Better technologies to handle and sort mixed waste streams promise to unlock previously unavailable resources. Next-generation biofuels will use waste as feedstock. Methods to gather plastic waste from the oceans, dismantle refuse mountains and harvest energy are being developed and improved.

Organic material, paper, plastic, glass, metals, and other refuse; the annual volume of municipal solid waste could double by 2025, according to the Worldwatch Institute.

Sweden has come a long way towards closing the resource cycles. More than 97 percent of the domestic waste is recycled in some way – by reuse, materials recycling, or energy recovery. The rate of recycling differs a lot between countries. EU directives require recycling of at least 50 percent of household waste by 2020, but in many parts of the world, over 90 percent of municipal waste is sent to landfills.

Around 8 million metric tonnes of plastic waste go into the oceans each year. About 80 million tonnes of plastic is floating in garbage patches in the Atlantic and the Pacific Ocean, causing damage to the marine environment and the species living there. The microscopic plastic fragments derived from the breakdown of larger debris are especially problematic; in some waters, microplastics are found in six times higher abundance than zooplankton and pose an imminent threat to the food webs. The plastic also often contains toxic and hormone-disrupting chemicals.

Cleaning the oceans

In a global perspective, less than ten percent of the plastic we produce is currently recycled. But there are initiatives to improve the figures. Precious Plastic, for instance, is a company that develops tools for DIY-recycling, enabling people around the world to make new products locally.

The Ocean Cleanup project was founded by 20-year-old inventor Boyan Slat. The aim is to remove plastic debris from the oceans by means of 100-kilometre long networks of passive, floating barriers. Interacting with natural currents, the barriers funnel debris towards a central extraction point. Tests are underway, and the foundation is preparing for full deployment in 2020.

Energy recovery – a shortcut to electricity?

Waste prevention, reuse and recycling of materials are always the first priorities – but once a material has been degraded by several recycling cycles, energy recovery is a good way to handle it. Generated waste can be burned in an incinerator, powering steam turbines which generate electricity. Waste-to-energy facilities that also supply local cities’ district heating systems can reach an efficiency of 80-90 percent, and modern incinerators have advanced emission controls. Metals and other substances can be recovered from the bottom ash residue remaining after combustion, and fine particles and other pollutants can be efficiently removed from the flue gases with filters. In Sweden, improved cleaning technology has reduced the emissions of heavy metals from incinerators by 99 percent in a couple of decades, and less dioxin is released from them than from home fireplaces.

Burning waste for energy recovery could provide Africa with 20 percent of its electricity needs. This could be an important opportunity for a continent where both energy poverty and waste problems are wide-spread. The stringent emission controls make modern WTE plants expensive to build, but a more readily available option would be to start to capture and filter gasses already being generated in landfills where organic waste is left to decompose; the gas could then be burned in turbines and boilers to generate electricity.

Biofuel refineries right at the waste stream source

With growing prosperity, more countries will move towards the circular economy, improve their waste management and increase recycling rates. Meanwhile, we can make better use of existing landfills and waste streams, and mine them for resources; where there is waste, there is energy.

Creating liquid fuels is one way to recover that energy. First generation biofuels such as corn ethanol were produced from food crops. Second-generation biofuels are more advanced; they are made from lignocellulosic biomass, agricultural residues or other waste, and do not compete with food production. The Swedish company RenFuel, for instance, is currently building a facility to test manufacture an advanced biofuel based on lignin refined from black liquor, a renewable byproduct from the production of paper pulp. Sekab, Sveaskog and Preem have recently joined forces as well, aiming to develop a bio-petrol made entirely from forestry waste.

litter-460984_1280Even polymer waste can be used to create liquid fuels, through chemical recycling. Polymer waste is very carbon rich, and it can be used as feedstock for gasification or pyrolysis. It can also be used as a reducing agent in steel production.

In the future, small, modular bio fuel refineries could be located right at the waste stream source, whether a landfill, farm, or commercial facility. Ideally, they would be based on simple and economical technology, yet adaptable to diverse waste streams. Improved catalytic technologies and gasification processes are under development, but a huge challenge will be to make the technology able to handle waste streams of mixed composition, varying over time.

Automated sorting technologies is also an important way to make recycling more efficient. Many mixed waste streams are still manually sorted, but they don’t have to be – different materials could for instance be identified by the light spectrum they reflect.

In the old, linear economy, products manufactured from virgin material were used for a while before ending up in a landfill. We are in the process of replacing the linear economy with one where waste is not a meaningful term at all: a circular economy, where every residue is a resource in its own right and can be used as a feedstock for other processes. We have indeed inherited a refuse mountain from the linear economy – but technological progress is giving us the tools to dismantle it once and for all.

The article was published in April 2016