Background Information
Water Use, System Sustainability, and
Self-Sufficiency
The importance of water and water resources in our world is becoming progressively more critical. The availability of clean drinking water and water as a resource for sanitation, irrigation, fire protection and general use is a growing concern. As our cities expand and sprawl outward, we are forced to devise new ways to conserve and reuse this valuable resource. In fact, the National Academy of Engineering, in listing the Grand Challenges for Engineering, included “Provide Access to Clean Water” as a critical focus for engineers in the 21st Century.
The home can be considered a microcosm of our global situation. Homes use water for all the uses above, and many others. Green Homes are increasingly being built to conserve and reuse water, and in some instances avoid water use entirely. The average water use in today’s homes is approximately 64 gallons per person. Green homes often conserve water both indoors and outdoors. More efficient water delivery systems and using native and drought resistant landscaping choices can help prevent unnecessary waste of valuable water resources.
In some ways, the home can also be considered a closed system. Within a closed system (in this case, the home) no material leaves the system; it is self contained. Water is used as an input, both indoors and outdoors, and from piped and natural sources. Our water can come from a variety of sources including rivers, streams, aquifers, reservoirs, and even desalinization of salt water or molecular fusion. The water is piped to homes through local utility companies, municipal systems or in some cases, supplied to the homes through individual well sites. Within our home we utilize water for irrigation, drinking, cleaning, cooking and in appliances.
In an ideal situation, the home would become a self sufficient closed system. Water would be recycled for other uses, and rain and infiltration utilized in a highly efficient manner. For this essay, students will research and devise a system to conserve, recycle and reuse water within the home. The water needs to be cleaned to the level of safety adequate for its use- drinking water, sanitary systems, etc. For the purpose of this essay, a home will include both the interior and immediate exterior landscape surrounding the home structure. A home will also include multi-family units. In that instance, while each unit would be expected to conserve water, the building as a whole will be considered the closed system.
In an age where water is becoming more precious and more scare every day, the students are challenged to go beyond the ordinary and traditional conservation, desalinization and water treatment discussion. They are challenged to design a self-sustaining home system or process that requires little or no water from commercial or municipal sources, public or private wells or water supply trucks to replenish the home supply. They are challenged to consider the following critical factors in their discussion of the topic:
| Re-use | Nature |
| Run-off | Treatment |
| Conservation | Reclamation |
| Distribution | Reclamation by-products |
| Gray water | Creation or manufacture |
| Independence or autonomy of water supply | Collection |
To put the topic in context, think of the home unit as a space station circling the earth or existing on a planet that has virtually no water resources. The challenge is to be as nearly totally self-sustaining as possible.
Maybe your unit is located where you can individually harness nature to provide some of the water supply you need. Maybe the process you devise is super efficient at reclaiming wastewater. Maybe you devise ways to extract and collect water from other chemical or mechanical processes.
A search of literature and Internet sites will reveal a large amount of material about conservation, reuse and other reclamation processes. But those are today’s methods with just a hint of tomorrow’s technology. Can you take it further? Can you actually devise ways to create water to add to your supply?
Collection, treatment and distribution are facets that any process must address, even if the total capacity of the system is only enough for one unit.
To design a system of the future, you must have some understanding of today’s methods and problems.
Treating Wastewater
Treating wastewater normally incorporates three elements: Physical, Biological and Chemical.
Physical
Physical processes were some of the earliest methods to remove solids from wastewater, usually by passing wastewater through screens to remove debris and solids. In addition, solids that are heavier than water will settle out from wastewater by gravity. Particles with entrapped air float to the top of water and can also be removed. These physical processes are employed in many modern wastewater treatment facilities today.
Biological
In nature, bacteria and other small organisms in water consume organic matter in sewage, turning it into new bacterial cells, carbon dioxide, and other by-products. The bacteria normally present in water must have oxygen to do their part in breaking down the sewage. In the 1920s, scientists observed that these natural processes could be contained and accelerated in systems to remove organic material from wastewater. With the addition of oxygen to wastewater, masses of microorganisms grew and rapidly metabolized organic pollutants. Any excess microbiological growth could be removed from the wastewater by physical processes.
Chemical
Chemicals can be used to create changes in pollutants that increase the removal of these new forms by physical processes. Simple chemicals such as alum, lime or iron salts can be added to wastewater to cause certain pollutants, such as phosphorus, to flock or bunch together into large, heavier masses which can be removed faster through physical processes. Over the past 30 years, the chemical industry has developed synthetic inert chemicals know as polymers to further improve the physical separation step in wastewater treatment. Polymers are often used at the later stages of treatment to improve the settling of excess microbiological growth or bio-solids.
Wastewater treatment refers to the process of removing pollutants from water previously employed for industrial, agricultural, or municipal uses. The techniques used to remove the pollutants present in wastewater can be broken into biological, chemical, physical, and energetic. These different techniques are applied through the many stages of wastewater treatment. Typically wastewater treatment facilities include the following elements or processes:
| Primary Treatment | Secondary Treatment |
|---|---|
Screening |
Aeration Tank |
Comminutor |
Secondary Clarifier |
Grit Chamber |
Disinfectant |
Primary Clarifier |
Ultraviolet Disinfection |
Coagulation |
|
Membrane Filtration |
|
Constructed Wetlands |
Primary treatment usually includes the removal of large solids from the wastewater via physical settling or filtration. The first step in primary treatment is screening.
Secondary treatment typically removes the smaller solids and particles remaining in the wastewater through fine filtration aided by the use of membranes or through the use of microbes, which utilize organics as an energy source. Energetic techniques may also be employed in tandem with biological techniques in the secondary phase to break up the size of particles thus increasing their surface area and rate of consumption by the microbes present. A common first step in the secondary treatment process is to send the waste to an aeration tank.
Microbial Degradation – Aeration Tank
Bacteria are single celled organisms, which have basic requirements for existence and reproduce rapidly. Many occupy unique niches and consume only certain types of food. Many types of bacteria have been utilized in wastewater processing. If certain bacterium is supplied with an environment in which the proper pH, temperature, micro and macronutrients, and oxygen levels are present, it can quickly and effectively break pollutants present in wastewater down into less harmful components.
The types of bacteria utilized in wastewater processing can be categorized based upon their necessity or intolerance of oxygen to survive. Those bacteria that require oxygen to convert food into energy are called aerobic, those that will perish in the presence of oxygen are anaerobic, and finally facultative anaerobes may thrive in either the presence or absence of oxygen. Typically aerobes, which can degrade pollutants 10-100 faster than anaerobes, are utilized most frequently. Increases in temperature and pollutant food source have shown to increase the rate of degradation, but if all elements necessary for conversion of food to energy are not in balance, the microbial degradation will be thwarted.
Tertiary treatment involves the disinfection of the wastewater through chemical or energetic means. Increasing the number of steps in a wastewater treatment process may insure higher quality of effluent; however employing additional technologies may incur increased costs of construction, operation, and maintenance.
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Water Use References
Search Terms
- Water Use and Efficiency
- Water purification, Water treatment, Municipal Water Systems
- Reclamation, Conservation
- Graywater, Runoff
- LEED, EPA
USGS
http://ga.water.usgs.gov/edu/wateruse.html
Water – Use it Wisely
http://www.wateruseitwisely.com/
Personal Water Use Calculator
http://ans.engr.wisc.edu/eic/WaterForm.html
House Water Saver
http://www.h2ouse.org/tour/index.cfm
Use of Graywater and Rainwater to conserve and save money
http://ag.arizona.edu/AZWATER/arroyo/071rain.html
Home Water Treatment Systems
http://www.engr.uga.edu/service/extension/publications/c819-10c.html
NSF Water Treatment Devices
http://www.nsf.org/consumer/drinking_water/dw_treatment.asp
Understanding Home Water Treatment Systems
http://extension.missouri.edu/xplor/envqual/wq0104.htm
Sustainable Infrastructure for Water and Wastewater
http://www.epa.gov/waterinfrastructure/
Green School Operations Guide, Sustainable Water Use
http://gonextgeneration.org/programs/Next%20Generation%20Water%20Green%20Operations%20Guide.pdf
GE Ecomagination
http://ge.ecomagination.com/site/index.html?c_id=googwfeb5#admt
EPA: Water Recycling
http://www.epa.gov/region09/water/recycling/index.html
EPA Guidelines (Chapter 7)
http://www.epa.gov/nrmrl/pubs/625r04108/625r04108.pdf
EPA Primer for Municipal Wastewater Treatment
http://www.epa.gov/OWM/primer.pdf
Pall Corporation
http://www.pall.com/water_8161.asp
National Association of Home Builders (NAHB) Model Green Home Building Guidelines
http://www.nahb.org:80/generic.aspx?sectionID=1195&genericContentID=56077
LEED for Homes
http://www.usgbc.org/displaypage.aspx?cmspageid=147
H2ouse – Water Saver Home
