Effect of Aluminium on Microbial Respiration Caetano C. Dorea & Brian A. Clarke Received: 27 June 2007 / Accepted: 20 October 2007 / Published online: 14 November 2007 # Springer Science + Business Media B.V. 2007 Abstract Aluminium is a non-essential element for biological systems and is used in water and wastewater processes that rely on (micro)biological purification processes. The effect of Al doses ranging from 100 to 2,000 μg/l on the microbial dissolved oxygen uptake (respiration) over a 24-h period was assessed. Results indicated that Al can reduce the 24-h respiration, but the effects of pH depression due to Al dosing during testing should be taken into account. Keywords Aluminium . Dissolved oxygen . Microorganism . pH . Respiration . Toxicity 1 Introduction In water and wastewater treatment, Al salts are used as coagulants to condition and pre-treat water. Residual metal concentrations due to coagulant addition can remain in the treatment stream and can possibly affect downstream biologically-assisted treatment processes and natural purification mechanisms in waters receiving Al-laden discharges – in both of which microorganisms play an important role. It is generally accepted that biological systems do not require Al to function properly (Wood 1984; Wood 1985; Eichenberger 1986 –cited by Gensemer and Playle 1999). The free (hydrated) Al ion is considered the Al form which is most toxic to aquatic life (Florence and Batley 1980). Much of the research on Al toxicity and bioavailability has been directed either to the effects of the metal on humans (e.g. Reiber et al. 1995) and other organisms, particularly aquatic forms (e.g. Gensemer and Playle 1999). Usually, these aquatic organisms refer to higher forms of life; with the exception of algae, few studies contemplate the effects of Al on aquatic microorganisms. The effect of Al on aquatic (aerobic) microbial activity has been assessed in some studies using biochemical oxygen demand (BOD) tests or other respirometric techniques (i.e. effect on microbial oxygen uptake). Sheets (1957) determined that an alum dose of 18 mg/l as alum (degrees of hydration not stated) on a sample of sewage was sufficient to cause a 50% decrease of BOD over 24 h. Similar tests were conducted by Mowat (1976) in 5- and 14-day BOD tests on raw wastewater, which evaluated the effects of alum doses varying between 0 (control) to 20 mg/l as Al. A decrease in relative DO uptake occurred with increasing Al doses and that the effect Water Air Soil Pollut (2008) 89:353–358 DOI 10.1007/s11270-007-9553-3 C. C. Dorea (*) Department of Civil Engineering, University of Glasgow, The Rankine Building, Oakfield Avenue, Glasgow, G12 8LT, UK e-mail: caetanodorea@hotmail.com B. A. Clarke Centre for Environmental Health Engineering (CEHE), School of Engineering, University of Surrey, Guildford, Surrey GU2 7XH, UK