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Dr. Charles M. Wolf Water Reclamation Facility

Wastewater Treatment Plant 
The city of Avondale’s largest ever public works project, at a total cost of about $40 million, will reach a milestone in October 2007 when construction will start on the expansion to the existing wastewater treatment facility. This construction project will increase capacity of the facility from 6.4 Million gallons a day (MGD) to the ultimate 
build-out of 15 Million Gallons a day (MGD). The Master plan which was used as the basis for this expansion will be implemented in three phases to meet the projected growth of 
the community. 

Aeration BasinAvondale’s facility uses a treatment process whereby a liquid suspension (mixture) of aerobic (oxygen-requiring)Avondale’s facility uses a treatment process whereby a liquid suspension bacterial species, collectively referred to as activated sludge, "feed" upon pollutants contained in the sewage. In large tanks (aeration basins), air is bubbled through a diffuser grid to aid the bacterial decomposition of the pollutants. To ensure the right types of bacteria are "selected", special "growth" zones called bioselectors are used. 

Ammonia nitrogen is also removed using biological (bacterial) nitrification and denitrification processes. The conversion of ammonia nitrogen – which can be harmful to the river environment - to other nitrogen forms and finally to nitrogen gas (the largest component of air) is also accomplished through the use of specialized microorganisms which proliferate under controlled conditions maintained in the aeration basins. 

After the nitrification and denitrification processes, there is a separation of the solid and liquid portion of the wastewater stream performed by the clarifiers. The solid portion is either sent to the anaerobic digestors to be stabilized or put back into the aeration process. The liquid portion called effluent will flow out of the clarifiers into the chlorine contact basin where it is disinfected and subsequently dechlorinated to meet permit and licensure requirements. 

The treated wastewater effluent is currently discharged into the Aqua Fria River, but as the expansion project continues through all three phases, the majority of the effluent will be redirected to the McDowell Recharge Basins. At this site, the water will be recharged and collected for water storage credits. 

Wastewater Treatment facilities are often among a municipality's most technically complex operations. The City's operational staff brings degreed, experienced, technically trained, and state licensed individuals to the realms of operations, process control, laboratory, maintenance, and administration. The benefits of having diversified and knowledgeable operating staff are both environmental and fiscal: high quality treated effluent protects both human health and the environment while, at the same time, operations and maintenance costs are minimized. 

Wastewater Treatment Process 
Influent PumpsFour (4) Influent Pumps, each capable of pumping up to 5 million gallons of wastewater a day, raise the sewage influent flow up to a higher elevation to allow for pass through the treatment plant by gravity flow. 

As a "primary" treatment step, water passes through mechanical bar screens, a grit removal system, and large settling tanks (primary clarifiers) where some of the particulate and floatable pollutants are removed. Suspended and dissolved pollutants still remain. 

Scraper devices that travel along the surface and floor of the primary clarifiers mechanically collect floatable and settleable material. The collected material is then pumped through a device that removes inorganic material and is subsequently pumped to the anaerobic digesters. 

BasinThree large "aeration basins", with a total volume of 4,200,000 gallons, use a variety of hungry microorganisms (bacteria) to remove the suspended and dissolved pollutants remaining from the primary treatment step. This process, one of many, is known as "secondary treatment". Special "zones" within these tanks encourage the growth of specific types of microorganisms that perform specific jobs such as the removal of ammonia nitrogen. 

After "feeding", the microorganisms are settled in large tanks called "secondaryDigesterclarifiers". Some of the settled microorganisms are recycled back to the aeration basins to feed again and are called return activated sludge, while others called waste activated sludge are removed from the system. Treated effluent (water) exits from the top of the tank, overflowing serrated plates around the circumference called weirs. Weirs ensure uniform flow distribution and prevent "short circuiting" or incomplete treatment, in the tank. 

At the chlorine contact basin, the effluent is subjected to a disinfection process by use of a strong bleach solution. This kills most of the remaining bacteria in the secondary effluent. A subsequent dechlorination step is added to remove the residual chlorine in the discharge stream before the final effluent either flows to the Aqua Fria River outfall or up to the McDowell Recharge basins. 

The plant operates large machines, called rotary drum thickeners, which use screens and an emulsion polymer to separate the waste activated sludge. In this case, water is being separated from an organic solid material. The removal of water prior to anaerobic digestion requires less tank volume and less volume to be heated. 

TankCovered, heated and mixed tanks, referred to as anaerobic (absence of free oxygen) digesters, are used to stabilize solid organic material often referred to as sludge. The process reduces objectionable organic matter to relatively stable organic and inorganic compounds. This process utilizes anaerobic bacteria, and in a complex biochemical reaction, produces methane gas that is used for heating the sludge. 

Stabilized material from the anaerobic digestion process, now referred to as biosolids, are run through devices known as centrifuges. This equipment with the aid of another type of polymer removes large amounts of water and reduces this material to a thicker and dryer form. The dewatered biosolids can now be readily hauled by truck to agricultural fields or a landfill where nutrients (nitrogen, phosphorous, potassium, etc.) contained in the biosolids can be recycled back into the soil. Before land application or disposal to the landfill is permitted, biosolids must meet a number of quality requirements established by the U.S. Environmental Protection Agency and the State of Arizona.