Article pubs.acs.org/IECR
Removal of Arsenic and Heavy Metals From Potable Water by Bauxsol Immobilized onto Wool Fibers M. Mahbubul Hassan*,† and J. Falcon Davies-McConchie‡ †
Food & Bio-based Products Group, AgResearch Ltd., Cnr Springs Road and Gerald Street, Lincoln, Christchurch 7608, New Zealand ‡ Mt. Aspiring Geochemical Ltd., 58 Rata Street, Wanaka 9305, Otago, New Zealand ABSTRACT: Arsenic and heavy metals in drinking water are of particular concern. Of them arsenic is the most potent toxin as well as it is a carcinogen. Arsenic exists in groundwater as uncharged arsenite or anionic arsenate depending on the reducing or oxidizing environment, and the former is more toxic and more difficult to remove than the latter. In this work, varous types of filters made from Bauxsol immobilized onto wool were investigated to remove arsenite and heavy metals from water. Several techniques were investigated to immobilize Bauxsol onto wool, and of them the exhaustion technique was found the best. Two types of Bauxsol, unneutralized (Bauxsol-A) and acid-neutralized (Bauxsol-B), have been investigated, and the removal efficiency of arsenite by Bauxsol-B was found considerably higher (53.3%) than that of Bauxsol-A (34.4%). A pilot-scale trial of Bauxsol-Bbonded wool fiber-packed column-based filtration system showed that it successfully removed arsenite, lead, copper, and zinc from water, but the best results were obtained for the removal of lead and copper as their removal reached 100 and 96%, respectively. The increase in contact time had a significant effect on the removal efficiency; e.g., the removal of copper increased from 10.2 to 96% when the contact time was increased from 5.4 to 86.4 min. The developed filtration system could be used for the removal of arsenic, lead, copper, and zinc from potable water.
1. INTRODUCTION Arsenic, lead, and copper are naturally occurring contaminants of groundwater and surface water. However, arsenic contamination is also as a consequence of human activities such as mining, use as a wood preservative, and industrial processing of arsenic. The United States Environmental Protection Agency (U.S. EPA) estimates that 10−20% of human exposure to lead may come from drinking water.1 Lead and copper may enter drinking water after the treatment process due to the corrosion of pipes or faucets made of lead and copper. The amount of lead allowed in brass faucets is now strictly controlled in many western countries; however, so-called lead-free brass faucets may still contain up to 8% lead. The primary sources of copper in drinking water are corrosion of household plumbing systems, erosion of natural deposits, and leaching from wood preservatives. Arsenic and lead may accumulate in the body and can reach toxic levels. Arsenic is the most dangerous as it can cause lung, liver, skin, bladder, and kidney cancers.2 Long-term consumption of even low levels of arsenic could be dangerous.3 Lead also can cause serious health problems, such as damage to the brain and kidneys, and may cause lowered intelligence in children.4 Furthermore, in the case of women, lead is stored in the bones, and it can be released later in life and during pregnancy. The released lead from the mother’s bones migrates to the fetus and affects its brain development.5 Copper and zinc have comparatively low toxicities compared with arsenic and lead, but at high levels they can be dangerous. The maximum allowable concentration (MAC) of arsenic in drinking water was 50 parts per billion (ppb), but in 1993 it was lowered to 10 ppb by the World Health Organization (WHO). This resulted in reduction of MAC in several countries; e.g., in © 2012 American Chemical Society
2001 the U.S. EPA lowered its drinking water standard for arsenic to 10 ppb.6 Elevated concentrations of arsenic in groundwater exceeding 100 ppb are well documented, for example, in India and Bangladesh.2,3 The current allowable concentrations of lead, copper, and zinc in drinking water as set by the U.S. EPA are 15 ppb, 1.3 parts per million (ppm), and 5 ppm, respectively.3,6 Arsenic contamination of water recently drew attention due to the use of deep tube wells for water supply in the Ganges Delta in the Indian subcontinent which caused serious arsenic poisoning to large numbers of people.7 A recent study found that over 137 million people in more than 70 countries are probably affected by arsenic-contaminated drinking water.7 Arsenic is widespread in aquatic and terrestrial environments in New Zealand, especially in the Taupo Volcanic Zone (TVZ). It was reported that, in some lakes and rivers of the TVZ, arsenic concentrations often exceeded the maximum allowable concentration of arsenic in drinking water set by the WHO.8 Arsenic is present in groundwater in several forms depending on the pH value and the redox potential. In groundwater and surface water environments, arsenic is present as arsenate [As(V)] in oxidizing environments, while arsenite [As(III)] is the predominant species in reducing environments. In reducing environments, arsenite remains as an arsenious acid (H3AsO3) in a wide range of pH values (pH 0−9) and at pHs greater than 9 it remains as H2AsO3−, HAsO32−, or AsO33− as shown by Ferguson and Gavis.9 Similarly, arsenate exists in four forms: at Received: Revised: Accepted: Published: 9634
February 2, 2012 June 10, 2012 June 20, 2012 June 20, 2012 dx.doi.org/10.1021/ie300286k | Ind. Eng. Chem. Res. 2012, 51, 9634−9641
Industrial & Engineering Chemistry Research
Article
pH 0−2 as H3AsO4, at pH 2−7 as H2AsO4−, and at pH >7 as HAsO4− or AsO43−.9 Arsenite is the most common arsenic species available in groundwater and is 25−60 times more toxic and more mobile in the environment than arsenate.10 As arsenite is uncharged for pH
