5 Introduction to Remediation of Arsenic Toxicity

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Introduction to Remediation of Arsenic Toxicity

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Application of Biological Treatment Methods for Remediation of Arsenic Toxicity from Groundwaters Ioannis A. Katsoyiannis, Manassis Mitrakas, and Anastasios I. Zouboulis Contents 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9

Introduction................................................................................................... 114 Biological Iron Removal................................................................................ 115 Biological Manganese Removal.................................................................... 116 Arsenic Occurrence and Speciation in Groundwaters.................................. 117 Arsenic Removal during Biological Iron Oxidation...................................... 118 Arsenic Removal during the Biological Oxidation of Mn(II)....................... 119 Effect of Phosphate on the Removal of As(III)............................................. 120 Use of Plug Flow Reactors Combined with Microfiltration.......................... 121 Arsenic Removal Units in Greece................................................................. 121 5.9.1 Arsenic Occurrence in Greek Groundwater Sources........................ 121 5.9.2 Applied Treatment Technologies in Full-Scale Plants in Greece...... 122 5.10 Case Study: Arsenic, Iron, Manganese, and Ammonia Removal by Biological Oxidation Followed by Coagulation–Filtration........................... 123 5.10.1 Description of Treatment Unit........................................................... 123 5.10.2 Groundwater Characterization and Decision on the Treatment Method............................................................................................... 124 5.10.3 Fe(II), NH4, Mn(II), and PO4 Removal............................................. 125 5.10.4 As(III) Oxidation and As Removal................................................... 126 5.11 Phytoremediation for Arsenic Removal by Aquatic Macrophytes................ 126

113

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Arsenic Toxicity: Prevention and Treatment

5.12 Arsenic Removal by Bacteria and Algae....................................................... 128 5.13 Summary....................................................................................................... 128 References............................................................................................................... 129

5.1 Introduction

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Arsenic poisoning through drinking water is a matter of worldwide concern. In Southeast Asia (Bangladesh, Vietnam, West Bengal, Nepal, Cambodia, Mongolia), over 100 million people consume water with arsenic over the WHO, U.S., and European Union (EU) limits of 10 µg/L. In the United States, more than 13 million people, mostly in western states, consume drinking water with more than 10 µg As/L. In Europe, many regions are affected by elevated arsenic concentrations (Hungary, Romania, Greece, Spain, Finland, Germany). Table 5.1 shows the most severe cases of arsenic contamination in the world and Table 5.2 the most prominent cases of arsenic contamination in European countries [1,2]. In Europe, the situation is particularly severe in some regions of Eastern and Southeastern Europe where smaller communities depend on local groundwater resources that are contaminated with arsenic, and according to the EU directive 98/83, all drinking water sources within the EU should have complied with the new limits by December 2003. However, until to date, there are still areas in Greece, Hungary, and West Romania where the local population depends on drinking water contaminated with arsenic concentrations over 50 µg/L [3,4]. It has been well demonstrated that almost all the MCL violations of toxic metals (i.e., arsenic, uranium) have been observed in small communities with a population of less than 10,000 people [5]. Large drinking water plants in Northern and Central Europe normally find alternative and arsenic-free water resources, or they treat the water with conventional hi-tech multibarrier treatment plants, including methods such as coagulation–filtration, ion exchange, and nanofiltration. Smaller towns, communities, and individual users in rural areas often rely on local water resources, and removal methods developed for large plants are not applicable because of high operational and capital costs. Consequently, small drinking water

Table 5.1 Most Prominent Cases of Arsenic Contamination in the World Country/Region Bangladesh West Bengal, India Cambodia Argentina Chile Mexico

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Maximum Concentration (μg/L)

Potential Population Exposed

2.5 × 103 3.2 × 103 1.3 × 103 10 × 103 1 × 103 620

30 × 106 6 × 106 320 × 103 2 × 106 400 × 103 400 × 103

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Table 5.2 Arsenic Concentrations in Some European Areas Country/Region

μg As/L

Czech Republic/Mokrsko Croatia Finland Germany/Northern Bavaria and Wiesbaden Hungary Iceland Italy/volcanic areas of Ischia, Vesuvius, Etna, Stromboli Romania/Transylvania and Western Plain Serbia/Vojvodina Spain/Duero Basin, Ambles Valley in Avila, Caldes de Malavella Switzerland/Ticino, Wallis Turkey/Kutahya plain

1.690 610 1040 150 800 310 1.558 200 150 615 370 10.700

Groundwater Use Drinking water Drinking water Drinking water Drinking water Drinking water No drinking water Drinking water in the case of Etna Drinking water Drinking water Drinking water in Duero basin Wallis drinking water Drinking water

systems face this difficult challenge: to provide a safe and sufficient supply of water at a reasonable cost. In Bangladesh and West Bengal, a number of simple treatment units have been developed (e.g., oxidation of As(III)) with chemical oxidants or with sunlight followed by precipitation with naturally present or with added iron and aluminum salts, removal with zero-valent iron, and sorption in prefabricated filters with iron and aluminum oxide sorbents [6]. Alternative removal units based on biological oxidation of iron and manganese and avoidance of the use of chemical reagents for preoxidation have been examined in lab scale [7,8]. The application of such technologies comprises nowadays the state of the art for arsenic removal in Greece [5] and other countries in Europe, such as in Italy [9] and France [10]. Therefore, in this chapter, we will review the application of biological iron and manganese oxidation for the removal of arsenic from groundwaters, and we will present case studies of the application of this technology in full-scale treatment plants in Greek water treatment units. Besides, a brief overview of arsenic removal methods by macrophytes, bacteria, and algae will be presented.

5.2 Biological Iron Removal Iron-containing groundwaters have been traditionally treated by chemical oxidation, promoted with the vigorous aeration and/or the addition of chemical oxidizing agents. Although the oxidation of iron by dissolved oxygen at conditions normally found in natural waters (i.e., pH value 6.5–7.5) is in the order of several minutes [11], it was noted that various conventional methods removed iron efficiently, even when the raw water characteristics pointed to poor Fe(II) oxidation. The examination under a microscope of relevant sludge samples revealed that in all similar cases,

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there has been a massive growth of iron bacteria, that is, Gallionella ferruginea, or filamentous ones, such as Leptothrix ochracea [12]. It was apparent that iron was removed by biological means. Since then, several studies have been performed and treatment units for the biological removal of iron have been installed in several European countries, such as in Greece, France, Germany, Denmark, the United Kingdom, and Croatia [13]. The efficient removal of iron in the presence of microbial activity has been also reported during the operation of rapid and slow sand filters, of fluidized bed reactors, and of granular activated carbon filters and during soil percolation [14]. However, the most commonly applied system relies on the presence of a simple sand filter and a limited amount of aeration (i.e., less than 50% of saturation) [7]. Iron-containing groundwater is firstly subjected to aeration and then passes through the sand filter, where Fe(II) is oxidized to Fe(III), and Fe(III) is precipitated in the form of hydrous FeOOH, creating an orange-colored sludge on the sand surface. The excessive sludge, which contains iron bacteria, and the precipitated iron are removed by backwashing, and these suspensions are left to settle out, for example, in a lagoon or in another sedimentation basin. The necessary iron bacterial inoculum is derived from the groundwater (indigenous) and it is therefore self-seeding [12,15]. The biological removal of iron is very efficient over a long operational period, and residual iron concentrations below 10 µg/L can be constantly achieved. Even when this procedure was cut off for 1 month, the efficient restart of this method and the effective removal of iron were reachieved within only few days (2–3) after restarting the operation [16].

5.3 Biological Manganese Removal Biological oxidation and removal of manganese have been also reported and applied for the removal of dissolved manganese from groundwaters [12,15]. The concentrations of dissolved manganese in anaerobic groundwaters can reach the order of several hundreds of mg/L; however, the usual manganese concentrations fall in the range between 0.1 and 1 mg/L [17]. The removal of dissolved manganese (Mn2+) from groundwaters is generally accomplished by oxidation, followed by precipitation and (sand) filtration for the removal of the oxidized insoluble products [18]. The abiotic oxidation of dissolved manganese by oxygen can be described by the following general equation [17]:

−

d[ Mn(II)] = k0 [ Mn(II)] + k1[ Mn(II)][ MnO x ] dt

(5.1)

This expression implies that the homogenous manganese oxidation can be accompanied by an autocatalytic action, in the presence of existing manganese solid phases [17]. The abiotic homogenous manganese oxidation by the presence of oxygen is a slow process at pH values below 9 [17]; thus, in the usual pH values encountered in most surface or groundwaters intended for human consumption (i.e., between 6 and 8), it will not be oxidized. Therefore, manganese is very difficult to be removed by application of simple aeration and the subsequent precipitation [19].

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Table 5.3 Rates of Oxidation of Mn(II): (a) Abiotic Oxidation in the Presence of Goethite and (b) Biological Oxidation pH

k (min−1)

Comment

Literature

8.5 7.2

0.0117 0.174

In the presence of goethite Biological oxidation

[20] [15]

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It is for these reasons that chemical oxidation is generally required, in order to achieve the precipitation and the effective removal of manganese within reasonable time periods and for the pH values often met in natural waters. It has been well established that KMnO4 is an effective oxidant of dissolved manganese over a broad range of pH values, whereas chlorine and ozone can also be applied [18]. To avoid the use of chemicals, biological oxidation of manganese has been considered as a viable alternative for the efficient treatment of groundwaters, which is generally carried out by the presence of microorganisms, which mediate the biotic oxidation of Fe(II), apart from the stalked bacteria of Gallionella genus [12]. These bacteria require more stringent conditions to oxidize manganese, than for iron oxidation. Particularly, a completely aerobic environment is required; dissolved oxygen concentration should be higher than 5 mg/L and redox potential over 300 mV (often between 300 and 400 mV), depending on the pH value. In any case, the required redox potential is lower than the value corresponding to the introduction of a chemical oxidant agent, which is stronger than oxygen. Under these conditions, manganese removal is very efficient, and residual manganese concentrations are below 20 µg/L. As in the case of iron, the kinetics of biological manganese oxidation is quite fast (Table 5.3). When ammonia coexists in the groundwater, biological removal of manganese can take place only after the previous complete nitrification, due to the necessary evolution of redox potential. Low ammonia concentrations (