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Trends in urban storm water quality in Tallinn and influences from stormflow and baseflowPublicationresearch articleJournal of water security, 2016, vol. 2, p. 1-11Temporal trends provide a good interpretation of change in stormwater quality over time. This study aimed to analyse trends and influences due to stormflow and baseflow. Grab samples of 18-19 years from 1995 to 2014 recorded at outlets of 7 Tallinn watersheds were analysed for monotonic trend through seasonal Mann Kendall test for long-term, short-term, baseflow and stormflow. Statistically significant downward trends (P-value (p) < 0.05) were found for 6 – hydrocarbon (HC), 1 – suspended solids (SS), 3 – biological oxygen demand (BOD), 4 – total nitrogen (TN) and 2 – total phosphorus (TP) out of 7 sampling outlets over the last 10 years. Less significant decreasing trends (p > 0.05 and < 0.2) for 3 – SS, 1 – BOD, 1 – TN and 1 – TP were identified. Statistically significant long-term upward trends of pH were revealed in 5 basins, which reduced to 2 with 5 less significant upward trends over the 10 year period, indicating improvements in pH reduction. Härjapea has the highest pH without trend but it includes an upward trend of TN at p = 0.051. The highly possible causes for downward trends are street sweeping, sewer network improvement, decline in sub-urban agricultural areas, etc. The upward trend results of pH are related to increased alkalinisation due to acidic rain, weathering of carbonate rocks, sewage discharge and alkaline road dust. In most of the basins, stormflow has more influence on trends than baseflow. 31 62
- research articleJournal of water security, 2016, vol. 2, p. 1-7A theoretical model was developed to model the fate of two common pharmaceutical residues: diclofenac and ibuprofen in eight Estonian seaside cities that discharge their wastewaters directly into the Baltic Sea. The consumption rates of the active ingredients of diclofenac and ibuprofen from 2006-2014 were analysed. A decrease of 19.9% for diclofenac consumption and an increase of 14.1% for ibuprofen were found. The fate of diclofenac and ibuprofen were modelled by considering the human metabolism removal rate for pharmaceuticals, the removal rate of diclofenac and ibuprofen in activated sludge wastewater treatment plants (WWTP) and annual flow rates. An average decrease from 1 to 0.8 µg/l (decrease of 20%) for diclofenac and an increase from 11.4 to 13.4 µg/l (increase of 14.9%) for ibuprofen for the concentration in the effluents of the WWTP were modelled. The model gives us a good overview about the theoretical concentrations of pharmaceutical residues in the environment and is helpful for evaluating environmental impacts.
- research articleJournal of water security, 2016, vol. 2, p. 1-9The simplest and most effective method of removing low concentrations of anionic surfactants such as sodium dodecyl benzenesulfonate (SDBS) and sodium lauryl sulfate (SLS) is adsorption. Among adsorbents the natural clays are cheap and promising for these purposes. However, there are significant difficulties in removal of spent sorbent after the adsorption process. So, the creation of magnetic sorbents that can be effectively removed from water after sorption by magnetic separation will be a successful decision. The aim of this investigation is the creation of cheap and efficient magnetic sorbents based on natural clays and magnetite for anionic surfactant removal from wastewater. We have synthesized a series of magnetic sorbents from different natural clays with a content of magnetite from 2 to 10 wt%. The ability of magnetic sorbents to remove SDBS and SLS from aqueous solutions has been studied for different adsorbate concentrations by varying the amount of adsorbent, temperature and shaking time. Thermodynamic parameters were calculated from the slope and intercept of the linear plots of ln K against 1/T. Analysis of adsorption results obtained at different temperatures showed that the adsorption pattern on magnetic sorbents correspond to the Langmuir isotherm. It is shown that with increasing the content of magnetite in the magnetic sorbents improves not only their separation from water by magnetic separation, but adsorption capacity to SDBS and SLS. Thus, we obtained of cheap magnetic sorbents based on natural clays and magnetite by the easy way, which not only quickly separated from the solution by magnetic separation, but effectively remove anionic surfactants.
37 107 Dissolved oxygen modelling using artificial neural network: a case of River Nzoia, Lake Victoria basin, KenyaPublicationresearch articleJournal of water security, 2016, vol. 2, p. 1-7River Nzoia in Kenya, due to its role in transporting industrial and municipal wastes in addition to agricultural runoff to Lake Victoria, is vulnerable to pollution. Dissolved oxygen is one of the most important indicators of water pollution. Artificial neural network (ANN) has gained popularity in water quality forecasting. This study aimed at assessing the ability of ANN to predict dissolved oxygen using four input variables of temperature, turbidity, pH and electrical conductivity. Multilayer perceptron network architecture was used in this study. The data consisted of 113 monthly values for the input variables and output variable from 2009–2013 which were split into training and testing datasets. The results obtained during training and testing were satisfactory with R 2 varying from 0.79 to 0.94 and RMSE values ranging from 0.34 to 0.64 mg/l which imply that ANN can be used as a monitoring tool in the prediction of dissolved oxygen for River Nzoia considering the non-correlational relationship of the input and output variables. The dissolved oxygen values follow seasonal trend with low values during dry periods. 21 52