While waste from septic tank is cleaned out by private contractors and carried to treatment plants from where it is disposed off into the sea, in an efficient underground sewer networking, residential waste is collected through tertiary lines that join the trunk main lines which in turn are connected to STPs. Today, in urban India, around 70% of every city comes under the UGD network but a good 30% is yet to be connected, while in the rural side or the nagars like Aurangabad, Thirupur and Salem, it is the reverse with 70% yet to be connected with sewer lines.
So, the potential that the country holds in terms of networking the entire underground drainage system creates extended market prospects to the tune of multiple crores of rupees for various sectors from sewer pipe manufacturers and contractors for laying the pipes to sewer cleaning & maintenance equipment manufacturers and maintenance contractors.
This sector is more of a municipal driven market whereby machines are manufactured to suit tender requirement. Hence, the requirement is more basic and simpler than that of automation. But with more and more contractors coming in, demand for automation is likely to increase. These machines are bought by municipalities and also industries, including hotels, hospitals, manufacturing units, etc., where the generation of sewage is more.
Sewage generated is in proportion to the water consumed. The sewerage pumping station on an average receives –150lt per person x population = the mld per day.
The maximum diameter of the sewer pipes carrying the waste of the entire populace varies from 700mm to 2400mm from city to city. Sewer blockages in the existing lines are common with population increase and dumping of plastic bags, hair and solid material in the sewer system.
Traditionally, sewage blockages were detected and cleared manually. Thanks to the bhungee community that has been getting down into the sewer pipes and cleaning blockages with no safety gears on, not just as of yesterday but for generations. However, the increasing awareness and government strictures banning manual cleaning of sewage pipes, have created demand for automatic blockage detection systems and mechanical cleaning of sewer lines. Rapid urbanisation has stalled the pace and growth of maintenance networks leading to silting of sewer pipes and increase in blockages. It has extended the necessity to refurbish and rehabilitate the existing lines through modern technology.
Various cleaning tools and equipment to clean and remove blockages and obstructions from storm and sanitary sewer lines are now being used by various municipal corporations.
With the sewer pipes operating beyond capacity, it tends to crack and through leaks, waste water seeps into the underground drinking water table, thus contaminating it. Further, the fresh water lines run along the sewer lines. The fresh water lines are pumped under pressure and when there is no water in the afternoon it works as a vacuum and sucks whatever comes by. It sucks sewer water into the drinking water line.
Talking about the seriousness of sewer maintenance and proper functioning, M. Krishna, Managing Director, Kam-Avida Enviro Engineers Pvt. Ltd, said, “You can stay in the house if you don’t get water, you can buy it probably, but just imagine the bathroom overflowing or for that matter the flush overflowing. Similarly, unless the sewer tanks begin to overflow, no one takes notice. Even if they take notice, they do not have access to clean the tank as they do not have the right tools or expertise to handle this choke. In most cases, as a temporary solution, people tend to puncture the nearest sewer line leading to several other problems. At many places across India, there are punctured lines causing overflow on to the roads and in some cases also into the houses. Unless, the right kinds of tools are available, it is difficult to access these lines.”
A bigger challenge, he added, is the velocity of the flow in the sewer lines. “The peak loads during 6 and 9.30 in the morning & evening and a vacuum during the interim period can hardly be of self-cleaning velocity. Due to uneven flow, there tends to be accumulation of silt. Maintaining the right kind of gradient throughout is also a challenge from the point of how it is laid. Basically, there is no foundation, the ground is dug up, the pipes laid and joined at the collar. This error can only be resolved through maintenance.
Majority of the sewer lines across India are silted between 70-90%. Designed in 1940 for a load of 1980 or say designed for a population of 10 lakhs the sewer lines are now taking 100% more load of 20 lakhs. The volume of the sewer lines to hold this capacity has shrunk by 80%! In short, what we have before us today is 20% of the available volume handling three times the quantity of sewer generated. During the peak hours, all these sewer lines are charged. In the manholes the water begins to rise and wherever there are cracks and leaks, it starts flowing out. The trees in the vicinity have an affinity toward water and roots make a beeline and find a way to enter these lines. They encapsulate the entire sewer and even tend to break it over a period of time.
“Cleaning these sewer lines, firstly, in itself is a big challenge; secondly, maintaining it, and thirdly, to clean something which you can’t see. Further, with generation of hazardous gases inside the sewer line, the crown of the sewer is getting corroded leading to mud penetration and resultant blockage. During winter, the oil in the waste solidifies and forms a scale on the walls of the sewer leading to blockage. Hence, it is given the lowest priority, even by the governing bodies. Unlike solid waste that is garbage, sewage waste is not visible to the eyes instantly.
“Going by the simple calculation of the requirement of these machines is one machine per 15,000-20,000 people. Hence for one lakh population, the requirement is about five machines. On the basis of this calculation, a city like Mumbai would require around 5000 machines but it hardly has 500 machines now. Inspections and desilting are perhaps the first step towards preventive maintenance,” said Krishna.
Silting of sewer lines
Sewer lines are of two types – lateral lines and main/trunk lines. Lateral lines are those that carry sewerage from residential, commercial and industrial complexes (from the point of generation) in to the trunk lines. Trunk lines are those that receive sewerage from all the lateral lines and carry in to the treatment plants.
Lateral lines are normally smaller in diameter, non-man entry in nature; whereas trunk lines are by and large man-entry lines, some round and some oval in shape.
Many leading Corporations are currently carrying out de-silting of trunk lines by deploying powerful de-silting equipment consisting of high powered jetting system and a vacuum plant capable of working together to dislodge and convey large volumes of silt from within these main lines, without man-entry in compliance with the recent Supreme Court order.
Only when these methods are used will our cities ever be relieved of this acute and chronic problem.