Water jets under high pressure of at least 140 bar 200-300lpm per minute are sprayed into the sewer line through the manhole that dig out the mud/silt probably homogenised with the sewer line over a period of time.
The water passing through the jetting nozzle hits the water backward and the reverse thrust pushes the nozzle forward. The nozzle maintains constant jet spray towards the rear. As the nozzle moves, the water slices the mud and pushes it towards the manhole. Nozzles of various sizes and shapes are used to clear chokes at different levels.
This is preventive method which is usually not done on a regular basis which could save crores of rupees.
Another conventional process is the bucketing system. An inverted bucket is passed from one manhole to another. In the process of pulling, it scrapes the mud from the sewer system, which gets collected in the bucket and passed out from the other manhole. This is a chain system. It is a conventional system and is called the bucketing system. The only risk is these metal buckets are hard and in the event it gets wedged, it could rupture the sewer line. The municipal corporation in Mumbai and Pune, have an efficient system of pulleys which keeps these buckets moving layer by layer. Nevertheless, it does not undo the entire silt.
“In many places the trunk lines stand because of this silt and when removed the lines could sink in. At Kolkata, one of the tram lines sunk in, as the sewer line caved in,” said Krishna.
This unique concept is based on the fact that force alone does not clean best. High speed drilling action with the help of rods is capable of pushing, pulling and rotating high strength special sectional steel sewer rods, with various cleaning tools to clean and remove blockages and obstructions from storm and sanitary sewer lines.
“This process is equivalent to angioplasty of sewer pipes and if not done could lead to a “bypass” requirement which is more difficult and chaotic,” said Rajesh Khatwani, CEO, Industrial Plants & Waste Treatment Corporation (IPWT).
A further extension of this technology is seen in the use of a wheel where the rod from the wheel cage is released and introduced into the sewer line through the manhole pipe. It is pushed gently until it reaches the choke and forcefully pushed to de-choke. The right property of the rod ensures maximum transfer of impact.
In preventive maintenance, the rod is allowed to travel further until it reaches the connecting manhole. The rod is pulled out, attached to a brush and the rod is fed into the wheel. The brush, on its way backwards dislodges deposited material.
Efforts by civic bodies
The failure of proper grades for gravity lines has necessitating an all-weather round pumping due to sluggish flow. Moreover, the present state of affairs is that after an extremely long period of neglect, now the utility service providers have started feeling the pinch as to the failure of the networks, which are now leading to serious environmental disasters.
Faced with such situations all over, several utility service providing authorities have embarked upon Environmental Improvement Projects (EIPs). Some of the examples are Rajasthan Urban Infrastructure Development Project (RUIDP), Tamil Nadu Urban Development Project-III (TNUDP-III), Kolkata Environmental Improvement Project (KEIP), etc.
The RUIDP under a systematic sewer maintenance programme under their ADB funded project for eight towns in Rajashthan, uses Auto Gas Jet units, the state-of-the-art mobile sewer cleaners mounted on three-wheel auto vehicles. A high power water jetting unit with hose reel and 500lt water tank uses high pressure water to flush out the blockage. It is equipped with triplex pump with vibra pulse which drives the hose around tight bends and long pipes. These machines are supplied by IPWT Mumbai. “Around 70-80 IPWT machines for sewer cleaning are running for the BMC, 20 at Ahmedabad, 17 machines were supplied to Gujarat Urban Development Corporation besides Chennai, Kolkata and other places,” said Jignesh Parekh, GM-Sales, IPWT.
At present, the collection and disposal of waste water and sewage in Mumbai is divided into seven zones, viz., Colaba, Worli, Bandra, Versova, Malad, Bhandup and Ghatkopar. From each of these, sewage and waste water is conveyed to the respective final discharge points for disposal through marine outfalls, some three kilometres into the sea. There are 53 pumping stations for pumping the sewage/waste water from lower level to higher level and there are 54,000 manholes for maintenance of 1,400km long network of the sewerage system.
The Brihanmumbai Municipal Corporation has now a systematic sewer maintenance programme which uses dredgers that can walk or swim thereby accessing all locations of the nallahs. It enables vigorous desilting and in the process has helped the BMC to come closer to their goal of ‘flood free monsoons’ by keeping the nallahs free of silt.
These machines, a part of procurement programme of BMC, are being supplied by Kam-Avida and IPWT Mumbai.
There are 10,000km-network of sewer pipelines in Delhi – approximately 6,500km of main lines, the trunk sewer lines stretch to about 150km, the peripheral lines approximately 1,500km and the rest are internal lines. To relieve Delhi of the constant drainage and choked sewer problems, the Delhi Jal Board has put in place multiple projects in 2008, including rehabilitation and reconstruction of various sewers. It is also laying of interceptor sewers along the main three drains of the city – Shahdara drain, Najafgarh drain and the Supplementary drain
The New Delhi Municipal Council (NDMC) has recently bought from Kam-Avida two of India’s largest jetting cum suction machines built on 25 tonnes GW trucks along with four tanks to carry the silt to the treatment plant. It has also bought other supporting equipment, including security apparatus, generator, etc. The machine is desilting sewers at several locations in Delhi. “These large machines are stationary and are attached to tankers for pumping fresh water and for sucking in the waste water. This is one of the few areas where we do the O&M, otherwise it is the contractors who buy and deploy these machines,” said Krishna.
Kam-Avida along with Michigan Engineers Pvt. Ltd has designed high capacity desilting equipment which can use two pumps on tandem to generate a flow of 700lt per minute. It has been deployed for desilting trunk lines in Kolkata. Kolkata’s 100-year-old network of about 2600km of sewer is facing severe problems.
Ahmedabad and Baroda too has bought two of these machines. Bangalore is getting into desilting in a big way with JBSC funding.