Granular ferric hydroxide [GFH] as an adsorbent for removal of arsenate and arsenite from drinking water

The pollution of water resources with arsenic [As] is considered as a serious problem and there are several reports about pollution of superficial and underground water with arsenic, in particular arsenate and arsenite in our country specially in some areas of Kurdistan province. There are various methods for removal of arsenic from drinking water which are generally costly. In this study, granular ferric hydroxide [GFH] was used as a synthetic adsorbent for removal of arsenate and arsenite with concentrations of 0.5, 1.0 and 2.0 mg/L. The effects of changing contact time, pH and concentrations of competitive anions, concentration of iron added to water during removal of arsenic and the effect of sulfate and chloride ions on removal of arsenic and compatibility of adsorption with Ferundlinch and Langmuir equations were evaluated. Excel soft ware was used for data analysis. According to this study, GFH showed removal efficiencies of 95, 86.5 and 83.75 for arsenate and 91, 83.5 and 80 percent for arsenite [in initial concentrations of 0.5, 1 and 2 mg/L and at a PH of 7.5]. The dosage of adsorbent for this treatment was 0.5 g/L and 30 minutes was required for contact time. SO[4][2-] and Cl[-] revealed no significant effect on removal of arsenic. Adsorbability of both arsenate and arsenite by GFH followed Ferundlich isotherm with R[2]=0.96, whereas arsenate adsorption [with R[2] value of more than 0.94] complied more with Langmuir isotherm in comparison to arsenite adsorption [with R[2] value of more than 0.92]. Results of our study also indicated that the amount of iron added to water was much more than the standard value of 0.3mg/L used for dinking water. The results of our study showed GFH is highly efficient in removal of arsenate and arsenite after modification of water PH, but it has disadvantages of addition of iron to water, need of import of GFH and high cost. The problem of addition of iron to water can be managed by traditional methods

[Investigation of nitrate concentrations in some bottled water available in Tehran]

Bottled water is a main beverage at many developed and developing countries. It can be polluted with chemical agents. One of these agents is nitrate which affects the safety of bottled and mineral water and cause healthy effects on consumer health. Today's consumption of bottled water get a grate develop, thus infer of the quality of this matter is compulsive for each consumer. A descriptive-analytical and cross- sectional study was done with the aim of determination of nitrate in bottled water available in market of Tehran City in 2007. In this study, 18 samples of six various manufacturers of product were examined. Results showed that the mean of nitrate is 9.02 mg/L and all samples have nitrate bellow 50 mg/L and they are at the standard level. Also, the results of the examinations have good correspondence with the concentration of nitrate on bottled water labels and according to statistic meaningful relation, was considered. The nitrate content of these bottled water available in market of Tehran city is located at the level of national and global standards and it can not be a serious problem for health of consumer

Control of disinfection by products formation potential by enhanced coagulation

Jar-test experiments were conducted to study enhanced coagulation effectiveness in removal of disinfection by products [DBPs] from Zayandehrud River at Isfahan Province-the center part of Iran- in 2004. In this study, the removal of suspended and colloidal particles and natural organic matter [NOM] at various coagulant doses and coagulation pHs was assessed through raw and treated water measurements of turbidity, UV254 absorbance, TOC, and dissolved organic carbon [DOC]. The trihalomethane formation potential [THMFP] was also determined by a mathematical relationship with TOC. Results indicated that NOM removal was a function of coagulant type, coagulant dose, and pH of coagulation. In general, TOC, DOC, and UV254 absorbance removal enhanced with increasing coagulant dose. However, further increases in coagulant dosage had little effect on disinfection by-products precursors removal. Ferric chloride was consistently more effective than alum in removing NOM. Coagulation pH was appeared to be a determining factor for maximum NOM removal and the removal of DBPs precursors by enhanced coagulation was significantly enhanced at pH 5.5 in comparison with initial pH of water. Furthermore, it is specified that preadjustment of pH with sulfuric acid reduced the coagulant dosage and thus, production of sludge. The reduction in THMFP was consistent with the trends observed for DBPs precursors removal data [i.e. UV254 and TOC data]

Improvement of NOM removal from water resources by modifying the coagulation process

As a result of the regulations on DBPs, interest in NOM removal is increasing and many water treatment plants in developed countries have started to measure the concentration of TOC in their finished waters. Promulgation of the rules will substantially increase these efforts in other countries too. Since the cost of TOC [and DBPs] determination was high, it was decided to study the traditional analysis of COD as a surrogate measure to detect the organic constituents in raw water and the extent to which optimized coagulation with ferric chloride can increase COD removal. The two water samples studied belonged to Karaj and Jajrood Rivers. For both samples the observed values of COD removal by coagulation at lower pH [about 1-1.5 pH values less than the regular pH] were about 85-95 percent without making water turbidity unacceptable. In order to determine the effects of organic content on coagulation, synthetic samples were also prepared with much higher COD values. Again, considerable increases in COD removal have been observed for most of these samples only by decreasing 0.5-2 pH value. The results indicated that a modified coagulation process without need to much increasing the amount of coagulant can be developed for these water samples