"When the well is dry, we know the worth of water." – Benjamin Franklin
Did you know that water is needed in almost everything we use, we do, and we eat? Table 1 shows a summary of how much water we use every day for food and products we use in our homes and daily lives without even thinking for a moment how much water is needed to make these products.
Did you also know that the human body contains 70 to 75% of water by weight? So a person weighing 160 pounds contains about 115 pounds of water. This is simply mind boggling. To put it mildly, we cannot live without water — a lot of water.
So philosophically, not buying and consuming too much – clothes, furniture, cars, toys, i-phones, big luxury homes, unneeded appliances — will save a lot of water. Recycle and donate these to charities so that, in the big picture, water consumption is reduced. Overconsumption reduces our supplies of water.
It is a moral imperative that we, as a society, should discard the culture of excessive consumerism and waste since it needlessly consumes large quantities of water which is worth conserving.
This article presents three important ways of water management:
Water conservation is an important yet practical and simple-to-implement way to ensure that our water supplies last longer at home, in our neighborhoods, in our cities and villages, in our states and countries and by extension on our planet as a whole.
Below are many practical ways to conserve water that we can take in our everyday life in a handful of categories.
Did you know that wastewater is 99.9 to 99.95% water? It is only the remaining 0.05 to 0.1% (about 500 to 1000 mg/L) that is composed of impurities originating from industries or from human consumption of water. Wastewater treatment and recycling, therefore, involves removing only these impurities. Why then should we not reuse and recycle water?
The population on our planet is projected to increase to more than 9 billion from the current 7.5 billion by the year 2040. In addition, standards of living are continually increasing all over the globe, which are further stressing our water resources. However, water quantities available for use are constant and always have been since the dawn of time. Water recycling is a resource which therefore must be tapped to meet the continually growing demand of water. This serves as another reason why we should reuse and recycle water.
There are five stages or levels of wastewater treatment, some or all of them are necessary before water can be reused and recycled. How many stages should be employed before reuse depends upon the type of intended reuse. The purpose and level of treatment in all cases is the protection of public health. For example, if the water is going to be reused for growing alfalfa intended for animal feed, the requirements will be less stringent than if it is to be used to grow edible crops like tomatoes and lettuce. Similarly, if the intended use is for irrigation of golf courses at night time, the requirements would be less stringent than if the intended use is for irrigation of school playgrounds used by children. Reuse for drinking purposes — direct potable reuse (DPR) or indirect potable reuse (IPR) applications — would require the highest quality of recycled water and all five stages of treatment. In addition very aggressive monitoring, redundancy and reliability in design and operation would be required, and reuse applications in between these two extremes — of which there are numerous — will similarly require fewer stages of treatment.
These five stages of treatment (see Figure 1) schematically are:
Figure 1: Conceptual Schematic Showing Typical Wastewater Treatment (Treatment of by products – sludge/bio-solids not shown for simplicity)
Different stages remove different constituents from wastewaters. Preliminary treatment primarily removes grit and screenings; primary treatment removes organic and inorganic suspended matter; secondary treatment removes both suspended and dissolved organic substances mostly by biological means; tertiary treatment in most part removes particles not removed in previous stages of treatment; and the last and fifth stage removes refractory and nonbiodegradable materials, and after disinfection with high doses of disinfectants and oxidants such as ultraviolet light, ozone and hydrogen peroxide to prepare the water for many unrestricted reuse applications including DPR and IPR.
Although most of us are quite familiar with the first four stages of treatment since almost all wastewater treatment plants today employ these treatment stages in some form or the other, the advanced treatment stage (AWT) is not that common. In water scarce parts of the country — such as California — AWT has been provided by a few large water agencies and is being considered by many others. This opens up other avenues for water reuse such as IPR and DPR via groundwater recharge, storage in underground water aquifers, storage in large raw water reservoirs used as a source of drinking water supplies, and many others.
AWT essentially removes refractory materials, not removed in the first four stages of treatment, which are present at parts per trillion levels (ppt) in wastewater. The sources that contribute to these refractory and recalcitrant materials are industries (most often their products have proprietary formulations and contain chemicals, which do not have to be disclosed and therefore are not disclosed by the industries), personal care products used in homes such as fragrances and others, medicines and drugs, antibiotics, pesticides, and various pharmaceutical compounds, to name a few.
These materials are believed to be carcinogens and endocrine disruptors and must be removed for IPR and DPR applications per regulations promulgated by many states and local jurisdictions to protect public health. If not removed, they could interfere with the body's endocrine system with long enough exposure, and can produce adverse developmental, reproductive, neurological and immune effects in humans and wildlife.
The Terminal Island WRF in Los Angeles employs advanced water treatment at its facility to aid in a barrier to protect groundwater aquifers from salt water intrusion.
With new analytical methods now available, these chemicals — even though present in parts per billion and parts per trillion concentrations — can be easily measured. Their long-term effects on human health are not always fully known, but are of concern in reuse of water for IPR and DPR.
Each stage of treatment produces a waste stream (screenings, grit, biosolids or sludge, etc.) which must be hauled away, or treated to produce beneficial materials such as soil conditioners, compost and some form of aggregate with potential reuse applications in roads, land reclamation, and others. Once again, there are state and federal requirements and standards that govern these uses with the sole objective of protection of public health.
In addition, anaerobic digestion of biosolids can produce up to 60 kW of electricity per 1 mgd of wastewater flow. New processes are being developed to increase this further so that wastewater treatment plants are close to being energy neutral (and some already are achieving that). Treatment of these waste streams is beyond the scope of this paper.
Table 2 below presents a summary of potential reuse and recycling applications and general water quality requirements for these uses. This table is meant to be very general because each state and local jurisdiction may have different requirements that must be determined before a reuse project is planned and implemented.
Please note the method of applying water for irrigation-spray versus subsurface drip, for example- can make a difference in the level of treatment required. The public exposure to spray irrigation systems is much higher than subsurface drip irrigation and thus may require higher levels of treatment and associated application restrictions.
Use the following key to identify the treatment guidelines in the second column of Table 2 below.
Landscape irrigation of public areas without restriction
Landscape irrigation of areas with restricted public access such as highway landscaping
Nurseries, Christmas tree farms, tree farms, and sod farms
Food crops that undergo commercial, pathogen destroying processing before consumption
Pasture and fodder for animals, fiber (cotton) and seed crops not eaten by humans
Orchards and vineyards not bearing food crops during irrigation
Supply for non-restricted recreational impoundments
Supply for restricted recreational impoundments, fish hatcheries
Toilet and urinal flushing in commercial buildings
Commercial and public laundries for clothes washing
Industrial process water (potential worker exposure)
• Fire fighting by dumping from aircraft
• Water jetting for backfill consolidation around potable water lines
• Water jetting for backfill consolidation around other than portable water lines
• Washing aggregate and making concrete
• Dust control and fill moisture control
Industrial process water (no worker exposure)
• Fire fighting by dumping from aircraft
• Water jetting for backfill consolidation around potable water lines
• Water jetting for backfill consolidation around other than portable water lines
• Washing aggregate and making concrete
• Dust control and fill moisture control
Future of wastewater treatment and water reuse seems to be limitless. In general, it will necessitate innovations in the following areas:
The future wastewater treatment plants will be resource recovery plants, not just in euphemism, but in actuality.
A boat sails in the Washingon Channel off the District Wharf in Washington, D.C. during Water Week in 2019.
Water management for our growing population and water needs is a tall order. But as water sector engineers and planners have demonstrated repeatedly over the years, this is a task that is not only important but achievable. Remember It will involve conservation, recycling and innovation. We have come a long way from septic tanks to modern-day plants employing complex technologies, so moving forward is certainly easier than the journey of the past.
Madan Arora Ph.D., P.E., BCEE is a technical director at Parsons. Arora can be reached at madan.arora@parsons.com.
The Water & Wastes Digest staff invites industry professionals to nominate the water and wastewater projects they deem most remarkable and innovative for recognition in the Annual Reference Guide issue. All projects must have been in the design or construction phase over the last 18 months.
7 Basic Types of Temperature Measuring Sensors
The Flint Water Crisis: 7 Years Later
What is Biological Oxygen Demand (BOD)?
What is Aeration for Wastewater Treatment?
What is Total Suspended Solids (TSS)?
©2022 Scranton Gillette Communications. All Rights Reserved Sitemap | Privacy Policy | Terms & Conditions