DE NORA TETRA FILTRATION – Don’t Underestimate the Underdrain

De Nora Water Technologies, in collaboration with Water & Wastewater Asia, hosted the De Nora TETRA Filtration – Don’t Underestimate the Underdrain webinar last December

In an attempt to share its expertise in water filtration, De Nora Water Technologies, in collaboration with Water & Wastewater Asia, hosted a webinar entitled De Nora TETRA Filtration – Don’t Underestimate the Underdrain last December.

Stanley Shmia, global product manager for De Nora Water Technologies and a member of the Water Environment Federation, shared with webinar attendees different underdrain options

Speaking at the webinar was Stanley Shmia, global product manager for De Nora Water Technologies, who shared with attendees on the different underdrain options, and explained how choosing the right filter underdrain solution and improve efficiency and bring peace of mind for water treatment facilities. In municipal drinking water application or pretreatment for desalination plants using gravity filters, the filter underdrain is one of the most important components contributing to overall system performance and operation – whether a new filter design or retrofitting an existing filter.

Also a member of the Water Environment Federation himself, Shmia explained that filtration is the process to remove total suspend solids (TSS) from both water and wastewater treatment plants. It can be used in any facility, whether is a water or wastewater plant, to remove solids. Moreover, drinking water regulations are now more stringent, driving municipalities to install reliable filtration that is high-performing, low maintenance, while lasting a long time.

As such, De Nora Water Technologies developed the De Nora TETRA LP Block dual parallel lateral underdrain, which provides an improved distribution of backwash water to the filter media through the use of dual compensating laterals. The De Nora TETRA Filtration system comprises six main components – clean effluent and backwash inlet; air header; De Nora Underdrain Blocks; De Nora TETRA media retention plates; filtration media such as sand and anthracite; and water troughs.

At the core of the LP Block is the dual laterals – the primary lateral is designed with one row of orifices for water and three rows of orifices for air; and the secondary lateral for recessed distribution orifices on the top of the underdrain.

De Nora Water Technologies, in collaboration with Water & Wastewater Asia, hosted the De Nora TETRA Filtration – Don’t Underestimate the Underdrain webinar last December

Explaining the uniform backwash flow from the top of block, Shmia said: “Unbalanced flow in the primary lateral creates an opposing flow that form a compensating velocity pressure gradient, which puts the secondary lateral into a uniform hydraulic pressure condition.” Hence, the dual parallel design ensures “even air and water distribution, efficient bed cleaning, and no dead zones is left out”.

When in operation, the backwash water enters the primary laterals and then passes through the control orifices into the secondary laterals. Backwash air is then distributed by the design of the upper control orifices between the primary and secondary laterals, providing even air distribution. Constructed of HDPE, the LP Block is also equipped with media retention plates to maximise the available filter tank depth. Careful quality control and testing during the plate manufacturing process is used to ensure that the media retention plates prohibit media pass through, and provide proper flow characteristics.

Designed to retrofit any air and water backwash scheme, the De Nora TETRA features improved distribution of backwash air and water while providing better filter performance and longer filter runs

The De Nora TETRA LP Block also features two optional designs – GroutGrip and Anchor-Rite. The former, which Shmia described “integral to the block”, increases resistance to uplift from the filter floor. Besides offering increased adhesion to filter floor, The LP Block with GroutGrip includes six rows of integrally moulded dovetail wedges that become embedded to the floor grout, offering 1.75 times the pull-out strength of a conventional underdrain block, De Nora claimed. As for Anchor-Rite, it fastens the block to the filter floor to prevent buoyancy.

“Overall, the LP Block is a lower profile design as it requires fewer parts and less grout, meaning it’s easier to install, less concrete, and lower costs. Low profile reduces the filter box depth for added savings on new construction,” he said.


Besides the highlight of the De Nora TETRA LP Block, Shmia also shared some successful installations of the solution around the region. In the Middle East, Toshiba Water Solutions Sohar Industrial Port located in Oman was faced with the issue where existing seawater reverse osmosis experienced high silt density index (SDI), turbidity, and fouling from seasonal harmful algae blooms (HAB). To resolve this problem, a rapid gravity filtration system using six dual-filter De Nora TETRA LP Block underdrains was installed between fine screens and ultrafiltration steps.

Closer to South East Asia, De Nora worked with the Manila Water Company (MWC) in the Philippines to meet the needs of the region’s population growth and increasing water quality regulations. To accommodate operation at higher flow rates, the company supplied 19 TETRA LP Block with GroutGrip to MWC’s Balara 1 Plant and Balara 2 Plant to provide a more effective backwash and allow for more efficient use of the available filter depth.

And over at a drinking water plant in South Vietnam, De Nora TETRA LP underdrain was deployed to treat the water plant with the capacity of 100,000m3/day. Besides meeting the local discharge regulatory compliance, this also marks one of the largest De Nora TETRA installation in the country.

The webinar is available for viewing.