Co-disposal landfilling is the method of combining wastewater solids with municipal solid waste and then placing this mixture in a permitted landfill. Typically, municipal solid waste is first spread near the working face of the landfill. Then, the next layer would be the wastewater solids. The two solids would then be mixed with traditional landfill machinery. The ratio is dependent on the solids content of the wastewater solids, though the most common is 10 percent biosolids to 90 percent solid waste. This mixture would need to be compacted and covered daily.
Landfill operators usually have a freehand in accepting biosolids in the facility. The co-disposal landfilling follows no special regulations or guidelines. There are also no permit constraints, though this method is governed and regulated by the EPA under Subpart I of 40 CFR, Part 258, Criteria for Municipal Solid Waste Landfills.
The regulation addresses general requirements, best management practices, pollutant limits, operation standards for pathogens and vector attraction, and monitoring and keeping a record of the requirements.
Co-disposal landfilling is generally the method used when biosolids cannot be beneficially applied on land or used for the reclamation of forestlands and mining sites.
The most common reasons why biosolids are landfilled are: constraints instigated by the acquisition of lands, presence of metals and other toxins in the final biosolids product, and foul-smelling by-product that could be a public concern when applied on land.
But before landfilling the biosolids, it’s important to note just how much the amount of solids is in the final product. The requirement is to have a solids concentration of 15 percent or higher, though the soil may be mixed with the biosolids to make it viable for co-disposal landfilling.
This method, however, isn’t exactly cost effective because disposal of biosolids should not require the landfilling facility to spend on extra soil for the mixture. Instead, biosolids are typically stabilized before monofilling.
There’s a strict rule on the free liquids contained in biosolids. As a general rule, the biosolids should have a solids concentration of not lower than 18 percent. There are two tests available to determine whether the biosolids are viable for landfills: the paint filter test for free liquids and the Toxicity Characterization Leaching Procedure (TCLP). The latter is performed to ensure that the biosolids are non-hazardous.
Finally, the price of landfilling the biosolids would also play into account. The reuse of biosolids is the most cost-efficient method of disposing it and returning it to its original form. However, if the biosolids cannot be reused, landfilling would be the only option. Landfill tipping fees are affected by market changes and thus, may increase (or decrease) accordingly.