INTRODUCTION | CONTEXT          

The city of Phoenix is the capital of the southwestern U.S. state of Arizona. It is located between the state of New Mexico, Colorado, Utah, Nevada, California and borders with Mexico. In a regional context, the city is surrounded by beautiful and important national forests such as: Prescott, Coconino, Apache-Sitgreaves, Tonto, Sonoran Desert Monument, Organ Pipe National Monument. The richness and value of this land comes partly from tribes that settled in the region centuries ago and from the scenery of the unique desert landscape.

INTRODUCTION | HISTORIC TIMELINE

Objects found indicate that ancient tribes settled in the land between 700AD-1400AD. When these tribes settled in the region they built a massive irrigation system that roughly consisted of 135 miles of canals that turned the land into fertile soil. But these tribes vanished, leaving the ruins of their settlements, with no evidence nor trace to why they disappeared. In 1968 Jack Swilling from Wickensburg was exploring the lands and saw the potential of the already in place irrigation canal system. He moved into the area and established an irrigation canal company. This is where Phoenix started flowering and quickly expanded.

INTRODUCTION | POPULATION

Population presents a major threat to the distribution and water source allocation of the city, especially in terms of climate change. In 2017, Phoenix was the second largest in population growth in the US.The city of phoenix went from 1.575 million in 2015 to 1.626 million in 2017. In just 2 years, the population in phoenix grew by roughly 51,000 people. This means additional 51,000 people consuming water, electricity, food and using transportation.

INTRODUCTION | CLIMATE

Phoenix’s climate is classified as hot and dry, Arid and Semi-Arid. About 6 months of the year, the city experiences extremely high temperatures that can cause water to evaporate.

At the same time, rainwater as a water source is unreliable. Yearly precipitation yields about 8 inches of rain, with no snowpack during the winter. As climate change continues to increase temperature, the city of Phoenix is expected to experience longer periods of drought and lower levels of surface water.

WATER SOURCES |  SALT RIVER PROJECT AND CENTRAL ARIZONA PROJECT

Two of the main water sources of Phoenix are the Salt River Project and the Central Arizona Project. The charts below best summarize the main water sources (in dark blue) and secondary water sources, respectively.

The current wastewater treatment plants are being utilized only for irrigation and cooling of the power plant, while the recharge projects are storage basins created to recharge the aquifers – meant to serve as water sources should drought occur later on.

WATER SOURCES |  AQUIFERS

The three largest regional aquifers are the D-, N-, and C-aquifers. Primary recharge areas are along the southern and eastern periphery of the Active Management Area (AMA) planning area. In addition to these regional aquifers, several local aquifers are important groundwater sources. One of the most extensive is the Bidahochi aquifer in the east central part of the planning area.

PROBLEMS | DROUGHT + ENERGY USE

Problems of water vulnerability come from climate, water sources, energy usage, consumption and lack of regulations. The Colorado River is drying up and there is a lack of adequate inflow to maintain the necessary water level at the water reservoirs. At the same time, water will run out of the aquifers if drought continues for a long amount of time. The recharge projects can only do so much – especially if consumption does not go down.

The orange and red colors in the graph below indicate the times of drought within the Colorado River from 2000 – 2019.

The growing populations in California, arizona and Nevada use 1.2 million acre feet more water each year. The demand is so much higher than the supply, such that supply is unable to recover.  In 2015 the residential water consumption was approximately 108 Gallons per Capita per Day compared to the U.S estimated approximately 85 GCPD.

This water consumption from residents is very high and there are no regulations that promote water conservation. The city has minimum incentives through rebates for water conservation. Because there are no programs addressing the problem, the residents do not understand how vulnerable phoenix really is.

This high water consumption can also be equated to high energy consumption, as the water is being pumped uphill to Phoenix, Casa Grande and Tucson, using about 2.8 million megawatt-hours to deliver 1.6 million acre-feet of Central Arizona Project water.

The practice is over-all very unsustainable for both water and energy stand-points.

Currently, new master plans for development are including even more golf courses and resorts, as if current water consumption were not enough.

The proposed solution will try to tackle the unsustainable water and energy consumption while touching on policies for water conservation.

In doing so, the proposal will also be able to touch on solving these related problems (in light blue):

PROPOSAL | DECENTRALIZED WASTEWATER TREATMENT

Phoenix’s climate is an unreliable source of water due to its lack of precipitation and high temperatures that can cause drought throughout the year. Instead of using groundwater and surface water, the city would benefit from tapping into wastewater management in a distributed/building scale.

A centralized wastewater treatment plant is not viable due to the amount and number of plants needed to accommodate Phoenix’s daily usage. Even if the processing power of the plant is raised to 600,000 GPD, the city would still need around 200 wastewater plants to address its daily usage. This amount of plants – together with the amount of capital necessary ($1.2-Billion) makes it highly unlikely for the centralized wastewater option to proceed in the next few years.

Instead, decentralized wastewater systems can be placed within buildings and throughout the city to address total usage.

WASTEWATER TREATMENT  | FINANCIAL FEASIBILITY

Buildings pay for water twice – once for potable needs and again to discharge sewage. There should be strong motivation to combine the process and lessen costs.

As with most projects, cost plays a large role in actual implementation. Wastewater treatment plants may seem to have a larger initial capital cost, but a closer look at Phoenix’s water and sewer rates together –  not to mention the environmental and maintenance costs, show that a large commercial building using 22,000 GPD (See Figure below) will be able to save $47,172 each year after the 6 initial years from installation of a wastewater treatment plant.

Additional computation shows that any building with more than a 30-person occupancy (108 GPD/person) would benefit from having a wastewater treatment plant after 12 years, with the payback period decreasing as the occupancy load increases. (See Figure below)

The Figure above shows that having an individual plant per residence or for buildings less than 20 persons does not make sense financially, but a residential area could benefit from installing a common wastewater treatment plant for the entire neighborhood. With a payback period of only 8 years for 50 persons, a small neighborhood  would no longer be paying for water after 8 years. In fact, this could act as an incentive for developers who want to attract more residents.

WASTEWATER TREATMENT  | PRECEDENTS

San Francisco’s tallest tower – the Salesforce Tower (See Photo below) is installing a wastewater management system that will treat both gray and black water from the building which will reduce the need for 30,000 gallons of freshwater per day, saving about 7.8 million gallons of water per year.

The system will collect rainwater from the rooftop, showers, sinks, toilets, urinals and cooling towers, then treat the water and send it back into the building for non-potable use, reducing the building’s water intake (from outside sources) by 76% daily. Like Phoenix, California is another state that experiences moments of drought. This led San Francisco to pass an ordinance a few years ago requiring buildings larger than 25,000 sqft to recycle gray-water. A grant was given to the Salesforce developer to help build this system that goes above the ordinance, by recycling 100% of its wastewater

WASTEWATER TREATMENT | ENERGY PRODUCTION

Energy and water work together and are closely linked to one another. Energy is needed to transport and transform water. At the same time, that water can be used to produce energy (e.g. hydropower). Because they are so closely linked, it is important to explore the different possibilities of cutting down consumption for both resources.

The technology of today has made possible the process of using wastewater by-products to create energy.

This type of wastewater plant has the capability of turning wastewater into energy through its sludge by-product. Methane gas can be taken from the sludge then used for energy production, while remaining sludge can be used for composting and fertilizer.

The entire process allows the user 2 by-products – the fresh water originally needed, and energy.

WASTEWATER TREATMENT + ENERGY PRODUCTION | PRECEDENTS

San Antonio Water System (SAWS) in Texas is currently harnessing the methane from its wastewater treatment, and using it an energy source. The city receives around $200,000 in annual royalties from its sale of biogas, allowing SAWS to lower their operation rates while reducing 19,739 tons of carbon dioxide each year.

Similar to SAWS, Helsinki Viikinmaki Wastewater Treatment Plant that follows the same process. Sludge from the wastewater treatment is processed in digestion tanks and generates methane which produces electricity and heat. This electricity takes care of 70% of the plant’s usage.

Portland and Stockholm are also participating in the same process with Portland aiming to cut greenhouse gas emissions by 21,000 tonnes a year and generating over $3-million in revenue, replacing 1.34 million gallons of diesel fuel.

PROPOSAL | BUILDING CODES AND GUIDELINES

But pushing developers and homeowners to install wastewater treatment plants and lowering water supply and energy consumption could take several years of education and marketing. Phoenix is already experiencing drought and needs a quicker solution to addressing the problems in water supply and energy building consumption. Changing the building codes and adding incentives and rebates to be more in-line with water conservation will push the city to move faster into seeking alternative methods of water supply and energy generation.

Why building codes? Much of the water consumption and loss comes from the residential and commercial sector. Building codes set a minimum standard on different sectors and stages for  design and construction. They oversee and ensure that the minimum requirements are being met especially through review process, compliance and benchmarking. In 2018 Phoenix adopted the Phoenix Building Code.

The downside of building codes is that building codes establish “minimum” requirement instead of establishing the “highest” efficient standards for all sections. As of today, there is no international building code established that sets up minimum compliance requirements for water conservation. Out of the adopted codes in Phoenix, the ones related to water consumption are highlighted in orange in the list below.

Mechanical systems matter because water is not visible in the processes involved in mechanical systems it is hard to find the correlation between them and water. Many of these processes, which depending on the system type, require large amounts of water and electricity for combustion and refrigeration. Setting up minimal codes for new buildings and upgrading existing buildings with higher efficient mechanical systems will help reduce the amount of water consumption in both commercial and building sectors.

At the same time, the 2018 International Plumbing Code and the 2018 Uniform Plumbing Code are the closest in relation to water conservation, but their primary focus does not include conservation. The weak spots from these codes are that (1) they do not enforce water efficient systems in the residential area for existing and new construction, and (2) In places like Phoenix, drought vulnerable area, “minimum” might not be sufficient.

As previously mentioned, energy works in a closed loop with water and that both can be made to work more efficiently together. The adoption of the 2018 International Energy Conservation Code is a great option for Phoenix. Especially relevant as it focuses on commercial energy efficiency, existing buildings and residential energy efficiency.

Out of all the adopted building codes, the 2018 International Swimming and SPA Code has the highest potential for water conservation. 62/% of the houses in Scottsdale have a back pool. Although the code imposes regulations on building safety entrances and exits on public pools, it does not specify where the water should come from or what should be done with the water when the pools are cleaned and the water is changed.

The Whole Building Design Guideline specifically for water conservation and drought mitigation should also be looked into for a more holistic approach. The Whole Building Design Guideline lists the improvement of all systems, mechanical, plumbing, green infrastructure, recycling and management practices. They ensure the protection and conservation of water throughout the building’s life cycle.

All in all, reviewing the building codes and adopting the proper measures applicable to Phoenix’s water problem with water and energy consumption in the building sector will greatly affect the mechanical systems and materials explored to meet new codes and build more energy efficient buildings. These codes will create the added push needed for developers and homeowners to act today, to help conserve water and energy.

CONCLUSION | DECENTRALIZED WASTEWATER + POLICY IMPLEMENTATION

Shifting water supply reliance from surface and groundwater to wastewater will afford Phoenix  greater water security. Wastewater treatment shifts the dependence on climate to mechanical systems that can be controlled. The process can be further utilized to address not only water shortage but also energy usage. Together with a change in policy that favors water conservation, the wastewater treatment plants may be able to entirely eliminate water shortage in Phoenix.

References
Arizona | Drought.gov. March 25, 2019. Accessed April 20, 2019. https://www.drought.gov/drought/states/Arizona.
“City of Phoenix” Accessed April 20, 2019. https://www.phoenix.gov/
“Central Arizona Project” Home. Accessed April 19, 2019. https://www.cap-az.com/
CAPH20. “CAPH20.” YouTube. Accessed April 11, 2019. https://www.youtube.com/user/CAPH20/featured.
“Wastewater Energy Plants Are Now Fuelling Themselves.” Impact4All. May 02, 2018. Accessed May 11, 2019. https://impact4all.org/wastewater-energy-plants-are-already-fuelling-themselves-and-buses-and-cities/.
“Salt River Project” Home. Accessed April 20, 2019. https://www.srpnet.com/
“A New Sustainability Milestone: Innovative Water Recycling System in Salesforce Tower.” Salesforce Blog. Accessed May 9, 2019. https://www.salesforce.com/blog/2018/01/salesforce-tower-innovative-water-recycling-system.html.
James, Kirsten. “San Francisco’s Tallest Building Makes Big Water Recycling Statement.” Water. January 31, 2018. Accessed May 11, 2019. https://www.newsdeeply.com/water/community/2018/01/31/san-franciscos-tallest-building-makes-big-water-recycling-statement.