Wastewater treatment facilities produce biosolids as a final by-product of the treatment process. The term “biosolids” was crafted by the U.S. Environmental Protection Agency (EPA) to promote the idea of recycling sewage sludge. Biosolids are really just treated human sewage. Class A biosolids have been treated to reduce bacteria, while Class B biosolids have not been treated.
Current options for managing wastewater biosolids can be broken down into two groups: beneficial reuse and non-reuse options. Beneficial reuse options include land application, landfilling with biogas recovery and energy recovery through incineration. Non-reuse options include landfilling. It is preferred for a municipality to implement a beneficial reuse technology, but it is not always possible. Municipalities may face land acquisition constraints, have biosolids with high metals or toxins concentrations or create a public nuisance by implementing a reuse option. Therefore, many municipalities must landfill their biosolids as a means of disposal.
Landfilling biosolids raises many environmental issues. Leachate from the landfill can transport nitrate, heavy metals, organic compounds and/or pathogens to groundwater. Water infiltrating the landfill and producing leachate must be contained and treated. Methods for controlling leachate include proper drainage methods, installing a liner or collecting and treating the leachate. Rainfall runoff from an active landfill may carry contaminants to surface waters. Surface water runoff must be collected and disposed of in accordance with NPDES requirements. The runoff collection system must be designed to contain a 25-year, 24-hour storm. Biosolids in a landfill will be further decomposed by anaerobic bacteria. This activity will create “natural” gas, namely methane and carbon dioxide. Passive or active gas collection systems can be effective in preventing gases from accumulating or migrating. Methane can be recovered from a landfill and used in boilers or space heaters or in turbines to generate electricity.