The impact of seasonal variations in DOC arising from a moorland peat catchment on coagulation with iron and aluminium salts Emma L. Sharp, Simon A. Parsons, Bruce Jefferson * School of Water Sciences, Cranfield University, Cranfield, Bedfordshire, MK43 OAL, UK Received 17 May 2005; received in revised form 1 August 2005; accepted 6 August 2005 The variations in natural organic matter (NOM) composition and character, particularly in terms of charge, will directly impact on the coagulation process. Abstract Natural organic matter (NOM) is one of the main sources of environmental pollution to drinking water supplies in much of the UK and the US. Whilst traditional treatment with trivalent coagulants has proven a successful strategy in the past, operational problems are now being reported during periods of elevated organic levels in the water. Characterisation of the pollutants in terms of polarity, molecular weight and charge, provides a method to understand the impact of the observed temporal and spatial varia- tions in terms of a mechanistic parameter relevant to the treatment processes. Results from this study demonstrate that it is not simply the increased organic concentration, but also the change in NOM composition and character, which influences the impact on the treatment processes. Consequently, monitoring of these parameters provides an insight into how to manage the impact caused by environmental changes to the catchments. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Charge density; Coagulation; Natural organic matter; Water treatment; Zeta potential 1. Introduction Natural organic matter (NOM) is one of the main sources of environmental pollution to drinking water supplies in the UK and the US, especially for low alkalinity, low turbidity source waters delivered from moorland or mountain catchments. Changes in land management, such as the disturbance of peat or vegeta- tion damage, can lead to increased decomposition and the production of loosely bound NOM (Worrall and Burt, 2004). The accumulated organics are then flushed into the aquatic environment as a result of increased sur- face runoff, such as a rainfall event or snowmelt runoff (Hurst et al., 2004). Whilst traditional treatment with trivalent coagulants has proven a successful strategy in the past, operational problems are now being reported during these periods of elevated organics, the impact of which has been ob- served as an increase in the production of potentially carcinogenic disinfection by products (DBP), formed when residual organics react with chlorine during water treatment. NOM is defined as a highly heterogeneous mixture of organic compounds which are known to vary both spatially and temporally in terms of molecular weight * Corresponding author. Tel.:C44 1234 750111x4813; fax: C44 1234 751671. E-mail address: b.jefferson@cranfield.ac.uk (B. Jefferson). 0269-7491/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.envpol.2005.08.001 Environmental Pollution 140 (2006) 436e443 www.elsevier.com/locate/envpol