I. Principles

Up to the present time, the most common process for iron removal from water is to allow water-soluble ferrous (Fe²⁺) iron in water to turn into water-insoluble ferric iron (Fe³⁺) by, and then capturing FeIII (iron oxide) particles by filtration in some form. For this process, air or some oxidation (e.g., chlorine) is added to raw water first before entering a reaction chamber, where a slow oxidation reaction (spontaneous oxidation) occurs. The water is then filtered, with the filtration media primarily being a mechanical-physical barrier.

In typical iron removal systems for all but small flows, the reaction chamber necessary for complete oxidation can be very large to permit the flow transit time needed for this slow spontaneous oxidation to occur. Such systems usually require considerable land space and are costly to construct. They are relatively complex hydraulically and mechanically. Because various well in a wellfield produce differing concentrations and qualities of iron, and because these concentrations and qualities vary day to day, oxidation-filtration plants require frequent attention and adjustment to work properly.

It has been confirmed by practical experience of several decades in China and thousands of experiments that “new filter media” produced under certain chemical conditions will react immediately on contact with Fe²⁺ in raw ground water to form Fe³⁺.

In this “contact oxidation”, the rate of oxidation is about 60 times that of spontaneous oxidation. Consequently, the time needed for iron removal is greatly shortened. Because the iron is both oxidized and captured in the media, the process is greatly simplified. There is no need for a huge oxidation chamber.

The ferric hydroxide (FeO(OH)) formed is a rusty-red membrane attaching to the surface of the filter media. The “new” or “contact oxidation” filter media consists simply of the media and a coating of a specially structure ferric hydroxide –
Γ-FeO(OH) – that has a very strong contact oxidation ability. Anion exchange absorption reactions occur on the surface of the oxide when pH in the water is under the isoelectric point, while cation exchange occurs when water pH is over the isoelectric point. The pH of iron-containing ground water is generally with a range over the isoelectric point of Γ-FeO(OH), so cation exchange absorption occurs. Ionic exchange absorption of Fe²⁺ in water occurs first, with equimolar H⁺ lost from the surface.

After the initial exchange absorption, Fe²⁺ goes on hydrolyzing and oxidizing, and new Γ-FeO(OH) is continually is produced. This autocatalysis reaction ensures new contact oxidation iron filter media against aging.

Chemical controls on the Fe-removal process:

Chemical characteristics of natural ground water are changeable. Various chemical factors may affect the results of reaction (2) and (3). Comparative experiments have been carried out on different chemical factors such as iron concentration, pH, alkalinity, SO₄^2-, HCO₃-, soluble SiO2, water temperature, types of filter media, filtration rate, and so on. The results have demonstrated that all of the above-mentioned factors influence the results.

The best process can obtained simply by the control of and pH factors, although the other factors are also effective on
Γ-FeO(OH) formation.

II. The Manufacture of “New Filter Media”

Carrier of filter media: The media uses a hard, granular material as a nucleus. Formation of Γ-FeO(OH) membrane on the “new media” surface: The membrane is formed by controlling the ratio in the solution and the pH of the solution. Media can thus be regenerated on-site on almost any media material.

III. Advantage and Applications of this “new Filter Media”: Manufacture process of Γ-FeO(OH) Membrane:

Advantages:

The chief advantages of the invented process are that it is
        ● simple yet effective
        ● economical
        ● easy to master in operation and practical

for the removal of iron, manganese, and hardness in raw ground water to provide an improved product water for drinking or many other uses.

Simple and effective: In this new, advanced process, the entire filter becomes an Γ-membrane possessing high-contact oxidation filtering system. As such, it is a high-speed, one-process filtering system.

The well water (with proper pre-adjusted air mixture) can flow directly from the well to the filtration system, often using well pump pressure only. The iron, manganese and hardness will be removed without other effects on product water quality. Once the Γ-FeO(OH) if formed, it will continue renewing itself, which means the system is self-regenerating.

The system is 25 time faster than other media and 60 times faster than spontaneous oxidation. The system can filter up to 50 mg/L of Fe, Mn, and total hardness.

Economical: Because the system is simple, it is economical in construction, process, and operational terms. For the same capacity, the system requires much less space and building capacity, and many fewer system components, including repressurization pumps. Operator time is minimized for adjustment, maintenance, and repair.

Easy to operate: The system requires no pH adjustment and is very “forgiving” in adjusting to changes in constituent concentrations and ratios of Fe²⁺/ Fe³⁺ and Mn²⁺/Mn⁴⁺ due to changing wells and variable pumping conditions. There is no longer a need to maintain an aeration mixing chamber and its environment. There are no chlorine or permanganate feed systems or ozone generators to maintain.

Applications:

Ground Water Source Drinking Water Systems: Any size system from very small public or village or commercial (schools, restaurants) systems to large community systems.  “New media” systems provide an economical step up from sequestrant-feed treatment, and an alternative to complex and cumbersome aeration-filtration or oxidant-feed and filtration plants. There is no need for chlorine, permanganate, or other corrosive chemical feed systems.

Ground Water Source Industrial Water Systems: Low maintenance and “forgiveness” in media operation make “new media” ideal for industrial systems where low operational costs and consistent product water quality are a must. Sophisticated iron-and manganese-removal system quality with softener-like “use and forget” operating simplicity. A real alternative to the cost and difficulty of switching to a regional piped public water system.

High-Quality Bottled Water or Ultra-Pure Systems: The “new media” system provides high quality and low maintenance Fe and Mn removal prior to ozonation, ultraviolet irradiation, and membrane filtration. Cuts down on Fe and Mn interference with ozone and UV, coating and clogging of UV lamps, and clogging and corrosion of membrane filters and elements.

Ground Water Remediation "Pump-and-Treat" Systems: Provides a simple, low-maintenance, small "footprint" alternative to chemical-feed iron removal prior to strippers or carbon filtration. No need for chemical use that may encourage bacterial growth,, harm receiving waters, or cause clogging in recharge wells. Drastically cut maintenance on stripper towers and improves carbon filter service life. Reduce solid and chemical waste due to system maintenance.

Ground Water Source Horticultural and Agricultural Irrigation Systems: Remove staining and orifice-clogging iron and manganese using a simple system with softener-like low maintenance. No need for chemical feed that may harm plants and drives up costs.


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Yun H. Zhang, an engineer, inventor and contractor for the World Construction Co., San Francisco, California, USA, holds patent in China for the Γ-FeO(OH) Membrane.