Micro-pollutants: Heavy Metals

SUWIC has studied the impact and control of heavy metals and the environment

Three projects highlight work in this area:

 

Project 1 - Identification and Control of Metal Pollutant from Industrial Processes

 

Academic Staff: Dr V.Nasserzadeh Sharifi , Professor J.Swithenbank, Professor C.McLeod,
Research Staff/Students: Dr Y.R.Goh, Dr P.J.Clarkson, Dr D Poole, J.Stoves, A.Cox,

The main objectives of this research are to study the emissions of metals in the waste gas from industrial processes and to develop an optimised measurement method for continuous emissions determination. The emission of heavy metals from industrial processes has become a question of considerable public and scientific concern in the light of evidence of their extreme toxicity to human health. The principal need for this study is due to the fact that metal emissions depend strongly on the local combustion temperature in the industrial processes.

Previous work in the department led to metal emissions from gas-solid bed combustion being identified as a key area requiring further fundamental study. Formation and destruction of transient channels within the burning bed dominate the combustion process, and these sudden changes result in the release of fly ash, and other gaseous pollutants into the flue gas. It was assumed that heavy metal releases accompanied these events, also being highly dependent on temperature, chemical environment in the bed, and metal content and distribution in the waste. In contrast, most models of metal volatilisation in combustion systems assumed thermodynamic equilibrium of the whole combustion chamber. These models were poorly verified experimentally, and there was considerable question over whether a global equilibrium could adequately describe such an inhomogeneous system.

Exclusive information has been obtained on the concentration and variation of metallic pollutants in flue gas, using our unique continuous emissions monitoring laboratory. This mobile laboratory, deigned around the Spectro Ciros- CCD ICP-OES, and equipped with a 40 m heated sampling line, is used to simultaneously monitor the concentrations of over 30 elements, including As, Ca, Cd, Hg, K, Na, Pb, Sn, V, Zn, with detection limits as low as 0.0004mg m-3, and a time resolution of one minute or less.

We have conducted considerable experimental investigation of a waste to energy plant in the UK. This unit handles 20 tonnes of waste per hour on two lines, with Martin reverse-acting reciprocating grates and a steam- raising energy recovery system. Flue gas cleaning comprises of hydrated lime and activated carbon injection followed by bag-house filters. Measurements of metal concentrations in emitted flue gas have shown them to be extremely low; certainly below regulatory limits, and without significant variation. Measurements made prior to flue gas cleanup have revealed high in-process concentrations of a number of metals, including Na, Pb, and Zn. These show significant temporal variation, which can be linked to process conditions, such as bed temperature and waste feed. Concentrations of certain key pollutants, such as Cd and Hg, are seen to be generally very low, but with occasional peaks, which are attributed to individual sources of these metals in the waste.

The data obtained from this research is fundamental in understanding the temporal fluctuations in the incineration system, which is essential for improving new thermodynamic models of metal behaviour in combustion, which are currently being developed. Where occasional high-concentration spikes dominate the release of a metal, this provides strong evidence that better segregation of certain key items from the waste stream could help to considerably reduce the level of key toxic metals in process residues. Careful control of plant conditions could also have a significant impact on the volatilisation of other metals. This work has attracted a great deal of interest from the academic and industrial communities, and has already led to two journal publications, and numerous oral presentations.

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Project 2 - Occupational Exposure to Metals at Industrial Plants

 

Academic Staff: Dr V.Nasserzadeh Sharifi , Professor J.Swithenbank, Professor C.McLeod,
Research Staff/Students: Dr P.J.Clarkson, Dr Y.R.Goh, O.Mitafsi, A.Cox.

The burden of metals and its compounds in air in industrial plants depends significantly on the process. Certain tasks in particular, metals processing tasks produced an increased burden of metals into the work environment, usually in the form of dust. Ingestion of dust through breathing and dermal exposure by the plant personnel may be significant. The overall objective of this project is therefore to develop a methodology for assessing the potential exposure to the work force inside the industrial plants posed by the metals emissions, which can be used as a basis for the assessments of the comparative benefits of alternative operation management strategies.

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Project 3 - Human Exposure to Metal Pollutants from Voluntary Daily Activities

 

Academic Staff: Dr V.Nasserzadeh Sharifi , Professor J.Swithenbank, Professor C.McLeod.
Research Staff/Students: Dr. P.J.Clarkson, Dr. Y.R.Goh, B.Zhang, A.Cox,

Metal pollutants are known to have a wide range of impacts on health in humans. It has also been reported these potentially toxic heavy metals are emitted in the flue gases from waste incineration as well as many other types of industrial processes. The main argument from pressure group against the construction of more incinerators to manage our waste is focused on the associations between the metals emission from the process and the risk of cancers, cardiovascular diseases, respiratory health and reproductive outcomes among incinerator plant personnel and nearby community.
In order to produce balanced view and to elevate public perception of the potential health risks associated with these plants, the extent of human exposure to metals through their voluntary activities such as smoking and home improvement activities is investigated in this project.

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Unique continuous emissions monitoring laboratory.

The Continuous Emissions Monitoring (CEM) mobile laboratory, deigned around the Spectro Ciros- CCD ICP-OES, and equipped with a 40 m heated sampling line, is used to simultaneously monitor the concentrations of over 30 elements, including As, Ca, Cd, Hg, K, Na, Pb, Sn, V, Zn, with detection limits as low as 0.0004mg m-3, and a time resolution of one minute or less.