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Improving anaerobically digested dairy manure solids by economical post treatment to create value-added and sustainable greenhouse potting mix fiber products

We propose to research an economical anaerobic digestion (AD) post-treatment process for improving anaerobically digested dairy manure fiber. Digested dairy manure fibers are value-added solids used in potting mixtures (e.g., Magic Dirt, www.magic-dirt.com). However, there are some undesirable characteristics that limit the peat-like digested fiber from being a peat substitute. These include a relatively high electrical conductivity (EC), non-Class A biosolids classification, and potential for residual herbicide levels. The proposed post-treatment step is comprised of an extended heating and mixing treatment to make Class A biosolids. The process would incur minimal cost as heat can be supplied by available waste engine heat. A limited number of samples have been tested and EC and fecal coliform (indicator pathogen) levels were within the acceptable range. Herbicide concentrations have not been determined. A more rigorous research study needs to be conducted to demonstrate the effectiveness of the post-treatment process on the fiber product quality in terms of EC, fecal coliform, and herbicide levels. This project falls under the topic area “biologically-intensive and organic approaches to sustainable management of organic wastes” because dairy manure wastes are used to create a higher value solid fiber product that can be a peat alternative and used in organic crop production. Bench-scale studies will statistically test the treatment effect on EC, fecal coliform, and clopyralid levels. An optimized full-scale operation will generate fiber product samples for further testing and greenhouse trials. EC, fecal coliform, and herbicide contents will be determined. AD fiber with high EC and post-AD fiber with low EC will be compared to a peat-lite control during greenhouse plant growth trials.

Grant Information

  • Project ID: 147
  • Project Status: Complete


  • Principal Investigator(s): Hummel, R.
  • Investigator(s): Mitchell, S.
  • Grant Amount: $23000
  • 2015 Progress Report