A Letter to President Arif Alvi
By Dr Ismat Kamal
Dublin, CA
My heartiest congratulations on the victory of your party, and on your richly-deserved elevation to be the president of the country"
"Phir charaaGh-e-laala sey raushan huwey koh-o-daman".
I am writing to you on the subject of sea and brackish water desalination, which had been my field of specialization since I returned to Pakistan after my PhD in 1966. I was the Project Director for the first solar desalination plant at Gwadar, working for Dr I.H. Usmani, the visionary Chairman of the Pakistan Atomic Energy Commission. I am glad to hear that desalination is again being seriously considered as part of the solution to the water problems of Karachi.
Currently, the most economical process for the desalination of saline water is reverse osmosis (RO). Unfortunately, the 'kachra laden' sea water off the seacoast around Karachi is unsuitable for feed to seawater desalination plants.
On the other hand, large parts of lower Sindh are sitting over lakes of brackish water, owing to the twin problems of water logging and salinity. The LBOD and RBOD projects were conceived as a means of diverting the brackish water to the Arabian Sea through a system of tube wells and drainage canals. In my opinion, this underground water would be the best source of feed water to RO plants supplying drinking water to Karachi for the following reasons:
• The cost of water from RO plants depends on salinity. While the sea water off Karachi has a salinity of about 38,000 parts per million (ppm), the salinity of the sub-soil brackish water can be as low as 4,000 ppm.
• RO feed waters in general require extensive pretreatment, which increases the cost. Well water is regarded as the best source for RO feed (since it already comes filtered through the sand), requiring minor pretreatment.
• Inland RO plants have a problem with disposal of the spent brine discharged after treatment. In the case of lower Sindh, this will not be a problem, because the infra-structure for brine disposal already exists in the form of the drainage projects. At selected locations, RO plants will simply intercept the sub-soil drains and turn them into two streams: one for fresh drinking water and the other for brine discharge to the sea.
This requires intensive studies and investigations, and I am hoping that you will be able to pass this on to someone who could get things going in the right direction.
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