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| Professor Chua Hong shows a product made of PHA |
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Hong Kong has pioneered a method to recycle sludge into useful, everyday products. The innovation, developed by a team from the Hong Kong Polytechnic University's Department of Civil and Structural Engineering, turns waste material into 100 per cent biodegradable plastic bags, as well as ecologically friendly bricks.
Sludge, a by-product of treated industrial waste water, often ends up in landfills, which merely transfers the problem elsewhere.
"We have found a way to produce biodegradable plastic from polyhydroxyalkanoates (PHA) derived from sludge," explained Professor Chua Hong, Director of the PolyU-HIT Joint Research Centre for Water and Wastewater Treatment Technology.
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PHA is now used in limited applications, including thin
film pads |
PHA is already being used in several industries, but for more specialised products, including medical sutures and thin film pads. But producing them for more conventional applications, such as plastic bags, costs up to 12 times more than the current method.
Cheaper Solution
Professor Chua and his team, however, have devised a way to produce PHA cheaply from sludge.
"The sludge goes through a fermentation process, which creates unfavourable conditions for the bacteria to produce PHA, basically a type of food reserve for them," Professor Chua said.
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| A pilot project for the technology is being conducted in this Guangzhou dyeing plant |
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The innovation has earned the team overseas recognition. The project was awarded a Gold Medal at the 60th International Trade Fair "Ideas-Invention-New Products" in Nuremberg, Germany, last October.
A pilot project, underway for more than two years at a plant in the southern Chinese mainland city of Guangzhou, hopes to find the optimal operating condition for the production of PHA from activated sludge.
The so-called biodegradable bags now on the market are not 100 per cent biodegradable because the major component is still petroleum. But if PHA is used to make plastic bags, the implications will be enormous, according to Professor Chua. "China is the main producer of the world's plastic bags. If it adopts the method, you are talking about solving 30 per cent of the world's plastic problems."
The project is expected to continue for another year before Professor Chua submits his findings to municipal authorities. "It's technically ready; it's just a matter of promoting the idea to authorities," he said.
Greener Bricks
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Eco bricks made from dried sludge |
While it may take some time before PHA plastics hit the market, environmentally friendly bricks are already here. While some bricks are derived from glass and construction waste, they can also be made from dried sludge.
"We are currently in discussion with the coastal city of Wuxi, in Jiangsu Province, to upgrade an existing waste-water treatment facility to produce bricks using sludge from nearby lakes," said Professor Chua.
Turning dried sludge into bricks is not a new idea. But Professor Chua's team has perfected the process by ensuring that toxic material embedded in the sludge doesn't leach out because of chemical or heat exposure.
Previous efforts to tackle the problem by coating the bricks failed to prevent leakage after normal wear and tear. Professor Chua's team, however, has chemically reformulated the sludge to ensure that the toxic material stays in.
"We subjected these bricks through rigorous toxicity tests, and they were able to withstand various chemical, temperature and compression tests," he said.
Investor Sought
Besides being derived from recycled sludge, the bricks are also more environmentally friendly, in that they are produced without using heat or chemicals. They are also 20 per cent cheaper than conventional bricks.
Professor Chua said the company is now looking for a private investor to manage the operation.
Related Link
Hong Kong Polytechnic University
