THE Chief Justice of Pakistan inaugurated the upgraded Mauripur sewage treatment plant on July 22. The sewage treatment plant’s capacity has been enhanced from 54mgd to 77mgd, which will be further enhanced to 180mgd after the completion of phase-II of the plant.

The Mauripur treatment plant consists of the ponds system, comprising anaerobic ponds, facultative ponds and maturation ponds. Owing to poor operation and maintenance over the years, all the ponds had become anaerobic ponds.

Anaerobic ponds are septic ponds that stabilises organic matter in the absence of oxygen. Any ditch with stale sewage is an anaerobic ditch. Anaerobic ponds emit hydrogen sulfide gas, which has a rotten egg-like smell. The ponds also release massive quantities of methane gas, which is a potent gas that causes global warming.

Anaerobic digestion is a three-stage process. In the final stage, methane bacteria (species of Methanobacterium, Methanococcus and Methanosarcina) utilise the organic acids and metabolize them to methane and carbon dioxide.

Because the system is unaided, methane bacteria are highly frail in nature. They are difficult to cultivate and, are highly sensitive to low pH (acidic) conditions. They are not suitable for urban wastewaters like Karachi’s wastewater, because urban wastewaters contain toxic constituents that can wipe out the methane bacteria.

The Mauripur ponds caused massive marine pollution, as they simply discharged untreated and polluted wastewater into the sea.

The choice of technology (anaerobic ponds), in this particular case, is inappropriate technically. What is required is technology that is based on an extended aeration system, like aerated lagoons.

Where properly designed and operated, the aerated lagoons are reputed to produce high-quality effluent (over 90 per cent biochemical oxygen demand (BOD) and suspended solids removals). Aerated lagoons do not produce rotten egg-like gas or methane gas.

The Sindh government should revisit this project and redesign the Mauripur wastewater treatment plant.

A senior citizen

Hyderabad

Published in Dawn, August 7th, 2018