These residuals typically require additional equipment and oversight to collect, thicken and dewater them. Depending on the size of the water plant, the installation of conventional residual management equipment could add several million dollars in capital costs, as well as ongoing operating costs.
Passive dewatering saves about $6 million in capital costs
A town was facing costs of over $7 million to add a complex mechanical treatment system that would decant and pump process residuals from the water plant to the town’s wastewater lagoons.
But, rather than opting for the conventional mechanical treatment process, It chose a simple, passive dewatering solution that uses only Geotube containers, specially selected polymers and gravity to collect and dewater process residuals in a single step. The entire solution was installed for $1.25 million, saving about $6 million in capital costs for the community. The solution, which has been operating since December 2014, consistently exceeds discharge requirements, with operating costs that are significantly lower than alternatives.
How it works
Residuals from the water treatment process are first pumped to a 10,000-litre storage tank. About four times per day operators will process the residuals, pumping the solids to one of two Geotube containers. As the solids are pumped, polymer is added to accelerate dewatering and enhance solids retention.
A manifold system enables operators to easily switch the receiving container, so that one Geotube can be filled, while the other dewaters. A third Geotube container is positioned inside a greenhouse, which allows operators to continue using the system through the winter months.
The filtrate released from the Geotube containers consistently exceeds discharge requirements—with TSS that is typically in the range of 3 to 4 mg/L—and can be released directly into the Tay River with no additional treatment.
The solution also supports an initiative to reduce influent loading and extend the life of wastewater treatment lagoons, which are approaching their rated hydraulic capacity. The solution helps conserve precious wastewater treatment capacity and enables the town to build about 80 new homes, adding roughly $250,000 annually in new tax revenue for the city and avoiding the capital cost to expand the treatment lagoons.