In the United States, the current options for managing wastewater biosolids is beneficial reuse and non-reuse. Beneficial reuse includes land application, landfilling with biogas recovery, and energy recovery through incineration while non-reuse options include disposing the biosolids in landfills.
Although it is preferable to reuse the biosolids in land application and energy recovery, this is not always the case. The poor quality of some biosolids material could force a wastewater treatment facility to dispose the biosolids in landfills. That is the viable alternative.
Landfilling biosolids include disposal in a monofill (a landfill that accepts only wastewater treatment plant biosolids) or in a co-disposal landfill (a landfill that combines biosolids with municipal solid waste). Co-disposal landfill is the more popular type of landfilling biosolids, but studies have found out that biosolids represent only a small percentage of the total waste in the co-disposal mix.
This type of landfill disposal includes preparing the site, transferring the biosolids to the site, and covering the biosolids with a layer of cover material.
Before doing this, the biosolids material needs to be tested for the level of pollutants and contaminants there. The concentration of pollutants will affect the site preparation process, which may include installing a liner to prevent contaminants from migrating downward into the site soil.
There are three methods of monofilling wastewater biosolids. These are trench, area, and ramp methods. Trench monofilling involves excavating a trench and placing the biosolids in the trench. Afterward, the trench would be backfilled to return the soil to its original contours. Monofill trenches are either narrow or wide, but this will depend on the concentration of pollutants contained in the biosolids.
Narrow trenches are used for biosolids with low solids content while wide trenches are used for disposal of biosolids with a solid content of 20 percent or more.
In the area method, biosolids are placed in a natural or excavated depression or they are mixed with soil and placed on top of the existing layer of soil. In this manner, biosolids must be stabilized because the area method does not always apply a daily cover.
This method is used in areas where bedrock or groundwater are shallow and where excavation is difficult. The downside is that this requires a huge amount of soil to fill the area. There could also be changes in the local topography.
Finally, the ramp method involves spreading and compacting the biosolids along a slope. The soil on the high slope will be pushed over to cover the biosolids.