1
|
Roy M, Kraaijeveld E, Gude JCJ, van Genuchten CM, Rietveld LC, van Halem D. Embedding Fe(0) electrocoagulation in a biologically active As(III) oxidising filter bed. WATER RESEARCH 2024; 252:121233. [PMID: 38330719 DOI: 10.1016/j.watres.2024.121233] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/25/2023] [Revised: 12/07/2023] [Accepted: 01/28/2024] [Indexed: 02/10/2024]
Abstract
Long-term consumption of groundwater containing elevated levels of arsenic (As) can have severe health consequences, including cancer. To effectively remove As, conventional treatment technologies require expensive chemical oxidants to oxidise neutral arsenite (As(III)) in groundwater to negatively charged arsenate (As(V)), which is more easily removed. Rapid sand filter beds used in conventional aeration-filtration to treat anaerobic groundwater can naturally oxidise As(III) through biological processes but require an additional step to remove the generated As(V), adding complexity and cost. This study introduces a novel approach where As(V), produced through biological As(III) oxidation in a sand filter, is effectively removed within the same filter by embedding and operating an iron electrocoagulation (FeEC) system inside the filter. Operating FeEC within the biological filter achieved higher As(III) removal (81 %) compared to operating FeEC in the filter supernatant (67 %). This performance was similar to an analogous embedded-FeEC system treating As(V)-contaminated water (85 %), confirming the benefits of incorporating FeEC in a biological bed for comparable As(III) and As(V) removal. However, operating FeEC in the sand matrix consumed more energy (14 Wh/m3) compared to FeEC operated in a water matrix (7 Wh/m3). The efficiency of As removal increased and energy requirements decreased in such embedded-FeEC systems by deep-bed infiltration of Fe(III)-precipitates, which can be controlled by adjusting flow rate and pH. This study is one of the first to demonstrate the feasibility of embedding FeEC systems in sand filters for groundwater arsenic removal. Such systems capitalise on biological As(III) oxidation in aeration-filtration, effectively eliminating As(V) within the same setup without the need for chemicals or major modifications.
Collapse
Affiliation(s)
- Mrinal Roy
- Water Management Department, Faculty of Civil Engineering and Geosciences, Delft University of Technology, Stevinweg 1, 2628CN Delft, the Netherlands.
| | - Erik Kraaijeveld
- Water Management Department, Faculty of Civil Engineering and Geosciences, Delft University of Technology, Stevinweg 1, 2628CN Delft, the Netherlands
| | - Jink C J Gude
- NX Filtration BV, Josink Esweg 44, 7545PN Delft, the Netherlands
| | - Case M van Genuchten
- Department of Geochemistry, Geological Survey of Denmark and Greenland, Copenhagen DK-1350, Denmark
| | - Luuk C Rietveld
- Water Management Department, Faculty of Civil Engineering and Geosciences, Delft University of Technology, Stevinweg 1, 2628CN Delft, the Netherlands
| | - Doris van Halem
- Water Management Department, Faculty of Civil Engineering and Geosciences, Delft University of Technology, Stevinweg 1, 2628CN Delft, the Netherlands
| |
Collapse
|
2
|
Keithley AE, Gomez-Alvarez V, Williams D, Ryu H, Lytle DA. Depth profiles of biological aerated contactors: Characterizing microbial activity treating reduced contaminants. JOURNAL OF WATER PROCESS ENGINEERING 2023; 56:1-11. [PMID: 38357328 PMCID: PMC10866302 DOI: 10.1016/j.jwpe.2023.104360] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/16/2024]
Abstract
The biological treatment process consisting of an aerated contactor and filter is effective for groundwaters containing elevated ammonia and other reduced contaminants, including iron, manganese, arsenic, and methane. Depth profiles characterizing microbial activity across aerated contactors are lacking. A 1-year pilot study comparing gravel- and ceramic-packed contactors was conducted, and media depth profile samples were collected at the conclusion of the study. Media and water samples also were collected from pilot-scale aerated contactors at 4 other water systems. Water quality, media surface metals concentrations, and a suite of biofilm parameters were analyzed. Media surface metals concentrations were greatest at the influent end. ATP concentrations, extracellular polymeric substances, and extracellular enzyme activities tended to be similar across depth. Bacteria and functional genes involved in contaminant oxidation co-occurred and tended to decrease across depth, but were not correlated to the media metals concentration. Microbial community composition changed with depth, and the diversity either decreased or remained similar. The microbial activity profiles through aerated contactors differed from what is typically reported for groundwater biofilters, suggesting that the different reactor flow and dissolved oxygen profiles impacted the microbial community.
Collapse
Affiliation(s)
- Asher E. Keithley
- U.S. Environmental Protection Agency, ORD, CESER, WID, Cincinnati, OH 45268, United States
| | - Vicente Gomez-Alvarez
- U.S. Environmental Protection Agency, ORD, CESER, WID, Cincinnati, OH 45268, United States
| | - Daniel Williams
- U.S. Environmental Protection Agency, ORD, CESER, WID, Cincinnati, OH 45268, United States
| | - Hodon Ryu
- U.S. Environmental Protection Agency, ORD, CESER, WID, Cincinnati, OH 45268, United States
| | - Darren A. Lytle
- U.S. Environmental Protection Agency, ORD, CESER, WID, Cincinnati, OH 45268, United States
| |
Collapse
|
3
|
Roy M, van Genuchten CM, Rietveld L, van Halem D. Integrating biological As(III) oxidation with Fe(0) electrocoagulation for arsenic removal from groundwater. WATER RESEARCH 2021; 188:116531. [PMID: 33126004 DOI: 10.1016/j.watres.2020.116531] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/07/2020] [Revised: 10/13/2020] [Accepted: 10/16/2020] [Indexed: 06/11/2023]
Abstract
Arsenic (As) is a toxic element present in many (ground)water sources in the world. Most conventional As removal techniques require pre-oxidation of the neutral arsenite (As(III)) species to the negatively charged arsenate (As(V)) oxyanion to optimize As removal and minimize chemical use. In this work, a novel, continuous-flow As removal system was developed that combines biological As(III) oxidation by bacteria with Fe electrocoagulation (EC), an Fe(0)-based electrochemical technology that generates reactive Fe(III) precipitates to bind As. The bio-integrated FeEC system (bio-FeEC) showed effective oxidation and removal of 150 µg/L As(III), without the need of chemicals. To remove As to below the WHO guideline of 10 µg/L, 10 times lower charge dosage was required for the bio-FeEC system compared to conventional FeEC. This lower Fe dosage requirement reduced sludge production and energy consumption. The As(III) oxidizing biomass was found to consist of bacteria belonging to Comamonadaceae, Rhodobacteraceae and Acidovorax, which are capable of oxidizing As(III) and are common in drinking water biofilms. Characterization of the As-laden Fe solids by X-ray absorption spectroscopy indicated that both bio-FeEC and conventional FeEC produced solids consistent with a mixture of lepidocrocite and 2-line ferrihydrite. Arsenic bound to the solids was dominantly As(V), but a slightly higher fraction of As(V) was detected in the bio-FeEC solids compared to the conventional FeEC.
Collapse
Affiliation(s)
- Mrinal Roy
- Water Management Department, Faculty of Civil engineering and Geosciences, Delft University of Technology, Stevinweg 1, 2628CN Delft, The Netherlands.
| | - Case M van Genuchten
- Department of Geochemistry, Geological Survey of Denmark and Greenland, Copenhagen DK-1350, Denmark
| | - Luuk Rietveld
- Water Management Department, Faculty of Civil engineering and Geosciences, Delft University of Technology, Stevinweg 1, 2628CN Delft, The Netherlands
| | - Doris van Halem
- Water Management Department, Faculty of Civil engineering and Geosciences, Delft University of Technology, Stevinweg 1, 2628CN Delft, The Netherlands
| |
Collapse
|
4
|
Lytle DA, Williams D, Muhlen C, Riddick E, Pham M. The removal of ammonia, arsenic, iron and manganese by biological treatment from a small Iowa drinking water system. ENVIRONMENTAL SCIENCE : WATER RESEARCH & TECHNOLOGY 2020; 6:3142-3156. [PMID: 33628452 PMCID: PMC7898138 DOI: 10.1039/d0ew00361a] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
Although not regulated in United States drinking water, ammonia has the potential to increase chlorine consumption and cause nitrification problems in the distribution system. Many groundwaters with elevated ammonia are also contaminated with other inorganic analytes such as arsenic, iron, and manganese, all of which have primary or secondary maximum contaminant levels (MCLs). The objective of this work was to demonstrate the effectiveness of an innovative biological treatment process to simultaneously remove ammonia (2.9 mg N per L), arsenic (23 μg L-1), iron (2.9 mg L-1) and manganese (80 μg L-1) from a groundwater source in Iowa. The biological treatment system consisted of an "aeration contactor" followed by a conventional granular media filter. Orthophosphate was also added, as a biological nutrient, at 0.3 mg PO4 per L. Ammonia, manganese, and iron were consistently reduced through the pilot system by 98 to 99%. Complete oxidation of ammonia to nitrate was observed (i.e., no nitrite was released) and arsenic was consistently removed to below the 10 μg L-1 MCL. Ammonia was oxidized by ammonia and nitrite oxidizing bacteria and arsenic by bacteria which converted As(III) in the source water to more readily removable As(V). Iron was presumably oxidized by oxygen during aeration although some biologically assisted oxidation could not be ruled out. As(V) bound iron particles were removed in the filter resulting in effective arsenic (and iron) reduction. A surprising treatment benefit was the effective manganese reduction, the mechanism of which was not so clear, but was attributed to biologically assisted oxidation of Mn(II). While some system acclimation time was necessary to achieve desired ammonia and manganese reductions, acceptable arsenic and iron reductions were observed shortly after start-up.
Collapse
Affiliation(s)
- Darren A Lytle
- U.S. Environmental Protection Agency, Office of Research and Development, Center for Environmental Solutions and Emergency Response, Water Infrastructure Division, Cincinnati, Ohio 45268, USA
| | - Daniel Williams
- U.S. Environmental Protection Agency, Office of Research and Development, Center for Environmental Solutions and Emergency Response, Water Infrastructure Division, Cincinnati, Ohio 45268, USA
| | - Christy Muhlen
- U.S. Environmental Protection Agency, Office of Research and Development, Center for Environmental Solutions and Emergency Response, Water Infrastructure Division, Cincinnati, Ohio 45268, USA
| | - Eugenia Riddick
- U.S. Environmental Protection Agency, Office of Research and Development, Center for Environmental Solutions and Emergency Response, Water Infrastructure Division, Cincinnati, Ohio 45268, USA
| | - Maily Pham
- U.S. Environmental Protection Agency, Office of Research and Development, Center for Environmental Solutions and Emergency Response, Water Infrastructure Division, Cincinnati, Ohio 45268, USA
| |
Collapse
|
5
|
Ahmad A, Heijnen L, de Waal L, Battaglia-Brunet F, Oorthuizen W, Pieterse B, Bhattacharya P, van der Wal A. Mobility and redox transformation of arsenic during treatment of artificially recharged groundwater for drinking water production. WATER RESEARCH 2020; 178:115826. [PMID: 32361349 DOI: 10.1016/j.watres.2020.115826] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/23/2019] [Revised: 03/22/2020] [Accepted: 04/10/2020] [Indexed: 06/11/2023]
Abstract
In this study we investigate opportunities for reducing arsenic (As) to low levels, below 1 μg/L in produced drinking water from artificially infiltrated groundwater. We observe that rapid sand filtration is the most important treatment step for the oxidation and removal of As at water treatment plants which use artificially recharged groundwater as source. Removal of As is mainly due to As co-precipitation with Fe(III)(oxyhydr)oxides, which shows higher efficiency in rapid sand filter beds compared to aeration and supernatant storage. This is due to an accelerated oxidation of As(III) to As(V) in the filter bed which may be caused by the manganese oxides and/or As(III) oxidizing bacteria, as both are found in the coating of rapid sand filter media grains by chemical analysis and taxonomic profiling of the bacterial communities. Arsenic removal does not take place in treatment steps such as granular activated carbon filtration, ultrafiltration or slow sand filtration, due to a lack of hydrolyzing iron in their influent and a lack of adsorption affinity between As and the filtration surfaces. Further, we found that As reduction to below 1 μg/L can be effectively achieved at water treatment plants either by treating the influent of rapid sand filters by dosing potassium permanganate in combination with ferric chloride or by treating the effluent of rapid sand filters with ferric chloride dosing only. Finally, we observe that reducing the pH is an effective measure for increasing As co-precipitation with Fe(III)(oxyhydr)oxides, but only when the oxidized arsenic, As(V), is the predominant species in water.
Collapse
Affiliation(s)
- Arslan Ahmad
- KWR Water Cycle Research Institute, Groningenhaven 7, 3433, PE, Nieuwegein, the Netherlands; KTH-International Groundwater Arsenic Research Group, Department of Sustainable Development, Environmental Science and Engineering, KTH Royal Institute of Technology, Teknikringen 10B, SE, 100 44, Stockholm, Sweden; Department of Environmental Technology, Wageningen University and Research (WUR), Droevendaalsesteeg 4, 6708, PB, Wageningen, the Netherlands; Evides Water Company N.V., Schaardijk 150, 3063, NH, Rotterdam, the Netherlands.
| | - Leo Heijnen
- KWR Water Cycle Research Institute, Groningenhaven 7, 3433, PE, Nieuwegein, the Netherlands
| | - Luuk de Waal
- KWR Water Cycle Research Institute, Groningenhaven 7, 3433, PE, Nieuwegein, the Netherlands
| | - Fabienne Battaglia-Brunet
- The French Geological Survey (BRGM), 3 Avenue Claude-Guillemin, BP 36009, 45060, Orléans, Cedex 02, France
| | - Wim Oorthuizen
- Dunea Duin & Water N.V., Plein van de Verenigde Naties 11-15, 2719, EG, Zoetermeer, the Netherlands
| | - Brent Pieterse
- Dunea Duin & Water N.V., Plein van de Verenigde Naties 11-15, 2719, EG, Zoetermeer, the Netherlands
| | - Prosun Bhattacharya
- KTH-International Groundwater Arsenic Research Group, Department of Sustainable Development, Environmental Science and Engineering, KTH Royal Institute of Technology, Teknikringen 10B, SE, 100 44, Stockholm, Sweden
| | - Albert van der Wal
- Department of Environmental Technology, Wageningen University and Research (WUR), Droevendaalsesteeg 4, 6708, PB, Wageningen, the Netherlands; Evides Water Company N.V., Schaardijk 150, 3063, NH, Rotterdam, the Netherlands
| |
Collapse
|
6
|
Ahmad A, van der Wens P, Baken K, de Waal L, Bhattacharya P, Stuyfzand P. Arsenic reduction to <1 µg/L in Dutch drinking water. ENVIRONMENT INTERNATIONAL 2020; 134:105253. [PMID: 31810053 DOI: 10.1016/j.envint.2019.105253] [Citation(s) in RCA: 48] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/05/2019] [Revised: 10/07/2019] [Accepted: 10/08/2019] [Indexed: 05/12/2023]
Abstract
Arsenic (As) is a highly toxic element which naturally occurs in drinking water. In spite of substantial evidence on the association between many illnesses and chronic consumption of As, there is still a considerable uncertainty about the health risks due to low As concentrations in drinking water. In the Netherlands, drinking water companies aim to supply water with As concentration of <1 μg/L - a water quality goal which is tenfold more stringent than the current WHO guideline. This paper provides (i) an account on the assessed lung cancer risk for the Dutch population due to pertinent low-level As in drinking water and cost-comparison between health care provision and As removal from water, (ii) an overview of As occurrence and mobility in drinking water sources and water treatment systems in the Netherlands and (iii) insights into As removal methods that have been employed or under investigation to achieve As reduction to <1 µg/L at Dutch water treatment plants. Lowering of the average As concentration to <1μg/L in the Netherlands is shown to result in an annual benefit of 7.2-14 M€. This study has a global significance for setting drinking water As limits and provision of safe drinking water.
Collapse
Affiliation(s)
- Arslan Ahmad
- KWR Water Cycle Research Institute, Nieuwegein, the Netherlands; KTH-International Groundwater Arsenic Research Group, Department of Sustainable Development, Environmental Science and Engineering, KTH Royal Institute of Technology, Stockholm, Sweden; Department of Environmental Technology, Wageningen University and Research (WUR), Wageningen, the Netherlands; Evides Water Company N.V. Rotterdam, the Netherlands.
| | | | - Kirsten Baken
- KWR Water Cycle Research Institute, Nieuwegein, the Netherlands
| | - Luuk de Waal
- KWR Water Cycle Research Institute, Nieuwegein, the Netherlands
| | - Prosun Bhattacharya
- KTH-International Groundwater Arsenic Research Group, Department of Sustainable Development, Environmental Science and Engineering, KTH Royal Institute of Technology, Stockholm, Sweden.
| | - Pieter Stuyfzand
- KWR Water Cycle Research Institute, Nieuwegein, the Netherlands; Department of Geoscience and Engineering, Technical University Delft, the Netherlands
| |
Collapse
|
7
|
Gude JCJ, Rietveld LC, van Halem D. Fate of low arsenic concentrations during full-scale aeration and rapid filtration. WATER RESEARCH 2016; 88:566-574. [PMID: 26547752 DOI: 10.1016/j.watres.2015.10.034] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/04/2015] [Revised: 09/29/2015] [Accepted: 10/18/2015] [Indexed: 06/05/2023]
Abstract
In the Netherlands, groundwater treatment commonly consists of aeration, with subsequent sand filtration without using chemical oxidants like chlorine. With arsenic (As) concentrations well below the actual guidelines of 10 μg As/L, groundwater treatment plants have been exclusively designed for the removal of iron (Fe), manganese and ammonium. The aim of this study was to investigate the As removal capacity at three of these groundwater treatment plants (10-26 μg As/L) in order to identify operational parameters that can contribute to lowering the filtrate As concentration to <1 μg/L. For this purpose a sampling campaign and experiments with supernatant water and hydrous ferric oxide (HFO) flocs were executed to identify the key mechanisms controlling As removal. Results showed that after aeration, As largely remained mobile in the supernatant water; even during extended residence times only 20-48% removal was achieved (with 1.4-4.2 mg/L precipitated Fe(II)). Speciation showed that the mobile As was in the reduced As(III) form, whereas, As(V) was readily adsorbed to the formed HFO flocs. In the filter bed, the remaining As(III) completely oxidized within 2 min of residence time and As removal efficiencies increased to 48-90%. Filter grain coating analysis showed the presence of manganese at all three treatment plants. It is hypothesized that these manganese oxides are responsible for the accelerated As(III) oxidation in the filter bed, leading to an increased removal capacity. In addition, pH adjustment from 7.8 to 7.0 has been found to improve the capacity for As(V) uptake by the HFO flocs in the filter bed. The overall conclusion is, that during groundwater treatment, the filter bed is crucial for rapid As(III) removal, indicating the importance to control the oxidation sequence of Fe and As for improved As removal efficiencies.
Collapse
Affiliation(s)
- J C J Gude
- Delft University of Technology, Faculty of Civil Engineering and Geosciences, Stevinweg 1, 2628 CN Delft, The Netherlands.
| | - L C Rietveld
- Delft University of Technology, Faculty of Civil Engineering and Geosciences, Stevinweg 1, 2628 CN Delft, The Netherlands
| | - D van Halem
- Delft University of Technology, Faculty of Civil Engineering and Geosciences, Stevinweg 1, 2628 CN Delft, The Netherlands
| |
Collapse
|
8
|
Microbial survey of a full-scale, biologically active filter for treatment of drinking water. Appl Environ Microbiol 2012; 78:6390-4. [PMID: 22752177 DOI: 10.1128/aem.00308-12] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The microbial community of a full-scale, biologically active drinking water filter was surveyed using molecular techniques. Nitrosomonas, Nitrospira, Sphingomonadales, and Rhizobiales dominated the clone libraries. The results elucidate the microbial ecology of biological filters and demonstrate that biological treatment of drinking water should be considered a viable alternative to physicochemical methods.
Collapse
|
9
|
Islam M, Mishra PC, Patel R. Arsenate removal from aqueous solution by cellulose-carbonated hydroxyapatite nanocomposites. JOURNAL OF HAZARDOUS MATERIALS 2011; 189:755-63. [PMID: 21470773 DOI: 10.1016/j.jhazmat.2011.03.051] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/07/2010] [Revised: 03/11/2011] [Accepted: 03/14/2011] [Indexed: 05/12/2023]
Abstract
Microwave-assisted synthesis of the cellulose-carbonated hydroxyapatite nanocomposites (CCHA) with CHA nanostructures dispersed in the cellulose matrix was carried out by using cellulose solution, CaCl(2), and NaH(2)PO(4). The cellulose solution was previously prepared by the dissolution of microcrystalline cellulose in NaOH-urea aqueous solution. Study was carried out to evaluate the feasibility of synthetic CCHA for As(V) removal from aqueous solution. Batch experiments were performed to investigate effects of various experimental parameters such as contact time (5 min - 8h), initial As(V) concentration (1-50mg/L), temperature (25, 35 and 45°C), pH (2-10) and the presence of competing anions on As(V) adsorption on the synthetic CCHA. Kinetic data reveal that the uptake rate of As(V) was rapid at the beginning and equilibrium was achieved within 1h. The adsorption process was well described by pseudo-first-order kinetics model. The adsorption data better fitted Langmuir isotherm. The maximum adsorption capacity calculated from Langmuir isotherm model was up to 12.72 mg/g. Thermodynamic study indicates an endothermic nature of adsorption and a spontaneous and favorable process. The optimum pH for As(V) removal was broad, ranging from 4 to 8. The As(V) adsorption was impeded by the presence of SiO(3)(2-), followed by PO(4)(3-) and NO(3)(-). The adsorption process appeared to be controlled by the chemical process.
Collapse
Affiliation(s)
- Mahamudur Islam
- Department of Chemistry, Purushottam Institute of Engineering & Technology, Purushottam Vihar, 10th km, Highway - 10, Mandiakudar, Kansbahal, Rourkela 770034, Orissa, India.
| | | | | |
Collapse
|
10
|
Zhu IX, Getting T, Bruce D. Review of biologically active filters in drinking water applications. ACTA ACUST UNITED AC 2010. [DOI: 10.1002/j.1551-8833.2010.tb11364.x] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
|
11
|
Pokhrel D, Viraraghavan T. Biological filtration for removal of arsenic from drinking water. JOURNAL OF ENVIRONMENTAL MANAGEMENT 2009; 90:1956-1961. [PMID: 19231065 DOI: 10.1016/j.jenvman.2009.01.004] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/03/2007] [Revised: 12/01/2008] [Accepted: 01/08/2009] [Indexed: 05/27/2023]
Abstract
The main objective of the study was to find a suitable iron to arsenic ratio in water to reduce arsenic to 5 microg/L or lower through sand filtration. Experiments were conducted by varying the quantity of iron(II) while keeping the arsenic concentration at 100 microg/L. A mixture of iron (II) and arsenic at different ratios (10:1, 20:1, 30:1 and 40:1) was pumped to the sand filters in a down flow mode and effluent arsenic and iron were analyzed. It was found that a ratio of iron to arsenic of 40:1 was necessary to ensure an effluent arsenic concentration of 5 microg/L or lower. Iron in the filtrate was found to be below 0.1 mg/L at all times.
Collapse
|
12
|
Andrianisa HA, Ito A, Sasaki A, Aizawa J, Umita T. Biotransformation of arsenic species by activated sludge and removal of bio-oxidised arsenate from wastewater by coagulation with ferric chloride. WATER RESEARCH 2008; 42:4809-4817. [PMID: 18817941 DOI: 10.1016/j.watres.2008.08.027] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/25/2008] [Revised: 08/07/2008] [Accepted: 08/26/2008] [Indexed: 05/26/2023]
Abstract
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.
Collapse
|