How might we collect factory premises' used water samples from various types of sanitary lateral connections for used water quality monitoring and surveillance, without the need for man-entry into the sewers?

Water Reclamation (Network) Department - Operation & Maintenance Division

The discharge of trade effluent containing prohibited substances or excessive concentrations of regulated substances into the public sewerage system may cause health and safety risks to workers maintaining the system an​d disrupt downstream used water treatment processes in PUB's water reclamation plants (WRPs). 

PUB regulates the discharge of trade effluent and adopts a risk-based approach to manage discharge from factory premises based on their industry trades. Industries with higher probabilities of discharging prohibited substances or excessive concentrations of regulated substances, such as the electro-plating and chemical manufacturing industries, are required to install online water quality monitoring instruments in their last inspection chambers (ICs) for continuous monitoring. PUB officers also conduct frequent inspections at these premises to ensure compliance with the trade effluent discharge limits. During these inspections, trade effluent samples may be collected for lab analyses and enforcement actions may be taken if non-compliance is detected.

Special operations are also conducted in targeted premises that are suspected of illegal trade effluent discharge activities. To avoid drawing the attention of the occupier, PUB staff may monitor a factory's trade effluent discharge from the sewage manhole outside its premise. If abnormal discharges are observed, effluent samples would be collected from the manhole and analysed. 

For factory premises whose sanitary drainage systems connect to the public sewer via a top saddle connection, PUB deploys an improvised robotic crawler. The crawler would enter the public sewer through an upstream / downstream manhole and travel underneath the sanitary connection of the targeted premise to collect effluent samples from the top saddle connection (refer to “Standard drawings for Sanitary and Sewerage Works" under Resources). The robotic crawler is retrofitted with small collection tanks to contain the effluent samples.

For other types of lateral sanitary connections, where trade effluent enters the main sewer in other directions, the current robotic crawler is unable to be deployed as its collection tanks are designed to only collect effluent that is flowing vertically down. 

On average, there are 24 deployments of the robotic crawler per year to collect samples from top saddle connections in the public sewerage system. At present, there are no suitable crawlers to collect effluent samples from other lateral sanitary connections.

PUB is interested in a customized robotic platform that can be deployed into the public sewerage system to monitor trade effluent discharge and collect representative effluent samples from various types of sanitary connections serving targeted trade premises, without the need for man-entry into the sewers. 

The customized robotic platform is expected to be controlled via tether by a human operator from the ground. It shall be ruggedised for manoeuvring in the sewer environment and comprise suitable sensing technologies to visually inspect the interior of the sewage pipe and monitor sewage gases. The operator shall be able to position the robotic platform at the sanitary connection, view the effluent discharge from above ground, and control the robotic platform to collect and retain representative effluent samples. The effluent sampling mechanism shall be designed for the different types of sanitary connections, including the top saddle.

A. Operational Requirements

I. ROBOTIC CRAWLER

The robotic platform shall be suitable for use in sewerage environments and shall be equipped with suitable

• Traction wheels or treads etc. to maneuver in flow conveying sewers with water level up to half bore and pipe invert filled with soft sediments.
• Odometer to record and display to the operator, the real-time distance traversed by the crawler in the sewer.
• 360° view, high-resolution (HD) cameras with adequate lighting to record and display to the operator, the real-time visual observations as seen by the crawler in the sewer. Recorded video footages shall be stored in HD quality.
• Gas meters to record and indicate to the operator, the real-time concentration of sewage gases and hazardous gases (e.g., volatile organic compounds, hydrogen sulfide, carbon monoxide and oxygen). Lower explosive limit (LEL) meters shall also be provided.
• Suitable winch with tether cables of sufficient length to traverse up to 400 m horizontal distance in sewers (excluding manhole depth).

II. CUSTOMISED SAMPLING MECHANISM

The robotic platform shall have a customised sampling mechanism that is

• Equipped with a suitable actuator arm that can collect effluent samples from all types of lateral sanitary connections indicated in the Code of Practice (Sewerage and Sanitary works), which include raised junction, Y-junction, tumbling bay and backdrop connections (refer to “Standard drawings for Sanitary and Sewerage Works”, under Resources), etc.
• Capable of collecting only the effluent discharged from the targeted sanitary connection, without cross-contamination from other streams in the public sewer
• Able to be remotely operated by the operator to activate sampling of up to five (5) discrete effluent samples from the sanitary connection.
• Equipped with containers to store the effluent samples. The material of the container shall be compatible with the discharge effluent and shall be break-resistant. To ensure that the collected samples are representative, the containers shall always be capped/covered unless samples are being collected. Each collected effluent sample shall be 250ml in volume. Filled containers shall be retrievable from the robotic platform at ground level.
• Equipped with suitable electronics and sensing technologies (e.g., high-resolution cameras for imaging and LIDAR sensors for depth perception) for tasks requiring human intervention such as controlling actuator to collect samples, capping of samples or blocking other sewage streams, etc.

B. Physical Requirements to Fit Working Environment

The robotic platform shall be

• Designed for use in sewers with diameters ranging from 300 to 600 mm, and manholes with depth of up to 10 m.
• Designed as a whole or modular to fit into 600 x 600 mm opening of standard sewage manhole.
• Equipped with neutral buoyant tether cables for power and data transmission, and of sufficient length to traverse up to 400 m horizontal distance in sewers (excluding manhole depth).
• Design to function in hazardous environment and complies with relevant standards.
  

Robotic platforms that are commercially available and deployed by PUB registered CCTV contractors are used solely for the purpose of carrying out CCTV inspections to check for the interior conditions of the sewer systems. These platforms are not designed to carry extra payload, nor do they have customized sampling mechanism to collect effluent samples from sanitary connections. 

• Illustrations of the types of sewer connections
  

• Code of Practice on Sewerage and Sanitary Works

• Standard drawings for Sanitary and Sewerage Works

• List of PUB registered CCTV contractors

•  PUB sewers as test sites
  

Total project period – less than 18 months

A site-tested robotic platform prototype system that can monitor a factory premise's discharge from the public sewer and collect representative effluent samples from the various types of lateral sanitary connections remotely, without the need for man-entry into the sewers. 

If the pilot is successful, the solution would be provided to PUB through a service model where the equipment is owned, operated, and maintained by the company. Solution providers may consider collaborating with a PUB registered CCTV contractor to tap on their existing competent manpower and resources for this project.

Q: Where should the robot take the water samples in the sanitary connections?

A: The robot should aim to collect the sample at the closest feasible point after the inspection chamber and from flowing liquids for accurate results.

Q: What are the environmental conditions for the sampling locations? What flow speed can we expect from effluent flows at the sampling locations?

A: You can consider a typical sewer environment in Singapore for your proposal but note that environment condition may change due to the illegal discharge (e.g., low visibility) depending on the type of substance being discharged. The flowrate of used water in most cases would be based on the gravitational pull generated between the inspection chamber and the discharge outlet at the manhole where robot will collect sample from. Sewers are typically designed gradient to achieve flow velocity of 1m/s.

Q: How does the current robot works? Does the system face any challenges when navigating the sewers?

A: The current robot is based on a four-wheel system. There may be soft sediments that robot may not overcome.

Q: How does the current sample container works? Why is the current robotics system limited to collecting samples in vertical effluent flow?

A: The current container used to collect sample is based on gravitational flow from the top of the container. Hence, current robot has to position itself directly at the bottom of the discharge outlet so that the containers to effectively catch the vertical effluent flow.

Q: Does the sewer sampling robot need to be certified by the ATEX or a similar agency, or could it be of intrinsically safe design?

A: The robot should minimally be designed to be intrinsically safe. It would be preferable for the robot to be certified by the ATEX or a similar agency.