Awardee: Ms Stephanie Leung Yuen Ting

Sewage treatment plays a vital role in sustainable urban development. Residential, commercial and industrial sewages are first collected at the wet well of sewage treatment plants (Figure 1). Due to the nature of its application, the bottom of the wet well often accumulates sediments which in turn adversely affect the downstream sewage pumping system, increase maintenance cost and decrease pumping system availability. Wet well cleaning is therefore essential maintenance work in sewage treatment.

Figure 1: Concept illustration of a typical wet well in sewage treatment plants

Conventionally, wet well cleaning is carried out by certified workers inside a confined wet well and during low sewage inflow condition only. These conditions make the cleaning works extremely dangerous, costly and inefficient. In view of the drawbacks of existing practice, a remotely operated underwater wet wells cleaning vehicle, named the "Mini Bull", was developed (Figure 2). It serves as a preventive maintenance tool for wet well in sewage treatment plants.

Figure 2: The Mini Bull

A safe and effective solution to replace confined space cleaning works in wet wells

The Mini Bull is an innovative robotic underwater vehicle developed under the "Smart City Blueprint for Hong Kong" project scheme. It aims to enhance safety and effectiveness of wet wells maintenance in sewage treatment plants. To perform wet well cleaning, the Mini Bull applies rotating tools in the front to fragment the accumulated or even hardened sediments, and its hydraulic dredging pump to pump the fragmented sediments to ground level for filtering and disposal. It is equipped with a compact sonar system consisting of Compressed High Intensity Radar Pulse (CHIRP) echo sounder and multi-beam imaging sonar and driven by a separate hydraulic power pack, which help reduce the vehicle size and weight to facilitate flexible navigation. Through the incorporation of sonar technologies, the Mini Bull overcomes challenges of continuous sewage inflow and low visibility environment to perform positioning and imaging, resulting in user-friendly control by operators outside the wet well.

This innovative project was funded by the TechConnect (block vote) administered by the Innovation and Technology Bureau. Having undergone off-site trials for design validation and on-site trials at the Wan Chai East Preliminary Treatment Works for performance evaluation, the Mini Bull has been commissioned with proven results. An over one-month man-entry cleaning works at a wet well could be shortened to complete within one day and with a lower cost. This invention not only enhances operational efficiency and saves maintenance costs, but also considerably improves the occupational health and safety level of the underwater works. Its application can also be extended to other sewage treatment facilities and underwater works with similar conditions.