An overview of the methods used in the characterisation of natural organic matter (NOM) in relation to drinking water treatment

Removal of natural organic matter from drinking water by advanced oxidation processes.

The importance of lakes and reservoirs leads to the high need for monitoring lake water quality both at local and global scales. The aim of the study was to test suitability of Sentinel-2 Multispectral Imager’s (MSI) data for mapping different lake water quality parameters. In situ data of chlorophyll a (Chl a), water color, colored dissolved organic matter (CDOM) and dissolved organic carbon (DOC) from nine small and two large lakes were compared with band ratio algorithms derived from Sentinel-2 Level-1C and atmospherically corrected (Sen2cor) Level-2A images. The height of the 705 nm peak was used for estimating Chl a. The suitability of the commonly used green to red band ratio was tested for estimating the CDOM, DOC and water color. Concurrent reflectance measurements were not available. Therefore, we were not able to validate the performance of Sen2cor atmospheric correction available in the Sentinel-2 Toolbox. The shape and magnitude of water reflectance were consistent with our field measurements from previous years. However, the atmospheric correction reduced the correlation between the band ratio algorithms and water quality parameters indicating the need in better atmospheric correction. We were able to show that there is good correlation between band ratio algorithms calculated from Sentinel-2 MSI data and lake water parameters like Chl a (R2 = 0.83), CDOM (R2 = 0.72) and DOC (R2 = 0.92) concentrations as well as water color (R2 = 0.52). The in situ dataset was limited in number, but covered a reasonably wide range of optical water properties. These preliminary results allow us to assume that Sentinel-2 will be a valuable tool for lake monitoring and research, especially taking into account that the data will be available routinely for many years, the imagery will be frequent, and free of charge.

First Experiences in Mapping Lake Water Quality Parameters with Sentinel-2 MSI Imagery

Increasing concentrations of organic matter ( OM) in surface waters have been noted over large parts of the boreal/nemoral zone in Europe and North America. This has raised questions about the caus ...

Thirty-five years of synchrony in the organic matter concentrations of Swedish rivers explained by variation in flow and sulphate

Advanced oxidation processes for the removal of natural organic matter from drinking water sources: A comprehensive review.

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 test 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.

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

A small full-scale ozonation/biofiltration plant was operated for 1.5 years in mid-Norway. A three-media biofilter was used to remove biodegradable organic matter from ozonated water. The biofilter contained granular activated carbon (GAC), phonolith and CaCO 3 and was operated at 26-30 min. empty bed contact time. The water temperature varied between 2 and 14°C but the biofilter was operated most of the time at temperatures below 10°C. Total phosphorus concentration in the raw water was also very low (1.1-2.0 μg/L). Batch tests showed that low phosphorus concentration and low temperature are potential limitations for microbial growth and organic carbon removal. Initially, the GAC adsorbed organic carbon while the microbial activity was building up. Most of the adsorption capacity was used after 1.5 months of operation. After this period, 14-33% of the TOC was removed (average 23%). Although the overall TOC removal in the process was modest, average BDOC removal of 55% was observed even at 3°C. Ozonation was effective in reducing colour with average removal of 80%. The results show that significant biological activity can be achieved and maintained in biofilter treating ozonated water even at low temperatures and phosphorus limited conditions.

Treatment of humic surface water at cold temperatures by ozonation and biofiltration

Contact filtration performance of a coarse expanded clay aggregates filter (Filtralite) is compared to a conventional dual media anthracite/sand filter. In a contact filtration pilot plant, humic water was coagulated using aluminium sulphate (AS), iron chloride sulphate (ICS), poly-aluminium chloride (PAC) or the bio-polymer chitosan. Filtration experiments were performed at optimum pH and dose conditions for each coagulant found from previous optimisation experiments in the pilot filter plant. The results reveal two main problems in coagulation/filtration of humic waters: short filtration run times for the most commonly used metal salts, and metal residuals in treated water. The best ways to overcome these problems in raw waters high in organic matter, was found to be by the use of a coarse filter bed in combination with chitosan, or a metal salt with the addition of polymer as filter aid. An increased turbidity level in the raw water (as bentonite clay) was found to increase the removal of humics in most cases, as well as increase the filterability of the flocs formed.

Contact filtration of humic waters: performance of an expanded clay aggregate filter (Filtralite) compared to a dual anthracite/sand filter

Absorbency of UV and visible light by dissolved natural organic matter (DNOM) is used in proxies (sUVa, SAR) to assess its physiochemical characteristics and thereby removability of the DNOM by waterworks. The ongoing browning of surface waters is partly due to increased concentration and change in characteristics of DNOM. However, it is also likely that the browning is partly due to the increased iron complexation by DNOM. The significance of absorbency by the Fe-DNOM complex needs to be assessed in order to distinguish between the drivers of brownification. key words – DNOM; Iron complex, adsorbency, sUVa, SAR

B. Eikebrokk

Papers

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

Treatment of humic surface water at cold temperatures by ozonation and biofiltration

Contact filtration of humic waters: performance of an expanded clay aggregate filter (Filtralite) compared to a dual anthracite/sand filter

Effect of dissolved natural organic matter proxies by increased complexation with iron