Safe drinking water in a changing environment : Membrane filtration in a Swedish context

Surface water is vital for Swedish drinking water supply. In the past decades, a trend of increased total organic carbon (TOC) concentrations has led to higher consumption of coagulants in drinking water treatment, and has pushed the levels in the outgoing water closer to the allowed levels of TOC. Also, two occasions of cryptosporidium outbreaks in northern Sweden have stressed the importance of reliable microbiological barriers.Ultrafilters and tighter membranes can, due to size exclusion, produce a safe water by reducing the occurrence of parasites, bacteria and virus 10,000-fold or more. Combined with a coagulation pretreatment, ultrafiltration has the additional benefit of removing natural organic matter (NOM), whereas nanofiltration can remove NOM without coagulant. This dissertation presents results for NOM removal by ultrafiltration and nanofiltration from several raw water sources. The results were collected in mobile pilot plants at several locations. The coagulation and ultrafiltration process could achieve similar NOM removal as current chemical treatment, to a similar cost, and with a lower environmental impact. Hollow fiber nanofiltration achieved advanced NOM removal, reducing TOC with around 90 % and UV-absorbing species at 254 nm of up to 97 %. Thus, it is selective to aromatic NOM, similar to conventional treatment. The cost for the operation of a treatment process would increase if coagulation/sedimentation would be replaced with a nanofiltration step, but the environmental impact would decrease substantially. The NOM removal was studied by the aid of fluorescence spectrometry. Fluorescence can be related to characteristics of NOM, which has been implemented in this study. The application of fluorescence as a monitoring method has been evaluated through indices and other fluorescence derived parameters. Some of these, e.g. fluorescence index, have showed significant correlations to treatment efficiencies. Similar to TOC and UV-absorbance, significant changes in the nanofilter permeate was possible to relate to integrity breaches, and these NOM related parameters have shown potential for integrity monitoring.With such advanced NOM removal and advanced monitoring techniques, membrane filtration has a promising future in Swedish drinking water treatment. It decreases the risk for waterborne pathogens. Specifically, nanofiltration can lead to lower risks for disinfection by-products and regrowth in the distribution system

Evaluation of Long-term Discharge in Swedish Rivers

Seasonal forecasting is not an easy task to deal with. A number of large scale atmospheric phenomena, e.g. Northern Atlantic Oscillation (NAO), Scandinavia (SCA) and Pacific Decadal Oscillation (PDO) affect the climate in Sweden and the effect on rivers is an integration of all the complex inter-relation among all these atmospheric phenomena. In this Master thesis, the river discharge from 107 stations, distributed over Sweden, were examined in the search for decadal oscillation. River discharge measurement data, collected from the Swedish Meteorological and Hydrological Institute, span periods between 40 to 100 years. In order to examine these time series, the Wavelet analysis was used. The discharge stations were divided into groups, depending on location and wavelet spectrum and these groups were compared to the wavelets of the climate indices that represent the atmospheric phenomena. Results show the presence of decadal oscillations in the river discharge in Sweden. It was also possible to make a rough grouping of stations with common features in their river discharge wavelet spectrum. Such groups followed roughly the climate zone distribution. Possible connections to climate indices were found, of which Pacific Decadal Oscillation (PDO) and Pacific/North American (PNA) were the two most evident. One thing to note is that SCA was the climate index that was least connected to the discharge. Why river discharge tends to depend more on PDO and PNA than on SCA, when SCA is the Scandinavian affecting pattern, could be due to the vast amount of decadal and multidecadal oscillations that PDO and PNA have, which also many of the river discharge time series have

Feasibility study of advanced nom-reduction by hollow fiber ultrafiltration and nanofiltration at a Swedish surface water treatment plant

Membrane technology, i.e., ultrafiltration and nanofiltration, is growing in popularity, as it is a space efficient alternative for surface water treatment. Two types of hollow fiber membranes were tested in a fully equipped and automated pilot at a Swedish water treatment plant. Raw water was treated by a nanofilter and by coagulation before an ultrafilter. Operation parameters recorded during these trials have been the basis for cost estimations and assessments of environmental impact, comparing the two membrane modules to the existing conventional treatment. The membranes required lower chemical consumption, but led to increased costs from membrane modules and a higher energy demand. Compared to the existing treatment (0.33 €/m3), the operational costs were estimated to increase 6% for ultrafiltration and 30% for nanofiltration. Considering the low emissions from Nordic energy production, the membrane processes would lower the environmental impact, including factors such as climate and ecosystem health. Greenhouse gas emissions would decrease from 161 g CO2-eq/m3 of the existing process, to 127 g CO2-eq/m3 or 83 g CO2-eq/m3 for ultrafiltration and nanofiltration, respectively. Lower chemical consumption and less pollution from the sludge leaving the water treatment plant lead to lower impacts on the environment

Uses of fluorescence excitation-emissions indices in predicting water treatment efficiency

Membrane filtration is a possible alternative for the increase of the natural organic matter (NOM) content in the raw water sources in boreal areas. In a pilot study, a new hollow fiber nanofilter (HFNF) has been tested. Water from four raw water sources were treated in membrane pilot plants, and three full-scale conventional plants were sampled. Three established fluorescence indices, humification index (HIX), fluorescence index (FI) and freshness index (β:α), were used for characterization, and were related to NOM removal by the two treatment methods Although the NOM removal in the treatment processes were related to SUVA, HIX has only a weak correlation to the total organic carbon (TOC) reduction of the HFNF, and none for the conventional treatment. FI and β:α are both correlated to the TOC reduction of the HFNF. Water hardness has a logarithmical correlation to the TOC reduction by the HFNF, plausibly due to moderation of the membrane surface. FI and β:α have potential to predict the efficiency of the HFNF and conventional treatment processes, and could be used online to identify changes in the raw water which affects the process efficiency

Integrity breaches in a hollow fiber nanofilter – Effects on natural organic matter and virus-like particle removal

Ultrafiltration and nanofiltration have become common methods to treat surface water for drinking water purposes. Common aims of a membrane step are removal of natural organic matter (NOM), softening or adding an extra microbiological or chemical barrier. In most cases, the membrane is considered a good disinfection step; commonly the viral removal is at least 4–log. To ensure a working disinfection, reliable integrity tests are required. In the present pilot study with a hollow fiber nanofilter, the membrane achieved a high NOM reduction, and the difference in parameters related to NOM quality before and after treatment proved to be useful indicators of integrity breaches. Changes in total organic carbon (TOC) concentration, UV-absorbance at 254 nm (UVA254) and fluorescence derived parameters in the permeate flow were related to leaking fibers. On average, UVA254 in the permeate was 3 times higher for a membrane with compromised fibers (0.041 cm−1) compared to an intact membrane (0.013 cm−1), while TOC was less than 2 times as high on average. Thus, this membrane had a higher reduction of UVA254 than TOC and the sensitivity for changes from leakage was higher. Therefore, it is suggested that UVA254 could be used as an indicator for membrane integrity. Additionally, there is a significant (P < 0.01) difference in fluorescence derived parameters between a leaking and an intact fiber, showing that fluorescence also has potential to be applied for online monitoring of membrane processes. During fiber failure, around 2% of the permeate flow passes through one single leaking fiber. The transport depends on the distance between the inflow and the leak, which in most cases are similar and most likely close to the middle of the fiber