Thursday, January 22, 2015

Reclaiming Drinking Water Saves Energy And The Environment

There is a critical nexus of interests to be connected between drinking water, energy use, and the environment.  This article explores a solution that dramatically conserves each.  Moreover, it is readily technologically feasible and easily introduced into all major population centers.

There are several observations to be made regarding water, electricity, and the environment.  First, virtually every agricultural and population center on the planet uses more fresh water than is naturally replenished, and indeed some are running through reserves at such a rate that they are already running out of fresh water.  Second, the amount of energy required to extract, distribute, treat, and dispose of water    or to create fresh water from salt water    is one of the single largest sources of energy consumption.  Third, man’s abuse of natural water cycles is wreaking havoc with a tremendous number of environmental systems around the world, leading to catastrophic and likely permanent damage to these ecosystems and their flora and fauna.

I propose that in all towns, cities, and metropolitan centers, the water distribution, sewer, and water treatment systems be tied together.  The purpose would be to create and maintain a permanent closed-cycle loop system to distribute, collect, treat, and re-distribute water.  Doing so will provide ideal water quality, greatly reduce the energy required to make water available, and dramatically reduce the amount of water taken from the ecosystems that depend upon it.

Let’s be clear on three things: first, it is certain that sewage water can readily be cleaned to standards beyond those required of existing water standards    this is well-demonstrated and beyond challenge.  Second, such closed-loop systems result in stunningly large savings in electricity, which has equally stunning implications for reducing global pollution (and can thereby also reduce energy-related geopolitical friction).  Third, this is an inevitable end-game given that natural aquifers are not replenishing at the rate humans draw them down, yet given our consistent pattern of thinking only of our species over the existence of every other species we may not come to this obvious conclusion until after we have caused the extinction of incalculable other species. 

Reclaimed Potable Water Is Pure

Cleaning sewage water to drinking water standards may accomplished through fairly new but very well-tested technologies.  Potable (i.e., drinking) water in the U.S. must meet many standards (  Among the monitored pathogens and chemicals and element contaminants are these categories: 

  • Micro-organisms (ex: giardia    zero acceptable tolerance) 
  • Cleaning agents (ex: chlorine    monitored to low levels) 
  • Inorganic chemicals (ex: the heavy metal barium    may have no more than 2 MCL (Micrograms per Liter, also known as Parts Per Million (PPM)))
  • Organic chemicals (ex: the petrochemical Toluene    1 MCL)
  • Radioactive materials (ex: uranium). 
There are nearly one hundred monitored contaminants.  If all are properly monitored and treated, the resulting water will be pure.

Importantly, all testing has revealed that reclaimed drinking water is remarkably pure.  In fact, having all water flow through a single treatment facility better enables complete and consistent testing to ensure the purity of the water.  The water coming out of such treatment facilities is cleaner than the water typically pulled from our waterways and aquifers: a recent National Research Council study concluded that reclaimed potable water had contaminant risk many times lower than that found in conventional water supplies (

It is against the law to discharge untreated sewage directly into the public waterways, which is the inevitable end-point for treated sewage water.  Therefore, in all developed nations, the infrastructure to collect, treat, and discharge the sewage water already exists.   Consequently, the basic transportation infrastructure for enabling sewage water to be fully treated already exists.

The Key Issue Is Energy 

In order to treat the sewage, there are three basic steps.  First is primary treatment, which is the separation of heavy solids, oils and light solids, and the remaining liquids.  Next comes secondary treatment, which is the use of beneficial micro-organisms to remove biological elements.  The final stage, tertiary treatment, is typically chemical treatment and/or physical filtering. 

The energy required to perform these basic sewage treatment steps is significant.  For instance, the Silicon Valley Advanced Water Purification Center uses 770KWH/AF (KWH = kilowatt hour, and AF = acre-foot of water, which is 325,853 gallons).  This is the amount of energy input into the treatment system.  Interestingly, there are developing technologies that actually extract some energy from some forms of treatment, and such energy harvesting systems would fit best with full water treatment systems built for reclaiming drinking water (;

In order to treat sewage water so as to make it potable turns out to require only a few additional steps and only a bit more energy.  The Silicon Valley Advanced Water Purification Center system begins with the described sewage treatment steps, and then adds the following additional processes: microfiltration (forcing the water through very fine hollow fibers);  reverse osmosis (forcing the water through membrane sheets with holes so small that a water molecule is almost the only substance that can pass through); and ultraviolet light (exposing the water to strong ultraviolet light to act as a powerful last stage disinfectant) (  The energy requirement for this system is 1600KWH/AF. 

Lastly, potable water can be created through desalination.  This process forces sea water under very high pressure through reverse osmosis filters similar to those identified above.  However, because there are far more salts and solids in sea water (that cannot be removed through any other form of treatment or filtration), the pressure required is much greater and the efforts required are much more energy intensive (and, some other steps as identified are also often still required).  Lastly, the system requires the construction of a wholly new plant, it requires long piping systems into the sea, and it results in the discharge of brine that is dangerous to local marine life.  But moreover, in addition to huge capital cost and direct environmental damage, the typical energy requirements for desalination systems is 6000-12,000 KWH/AF    many times more than the energy required for reclaimed drinking water.  (

The critical energy comparisons are clear in comparing the energy requirement for treatment of sewage (required) versus treatment for reclaimed drinking water versus desalination treatment.  The energy requirement comparison    770 v. 1600 v. 6000-12,000KWH/AF    speaks for itself.  But simply leaving the analysis there is far from complete.  The full comparison must also include analysis of all water energy use and full environmental impact. 

It is difficult to perfectly quantify the energy required to obtain new water for each region, but reasonable estimates can be made based upon overall numbers.  In California, fully 20% of total electricity use is for transporting water (   California’s annual electrical energy use is about 230,000,000,000 KWH (, and therefore water-transport-related electrical use was 46,000,000,000 KWH.  Even given California’s relatively low carbon footprint of 0.5LB of carbon dioxide (among other pollutants) per KWH of electricity (, this still amounts to 23,000,000,000 pounds of carbon dioxide annually related to water transportation.  This is equivalent to the tailpipe pollution of about 2,300,000 vehicles (about one fifth of all the vehicles in California) (  Simply stated, there is tremendous energy savings in NOT having to transport new drinking water. 

A Win For The Environment

As for the environmental savings, this is even more difficult to quantify, but the savings are even greater.  As a further example of environmental impact, California is struggling to avoid draining its rivers, streams, lakes, and wetlands to meet the demand for water.  A large percentage of the planet’s biological diversity is found in such waterways.  Once dried, the species that were native to those waterways are forever extincted, never to return.  (Humankind is already responsible for the planet’s sixth great mass extinction, leading to the disappearance of a potential 50% of all species.)  Also, underground water supplies have been drawn down so far that lands are subsiding; salt water is infiltrating into fresh water; and, pollution in the remaining water is rising.  The opportunity to avoid these losses should be a paramount concern.

… And A Win For The Economy

Lastly, there is a tremendous economic savings in avoiding water transportation.   In addition to the savings in electrical energy, multi-billion dollar projects are required to bring water to population centers.  The future costs of such projects continue to rise.  The alternative is restricting water use by individuals and businesses, including agriculture (the most water-intensive business).  Between the energy savings, the capital project costs, and the impact on business, the cost of transporting water is in the hundreds of billions of dollars.  By comparison, more robust water treatment plants take advantage of existing water infrastructure, and their costs are comparatively much lower.

The benefits of employing available technology to endlessly reclaim drinking water are obvious.  It will doubtless happen.  The only question is when.  Hopefully it will happen sooner rather than later, because the planet’s most pressing issues    energy and the environment    lie in the balance. 

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