Yasumoto Magara

Effect of pH on the removal of arsenic and antimony using reverse osmosis membranes

Abstract Increasing attention has been focused on the health effects associated with ingestion of low levels of arsenic and antimony in drinking water. Accordingly, this study was conducted in order to identify the effect of solution pH on the removal efficiency of arsenic and antimony for drinking water using recently developed RO membranes. In this study it was found that the removals of As(V) and Sb(V) are much higher than those of As(III) and Sb(III) over all investigated pH levels (pH 3–10). The removal of arsenic compounds was strongly affected by the solution pH, especially As(III), whereas the removal of antimony compounds shows no dependence on the solution pH since the oxidation state of antimony changes from Sb(III) to Sb(V) within very short periods of time. It was demonstrated that pH control for the membranefeed water is more essential for the successful removal of arsenic compounds than the case of antimony compounds. Consequently, it is assumed that the removal of antimony in drinking water by RO membranes has a higher efficiency than that of arsenic compounds, regardless of pH changes.

Performance of nanofiltration for arsenic removal.

Performance of rapid sand filtration inter-chlorination system was compared with nanofiltration (NF) to reduce the arsenic health risk of drinking water. It was found that rapid sand filtration with inter-chlorination is not effective in removing arsenic. If total arsenic concentration in raw water is below 50 microg/L regardless of the turbidity of raw water, arsenic can be removed below WHO guideline value of 10 microg/L by conventional coagulation (polyaluminum chloride dosage is about 1.5 mg Al/L). However, if the raw water arsenic concentration exceeds 50 microg/L, more coagulant dosage or enhanced coagulation is needed. To adopt optimum coagulant dosage for arsenic removal, it needs to monitor raw water arsenic concentration, but it is difficult because arsenic measurement is time consuming. In addition, if raw water contains As(III), it is difficult for rapid sand filtration inter-chlorination system to meet an arsenic maximum contaminant level of 2 microg/L, which would achieve reduction of cancer risk below 10(-4). On the other hand, the NF membrane (NaCl rejection 99.6%) could remove over 95% of As(V) under relatively low-applied pressure (< 1.1 MPa). Furthermore, more than 75% of As(III) could be removed using this membrane without any chemical additives, while trivalent arsenic could not be removed by rapid sand filtration system without pre-oxidation of As(III) to As(V). Because both As(V) and As(III) removals by NF membranes were not affected by source water composition, it is suggested that NF membrane can be used in any types of waters.

Development of boron reduction system for sea water desalination

Since boron has been showing to induce male reproductive impediments in laboratory animals, the 1993 WHO guidelines for drinking water quality set the recommended guideline value at 0.3 mg boron/l based on the NOEL (no-observed-adverse-effect level). Since boron is not effectively removed by the conventional water treatment not only for drinking water and domestic wastewater treatment, the concentration in ambient water as well as drinking water is affected by its consumption such as for soaps and detergents in the catchment area. Boron is also affected by leaching from the surrounding geology, drinking water derived water sources affected by a weak alkali spring contains high level of boron. Since the rejection ratio of boron is extremely less than that of salts in RO membrane system applying to drinking water supply in the areas where scarce a fresh water resources, desalinated water contains higher level of boron than that of WHO drinking water quality guidelines. In order to develop of boron treatment system either fresh water or desalinated water, multi stage RO membrane treatment system has studied by using a pilot plant. The boron rejection of RO membrane depends greatly upon pH and driving pressure of RO process. However, the boron rejection does not depends upon its concentration of raw water. Therefore, it is necessary to apply multi stage RO membrane treatment system for producing a finished water that meets the WHO drinking water quality guideline level of boron. Since the secondary and third RO membrane treat less dissolved salt concentration such as observed in fresh water, the driving pressure of RO process for removing boron can operate at low pressure such as about 0.6 to 1.3 MPa. Therefore, multi stage RO membrane sea desalination process and a low pressure RO process can be recommendable for boron management with a reasonable additional cost in drinking water supply.

Biochemical and physical properties of an activated sludge on settling characteristics

Abstract Settling characteristics of an activated sludge discussed from the physical and biochemical stands point of view in this paper. Corresponding to worsening of settling characteristics, conspicuous changes of the physical properties such as the size, density and floc strength, and also the biochemical properties such as the ECP, PHB and the electrophoretic mobility were observed. And these indices were closely related with the proposed mean TOC residence time of the process.

Fish test for endocrine-disruption and estimation of water quality of Japanese rivers

The LC50 values (72 h) of 17beta-estradiol (E2), p-nonylphenol (NP) and bis-phenol-A (BPA) to adult male and female medaka were 3.5 and 3.5, 0.85 and 0.87, and 6.8 and 8.3 mg L(-1), respectively; the LC50 values to embryos were 0.46, 0.13 and 5.1 mg L(-1), respectively. The IC50 values for inhibition to egg hatching were 0.47, 0.85 and 9.0 mg L(-1), respectively. These values were much higher than concentrations detected in river water in Japan and the chemicals were considered to have no lethal effect on the fish in an aquatic environment. Mature male medaka was continuously exposed to 0.005, 0.05 or 1.0 microg L(-1) of E2, or to 0.1, 10 or 100 microg L(-1) of NP or BPA. Female specific proteins (FSP) were induced in the blood of male medaka that were exposed for 5 weeks to E2 higher than 0.005 microg L(-1), NP higher than 0.1 microg L(-1), or BPA higher than 10 microg L(-1). Based on these FSP inducible concentrations and reported concentrations of E2, NP and BPA in Japanese river water, some river water contaminated by E2 or NP could be estimated as the FSP inducible in male medaka.

Comparing polyaluminum chloride and ferric chloride for antimony removal

Antimony has been one of the contaminants required to be regulated, however, only limited information has been collected to date regarding antimony removal by polyaluminium chloride (PACl) and ferric chloride (FC). Accordingly, the possible use of coagulation by PACl or FC for antimony removal was investigated. Jar tests were used to determine the effects of solution pH, coagulant dosage, and pre-chlorination on the removal of various antimony species. Although high-efficiency antimony removal by aluminum coagulation has been expected because antimony is similar to arsenic in that both antimony and arsenic are a kind of metalloid in group V of the periodic chart, this study indicated: (1) removal density (arsenic or antimony removed per mg coagulant) for antimony by PACl was about one forty-fifth as low as observed for As(V); (2) although the removal of both Sb(III) and Sb(V) by coagulation with FC was much higher than that of PACl, a high coagulant dose of 10.5mg of FeL(-1) at optimal pH of 5.0 was still not sufficient to meet the standard antimony level of 2 microg as SbL(-1) for drinking water when around 6 microg as SbL(-1) were initially present. Consequently, investigation of a more appropriate treatment process is necessary to develop economical Sb reduction; (3) although previous studies concluded that As(V) is more effectively removed than As(III), this study showed that the removal of Sb(III) by coagulation with FC was much more pronounced than that of Sb(V); (4) oxidation of Sb(III) with chlorine decreased the ability of FC to remove antimony. Accordingly, natural water containing Sb(III) under anoxic condition should be coagulated without pre-oxidation.

Evaluation of reactivity of pesticides with ozone in water using the energies of frontier molecular orbitals

The rate constants of ozone with four groups of pesticides (4 phenolic-, 8 organonitrogen-, 8 phenoxyalkylacitic-, and 4 heterocyclic N-pesticides) were determined under controlled conditions at a pH of 7.5, ionic strength of ca 10 ˇ3 M, and 100 mM NaHCO3. The rate constant for BPMC was first determined from a pseudo-first order reaction model, the rate constants for the other pesticides were then obtained by a competition kinetic method using BPMC as the first reference compound. The rate constants were found to vary widely according to the pesticides. The highest rate constant was 27,600 M ˇ1 s ˇ1 for PCP and the lowest was 61.8 M ˇ1 s ˇ1 for cyanazine. In order to quantify the eAects of structure on the reactivity of pesticide with ozone, for each group of pesticides the rate constants were correlated with the energies of the highest occupied molecular orbital (EHOMO). The logarithm of the rate constants was found to linearly increase with the increase of the EHOMO values except for the phenoxyalkylacitic group. When all examined pesticides were included in the correlation analysis, the rate constants gave a statistically unsatisfactory correlation with a coeAcient of 0.92, but showed a similar trend of increasing reactivity with increasing EHOMO values of pesticides. The results of the correlation analysis suggested that the reactivity of pesticides with ozone follows the frontier orbital theory and can be estimated by EHOMO. The rate constants for the phenoxyalkylacitic group could be estimated accurately by a two-parameter QSAR model based on absolute electronegativity and EHOMO. 7 2000 Elsevier Science Ltd. All rights reserved

A comparative study on the application of membrane technology to the public water supply

A series of experiments to demonstrate the applicability of micro- and ultra-filtration technology for purification of the public water supply were conducted using slightly polluted river water. The result of the first and second runs of the experiment was satisfactory from the viewpoints of treatment efficiency and effectiveness of contaminant rejection. There was almost no difference in the performance between MF and UF membranes. However, when an MF membrane was used, pretreatment by coagulation was necessary to maintain a high flux with the untreated water.

Exposure assessment of metal intakes from drinking water relative to those from total diet in Japan

Daily intakes of 17 metals (boron, aluminium, chromium, manganese, nickel, copper, zinc, arsenic, selenium, molybdenum, cadmium, antimony, lead, uranium, magnesium, calcium, and iron) via drinking water and total diet were investigated in six cities in Japan. The daily metal intakes were estimated and compared with tolerable daily intake (TDI) values proposed by the WHO or Joint FAO/WHO Expert Committee on Food Additives for toxic metals and with recommended dietary allowances (RDAs) or adequate intake (AI) values proposed for essential metals by the Japanese Ministry of Health, Labour and Welfare. Among the 13 toxic metals, mean dietary intakes of 10 (except arsenic, selenium, and molybdenum) were less than 50% of TDI, suggesting that for these 10 metals the allocation of intake to drinking water in establishing guidelines or standards could possibly be increased from the normal allocation of 10-20% of TDI. For the 13 toxic metals, the contribution of drinking water to TDI was 2% or less in all six cities. Mean dietary intakes of the essential elements magnesium, calcium, and iron were less than the RDA or AI values. Drinking water did not contribute much to essential metal intake, accounting for less than 10% of RDA or AI.

Removal efficiency and homologue patterns of dioxins in drinking water treatment.

Polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and coplanar polychlorinated biphenyls (Co-PCBs) analyses in raw and treated water throughout Japan were implemented to identify the concentration and homologue patterns of dioxins before and after the water treatment process. In 40 surface water and 5 ground water treatment plants, the removal efficiency of dioxins and the influence of extent chlorination on dioxins increase in drinking water were also studied. Raw water and treated water were sampled twice, summer and winter. The mean concentration in raw water and treated water of dioxins was 56.45 pg/L (0.15 pg WHO-TEQ/L) and 4.24 pg/L (0.019 pg WHO-TEQ/L), respectively. Location of water treatment plants not only significantly influenced the concentration level of dioxins but also resulted in different homologue patterns of dioxins. Levels of dioxins in ground water were much less than that of surface water in both raw and treated water. This study shows most dioxin congeners are well removed (87% removal efficiency) by water treatment. However, in some water treatment plants, the level of TeCDFs (pg WHO-TEQ/L) increased as a result of chlorination.