MBT for Compost-like outputs (CLO)
Municipal Solid Waste (MSW) generated from households and removed by doorstep collection is a mixture of organic biodegradable waste, metals, plastics, textiles and glass. The unique CRS Mechanical Biological Treatment (MBT) Process pulverises the biodegradable fraction of the waste into a form that can be composted, segregates the waste to enable recyclable metals to be recovered and then converts the resulting material into a quality material that contains no glass sharps or needles. This material is now referred to as compost-like outputs (CLO). The regulatory framework for CLO's is still under consideration by the authorities, but currently, these materials are being beneficially used by blending with subsoils to form restoration soils for landfills and other despoiled areas.
The CRS MBT Facilities are purpose designed and easy to manage to ensure that the process of converting waste into a soil-forming material runs efficiently and smoothly. The facilities are low noise with odour containment and treatment for minimum impact on the local environment.
The MBT Process consists of four distinct phases in the processing of the waste. The first phase is a mechanical treatment. The waste arriving at the CRS MBT Facility is visually inspected to confirm the absence of unacceptable waste such as abattoir waste. It is then loaded into a large CRS Hydrum which opens the plastic rubbish bags and the drum slowly revolves at 4 rpm for at least 20 min, macerating the waste. When the process is complete, the material passes over a screen where oversized particles i.e. those larger than 50 mm, are removed. These oversized particles containing metals, plastic, textiles and cans then pass over a large magnet to remove any ferrous metals. This non-compostable material is sent to landfill. The remaining material, which is now transformed into a friable mass, can begin the second phase, the composting process. This first phase removes approximately 50% of the waste by weight.
The second phase is a biological treatment. The key to this phase is the Composting Tunnel. Built of pre-cast concrete walls and roof with an easily removable steel door and two lightweight hinged doors at both ends, it can contain 120-150 tonnes of waste at any one time. The Tunnel is equipped with air supply pipes based in the floor connected to an Air Handling Unit and full temperature monitoring equipment and radio-telemetry to provide the operator with full process management data.
The Air Handling Unit recirculates air, drawing in fresh air from outside when needed and venting used air to the atmosphere after first treating it with ozone to eliminate odours.
The temperature probes continuously record the temperature inside the waste to monitor the decomposition process and to ensure that the minimum requirement of 60°C for 2 days is attained. Using radio-telemetry site personnel know the current status of each Composting Tunnel or waste batch, as well as the history of the batch for process management and batch tracking ensuring compliance with the Animal By-Products Regulation (ABPR).
When the waste has completed the two barriers required by ABPR, i.e. 60°C for 2 days twice, it is transferred to an enclosed Maturation Area for the third phase of the process, maturation and bio-drying. Here the maturing compost remains until it is dusty dry.
The resulting product then moves into the final phase, the CRS G2S process, a second mechanical treatment. Here unwanted contamination by metals, glass and plastics is removed by passing over a screen. The particles that do not pass through the screen, oversize particles, are then milled which shatters the glass and reduces it back into ‘sand'. This material is then rescreened and the combined undersized particles can be used as a soil-forming material. The oversized particles are sent to landfill or may be further utilised in a suitable waste to energy facility.
The CRS MBT Process therefore biostabilises the organic fraction of the waste and produces a CLO by a simple to operate system in an enclosed, controlled environment with minimum impact on the local environment and in full compliance with the Animal By-Products Regulation. It:
- recovers metals for recycling
- converts paper, card, food and garden waste into dry compost which can be used as a soil-forming material or CLO
- treats glass and recycles it back into a useful sand that provides the mineral fraction in the ‘soil'
- reduces the tonnage and biodegradability of waste going to landfill
