What are biosolids?

Biosolids are the nutrient-rich organic materials resulting from the additional treatment of sewage sludge at the Water Pollution Control Plant. During treatment, beneficial bacteria and other tiny organisms break the sludge down into simpler, harmless organic matter. The organic matter, combined with bacterial cell masses, settle out to form biosolids, which can then be safely recycled as a fertilizer and soil conditioner.

What does the WPC Plant do with biosolids?

After being fully processed for nine months in lagoons at the WPC Plant, the nutrient rich material is applied to farm land as fertilizer. This is a free service supplied to area farmers by the Water Pollution Control Plant. The quality of the biosolids, selected farmland and application process is held to strict standards set forth and enforced by the Virginia Department of Environmental Quality.  The application rate is determined by a nutrient management plan prepared by a certified nutrient planner who determines the needs of the crops being grown on specific soils. Biosolids rates vary with the soil and the crop. 

What are the benefits of biosolids?

The estimated value of the biosolids when land applied is over $350 per acre. This is direct savings to the farmer for what would have otherwise been spent on conventional fertilization methods.

In addition to the financial benefits, biosolids serve as an excellent fertilizer. Biosolids enrich the soil with essential nutrients and needed organic matter.

The agricultural benefits of biosolids have been documented for many decades by numerous scientific studies and through the practical experience of thousands of farmers. In Virginia, farmers report that the application of biosolids to land can, in some cases, more than double crop productivity. 

Plants need a complex mixture of nutrients, soil, air and water to grow. Biosolids contain many essential plant nutrients, including the primary macronutrients nitrogen, phosphorus, and, to a lesser extent, potassium; the secondary macronutrients magnesium, calcium and sulfur; and such micronutrients as copper, zinc, iron, manganese, molybdenum and boron.

Organic matter in biosolids improves soil quality, reduces compaction, increases water-holding capacity, and provides an energy source for necessary microbial activity. This reduces water runoff and soil erosion, increases water conservation and increases resistance to drought. Biosolids that have been lime-stabilized help neutralize acidity in soils, just like agricultural limestone. This helps maintain the proper soil pH for crop growth.

Chemically, biosolids increase the soil’s “cation exchange capacity” (CEC), which is a measure of how well soil retains certain plant nutrients. The organic matter in biosolids acts like a magnet and attracts plant nutrients. It helps hold plant nutrients in the root zone and prevents them from leaching.