In deciding on a water disinfection strategy there is always a tug of war between the customer end goal, which is restrained by budget and water specifications, and the disinfection strategy chosen, restrained by contaminants, water source and infrastructure.
With the current conditions in the global market for freight and raw materials, I see more and more customers and colleagues in the water industry experiencing challenges in treating water. These challenges can come in many forms from public pools in England running out of chlorine to disinfect pool water, to municipalities in South Africa where the infrastructure has gotten so bad that the water is contaminated after it leaves the treatment station.
Most of the time, these problems come up as short term problems which can be resolved by using a more expensive alternative treatment or bending the rules for “one” time. But what if these problems take longer to resolve, what if borders remain closed for longer periods as we have seen during the COVID19 pandemic where trucks with water treatment chemicals were stuck at borders across Southern Africa.
Let’s take some of the major threats to providing safe and disinfected water, aging infrastructure, availability of chemicals, safety issues, emerging contaminants, budget, and operating safety concerns. If we take all of these into consideration when choosing a disinfectant, it would be great to have the one universal solution (spoiler: I would not be sitting in an office if I had this solution). If we have a look at common methods used, we quickly find that there are pros and cons to all of them that restrain the use or the effectiveness for different challenges.
If we look at common methods used, there are pros and cons to all of them that restrain the use or effectiveness for different challenges
Chlorine is still globally the most used disinfectant because it has a good disinfection strength and is cost-effective in most cases. But with the rise in fuel cost and sometimes just not being available in the form that we are used to (liquid or gas form) we might have to look at alternative ways to use chlorine either by producing on-site or using this in solid form. Still looking at possible long-term effects from disinfection by-products, different disinfection methods might be a better option.
If we look at ozone, it does not have the drawbacks of chlorine, we just need air and electricity to make one of the most powerful disinfectants available to us. But because ozone is so reactive it’s also short-lived and cannot therefore disinfect large networks of pipes. Add to this the technology that requires high-level knowledge to operate and maintain and we quickly see that this is not ideal for a lot of situations.
Ultraviolet light would be a better candidate then? The only thing needed is power and depending on the flow to be treated it’s not that much. With UV disinfection there is no residual effect but also no residual disinfection making it an excellent gatekeeper for point-of-use disinfection but less suited to provide large networks with water disinfection. It is a robust method that requires very little intervention from operators and the investment cost is low.
Chlorine dioxide is a powerful disinfectant which is usually generated on-site; it actively removes biofilm and in low concentrations has no taste or smell to it. This might be the ideal disinfectant with its good residual value and a small percentage of by-products. The drawback would be that we still need chemical precursors to produce chlorine dioxide and there is still an addition of chemicals to water which might cause harmful effects in the long term.
Unfortunately, there is no one ready-made on the shelf solution for solving water disinfection challenges. Only by looking at the source of the challenge and having a clear understanding of the end-use for this water can we overcome these challenges. Whether you are filling a hotel pool in Mauritius or providing potable water for a rural village in Ghana the disinfection strategy will always have to be a vital part of that plan.