NOM increase in Northern European source waters: discussion of possible causes and impacts on coagulation/contact filtration processes

Abstract

A significant increase in the content of natural organic matter (NOM) has been observed in several surface water sources in Norway during the past 10–12 years. Similar observations are reported also from est sites in Europe and North America. Water works in the southern part of Norway have experienced a doubling and in some cases even a tripling of source water color levels during the last decade. Other important characteristics of NOM, e.g. the specific UV absorption (SUVA), have changed as well. The change in raw water quality increases the required NOM removal capacity in water treatment, and significantly affects treatment process selection, design and operation. However, the operational impacts on water treatment processes are poorly quantified. This paper addresses the observed NOM increase in parts of Europe and North America. Although the reasons are not fully understood or identified, possible causes are presented and discussed. Factors like climate change or variability, especially alteration in precipitation patterns and land-use, as well as reductions in anthropogenic sulfur loadings seem relevant. From pilot testing on relevant raw waters, major operational impacts of increasing NOM and SUVA levels on coagulation-contact filtration processes are identified and quantified. As an illustration, an increase in raw water color from 20 to 35 mg Pt L−1 increased the required coagulant dose, sludge production, number of backwashes per day and residual TOC by 64%, 64%, 87%, and 26%, respectively. In addition, hydraulic capacity and filter run time decreased by 10% and 47%, respectively.

Long-term Trends of Organic Carbon Concentrations in Freshwaters: Strengths and Weaknesses of Existing Evidence

“…Non statistically increases and decreases are considered "no trends"; d Values only given when trend statistically significant, except when mixed in the original publication (in this case, a cautionary note is added). When value in italics, original value in other units; e [88] includes data from two streams (Loch Ard Burn 2 and Allt a'Mharcaidh) but refers to this study for DOC long term trend values; f Data from one of the catchments (Langtjern) further treated in [89] by empirical regression analysis and a process-based model; g Original units: μmol C L −1 y −1 ; h [17] show exactly the same results. They cite [9] as a source; i Original units: μeq C L −1 y −1 ; j Probably slopes for non statistically significant trends included.…”

“…These reasons finally prevailed. Note, however, that in many cases these data are either totally or partially published later in refereed articles, cases in point being Freeman et al [14] and Evans et al [15,16], who refer to Monteith and Evans [8], and Eikebrokk et al [17] and Skjelkvåle et al [18], who refer to Skjelkvåle [9].…”

Abrupt changes in air temperature and precipitation: Do they matter for water chemistry?

“…Absorbance and COD are two methods of estimating the concentration of organic matter. Organic matter has a large impact on chemistry [Schwarzenbach et al, 2003;Stumm and Morgan, 1996], and biota [Wetzel, 2001], as well as on human society [Eikebrokk et al, 2004]. Increasing concentrations of organic matter in surface waters have been observed in many regions and several causes are debated, among them runoff processes [Erlandsson et al, 2008], atmospheric deposition [Evans et al, 2005[Evans et al, , 2006Monteith et al, 2007], and climate [Forsberg and Petersen, 1990].…”

Sensitivity of freshwaters to browning in response to future climate change

“…While particles can easily be removed from the water column by various filtration techniques, the removal of dissolved colored substances, commonly referred to as chromophoric dissolved organic matter, is far more complex and expensive (Eikebrokk et al 2004;Volk et al 2002). Chromophoric dissolved organic matter is usually dominated by brown-colored humic substances from terrestrial ecosystems (Thurman 1985), and frequently measured as absorbance of filtered water at a given wavelength, for example, 420 nm (a 420 ) (Kirk 2003).…”