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UV Disinfection

[box type=”shadow” ]“Ankur-ParikhUltraviolet technology is fundamentally a disinfection technology. It is used to inactivate dangerous pathogens in both water and wastewater, which if left untreated can lead to widespread disease and epidemics.” Ankur Parikh, Director- Industrial UV, Alfaa UV, highlights the UV wastewater disinfection.[/box]

Ultraviolet technology is chemical free, broadly similar to how sunlight is a natural disinfectant. About 90% of all new wastewater treatment plants in more progressive countries use UV technology for disinfection. Further, it is safe and mostly automated, requiring very little plant operator involvement.

Traditionally, chlorine is used for disinfection. However, in most developed countries chlorine is hardly used, especially in wastewater, due to reasons of safety and public health. Chlorination of wastewater leads to dangerous byproducts which have been proved to be carcinogenic. In India, since this treated wastewater is usually discharged back into rivers, which is a source of drinking water in many cities, can prove dangerous in the long run.

[box type=”shadow” ]People are at risk of getting infectious diseases such as dysentery, cholera and hepatitis. As per the SMF, there are parts of the Ganges where the faecal coliform levels measure two million per 100ml; which is alarming![/box]

BOD & TSS

Disinfection is usually the last process of WW treatment but in India it is given the least importance. While BOD and TSS are important parameters and could have a detrimental effect on the pollution levels and ecosystem of the receiving waters, they do not have a major impact on human health.

Pathogens on the other hand, that are removed through disinfection, are a major health hazard. Diseases such as Diarrhoea, Cholera, and Typhoid spread through bacterial pathogens are found in abundance in wastewater. If left without (or with inadequate) disinfection, lakes, rivers, and other receiving water bodies could get infected.

In a study done by E-LAW U.S. staff, scientist Dr. Mark Chernaik says that the Ganga is too contaminated for safe immersion. Bathing people risk getting infectious diseases such as dysentery, cholera and hepatitis. As per the SMF, there are parts of the Ganges where the faecal coliform levels measure 2 million per 100 ml; which is alarming!

If the treated wastewater is going to be reused, then the case for a higher level of disinfection is even more pressing. Several international standards exist for this (USEPA, NWRI, etc). However, there is no cohesive standard or strategy yet for disinfecting water for reuse in India.

Efficacy

A UV system can be designed to work in a range of different effluents by adjusting the critical UV parameters such as UV intensity, reactor/channel design and hydraulics.

In a wastewater plant treating secondary effluent, UV will function effortlessly with BOD/TSS parameters in the range of 20/30 mg/L. If levels are higher than this, then the system can be specially sized to meet the needs. The parameters of UV dose imparted to the water will determine the coliform levels in the treated water. The higher the UV dose, the better the disinfection (and lower the coliforms).

UV is actually a very cost effective technology. Taking a 100MLD wastewater treatment plant as an example and studying its lifecycle costs over 10 years, shows that UV is equally cost effective as compared to chlorination. Further, if dechlorination is also considered (as it should be when water is being discharged into lakes and rivers) UV actually saves a significant amount of money.

Indian Rules & Regulations

The National River Conservation Directorate has recently updated their norms for wastewater treatment which has significantly improved them as compared to previous standards. However, it is still a little weak as compared to international best practices. The desirable limits for Faecal Coliforms are < 500 MPN/100ml and maximum permissible limit is 2500MPN/100ml. It would be preferred to have the desirable limit as 200MPN/100ml and remove the maximum permissible limit of 2500MPM/100ml all together.

While these norms exist for wastewater treatment and discharge, India yet has to come up with a unified norm for wastewater recycling, which is a huge requirement. Even more dangerous, is that most norms that exist only address the physical and chemical parameters in the water and are weak on the microbiological front. If not adequately disinfected, this wastewater containing these dangerous organisms can spread diseases when used for applications such as toilet flushing, landscaping and irrigation.

To conclude, UV is an effective means of disinfection, and has proved to be effective against organisms which are very chlorine resistant, such as cryptosporidium. This ensures that the UV treated water can be safely used for various applications. 

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