How Municipal Waste is Processed
Over the years there has been an evolution in the methods of processing waste and diverting it away from landfill. We have seen the development of material recovery facilities (MRFs) and different sorting technologies which aim to separate and clean recyclable fractions. However, they have very high operating costs and low effectiveness.
Energy from Waste
The separating challenges are the main reason why today the majority of waste in developed countries goes to Energy-from-Waste (EfW) plants, also known as Waste-to-Energy. Their primary aim is to process the entire waste in order to generate energy rather than recover materials. Incineration is by far the most popular such technology which has been used for many years. It converts the energy content of the waste into gas, which combustion engines subsequently burn to produce electricity and heat. Incineration plants operate around the world and today they process a large proportion of the municipal waste.
Most incineration plants are not environmentally friendly and also have very high capital and operating costs. They are very large scale, often processing hundreds of thousands of tonnes annually. Due to the high costs, these plants rely heavily on high gate fees. Increasing competition for waste contracts has led to many plants closing down.
Advanced Conversion Technologies
In recent years, we have seen new emerging EfW technologies offering a more effective solution. They are known as Advanced Conversion Technologies (ACT) and their aim is to improve material recovery. The two most significant ones are Mechanical Heat Treatment (MHT) and Mechanical Biological Treatment (MBT). MHT incorporates various sorting technologies that separate recyclables. Furthermore, it uses steam injection to try and clean them from organic contamination. On the other hand, MBT integrates anaerobic digestion (AD) or composting in order to treat the organic fraction and produce renewable energy.
ACT plants are a step forward from the undesirable incineration but they similarly have high capital and operating costs. Their effectiveness also leaves much to be desired with most plants operating at 25-40% separation efficiency. The remaining waste is known as refuse-derived fuel (RDF) which is typically packed in bales and incinerated locally or exported to other countries for the same purpose.