For sustainable architectural design we should minimize waste and reuse much of the waste generated by human activities, and this goal includes paying careful attention to our use and recycling of liquid as well as solid waste. The guiding philosophy in efficient water use is reduction in the generation of wastewater and potable water demand, while at the same time making every effort to increase the local aquifer recharge. Ideas for best design practices abound. Designers can plan and facility managers can implement decentralized on-site wastewater treatment and reuse systems as part of eforts to recycle water. It is possible to decrease the use of potable water for sewage conveyance by utilizing gray and/or black water systems. Non-potable reuse opportunities include toilet flushing, landscape irrigation, etc. Many municipalities are considering providing advanced wastewater treatment by employing innovative, ecological, on-site technologies including constructed wetlands, mechanical re-circulating sand ilters or aerobic treatment systems. Institutions such as the University of California and Oberlin College have already implemented these wastewater treatment systems to meet the requirement of state and local regulatory authorities for eluent disposal. Disposal of treated eluent by applying it to the land, either by surface application or subsurface dispersal, should become integral to the wastewater treatment approach.
Residential end uses of water. (Source: American Water Works Research Foundation, 1999.)
Minimize Water Waste Daily indoor per capita water use, according to the American Water Works Association (waterfacts.net/ html/water_use.html), is 72.6 gallons for the typical single family home in the USA. Figure 5.4.1 shows how it breaks down. By installing more eicient water ixtures and regularly checking for leaks, households can reduce daily per capita water use by about 35 percent to about 45.2 gallons per day. Upper Figure shows water use for a household using conservation measures. Fixtures that are efficient in terms of water use – some of them using no water at all – can be installed in commercial settings such as offices, airports, manufacturing units, etc., to minimize the use of potable water. Where practicable, gray water (non-industrial waste water from domestic processes such as dishwashing), can be used for toilets and landscaping.
Efficient water use in residences.(Source: American Water Works Association.)
Efficient faucets and sinks
Reuse Gray Water:
Any water that has been used in the home or office, except water from toilets, is called gray water. Dish, shower, sink, and laundry water comprise 50–80 percent of residential “waste” water. his may be reused for other purposes, especially landscape irrigation. It is a waste to irrigate with great quantities of drinking water when plants thrive on used water containing small bits of compost. Gray water reuse is a part of the fundamental solution to many ecological problems. he beneits of gray water recycling include:
It is safe and legal to reuse gray water. In addition to conserving water and in many cases reducing water and sewer bills, using gray water can also “drought proof ” a family’s yard. With landscaping valued at between 5 and 10 percent of the value of a home, this back-up supply of water may be an important economic insurance policy for a family. In climates where water is in limited supply, gray water use should be seriously considered.
Use Solar Hot Water (Reduction of Fossil Fuel Use)
A solar hot water system (Figure 5.4.4) has a collector attached to a roof facing the sun, which heats some working fluid that is either pumped (active system) or driven by natural convection (passive system) through it. he collector is dark-colored and made of a simple glass-topped insulated box with a flat solar absorber made of sheet metal, attached to copper heat exchanger pipes. In this water-heating system the collector concentrates the sun’s rays to heat water, which makes a closed loop through the heating tank. he hot water passes through an already installed in-the-home tank that contains a heat exchanger in the tank; the water is pumped back up to the solar collector (determined by a controller unit). Cold water that passes through the tank heats up and makes its way to building faucets. Since solar energy pre-heats the water in the water tank, it uses a reduced amount of electricity, thus minimizing use of fossil fuel.
Lower Stress on Wastewater Management Systems
Several techniques for easing wastewater issues include rainwater harvesting, installing pervious surfaces, creating bioswales, and using living machines to treat water on site. Water harvesting involves collecting run-of from the soil’s surfaces, paved surfaces, and other sources, and storing it for future use such as irrigation. Harvested water can include stormwater and irrigation run-of; water from cooling towers and heating, ventilating, and air-conditioning (HVAC) systems; and water from swales and other drainage structures directed into collection areas. After collection in a storage tank or pond, harvested runof must be pressurized in order to be used in an irrigation system. Water harvesting has been practiced in countries like India, Sri Lanka, and many other parts of the world successfully for centuries. Most of the ancient methods utilize gravity low to collect run-of into harvesting areas such as storage tanks, open ponds, or detention basins. Also, rainfall from roofs and water from cooling towers can be directed into run-of harvesting areas.
Rainwater harvesting, practiced for centuries in arid parts of the ancient world, involves collecting and using precipitation from a roof or other catchment areas. This is an excellent way to take advantage of natural site resources, to reduce site run-of, and the need for run-of-control devices, and to minimize the need for utility-provided water. In the developing world where populations are dispersed, rainwater collection ofers a low-cost alternative to a centralized piped water supply. In moist climate zones, rainwater collection is an excellent supplemental source of water.
Rainwater harvesting is simply collecting, storing, and purifying the naturally soft and pure rainfall that falls upon your roof. Rainwater may be utilized for both potable and non-potable requirements such as:
Rainwater harvesting is the sustainable supply option. Rainwater can be utilized alone or together with other supply sources in residential, commercial, and industrial projects where pure water is desired.
Each rainwater harvesting system consists of at least the following components: a catchment area or roof surface to collect rainwater; delivery systems (gutters) to transport the water from the roof or collection surface to the storage reservoir; storage reservoirs or tanks to store the water until it is used; an extraction device (depending on the location of the tank, this may be a tap, rope and bucket, a pump, or an infiltration device if the collected water is used for well or groundwater recharge). Additionally, there are a wide variety of systems available for treating water before, during, and/or after storage.
Approximate Estimation of Rainwater Collection
The amount of rainwater that can be collected = catchment area in square feet × rainfall in inches × 0.62 gallons/sq.ft (conversion from inch units to gallons) × collection eiciency. As an example, where the roof area is 2,500 sq.ft and rainfall is 1.97 inches, the amount of rainwater that can be collected is: 2,500 sq.ft × 1.97 inches rainfall × 0.62 gallons/in rain/sq.ft × 0.85 collection efficiency = 2,595 gallons. In some developing countries (in Bangalore, India, for example) after filtering prior to sending it to the water tank, the rainwater is used for washing clothes, bathing and toilet flushing (Figure 5.4.5).
Rainwater harvesting in South India
In urban settings it is important to consider the quality of rainwater. Areas with extremely poor air quality may yield rainfall of poor quality. Rainfall in some areas is highly acidic, and therefore undesirable for reuse without treatment. If the collection area has many overhanging trees, the collected rainwater can contain more debris and may appear brownish in color (caused by tannic acids drawn from plant debris). In areas with hard water, clean rainwater is preferable for its softness, cleaning abilities, and ability to extend the life of appliances such as water heaters and cofeemakers. here are few federal regulations for rainfall harvesting, and guidelines pertaining to the collection and use of rainwater are not clear. Pervious surfaces and bioswales help address issues of urban rainwater quality.
Pervious surfaces:
These are ground covers that permit water to seep through to subsurface levels. One of the major advantages of this type of surface is that it will prevent storm run-of by absorption and thereby reduces the low of pollutants to streams and rivers. These surfaces can be used for simple street walkways or entire parking lots. Portland and several other cities are experimenting with such surfaces.
Bioswales :
These are land elements designed to stop silt and pollutants from joining the surface run-of. he slopes (less than 6 percent) of these elements are such that the water will low smoothly and be iltered by vegetation and riprap stone. These types of swales are designed to slow down the water low, elongating the filtering efect. Bioswales are commonly used around parking lots to ilter automobile pollution. A number of design options should be considered, such as the depth, wet or dry, grassed, rocky, and several other concepts. Also, a designer must take into account the direction of low, slope, quantity of run-of, placement of swales relative to drainage surfaces, and integration of additional bio-remediation features.
Living machines are on-site wastewater treatment facilities. Based on the principles of wetland ecology, the patented tidal process treats wastewater to meet high-quality reuse standards, making living machine technology the most energy-eicient of wastewater treatment options. The treatment is accomplished through a sequence of activities in which anaerobic and aerobic containers hold key bacteria that consume pathogens, carbon, and other nutrients in the waste-water, rendering it clean and safe for reuse and recycling for landscape use. The most common type of living machines have two types of anaerobic tanks, a closed aerobic tank, and three open aerobic tanks – a clarifier, artificial wetland, and an ultraviolet filter. Living machines are very useful since they work of the grid
Living machines require large land area and frequent maintenance. They require permits from city or local government (see he Green Studio Handbook [1]). Even though a typical living machine recycles thousands of gallons of gray water daily below the wetland surface, what an observer sees at the surface is lush greenery.
An example of gray water use for a typical family home
To verify whether a gray water system is right for a family, after checking with local codes, one has to learn approximately how much gray water the family will produce and how much landscape it can irrigate.
Estimating the Amount of Gray Water a Single Family Will Produce
The number of plumbing fixtures connected to the gray water system will determine how much gray water is available for irrigation use. The Greywater Standards use the following procedure to estimate a family’s daily gray water low. Assuming four occupants in the family, they all use:
Estimating the Amount of Landscape the Family Can Irrigate
Gray water is distributed subsurface and will efficiently maintain lawns, fruit trees, lowers, shrubs, and groundcovers. It can be used to irrigate all plants at the home except vegetable gardens. The following formula shows how to estimate the square footage of the landscape to be irrigated (from www.rainmaster. com/historicET.asp):
For the above family, which produces 160 gallons of gray water per day, how much lawn can be irrigated with that gray water?
Average evapotranspiration for selected areas in New Mexico, in inches. (Source: www.ose.state.nm.us/water-info/…/Albq…/rainwater-harvesting.pdf.
The above family produces enough gray water to water a lawn of 1,129 square feet.
Estimating How Many Trees and Shrubs this Family Can Have Instead of a Lawn If this family’s property had trees, another way to look at the gray water system is to determine approximately how much water an individual tree or shrub will need for one week during July (hot season):
The number of gallons of water per week a plant needs will vary from season to season, plant to plant, and site to site, but this will give a general idea about the number of plants one can successfully irrigate in July with gray water.
Summary
Water is essential to life, and yet we continue to undervalue it. As water demands increase, designers must look to new ways of managing water use through installation of more eicient water fixtures, recycling, reusing gray water, water harvesting, and effective, innovative wastewater treatments. Management of water resources is just one of many approaches to reducing our use of fossil fuel energy and decreasing alarming levels of all waste worldwide.
