An incineration trial conducted by Green Island Cement has shown the amount of toxic pollutants produced from burning waste is not excessive, the environment watchdog said.

Still, the company has been asked to do additional trial burns from next week before being allowed to undertake a 16-week trial.

The operator said the quantity of dioxins released reached only 0.0011 nanogram per cubic metre of air, against a standard of 0.1 nanograms per cubic metre.

Green Island Cement ran trial incinerations of non-construction waste from April 19 to 25, under a licence granted by the Environmental Protection Department.

A report on the trial results was submitted to the department two weeks ago. Despite some "process fluctuations", the department was satisfied with the trials.

It said: "The tests confirmed that municipal solid waste can be effectively treated by high temperature combustion. During the trial incineration, the treatment system effectively controlled emissions to within licence limits."

The company has been asked to demonstrate that the process can be operated stably.

Don Johnston, executive director of Green Island Cement, said the department had been satisfied with the emission readings, though it had some questions about the measurement of air flow within the incineration chamber during the tests.

"I am not unhappy with it. Of course, it would have been better if they accepted the report," he said.

Mr Johnston said the air flow measurement issue arose from one of the monitoring devices melting down during the process, meaning they had to calculate the reading manually. But he stressed that the problem would not affect the emission results.

"What we are doing is giving the department a huge amount of comfort that we can reproduce what we have done already and that we can satisfy some additional questions about measurement."

The trial, which also involved the University of Science and Technology, was funded by the cement company - a subsidiary of Cheung Kong Infrastructure - and also by the Innovation and Technology Fund.

Published under Cement News