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City of Phoenix Digester Cover Replacement

WCE completed the design for a cover replacement of one of the digesters at the City of Phoenix 91st Avenue Wastewater Treatment (WWTP) plant in Tolleson. This treatment plant provides wastewater treatment services for the Sub-Regional Operating Group (SROG) member cities of Glendale, Mesa, Phoenix, Scottsdale, and Tempe, in Maricopa County, Arizona. The facility is a municipal wastewater treatment facility that employs a nitrification/denitrification process to treat municipal and industrial wastewater generated in the metropolitan Phoenix area by the SROG communities, serving a population of over 2 million. The COP 91st Ave WWTP is presently operating at a capacity of about 180 MGD.

Specific processes for sludge treatment at the 91st Avenue WWTP include primary sedimentation (with enhanced sedimentation possible), activated sludge treatment, centrifuge thickening of both primary and waste activated sludge, anaerobic digestion, sludge drying beds, and centrifuge dewatering of digested sludge.

The Digesters that are being evaluated and repaired were put into service around 1980. The metal covers show significant corrosion and the concrete tanks exhibit minor cracks and some leaks in the launder area.

WCE engineers completed the design for the cover replacement on several of the digesters and also did construction administration and daily inspections during construction.

City of Nogales Meadow Hills Lift Station Improvements

The Meadow Hills lift station experienced frequent issues with pump failures. An extensive on-site visit was conducted. Possible factors contributing to the pump failures were studied and modifications to resolve these issues at the existing lift station were recommended in a report to the City. Recommendations included changes to electrical supply, wet well equipment, alarm system, and other facility areas where additional problems were found.

City of Tolleson Discharge Study and Permitting Assistance

WCE conducted a study using equipotentials and streamlines to calculate the seepage pattern as it disperses in the soil zone from the pond bottom (in the case of the Tres Rios wetlands) or canal (in the case of the Tolleson discharge). This method was developed by Herman Bouwer and others and is described in Groundwater Hydrology by H. Bouwer. This approach provided convincing evidence to ADEQ that the intermittent discharges by Tolleson will not adversely affect the groundwater water quality in the vicinity of the discharge.

City of Buckeye

Sundance Wastewater Treatment Facility Review

Study to review the plant and make recommendations to restore the permitted capacity. The service area flows are expected to increase as home sales return and the plant needs to be able to provide good reliable and economical service to the City. Currently the SBR treatment is underperforming and operational issues from SCADA and PLC errors to equipment errors do not allow the staff to run the plant optimal. Recommendations will include changes to equipment, plant components, operational logic, program updates, and electrical updates.