Giving neglected assets some TLC reaps rewards

When water and wastewater assets collapse through corrosion, it leads to system disruptions and costly repairs. Danny Heffernan, managing director of Ferro Monk Systems, believes a proactive cleaning and maintenance routine is the answer

Water and wastewater assets are often key elements of a business. This is not always recognised until they cease to function. After years of heavy use, sewers, drainage pipes, drains, manholes, chambers and other water and wastewater assets can become corroded and weakened.

This can lead to collapses, blockages and costly repairs. Such disruptions can occur for numerous reasons, but are frequently linked to badly maintained water and wastewater assets.

Problems can also occur for a variety of other reasons, such as:
  • Changes in ground or traffic loading, leading to cracking and collapse
  • Transfer of corrosive liquids, causing erosion and corrosion of the pipe and chamber fabric. This allows exfiltration or infiltration.
Another major enemy of sewers is hydrogen sulphide (H2S). It attacks concrete and mortar above the liquid level in pipes and chambers, causing deterioration and failure. H2S naturally occurs within sewer silts.

Chemical cocktail
When H2S is combined with production effluent, it can be a recipe for disaster. The chemical cocktail created within the effluent has a similar effect below the liquid level as the H2S does above. This places the entire system at risk.

It remains essential, therefore, that all foul water, or other aggressive waste-transfer systems, remain both functional and sealed. Infiltration of groundwater or surface water, for example, can lead to additional costs by increasing the volume of the waste being treated.

Exfiltration of waste liquid products can lead to environmental incidents if the waste finds its way into a watercourse. This results in heavy fines from the Environment Agency.

It is extremely important that water and wastewater assets are inspected and effectively maintained on a regular, planned basis. This will minimise any potential disruption to the business and its processes. Monitoring and maintaining assets need not be costly when carried out in a proactive, rather than reactive, manner.

The first step that needs to be taken in ascertaining the condition of any water or wastewater asset is cleaning and inspection. In many instances, this can be carried out remotely, using specialist CCTV and high-pressure water- jetting equipment. It is essential that trained and experienced personnel are employed to view the survey recordings to decide what, if any, action is to be taken.

There are two main methods used for rehabilitating, renovating or repairing systems - man entry and non-man entry.

As the name suggests, man-entry systems are carried out by operatives physically entering the pipes, culverts, tunnels, tanks or chambers to carry out rehabilitation. Many man-entry systems are identified as being type 1 linings.

A type 1 is where the lining and the existing sewer combine to act as a rigid composite section. To do this, a bond is required between the lining and the existing sewer.

Precast components
The Sewerage Rehabilitation Manual recommends that type 1 techniques should only be used in man-entry sewers. This is where there is a high degree of confidence in the bond with the existing structure.

Some of these techniques are based on the use of precast components. These rely on a grout around the annulus to transfer load between the new lining and the existing structure. This can have a significant disadvantage in sections of sewer where the existing structure varies in cross-sectional area, meanders - or both. This is not uncommon in older brick or stone-built culverts.

Techniques include Ferro Monk Systems' Ferrocement lining. Ferrocement - which is cement mortar - inverts can be used for pipes, culverts and tunnels. The precast inverts are designed and manufactured, then grouted into place within the existing structure. In most cases, this acts as a flume to maintain existing dry-weather flows. This cancels the need for costly over-pumping while the system is being worked on.

This is followed by the installation of layers of reinforcement, governed by design, to the remaining perimeter of the structure. This is then encapsulated in Ferrocement by spraying and trowelling. Chambers and tanks can be treated in much the same way.

A recent example is the structural refurbishment of more than 260m of Burlais Brook Culvert in Swansea, Wales.

Other techniques include glass-reinforced plastic (GRP) lining. GRP-manufactured units to a given size and thickness are installed within the existing structure being rehabilitated.

Hazardous materials
More recently, a 100% solids epoxy-sprayed lining system has become available, mainly in response to calls for environmentally friendly solutions. Such systems contain no volatile organic compounds, and can be used to rehabilitate wastewater systems within confined spaces. This is with no risk of combustion of hazardous materials.

It is highly resistant to aggressive effluent, algae and bacterial growth. Because it can tolerate high temperatures - and high levels of sulphur dioxide, acids and alkali - it can also be sprayed onto damp surfaces and applied quickly, bonding well. Assets can be back in use within as little as two hours after application.

The high bond strength of the 100% solid system means it can strengthen corroded or weakened structures. It sticks well to most surfaces, including concrete, steel, brick, fibreglass and clay. It can be used in tanks, chambers, manholes and culverts.

The solution is an exceptionally versatile substance which when sprayed in situ will take the shape of the substrate.

Non-man entry systems are often called no-dig technology or trenchless technology. They are also technically known as type 2 linings. It is a methodology that employs remote techniques and equipment to carry out the necessary rehabilitations, renovations or repairs. These are carried out, in most instances, using existing accesses such as manholes. This saves costly excavations.

Type 2s differ in that the lining is designed into a structural pipe and does not require a bond with the existing sewer. There are now a number of systems on the market, the main types being based around a resin-impregnated felt sock. The resins become cured either through exposure to increased temperature - using hot water or steam - or UV light.

A commonly used method is cured-in-place pipe lining for full-length or part-length manhole-to-manhole relining of pipes and culverts. It uses resin-impregnated polyester-felt lining tubes to effectively create a new pipe within the old. It can bridge gaps and holes in damaged pipes, and seal cracks in most shapes and diameters, ranging from 150mm to 1,200mm. Lateral connections can be reconnected into the newly lined pipes by using remotely controlled robotic cutting equipment. Many systems are based on the use of an epoxy-impregnated medium, such as glass-fibre matting, which is wrapped around an inflatable packer. The system is introduced into the sewer, positioned at the point of repair and allowing sufficient overlap into the defect-free host. The packer is then inflated, pushing the patch against the pipe.

Following cure, the packer is deflated and recovered for reuse.

Asset maintenance
Maintenance of water and wastewater assets need not be costly if dealt with in both a timely and correct manner. But it is essential to seek advice from a specialist company.

Identifying problems early can prevent major, often expensive, disruption to business. Reactive action often occurs too late, when the unexpected flooding, pollution, collapse and production disruption has already happened. Proactive-planned inspections can be the key to successful asset maintenance.

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