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 and 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.