WATER REUSE WITH UV DISINFECTION

India is at the threshold of becoming a water scare nation. Today, estimates are that water availability per capita stands at 1200m3 and the figure is expected to drop to 1050m3 by 2025. Growth in population, urbanization, demand for food, industrialization and climate change are chiefly responsible. Besides these, poor management of our water resources is also a factor.

Since this article focuses on reuse of wastewater in order to supplement demand for non potable water, let’s look at some facts.

Less than 50% of sewage in Class I and Class II cities and towns in India is being treated. In Maharashtra, wastewater treatment capacity stands at 58% of a total of 6383 MLD of sewage, generated from 26 municipal corporations. Although a few municipal corporations are charging for treated waste water for non potable uses, the water is not being treated adequately and poses grave risks to public health.

CPCB Norm and Guidelines

Until recently, the Central Pollution Control Board’s guidelines on treatment of wastewater for discharge were mainly focused on primary and secondary treatment, with the focus clearly on parameters such as turbidity, suspended solids, BOD and COD. Attention to  the presence of fecal coliforms was fairly lax and stood at less than 10,000 MPN per 100 ml. These invisible pathogens were never considered a serious health hazard with grave consequences to public health as they entered water bodies  and  polluted groundwater sources (as we have seen in Shimla recently).

In a welcome move, the CPCB in 2015 drafted a new set of guidelines for the treatment of wastewater with a revised set of norms specific to reuse for various non potable and potentially potable uses covering toilet flushing, fire protection, vehicle washing, landscaping, horticulture and agriculture.

In chapter 7 of the Sewerage and Sewage treatment Systems Manual of the Central Public Health and Environmental Engineering Organization (CPHEEO), Ministry of Urban Development, norms have been recommended for treated sewage quality for specified activities at the point of use. One sees that besides the traditional parameters, the norm for fecal coliforms has been recommended as NIL. This stringent norm is welcome, both in improving the quality of wastewater and for safe reuse.

UV Disinfection Of Waste Water

Primary and secondary treated wastewater for reuse is often more dangerous than using untreated waste water. This is because primary and secondary treated wastewater can often deceive the user, by virtue of its innocently clear appearance.

Microbes are invisible and therefore dangerous. Devoid of tertiary disinfection, treated wastewater may contain coliform counts of more than 1 million colony forming units per 100 ml. The consequences of using this water for landscaping, agriculture, toilet flushing, car washing etc can be very grave as human contact is a real possibility in all these cases. With properly designed Industrial UV water disinfection systems it is possible to achieve the recommended norms for safe reuse.

UV Disinfection – How it works

The UV treatment process is an extremely rapid physical process that causes a molecular rearrangement of the genetic material (known as DNA) of the microorganism which renders it inactive and incapable of causing infection. Due to individual cell make up, different organisms require different levels of UV energy for their destruction. This energy level is known as dosage.

Advantages of UV Disinfection for reuse of wastewater

UV for wastewater disinfection is an environmentally friendly technology and uses no chemicals and forms no by-products, unlike chlorine which produces carcinogens and pollutes the environment.

UV systems are energy efficient, with failsafe and simple operation and lower running costs. Compact in nature, UV systems use small footprint, saving valuable real estate especially in urban environments.

While designing UV systems for wastewater reuse, UV transmission of water being disinfected is an essential factor to be considered while sizing the UV system. The lower the UV transmission, the higher the UV power required, even to achieve the same dose. Additional safety features such as automatic cleaning of the quartz sleeve, temperature cut-offs, specially designed UV reactors for wastewater with high levels of BOD and suspended solids, assist in reliable and effective disinfection. UV dose monitors report UV dosage in real-time ensuring that disinfection is adequate.

It is important to remember that while UV technology is a tried and tested disinfection technology for drinking water, a UV system designed to treat drinking water will not work in the case of wastewater.

Sum Up

One can sum up by confidently saying that water stress will be the catalyst for recycling and reuse of wastewater, and in keeping with the PM’s vision of a Clean India, protection of water bodies will be paramount and better enforced by law in the future. UV being both environmentally friendly and cost-effective, will continue to play a significant role in process water disinfection, discharge water disinfection, etc, and the reuse of wastewater.

Blog By – Rajul Parikh, President of Water Quality India Association and Co-founder of Alfaa UV.