Question

Research examples of how water treatment practices and systems are being utilized across the globe and in your local community.

Answer 1

There are 5 water treatment practices and systems followed globally which are mention below:

1. Membrane Filtration (Low Pressure And High Pressure),
2. Ultraviolet Irradiation,
3. Advanced Oxidation,
4. Ion-Exchange, and
5. Biological Filtration.

Membrane Filtration Technology:

Membrane Filtration Technology has two types of filtration system (a) low-pressure membrane systems include microfiltration and ultrafiltration and (b) high-pressure membrane systems include nanofiltration and reverse osmosis.

Low-pressure membranes are works at a low pressure of 10 to 30 psi, whereas high-pressure membranes work at high pressures ranging from 75 to 250 psi. Microfiltration and ultrafiltration shows advantage towards low use of chemicals, high reduction of pathogens with no byproduct formation, however, limits its use towards the removal of dissolved color causing organic matter as well as taste- and odor- causing chemical compounds. Also, the use of powdered activated carbon (PAC) has provided added benefit to low pressure membrane filtration.

High-Pressure Membranes like nanofiltration (NF) and reverse osmosis (RO) membranes uses thin-film composite re-membranes (<1nm). With the efficient exclusion of calcium and magnesium divalent ions and softening of groundwater, NF membranes have been used productively. On the other hand, RO membranes basically used for desalination of seawater across the world helps to exclude total dissolved solids (TDS) present in the water including monovalent and divalent ions.

Two-Stage Membrane Filtration

Since low-pressure membranes are efficient for removal of various sized particles and high-pressure membranes are efficient for removal of both organic and inorganic dissolved matter, the two techniques were merged into one and named as Two-Stage Membrane Filtration for better and more comprehensive water treatment.

Ultraviolet Irradiation Technology

Ultraviolet (UV) irradiation technology is principally used for disinfecting the drinking as well as wastewater. UV kills the germs using a wavelength range of 250 to 270 nm. The UV technology incorporates the UV lamps around which water circulates resulting in inactivation of microorganisms. It is an easy and fast process which hardly takes seconds to kill microbes by disrupting their DNA and preventing them from reproduction.

Advanced Oxidation Technology

In advanced oxidation processes, the organic and inorganic water impurities are removed using the hydroxyl radicals (OH) by process of oxidation. Advanced Oxidation Technology has mainly three processes which are ozone, ozone with hydrogen peroxide addition, and UV irradiation with hydrogen peroxide addition.

Ozone

Ozone is used for removal of color, odor- and taste- causing microbes thereby disinfection of microorganism. Also, the byproduct formation due to chlorination and formation of chlorine-resistant pathogens, ozone is the best method to be used.

Ozone with Hydrogen Peroxide Addition

To accelerate the formation of hydroxyl radicals, hydrogen peroxide (H₂O₂) is added to ozonated water. The hydroxyl radicals are stronger oxidizer than molecular ozone and help in lowering the ozone concentration. This treatment helps in destructing the color, odor- and taste- causing compounds as well as various micropollutants.

UV Irradiation with Hydrogen Peroxide Addition

The combination of the use of UV and Hydrogen Peroxide has benefited in the formation of hydroxyl radicals which helps in killing the micropollutants from groundwater, and also for the devastation of color, taste-and-odor-causing compounds.

Ion Exchange Technology

Ion exchange technology mostly used for water softening (Ca2+ and Mg2+ removal), either at the water or wastewater treatment plant. However, with the use of various anions and cations, ion exchange technology helps in removal of nitrate, arsenic, selenium, barium, radium, lead, fluoride, and chromate. Addition to the list is a new contaminant which is perchlorate (C1O4-) in groundwater. It is a fixed bed process in which a synthetic resin is packed. In this when water passes, the harmful ions present in the water are exchanged with ions on the resin surface, thereby eluding the contaminant ions and collecting them on the resin.

Biological Filtration

Biological filtration utilises the use of beneficial microorganisms resulting in biologically stable water. It uses the increased concentration of biodegradable organic matter (BOM). The use of BOM can help in a stable environment and biological regrowth.

In our local community, water treatment is done in 4 steps.

First step: Coagulation and Flocculation

Cations are added to the water which neutralises the anions present as dissolved particles in the water forming larger particles called floc.

Second step: Sedimentation

During sedimentation, flocs come to the bottom of the water due to its heavy weight.

Third step: Filtration

After the floc has settled, the clean water will pass on top through various composition and pore sizes of sand, gravel and charcoal filters. This helps in the removal of dissolved particles.

Fourth step: Disinfection

After the filtration step, a disinfectant such as chlorine may be added for removal of left out pathogens.