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Fluorine (F) and arsenic (As) are inorganic elements present in the subsurface depending on the geology of the region. These compounds are found in high concentrations in the underground strata of Guadiana Valley of Durango affecting water quality for human consumption (NOM-127-SSA-1994). In the present research the main objective was to assess the behavior in time and space of fluoride (F-) and arsenic concentration, from 1996 to date, in the groundwater of the city of Durango and some wells of the rural area as a reference. The highest concentration of arsenic was found in a rural well, Colonia Hidalgo (0.149 mg/L or ppm), 6 times the maximum permissible limit (MPL); within the city well 54 located in the western sector had the highest value (0.076 ppm), 3 times the MPL, 67% of the wells in the city and 60% of the Guadiana Valley had levels that exceeded the MPL (0.025 ppm), the concentration in the city ranged from 0.009 to 0.149 ppm and from 0.08 to 0.15 ppm for the rural zone. With respect to F-, the highest value was also found in the Colonia Hidalgo well (17.8 mg/L), 12 times the MPL; within the city the highest value was recorded in well 16 in the eastern sector with 7.6 ppm (5 times the MPL) 97% of the wells in the city and 100% of the wells in the Guadiana Valley rural area had concentrations greater than MPL (1.5 ppm), the concentration in the city ranged from 1.1 to 7.6 ppm, while in the Guadiana Valley from 1.7 to 17.8 ppm. Statistical analysis showed no significant difference for fluoride concentration over time (1996-2013); whereas the concentration of arsenic decreased, probably due to the degree of precision required for such small concentrations in groundwater and different analysts ran the samples.
Arsenic and fluoride are elements known to cause human health problems and it has been documented that both elements are found in high concentrations in the Guadiana Valley aquifer, in the state of Durango, Mexico. Since underground water is the source for potable water bottling companies commercialized in Durango City; such high concentrations reduced the quality of bottled water for human consumption according to NOM-041-SSA1-1993. Legislation establishes a maximum permissible limit (MPL) of 0.7 mg/L for fluoride and 0.025 mg/L for arsenic. In this research the main objective was to evaluate the quality of bottled water expended in Durango City with respect to the well from which water is extracted. Findings showed that the highest fluoride concentration was 5.86 mg/L (8.4 times MPL), with 100% of sampled brands exceeding the MPL (range: 1.09 to 5.86 mg/L). On the other hand, for arsenic, the highest concentration was 0.076 mg/L (threefold), with 38% exceeding the MPL (range: 0.001 to 0.076 ppm). Statistical analysis showed significant differences only for fluoride, according to Fisher LSD (Least Significant Difference) test, with an F value of 14.5 at a p value of 0.0005. According to the comparison between the quantified concentrations in bottled water and groundwater, it was found that groundwater was subjected to treatment; however, although a significant decrease in fluoride and arsenic concentration was observed, the removal processes used were not efficient to meet set standards.
This paper reports an approach to estimate the sludge
density in a physicochemical treatment of municipal wastewater, experiments
considered 4 coagulants (aluminum sulfate SAl, iron sulfate SFe, aluminum
polychloride PAX, iron polychloride PIX), and 2 flocculant products (cationic
CP and anionic AP polymers). Experimental approach is based on running a set of
jar tests at different coagulant concentrations. After the stirring and resting
times took place, pH and conductivity were registered finding that SAl and SFe
either with or without polymers are the coagulants producing the higher pH
drop. Conductivity measures also establish two kind of data since higher
conductivity (about 2000 ) was observed for SAl, and
PIX, PIX + CP, PIX + AP; otherwise a conductivity about 1300 was observed for SAl + PC, SFe and PAX alone and with CP or AP.
Settleable solids (SST) determined with an Imhoff cone were similar for
sulfates and polychlorides, but dry sludge (DS) clearly set up two groups the
one with higher sludge content corresponds to sulfates group. The quotient of
DS divided by the SST provided an estimation of the apparent sludge density, in this way it was observed that higher densities
were obtained for sludge from sulfates at lower coagulant concentrations; also
sludge from SFe was heavier than the one from SAl. Otherwise, polychlorides produced a lighter sludge in respect to the one obtained with
sulfates, and between them the PIX
coagulant provided a heavier sludge than the PAX coagulan