Sewage Sludge Incineration

Sludge incineration is a two-step process involving drying and combustion after a preceding dewatering process, such as filters, drying beds, or centrifuges. Sludge incineration is usually considered to be a high-cost option, but it may be economical if adequate land area for sludge disposal is not available.

Sewage treatment and water treatment processes produce sludge as a by-product. Generally speaking, more sludge will be produced if higher level of treatment is required. Sewage, from which liquids have been filtered, enters the incinerator from above the highest tier. This sewage is retained for a time on the highest tier and heated. Sewage sludge incineration ash was sampled from several facilities, and XAFS measurements were carried out with a beam line BL01B1 at the SPring-8 facility.

The USEPA has conducted stack emission testing for dioxin from sewage sludge incineration at three multiple-hearth sewage sludge incinerators. The homologue profile was developed from tests on these three incinerators.

Humans have a high respiratory rate which means that low emissions can still build in the body for example adult inhalation rate is 13.3 cubic meters each day. Even a child 3-5 years old has an inhalation rate is 8.3 cubic meters each day.

The United Kingdom Experience

A population of more than 50 million people cannot live, eat and work on a small island without having an effect on the quality of the water. Nor can we, with or without the undoubted energy and powers of the Environment Agency, clean up the accumulated mess of centuries overnight.

Through sewage treatment the amount of sewage sludge is reduced to 25 million tonnes per year which, expressed as a dry weight, amounts to 1.1 million tonnes. This represents the amount of sewage sludge that the UK has to manage sustainably each year. In this case, the capital cost of the sludge processing facility was $8 million and the operating cost is approximately $180 per dry ton (pdt), versus about $275 pdt for the cost of sludge disposal by land applications. Harlingen's waste heat recovery credit plus its carbon dioxide credit amounts to $120 pdt which reduces the net operating costs to about $60 pdt. The plant became operational in mid-2006 and has a treatment capacity of 1 million population equivalent.

In (2004) the British government imposed tough new standards on emissions from incinerators, and waste-management experts say this will cut the amount of dioxin in the air. But, the Environment Agency's project manager for the new survey, points out that reducing the dioxin content of emissions from incinerator stacks will increase the amount of dioxin in the ash left behind.
Furthermore, the most part of the thermal energy generated in the incinerator is not possible to be utilized effectively such that it results in a waste of energy and a contamination of environment. In order to utilize the thermal energy generated in the incinerator, the furnace body in an incinerator of the prior art is provided with double water walls to contain cooling water.

Comparison with Incineration of Pharmaceutical Wastes

The combustor mixes auxiliary fuel, oxygen, and air to enhance the flame envelope's stability, luminosity, and flame core temperature and reduce the combustion volume per million BTU of heat released. The computer-controlled system adjusts the primary and secondary combustion chamber temperatures and the amount of excess oxygen. He figures the entire industry disposes of about 16 million pounds of pharmaceuticals a year. So, these emissions are small compared with sewage sludge volumes.

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