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When Britain’s biggest provider of higher welfare pork wanted to reduce processing plant sludge transport costs, WCS Environmental Engineering was not only able to reduce carbon emissions, but also drive green energy generation, explains Joanne Allen Head of Business Development. 

Pilgrim's UK is ambitious about energy and carbon emissions reduction targets and has pledged to become net zero by 2040. It has already reduced its companywide direct and indirect carbon emissions by 62.5% since 2019 and its indirect emissions in the supply chain by 9%.   

Pilgrim’s UK pork processing plant in Spalding, Lincolnshire, is no exception to this net zero target and saw an opportunity to reduce sludge tankering journeys to and from the facility. The company already treats its own wastewater which is processed through a dissolved air floatation (DAF) treatment system to meet high environmental trade effluent consents. 

A by-product of the DAF process is liquid sludge, which was historically collected from the plant and transported offsite up to six times a week for further processing by the sites waste management company. This was costing the site not only time and money but also carried a high carbon footprint. 

The Pilgrim's UK engineering team wanted to investigate the possibility of adding an extra stage to the wastewater treatment process to dewater the sludge onsite. This would reduce the cost of transportation and associated carbon emissions.  

The team also wanted to find a use for the dewatered sludge, to help realise Pilgrim's UK circular economy ambitions in designing waste out of the pork production process.  

Andrew Hill, Site Services Manager at Pilgrim's UK said, “Pilgrim's UK has ambitions to reduce its carbon footprint as part of its pledge to become net zero and reduce onsite waste through design and implementation of circular economy processes. The engineering team wanted to investigate the possibility of dewatering onsite, to reduce the cost of transportation and carbon emissions, and to see whether the dewatered sludge could be useful or had value.” 

Test and analysis 

Pilgrim's UK approached the engineering team at WCSEE to carry out a free laboratory test and analysis to find out more about the composition of the sludge and understand treatment options.  

The technical team at WCSEE then designed and developed optimal chemical and mechanical treatment options to economically process the sludge at the Pilgrim's UK Spalding plant. This involved a trial installation of the screw press for five days to demonstrate its dewatering and sludge thickening capability. 

The screw press model supplied was specified to meet the volumes of sludge the site was producing along with the correct blend of chemicals and precise dosing measurements. The plant was also assessed to identify the best location and configuration for the Volute Screw Press, including access to power and water. 

The 6m containerised unit, constructed off-site, was placed inside the existing processing plant containing everything Pilgrim's UK needed to start processing the sludge.  

Andrew Hill said, “With the screw press’ plug-and-play capabilities, the team quickly adapted to the technology, and after a five-day trial period, it was decided to extend the trial by directly renting the unit from WCSEE, to further understand the return on investment.”  

WCSEE Screw press and engineer close up (web res)

WCS Environmental Engineering process engineer with a screw press on site

Positive ROI 

The trial showed that the dewatered sludge produced at the Spalding site had a potential gas yield that could be used to generate biogas electricity. Pilgrim's UK was able to send the dewatered sludge to the nearest anaerobic digestion (AD) plant which proved to have such a high gas yield it was valuable feedstock for biogas electricity generation.  

Since the installation of the screw press, Pilgrim's UK has seen more than an 80% reduction in sludge volumes overall and is now only sending dewatered sludge cake from the AD plant once a week on average. This process is now operating at zero-cost due to its high biogas electricity generation value. 

The trial has provided an immediate return-on- for Pilgrim's UK and resulted in the three-month rental of the screw press becoming a full purchase.  

Pete Cranney, technical sales manager at WCSEE said, “Pilgrim's UK has seen very positive results from its trial, and it has been a privilege to work with the team at the Spalding site, from initial enquiry to delivering dewatered sludge cake on a permanent basis.  “The initial analytics service is offered at no cost to the client, which allows site to prove to themselves the suitability of the technology, the potential cost savings of the project, and the value of the Volute Screw Press as the most attractive return on investment option on the market.” 

Water and energy reductions 

The Volute Screw Press offers thickening and dewatering of DAF sludge with the addition of a self-cleaning filter that prevents clogging and enables constant dewatering without using large volumes of water. This delivers stable and constant dewatering, achieving up to 99% efficiency savings against belt presses, and 92% against conventional screw presses. 

Operated automatically by a 24-hour sensor control if required, the Volute Screw Press also requires 70% of the footprint of standard screw presses, and 5% of the power usage of a comparable centrifuge. 

Along with the direct sale of the screw press, WCSEE has entered into an ongoing relationship with Pilgrim's UK, which includes repair and maintenance along with chemical support with an optimised polymer used for the dewatering process. 

Pete Cranney said, “With approximately 5,000 Volute Screw Presses already in operation across Europe, WCSEE is seeing accelerated demand in the UK due to tighter environmental consents and sludge management regulations, along with growing interest for more sustainable processes in the food and beverage sector.  

“The screw press is an ideal solution for this sector and WCSEE is pleased to welcome Pilgrim's UK to our long list of valued customers seeking a simple to operate, simple to maintain, and simple to service screw press that cuts costs whilst delivering sustainability goals.”  

Screw press image and engineer

WCS Environmental Engineering process engineer operates a screw press on site

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