Tuesday , 10 December 2019
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(Left) Sewage from tankers being released into a chamber connected to the STP (Right) Clean water, after the sewage is subjected to treatment,  collected in a beaker

St Inez STP: from dirty sewage to clean water

 

SHOAIB SHAIKH | STAFF REPORTER

PANAJI: If your are told that the St Inez creek stinks due to the water being released into it by the sewage treatment plant (STP) at Tonca, then your are being misguided as the water that is let out after the sewage is treated at the plant is  clean and non-stinking.

This water from the STP is being used by the department of forest to water the gardens besides the plants and trees in Panaji and the ornamental plants planted on the road dividers across the city. The water is as clean as ground water that one draws from an unpolluted well.

The report, dated February 19 – signed by the chief chemist of the Public Health Engineering (PHE) Laboratory, on the analysis of water samples collected on February 15 states that the biochemical oxygen demand (BOD) level in the untreated sewage was 582.5 mg/litre whereas the BOD level in the water, released after the sewage treatment,  was at  1.8 mg/litre.

Similarly, chemical oxygen demand (COD) level in the untreated sewage was found to be 1040 mg/litre, while COD level in the water was only 24 mg/litre.  If that still does not seem good, the impurity which is visible to human eyes – the suspended solids, in the raw  sewage sample collected at the STP on February 15 measured  678 mg/litre, while the resultant water sample (after being treated)  was found to have 18 mg/litre of suspended solids.

Further, the coliform bacteria count, common bacterial indicator for sanitary quality of foods and water, was at 11×107 MPN/100ml in the raw sewage sample while a sample of the water collected after treatment had coliform count of 1100 MPN/100 ml.

Similarly, the count of Escherichia coli ( E coli) bacteria, which causes food poisoning symptoms such as abdominal cramps and diarrhea, was found to be at 43×106 MPN/100ml in the raw sewage sample while the count of same bacteria was found to have reduced to 75 MPN/100ml in the sample of water collected after the sewage was treated at the plant.

The STP treats on an average 9-10 million litres per day (MLD) of sewage sucked through the sewer lines laid across the city and also that is unloaded by more than 100 soil tankers, which collect sewage from the villages in the coastal belt of North Goa and the municipal areas of Bicholim and Sankhali.

The STP generates a revenue to the tune of Rs 12,00,000  every month for the government in form of the charges collected for unloading the sewage brought by the septic sucking tankers.

While a negligible quantity of the water let out by the STP is currently utilised for watering the gardens and the ornamental plants dotting the road dividers, a small quantity of it is being  used by one of the real estate developers in the city at his construction sites.

The other output from the treatment plant is the residue – sludge that is dried in the open at the 10 drying beds within the plant premises and sold to the farmers as manure.

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