Hydrotech Disc Filter Systems - a flexible filtration system

Reducing solid particles by between 40% and 100% for fine solids removal from water is enabled only through Veolia's Hydrotech® Disc Filter Systems. This patented system, which provides continuous water filtration, has the advantage of low power consumption, reducing overheads and contributing to a lower environmental footprint. In addition, it produces effluent with low turbidity and low total suspended solids while serving as a barrier against Helminth eggs. Importantly, this system can be used in multiple water filtering processes.

Hydrotech® Filter Systems, part of the Veolia Group, is the world's leading manufacturer of woven cloth filtration systems and micro-screen filters. Its disc filters have proven to be the ideal filter media for removing solids and assisting with product recovery and is therefore used in a number of processes application solutions.

Hydrotech® disc filter systems can be implemented as a secondary treatment for the Anoxkaldness™ MBBR process and designed as an additional treatment step following ActiFlo®, the balanced flocculating clarifier, providing additional polishing. However, the most common disc filter application is tertiary treatment of clarified effluent from activated sludge. Many applications recycle the high quality effluent from the disc filter in irrigation and cooling towers, for example, as well as many other applications.

How it works

The disc filter is manufactured with several discs mounted on to a central drum. The drum is rotated periodically while a moving nozzle assembly backwashes the filter media in order to maintain continuous flow through the unit.

Hydrotech's propriety woven filter media is attached to individual media panels which are installed on each side of the filter discs. Gravity facilitates the water flow into the unit which then passes through openings in the drum to the inside of the filter discs before moving through the filter media panels. As solids collect on the filter media, the flow of water is impeded and the water level inside the drum rises. The raised water level triggers a backwash process without stopping the filtration process, with the water being discharged over weir.

As the backwash cycle begins, clean media is rotated into the flow path and the water level in the drum reduces. The backwash cycle continues to remove solids from the previous submerged media. In addition, while the discs are rotated a small portion of treated water is pumped at high pressure to the nozzle assembly which, with a Hydrotech-patented oscillating spray bar, reduces the amount of water and power required for backwash.

The high-pressure spray clears the solids from the filter media into a sludge collection trough that carries the sludge out of the disc filter. Once the dirty panels have been cleaned the backwash cycle ends.

Veolia's Hydrotech disc filters result in an approximate 20% smaller footprint when compared to sand filters; have low installation and operational costs contributing to reduced bottom line costs, comprise a simple design requiring minimal maintenance, therefore contributing to increased uptime; while its modular construction enhances product flexibility.

Case study

Mossel Bay Municipality - South Africa's largest desalination plant

In 2010, the worst drought in over 132 years caused the southern Cape declared a disaster area. The only solution was to find a way of utilising the region's only constant water source - the ocean. Veolia Water Technologies, South Africa, was awarded the contract to design, manufacture, supply, maintain and operate a turnkey seawater desalination plant 10 times bigger than anything of this nature previously built in South Africa. The severity of the drought required the plant to be up and running in record time. The maintenance and operation contract was for an initial three-year period.

Water treatment processes used

  • Seawater is pumped to land from an intake located 600 metres offshore.
  • Using the Hydrotech® Disc Filter System, this water passes through drum screens, which retain particles greater than 500 microns in size, removing kelp, seashells, sand and other impurities. The impure water is then conveyed to a dedicated brine tank where a holding tank stores this fine screened water.
  • To prepare seawater for the reverse osmosis (RO) membranes, six dual media filters remove micro particles that could foul the RO membranes.
  • The RO process involves passing screened and filtered saltwater through semi-permeable membranes at extreme pressure. This causes the salt to stay behind while pushing through desalinated water on the other side. The concentrate (brine) produced during this process is sent to a dedicated brine tank.
  • The desalinated water is lifted from the RO units and transferred into two product storage tanks.
  • Five mega litres per day of desalinated water is pumped to a storage tank for use by PetroSA, while the remaining 10 mega litres per day is treated chemically to kill any bacteria and balance the pH - ensuring water is safe for human consumption.

The Mossel Bay Municipality oversees the service delivery of over 120 000 residents in an area that occupies roughly 2 000 square kilometres of the Cape Province in South Africa. Located 400 kilometres to the east of Cape Town, the municipality features a commercial harbour, commercial farms, a gas-to-liquids refinery and also plays a huge role in the tourism industry. The gas-to-liquids refinery is owned and operated by PetroSA, one of Mossel Bay's largest water users, as well as contributing to the city's economy as its largest employer.