ULTRAVIOLET TREATMENT in wastewater plants
The rapid expansion of De Doorns – a town located in the Hex River Valley in the Western Cape – has put added pressure on its already scarce water resources. As a result, a 1.5 Mℓ/day reuse plant was designed, engineered, manufactured, installed and commissioned to help save water.
From here, secondary municipal wastewater is treated to produce irrigation water (in place of potable water). The plant can be upgraded to process 2.5 Mℓ/day.
This is how the plant operates:
Wastewater filters through the inside of the drum screen to the outside by gravity pressure and flows to the ultrafiltration feed tank. From here, water is pumped through the ultrafiltration, granular activated carbon filters and ultraviolet (UV) light into the final water tank.
- Drum screen
Wastewater filters through the inside of the drum screen to the outside by gravity pressure and then flows to the ultrafiltration feed tank. The drum is fully automated – it starts to turn once a specific water level is reached in the drum – and it is automatically cleaned with a set of nozzles once the drum begins to turn.
Water from the feed tank is pumped into the ultrafiltration skid for removal of microbiological particles and suspended solids. The ultrafiltration system is a pressurised, pre-engineered membrane system with a modular building-block configuration, which simplifies design and operation, and reduces installation costs. It utilises the latest advancements in membrane technology where an enhanced PVDF membrane is 20% to 25% more permeable, which translates into lower transmembrane pressure, using less energy and reducing ownership costs.
- UV treatment
The advanced oxidation process (AOP) of UV radiation in combination with hydrogen peroxide (UV/H2O2) is well known and documented. The AOP process targets micropollutants through an oxidation process with the hydroxyl radicals.
Unlike chlorine, UV disinfection does not degrade the water. Xylem’s Wedeco LBX Series is a closed-vessel UV disinfection system, designed for energy-efficient disinfection of wastewater, water reuse, surface water and process water. With more than 1 000 installations worldwide, LBX UV systems have been tested extensively.
Manual maintenance is required but the operation of the entire system is automatic, with minimal input from operators. Xylem’s Wedeco LBX UV systems employ low-pressure, high-output, amalgam Ecoray UV lamps and ballasts. The Ecoray is used in combination with the variable power option and this results in excellent energy efficiency under all operating conditions. In dimmed mode, there is a 20% average energy saving.
- Granular activated carbon (GAC)
GAC media filters are used for the absorption of dissolved organics and micropollutants. Regular backwash sequence fluidises the bed to reduce the risk of channelling in the media.
These water recycling technologies save both water and money.