July 2007, Vol. 19, No.7

Plant Profile



City of Dinuba Wastewater Reclamation Facility Location: Dinuba, Calif.
Startup date: 1921
Service population: 19,000
Number of employees: 4
Design flow: 3.14 mgd (11,900 m3/d)
Average flow: 2.2 mgd (8300 m3/d)
Annual operating cost: $1.4 million

The City of Dinuba (Calif.) Wastewater Reclamation Facility does not actively disinfect its effluent. Nor does it discharge it to the sea — Dinuba is located about 150 mi (240 km) inland. Instead, treated wastewater from the secondary clarifiers is sent to ten disposal ponds. Eventually, most of the water percolates into the largest pond, dubbed The Lake, where several types of fish thrive and several mallard duck families nest.

The Dinuba facility received the Plant of the Year Award (less than 5 mgd category) from the California Water Environment Association Central San Joaquin Section in both 2004 and 2005.

The facility’s headworks passes influent through two 0.63-in. (16-mm) bar screens to remove large debris and then a distribution structure which sends the flow to the aeration basin. The basin provides treatment by aeration within an activated sludge system. The basin has a total volume of 2.89 million gal (10,900 m3) and a detention time of 22.6 hours. It is equipped with four surface aerators, each rated at 75 hp (56 kW).
From the aeration basin, wastewater is distributed evenly between the facility’s two secondary clarifiers. The secondary clarifiers are 65-ft (20-m) in diameter with a side water depth of 14-ft (4.3-m). The volume per clarifier is approximately 46,500 ft3 (1320 m3) with a
The City of Dinuba (Calif.) Wastewater Reclamation Facility received the Plant of the Year Award (less than 5 mgd category) from the California Water Environment Association Central San Joaquin Section in 2004 and 2005. (Photo by Carollo Engineers, P.C.)
5.3-hour detention time. The clarified effluent flows into the percolation ponds.

The return and waste activated sludge pump station includes three 15-hp (11-kW) pumps, each with a capacity of 1075 gal/min (4069 L/min). The pump station maintains the solids concentration in the aeration basin by recirculating calculated amounts of solids from the secondary clarifiers to the aeration basin. Any solids in excess of this calculated amount are applied to the facility’s eight solids drying beds.

The solids from the drying beds are provided an appropriate atmosphere and time to be sufficiently solar dried and dewatered. The dried solids are then hauled away to a licensed compost facility.

In the last few years, operators have been able to eliminate the need for the primary clarifier, anaerobic digester, trickling (roughing) filter, and associated processes. “I think that I am the only plant manager who is progressively getting a smaller plant and very pleased about it,” said Dinuba’s plant manager Kathy Hansen.

Additionally, the facility is planning a substantial upgrade to enact a reclamation, conservation, and recreation (RCR) project to help sustain the city’s new golf course. This municipal golf course is the area’s first 18-hole course and will be named Ridge Creek Golf Club. The facility wastewater reclamation will provide reclaimed water for irrigation at Ridge Creek.

With the RCR project taking form, staff members are working on various reclamation options to get treated water from under the percolation ponds to the RCR project next door. The reuse project will accommodate the treatment facility’s projected 4-mgd (15,100-m3/d) flow and also provide walking trails and recreation for the whole community.

“It is an odd day when the community is beating a path to the door of the wastewater plant, but one I wholeheartedly embrace,” Hansen said. “It has sparked genuine discussions and brought wastewater to the forefront of peoples minds, in a positive way. At least in Dinuba, wastewater is a community project.”

In addition to the RCR program, Hansen said she would like to recycle the facility’s biosolids for ornamental horticulture use and someday even place a solar array on an old sanitary landfill.

“It would be very nice to completely recycle our water and biosolids while producing our own energy,” she said.