Water quality and disinfection
For the first 75 years of the 1900s, chemical clarification, granular media filtration, and chlorination were virtually the only treatment processes used in municipal water treatment; however, in the last 30 years there have been newer technology developments in the field of water disinfection that we shall explore during the course of this article.
The key objectives for the research and development of newer technologies in this sector are targeted around the following factors –
- Lower capital expenditure
- More cost effective operations and maintenance
- Higher efficiency
- Ease of operations
- Better effluent water quality
- Lower cost of sludge management
- Reduced manpower cost
- Higher sustainability quotient
- Greener & eco-friendly technologies, and so on.
Based on the above factors, research has been conducted in almost all fields of science, from physics (membrane filters to UV radiations) to chemistry (using the latest innovations in biocides to chlorine kind of alternatives being used traditionally after World War II) to biology and microbiology (using cyno-bacteria to aquatic weeds to floating islands and so on) for both water quality improvement and disinfection. We’ve even seen some of the recent ecological approaches like Cownomics© technology being used in India.
We’ll try to evaluate each of these upcoming technologies and their pros and cons in this article for an easy understanding of the jargons for our readers. So let’s proceed to our first technology:
1- The Ionization Process – This is another widely used demineralization process for water softening, in which various chemicals are used for neutralizing calcium and magnesium ions, the presence of which is known to make water hard. The technology is commonly designed as a fixed-bed process in which a synthetic resin is packed. As water passes through the resin bed, contaminant ions present in the water are exchanged with ions on the resin surface, thus removing the contaminant ions from the water and concentrating them on the resin. The resin is frequently regenerated to remove the contaminant from the resin surface and replenish it with the original exchange ion.
Pros – As it is a chemical based process, industries finds it easy to use and implement due to the comfort with chemicals. Largely implemented in industries for demineralization needs and second largest implementation is in water softening.
Cons – Works primarily in demineralization only, not in qualitative improvement in water quality or disinfection. Moreover, every chemical reaction has its own residue, thus it makes it unsafe for human consumption.
2- The UV filtration – Ultraviolet (UV) irradiation technology is primarily used in the water and wastewater treatment industry as a disinfection process that capitalizes on the germicidal effect of UV light in the wavelength range of 250 to 270 nm. The technology focuses on microbial disinfection as most of the microbes cannot withstand the UV radiations. Therefore narrow channel of water is passed through UV lights and the radiation therefore kills the pathogens. The process consists of a series of UV lamps enclosed inside quartz sleeves that passes light through the quartz into the water. This process is considered apt for restaurants, highway rest areas, airports, schools, camps, factories, rest homes, and hospitals.
Pros – Wide acceptability, expected to be high precision in disinfection, considered compact process since the exposure takes just seconds, thus it is considered fast.
Cons – Because of the high energy emitted by the UV lamps, the temperature of the quartz sleeve rises substantially, causing precipitation of various scales on the surface of the sleeve, which blocks the passage of the UV light into the water and dramatically reduces the efficiency of the process. The scales are commonly caused by the precipitation of calcium, iron, or magnesium salts.
3- The Ozonization Process – This started somewhere in the late 70s or early 80s. The application of ozone in water treatment has is being done especially for color removal, taste-and-odor control, and microbial disinfection. Ozone is just a derivative of Oxygen, wherein instead of two atoms of Oxygen (O2) when they bind together as three atoms it becomes Ozone (O3).
Pros – off late this has become quite a popular technology and with increasing footprints it is also becoming affordable. This also help oxidation of water thus has a ripple effect in water quality improvement too.
Cons – installation of a separate system for Ozonizing adds to extra cost the whole plant. After the process, removal of ozone residual with hydrogen peroxide is not always very effective and almost nil in alkaline water. But the biggest threat or flipside to this technology is potential to form bromate (BrO3-), a carcinogen, when the water being treated contains bromide.
4- The membrane filters – As the name suggests, the concept is of a perforated membrane through which water can pass, but solids can’t. Thus passing water through the membrane is expected to clean the water up to some extent. There are many technologies as subset of the membrane technology like Reverse Osmosis (RO) technology, pressurized filtering through membrane, high pressure filtering, low pressure filtering, and so on. Then there are various sizes of filters (measured in microns) creating variations in the technology, but the basic principles remain the same. Water is passed through a membrane and whatever the membrane can hold is filtered with a variation subject to the filter size and the pressure.
This technology is being used widely and is considered quite successful due to huge acceptability across the urban local bodies and municipalities, from sewage treatment to water Softening plant to desalination plants till drinking water treatment plants.
Pros – Easily available, widely acceptable, huge install base, cost effective versions also available in the market.
Cons – Frequent service, device dependent, not very high precision in results.
5- The Cownomics© Process – This is an ecological process in which the aquatic ecology is reinstated. The process is easy to adopt and implement by urban local bodies and municipal corporations and has been fairly successful in Waterbody Rejuvenation projects across West, Central & North India and has resulted into remarkably good improvement in water quality among all parameters. The disinfection in the process is based upon the Oxidation Reduction Potential (ORP) negativity. It has been observed in various researches across the globe that most of the microbial infestation by disease carrying pathogens like Escherichia Coli, Salmonella, Klebsiella, Enterobacter, Cyntrobacter, Edwardsville, Streptococci, and Clostridium etc. die their natural death in ORP negative water. And thus in this treatment, the water gets disinfected as the water turns ORP negative with this treatment with the major electrolytes getting balanced in the restoration process.
Pros – Sustainable, treats the waterbodies in-situ, ease of use, cost-effective, eco-friendly, no dependency on machines / chemicals, zero energy usage.
Cons – Can only be used in natural waterbodies with soil in bottom, water on top of the soil surface and open on top, enabling Sunlight to penetrate the water surface.
Thus depending upon the kinds of requirement and usage, a technology can be adopted for a particular scenario. Each technology has its own highlights and flipsides, and therefore a careful selection and optimisation is required by the user authority for selecting an apt technology for the specific usage.