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Ammonium removal from drinking water to protect human and environmental health is one of the major global concerns. This study evaluates the performance of Purolite C100E, a commercial cation exchange resin, in eliminating ammonium in synthetic and real contaminated groundwater. The results demonstrate that the pH operation range of the resin for better ammonium removal is 3 to 8. Lower ammonium removal at low and high pH occurred due to competition from H+ and loss of ammonium as ammonia gas, respectively. Equilibrium data of ammonium removal fitted both the Langmuir and Freundlich isotherm models with the maximum Langmuir ion exchange capacities for initial ammonium concentrations of 10–200 mg/L and 50–2000 mg/L, reaching 18.37 mg/g and 40.16 mg/g, respectively. The presence of co-ions in the water reduced the ammonium removal efficiencies slightly (< 12%) in the order Mg2+ > Ca2+ > K+. The higher affinity of ammonium to adsorbent is due to its lower hydrated ionic radius and H-bonding. The maximum exchange capacity in the fluidized bed studies of the original Purolite C100E (bed height 27 cm, resin weight 75 g, initial ammonium concentration 17.4 mg/L, filtration velocity 0.5 m/h) was 10.48 mg/g. It progressively reduced slightly after three regeneration cycles to 8.79 mg/g. The column breakthrough data satisfactorily fitted the Thomas model. A household filter cartridge packed with 4 kg Purolite C100E (80 cm height) and operated at a filtration velocity of 1.9 m/h in Vietnam successfully reduced the initial 6 mg NH4+/L in groundwater (after sand filter pre-treatment) to well below the Vietnam drinking water standard (3 mg/L-QCVN 01:2009/BYT) continuously for 1 week, suggesting that such a filter can be adopted in rural areas to successfully remove ammonium from groundwater. [ABSTRACT FROM AUTHOR]

Household sand filters are used in rural areas of Vietnam to remove As, Fe, and Mn from groundwater for drinking water purposes. Currently, it is unknown what role microbial processes play in mineral oxide formation and As removal during water filtration. We performed most probable number counts to quantify the abundance of physiological groups of microorganisms capable of catalyzing Fe- and Mn-redox transformation processes in a household sand filter. We found up to 10 4 cells g −1 dry sand of nitrate-reducing Fe(II)-oxidizing bacteria and Fe(III)-reducing bacteria, and no microaerophilic Fe(II)-oxidizing bacteria, but up to 10 6 cells g −1 dry sand Mn-oxidizing bacteria. 16S rRNA gene amplicon sequencing confirmed MPN counts insofar as only low abundances of known taxa capable of performing Fe- and Mn-redox transformations were detected. Instead the microbial community on the sand filter was dominated by nitrifying microorganisms, e.g. Nitrospira , Nitrosomonadales , and an archaeal OTU affiliated to Candidatus Nitrososphaera. Quantitative PCR for Nitrospira and ammonia monooxygenase genes agreed with DNA sequencing results underlining the numerical importance of nitrifiers in the sand filter. Based on our analysis of the microbial community composition and previous studies on the solid phase chemistry of sand filters we conclude that abiotic Fe(II) oxidation processes prevail over biotic Fe(II) oxidation on the filter. Yet, Mn-oxidizing bacteria play an important role for Mn(II) oxidation and Mn(III/IV) oxide precipitation in a distinct layer of the sand filter. The formation of Mn(III/IV) oxides contributes to abiotic As(III) oxidation and immobilization of As(V) by sorption to Fe(III) (oxyhydr)oxides. [ABSTRACT FROM AUTHOR]

Household sand filters are applied to treat arsenic- and iron-containing anoxic groundwater that is used as drinking water in rural areas of North Vietnam. These filters immobilize poisonous arsenic (As) via co-oxidation with Fe(II) and sorption to or co-precipitation with the formed Fe(III) (oxyhydr)oxides. However, information is lacking regarding the effect of the frequency and duration of filter use as well as of filter sand replacement on the residual As concentrations in the filtered water and on the presence of potentially pathogenic bacteria in the filtered and stored water. We therefore scrutinized a household sand filter with respect to As removal efficiency and the presence of fecal indicator bacteria in treated water as a function of filter operation before and after sand replacement. Quantification of As in the filtered water showed that periods of intense daily use followed by periods of non-use and even sand replacement did not significantly ( p < 0.05) affect As removal efficiency. The As concentration was reduced during filtration from 115.1 ± 3.4 μg L − 1 in the groundwater to 5.3 ± 0.7 μg L − 1 in the filtered water (95% removal). The first flush of water from the filter contained As concentrations below the drinking water limit and suggests that this water can be used without risk for human health. Colony forming units (CFUs) of coliform bacteria increased during filtration and storage from 5 ± 4 per 100 mL in the groundwater to 5.1 ± 1.5 × 10 3 and 15 ± 1.4 × 10 3 per 100 mL in the filtered water and in the water from the storage tank, respectively. After filter sand replacement, CFUs of Escherichia coli of < 100 per 100 mL were quantified. None of the samples contained CFUs of Enterococcus spp. No critical enrichment of fecal indicator bacteria belonging to E. coli or Enterococcus spp. was observed in the treated drinking water by qPCR targeting the 23S rRNA gene. The results demonstrate the efficient and reliable performance of household sand filters regarding As removal, but indicate a potential risk for human health arising from the enrichment of coliform bacteria during filtration and from E. coli cells that are introduced by sand replacement. [ABSTRACT FROM AUTHOR]

Elevated arsenic concentrations in drinking water pose a health threat to millions of people. Although point-of-use sand filters provide an effective technical solution for mitigating arsenic exposure, the actual reduction in health risk also depends on psychological factors that influence behaviors related to this device. For example, acquiring a sand filter must be preferred to competing options for investing effort and money and, once installed, the users must regularly maintain the filters. These key behaviors of sustainable use are related to psychological factors, such as problem awareness, benefits and costs, social and affective influences, and the perception of practical difficulties. This study investigated the sustainable use of arsenic-removing sand filters in Vietnam. Based on questionnaire surveys, data were gathered in 319 rural households and analyzed with regression models. Psychological factors explained significant variance in the investigated key behaviors. Significant factors included perceived improvements in water healthiness and taste, monetary costs, social norms, and affective influences. In questions with open answers, interviewees mentioned various practical problems, particularly those related to the inflexibility of the device and the effort of changing the sand. Interestingly, many interviewees operate the sand filters for removing iron from the water but are unaware of problems with arsenic. [ABSTRACT FROM AUTHOR]

Abstract: To elucidate the role of genetic factors in arsenic (As) metabolism, we studied associations of single nucleotide polymorphisms (SNPs) in As (+3 oxidation state) methyltransferase (AS3MT) with the As concentrations in hair and urine, and urinary As profile in residents in the Red River Delta, Vietnam. Concentrations of total As in groundwater were 0.7–502 μg/l. Total As levels in groundwater drastically decreased by using sand filter, indicating that the filter could be effective to remove As from raw groundwater. Concentrations of inorganic As (IAs) in urine and total As in hair of males were higher than those of females. A significant positive correlation between monomethylarsonic acid (MMA)/IAs and age in females indicates that older females have higher methylation capacity from IAs to MMA. Body mass index negatively correlated with urinary As concentrations in males. Homozygote for SNPs 4602AA, 35991GG, and 37853GG, which showed strong linkage disequilibrium (LD), had higher percentage (%) of dimethylarsinic acid (DMA) in urine. SNPs 4740 and 12590 had strong LD and associated with urinary %DMA. Although SNPs 6144, 12390, 14215, and 35587 comprised LD cluster, homozygotes in SNPs 12390GG and 35587CC had lower DMA/MMA in urine, suggesting low methylation capacity from MMA to DMA in homo types for these SNPs. SNPs 5913 and 8973 correlated with %MMA and %DMA, respectively. Heterozygote for SNP 14458TC had higher MMA/IAs in urine than TT homozygote, indicating that the heterozygote may have stronger methylation ability of IAs. To our knowledge, this is the first study on the association of genetic factors with As metabolism in Vietnamese. [Copyright &y& Elsevier]

The characteristics of arsenic-contaminated groundwater and the potential risks from the groundwater were investigated. Arsenic contamination in groundwater was found in four villages (Vinh Tru, Bo De, Hoa Hau, Nhan Dao) in Ha Nam province in northern Vietnam. Since the groundwater had been used as one of the main drinking water sources in these regions, groundwater and hair samples were collected in the villages. The concentrations of arsenic in the three villages (Vinh Tru, Bo De, Hoa Hau) significantly exceeded the Vietnamese drinking water standard for arsenic (10 µg/L) with average concentrations of 348, 211, and 325 μg/L, respectively. According to the results of the arsenic speciation testing, the predominant arsenic species in the groundwater existed as arsenite [As(III)]. Elevated concentrations of iron, manganese, and ammonium were also found in the groundwater. Although more than 90% of the arsenic was removed by sand filtration systems used in this region, arsenic concentrations of most treated groundwater were still higher than the drinking water standard. A significant positive correlation was found between the arsenic concentrations in the treated groundwater and in female human hair. The risk assessment for arsenic through drinking water pathways shows both potential chronic and carcinogenic risks to the local community. More than 40% of the people consuming treated groundwater are at chronic risk for arsenic exposure. [Copyright &y& Elsevier]