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Bromide in water can form undesirable by-products such as bromate when treated by ozonation during drinking water production. The maximum contaminant level (MCL) for bromate is 10 µg/L in most countries because it is suspected of being carcinogenic. In this paper, the geographical distribution of bromide concentration in Croatian groundwater is presented covering the Pannonian basin and the Dinarides (Adriatic Sea). Groundwater in Croatian wellfields predominantly has a bromide content of less than 50 µg/L and thus belongs to the group with low potential for bromate formation. Waters with higher bromide concentrations were found mainly in the coastal regions of Croatia, probably due to seawater intrusion. In addition, bromide concentration showed a positive correlation of 0.6 with conductivity, chloride, and sodium. In addition, the potential of 123 groundwaters analyzed in this study to form bromate when treated with ozone was evaluated using models available in the literature. Analysis of water from Croatian wellfields indicated that the potential for bromate formation above the MCL during ozonation was relatively low. The models used from the literature predicted quite different values of bromate concentration when applied to the same water, with some values exceeding those theoretically possible. Selected models may be useful as a general warning of possible bromate formation.

The implementation of near-infrared (NIR) spectroscopy in the wastewater treatment has been continuously expanding. As an alternative to the conventional analytical methods for monitoring constituents in wastewater treatment processes, the use of NIR spectroscopy is considered cost-effective and less time- consuming. NIR spectroscopy does not in any way adulterate measured sample as no prior treatment is needed thus making it a waste-free technique. On the negative side, one must be very well acquainted with chemometric techniques to interpret results. In this study, filtered and centrifuged wastewater and sludge samples obtained from a lab-scale membrane bioreactor (MBR) were analysed. Essential wastewater constituents were determined and compared, employing two analytical methods (conventional and NIR spectroscopy). Special attention was given to the soluble microbial products (SMP) and the extracellular polymeric substances (EPS) which are known to promote membrane fouling. The measured parameters through NIR spectroscopy were analysed and processed by partial least squares regression (PLSR) and artificial neural networks (ANN) models to assess whether the evaluated wastewater constituents could be monitored by NIR spectroscopy. Very good results were obtained with PLSR models except for the determination of SMP thus limiting the model for their monitoring to qualitative rather than quantitative. ANN exhibited a better performance in terms of correlating NIR spectra with all the measured parameters, resulting in correlation coefficients in most cases higher than 0.97 for training, test, and validation. Based on the results achieved by this research, the combination of NIR spectra and chemometric modelling offers advantages compared to conventional analytical methods.

The purpose of this study was to investigate characteristics of treatment of spent filter backwash water (SFBW) from two full-scale drinking water treatment plants (WTPs) with immersed ultrafiltration membranes in order to achieve reuse of permeate. During this study, 10% of daily generated SFBW from the treatment plants in Croatia were treated on two pilot-scale UF plants. Three different types of immersed membranes were employed and operated with fluxes, which ranged from 10 to 54 L/m2 h in two continuous experiments, which lasted 75 and 96 days. During both experiments, transmembrane pressure, flux, and turbidity of filtrate were constantly measured. Rate of membrane fouling was very slow, and no chemical cleaning was needed but the membranes were regularly relaxed. Turbidity of permeate was always below 0.5 NTU. Results confirmed that permeate could be reused either for backwashing of sand filters, or as a source of raw water for drinking water treatment process.