Steam goes on-stream: A new solution for waste treatment in the UK?

Click here to enlarge image Steam technology - having been used in sterilization procedures for well over 100 years - has recently been adapted for the treatment of municipal solid waste. And it is attracting growing interest in the UK. by Guy Robinson Recovering value from waste materials depends to a large extent on effective separation. As an industry, we think in terms of ‘mining’ different waste streams for commercial scrap, or separating high calorific-value material to produce refuse-derived fuel. And, as members of the public, many of us think in terms of running one bin for food waste, one for paper, another for tins and a fourth for plastic (aside, of course, for a container for non-recyclables). But source separation is not always easy. In dense, high-rise flats - or even in busy places of work - there may not be scope for implementing a multi-stream recycling programme. And active support for ‘hands-on’recycling is not universal. In this context, it is not surprising that both the private and public sectors are examining the technologies available for treating mixed waste. One option that is attracting a growing interest in the UK is steam treatment - otherwise known as autoclaving. Steam treatment of waste - the basics We know about the use of steam generated during thermal treatment, which can then be used to generate electricity through gas turbines. Steam can also be put to work earlier in the process to sterilize the waste materials, using moisture, heat and pressure to kill off micro-organisms. Steam has been used as a treatment method for medical waste for many years (see box on the right), but its application to municipal solid waste (MSW) is more recent. The main advantage of steam is that it sterilizes the waste to produce clean recyclables that can be easily separated (unlike raw mixed waste). In addition, steam reduces the volume of the material by over 60%. Some of the technologies available in this sector are covered in the following section. This coverage is not intended to be comprehensive, but indicates some of the companies that are currently developing this technology for application in the UK. Sterecycle’s system Sterecycle - not to be confused with Stericycle mentioned in the box below - operates the Sterecycle® system, at the heart of which is a series of interconnected steam-conditioning autoclaves. Unsorted household bagged waste is introduced directly into the vessels and steam and pressure is applied at over 140°C. A combination of the steam pressure and the rotation of the vessels break down the organic fraction of the waste into a fibrous biomass, and sterilize and steam-clean the inorganic fraction. One aspect that Sterecyle is keen to emphasize is that other treatment solutions such as ‘mechanical-biological treatment’usually pre-treat waste by shredding or ball milling, which leaves a high percentage of plastics, metals and other contaminants in the organic fraction. As a result, the material produced is low-quality and can only be landfilled or burnt. In contrast, the Sterecycle process produces a high-quality clean biomass fibre that can be used as a green energy source, in land remediation or washed to produce a high-quality paper pulp. The Sterecycle process produces a high-quality biomass that can be used as an energy source or in land remediation Click here to enlarge image Sterecycle raised financing in October 2005 to build its first plant in the UK, which is now nearly complete and will have a capacity of 80,000 tonnes per annum of household waste. In September 2006 it raised a further US$15 million of equity financing from the leading US investment bank Goldmand Sachs. Michael Linse, Executive Director of Goldman Sachs and Head of Renewable Energy Investments, has joined the Sterecycle board. With debt facilities, the company now has over US$75 million of funding to build another four plants around the UK. Estech Estech Europe’s technology comes from the US. In 1992 a demonstration plant was built there for the steam treatment of waste. Nine years later, the European marketing rights for the process were acquired by Waste Cleansing Reduction & Recycling Ltd, which later merged with Tass Environmental Technology to form Estech Europe. From then on, Estech Europe worked on the technology for the European market. In 2003, Estech constructed a mobile demonstration plant capable of processing 5000 tonnes per year. Plans for three 100,000 tonnes per year plants are currently at an advanced stage, with planning consent and waste management licence for one of the sites now achieved. Estech’s Fibrecycletechnology processes unsorted or residual waste in a rotating autoclave, converting up to 80% of MSW into sterilized secondary recyclables. In practical terms, this means that a typical 20-tonne input load could output: 1.8 tonnes of mixed plastics 0.7 tonnes of ferrous 0.2 tonnes of non-ferrous 12.8 tonnes of cellulose fibre 1.0 tonnes of miscellaneous aggregate 3.5 tonnes of sterilized waste (including oversized items, glass, stone, wood and textiles) which can be further separated or sent for final disposal. PURAC With steam as the unifying theme, it is not surprising that companies from the water industry are entering this market. A case in point is PURAC, which has worked with Tempico since 2004 to market a process known as the Rotoclave. Currently there are approximately 100 Tempico Rotoclave units at 60 sites worldwide. As the name ‘Rotoclave’suggests, rotation of the autoclave is particularly important. Generally speaking, waste needs to be rotated inside an autoclave in order to ensure uniform heating and the generation of a product that is as homogeneous as possible. There are two main options for rotating waste in this way. The main vessel can either be made to rotate, or it can remain stationary while an internal vessel rotates. Purac has opted for the latter of these two strategies - which it claims overcomes many of the problems associated with rotating the main vessel. Estech’s Fibrecycle mobile plant autoclave converts up to 80% of waste into secondary recyclables Click here to enlarge image Cleanaway has recently awarded the contract for the Rainham Autoclave Processing Facility to Purac, which is expected to have a throughput of 160,000 tonnes per year. The plant will treat unsorted residual waste from the London Borough of Tower Hamlets, and will produce a range of outputs for recycling plus sterile floc for further treatment and energy recovery. The STAR system Again, steam is the key factor in the Steam Treatment And Recycling (STAR) system, developed by KP Wellman. The STAR system claims to handle - though no operational plants have been built in the UK as yet - up to 400,000 tonnes per annum at any given site using a modular design. It takes unsorted municipal solid waste, treats it with high-pressure steam, which breaks down the waste and sterilizes it. Once treated, the recyclable materials, ferrous, aluminium, plastics and glass are easily extracted and baled. For example, the process takes in food cans or glass jars, eliminates the bacteria and strips off all the labelling, leaving the bare metal or glass clean and ready for recycling. The STAR system gives several options for the end-use of residual waste, namely: firing through a biomass boiler, thus producing high-pressure steam which in turn is used to generate electricity (via a turbine) co-firing with coal or biomass to generate steam at a power station to produce a syngas suitable for fuelling a series of gas engines that generate electricity. Purac’s Rotoclave uses the rotational motion of an internal vessel to ensure uniform heating and a homogeneous product Click here to enlarge image And it is this closed-loop thinking that KP Wellman hopes will differentiate its offering from the competition. The company has power purchase agreements to supply 520 MW of green energy into the UK grid and is confident that it has in place a ready market for the fibre that is produced. Future potential Steam autoclaving has numerous benefits. First, there is the clear benefit of being able to handle mixed waste, thus reducing collection costs and simplifying the life of household owners. But also there is scope for increased landfill diversion (reducing landfilling by as much as 80%) and the production of recyclates and refuse-derived fuel. The STAR system takes in unsorted waste to produce a sterilized residual waste that can be used in several ways Click here to enlarge image It is therefore not surprising that further research is being undertaken to gain a clearer understanding of the impacts and commercial longevity of this technology. For example, a project supported by the Defra (Department for Environment, Food and Rural Affairs) Technology Research and Innovation Fund under the New Technologies Programme is currently investigating the benefits and drawbacks of autoclaving. The main objectives of the project are: determine whether autoclaving changes the rate of biodegradation of organic materials in composting and anaerobic digestion, and to what extent determine whether the product from bioprocessing can meet PAS100 requirements for heavy metal concentrations (PAS 100 refers to a Publicly Available Specification for compost, published by the British Standards Institute) examine the potential effects of thermal pre-treatment on release of gas during subsequent bioprocessing evaluate the polluting load of the organic fraction of the autoclave output, and any associated wastewater. The work is being carried out by a consortium that includes The University of Leeds, The University of Southampton, Cemagref and CalRecovery Europe Ltd. The reports from this project are being completed at the time of this magazine going to press. Early results indicate some areas for further research, including strategies such as anaerobic digestion and heat recovery to offset the energy demands of the system. Overall the project draws a number of positive conclusions that reflect the future potential of this technology. Guy Robinson is Commissioning Editor of Waste Management World.e-mail: wmw@jxj.com Note 1. Jerry Quickenden and Nic Tudge, Autoclave pre-treatment: enhancing municipal solid waste (MSW) separation and recovery, CIWM Poster Paper, June 2006, UK Acknowledgements Thanks to representatives of Sterecycle, Estech, PURAC and KP Wellman for providing information on their technologies. Also thanks to Professor Ed Stentiford from The University of Leeds and Defra for their kind co-operation. Medical waste treatment - then and now Steam autoclave treatment has been used for sterilizing medical instruments in hospitals and the treatment of waste in laboratories for many years. Commercial steam-heated autoclave was first used in medicine in 1889.1 According to Dwight Morgan, Chief Engineer with MCM Environmental Technologies, Inc., US, the first commercial steam sterilization process for infectious medical waste was introduced in 1978. Since then the technology has been adopted by various companies worldwide. A leading player in the field of medical waste autoclaving is Stericycle. Founded in 1989, Stericycle now operates 45 treatment/collection facilities and 105 transfer/collection sites throughout North America. It claims to be the largest and only US full-service provider and provides services to 339,000 customers worldwide, including a growing presence in Asia, Australia, South America, United Kingdom and Ireland. It has acquired over 100 companies since 1993, including - for example - White Rose Environmental Limited, UK in June 2004 and Sterile Technologies Group Limited, UK in February 2006.