Mechanical Biological Treatment (MBT): The New Kid on the UK Waste Management Block
Considering how the innovative combination of established treatment technologies in a new integrated fuel production system are gaining significant support as the solution for residual waste treatment in the UK.
Dr Adam Read, Keith Brown and Andy Godley
Waste management in the United Kingdom (UK) has undergone a revolution in the past 20 years. In 1990, the UK landfilled more than 90 percent of its municipal solid waste (MSW), incinerated about 8 percent and recycled the remaining 2 percent. It had one the highest landfill rates in Western Europe and one of the lowest recycling rates, reflecting the UK’s mining traditions and aggregates industries and the subsequent availability of cheap disposal sites. Twenty years on, in 2010, recycling of materials from MSW has increased to more than 45 percent and landfilling has decreased to only 40 percent with the country achieving the important European Union (EU) target of reducing the amount of biodegradable waste landfilled by 25 percent in 2010, compared with the base year of 1995. This target was set by the EU to reflect the impact that landfilling of organic wastes has on climate change through the emission of methane. However, further reductions in landfilling of the organic/biodegradable waste stream are required over the next decade which will be even more challenging (75 percent reduction on the 1995 baseline by 2020). Failure to meet these targets will result in heavy fines payable by the UK Government to the EU and as such the UK Government has initiated policy and funding support to drive biodegradable materials out of landfill. This has included increasing the landfill tax for every ton of material landfilled from £8 (about $13) in 1995 to £80 (about $130) in 2014, and research projects and central funds to help kick-start the delivery of newer waste treatment technologies.
Currently, there are other non-waste sector drivers influencing the development of newer approaches to the treatment of waste. The UK faces an incipient energy shortage because of its dependence for most of its electricity on aged coal and nuclear power stations, which will reach shut down within the next decade. Investment needed for replacements has not come forward, and the growth in power generation from natural gas in the 1990s is now stagnating as indigenous gas supplies are now dwindling, and the UK relies increasingly on imports from the Russia and the Middle East, which raises concern over future security of supply.
In addition, recent events in Japan have almost certainly ruled-out a nuclear renaissance for the foreseeable future. The government has also made commitments to reduce greenhouse gas emissions by 80 percent of 1990 levels by 2050, and to do this has established several incentive schemes (the Renewable Heat Incentive, and the Renewable Obligation Certificates [ROC]) to stimulate investment in renewable energy technologies (see ROC and RHI sidebar).
Problems to Consider
All this could be good news for developers of the traditional alternative to landfill, namely thermal treatment solutions (energy from waste plants) based on mass-burn incineration, especially as energy recovered from the biomass component of waste is considered to be “renewable” energy. However, there are problems with this solution. Firstly, to be eligible for support through ROCs, electricity from waste incineration has to be through treatment in a certified combined heat and power (CHP) facility. Although such facilities are the norm in continental Europe, in the UK most energy from waste plants generate electricity only. Most new facilities could export heat but users are deterred by the high costs of the associated distribution systems.
Secondly, the government is likely to introduce higher household waste recycling targets for local authorities. So far, recycling targets (up to 50 percent for MSW) have been met largely by segregating recyclables (cans, paper and card, plastics, garden waste and, increasingly, food waste) for separate collection.
However, further efforts to recover recyclables from residual wastes are expected to be needed if higher recycling targets are to be achieved. Both Scotland and Wales have set MSW recycling targets of 70 percent and England is expected to follow suit when the Waste Strategy Review is published in the Summer of 2011. Although incinerator ash is widely recovered for use as a secondary aggregate, this does not qualify as recycling in the UK. So, further processing of the waste is likely to be required, which will ultimately undermine the rationale for large-scale mass-burn facilities.
Finally, mass-burn incinerators are deeply unpopular with the public. Many proposed incineration schemes have failed in recent years to secure the necessary planning consents (Cornwall, Oxfordshire, East London, etc.), sometimes leaving local councils facing high costs for landfill disposal as projects fail. Against this background, councils have been showing increasing interest in the development and adoption of Mechanical-Biological Treatment (MBT), a technology widely used elsewhere in Europe although a late entry to the UK market, as a means of meeting EU targets.
Italy has some 11 million tons per annum (mtpa) of MBT facility capacity, with significant capacity in Germany (5 mtpa), Spain (3-4 mtpa) and Austria (1 mtpa). Currently, 10 English waste disposal authorities, including West Sussex County Council, are currently developing MBT facilities, representing about 2 mtpa of treatment capacity (see West Sussex County Council sidebar).
What is MBT?
MBT combines tried and tested technologies in one location, taking the best from materials recycling facilities (MRFs) and organic treatment systems (composting or anaerobic digestion) to allow a broad range of materials to be segregated and treated in-situ, with the intention of producing materials for market (composts, fertilizer, fuel, recyclables, etc.) The outputs from MBT include refuse derived fuel (RDF) and biogas fuel (from Anaerobic Digestion), recyclables such as metals, glass and plastics, and a compost-like output (CLO) that may have application in land restoration or as a soil improver. MBT may also produce a stabilized waste of less mass and biological activity than raw MSW, and, therefore, be more acceptable for disposal in landfill.
There are numerous designs and configurations of MBT that differ largely in whether the focus is on recovering materials for recycling (from 1 to 10 percent of mass), producing stabilized residue (10 to 50 percent) for landfill or producing a fuel (up to 50 percent). However, the degree to which these objectives are secured depends on the success of the operator in accessing long-term markets for the outputs. In the absence of such outlets, if the products end up being landfilled, then MBT can only ever be a partial solution for residual waste treatment and will incur high costs for the disposal of the materials that are left over.
A typical MBT system would include a mechanical pre-treatment system that shreds and sorts the waste according to size and density, separating out the dry combustible fraction (plastics, paper, card, wood and textiles) as the refuse-derived fuel (RDF). This may account for up to 40 to 60 percent of the input. Metals and aggregates can also be recovered for recycling. The residue from this separation process may then be composted (or stabilized) for several weeks as the “biological” step to stabilize the residue for landfilling, or to produce a CLO that may be used as landfill cover or licensed for land restoration. What is produced depends on the markets available and the time and management effort given to managing the organic fraction.
In some systems the biological process used is anaerobic digestion (AD), rather than composting. This has the benefit of producing a methane-rich biogas. This is usually used to power gas engines that generate electricity and use the reject heat to warm the digesters to stimulate gas production. Much of the electricity is used to power the MBT but the excess is exported to the local electricity grid. This is currently the most popular configuration in the UK as electricity generated is eligible for ROCs—the government incentive scheme. With diminishing reserves of indigenous natural gas, there is growing interest in using the biogas as a vehicle fuel, or, after purification, for injection into the gas distribution network.
Other systems exist where the whole waste is composted or heat treated, either dry or with added water, to recovery cleaner materials for recycling, to produce a more refined and higher calorific value RDF that can be traded as a commodity, or a stabilized residue for landfill.
While offering a flexible solution, unless non-landfill outlets for the products are secured, MBT remains only a partial solution for residual MSW arisings, and when public sector organizations are letting long term contracts for the treatment of their wastes, they seek to secure guarantees from the
tenderers about their markets.
A number of UK authorities are currently looking to secure long term sustainable, affordable and robust treatment solutions for their residual waste–after they have met their 50 percent recycling targets. In Essex County, the municipality is negotiating with their preferred bidders about an MBT technology which, for the first few years, will recycle an additional 10 percent and stabilize the remaining materials prior to landfill. The UK is expecting an increase in thermal capacity in the next five years to help offset the need for renewable energy in the UK and these new facilities—cement kilns, gasification, pyrolysis and biomass facilities will need a consistent and quality feedstock. As this market develops, the intention is for the Essex facility to switch operation to stop stabilizing waste and instead produce a RDF for use in one of the new facilities that is developed.
Meeting the Demands for Waste Recycling and Recovery
It is interesting times in the UK as newer technologies are introduced to the UK to meet the demands for waste recycling and recovery and as the government promotes more renewable energy solutions. MBT has proven a popular option, being both an affordable way of increasing recycling levels and meeting EU targets whilst avoiding reliance on unpopular thermal treatment solutions. However, for MBT to be a real success, markets for the recyclate must be found and end uses for the composts and RDF are essential, otherwise MBT plants will be little more than expensive transfer stations on the way to ever more costly landfill or ever more unpopular incineration end points.
Dr. Adam Read is Global Practice Director for AEA’s Resource Efficiency and Waste Management Practice. He has more than 17 years of operational experience both in the UK and overseas and was awarded an honorary professorship in 2002 for his pioneering work on waste communications and public engagement. He is recognized as a leading waste management thinker with an extensive portfolio of research papers, conference articles and collaborative investigations both in the UK, U.S. and Europe. Adam is project directing AEA’s work on MBT solutions with Essex County Council. He can be reached at 07968 707 239 or e-mail [email protected].
Dr. Keith A. Brown is a principal consultant with AEA’s Resource Efficiency and Waste Management Practice with more than 20 years of experience in waste management and power generation. Keith represents the UK on the Intergovernmental Panel on Climate Change, and for the last three years, he has been advising West Sussex County Council on technical aspects of its residual waste treatment procurement. Keith can be reached at 07968 707 192 or e-mail [email protected].
Dr. Andrew Godley is a senior consultant with AEA’s Resource Efficiency and Waste Management Practice with more than 20 years of experience in organic treatment and the oil and gas sectors. Andy is a renowned expert on MBT system design, organic waste degradation and materials quality. He is leading the AEA team that is supporting Essex County Council on the procurement of their MBT system, and is providing similar support to the North London Waste Disposal Authority.
Andrew can be reached at 07800 586 193 or e-mail [email protected].
Case Study: West Sussex County Council
West Sussex County Council achieved its 45 percent recycling target for household waste largely by sending the commingled collected paper, cardboard, metals, glass and plastics to a new materials recycling facility for segregation. But source segregation of recyclables alone will not deliver the challenging Landfill Directive targets set for 2020. West Sussex’s solution for their residual household waste is based on MBT, which will produce RDF, recover metals for recycling and treat the food waste in an AD plant. Phase 1 of the residual waste disposal contract, procured with AEA’s help, was signed in June 2010 and the MBT is expected to come on-stream in 2013. Having tested the market for RDF outlets, the Council decided to commence procurement of treatment services for the RDF (and the CLO) through competitive tendering, rather than to trigger an optional Phase 2 of the MBT contract in the form of an onsite thermal treatment plant for the RDF. The Council’s analysis suggested that sending RDF to market could offer better value for money than building a dedicated plant in Phase 2.
To meet recycling targets, many municipalities are now starting to collecting food wastes for centralized composting or digestion separately from the residual household waste. The compost/digestate (unlike CLO) can be used in agriculture or horticulture as it is not classified as waste as it has been source segregated and treated in isolation of any residual waste.
Wouldn’t possible future separate collection of food waste in West Sussex starve the AD plant of feedstock? No, because the plant is based on a flexible design that can be adjusted to treat food waste from separate collections separately from food waste as part of the residual waste stream. This would allow a smooth transition at the MBT facility, ensuring it can cope with changing feedstocks in response to a possible shift to separate collections of food waste. This identifies the clear need for MBT facilities that are being built as part of 25 year local municipal funded contracts to be flexible in their design and operation.
ROC and RHI
Under the current Renewables Obligation (RO), support for large scale renewable electricity projects will be provided for up to 20 years, and will run until 2037. ROCs are able to be claimed for the biomass fraction of waste, and for EfW schemes this process is accredited under the CHP Quality Assurance (CHPQA) scheme until March 31, 2017 when the RO will be “vintaged” or no longer open to new accreditations.
In March 2011, the UK Government announced details of the Renewable Heat Incentive (RHI) with the aim of having the underpinning regulations approved by Parliament in the summer of 2011. This scheme will be introduced in two phases with the first being a long-term (20 year) tariff to support the non-domestic (industrial, commercial and public) sectors in 2011, and the second for the domestic sector to be introduced in late 2012. In 2011, eligible solid recovered fuel (SRF) for the RHI will be limited to SRF from municipal solid waste (MSW) and SRF waste streams containing no more than 10 per cent fossil fuel.
These two schemes will not only encourage greater delivery of renewable energy solutions, but more importantly will offer the waste sector a viable and attractive end point for materials collected from households and businesses.
—Excerpt from “The Shifting Landscape for Renewable Energy in the UK” (Waste Advantage Magazine; June 2011). For more information, read the full article at www.wasteadvantagemag.com.