What is safer for the environment

Hello Everyone, I have an question, what is safer for the environment - to produce drinking water by desalination or to treat wastewater for direct or indirect potable reuse?

7 Answers

1. thanks everyone for the reply.

2. It is worth mentioning at this stage the PROGREEN TM Technology that was developed by Dr. Liberman, IDE Technology's CTO, and fully commercial by now. It is a chemical free seawater desalination process, with reduced energy and very high sustainability. It was developed to address the issues of disposing brine with chemicals back to the sea in sensitive regions of the world More information, can be obtained in our website www.ide-tech.com and I'll be happy to put in contact the PROGREEN TM line manager with anyone who is interested to learn more.

3. Hi Grace: I agree with Valentina. With appropriately designed outfall for diffusing the discharge from desalination and wastewater plants such discharges are equally safe for the environment. Usually well designed discharge diffusers are sized to achieve 1:20 to 1:50 dilution within 100 meters from the discharge and at that point the water quality is indiscernible from ambient waters. Site specific issues however may make one type of discharge more palatable for the environment from another. In Australia for example, the reasoning for preferring desalination over indirect or direct potable reuse was the concern that as we remove fresh water from the wastewater to produce drinking water, we are concentrating man-made compounds contained in the wastewater treatment plant discharge form where the source water for production of frehs water came fro - such as endocrine desruptors (female hormones contained in contraceptives, antibiotics, etc.). Since most of such compounds (i.e., female hormones) act when they reach certain concentration threshold, the more concentrated the discharge the more likely it is that we will reach the threshold levels which may impact the environment - change the sex of male fish into female fish for example. In drinking water produced from purified wastewater such compounds are destroyed by advanced oxidation - combination of peroxide and ultraviolet irradiation - so the water is safe for drinking. We do not apply this advanced oxidation treatment however to the discharge - at least not for now. If we are to apply the same treatment to the concentrate as we do to the drinking water, the energy used for destruction of endocrine disruptors would in many cases be higher than that needed for desalinating seawater. Until we learn how to cheaply destroy endocrine disruptors in the discharge in some water reuse applications this issue may pose a challenge. Desalination plant concentrate does not contain endocrine disruptors and ultimately gets recombined with the water from which it was separated as it turns in wastewater. In over 99 % of the coastal communities worldwide the drinking water produced by desalination is returned as treated wastewater into the ocean within several kilometers distance from the point of intake. That being said, discharge of concentrate from desalination plants into shallow water bodies with limited mixing or into seagrass beds, corals, or other "ocean nurseries" could cause environmental impacts if the volume of discharge is large. So the impacts of both types of plants will be very site specific and it is practically impossible to generalize a conclusion on which of the two water production methods is better for the environment. Most marine species develop natural mechanisms to adopt to increased osmotic pressure originating from concentrate discharge or natural evaporation. However, as we are not born with the ability to walk right way after birth, many marine species in their early embryonic phases of development do not have such mechanisms to deal with higher osmotic pressure yet - so discharging concentrate into such area will have negative impact on embryos - by osmosis - it will suck out the water of the embryos bodies by osmosis - which hinders their development or may cause death. So discharging concentrate in locations where marine organisms go to spawn could be environmentally damaging. If we stay away from such areas (i.e., seagrass beds, corals, etc,.) difusers do adequate job to protect aquatic environment. Practice shows that when done right both methods are complimentary and a part of a diversified water supply portfolio of coastal municipalities worldwide.

4. I am in the middle east and with largest deasal plants operating here I would prefer that the treated effluent is sent to RO for recovery this will reduce the burden of rO reject back to sea ( at least some %)

   1 Comment

   1. RO operation at recovery lower than 36 % will reduce the discharge salintiy of SWRO concetrate for plants in the Gulf and Red Sea to levels safe for direct discharge to most aquatic habitats except for corals.

5. Dear Grace, You are asking a question on a very complex issue: desalination and water reuse are two alternative water resources that are helping to secure water supply. Their technical-economic viability and environmental impacts depend on many local conditions and constraints. If additional water volumes are required for non-potable applications, water reuse should be considered first. When you have desalination in arid regions, water reuse will help to valorize the economic value and embodied energy in desalted water. It is important to stress also that the choice of the tools how to estimate environmental impacts can also influence the final results (LCA, eco footprint, etc). Another important issue is the public attitudes and acceptance.

6. Along the same line - Is there such thing "best" or "acceptable" desal brine discharge in today's technology? evaporation pond? deep well diffuse? remote discharge? deep sea discharge? or (electro)chemical neutralization using (free) solar energy?

7. Hi Grace, treated wastewater would be a safer way to produce drinking water in terms of environmental impacts - no huge seawater intake structure and no discharge of huge brine flows back into the sea. furthermore you would have minimized discharges from the water treatment plant by the advanced treatment. On the other hand you need to be careful with acceptance of direct potable use of treated wastewater.