by Claudine Capel
Anaerobic digestion came about as the result of a long process of people searching for the best way to deal with biowaste. Even before awareness of climate change made us realize landfill was not the right home for our organic waste, we had problems with leachate and gas. So, early technologies found ways to convert organic waste into compost and fertilizer instead. This process was completed on open air windrows until odour became a problem and ‘in-vessel’ composting plants were developed.
Anaerobic digestion is the latest and greatest process of in-vessel treatment of waste, and is generally considered to be one of the most innovative and useful technologies developed by our industry in recent years. Not only does it give us a large-scale solution to our organic waste but it allows us to turns the resulting gases into energy.
The process, put simply, is the degradation of waste by microorganisms in an environment starved of oxygen. It can be used to treat organic solid waste and wastewater of almost any kind. The process works quickly and the remainder can be used as fertilizer while the biogas produced is converted into energy.
As people will always produce biowaste, whether it be food or sewage, anaerobic digestion is seen not only as a waste management process but also as a source of renewable energy.
Waste to energy
Waste to energy Waste to energy (WTE), sometimes known as energy from waste (EfW) has seen some of the most interesting developments in the industry, as it has the advantage of being able to completely remove waste, rather than reuse or process it.
Traditionally, WTE plants have operated by incinerating waste and converting the resulting heat into energy – and most plants still use this technology today. But public opposition to incinerators, which are often seen as dangerous and noisy has meant new types of WTE – such as gasification, pyrolysis, thermal depolymerization and plasma arc gasification – have been developed and are leading the way forward in this area.
Gasification and plasma arc gasification are used to convert organic materials into a synthetic gas (syngas) made up of carbon monoxide and hydrogen. The gas is then burnt to produce electricity and steam. A plasma gasification plant uses plasma torches which operate at approximately the same temperature as the surface of the sun (yes really!) to create an environment in which solid or liquid waste is turned into syngas. The process breaks down the molecular bonds of the waste and leaves it in elemental components. This syngas is then converted to energy, and the waste completely disappears.
‘Zero Waste’ is a philosophy, rather than a process or technology, but it certainly can be considered an innovation. The Zero Waste International Alliance define it as this: ‘Zero Waste is a goal that is ethical, economical, efficient and visionary, to guide people in changing their lifestyles and practices to emulate sustainable natural cycles, where all discarded materials are designed to become resources for others to use.
‘Zero Waste means designing and managing products and processes to systematically avoid and eliminate the volume and toxicity of waste and materials, conserve and recover all resources, and not burn or bury them. Implementing Zero Waste will eliminate all discharges to land, water or air that are a threat to planetary, human, animal or plant health.’
The idea of reusing every bit of waste possible and turning the remainder into energy is a commendable and sustainable system of waste management, which could solve many of the world’s environmental problems. When one considers the way waste is managed worldwide currently, however, it starts to sound like an unrealistic fantasy. It is hard to know where to begin when implementing this kind of system. Yet there are towns, regions and countries which have given us all an example of how things should be done.
Scotland is one such place. Authorities announced plans to work towards Zero Waste in 2008, and the target to achieve the goal is 2025. Zero Waste can also be implemented by individual companies and organizations; the Zero Waste Alliance list Xerox Corp (Rochester, New York), Hewlett Packard (Roseland, California), Fetzer Vineyards (Hopland, California), Epson Portland Inc (Hillsboro, Oregon), Collins & Aikman (Dalton, Georgia) as companies that have committed to this path.
Ron Wainberg, the national president of the Waste Management Association of Australia, said in recent interview with Waste Management World. ‘The ISWA meeting during the last Annual Congress debating the ‘Zero Waste Concept’ showed [a] change in attitude. Most people will accept there will always be waste in society and the concept of zero waste is more about not wasting the value of the waste.’ This shows that Zero Waste is a question of changing attitudes, and taking responsibility for the waste that we produce by making sure it is reused, recycled, resold or turned into energy. We can’t stop producing it altogether but we can make sure we deal with it in the best ways possible.
The best thing about Zero Waste is that by working to it people stretch the boundaries of their imaginations. By aiming high they create an environment in which innovation abounds.
Extended producer responsibility (WEEE)
The WEEE issue is one of the greatest challenges facing the waste industry today. We know that when it comes to expensive, electrical equipment, repair is better than disposal. The toxicity and complexity of these types of product make them notoriously difficult to recycle, and sadly the rate of production is far greater than our ability or willingness to recycle them. The result? A violation of human rights, with the developed world sending piles of WEEE to developing countries to be dumped.
Clearly, this is a practice which must be controlled and stopped, but with many of these shipments being sent illegally it is very difficult to monitor the numbers involved.
One solution which seems to be providing part of the answer to this problem is Extended Producer Responsibility, sometimes known as ‘Product Stewardship’. Governments and authorities have begun introducing policies which hold the manufacturers of electrical and electronic equipment responsible for managing their ‘end of life’ products when people have finished using them. And sometimes companies are opting to do this voluntarily. While this does not give us a way to deal with the mountains of WEEE piling up in Asian and African countries, it does look at the problem from a prevention angle which will surely be beneficial in the longer term.
Extended producer responsibility takes the onus for finding effective ways to reuse and recycle the components of electrical and electronic goods off waste management companies and puts it back on the producers themselves. This is an infinitely more sensible solution as manufacturers are able to recycle separate parts and use them to build new products of the same type, or more easily create a system to achieve this.
Companies participating in these schemes use methods such as reuse, buy-back or recycling programmes. They also sometimes pay separate organizations to deal with their waste.
Waste fighting climate change
Emissions from landfills can contribute directly to climate change when organic waste is left to biodegrade in a landfill. The solution is to either prevent organic waste being sent to landfill by separating at source or pre-processing the waste or, as a secondary measure, to capture the methane being emitted from the landfill and turn it into energy.
The International Solid Waste Association (ISWA) established a task force in November 2007 to look at the interaction between waste management and the production of greenhouse gases. This group examined and made recommendations on the issues surrounding the subject. They produced a white paper which was released in the run up to the COP15 global climate change conference, and was discussed at a separate conference on ‘Waste and climate change’. Here are some of the findings of the ISWA white paper:
- The waste industry occupies a unique position as a potential reducer of greenhouse gas (GHG) emissions. As industries and countries worldwide struggle to address their carbon footprint, waste sector activities represent an opportunity for carbon reduction.
- The waste sector offers a portfolio of proven, practical and cost effective technologies which can contribute to GHG mitigation. When adapted and deployed according to local traditions and needs, they can help secure significant global GHG emission savings.
- Waste prevention, minimization, reuse and recycling are on the increase across the globe, representing a growing potential for reducing GHG emissions by conserving raw materials and fossil fuels.
- Through aerobic and anaerobic biological treatment technologies, organic wastes can be recovered and transformed into soil conditioners and fertilizers. These processes reduce GHG emissions by sequestering biogenic carbon in soils, improving soil physical properties, and adding soil nutrients.
- Waste offers a significant source of renewable energy. Incineration and other thermal processes for waste to energy, landfill gas recovery and utilization, and use of anaerobic digester biogas can play important roles in reducing fossil fuel consumption and GHG emission.
Using waste management as a way to combat GHG and climate change is one of the most innovative and common-sense concepts in waste today. The role that the waste industry can play in helping to avert climate change must not be underestimated. Given the correct legislation to work to the technologies which are already making great leaps in this area will show how much good they can really do. Although the costs of implementing these processes is often seen as prohibitive, the cost to the planet and the resulting financial cost of dealing with this, make all of these moves more than worthwhile.
Waste to fuel
Given the oil crisis and the ever-increasing price of fossil fuel, turning waste into fuel is a fantastic solution. Biofuel is the most common form, and the term encompasses a range of different fuels derived from organic matter, including biowaste. Biofuel can be solid, liquid or gas and be used to power vehicles or used to enhance other types of fuel. Biogas – a product of anaerobic digestion – and syngas – which is produced during gasification – are both types of biofuel.
Landfill gas also has an up-and-coming role in this field. Most landfill-gas-to-energy projects involve turning otherwise harmful emissions into electricity to power homes. But it is also being increasingly used as a vehicle fuel or as a substitute for mains household gas supply.
Source separation of waste
The waste hierarchy as laid out in European law states the ideal chain of events when it comes to waste is reduce, reuse, recycle, energy recovery, and dispose, and it is interesting to look at the wide variation of systems in Europe today for citizens disposing of their household waste. Where some countries such as Germany and the Netherlands have had efficient methods in place for years, other countries still have the majority of residents throwing all their household waste into one bin and leaving it for the local authority to separate it. It seems that more stringent measures need to come into play to ensure that the waste hierarchy is followed wherever possible.
While streams of mixed MSW can be collected and then separated into the various components, i.e. recyclable items and organic waste, it is much better to separate the waste stream at the source. This has several benefits:
- maintains a higher quality of material for recycling, meaning there is more value to be recovered,
- decreases the occupational risks for waste workers, and
- means that waste can most often be sent straight to the correct place for processing, instead of one facility to be separated and then another to be processed.
There are many separation schemes in effect across the world and it depends on each municipality as to what will work best. The collection of food scraps into a separate bin is one of the most common and has an important role to play in making sure organic waste does not end up in landfill. It also means that biowaste can be turned into compost or biodegraded in a safe manner without emitting harmful gases. Systems for separating glass bottles, aluminium cans and plastics also mean that recycling becomes easier, safer and more efficient.
People will always, either through ignorance or carelessness, throw their waste in the wrong bin every now and then. So, however good our separate collection schemes may be – and let us remember that it is not always practical to have them in place; we need a way to take a mixed waste stream and divide into reusable, separate waste streams. Enter one of the greatest innovations in waste technology – the sorter.
Sorting technology comes in many guises, from water-based technologies such as ArrowBio which separates the organic fraction from recyclables, to the whirring, whizzing, sorting machines we see at trade shows every year.
When mixed waste is fed into a single stream recycling facility the process will include some or all of these processes:
- removal of larger items by hand
- separation of items by weight, which means metals, plastics, paper, glass etc. are sorted from each other
- use of screens to separate items by size
- Magnetic separation of metals, such as eddy current separators for aluminium
- ultraviolet optical scanners (Near Infra-red and Medium Infra-red) combined with targeted air jets that send items of certain types in separate collection bins e.g. PET and non PET plastics
Many companies have done brilliant work in this field over the past few years, leading the way in the development and manufacture of these types of technologies. One example is France-based Pellenc ST which has recently launched a new MIR (Medium Infra-red) sorter which sorts paper according to its quality, and has improved its NIR (Near Infra-red) system to sort wood into category A and category B.
Pellenc ST is working on a research project in partnership with OSEO dedicated to the development of new machines and sorting technologies worth over 18 million euro (US $24.5 million). So we can expect to see even greater things in future.