Sludge dewatering: DAF system helps sort the sheep from the goats

3 min read

A UK sheep pelt tannery required a DAF sludge dewateringsystem that could cut costs while dealing effectively withvery wet, fatty animal waste. GEA installed a system featuring a decanter which reduced sludge by 90% and made a positive environmental impact.

Hutchings & Harding produces chamois leather from sheep pelts – resulting in a range of fatty animal waste requiring dewatering.
Hutchings & Harding produces chamois leather from sheep pelts – resulting in a range of fatty animal waste requiring dewatering.
GEA Westfalia's UCD205 high efficiency decanter saved money for the UK tannery.
GEA Westfalia's UCD205 high efficiency decanter saved money for the UK tannery.

The current drive for sustainable industrial processing solutions and environmental best practices is matched by the demand for cost effective waste recycling and disposal options. With utility costs escalating and waste disposal costs and landfill taxes increasing year on year, many companies are seeking ways to reduce these expenses and evaluating ways to create revenue streams from by-products and waste which was once discarded as worthless.

A recent dissolved air flotation (DAF) sludge dewatering system installed by liquid/solid separation specialists GEA Westfalia Separator UK Ltd demonstrates how, with minimal investment, one company has not only reduced waste disposal costs but can potentially generate an income from a new revenue source from their raw material and further develop best environmental practices.

Results from the installation that integrates two tried and tested technologies, dissolved-air flotation and centrifugal separation, demonstrate how sustainable profits can be achieved from sustainable practices. 

Dewatering animal fat

Hutchings & Harding Ltd, a specialist tannery in Cambridgeshire, UK, required a DAF sludge dewatering system for its animal fat waste products. DAF systems are increasingly used in animal/meat/food processing applications to remove suspended solids, fats, oils and greases from a variety of wastewaters. Their high process rates, small footprints and flexibility of operation being seen as advantageous in these applications. DAF systems use air to create microbubbles to which the solids attach and float to the surface to be skimmed off.

“One of the disadvantages of such systems is the cost of disposal of the very wet waste, and it was this problem we addressed at the Hutchings and Harding Ltd tannery,” says David Cawdery, market manager – industry, from GEA Westfalia Separator UK Ltd.

“Hutchings & Harding is a renowned and long established tannery producing chamois leather from sheep pelts and they utilise a DAF system to recycle and clean the water used in the processing of skins. The largely liquid DAF sludge was previously transported off site to landfill and it was these costs that we were asked to reduce.”

Reducing sludge

Using previous knowledge of similar installations and applications, GEA Westfalia prepared system designs and costing projections for reducing the amount of DAF sludge for disposal by approximately 45% to produce weekly disposal cost savings. The system is based upon the company's UCD205 high efficiency decanter that is compact, reliable and simple to use and maintain. DAF sludge is fed to the decanter using a Seepex pump, specially designed for handling a high volume of fatty solids.

“When GEA Westfalia Separator UK Ltd presented their proposals to us for dewatering the DAF sludge utilising a UCD205 Decanter we were confident the system would work and give us cost savings but were finally convinced after a week's on site trial with their mobile unit,” says Steve Pool, technical manager, Hutchings & Harding Ltd. 

Ensuring acceptable dryness

The installation includes a specially designed chemical dosing unit from Biochemica that supplies regulated amounts of polymer chemicals that help breakdown the solids and liquids in the DAF sludge to improve dewatering rates. The dosing rate is easy to adjust and together with decanter controls ensures the acceptable ‘dryness' of the end waste product.

“Now that the equipment is installed and working at production capacity we have been surprised just how effective it is and have been astounded by the amount of water that is removed from the DAF sludge,” said John Ettling, MD, Hutchings and Harding Ltd. “We are now seeing an actual 90% reduction in the DAF sludge, through the system. We believe this could be improved upon even further but as we have no need for an absolutely dry product we are very happy with the production results.

“The disposal cost saving potential we are seeing means we can also now see the potential for us in removing from the protein fibre and fat rich sludge, the oil as a separate fraction to produce a saleable by-product. We are also investigating further cost savings and revenue generation in putting the fleshings through the decanter,” he added. 

Secondary decanter use

Plans to optimise the use of the GEA Westfalia Separator decanter have been discussed, as it is currently running for only three hours a day with a half to one tonne of DAF sludge throughput per hour, which is under the machine's capability. This secondary use involves macerating the flesh and adding water to produce a slurry which can then be fed through the decanter system in order to separate, and then sell, the oil fractions. This will also save costs on the removal of a lower weight dewatered end product, potentially making the process a self funding and profitable alternative to current disposal routes. 

Creating cost savings

“The cost savings on the DAF sludge disposal plus the additional or optimised service of the decanter system shows an acceptable payback time on this systemwith a very pleasing return on the customer's investment,” said Cawdery. “There are also the added environmental benefits associated with water recycling, reduced vehicular transport of waste, minimal landfill requirements and the best use practice of a natural resource, the sheep skins themselves.

“This installation demonstrates clearlyhow DAF system users can add a further stage to their process that can reduce the amount of sludge for disposal and create cost savings that equate to rapid paybackof investment.”