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Growing international concern for the environment is leading many companies to step up research into new methods to minimise their environmental impact and seek 'green' credentials.

More than 9,000 tonnes of waste is dumped into landfills every day in Hong Kong and, at this rate, Hong Kong's three landfills will be filled by 2016.

The sheer volume presents one problem but landfills create their own environmental concerns - they produce high volumes of methane,  a greenhouse gas, and leachate,  which can contain harmful heavy metals.

This problem is shared by many communities worldwide: how to reduce the volume of waste and find sustainable ways to deal with non-recyclable materials.

Green Island Cement has taken the initiative to find a solution to this problem.

The Hong Kong cement supplier looked at how the combustion process in cement manufacturing could be used to create an alternative to traditional waste incineration.

The company's engineers developed a thermal treatment technique that produced three products: electricity, low-pollution gas emissions and ash for use in cement. The company calls this technique the 'co-combustion process'.

The process involves sorting the recyclable waste from the non-recyclable. The non-recyclable material then undergoes primary combustion in a kiln at temperatures not less than 800 degrees Celsius.

A substantial proportion of

the residue ash from the kiln will

be used in cement manufacturing, resulting in less residue to

dispose of.

The hot gas from the primary combustion chamber goes through a secondary chamber where it is heated to at least 1,000 degrees.

The final process simulates a boiler process where steam is generated to produce power. When this process is commercialised, the hot gas generated is sufficient to operate the plant.

In 2003, after working with the Hong Kong University of Science and Technology (HKUST) to fine-tune the process, the Environmental Protection Department (EPD) granted Green Island Cement a licence to operate a pilot co-combustion plant limited to produce 24 tonnes of municipal solid waste a day.

After 50 days, 500 tonnes of solid waste had been treated and the air pollution monitors showed spectacular results. Independently tested by Hong Kong Baptist University, the dioxin levels were 100th of Hong Kong's existing 'Best Practical Means' and significantly better than the world's highest standards.

The objective of the pilot operation was to ensure that gas emissions were kept to a minimum to protect the atmosphere while maximising the production of ash from waste that could then be used in cement manufacturing.

Gordon McKay, associate professor of department of chemical engineering at the HKUST,  said: 'All of the tests were positive and well below the minimum pollution emission levels allowed by the EPD.'

Co-combustion seems to offer a real alternative for waste disposal. It reduces the volume of waste going into landfills, creates renewable energy and keeps harmful gas emissions low.

Green Island Cement executive director Don Johnson  said: 'It is a win-win technology as it turns waste into a source of energy and construction materials, and has excellent world-beating air emission results.'



Firm gets world-beating results from enhanced manufacturing process