Pile cloth proves an efficient filter

Southern Water and Morrison Utility Services have been trialling the Swiss produced Pile Cloth Media Filtration technology, and find it is a viable option for future consideration.

The long pile fabric enables filtered solids to be stored within the whole depth of the pile, ensuring consistent removal of fine particulate matterThe long pile fabric enables filtered solids to be stored within the whole depth of the pile, ensuring consistent removal of fine particulate matter

Morrison Utility Services has recently undertaken a series of trials for Southern Water that have seen innovative Pile Cloth Media Filtration technology introduced to the Hailsham North Water Treatment Works in East Sussex.

With the sand filters at Hailsham North undergoing a period of routine maintenance, Southern Water and Morrison US were keen to look at innovative filtration solutions that could offer improved efficiencies at Hailsham North.

The contract management team led by Morrison US operations manager Neil Hancock and project engineer Adam Stephens and Southern Water’s Nigel Palmer and Graham Welch, supported by external consultancy Setford Consultants, considered a number of options including lamella separator tanks, drum filters, submerged aeration filters and NSAFs. But the team decided that the innovative Pile Cloth Media Filtration technology developed by Swiss-based wastewater treatment specialist Mecana was the most appropriate and efficient engineered solution.

This project was not without its challenges. Cornwall-based Hydrok UK was appointed to undertake the installation of the Pile Cloth Media Filters, as well as the transportation of the plant from Mecana’s Reichenburg manufacturing base in the canton of Schwyz in central Switzerland.

Neil Hancock, operations manager at Morrison US, comments: “Although we were certain that the new plant would deliver significant benefits, the project was obviously going to be complicated by the fact that the technology was not available in the UK. Despite the inevitable transportation hurdles that the project team had to overcome, we worked very closely with the teams at Mecana and Hydrok and the unit was delivered by lorry from Switzerland within three weeks – seven weeks ahead of the standard ten-week delivery period.

“The installation process, including all steelwork, also progressed very smoothly ensuring that the new plant was fully operational within two and a half days of its arrival in the UK.”
The plant delivers a number of key benefits:

  • Highly efficient 3D filtration and solids separation
  • High throughput and an ability to withstand shock loads 
  • Continual operation during backwash cycles eliminating the need for standby units as solids are “vacuumed” away with the filter in operation
  • Gravity flow typical − only 300mm head required
  • Low backwash volumes and no requirement for any backwash system external to the filter 
  • No day-to-day maintenance requirements as the pile cloth media can be jet washed from the inside approximately once every two years
  • Small footprint
  • Easy cloth replacement
  • Low power and maintenance costs

Comprised of a series of very fine fibres, only microns in diameter, woven into a filter cloth less than 10mm in depth, the Pile Cloth Media Filters enable the removal of suspended solid particles from municipal wastewater, industrial process water, or storm water. The Pile Cloth Media combination creates a very large surface area for particle interception and removal but also allows for easy backwashing, which is activated once the head loss reaches 250mm.

"As a team, we are always looking to introduce new and innovative plant that can deliver cost savings and operational efficiencies"

The typical backwash frequency at the Hailsham North Works is once every one to two hours for approximately five minutes. Backwash volumes are typically around 2% of average flow with a vacuum pump returning dirty water back to the head of the works.

A key feature of the technology is the filtration material, itself, a “unique” long pile fabric that enables filtered solids to be stored within the whole depth of the pile, ensuring the consistent removal of fine particulate matter and the handling of very high influent solid concentrations.

The structure of the pile fabrics used are comparable to furs, which lie flat during the filtration process to form a tight layer of fibres. During the cleaning process the fibres straighten up briefly within the suction bar, enabling retained solids to be removed. This modified cloth filtration technique allows the use of much finer fibre materials, delivering higher separation efficiencies, whilst simultaneously enabling greater hydraulic throughput, extreme tolerance to shock loadings and minimal backwash effluent volumes.

In the event of a power failure the plant will continue to operate for extended periods as the filtration is passive and non-reliant on electricity. The de-sludge / backwash system can also be operated manually in the event of an extended power failure.

The filtration process is kept simple. Secondary effluent is filtered from the outside of the pile cloth media to the inside, allowing larger particles to settle and be removed separately by the bottom sludge pumps provided.

This prolongs the lifespan of the cloth and enhances the process as it prevents the media from blockages caused by larger solids as in the case of inside-outside Micro-strainers.

Backwashing, which initiates automatically once water reaches a certain level, uses pump suction to remove solids from the pile cloth. The process is extremely efficient as the fibres raise during the suction, ensuring the comprehensive removal of accumulated solids.

The filtering operation is continuous throughout the backwash process. Pile cloth filters are low maintenance systems with automatic control, no requirement for chemical cleaning of the cloths and low power consumption as energy is only required during the short backwash events, the rest of the filtering being typically gravity flow. The low overall head loss required across the system (500mm) ensures that the system will suit most hydraulic profiles.

Adam Stephens, project engineer at Morrison Utility Services, concludes: “The decision to trial the Pile Cloth Media Filtration technology at the Hailsham North Works has proved to be very successful with the unit performing well and initial results proving extremely encouraging.

“As a team, we are always looking to introduce new and innovative plant that can deliver cost savings and operational efficiencies to our clients.

“The considerable cost and maintenance benefits that these pile cloth filters provide far outweigh those of existing, standard methods, would make this process method a viable option for future consideration.”

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