STEP 1 – Preliminary Treatment
Raw wastewater throughout the District’s boundaries is collected and transported through a network of piping and lift stations to the American Gulch Water Reclamation Facility located west of the Payson Golf Course. Flow enters the treatment plant into the headworks for preliminary treatment. The wastewater is screened to remove large objects and debris. Flows are measured in a Parshall flume. Next, grit and other inorganic material are removed prior to entering the biological treatment units. Wastewater flows to the volatile fatty acid (VFA) basin where conditions favor the production of volatile fatty acids, which help to achieve increased phosphorus removal in the biological treatment units.
STEP 2 – Bardenpho Process
The District employs a unique five stage treatment process for the removal of nutrients and organic pollutants. The Bardenpho Process was first developed in South Africa. The Payson facility was the first to use this innovative technology in the Western United States.
The first stage is the fermentation zone, where the incoming flow from the VFA basin waste is mixed with return activated sludge (RAS) from within the treatment process. Stored phosphorus is released by the microorganisms, which are then able to reabsorb very large amounts at a later stage in the process.
From the fermentation zone, flow enters the first anoxic zone where it is mixed with recycled liquor from the nitrification zone. In the absence of dissolved oxygen, the microorganisms scavenge under stressed conditions to strip oxygen from the nitrates contained in the recycle flow, reducing the nitrates to nitrogen gas.
As the flow continues on into the nitrification zone, oxygen is provided by fine bubble diffusion to oxidize the biochemical oxygen demand (BOD) remaining from the first anoxic zone and to oxidize the ammonia nitrogen to nitrate nitrogen. The biomass in this cell is recycled to the first anoxic zone to assure complete nitrogen reduction. Phosphorus uptake occurs in this treatment cell. The second anoxic zone is used as a polishing stage to remove more nitrates coming through the prior basin. Finally, a short reaeration zone is used to provide oxygen for microorganisms and to prevent phosphorus release further in the treatment process.
STEP 3 – Clarification
Effluent from the Bardenpho process is transported by pipe to a splitter box and directed into the final clarifiers for separation of the biosolids. Clear water results from the separation and is collected by radial weirs and transported for further treatment.
As the biosolids settle under calm conditions in the tanks, a collector mechanism directs the solids to the return activated sludge (RAS) pump area, where a portion of the flow is returned to the Bardenpho basins for repeated treatment.
The recycled biomass also serves as a seed material for incoming raw waste. A portion of the settled biomass is also wasted to the biosolids treatment process.
STEP 4 – Tertiary Treatment/ Ultraviolet Disinfection
The final “polishing” of the water from the clarifiers occurs as the water is directed to the tertiary sand filters for removal of fine suspended and colloidal solids. The filters contain a dual-media to trap these fine solids which are returned to the Bardenpho process for further treatment.
Following filtration, the effluent is disinfected through the use of ultraviolet treatment. The water passes through enclosed vessels containing lights that emit ultraviolet light. The ultraviolet light kills any remaining bacteria, to conform with discharge and reuse compliance standards issued by the U.S. EPA and the Arizona Department of Environmental Quality.
STEP 5 – Lab – Quality Control
The District has its own on-site laboratory. The lab is annually certified for wastewater analysis through the Arizona Department of Health Services. On a routine basis, the lab tests the effluent for bacteria (e.coli), pH, total suspended solids, biochemical oxygen demand, various nutrients, volatile fatty acids, dissolved oxygen, and temperature, to name a few parameters. The effluent meets or exceeds water quality parameters for Class A+ water as determined by testing limits set by the Arizona Department of Environmental Quality. The data from the water testing is reported on a monthly basis to ADEQ and any variances from the set limits must be reported and corrective action is taken.
STEP 6 – Biosolids Handling
As a result of removing contaminants and pollutants biologically, and nearing the completion of the treatment process, there is an excess of residual matter, called “Biosolids”. The excess biosolids are removed from the system and require further treatment before ultimate disposal. The District employs large solids pressing machines which dewater the biomass to reduce the moisture content and allow the material to be placed in a dump truck where it is transported off-site for ultimate disposal in a private landfill.
STEP 7 – Final Effluent & Reuse of Effluent
High quality effluent is captured at the end of the treatment plant through an effluent pumping station on site. Portions of the treated effluent are used throughout the plant as an alternate water source. The pumps send the water via pipeline to the Green Valley Lakes. At the Lakes, effluent is percolated into the ground to aid in groundwater recharge of the underground water supply. The Park area is also irrigated throughout the warm weather season.
Effluent is also removed from the Lakes by means of additional pumps and sent to various reuse customers for use as irrigation water. The Payson Golf Course, Payson High School, Chaparral Pines and the Rim Club Golf Courses are just a few of the recipients. The District distributes about 95% of it’s available high quality effluent to various reuse sites within the community. Doing so has alleviated demand on the Town’s underground water reserves within the local aquifers.