By Dr. John Abel :Circular Byproduct Management Group
The food system depends on productive soil, yet manufacturing leaves behind organic materials that never reach a retail package. For dairy manufacturers, one of those materials is dissolved air flotation sludge, commonly called DAF sludge. When its composition, treatment, and receiving site are properly evaluated, this residual can become a resource for nutrient recovery and soil improvement. My focus at Circular Byproduct Management Group is to connect that opportunity with accountable management from the processing plant to the final outlet.
DAF systems separate suspended solids and fats from wastewater, often with the help of coagulants and polymers. The recovered material can contain organic matter and nutrients, but its properties depend on the plant and treatment process. Dairy processing sludge is not automatically finished compost, a standardized fertilizer, or suitable for unrestricted spreading. Research on dairy sludge phosphorus shows that treatment chemistry and soil conditions influence nutrient behavior and availability. Each material needs its own evaluation.
That evaluation begins with understanding the source: what enters the wastewater system, which treatment chemicals are used, and how production or cleaning changes affect the residual. Representative laboratory testing should establish solids content, organic matter, nutrient concentrations, pH, salinity, and any other parameters needed to determine suitability. Metals, pathogens, sodium, and source-specific contaminants may require assessment. The receiving operator must know what is arriving and whether its process and authorization can accept it.
At Circular, the management approach I advocate brings together manufacturers, laboratories, qualified agronomic specialists, transport providers, and receiving facilities. The objective is to identify an appropriate beneficial use and document the conditions under which it can occur. Depending on the material, that may involve a compost yard, a fertilizer developer, or a farm operating under a site-specific nutrient management plan. A material that fails the acceptance criteria needs another outlet.
Soil improvement starts with the soil itself. Acidity and alkalinity describe soil chemistry; clay, sand, and loam describe texture. These are separate characteristics that must be considered together. An alkaline clay field presents different challenges from an acidic sandy loam. Soil testing, field history, crop demand, drainage, and water availability establish the starting point for choosing an amendment.
In acidic soils, a material with demonstrated neutralizing capacity may help address acidity when matched to a measured lime requirement. Its pH alone does not establish that capacity. In alkaline soils, adding more alkaline material may be counterproductive, and nutrient availability and salt loading deserve particular attention. For clay-rich soils, appropriately prepared organic amendments can support aggregation and pore space, but traffic on wet ground can undermine those gains. In sandy soils and sandy loams, mature compost can improve water and nutrient retention, while application planning must still account for leaching.
The technical task is to match nutrient forms, carbon characteristics, and amendment properties to the receiving soil. There is no single molecular formula that repairs every field. Carbon-to-nitrogen balance, nutrient release, phosphorus chemistry, and salinity all matter. For compost producers, feedstock selection must also support adequate aeration, moisture control, stabilization, and a suitable finished product. The benefits of mature compost should not be attributed automatically to untreated DAF sludge. [1, 4]
Application rates must follow calculations rather than disposal pressure. A nitrogen-based starting rate divides the crop’s remaining nitrogen requirement, after existing nutrient credits, by the estimated plant-available nitrogen supplied per ton or per thousand gallons. Laboratory results must be converted consistently between wet and dry bases. Total nitrogen is not the same as first-season available nitrogen. The proposed rate must then be checked against phosphorus constraints, salt loading, hydraulic capacity, and other site limits; the most restrictive applicable condition governs. [2, 5]
For dryland farmers, realistic yield expectations and rainfall conditions are especially important. Recycled nutrients cannot overcome a lack of water, and liquid residuals should not be treated as an unrestricted irrigation source. The aim is to support soil function over time alongside appropriate crop rotations, residue retention, and erosion control. Progress should be measured through repeat soil testing and field observations, including changes in organic matter, infiltration, nutrient status, and crop performance. [2, 6]
This work also gives multinational manufacturers, including Fortune 100 companies, a practical way to advance environmental, social, and governance objectives. Where suitable materials would otherwise go to landfill, a documented beneficial-use program can support diversion goals and nutrient circularity. The value lies in verified outcomes: quantities moved, material characteristics, receiving-site acceptance, treatment records, and evidence of final use. Diversion alone does not establish carbon neutrality or prove that every ESG goal has been met. Any emissions claim needs a defined baseline and a suitable accounting method.
Preventing food loss remains the priority. Materials that can safely remain in the food supply should be evaluated for those uses first. For residuals requiring other management, the best route depends on their composition and the receiving system. Circular’s role is to coordinate those decisions, maintain traceability, and keep the generator and recipient aligned on responsibilities.
My vision is a full-circle approach in which appropriate organic resources return to land that can benefit from them. Restoring depleted soils takes repeated, well-managed effort; a truckload alone does not rebuild a region. But when manufacturers, composters, fertilizer developers, and farmers work from reliable data, dairy residuals can contribute to that effort. I invite food manufacturers and prospective receiving partners to begin with a material assessment and a clear question: what beneficial use can we demonstrate, manage responsibly, and measure?
Dr. John Abel leads Circular Byproduct Management Group. Inquiries: john@circularbyproduct.com | 208-223-1280.
Sources :
- [1] Journal of Soil Science and Plant Nutrition. Contrasting Phosphorus Build-up and Drawdown Dynamics in Soils Receiving Dairy Processing Sludge and Mineral Fertilisers.
https://link.springer.com/article/10.1007/s42729-023-01585-w - [2] USDA Natural Resources Conservation Service. Nutrient Management.
https://www.nrcs.usda.gov/getting-assistance/other-topics/nutrient-management - [3] Utah State University Extension. Using Compost in Utah Gardens; Soil Care.
https://extension.usu.edu/yardandgarden/research/using-compost-in-utah-gardens - [4] U.S. Environmental Protection Agency. Composting.
https://www.epa.gov/sustainable-management-food/composting - [5] University of Minnesota Extension. Tips for fall manure application and how to avoid nutrient loss.
https://blog-crop-news.extension.umn.edu/2021/08/tips-for-fall-manure-application-and.html - [6] USDA Natural Resources Conservation Service. Role of Organic Matter.
https://www.nrcs.usda.gov/conservation-basics/soil/soil-health/role-of-organic-matter - [7] U.S. Environmental Protection Agency. Wasted Food Scale.
https://www.epa.gov/sustainable-management-food/wasted-food-scale
