While organic waste processing solutions are easily implemented for source-separated materials, the organic content of MSW can also be diverted to these facilities through use of a single stream or “dirty MRF”.
For organic wastes, the EPA points to composting as a preferred waste management practice following source reduction and reuse. Through composting, yard waste and other source-separated organic wastes can be recycled into mulch and compost. Anaerobic digestion (AD) presents an additional organic waste processing solution that falls into the energy recovery category for waste management. Organic material processed by digester systems may include animal manure, organics separated from mixed MSW, food scraps, food production residuals, agricultural residues, wastewater solids, or some combination of the former.
In AD systems, the controlled decomposition of the biodegradable waste by microbes yields two primary products: biogas and digestate. The biogas can be used to create energy in the form of electricity, heat or vehicle fuel, while the digestate may be used in byproducts such as soil amendments, fertilizers, and even as a feedstock for plastics and chemicals (USDA, 2014).
Because of the variety of applications for AD systems, there are several benefits that can be realized through effective use of the technology (EPA, 2015):
- Nutrient management alternatives
- Soil improvement opportunities
- Methane emissions reduction
- Production of renewable energy
- Diversion of organic wastes from less preferred disposal options.
Depending on the source of organic waste and the objective for the AD installation, i.e., waste processing or energy generation, different types of AD systems can be selected or combined. While older systems were typically designed to process one feedstock, new systems are usually designed for co-digestion to enhance biogas production.