewer restrictions and greater loading rates in the Land Management Plan associated with their WPDES permits.
Land application of cake sludges isn’t necessarily the end of the line for this emerging technology. One Wisconsin dairy processor is testing concentration methods for industrial sludge with the goal of reaching 20 percent solids, a level optimal for further moisture removal in conventional drying equipment. Dried and bagged dairy nutrients could then be commercially sold as fertilizer, a fertilizer ingredient or soil amendment
Chlorides
Levels of chloride in dairy wastewater – from salt used in cheesemaking, for example – are a key factor in restrictions on loading rates for wastewater sludges on land application sites. Dairy processors capture waste streams such as salt whey, higher in chlorides, as high strength wastewater bound for land application.
One dairy processor in Wisconsin is working at the cutting edge of technology: collecting and processing salt whey to remove and recycle salt. This processor has installed and is running trials now on equipment that crystallizes and dries salt from the salt whey stream – with the ultimate goal of reusing salt in processing. This technology is important to the processor’s sustainability goals and can help reduce levels of, and land application restrictions on, high strength waste.
Additional challenges in wastewater management – phosphorus limits, increasing complexity in whole effluent toxicity testing, declining land acreage for land application – keep this key segment of dairy processing top of mind for WCMA and dairy manufacturers. Advancing technology, and solutions-based dialogue with regulators, are key to dairy growth and a healthy environment.