Recovery of phosphates(V) from wastewaters of different chemical composition

Phosphate(V) ions were recovered from wastewaters of different chemical compositions in a continuous reaction crystallization of struvite. Two real wastewaters were represented by an effluent sample from the phosphorus mineral fertilizer industry and by liquid manure derived from a cattle-breeding farm. Two other wastewaters were prepared under laboratory conditions. Impurities present in the wastewaters caused the precipitation of solid products of distinctly different quality. The mean size of struvite crystals varied from ca. 18 to ca. 40 μm. Homogeneity within their populations, quantified by the coefficient of variation CV, varied from satisfactory (CV ca. 75%) to unfavorable (CV ca. 100%), which resulted in the elongation of necessary filtration time. Calcium ions in wastewater precipitated as amorphous hydrated calcium phosphates ACP. Their content in the products varied from 33.4 up to 73.1 mass %. Also 28.32 – 32.74 mass % of P2O5, 6.35 – 14.12 mass % of MgO and 4.35 – 16.94 mass % of CaO were confirmed in the products, together with hydroxides of some metals and salts of other impurities. Based on the chemical composition of the products derived from the investigated wastewaters, their application in agriculture as valuable mineral fertilizers is recommended

Size-dependent growth kinetics of struvite crystals in wastewater with calcium ions

Kinetic parameters describing continuous reaction crystallization of struvite from aqueous solutions containing also calcium ions (from 100 to 2000 mg Ca2+/kg) were estimated. Test results were compared with kinetic data of struvite manufactured from real cattle liquid manure. Kinetic model for ideal MSMPR (Mixed Suspension Mixed Product Removal) crystallizer was used assuming dependence of crystal growth rate G on its size L (size-dependent growth, SDG MSMPR model). Based on nonlinear regression and statistical analysis, one from within five considered G(L) models was selected – Rojkowski exponential (RE) model – rendering the experimental population density distributions the best. It was concluded, that calcium ions influenced all components of struvite manufacturing process disadvantageously. A rise of Ca2+ concentration in a feed from 100 to 2000 mg/kg increased nucleation rate ca. 160-time, whereas growth rate of nuclei up to macroscopic size G0 decreased more than 10-time. Linear (larger) crystal growth rate G¥ was nearly two-times smaller: 1.71·10–8 m/s (100 mg Ca2+/kg) – 9.10·10–9 m/s (2000 mg Ca2+/kg). Resulting in a product with deteriorated quality. Mean size of the crystals decreased nearly two-times (to 18.4 μm), non-homogeneity within product population enlarged and calcium fraction in the product increased. The product, beside struvite MgNH4PO4·6H2O, also contained hydrated amorphous calcium phosphate(V) Ca3(PO4)2·nH2O (ACP). It was observed, that 5-times smaller concentration of phosphate(V) ions in a feed and magnesium ions excess in relation to phosphate(V) and ammonium ions (1.2 : 1 : 1) influenced all kinetic parameters of continuous struvite reaction crystallization advantageously

Electronic cigarette youth access in Poland

Introduction Electronic cigarette (e-cigarette) use among youth in Poland become very popular. Since the onset of this product access to these products was unrestricted. The aim of this study was to establish functioning of channels of e-cigarettes supply among students aged 16-18 in Poland. Methods A school-based, cross-sectional survey was administered in 2016 to 21 secondary/technical schools across two regions of Poland. Analyses focused on students aged 16-18 who reported use of e-cigarettes (both exclusive use and dual use with tobacco cigarettes). After exclusions, 531 students (166 exclusive users, 365 dual users) remained in the final analytic sample. Pearson chi-square tests were used to examine associations between dual and exclusive users of electronic cigarettes, supply channels and possible difficulties in accessing e-cigarettes. Results For youth exclusive e-cigarette users most common source of obtaining their first e-cigarette was getting from a friend (47%) and vapor shops (22%), for dual users purchase in vapor shops (32%) and getting from a friend (30%). Teens buy mostly e-liquids in vapor shops (52%). Internet is the source for only 4,6% of them. Overall, only 7 % of youth e-cigarette users (10% in exclusive and 6% in dual users) reported having difficulty obtaining (purchasing or getting from other sources) an e-cigarette. Most youth reported no difficulty obtaining cartridges/e-liquid containing nicotine (93%). Conclusions In Poland, teenagers get their first e-cigarettes with the help of friends and in vapor shops. Internet is not a popular source of products. Mostly students did not have problems supplying themselves with electronic cigarettes and cartridges/e-liquids. Introduction of a regulation of age limit on e-cigarette sales should restrict the number of youth who start vaping. Continued surveillance efforts are needed to assess the effectiveness of this policy on curtailing youth e-cigarette use in Poland. Funding This work was supported by the Medical University of Silesia, Katowice, Poland (Grant No KNW-2-127/D/6/N)