Metro Water Services Central WRF Headworks Facility
Hazen designed and is overseeing construction of a new headworks rated for 440-mgd at the Central WRF. The headworks will replace two aging and poorly performing headworks and will provide the Central WRF with the latest preliminary treatment technology to greatly improve plant operations.
The Central WRF operates two separate headworks facilities to provide preliminary treatment of influent wastewater. The South Headworks, consisting of coarse screens and aerated grit channels, serves the combined sewer system while the North Headworks, consisting of aerated grit channels, serves the separate sewer system. Both facilities are aged and perform poorly, in particular when flows are elevated during wet weather events.
The new headworks facility that Hazen designed will replace the existing North and South Headworks and combine preliminary treatment into one facility. The new headworks facility design consists of coarse screening, followed by stacked tray grit removal, followed by fine screening. The combined system flows and separate sanitary system flows will be discharged into the headworks individually for segregated treatment of the two flow streams for permit purposes, however the facility will have the ability to co-mingle the flow streams to reduce the number of duty units required to be online during dry weather. The separate sanitary system peak flow is 200 mgd while the combined system peak flow is 240 mgd, for a total influent flow of 440 mgd.
Coarse screen design is for ½-inch chain and multi-rake catenary style bar screens, each rated for 60 mgd. Coarse screenings conveyance is via troughed belt conveyor direct to dumpster. Grit removal consists of 13 stacked tray units, each 12-feet-diameter with 12 trays and designed for a grit cutpoint of 150 micron.
Grit handling is via cyclones and classifiers with dewatered grit discharge to dumpsters. Fine screen design includes 6 mm perforated plate screens, rated for 60 mgd each. Fine screenings handling consists of sluice trough conveyance to washer/compactors with discharge through a trough dumpster loader.
Project Outcomes and Benefits
- New facility will replace two existing headworks and combine preliminary treatment into one facility.
- The grit removal system consists of 13 Headcells and once complete, will be the largest single Headcell facility in the world.