DEAR MUHAMMAD ILYAS KHAN , ...

DEAR MUHAMMAD ILYAS KHAN , GOOD QUESTION

In view of the ever-increasing threat of marine pollution along Karachi coast and its possible danger to the coastal and marine environment. Although there have been a number of overviews on status of marine pollution in Pakistan, to quantify the level of oil pollution in the coastal environment of Karachi, Pakistan. Water and sediment samples were collected from various locations along Karachi coast bordering northern Arabian Sea. Water quality was assessed using the parameters salinity, dissolved oxygen, suspended load, organic matter (in particulate carbon) and total oil and grease. The salinity in Karachi Harbour ranged between 25.062–36.042 ppt in the Down Stream Lyari River Mouth and outside Manora Channel to open sea respectively. The dissolved oxygen values observed at all stations ranged between 0–6.01 mg/l . Complete anoxic condition with zero oxygen value was found at Lyari River Mouth the discharge point of mostly untreated industrial and domestic wastes. The very high concentrations of suspended load have been found at Korangi creek and Gizri creek Tip which are 177.6 ppm , and 100 ppm respectively. Concentrations of the suspended load in Karachi Harbour were in the range of 28.30–61.60 mg/l however, higher values have been found in the Manora Channel and its surrounding area. The level of organic matter ranged between 2.35–11.50 mg/l, with high values detected in Korangi creek and Gizri creek, which were 11.5mg/l and 7.15 mg/l respectively. The concentration of total oil and grease in seawater was detected in the range of 0.9–49.9 mg/l . The highest concentration of total oil and grease (49.9 mg/l) in seawater had been observed in Manora Channel. Similar results were also observed for total oil and grease in sediments. The highest concentration in sediment was found in Manora Channel, and Korangi creek which were 115 mg/kg, and 81 mg/kg respectively. The lowest value 0.9 mg/l was detected in water sample collected out side Manora Channel in the open sea, which clearly showed that the pollution level decreased from Karachi Harbour towards open sea, due to tidal flushing and mixing of pollutant with seawater. Karachi the largest industrial and thickly populated city of Pakistan which is situated at the north western boundary the Arabian Sea is highly vulnerable to flood damages either due to flash floods during SW monsoon or impact of sea level rise and storm surges coupled with cyclones passing through Arabian Sea along Pakistan Coast.

To begin seawater desalination water treatment, a stable, high quality feed water is required – this optimises membrane durability. Depending on the water purification system, from here water heads either to the distillation solution or membrane solution. For distillation processes, the technology used to vaporise is Multiple Effect Distillation(MED), a low temperature sea water distillation process used to evaporate seawater in numerous stages – up to 14 stages in some instances – at temperatures of 70° C or lower to produce clean distillate water. 

Make the water suitable for drinking purposes the following procedures should be carried out:

1. Removal of suspended matter.
2.  Decolourisation and oxidisation of the inorganic material and killing of all pathogenic micro-organisms by adding chlorine (pre-chlorination).
3.  Aeration of water.
4. Oil removal by gravity settler Or disc oil system.
5.  Flocculation of colloidal/organic matter with aluminium sulphate and anionic polyelectrolyte.
6.  Sedimentation.
7.  Filtering.
8. Addition of lime. .
9.  Post chlorination

Regards,

Prem Baboo