Biosolids Reuse

Metro Water Recovery beneficially reuses 85 dry tons of biosolids per day, maintains METROGRO’s 52,000-acre farm, and distributes and land applies biosolids at 379 permitted private farms.

Biosolids are treated, nutrient-rich, biologically-produced, mostly organic material produced from the solids removed during the wastewater treatment process. Federal and state biosolid regulations provide options for how treatment plants can manage the treated product. Biosolids are one of the most studied materials regulated by the U.S. Environmental Protection Agency (USEPA). Decades of studies have demonstrated that biosolids can be safely used for the production of crops.

Farmers and gardeners have been recycling biosolids for ages, reducing the need for chemical fertilizers.

After treatment and processing, biosolids can be recycled and applied as fertilizer and soil amendment to improve and maintain productive soils and stimulate plant growth. Metro’s biosolids are applied to promote the growth of agricultural crops on the eastern plains of Colorado. When applied to crops, application rates are restricted to the nutrient needs of the crop. The plant nutrients are slowly released throughout the growing season, enabling the crops to absorb these nutrients as they grow.

METROGRO® Cake

Metro hauls the biosolids that our treatment plants produce as a product called METROGRO® Cake, named for it’s batter-like consistency. Biosolids are regulated in two classes: Class A and Class B. Class A biosolids can be applied to agricultural land in addition to public access areas, such as private lawns and home gardens. Class B biosolids are almost exclusively applied to agricultural land. Metro produces Class B biosolids which are applied to the METROGRO farm and over 300 privately owned farms.

The final cake product is regulated as a Class B biosolid.

Biosolids are designated Class B if pathogens are detectable but have been reduced to levels that do not pose a threat to public health and the environment, as long as actions are taken to prevent exposure to the biosolids after their use.

Pathogens are not the only contaminants that are monitored. Biosolids must also be sampled for arsenic, cadmium, copper, lead, mercury, molybdenum, nickel, selenium, and zinc. There are average limitations which these metals must remain below. The biosolids must be sampled according to annual throughput. RWHTF generates more than 15,000 metric tons of sewage sludge per year. This results to, at a minimum, sampling on a monthly basis. NTP generates less than 1,500 metric tons per year and only is required to sample, at minimum, quarterly. However, both plants sample the product on a weekly basis.

In addition to the pollutants listed above, the cake is also sampled for nutrients such as total nitrogen, total phosphorus, and total potassium to determine the agronomic rate of the biosolids application for a given field or area. Depending on where the biosolids are being applied, and what crop is being planted, the quantity applied may vary.

Treatment Process Map