Westbury: Northacre Resource Recovery Centre Mechanical Biological Treatment (MBT)
Northacre Resource Recovery Centre Mechanical Biological Treatment, Westbury
What is this site?
The site is located on Stephenson Road (NGR ST8574451869) in an industrial area to the north of Westbury.
The facility accepts residual municipal solid waste (MSW) predominantly from household waste collections. The wastes are those which have not been removed or segregated previously for recycling prior to disposal and arrives as black bag waste.
The Mechanical Biological Treatment (MBT) process carried out at the facility, produces a solid recovered fuel (SRF) / refuse derived fuel (RDF) and helps reduce the amount of biodegradable waste being landfilled. It also separates out other recyclable materials, for instance ferrous metals and aluminium.
What activities are covered by the environmental permit?
The permit for Northacre Resource Centre LP3491EE was issued to Hills Waste Solutions Limited by the Environment Agency in 2009.
The permit sets out the types of waste that can be accepted and the techniques used to treat the waste. It also includes infrastructure standards, permitted emissions and reporting requirements.
The permit for this site was last reviewed in 2020.
How do we regulate this site and check for compliance?
In line with the permit conditions set we will undertake regular visits of the site to ensure compliance with conditions of the permit.
We will review the operator’s documents / data submissions.
Where raised odour levels have been reported by the public, we will increase the frequency of visits to establish the effects of the activity on the area.
Reception and pre-treatment
Bio stabilisation (Bio-drying hall)
Mechanical refining (Refinement)
Baling, wrapping and storage (warehouse and despatch)
How does the Mechanical Biological Treatment process work?
The plant consists of four main areas:
Municipal Solid Waste (MSW) is delivered on refuse collection vehicles and deposited into reception pits. The material is then moved from the reception pit by automatic cranes/conveyors through a drum screener that creates two waste streams: oversized material (anything over 220mm), and undersized materials (primarily the biodegradable fraction).
Oversized material is collected in a dedicated storage bay where it is sent directly to the solid recovery fuel (SRF)/ refuse derived fuel (RDF) refining plant. This stream is composed of biologically inactive material (typically plastic, paper, and card) and is not suitable for biological treatment.
Undersized material, the biological active fraction, is collected in a second dedicated storage bay before being placed in windrows (sectors) within the bio-drying hall, by automated cranes.
An automated crane moves material from the undersized storage area into the main bio-drying hall, creating windrows of approximately 3 to 5 metres in height. Air movement/extraction through an underfloor area of the bio-drying hall assists with the drying process and stabilisation of the material by removing moisture in the air flow. It also acts to prevent the windrows from overheating by removing heat from the body of waste.
Each windrow is managed separately to maximise bio-stabilisation. Air is drawn through the material to promote aerobic decomposition and oxidation of the organic content for a period of up to 15 days. During these 15 days, the windrows remain static. Once a windrow is completed its 15-day cycle, the stabilised material is sent to the refinement area. The windrows are filled with new waste and emptied of stabilised decomposed waste on a rotational basis.
The time that waste is held in the bio-drying hall is monitored through the control system. The temperature and air flow within each windrow is monitored and air flows can be adjusted to optimise the drying process and/or heat removal.
Through the refinement area, material which is unsuitable for SRF production is removed by: primary shredder, drum screener (20mm mesh), air drum separator, magnetic belt, secondary shredder (SRF production only), Eddy current separator, conveyors, chutes, dust extraction system.
The SRF/RDF material generated by the mechanical refining process enters the warehouse for baling and wrapping. The SRF/RDF, once baled and wrapped, is stored in the warehouse in preparation for loading onto enclosed trailers and transfer to energy from waste (EfW) facilities.
The facility accepts up to 90,000 tonnes of waste per annum.
Timeline
2021
Residents reported odour concerns to ourselves.
The odour was identified as originating from the bio filter, which needed replacing.
In summary, air collected within the waste treatment buildings passes through a three-part bio-filter. This is a filter which uses natural materials (media) and biological processes (bacteria) to remove odour. The materials in the bio filter had reached the end of their useful life and needed to be replaced in all three parts. Work started to replace these bio-filters on 14 June 2021 and involved removing all the ‘spent’ material and carrying out a deep clean of that section before adding new material. The deep clean and replacement of filters took 18 weeks. Hills installed extra deodorising units in their buildings to help reduce odours whilst refurbishment of the bio-filters was underway. The site also used a deodorising agent at their site boundary, again to help reduce any smells off site.
2025
Following an increase in odour reports. We required the operator to carry out additional testing of the biofilter and odour control measures on site. We believed that the site is not currently taking all appropriate measures to reduce odour. The operator has installed additional extraction within the building to ensure that negative pressure is maintained at all times. Negative pressure should mean that less odour escapes from the building. The operator continues to work with us to identify and use all appropriate measures.
Hills undertook additional monitoring as requested by the Environment Agency as refurbishment progressed.
We are requiring the company to make improvements to reduce odour. These include increasing the height of the biofilter stacks to meet Best Available Techniques (BAT), improving the containment of odour within the building and compliance with the limits within the company’s permit and BAT.