Engineering teams from Tema Engineers were invited to review the water treatment needs of Denman, a town with a population of 1500, located on the Hunter River. The Denman area water supply is pumped directly from the Hunter River. The water was found to have varying levels of contaminants at different times, with particularly high turbidity and hardness. Their team were asked to recommend and implement a solution that would create a secure, high quality water supply to meet public health standards.
Having tested the Hunter River water supply to Denman during a six month period, Tema engineers installed a customised, end to end water treatment plant at the Denman Service Reservoir site. The new plant has the capacity to produce 2.7 megalitres of treated Hunter river water per 22 hour period. The water treatment plant is designed to meet the fluctuating rates of turbidity and hardness and is capable of operating 24 hours per day, every day of the year.
Sand Filtration - raw water from the Hunter River is filtered using six Arkal rapid sand pressure filters. These filters are designed to remove large particles that may affect the membranes in the next filtration stage. Aluminium Chlorohydrate (ACH) is dosed as a coagulant prior to sand filtration to increase effective removal of the particles during this stage. Membrane Filtrat ion - the pre-filtered water is passed through an ultra filtration (UF) system consisting of 14 modules (4 elements per module) of Norit Xiga UF membranes. The membranes remove suspended solids from the water as well as bacteria and viruses. The system is backwashed by reversing the flow direction through the membrane at regular intervals to remove any residual solids. The membranes also undergo chemical enhanced backwashing approximately once a day to remove organic substances. Filtered water from the system is stored in the product water tank on site where it is disinfected with sodium hypochlorite and pH adjusted before flowing to the service reservoir.
Water Softening - If the raw water is too hard then a split stream dealkalisation process is used to remove the calcium and magnesium hardness. This is followed by degassing of the dissolved CO2 to restore the pH. The pre-filtered water is stored in a 120 kL tank on site. The backwash water from the UF system and the pre-filtration is clarified and recovered via a Lamella Separator. The thickened sludge from the Lamella is discharged to two sludge lagoons with 6 months storage in each. The supernatant from the lagoons is returned to the head of the plant for reuse.
Following installation of the Denman Water Treatment Plant, the quality of the town water supply now exceeds the standards of the NSW Health Department.
Water test results demonstrated the following improvements:
- Water turbidity reduced from a range of 20 - 450 NTU to < 1NTU
- pH content reduced from a range of 8.2 – 9.2 to between 6.5 – 8.5
- Total Hardness as CaCO3 reduced from 200 – 350 mg/L to < 200 mg/L