Building a waste treatment plant is always a challenge, but add three different treatments types, the need to meet council targets, dealing with multiple contractors and meeting the environmental and future needs of the community it supports into the mix and it becomes considerably more complex.
This is the situation at the new Milton Keynes Waste Recovery Park. The local authority has decided to incorporate three separate waste management systems under one roof in an industry-first plant, with the mechanical treatment (MT) element designed by Stadler UK.
Milton Keynes Council already enjoys significant recycling success. The combination of a solid recycling infrastructure and good buy-in from residents has resulted in a recycling rate of 53.5% (2012/13), which is well above the English average of 42% for the same period.
However, key to the council’s ambitious plans, which include a 70% recycling rate by 2024/25, is the Waste Recovery Park. This facility, situated across the road from the council’s existing MRF, will see 132,000 tonnes of residual municipal waste processed every year, collected from residents’ non-recycling bins.
In terms of targets, the council currently has a ‘no mass burn’ policy, but it has also committed to reducing its current landfill percentage (approximately 35%) to less than 5% by 2019/20. The Waste Recovery Park is incorporating MT, advanced thermal treatment (ATT) and anaerobic digestion (AD) in one waste treatment site – making it the first of its kind.
This facility is not an MRF. Instead it is termed a ‘waste treatment’ plant. Significant amounts of clean and good quality paper, plastics, glass and cans are already collected by the council and processed at the other facility – also supplied by Stadler UK – so what it is dealing with is pure ‘black sack’ waste.
Stadler UK was commissioned to design and build the MT element of the plant by Amey- Cespa, which is responsible for the construction and operation of the facility, based on the company’s experience in complete sorting and treatment plants for the waste management industry. Complex it may be, but as with any system design, Stadler first needed to ascertain two simple but crucial factors: first, the composition of the material coming into the plant; second, what the plant operator wanted the end product to be.
Design of the plant is such that this waste will first be passed through trommels before going through ballistic separation for both 2D and 3D materials. Once this waste has passed through the mechanical sorting systems and the recyclates are removed, the prepared feedstocks will be diverted to the appropriate treatment system, either AD or ATT. By combining these three methods, the plant, with its unique logistics, will contribute to Milton Keynes Council delivering effectively on both its no burn and its aims for landfill reduction.
The primary consideration when this plant was designed was that the MT process sits in between the other two, and it had to be flexible in order to be able to keep processing the waste if the ATT or AD processes are full or offline. Municipal waste deliveries do not stop if part of the system needs servicing, upgrading or repairing so the MT plant design has to ensure it can cope with a number of operational possibilities.
Additional equipment has been included in the design to ensure the process is robust in order to fulfil the service delivery requirements of AmeyCespa to the council.
Another significant challenge for the design is keeping the plant clean. If you imagine what the bottom of your household waste bin would look like if no refuse bags were used and your rubbish was just piled in, and then multiply this by the sheer volume of household waste that will be heading to the plant, then you have some idea of the challenge faced in the design.
The amount of muck going through the machinery is immense. To deal with this and to keep the plant as clean as possible, a number of design features, including scrapers to clean the machinery and special chutes for getting rid of organic material into suitable containers, have been incorporated.
An additional factor to overcome was meeting the needs of the many companies involved in such a significant project. Stadler is contracted with AmeyCespa to deliver the sorting system. But there is also interaction with the main building contractor, combined with the process contractors for the AD and ATT plants – all of which have their own inputs and opinions for consideration.
Planning for all future possibilities is a key factor in plants’ ongoing success. There is rarely any situation that does not change; this can include issues such as a change in the type and volume of feedstock, fluctuating prices for different materials, meeting modified targets and changes in government. As a result, the new facility has been planned to be as fully flexible to the potential changing demands placed upon it as possible.
As well as recovering viable levels of valuable resources from waste that previously held no financial value, the plant design should significantly contribute to Milton Keynes meeting its targets to reduce waste sent to landfill to less than 5% by 2020. In addition, the ATT facility will produce enough electricity to power 11,000 homes, with the AD plant producing renewable energy and a compost-like product which will be used on brownfield sites.
Overall, Milton Keynes Council anticipates savings of £50m against the cost of landfill during the life of the facility, based on the current landfill cost of £80 per tonne.
The facility is currently in the advanced stages of development, with the plant due to be commissioned in early 2016 and extensive testing planned before it becomes fully operational in September 2016. This will be the first fully integrated waste treatment plant Stadler has been involved in, and the potential landfill saving, increased recycling and energy and product recovery makes it an exciting project.
Trevor Smart is UK sales manager for Stadler UK