Council has changed the way we dewater sludge at our wastewater treatment plant which has significantly reduced the cost for this process.
Tamworth Regional Council’s Westdale Wastewater Treatment Plant (WWTP) produces residual solids as a by-product of the treatment process. These solids are separated from the treated effluent and stored in three anaerobic storage lagoons (sludge lagoons), of approximately 25,000m3 each, where stabilisation occurs.
The stabilisation process is designed to stop the material breaking down any further and requires a minimum of six months storage to meet NSW EPA guidelines for reuse. Following stabilisation, the sludge still contains approximately 95 to 97% water and needs to be dewatered to turn it into a dry solid.
The first step of the dewatering process is to place the sludge within a sludge drying area onsite at the WWTP, where the solid’s content is decreased to 40-60% water over 12 to 18 months through natural evaporation.
The second step of the dewatering process sludge is what has changed.
Historically, the sludge has gone through a second dewatering process using centrifuges which are machines with a rapidly rotating container that applies centrifugal force to its contents to separate the water from the sludge. This process produces turns the sludge into a ‘sludge cake’ which is approximately 16-18% dry solids.
The different process we are using for secondary dewatering are GeoTubes. GeoTubes are large bags that are made of fabric with a one-way membrane that are made to retain the solids whilst allowing the liquids filtrate through
After approximately 6 months the sludge has been dried to a point that the solid material can be removed from the tubes, tested and transported offsite to the Effluent Reuse Farm to be beneficially reused in agriculture.
Council reviews this process and goes to tender every two to three years to ensure we are undertaking the most efficient and economical option.
