Sorption kinetic studies of ammonium from aqueous solution on different inorganic and organic media.

In this study, the sorption of ammonium from aqueous solution onto activated carbon, natural zeolite, peat and potting soil was studied by performing batch kinetic sorption experiments. The activated carbon wasn't efficiently removing ammonium at concentrations higher than 50 mg L(-1). Sorption isotherms of ammonium on zeolite, peat and potting soil were determined at 25 degrees C and 200 rpm with the initial concentration of 50-7000 mg L(-1). Equilibrium data were fitted by Freundlich, Langmuir and Temkin isotherm and parameters were evaluated according these models. Langmuir model gives better fit to experimental data than Freundlich and Temkin models. Maximum adsorption capacities were for activated carbon 0.631 mg g(-1), zeolite 58 mg g(-1), peat 595 mg g(-1) and for potting soil 575 mg g(-1). The equilibrium kinetic data were analyzed using adsorption kinetic models: the pseudo-first and second-order equations and were found to follow the pseudo-second-order kinetic model. A comparison between linear and non-linear regression method for estimating the adsorption and kinetics parameters was examined. The obtained results showed that non-linear method may be a better way to determine the kinetic parameters. Thermodynamic studies showed exothermic and endothermic nature of the adsorption of NH4(+) on inorganic and organic adsorbents, respectively. From present results it can be seen that zeolite, peat and potting soil are good adsorbents for removal ammonium from aqueous solution.

Exposure of children to sexual content on the Internet in Croatia.

OBJECTIVE: To determine the prevalence of children and youth exposure to sexual content and inappropriate sexual questions on the Internet; and to identify emotional and behavioral reactions of children after such exposures. METHODS: Sample of the study included 2,880 of children and youth aged 10-16 who identified themselves as Internet users. Participants were questioned using Questionnaire on Child Experiences in Internet Use. RESULTS: Results show that 27% of children were exposed to messages of sexual content, mostly containing images of human nudity and sexual activity. Study also shows that children have experienced inappropriate sexual questions on the Internet. Exposure to questions of intimate nature increased with their age with certain differences in exposure and disturbing emotional reactions related to gender and age. CONCLUSION: Results obtained by this study show that about a quarter of children are at risk for exposure to sexual content on the Internet. PRACTICAL IMPLICATIONS: Research results can be used as a starting point for further research in order to throw more light on children and youth exposure to sexual content on the Internet. Furthermore, results can be used in developing prevention strategies for high-risk behavior of children and youth using the Internet and in working with children, parents and teachers.