Urban Water Treatment

Team Chemical Market

29 Feb 2024

Introduction

In the bustling thoroughfares of urban existence, there exists a silent provider: Water supply systems. The maze of pipes that lie beneath the city's surface, mirrors the complexities of human relationships. It is amidst the ceaseless movement of city life, that one finds the true essence of Urban water infrastructure - a narrative of sustenance, progress, and the unseen forces that bind us together. From the grand boulevards adorned with majestic fountains to the humble tenements where taps trickle with life-giving sustenance, every corner of the city is touched by this network. From ancient aqueducts that harnessed the power of gravity to modern engineering, the evolution of water supply systems reflects humanity's relentless quest for progress. In this article, we attempt to give a comprehensive view of urban Water supply systems.

Typical process

Please refer to the figure above. Detailed below are the individual components:

Water source - Typically the intake is from a barrage, large lake, or riverbed. Raw water is pumped into a coagulation tank using electric motor-driven pumps.
Coagulation - If you hold a glass of untreated water against light, it will be hazy. This is called turbidity due to the fine suspended particles. It should not be confused with chemical contamination. Aluminium Sulfate or Alum is added to the water causing fine suspended particles to clump together.
Aeration and sedimentation - Water falls in thin sheets over several steps. As these steps are in cascade, the water absorbs oxygen leading to oxidation, killing some amount of bacteria. However certain volatile compounds are removed. Sediment from the coagulation process above is removed.
Filtration - If there are organic, chemical, or pesticide contaminants, the filtration process through activated carbon is used. It works through the process of adsorption, where the contaminants adhere to the surface of the carbon particles.
Disinfection and final treatment - The addition of chlorine in its gaseous form is injected into the water by pipes. They kill harmful organisms in the water. Chlorine dioxide can also be used and is effective against a broader range of microorganisms. Ozone is another gas that can be used. It is a very powerful oxidizing agent which effectively kills bacteria and viruses. It also removes color, taste, and odour causing compounds.
Advanced treatment:-
pH Adjustment and water softening- Compounds like Calcium Hydroxide (lime),

Sodium Hydroxide ( Caustic soda), Sodium Carbonate (soda ash), etc. are carefully dosed and monitored to ensure that the treated water pH value falls within the desired range.

Anti Corrosion agents - These are added to prevent corrosion in the pipes of the distribution system. Sodium or Zinc orthophosphates, Polyphosphates, and sodium silicate are some of them. They form a protective layer in the interior of the pipes forming the Drinking water distribution system and thus prevent corrosion from dissolved oxygen and other substances.

Water Quality Management

In India, the quality of water supplied to towns and cities is governed by IS 10500 - 2012 titled: Drinking Water. Assistance for making this standard has been taken from :

EU directives 80/778/EEC and 98/83/EC
USEPA standards EPA - 816- F - 02-013 DT 2002
WHO guidelines 2008
Manual on water supply and treatment, May 1999, Ministry of Urban Development, New Delhi.

Acceptable levels and the method of testing for the following parameters are specified therein :

Bacteriological
Virological
Organoleptic
Physical
Undesirable substances
Toxic substances
Radioactive substances
Pesticide residue

It should be noted that much of the water treatment which is a part of Urban Water Infrastructure depends on the quality of water received at the input stage. Coagulation, aeration, filtration, and chlorination stages will most often be present.

Various companies in India have business operations in this field. A few of them with their broad range of activity are listed below :

Lanxess India Pvt Ltd - Ion exchange resins, Microbial control agents.
Ion Exchange India Pvt Ltd - Water treatment plants, Ion Exchange resins, Instrumentation and Automation.
SMPL Infra Ltd - Smart City Infra. Includes IT-enabled integrated water management system.

Groundwater

India is a growing economy. One of the sure signs of this is the expanding geography of our towns and cities, especially on the periphery. It sometimes takes months if not years for urban water supply to reach these parts. The only solution is groundwater. This is accomplished by either a borewell on the premises or a supply of groundwater from wells and borewells through water tankers.

Groundwater could contain some of the following impurities:

Arsenic, lead, cadmium, etc through leeching from natural mineral deposits or industrial activity.
Nitrates and nitrites from fertilizers and animal waste.
Dissolved minerals such as calcium, magnesium, etc cause water hardness and scaling in pipes.
Organic compounds such as pesticides and industrial chemicals.
Sulfates from rock weathering
Chloride ions intrusion from seawater.
Pathogens

Each one of the above has detrimental effects on health when their levels exceed specified limits. To mitigate the above, the following processes are used to make Potable water delivery possible :

Ion exchange resins for the removal of dissolved ions in the water. Causes softening of water and removal of nitrate sulfate and heavy metals.
Reverse osmosis removes the majority of dissolved contaminants like organic compounds, dissolved salts, and minerals.
UV(Ultraviolet) light, typically of wavelength 254 nanometres. Bacteria and protozoa exposed to this light are unable to replicate. Their DNA is destroyed by UV light.
Filtration for the removal of suspended solids. This is done using activated carbon or ceramic filters.

Conclusion

Our endeavor in this article was to offer a comprehensive view of the subject. However, as with any system devised by human ingenuity, challenges emerge when extending its reach to newer territories. Such expansions invariably confront technical hurdles, where every turn presents a new obstacle to navigate. Yet amid these challenges, there exists an enduring pursuit: a journey in search of untainted aquifers and untapped reservoirs. This pursuit is not for the sake of novelty, but is driven by a fundamental imperative: to safeguard the well-being of our urban denizens for generations to come.

Technological advancements often yield improvements in the quality of water supply. From primitive filters, we have propelled ourselves into sophisticated filters of the modern era. Each stride forward has brought us a step closer to the elusive ideal of pristine water.

For, in the seemingly mundane task of treating water lies a profound truth: neglect is the harbinger of affliction. A casual approach in its operation could raise the specter of gastrointestinal diseases. Again a reminder that the price of indifference is not paid in coin but in suffering.