Sewere Maintenance

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.

Mechanised Maintenance

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.

The problems that typically confront lateral lines are blockages and stoppages caused by settling of solids, root growths, infiltration… which are cleared either manually or by using machines.

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.

Technology

Suction-cum-Jetting

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.

Bucketing system

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.

Rod system

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.

Rajasthan

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.

Mumbai

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.

Delhi

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.

Rehabilitation

Trenchless technology

Trenchless technology, often referred to as “no dig”, is a rapidly growing engineering industry that eliminates the need for surface excavation. It provides cost-effective sewer asset management through pipe and sewer inspection, rehabilitation and cleaning services. One of the most recent developments in trenchless technology is the use of robotics which provides users with digital data. This includes sonar sewer profiling which allows for pipe inspection while the pipe is in service.

Virtual CCTV pipe inspection is another trenchless technology that provides you with a high resolution, front hemispherical picture of the pipe giving you the ability to pan, zoom, tilt, and classify defects from a desktop computer.

Some trenchless robots are also capable of laser scanning. Laser scanning creates a three dimensional model of the surrounding environment, allowing for measurable results and visualization of features that may not be visible with CCTV pipe inspection.

Indian subsurface infrastructure has a varied age, starting from newly laid pipes to ones that are as old as 200 years. Lengthwise, New Delhi has one of the largest subsurface pipe networks with approximately 5,000km in length. There are functional sewers in old cities such as Benaras, Kolkata or Mumbai, with pipe ages exceeding 100 years.

Probably the first use of trenchless technology in India was the lining of a 2.4 feet x 3.75 feet brick sewer in Maharshi Karve Road in Mumbai by a Baltiboi-ITI joint venture. Though the project was complicated and had several pitfalls, it was finally completed well over budget but demonstrably up to all technical standards of the day.

Application-wise, the largest need for trenchless techniques is in the water and sewer sector, where the networks are either failing badly or deteriorated to an extent where new installations are becoming a necessity. There are, however, lines where rehabilitation work can still be done and even this work is substantial.

Said Saurin Patel, Managing Director, Michigan Engineers Pvt. Ltd, Mumbai, pioneers in the trenchless technology, “Rehabilitation of old sewer lines running underground in urban areas, using modern module like fiberglass gives it a lease of life by another 100 years, besides it increases the velocity of flow causing less frictional loss and in default increasing the capacity of these lines. These lines can be in shapes like circle, oval, ovoid, egg-shaped, basket handles or boxes that are under rehabilitation all over India. Egg shapes and circles are the most common. From GPO to Lovegrove pumping station in Worli, there are three main networks coming into the pumping station, that will be rehabilitated by either this year end or mid next year. Delhi has horseshoe, circles, boxes and egg shaped sewer on which the rehabilitation is on. In Kolkata, you have eggs, ovoid and basket handles. Rehabilitation is going on in the metro, including the Rashbehari Avenue, Bose Road, Beaten street and Canning Street. We are one of the few Indian companies to have the expertise to provide such services, as most of them working on the Indian sewer lines are international service providers. Now with the sewer lines being rehabilitated, the only preventive maintenance method that can be used is the suction jetting system.”

But trenchless technology is not just the need of the hour but the only option available where rehabilitation of the Indian lines are concerned, said Ashok Gandhi of Gravit Engineering Works, who are in this field for over 28 years. “Relaying is not a practical option. It requires digging up of roads, pulling out the existing lines and fitting in new pipes, calling for colossal expenses and causing inconvenience to traffic. The Delhi and Mumbai municipal corporations have extensively adopted this European technology to rehabilitate the sewer lines. There are seven to eight technology in the trenchless method, including GRP lining/coating, In-situ form CIPP, uPVC spiral, micro tunneling, pipe bursting and cast in-situ (GRP coating). But in India, we are using the man-entry trenchless technology whereby taking a small pit at one place the fibre glass pipe is pushed inside relaying the entire pipe. We too offer this technology availed from Denmark but we are more into consultancy, compiling data and assessment.”

Cleaning workers

Unlike janitors in other sectors, the sewer cleaners are one of the most unskilled labourers who are prepared to enter a manhole filled with sewage just for a price. At a time when cleaning contractors are facing a crunch of labourers, sewer cleaners are still available in abundance, said Krishna. But, he warned, the scene is likely to change for the better soon. “Gone are the days when a bhungee’s son or daughter is a bhungee too. Today, with increasing reservations, children in this community are opting for higher education. Sewer cleaning essentially calls for manual entry into the sewer line at one point or the other. Even in other Western countries, workers do enter the manhole but are equipped with the right gadgets and suit to protect them. The mask, the cylinder, suit, boots, etc., are part of any worker. But, in India, the worker would want to jump into the manhole without caring to carry a cylinder on his shoulder.”

In a paper on Partial Automation of the Current Sewer Cleaning System, Ajay Kumar Shrivastava, Ashish Verma and S.P. Singh have proposed a robtic vehicle that goes inside the sewage pipeline, locates the blockage and also places the nozzle of the pressure pipe at the point. It can work in water-filled pipes and therefore, no human being will be required to go inside the sewage water.

The complete system will consist of robotic vehicle, a sensor unit and two robotic arms and embedded system to control the working of the system.

The detection of blockage will be done by using ultrasonic sensors, which can work satisfactorily inside water & sewage filled sewer network. The sensor will be moved inside the sewer line by the robotic vehicle. The direction of the sensor can be varied by a robotic arm. The embedded hardware and software will provide proper signal to the ultrasonic transmitter and also receive signal from the receiver.

A cart can be attached to the same robotic vehicle. Solid materials like polythene bags, bricks, etc., of the blockage can be collected by the arm and placed in the cart. A crusher can also be added to crush some solid materials. It can also be useful for other pipeline system inspection like oil pipeline, gas pipeline and drinking water pipeline, with some small changes.

Why Sewer Cleaning?

A wastewater collection system is typically a network of pipes, manholes, clean outs, traps, siphons, lift stations and other required structures to collect all the wastewater from an area and transport it to an environment safe place such as a treatment plant or disposal system.

Sewer systems are located underground, typically running parallel to streets. This series of pipes and culverts are engineered as gravity flow systems, built on a slight grade to assist material flow.

Most sewers are designed to convey material at a velocity of 2 feet (61cm) per second. When velocity falls below this rate, solids remain at the bottom of the pipe, reduce flow capacity and eventually cause a blockage. If the velocity is designed to flow greater than 10 feet (300cm) per second, solids could separate from the flow during low usage. At high velocity splashing occurs when the water changes directions, releasing odours and accelerating corrosion of concrete structures.

Partial or complete interruption of the flow may result from an obstruction in a sewer, when such interruption occurs, material will backup and eventfully overflow affecting the neighboring streets, homes and businesses.

The objective of a Sewer Cleaning and Maintenance Programme is to operate & maintain the wastewater collection system. The regular maintenance programme will minimize the number of stoppages per length of sewer pipe, reduce odour complaints and lift station failures.

Current deficiencies

1. Poor maintenance: The majority of the branch sewerage system is at any time either completely blocked or its capacity is severely reduced by silt and solid waste. Sewer maintenance is restricted to emergency clearing of blockages and is given low priority.
2. Silting and surcharging: Sections of the trunk sewers are heavily silted. Reduced capacity from silting results in sewage overflows from manholes to surface drains during peak flow periods. Problems may also be caused by structural damage in some sections.
3. Ageing infrastructure: The existing trunk sewer system is over 75 years old and has been allowed to deteriorate to the point where rehabilitation or replacement is necessary. Many of the sewers have not been inspected.
4. Storm water and solid waste ingress to sewers: Damaged manholes, sewer defects particularly around the drains and linking of drains to the sewerage system have led to increased risk of solid waste entering and blocking the system.