21.+Sustainable+Water+Infrastructure

=Authors:= Dan Stout, Jordan Pugmire, Dustin Pennington, Steven Arhart

Chapter Goal Briefly describe two approaches to urban water infrastructure systems; namely centralized and decentralized water distribution systems. Each system will be analyzed for sustainability using the triple bottom line framework.

= Introduction =

It should not be any surprise to anyone that water is one of the most important and significant basic needs for all living creatures to survive. As civilizations are built one of the first things needed for the success of the people is access to clean and safe water. The method in which this water is accessed and transported to people is called the water infrastructure system. In this chapter, we will look into two different types of urban water infrastructure systems. We will be focusing on urban water infrastructure systems only, because these systems are the most common and service the most number of people. Other systems are beyond the scope of this book. The first system we will discuss is centralized water infrastructure systems, while the second is decentralized water infrastructure systems. The basic layout of each system will be discussed along with some examples of these systems. Lastly a simple sustainability analysis will be discussed for each system using the triple bottom line sustainability framework. The purpose of this chapter is not to lead one to a conclusion about which system is more sustainable, but instead to lay out some of the issues concerned with each system.

= Description of Urban Centralized Water Infrastructure Systems =

The currently most predominant method of water distribution in the US and most of the developed world is a very large-scale and centralized system. Centralized in this case is referring to the fact that all (or most) of the water for a particular area of people is all managed at one location (usually on the outskirts of the community/city) and then transported long distances to get to the end user. This distribution technique has traditionally been considered to be the best method for getting potable water to large and densely populated urban areas. Centralized water infrastructure can be used to provide water for communities of hundreds of people to millions.

For centralized water distribution to work several conditions need to be met (see Figure 1). First a large source of water is needed to be accessible, as close to the urban area as possible. Some of these sources can be a lake, reservoir, river, groundwater well, etc. Second (generally), the water needs to undergo some kind of treatment to be suitable for human consumption (labeled as “water treatment plant” in Figure 1). Third, a method of transporting/distribution must be available (generally it is constructed) that is capable of carrying the large volume of water needed (labeled as “water distribution system” in Figure 1). This system needs to start with a large pipe(s) leaving the facility, and then branching out into many branches of pipes in decreasing diameter until the end use location(s) are reached. These lengths of pipes can be many miles long, and in some extreme circumstances they can be hundreds of miles long. Once the water has been used, a similar system is needed to transport the waste water (sewer system) to a centralized treatment plant to clean it again and discharge back into the environment (this will be discussed in a following chapter). Figure 1: Basic schematic of a water distribution system from source, distribution, use and discharge (Crognale, 1999)

A brief description of potable water sources: a lake and a reservoir are similar, but have a couple of differences. The main difference is that a reservoir is a manmade lake that is created from constructing a dam at a river. A river is a natural path of flowing water across land, decreasing in elevation. A viaduct is a manmade, and can be used in older systems to carry potable water or just constructed and used for removing storm water runoff from one location to another. A groundwater well is a hole that is dug or drilled into the ground to a depth deep enough to reach the water table. The water table is where the underground water is located. All locations on earth have a water table, but the depth to the water table can vary greatly from a few feet to hundreds of feet deep. Once the water table is reached, a pumping station (pump house) needs to be put in to lift the water from underground to ground level for processing.

Figure 2: A manmade reservoir with a dam (Wikipedia, 1999) || Figure 3: Aerial view of Charley river in Yukon (USGS) || Figure 4: Potable water viaduct (Wrexham) || Figure 5: Los Angeles County storm water viaduct (Kelley, 2011) ||
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Once a source of water has been established, the water generally needs to undergo a cleansing/purification process before it can be sent onto the customer/end use. Nearly all water will need at least basic treatment in order to be safe for human consumption, even groundwater which is generally much cleaner than surface water (generally not contaminated from animal feces and human activities, but higher in mineral content which can make the water harder) needs to undergo at least a disinfection step.

Figure 6: Schematic of a drinking water treatment facility (Crognale, 1999)

As water enters a potable water treatment plant (see Figure 6), it first encounters a screening process (labeled as “screen and grit chamber” in Figure 6). A screener is a large metal screen (sieve or filter) that removes large objects that are floating in the water like branches, pebbles, garbage, etc. Pumped groundwater can skip this step of the process, as it will not have large objects suspended in the water. After passing through the screen filter, the water will generally then enter a large pool area which has the inlet on one side and the outlet on the opposite side (or it can enter through a pipe in the middle and leave anywhere on the outside). This pool is a settling basin where smaller suspended solids can fall down into the bottom of the tank (labeled as “primary sedimentation” in Figure 6). The inlet and outlet are at the top of the basin, and the length of the basin is specifically designed to be long enough that the majority of the solids have time to fall to the bottom before the water reaches the other side of the tank and flows out (generally through a weir) and leaves the tank.

Once primary settling has taken place, another process is needed in order to get the harder to settle particles (often referred to as suspended solids) out of the water. A process called coagulation and flocculation is applied to the water. The water enters a tank and a special chemical, called a coagulant, is added to the water. The water moved onto another tank that has mixers dispersed throughout the tank. The coagulant is a chemical that causes the suspended solids to attract to each other and form larger clumps. This process is called flocculation. Once these flocs are formed, the water is sent to another settling basin (secondary settling) for the flocs to settle out. One more step is utilized to remove any remaining solids and this is a filtration process, which is generally a media type filtration tower (labeled “filtration” in Figure 6).

A media filtration tower can have one, two, or three different types of media in it, that decrease in size as the water moves down through the tower. For example the top layer can be a fine gravel to catch the larger items, then change to sand in the middle for the smaller solids, then finish off with a manufactured media or activated carbon to remove the micro-particles.

The final step for processing of potable water is disinfection (labeled “disinfection contact” in Figure 6). Disinfection is needed to kill any remaining organic matter, pathogens, bacteria and viruses. This is an essential step in the preparation of all water that will be in direct contact with humans. Throughout the years water borne disease has killed many million people from lack of disinfection.

Several different methods of disinfection exist, and each has its pros and cons. Chlorine disinfection is by far the most common and longest used method, but many water distributors are changing to other methods. Chlorine disinfection is beneficial because it provides residual disinfection during distribution. Recently it has been discovered that if certain molecules are in the treated water, that the chlorine molecules will make some carcinogenic disinfection byproducts. Thus caution must be used when disinfection with chlorine. Also, if using chlorine gas and a leak develops the gas is extremely fatal, but these occurrences are rare.

Some of the newer disinfection processes include adding small ozone bubbles to the water and using UV radiation to kill all living things remaining in the water.

Once the water has been cleansed to the necessary levels to be safe for human contact, the water enters the distribution system. This system is a series of pipes that transport the water to its intended end user. As the water first leaves the treatment plant, a very large pipe will be needed. As the pipes diverge to head different directions, the diameters can decrease. Sometimes intermediate storage tanks can be used to keep the water closer to the customer. Once the water arrives at the end customer, the urban water Infrastructure system comes to an end.

Case Study of Urban Centralized Water Infrastructure Systems
As in the case of the Provo, UT canyon river water treatment plant, some of the river water is diverted through a pipe and it enters a potable water treatment plant. All of the water in the Provo River is runoff from snow melt in one way or another (some snow melts and directly runs into the river, while some infiltrates into the ground, moves through the soil and at some lower elevation leaves the ground and becomes surface flow). The first thing the water encounters at the treatment plant is a screening process. After passing through the screen filter, the water then enter a large settling basin which has the inlet on one side and the outlet on the opposite side. Interestingly enough, the water encountered several walls across the basin, the walls had various heights, such that the water had to vary going above or below the walls.

After the settling basin the water encounters a media filtration unit (see Figure 7). In the case of the Provo river treatment plant, there is a two layered filtration tower of both activated carbon which is able to adsorb (not absorb) solids in the water, and sand. The activated carbon is a specially manufactured material that attracts charged material that is in the water. Every day the filtration tower’s media is cleansed by sending water back through the filter in the reverse direction, this process is called backwashing (see Figure 8).

Figure 7: Model of the filtration tower, showing the layering of the activated carbon (black) and the sand (brown) (Plant, 2011) || Figure 8: Top view of actual filtration tower undergiong backwash cleaning (Plant, 2011) ||
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Provo River water treatment plant currently uses chlorine disinfection, but is also performing tests with Ozone treatment to see if a future change would be possible.

Figure 9: Chlorine gas storage tanks (Plant, 2011) || Figure 10: Ozone treatment pilot testing unit (Plant, 2011) ||
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The Provo river water treatment facility has the capacity of cleansing 80 million gallons per day with a maximum design capacity of 100 million gallons per day. The facility and can services all the potable water needs, including irrigation for all of Orem city and surrounding communities in northern Utah County, Utah (Central Utah Water Conservancy District, 2011). The facility is currently selling some of its water to southern Salt Lake County also (Plant, 2011).

Triple Bottom Line Analysis of Urban Centralized Water Distribution Systems
 A triple bottom line analysis of the urban centralized water distribution system will now be conducted, see chapter 7 for an overview of this method. Centralized water distribution infrastructure is generally successful in fulfilling the social and the economic aspects of the triple bottom line. Humans and society at large need access to clean water for survival. Beyond drinking water is essential for food production and even power generation. Water is also used for entertainment ranging from back yard water fights, for profit water amusement parks, to watering of golf courses and lawns (watering of lawns is considered entertainment given its nonessential role in survival). Centralized systems should have no problem fulfilling these needs and wants of the society, and if not it is likely the fault of a poorly designed or scaled system.

The big question when dealing with centralized water infrastructure is the environmental impacts. This topic alone has the potential for great debate among various parties of interest, and a book could be written about this topic alone. The man things to keep in mind when analyzing the environmental impacts of centralized treatment are the following: - The materials need to construct the treatment plant and conveyance infrastructure is generally large, especially when compared to decentralized infrastructure (discussed later). For example the pipes will need to run further and be larger - The action of removing large amounts of water from a waterway will alter the ecosystem from the point extraction to the point of return - If the point of water returning to the waterway is not in the same waterway of extraction, both waterways will be effected - Extracted water that would have naturally infiltrated is now unavailable, thus effecting the water table - When the water is returned to the natural environment, there are many factors that if not closely monitored can harm the ecosystem, including: pH, temperature, dissolved oxygen level, nutrient level, etc.

= Description of Urban De-centralized Water Infrastructure Systems =

Unlike centralized water distribution systems which are very large scale and located on the outskirts of the population, decentralized water infrastructure is generally small scale and is integrated into the community. The idea of decentralized water distribution systems is to make many small water treatment plants that each serves a smaller group of people whom all live close to the water extraction point and treatment center. Since the customers live close, the distribution system is also small scale. The distances the water needs to travel are small and the pipes can be small.

Basic Overview of the Concept of Decentralized Water Infrastructure
Decentralized water infrastructure attempts to break up the currently predominant water distribution system of cleansing massive volumes of water for huge populations and transporting it long distances to the end user. Instead water is extracted, used and treated in the same location (or at least very close), theoretically minimizing the environmental impacts. This approach to water infrastructure also minimizes the amount of conveyance infrastructure required.

Decentralized systems can be implemented on many scales from a single house to a small neighborhood, or a commercial (or industrial) center. Water is gathered, undergoes treatment in a small area (footprint) and minimally transported for use. If decentralized wastewater treatment is also implemented, then the water will be cleaned on site (again in a small footprint) and returned to the environment close to the point of extraction. All of the same cleansing processes would still need to be performed on the water for a decentralized water treatment plant, but everything would be much smaller scale. The overall footprint would be small, and can often be integrated into other constructed features to make them blend in with their surroundings.

Case Study of Urban De-centralized Water Infrastructure Systems
At Volcan Irazul National Park (San Jose, Costa Rica), the toilet and hand washing water is provided all by rain water harvesting (see Figure 11). Two methods of catchment and storage are used. At the souvenir shop / restaurant there was a tank that uses the roof of the establishment as the catchment area (see Figure 12). He roof is pitched and covered with shingles. The water can run across the roof to the gutters for guttural flow. The gutters flowed directly into some storage tanks. The first tank (the lower green metallic one) is used as a first flush system, to remove the initial and larger solids. Relative to the first flush systems used in the USA, this first flush system is much larger. This is likely because of the enormous amounts of rain received in this part of Costa Rica is way more than is needed for the needs of the small store and restroom. As the water enters the down pipe, it will first be diverted into the first flush bucket. The majority of the pollutants will enter this container and stay there, settling to the bottom. Once full, the water will then flow into the actual harvester tank. And remain there in storage until it is needed in the buildings. The first flush tank needs to be emptied between each storm to be effective in removing pollutants.

Figure 11: Sign advising visitors of rain water harvesting use on site (Park, 2012) || Figure 12: Souvenir shop rainwater harvesting system (Park, 2012) ||
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The second method of water capture seemingly used in this location is water pumped from an open air storage (small reservoir). The water is pumped up from the reservoir through the small pipes (see) into the storage tank. This method is likely used (instead of directly harvested from the restroom roof) because of the odd shape of the roof (see ) makes it difficult to control the water. A small pumping station is used to supply the restrooms needed demand (see ). Also pictured is the inside of the restroom storage tank with a floater which is used to signal to the pump when to turn on or off (see ).

Figure 13: Piping system of open air water source (not pictured) into storage tank (grey on bottom right) (Park, 2012) || Figure 14: Odd layout of restroom roof (Park, 2012) || Figure 15: Restroom pumping station (Park, 2012) || Figure 16: Tank floater for monitoring pump use (Park, 2012) ||
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Something which is interesting to note with this setup for the restrooms is that the toilets flush with normal pressure because of the toilet’s tank storage, but the faucets water pressure is low. This problem could be improved by adding pressure head to the water tank. This can be accomplished through mechanical head (buying a larger pump) or elevation head (pumping water to a tank on the roof for storage, when the water is needed for the faucets, the water can drain from the tank on the roof and the pump kicks back on to refill). This second option allows for a smaller pump with less electricity consumption, because it does not need to pump the water necessarily fast (depends on the demand) but it would requires an additional storage tank. A cost benefit analysis could be conducted to see the cost/benefit ratio of both options.

Triple Bottom Line Analysis of Urban De-centralized Water Infrastructure System
In the same manner of centralized water infrastructure, decentralized water systems fulfill the social and economic needs of the triple bottom line.

The systems would still need to be operate by trained professionals, so the same amount of economic gain that was possible with the centralized system will also be possible with decentralized. In some ways centralized may be more economically profitable given the ease of expansion. If more water is needed in a location (from population growth, etc) a new small treatment plant and conveyance can be constructed at a fairly low cost to service those needs. In contrast with centralized systems, expansion is very difficult and expensive since existing and functioning infrastructure is not easy to expand. To prevent these costs, when a new centralized treatment facility is in the planning stages, they are built too large in order to accommodate future projected growth. Until this growth is realized, the treatment company is not realizing the full economic potential of the plant. If the population projections are not met, then the company will never achieve full economic potential.

The societal demands will be fulfilled as the decentralized infrastructure can be built wherever (usually) it is needed. If a new development is to be built, a new small treatment plant can be rapidly constructed and completed as the new development is completed. For any reason water was needed from the centralized system, it can also be accessed with a decentralized system.

A decentralized water infrastructure system should be more environmentally friendly than a centralized system for the following reasons:

- The infrastructure is much smaller scale and a much smaller footprint. Less raw materials needs to be extracted and used for the equipment. The area of the treatment is minimal, leaving more land for development or natural ecology

- The conveyance infrastructure is incredibly less. Massive pipes need never be constructed, transported, nor installed (all three of these actions require the use of fossil fuels and cause dangerous emissions).

- The extraction from the natural waterways is much less, minimizing the harm to the ecosystem. The water is also returned to the same (or close to the same) location which also minimizes the ecosystem harm.

= Conclusion = While there is never a perfect answer to which option (centralized vs. decentralized) is better to use when implementing a new or refurbished water distribution system; there may be an option which is better. Overall the environmental impacts of a decentralized system seem to be less, while still delivering the needed economic and social impacts needed. This does not mean that decentralized treatment is always the best option. Both types of water infrastructure systems is completely dependent on access to a source of water. If water is sparse in the intended area for development, then likely a centralized water distribution system is the only option. If water is abundant in many parts, especially year round, then decentralized systems may be the best option for this area. Decisions of this type need to always be made in a context sensitive manner. The question should be asked: What is the best option for the given sets of circumstances?

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