I refer to the report (“Sewage could be energy source, scientist says”, September 28).
While the studies of Herbert Fang, chairman of environmental engineering at the University of Hong Kong, should be encouraged, I wish to point out that the use of sewage sludge as a refuse derived fuel is not an entirely new concept. There are many operations all over the world that treat sewage sludge and use it as an environmentally-friendly and cost-effective refuse derived fuel.
At Green Island Cement, we have been working on our waste management technology, the eco-co-combustion system, for the past nine years.
We have already presented the government with our environmentally-friendly and cost-effective solution for sludge treatment. However, it has rejected our proposal and decided to construct a conventional sludge treatment incinerator in Tsang Tsui to manage Hong Kong’s growing waste management problem.
Through our eco-co-combustion system, sludge would be used as a refuse derived fuel at our cement plant in Tap Shek Kok. Sludge would be taken from Stonecutter’s Island (using existing transport containers) and further dewatering would be carried out at our site to create sludge pellets. These refuse derived fuel pellets would then be fed into the cement plant’s burner system to replace imported coal.
Together with this technology, the refuse derived fuel could replace about 40 per cent of coal currently burnt at the cement plant.
Our eco-co-combustion system pilot plant tests have demonstrated excellent emissions results, far better than the government’s best practical means.
In sum, our system offers a waste management solution that will result in an overall net improvement in air quality. All residual ash is recycled and used in the manufacturing of cement clinker, thereby further reducing the burden on landfills.
We estimate that the quantity of dewatered sludge which can be treated by our proposed facility would be up to about 2,000 tonnes of sludge per day, the same as the government’s proposed incinerator.
The capital required to install such a sludge processing facility at Tap Shek Kok is around HK$950 million.
This is a substantial saving on the government’s proposal to spend HK$5.2 billion.
It is a significant saving for the public purse.
Despite these numerous benefits, the administration has pressed ahead with its own conventional sludge incinerator proposal, without giving due consideration to our technology.
So while Professor Fang should be encouraged with his studies, we hope officials can provide a forum in which new technologies can be assessed and brought into fruition. If the government will only consider conventional technologies, any new scientific studies or advancements will prove pointless.
Don Johnston, executive director, Green Island Cement (Holdings) Limited