Seven and a half kilometers of tunnels lie beneath us. This is the Aberdeen Preliminary Sewage Treatment Works. Imagine the intricate network hidden from view. This isn’t just a sewage treatment plant. It’s a crucial piece of Hong Kong’s infrastructure. A testament to engineering ingenuity.
The Aberdeen Preliminary Sewage Treatment Works is one of eight such plants on Hong Kong Island. They’re all part of a larger system. The Harbour Area Treatment Scheme. Its purpose is simple yet monumental: to cleanse Victoria Harbour. To restore its water quality. To bring back marine life.
Before the Harbour Area Treatment Scheme the harbour was severely polluted. Beaches were closed. Development stalled. The water quality was so poor that it negatively affected the entire area. The Harbour Area Treatment Scheme changed all of that. Stage 1 of the project treated 75 percent of the sewage. Stage 2A completed in 2015 finished the job. It upgraded and expanded the Aberdeen Preliminary Sewage Treatment Works and seven others. It also created a new conveyance system. This system consists of 21 kilometers of deep sewage tunnels. These tunnels carry wastewater from the preliminary treatment works.
The construction of the tunnels was a feat of engineering. They were dug to a depth of 70 to 120 meters below sea level. This was exceptionally challenging. The engineers used a drill-and-blast method. This method allowed them to control water ingress. They could stop and apply high-pressure grouting to seal up rock joints. It was a slow process. Much slower than using a tunnel boring machine. But the result was a watertight system.
The Aberdeen Preliminary Sewage Treatment Works itself underwent significant upgrades. New fine screens and grit traps were installed. These remove materials larger than four millimeters and grit smaller than 0.2 millimeters. This prevents sediment build-up in the conveyance system. The plant also received new pumps and a deodorization system. Landscaping added a touch of beauty to the site. All of this happened while the plant continued to operate.
Consider the scale of the project. Two hundred thirty-five thousand cubic meters of material were excavated. The tunnels themselves are oval-shaped. Their size ranges from 1.5 to 2.1 square meters. The completed project serves approximately 300000 people. It’s a silent guardian of Hong Kong’s environment. A testament to human ingenuity. A vital part of the city’s infrastructure.
So as you stand here today take a moment. Appreciate the unseen work. The unseen heroes. The complex system that keeps Hong Kong clean and healthy. The Aberdeen Preliminary Sewage Treatment Works is more than just a plant. It’s a vital part of this city’s story.