GIASPURA GAS TRAGEDY: Experts also endorse NGT panel ‘clean chit’ to polluting industries

Tribune News Service

Nitin Jain

Ludhiana, October 15

Endorsing the “clean chit” given to the polluting industries by the National Green Tribunal (NGT)-appointed panel to probe the Giaspura gas leak tragedy, experts have also opined that the industrial untreated discharge could not be the possible reason for the mishap.

The eight-member fact finding joint committee, headed by the Punjab Pollution Control Board (PPCB) Chairman Adarsh Pal Vig, had taken over five months to investigate the incident but no culprit had been nailed in its report.

To arrive at some definite conclusion, the panel had sought information from various experts in the field and their opinions were recorded in the report.

Dr Anoop Verma, Head, School of Energy and Environment, Thapar Institute of Engineering and Technology (TIET), Patiala, has opined that if it could have been the industrial untreated discharge, the long stretch of houses could have been affected. “However, the diameter of the affected area was limited to 3-4 houses. So, the hypothesis of industrial discharge could be neglected,” he said.

He submitted that there were no ventilation pipes provided with sewer lines along the affected stretch and it was a densely populated area without any proper arrangement of sewer flow. “The incident is a case of sewer blockage, where anaerobic digestion of organic matter had led to the formation of H2S,” Dr Verma concluded.

An expert committee, comprising of Prof Sushil Mittal, member, Royal Society of Chemistry, United Kingdom, and Vice-Chancellor, Punjab Technical University, and Prof Raj Kumar Gupta from the Department of Chemical Engineering, TIET, opined that the low pH in the range of 2.5 reported in the sewerage samples collected from the manholes near the affected site, indicated anaerobic conditions in the said sewer line portion.

“pH conditions are reported to be in the range of 4.4 to 5.7 in the upstream and downstream stretches of the sewer line, which indicates building up of anaerobic condition only in the accident area and sustaining in adjoining pockets,” they said.

The experts felt that the presence of metals, especially iron, zinc, nickel, chrome or any other heavy metal in the sewerage sample cannot lead to generation of H2S. “In case of a waste water stream in running condition with proper ventilation of sewerage network, the generation of H2S at such high concentrations is not possible, as there would be no anaerobic conditions developed in the sewer line,” they observed.

According to them, the high concentration of sulphides in the range of 56-60 mg/l in the affected stretch as compared to 6-8.8 mg/l in the upstream and downstream have come from anaerobic biodegradation of organic matter and conversion of sulphates to sulphides, especially in the focused stretch of the underground sewer line accompanied with inadequate slime stripping, long detention and insufficient design planning of the sewer line.

The Regional Director of Central Pollution Control Board (CPCB), who was also member of the probe panel, has submitted that the Municipal Corporation has claimed that the sewer line was cleaned in 2019 and it was not choked while the same sewer line was cleaned on the fateful night with the help of machines and fire tender.

“There may be a possibility of sludge deposition in the sewer line near Arti Clinic, where the incident occurred. Due to prolonged deposition of sludge in sewer line near Arti Clinic, anaerobic conditions might have been developed and high concentration of H2S gas found its way into two houses through their connections to the sewer line,” the CPCB said

In its report, the Central Scientific Institute of Research (CSIR) told the inquiry committee that the main process responsible for the formation of hydrogen sulfide was the microbial reduction of sulfate ions. “This occurs in the absence of oxygen and the presence of organic matter such as sludges. H2S tends to accumulate in confined and poorly ventilated areas where there are sewage holding tanks or other parts of sewage systems. If the system is damaged or malfunctioning or there are loose connections, gas can escape. This can happen when organic matter or sludges are disturbed,” it said.

Distinctive incident

“Surprisingly, this is the first-of-its-kind incident where the humans were affected due to inhalation of sewer (H2S) gas coming out of the unexpected domestic openings instead of individuals who enter the sewer chambers for cleaning, including manual scavenging or to clear the blockage inside the sewer chamber,” the panel noted.

The panel opined that if a proper traditional vertical ventilation system existed along the sewer systems, the incident could have been averted.

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