The newsletter of the Institute of Inventors and Innovators
ANNOUNCEMENT The first piece of news is very important for those who attend our monthly meetings in Johannesburg. Due to the non-availability of our Resolution Circle venue we will not have a March meeting. Hence our next meeting will be on Wednesday 11th April 2018.
At our February meeting we had a very interesting and knowledgeable speaker informing us about the latest technology in sea water desalination a topic of much interest at present. This expert was Chris Braybrooke the General Manager Marketing, South Africa of Veolia, the largest manufacturer of such water treatment equipment. Chris enlightened us about this process and taught us about the extent to which this is used in South Africa and elsewhere. To set the scene Chris said that our daily water consumption is between 150 and 250 litres per person. Desalination has been around a long time and there is more than one process. Distillation is the original process and it requires a lot of energy but is in use in Saudi Arabia where energy is plentiful and cheap. The modern method is reverse osmosis where water molecules are forced through a membrane leaving the salty brine behind, a litre of raw water produces 400ml of potable water. This process is also used to treat waste water in general and this is becoming more and more popular as a water saving measure. The membranes mostly supplied by Dow cost approximately $3000 and there may be up to 80000 in a very large installation, which have to be cleaned weekly. However, it is first necessary to pre-treat the raw water to remove all the other contaminants beforehand. The pre-treatment is a large part of any plant depending on the intake water quality. Sand mud, red tide, microscopic bio hazardous contaminants, drugs etc. all have to be removed. Processes that do this include drum filters for large debris; sand filters; clarification with ph. adjustment; dissolved air filtration. Even after all this the reverse osmosis sometimes has to have a second pass, and finally minerals must be added to what is now basically demineralized water which itself is aggressive and unpleasant. Finding a suitable source for raw water is also a mission. Because of human and natural activity water close to shore can be unsuitable and long intake pipes up to 700m are expensive. In Windhoek a severe storm moved pipelines 250km along the coast. Some cities dump raw sewage up to 4.5 km into the sea. The Indian ocean off Durban has on average 34000 parts per million of various salts. Atlantic water has high organic content. River mouth water is difficult to process because of inconsistent salt content. Re-use and recycling of waste water is quite a good source and is in use in Durban and Windhoek, in the latter case ultra-filtration is used. Power station boiler feed water also has to be ultra-pure. In Israel 95% of waste water is reused. In Plettenburg Bay there are ten beach wells that feed the treatment plant. These act like sand filters and provides filtered raw water with a consistent salt content. In Mossel Bay, open intakes are being used and concentrated brine is returned to the sea in pipelines with active current diffusers for safe dispersion.
Off take of water is also important. Reverse osmosis plants need to run at a steady load not stopped and started. This means that in times of low demand the output has to be stored. One way to do this is to pump it back into aquafers for later use.
So, is all this treatment too expensive for us? The answer is compared with what? The processes are constantly getting more efficient, less costly and small enough to put into a container. Provided a 20+ year view is taken they are economically viable for the investors and the users. One thousand litres of water costs 1$ (R12) to process and uses 3,850kw hr of energy. This energy cost is 50% of the total operating cost so there is a good case for renewable energy use with non renewables as backup. So the cost is not really so high.
Veolia assemble and factory test all modular plants prior to disassembly and dispatch. This way they can be sure that the plant will go together correctly on site, which is often far from any engineering services.
For those of you who want to get technical Chris referred us to NFA Specification NSF401.
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