Backwashing: a critical factor in water treatment plant performance

In water treatment plants, the quality of water output is determined by how well the filtration system is operating. A key ingredient in keeping the filtration system working at its best is the frequency and quality of backwashing processes.

Over time, the media in a water treatment facility becomes coated and even clogged by particles and debris. Regular filter cleaning is crucial to ensure the system remains efficient and the quality of the water output, sound.

“The effectiveness of the filtration system is the linchpin of every water-treatment program,” said Graeme Cooper, Managing Director of Tecpro Australia. “To keep it running at optimum performance, it is vital to regularly clean the filter, and this is done by backwashing.”

Backwashing involves shutting down filtration and reversing the flow of water to run backwards through the filter at a higher velocity, which dislodges particle build-up. Airflow is sometimes used to amplify the cleaning process, either before or during backwashing with water.

“Typically there are three different approaches to backwashing,” said Cooper. “Some systems use water only, while others use air and water consecutively, or air and water simultaneously.”

The optimal approach depends on the type and rate of particle build-up in the filter.

“It’s fair to say that the combination of air and water simultaneously gives the strongest scour rate, and therefore a more rigorous clean,” said Cooper. “During air backwashing, holes in the stem allow air to be pumped into the nozzles from where it flows up through the media, helping to dislodge material that has built up. The following water backwash raises the filter media and flushes away all the unwanted material.”

Installing nozzles with the correct size air holes (and/or slots) in the stem for air scouring is critical to achieving the right amount of airflow and back pressure. The location, dimensions and number of air holes and slots is another important factor in the design of the filter nozzle. For the nozzle to work effectively it is essential that the air holes and slots are specifically designed to suit the capacity of the backwash air supply.

“Nozzles that have a short stem without backwash holes/slots are not suitable for air scouring as they will use too much air and so they are not able to guarantee the equal air distribution in the total number of nozzles installed in the filter drain floor. They are only for use with water backwashing,“ said Cooper.

Cooper said that designing, constructing and installing the correct nozzles to suit system demands is fundamental to the effectiveness of water treatment plants.

“We help managers who are responsible for water plant maintenance to get maximum performance and life from their filters by selecting the right filtration and backwashing nozzle to match their needs,” said Cooper. “The ILMAP range of sand filter nozzles is particularly useful for system upgrades because it is available in 22 different models, eight standard stem lengths, eight types of thread and 10 different slot widths. This means there is a choice available to match the precise dimensions of systems of any age. ILMAP will also manufacture nozzles to individual client specification.”

Tecpro Australia is the exclusive Australasian distributor of the ILMAP range of sand filter nozzles and accessories, which are designed and manufactured in Italy.

“There are differing opinions regarding nozzle slot width but Tecpro Australia believes that it is preferable to have slot widths which are smaller than the smallest media particles that will come in contact with the nozzle,” said Cooper. “The slot widths in ILMAP’s sand filter nozzles are precision moulded so they are extremely accurate and reliable. ILMAP sand filter nozzles are also strong, durable and are available in a range of materials making them temperature and chemical resistant to suit any environment.”