Food / beverage
Wastewater / effluent
The Dairy Crest Davidstow plant in Cornwall, UK, is the largest producer of mature cheddar in Europe and the company’s most advanced cheese making creamery.
When the plant was updated with new cheese-making equipment in 2003, an upgrade to the existing effluent treatment plant (ETP) was required.
Various process solutions were presented to Dairy Crest on how to handle effluent from their new equipment and the technologies required to meet the stringent discharge quality consent for the River Inny. The company opted for Wehrle’s creative process engineering design approach, which proposed that the existing two stream activated sludge plants on-site were upgraded and MBR technology was added.
The ETP upgrade included refurbishment to minimise operational and environmental issues associated with noise, odour, and general appearance.
The detailed process design upgrade provided for effective pre-treatment, with improved inlet screening and larger capacity divert and balancing tanks to minimise possible shock loadings and provide a more consistent feed quality for ongoing biological treatment in the upgraded plant.
A DAF system was installed to reduce the organic load to the biological stage, with minimal use of chemicals under normal design conditions. It prevented the need to tanker away high strength wastewater, reducing the associated traffic from the main factory.
The biological treatment capacity of the ETP was increased by replacing the relatively inefficient high-rate CAS process with advanced MBR separation technology, which treats approximately 60% of the wastewater flow under normal load condition.
Separation of the activated sludge in the MBR system takes place using UF membranes rather than clarification, which enables operation at high activated sludge concentrations, promoting better oxidation, complete nitrification and reduced biological solids production.
The increased organic loading is treated in a relatively small tank volume, providing increased sludge age, with reduced surplus sludge for disposal and a consistently high quality of final treated water, which is suitable for direct river discharge.
The turnkey project provided a flexible hybrid solution that proved to be an asset during commissioning of the new cheesemaking equipment. The upgraded ETP treated all wastewater up to and beyond the parameters of Wehrle’s design.
The design offers operational flexibility to achieve optimum performance for each stage of the process, using an efficient biological approach to treating mostly soluble chemical oxygen demand (COD) in the creamery effluent, avoiding the use of additional chemicals, associated labour costs and increased chemical and sludge handling requirements.
The plant treats an average flow of 2000m3/day at a COD loading that was 7000kg/day during commissioning. Treated effluent has a biological oxygen demand of <9mg/l and total suspended solids of <12mg/l.