WWD Associate Editor Cristina Tuser spoke to water treatment expert Lior Eshed, product development manager at IDE Technologies, on the usage of chlorine in drinking water
Note: Responses have been edited for clarity
Cristina Tuser: Can you summarize the implications of using chlorine/chloramine in water reuse?
IDE Technologies: Conventional water reuse process typically includes UF, RO and UV/AOP process units, with the dosage of Chloramine to control biofouling on the membranes.
Chloramine is used in standard water reuse processes as a means to control biofouling.
Since feed water is usually a secondary effluent from a municipal wastewater treatment plant, residual organic matter in the water serves as food for bacteria that settles on the RO membrane surface.
Chlorine reacts with ammonia to form Monochloramine (NH2Cl), a relatively weak oxidizing agent that acts as a bacteriostatic agent, hence it doesn't completely eliminate microorganisms, like stronger oxidizers do. Instead, it slows down their reproduction rate and helps to keep the membrane in a working status for longer periods of time between CIP (cleaning In Place) cycles.
Chlorine in water reuse is used as an operational tool, to help keep the membranes in a relatively clean state. This is different from chlorination of drinking water, in which chlorine is used for disinfection, in order to meet the regulations of pathogens in drinking water.
The implications of chlorine usage in water reuse facilities are as follows:
- Health risks – Chlorine reacts with organic matter in feed water to form Disinfection Byproducts (DBP).
- Process risks – Chlorine injection adds complexity to the water reuse process. As explained above, chlorine needs to react with ammonia in order to form chloramine. If not enough ammonia is present, chlorine may form free chlorine – a stronger oxidizing agent that damages the thin polyamide layer of the RO membrane. Therefore, the process of chloramine generation has to be tightly controlled;
- Cost – Chlorine (and occasionally ammonia) injection adds operational and capital costs to the water reuse process.
Tuser: What health risks are associated with the use of chlorine? Who is vulnerable to these effects?
IDE Technologies: The main health risks associated with chlorine injection to WWTP effluent are related to the formation of Disinfection Byproducts (DBPs). The main known DBPs are Trihalomethane (THM), Haloacetic acids (HAA) and N-nitrosodimethylamine (NDMA), where the latter is limited to 10 ng/l in California and other states.
DBPs are suspected as carcinogenic and associated with a range of health hazards such as cell damage, increased risk of asthma and heart problems, with children being at higher risk. DBPs partially pass through RO membranes (in the case of NDMA, more than 50% of it passes through) and usually are mostly disintegrated in the subsequent UV/AOP, if present.
That being said, DBPs formation is best to be avoided. Growing worldwide concerns regarding DBPs caused regulators to tighten regulations around DBPs presence:
Tuser: What are the alternative methods for reusing water?
IDE Technologies: Chloramine-free water reuse process is made possible by using alternative bacteriostatic agents. Although several such products exist in the market, their cost is significantly higher than chlorine and therefore not commonly used.
The solution of continuously dosing chemicals to control biofouling is basically a symptomatic treatment – a response that is given to a specific problem (biofouling formation), but doesn't treat the problem itself.
Tuser: How does IDE’s Eco-Reuse technology fit into the equation?
IDE Technologies: IDE's Eco-Reuse Pulse Flow Reverse Osmosis (PFRO) technology does not involve Chloramine or other oxidizing agents. It fights biofouling by implementing a different mode of operation: standard RO facilities operate in a continuous flow regime, where feed, permeate flows and other operating conditions such as osmotic concentration and shear force - are all constant.
This mode is convenient for designers, but creates operational challenges such as the formation of scaling and biofouling: the result of operation in endless induction time (scaling) and the creation of convenient conditions for bacteria to form biofilms. Bacteria is situated on the membrane surface and utilizes the flux of nutrients through the membrane.
PFRO tackles the formation of scaling and biofouling by applying constantly varying hydraulic and osmotic conditions, that force bacteria to spend energy on continuous adaptation to those varying conditions, minimizing reproduction and significantly lowering biofouling potential (Boris.L et al, Pulse Flow RO - the new RO technology for waste and brackish water applications. 2020).
Tuser: What information should consumers know in light of the results of the study?
IDE Technologies: There is a more efficient, Chloramine-free and cost-effective alternative to standard water reuse. PFRO has been successfully implemented in multiple global facilities and has proven itself as a ground-breaking, environmentally-friendly water reuse technology that enables significant savings in both capital and operational expenditures.