Exploring the Options
As we become more aware of the need for better water quality, we are reminded that the availability of good, clean potable water is becoming scarcer. The public in the U.S. and many parts of Europe have taken for granted the availability of low-cost water right out of the tap because many municipal water supplies have been in existence for generations.
The oft-misquoted line above refers to the plight of a sailor stranded on a crippled vessel in the Antarctic Ocean. The mariner, an ill-fated voyager trapped on a ghost ship due to his own recklessness, is caught in a nautical Catch-22: his desperate thirst contrasts his fear of the frigid, watery grave all around him.
Although water covers more than 70% of the earth’s surface, the availability of clean water is a global problem. (1 billion people live without access to clean water.1) And while in the U.S. the general situation is neither chronic nor deadly, water access and treatment is an increasingly complex issue. At what point do we realize the importance and scarcity of quality water?
Although the industrialized world certainly has the infrastructure to build and expand clean water facilities as population increases, the reality of clean water begins at the source and ends at the tap. What is your municipal water district doing for water treatment today? What is it planning 25 years down the line? A recent GMI Poll found that 56% of Americans are worried about clean water supplies running out in their lifetimes.
As new communities and towns develop and grow, one of the limiting factors in their expansion is new water sources. Where is the new water? Large municipalities secured some of the large, easy sources of water many years ago, and these water rights are litigiously guarded.
Effectively, developing communities and municipalities in Northern California, for example, are locked out of access to some of the world’s best water. San Francisco gets its water, pristine Sierra Nevada snow runoff, from the Hetch Hetchy Valley. Just across the bay, the East Bay Municipal Water Utilities District preserves large amounts of high quality water drawn from the Sierra foothills in reservoirs around the East Bay. These resources were secured generations ago. Other, less-developed areas have limited access to the lakes, reservoirs and pipelines that feed the San Francisco Bay Area and Northern California.
In many instances, as communities grow beyond current urban limits, developers (and many times cities) are forced to make the expensive infrastructure improvements. Wells and lakes are only so numerous, and running a pipeline from a better water source could be prohibitively expensive. Often, older communities grandfathered into the current water system are faced with new standards and restrictions.
Practical development requires effective investments in infrastructure, including water acquisition and treatment. Certainly, any new community development or updated utility plan requires a large expenditure of capital—sometimes funds are acquired through a bond measure. The focus should be on investing funds to ensure predictably clean water, the scalability to allow for expansion, and the satisfaction of increasingly stringent environmental standards.
The following methods can be considered in the search for new water sources:
- Extending current water distribution systems from existing cities and towns;
- Capturing rain and snow water behind dams and reservoirs;
- Drilling wells and pumping from the water tables beneath;
- Desalinating ocean water;
- Reusing treated water; and
- Condensing water from the air.
All of these methods are being pursued to meet municipal needs in various areas. After a reliable source is acquired, the water must be treated for salts, dissolved solids, organisms, dissolved metals and odors. In the treatment, we need to consider all technologies available to us: distillation, radiation (electrical and solar), and chemical treatment.
The first two can be relatively expensive, as the technology for distillation and radiation is either very energy-intensive or of limited availability. Again, developers are obligated by regulations and codes to provide water that meets certain federal and state standards.
Previously, a growing municipal water treatment system required more chlorine, pH stabilizers and flocculation agents. Sometimes older sources had yet to be treated, so the treatment decision often focused on expanding the current chemical processes.
As a general rule, water is disinfected, and the components that give poor taste and odor are removed. There are several steps in water treatment to remove the salts, dissolved solids and bacterial content:
- Oxidation; and
- Residual disinfection.
Ozone in Chemical Treatment
One chemical that can be a primary treatment source is ozone. Ozone is a very powerful oxidant with an unstable chemical structure. Ozone is used successfully in the removal of bacteria and dissolved metals in industries such as aquaculture, food processing, wastewater and groundwater remediation.
Ozone (O3) is generated by applying an electrical charge to gaseous oxygen (O2), and the combined gas then is transferred into water either by bubble diffusion or pressure injection.
Because of the wide variety of commercially available ozone generator models and sizes, just about any community with five or more homes (about 7,500 gpd) can find ozone to be one component of an economically feasible water treatment system.
The highly reactive nature of ozone makes this chemical an ideal source for pretreatment and oxidation since it has very low activation energy, and its reactions are exothermic. A relatively small amount of energy is required to begin the oxidation reactions where ozone aggressively attacks metals, solids, bacteria and cysts.
Ozone works well in conjunction with several different stages of the water treatment process. Ozone’s oxidation reactions often leave previously soluble molecules to precipitate out of the water, and ozone also enhances flocculation.
Additionally, these previous steps eliminate suspended pollutants before ozone is applied, which allows ozone to work more efficiently upon the remaining material. Ozone’s reactivity also translates into low Concentration x Time (CT) values, which saves on both chemical costs and treatment space.
In the pretreatment stage, removing iron (Fe), manganese (Mn), and sulfur (the major oxidizable chemicals in a municipal water source) are shown by the simplified equations:
Fe+2 + O3 — Fe(OH)3(s)
H2S + O3 — H2O + S(s)
Mn+2 + O3 — MnO(OH)2(s)
All of these products can be removed by filtration or other separation means. For many bacteria and cysts, the oxidation might take a bit longer, so pilot and/or laboratory testing is highly encouraged to best determine the ozone demand and the contact time. Once the CT value is defined, the key is to integrate the ozone application with the water treatment process.
Woodland Heights Mutual Water District
The Woodland Heights Mutual Water District serves 200 homes in a brand new housing community atop a vital agricultural region south of the San Francisco Bay. Because the groundwater, drawn from a local well, is mostly free of metals and solids, the main work for water treatment is disinfection of bacteria and other organisms.
The laboratory found the iron level to be around 400 ug/L and the manganese level to be around 60 ug/L. With a design water flow of 100 gal/min (378.5 L/min), the stoichiometric ozone requirements are:
Ozone demand for iron = 0.400 mg/L x 0.43 mg/L ozone per mg/L of Fe = 0.172 mg/L
Ozone demand for manganese = 0.060 mg/L x 0.87 mg/L ozone per mg/L of Mn = 0.0522 mg/L
Total inorganic ozone demand = 0.2242 mg/L
An ozone generator that doses at 1.98 mg/L was chosen so 1 mg/L is available for potential disinfection duty, even as more water is demanded by new homes and growing families in this community. Ozone allowed this development to utilize the water resources currently in place as opposed to piping the water up from Monterey or installing more expensive equipment.
Konocti County Water District
Konocti County Water District serves about 720 homes around Clear Lake, 300 miles north of San Francisco. Currently, the water flow averages about 500 gpm. The treatment design at 1,500 gpm allows for maximum flow as well as expansion in this growing residential, recreational and agricultural region.
Konocti expanded its current water treatment design to meet population growth and needed both full redundancy and remote monitoring and control. Water quality varies as the source water is from both Clear Lake and the streams and aquifers feeding it. The California State Health Department mandates a disinfection residual, so all water companies have to use chlorine; however, the chlorine smell and taste is the biggest complaint from Konocti’s customers.
“The very first thing we do is ‘zap’ (the water) with ozone,” said Frank Costner, general manager of Konocti County Water District. “We’re using the ozone to disinfect the water and also to oxidize the water before it goes into the clarifiers.”
Ozone not only disinfects and oxidizes the water, but it also minimizes chlorine use and eliminates the disinfection byproducts. That way, ozone helps Clear Lake have a chance of staying aptly named.
In summary, ozone is very practical for both expanding towns and new communities, especially where access to good water sources is limited. Ozone treatment of the water does not need to be complicated or expensive, but it does need to be carefully planned in regards to the water quality and growth in the water district. When applied appropriately in conjunction with either current or standard water treatment methods like filtration, ozone maximizes the efficiency of the water treatment process.
Existing water sources can be treated and brought up to necessary standards without hurdling the geographic, regulatory and environmental obstacles. The water may not be everywhere, but with ozone, at least you can have some to drink.