How to achieve clean-up of Karachi's Nehr-i-Khayyam

Published February 6, 2020
The present state of Nehr-i-Khayyam — quite far from its poetic connotations — resembles a cesspool of waste water.—Fahim Siddiqi/White Star
The present state of Nehr-i-Khayyam — quite far from its poetic connotations — resembles a cesspool of waste water.—Fahim Siddiqi/White Star

THE Sindh chief minister has recently given his consent for signing an agreement with a private party for the development of Clifton’s Nehr-i-Khayyam. He said that this would be a gift to the people of Karachi and it would be for families to have picnic and enjoy sailing in boats.

Mr Shah needs to keep the gift aspect in the background because clean-up of a water body is a very time-consuming and complicated process.

If the people of Karachi use the Nehr while its water quality is poor, the people will suffer from waterborne diseases, water-washed diseases, water-based diseases and water-related vector-borne diseases.

Contains septage, not water

A visit to the Nehr shows that it is an extremely polluted water body. It emits very strong pungent smell and does not contain water. It contains septage, which is a combination of liquid and solid material as found in septic tanks and cesspools. Septage contains four major types of human pathogenic (disease-causing) organisms: bacteria, viruses, protozoa, and helminths.

Its physical characteristics make septage difficult to treat. High levels of grease, grit, hair and large solids in septage can clog pipes and pumps. The anaerobic nature of septage results in the presence of odorous compounds. Foaming can also be a problem when air is blown into the septage. The proponents intend to establish waste-water treatment plant for septage treatment. This will not be feasible and should not be done. Putting septage in a municipal waste-water treatment plant will spoil the pumps and other mechanical equipment.

The Nehr water in its present state can be a source of waterborne diseases

Currently, the Nehr receives the raw municipal waste water. The site visit also showed that it has almost no water flows. The constituents were stagnant, indicating that its inlet and outlet are probably blocked. The bottom constituents of the water body seem to be comprising of odour-emitting substances. Water quality improvement, therefore, will be the major component of the Nehr’s development.

Karachi does not have a proper sewerage system. Wherever system exists, the ‘invert’ levels of sewer pipes were never maintained properly. Waste water at the farthest upstream end cannot flow down to the final outfall point, unhindered. Sewer pipes are now laid in ad hoc fashion. To secure a way out, the storm-water drains are used for conveying waste water. Besides, as is the present case, the sewer pipes drain in the Nehr to dispose of the waste water.

Clean-up strategy

The first thing the sponsors should do is to stop flow of waste water in the Nehr. At the same time, a detailed survey should be carried out to see that there are no other inlet pipes, draining in the water body, especially the industrial effluent.

The second step should be that of sediment dredging and removal of solid waste. The dredging will be a problem for workers and for the people living in the adjacent buildings.

Still, this will not be enough. Since septage is hazardous to human health, it must be stabilised with lime. Lime or other alkaline material is added to the septage to raise the pH to 12 for a minimum of 30 minutes. While the septage characteristics vary, approximately 20 to 25 pounds of lime are used for every 1,000 gallons of septage (2.4 to 3.0 kg per 1,000 litres).

The pH must be measured to ensure that pH 12 is achieved and maintained for 30 minutes. After pH 12 is reached, pH should be measured every 15 minutes using a pH meter. If the pH drops below 12 during the 30-minute period after mixing, more lime or other alkali must be added. The pH of the mixture must be maintained at 12 or greater for a full 30 minutes. The septage can then be disposed of by applying at 20 centimetres depths on sand beds.

Canal should be filled with fresh water

Once the canal bed is cleaned, the third step should be securing the canal linings through stone pitching, and embankment reconstruction.

The fourth and important step is that of filling the canal with water. The sponsors say that 40 per cent of the water that will be filled will be treated waste water. In Karachi, there is currently no waste water treatment that is working at over 90pc of treatment efficiency, which produces treated waste water of acceptable quality. The use of treated waste water will mean the use of “raw waste water”. This will spoil the water quality and will be a waste of time and money.

The sponsors must not use waste water. The canal should be filled with fresh water. It is admitted that obtaining fresh water will be a problem, but then, there is no way out, other than to pray for rains, heavy rains.

Once the Nehr is filled with fresh water that will not be the end of the story. Since the water body has almost no flows, it means, over a period of time, the water quality will slowly deteriorate. To prevent this, the aeration technology, commonly used in Bangkok for this purpose, shall be adopted.

Well-designed cage rotors, fabricated locally, which the writer used at the North Karachi aerated lagoons waste-water treatment plant, will do the job. Inspection of the water body, once the work is completed, would show the number of cage rotors that will be required and their mounting and placement details.

During operation of the cage rotors, the public should be kept away, as aerosols created by the splash of water, produced by the cage rotors, would be injurious to human health, upon inhalation.

Construction activities for dredging, septage removal, solid waste cartage and other activities at the site will involve the use of heavy machinery and trucks. It will produce noise, vibration, create air pollution, create muddy runoff, safety hazards and traffic congestion. Environmental protection measures will be required as integral parts of the engineering works.

An environmental assessment of the project will be required. While the environmental impact assessment (EIA) is commonly used in Sindh to assess the impacts and monitor mitigation activities, the strategic environmental assessment (SEA) is used globally.

The chief minister may ask the people of Karachi to enjoy the scenic beauty of the Nehr only when its water quality meets required guideline values.

The writer served for five years as director, Sindh Environmental Protection Agency.

Published in Dawn, February 6th, 2020



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