Bioremoval of arsenic species from contaminated waters by sulphate-reducing bacteria

A mixed culture of sulphate-reducing bacteria was used to study the bioremoval of arsenic species (As(III) or As(V)) from groundwater. During growth of a mixed SRB culture adapted to 0.1 mg/L arsenic species through repeated sub-culturing, 1 mg/L of either As(III) or As(V) was reduced to 0.3 and 0.13 mg/L respectively. Sorption experiments on the precipitate produced by batch cultured sulphate-reducing bacteria (SRB-PP) indicated a removal of about 77 and 55% of As(V) and As(III) respectively under the following conditions: pH 6.9; biomass (2 g/L); 24 h contact time; initial arsenic concentration, 1 mg/L of either species. These results were compared with synthetic iron sulphide as adsorbent. The adsorption data were fitted to Langmuir and Freundlich isotherms. Energy dispersive X-ray analysis showed the SRB-PP contained elements such as sulphur, iron, calcium and phosphorus. Biosorption studies indicated that SRB cell pellets removed about 6.6% of the As(III) and 10.5% of the As(V) from water containing an initial concentration of 1 mg/L of either arsenic species after 24 h contact.     

Effects of pH and competing anions on the speciation of arsenic in fixed ionic strength solutions by solid phase extraction cartridges

Anion exchange resins (AERs) separate As(V) and As(III) in solution by retaining As(V) and allowing As(III) to pass through. Anion exchange resins offer several advantages including cost, portability, and ease of use. The use of AERs for the instantaneous speciation of As minimizes the effects of preservatives on As species analysis. The aims of this study were to: (1) Examine the effects of pH and competing anions on the efficacy of solid phase extraction cartridges (SPECs) for speciation of As in a 0.01 molL(-1) NaNO(3) background electrolyte. (2) Identify optimal conditions (e.g. flow rates) for As speciation. (3) Calculate method detection limits (MDLs) from spiked background electrolyte and percent recoveries of As species from spiked extracts of mine wastes. The most effective SPEC retained As(V) through a range of environmentally relevant pH values (4-8). The mass loading capacity for As(V) was reduced in the background electrolyte (0.006 mg) compared with As(V) in deionized H(2)O (0.75 mg). Some retention (10-20%) of As(III) occurred on pre-wetted cartridges. Approximately 98% of spiked As(III) passed through dry cartridges. The recommended flow rate (0.5 mL min(-1)) was increased to 5 mL min(-1) without significant effect on As(V) retention. The presence of anions decreased the retention of As(V) with sulfate and phosphate having the greatest impact. MDLs were 0.004 mg L(-1) for both inorganic species. Spike recoveries in 0.01 M NaNO(3) mine waste extracts averaged 94% for As(III) and 107% for As(V).     

Cloud point extraction for speciation of chromium in water samples by electrothermal atomic absorption spectrometry

A new method based on the cloud point extraction (CPE) separation and electrothermal atomic absorption spectrometry (ETAAS) detection was proposed for the determination of chromium species. When the system temperature is higher than the cloud point extraction temperature (CPT) of selected surfactant p-octyl polyethyleneglycolphenyether (Triton X-100), the complex of Cr(VI) with dibromophenylfluorone (Br-PF) could enter surfactant-rich phase, whereas the Cr(III) remained in aqueous phase. Thus, an in situ separation of Cr(VI) and Cr(III) could be realized. Cr(VI) in surfactant-rich phase was analyzed by ETAAS and Cr(III) was calculated by subtracting of Cr(VI) from the total chromium which was directly determined by ETAAS. The main factors affecting the cloud point extraction, such as pH, concentration of Br-PF and Triton X-100, equilibration temperature and time, were investigated systematically. Under the optimized conditions, the quantitation limit for Cr(VI) as low as 0.01 microg/L was obtained by preconcentrating a 10 mL sample solution, and the relative standard deviation (n=6, c=2.0 microg/L) was 2.6%. The proposed method was applied to the speciation of chromium in different water samples and the recoveries in the range of 98.9-105.3% were obtained by spiking the real samples. In order to verify the accuracy of the method, a certified reference water sample was analyzed and the results obtained were in good agreement with the certified values.     

Biotransformation of arsenic species by activated sludge and removal of bio-oxidised arsenate from wastewater by coagulation with ferric chloride

The potential of activated sludge to catalyse bio-oxidation of arsenite [As(III)] to arsenate [As(V)] and bio-reduction of As(V) to As(III) was investigated. In batch experiments (pH 7, 25 degrees C) using activated sludge taken from a treatment plant receiving municipal wastewater non-contaminated with As, As(III) and As(V) were rapidly biotransformed to As(V) under aerobic condition and As(III) under anaerobic one without acclimatisation, respectively. Sub-culture of the activated sludge using a minimal liquid medium containing 100mg As(III)/L and no organic carbon source showed that aerobic arsenic-resistant bacteria were present in the activated sludge and one of the isolated bacteria was able to chemoautotrophically oxidise As(III) to As(V). Analysis of arsenic species in a full-scale oxidation ditch plant receiving As-contaminated wastewater revealed that both As(III) and As(V) were present in the influent, As(III) was almost completely oxidised to As(V) after supply of oxygen by the aerator in the oxidation ditch, As(V) oxidised was reduced to As(III) in the anaerobic zone in the ditch and in the return sludge pipe, and As(V) was the dominant species in the effluent. Furthermore, co-precipitation of As(V) bio-oxidised by activated sludge in the plant with ferric hydroxide was assessed by jar tests. It was shown that the addition of ferric chloride to mixed liquor as well as effluent achieved high removal efficiencies (>95%) of As and could decrease the residual total As concentrations in the supernatant from about 200 microg/L to less than 5 microg/L. It was concluded that a treatment process combining bio-oxidation with activated sludge and coagulation with ferric chloride could be applied as an alternative technology to treat As-contaminated wastewater.     

钨钽基体—石墨炉原子吸收法测定水中铝

以钨与钽基体替代石墨管涂钽,采用直接石墨炉原子吸收法测定水中铝,该方法克服了涂钽石墨管制备繁琐和使用次数少的缺陷,且测定灵敏度高、基体干扰少、结果稳定准确,检出限可达到1．0μg／L。应用此方法测定4种水样中的铝,相对标准偏差为2．6％～5．3％,加标回收率为95％～108％。     

火焰原子吸收光谱法测定玻璃中钾、钠含量

建立了一种火焰原子吸收光谱法（FASS）测定玻璃中的钾、钠含量的方法，对火焰原子吸收的狭缝宽度、燃烧头角度和元素的测定波长进行了优化。结果表明，该方法测定钾含量的相对标准偏差（RSD）为3.4%~4.8%，加标回收率为95%~102%；测定钠含量的相对标准偏差（RSD）为0.8%~4.8%，加标回收率为92%~105%。     

Role of Fe(II), phosphate, silicate, sulfate, and carbonate in arsenic uptake by coprecipitation in synthetic and natural groundwater

Competitive effects of phosphate, silicate, sulfate, and carbonate on As(III) and As(V) removal at pH approximately 7.2 have been investigated to test the feasibility of Fe(II)(aq) and hydroxylapatite crystals as inexpensive and potentially efficient agents for remediation of contaminated well-water, using Bangladesh as a type study. Arsenic(III) removal approximately 50-55% is achieved, when Fe(II)(aq) oxidizes to Fe(III) and precipitates as Fe(OH)3 at 25 degrees C and 3h reaction time, in the presence of all the oxyanion. Similar results were obtained for well-water samples from two sites in Bangladesh. Heating at 95 degrees C for 24h results in 70% As(III) uptake due to precipitation of magnesian calcite. A two-step process, Fe(II) oxidation and Fe(OH)3 precipitation at 25 degrees C for 2h, followed by magnesian calcite precipitation at 95 degrees C for 3h, yields approximately 65% arsenic removal while reducing the expensive heating period. In the absence of silicate, up to 70% As(III) uptake occurs at 25 degrees C. In all cases, As(III) was oxidized to As(V) in solution by dissolved oxygen and the reaction rate was probably promoted by intermediates formed during Fe(II) oxidation. Iron-catalyzed oxidation of As(III) by oxygen and hydrogen peroxide is pH-dependent with formation of oxidants in the Fenton reaction. Buffering pH at near-neutral values by dissolved carbonate and hydroxylapatite seeds is important for faster Fe(II) oxidation kinetics ensuring rapid coprecipitation of As as As(V) in the ferric phases.     

石墨炉原子吸收光谱法测定石英玻璃中痕量铁检出限的探讨

以铁元素为例,讨论了石墨炉原子吸收光谱法测定石英玻璃中痕量元素检出限的空白选择、方法检出限的常见两种测定方法和计算依据,以及样品检出限的计算与表示.一个月内,不同时间段,分五次测定至少20个样品空白,所得检出限为真实的方法检出限,可作为日常分析使用.结果表明,增加进样量和使用新的石墨管可以提高灵敏度.     

Evaluation of selenium in biological sample of arsenic exposed female skin lesions and skin cancer patients with related to non-exposed skin cancer patients

The antagonistic effects between selenium (Se) and arsenic (As) suggest that low Se status plays an important role in arsenism development. The objective of present study was to assess Se contents in biological samples of As exposed females have skin lesions and cancer with related to non-exposed skin cancer patients. The biological samples (blood and scalp hair) of As exposed group comprises, female skin cancer (ESC) patients admitted in cancer hospitals have skin lesions (ESL) and exposed referents have not both diseases (ER), belongs to As exposed area of Pakistan. For comparative purposes, age matched female skin cancerous patient (RP) and non-cancerous females (NER) belong to non-exposed areas were also selected. The As and Se in acid digests of biological samples were pre-concentrated by complexing with chelating agent (ammonium pyrrolidinedithiocarbamate), and resulted complexes were extracted into non-ionic extractant (Triton X-114), prior to analysis by electrothermal atomic absorption spectrometry. The enhancement factor of about 25 was obtained by pre-concentrating 10 mL of sample solutions. The accuracy of the optimized procedure was evaluated by using certified reference material (BCR 397) with certified values for Se and As and standard addition method at three concentration levels in real samples. No significant differences was observed (p > 0.05) when comparing the values obtained by the proposed method, added and certified values of both elements. The biological samples of ESC patients had 2-3 folds higher As and lower Se levels as compared to RP (p < 0.001). Understudied exposed referents have high level of As and lower Se contents as compared to referents subjects of non-exposed area (p < 0.01). The higher concentration of As and lower levels of Se in biological samples of cancerous patients are consisted with reported studies.