CANALS, which used to be a dependable source of water supply, are now being subjected to massive degradation. First, it was the release of municipal wastewater into the canals which used to contaminate it.

This, to some extent, was tolerable as the discharge of municipal wastewater into a canal caused temporary dissolved oxygen sag, lowering the dissolved oxygen content of the water.

As the water flows, the turbulence in water allows atmospheric oxygen to be taken in. The re-aeration of water occurs and its quality returns to its original position. However, if the assimilative capacity of stream is exceeded, the stream will not recover. This never happened in the canals of Sindh, as they happened to be large bodies of water.

However, things started to turn bad, when industrial wastewater was discharged into the water bodies. Unlike municipal wastewater, which causes temporary dissolved oxygen sag, the fate of toxic industrial elements persists all along the canal. The toxic elements remain in the water for all times, so much so, that even the conventional water treatment plants cannot remove them. The deaths in Hyderabad which occurred in recent past, were due to the toxic elements discharged by Manchar Lake into the Indus River, despite the fact the water was treated by the Jamshoro water treatment plant.

In conventional water treatment plants, toxic elements pass through the plant without any hindrance. Advanced water treatment, also called tertiary treatment is required for the removal of toxic elements. Since, tertiary water treatment is costlier, it is generally not applied in the conventional water treatment plants.

Kalri-Baghar (KB) Feeder Canal: The canal receives industrial liquid wastes from industries located in the Kotri industrial area. The industrial wastewater discharge into the turbid KB Feeder waters makes a vivid difference. The canal serves as a source of water for Thatta, Dhabeji, Gharo and Karachi.

Industrial wastewater treatment: The Kotri Association of Trade and Industry has constructed oxidation ponds for the treatment of wastewater from their industries with a grant of Rs500 million by the Sindh government. The effluent of the oxidation ponds is discharged into the K. B. Feeder Canal.

There are reports of foul smell emanating from the ponds, signifying non-functioning of the plant. The DCO, Hyderabad, himself admitted at a meeting held recently that the oxidation ponds system was ineffective. This is because the wastewater engineering system is a specialised field. And what happened at Kotri was because people non-conversant with the technique handled the treatment plant.

Oxidation pond is a large shallow pond, usually 1.5 meters deep, in which raw wastewater is added at a single point at one edge and, removed through a single point on the other side of the pond. The minimum depth is governed by the weed growth. The maximum depth is related to the mixing of the contents of the pond by wind action. The shallower the pond the greater will be the surface area with better mixing potential.

Oxidation pond is an aerobic treatment system. Bacteria metabolises organic matter in the pond to carbon dioxide and water. While doing so, the bacteria utilises oxygen. Algae utilises carbon dioxide and releases oxygen. Oxygen is used by the bacteria in stabilising the organic matter. Bacteria also produces new cells, ammonia and other inorganic matter.

The parameter used for measuring the extent of pollution is BOD (5-day, 20 degrees Celsius biochemical oxygen demand). The lower the BOD, the lesser is the pollution in wastewater. The BOD in the effluent of the pond will be low only, when carbon dioxide and water are the end products of the metabolism. And, this will happen only when the system is aerobic. At an organic loading of 20 kg biochemical oxygen demand (BOD) per acre per day, a 1.5 meters deep pond would have an average retention time of 40 days.

Disadvantages of oxidation ponds: Since the process is based on natural bacteria-algae symbiosis and is mechanically unaided, unlike aerated lagoons wastewater treatment plants which are mechanically aided, in a sense that, oxygen is provided by surface aerators, the bacterial population is relatively weak and is adversely affected by the shock loadings (both organic and hydraulic) and by the increase in organic loading (that is, overloading the system).

Increase in organic loadings would impose a drain on dissolved oxygen, which cannot be met by algae or by natural surface aeration. Pond will then become anaerobic (septic) and, will not function biologically. It will start generating rotten egg-like odors (as in the Kotri case).

Certain heavy metals present in industrial wastewaters are toxic to bacteria. Industrial wastewaters are, depending upon the constituents, subjected to precipitation process, where toxic elements are precipitated. In the case of Kotri, the three reasons, which have caused the “biological struck-up” of the ponds, are the toxicity imposed by the heavy metals in industrial wastewaters; over loading of the pond system; and improper operation and maintenance of the ponds (assuming that the design of ponds is proper).

Some industrial estates use up-flow anaerobic sludge blanket (UASB) reactors for industrial wastewater treatment. This is also not advisable, as methane bacteria are relatively sensitive to the “negative of the log of hydrogen ion concentration” and, to the temperature changes. In addition, methane bacteria must utilise the organic fatty acids produced by acid-forming bacteria, at the same rate at which they are produced. If this does not happen, over production of organic acids will prove fatal for methane-forming bacteria.

Oxidation ponds require relatively large land area. An estimated 10-time more land area will be required, as compared to aerated lagoons, for the same range of operation parameters, treatment efficiency and influent loadings. They are reputed to cause massive mosquito breeding. The effluent of oxidation ponds contains algal cells, which contribute to BOD. Algal BOD, however, is not the same as wastewater BOD. Oxidation ponds are suitable for rural areas, where land is easily available at a lower cost and, the constituents of village municipal wastewaters are simple.

While the term oxidation ponds also apply to waste stabilisation ponds (WSPs), they typically constitute three types of ponds in series. These are: anaerobic pond, facultative pond, and maturation pond. The WSPs were constructed in Mauripur and in Hyderabad. They ran into problems and are producing poor quality effluent. The main cause is the presence of toxic metals in the influent, overloading of the system and poor operation and maintenance.

Rational way forward: The grant of Rs500 million was enough to design and construct a proper, rational and appropriate industrial wastewater treatment plant. This was not done and, the KB Feeder continues to be polluted. In Karachi many people die a natural death, at times without any tangible reason and apart, from any specific health condition. The cause may be apprehended to be the use of unsafe and unwholesome drinking-water. The drinking water supplied in Karachi contains, among other pollutants, traces of DDT, a deadly pesticide.

While the grant has been wasted, technical options have not exhausted. It is still technically possible to modify the oxidation ponds and develop a full-scale proper wastewater treatment plant. Development of various unit processes of the plant will depend on the analysis of the constituents of raw industrial wastewaters. The treatment plant may have been depending upon the wastewaters’ constituents, advanced treatment units like activated carbon, air stripping of ammonia, flotation, chemical clarification, selective ion exchange, reverse osmosis, or electro-dialysis.

For example, chemical clarification (coagulation, flocculation, and sedimentation), depending on the type of coagulants used (lime, iron salts or alum), will remove heavy metals like cadmium, chromium, copper, nickel, lead and silver. Removals of some dissolved phosphate, calcium, magnesium, silica and fluoride can also be achieved. Higher removals of calcium and magnesium can be achieved with lime in wastewaters with high carbonate hardness content.

Industrialists have wrong notions that wastewater treatment plants are very costly propositions. They are significantly cost-effective and their cost, depending on the design, would not exceed beyond five per cent of the cost of the industry. Significant economies of scale can be achieved, if a number of industries jointly set up the wastewater treatment plant, provided reputed civil engineering consultants are hired. In case of the Kotri industries, further economy of scale can be achieved, as Karachi-based reputed civil engineering consultants are already working in Hyderabad.

The Sindh chief secretary, Mr. Fazl-ur-Rehman, in a meeting held on Feb 3, has taken notice of Manchar Lake pollution. He should put his foot down and, prevent pollution of the KB Feeder. The players in the game are the industries of Kotri industrial area and, the mandate for controlling water pollution of water bodies in Sindh lies with the Environmental Protection Agency.