Emerging and Innovative Techniques for Arsenic Removal Applied to a Small Water Supply System

Sustainability 2009, 1, 1288-1304; doi:10.3390/su1041288 OPEN ACCESS sustainability ISSN 2071-1050 www.mdpi.com/journal/sustainability Article Emerging and Innovative Techniques for Arsenic Removal Applied to a Small Water Supply System António A.L.S. Duarte 1,*, Sílvia J.A. Cardoso 2 and António J. Alçada 2 1 2 Department of Civil Engineering, School of Engineering, University of Minho, Largo do Paço, 4704-553 Braga, Portugal Águas do Zêzere e Côa, SA, Rua Dr. Francisco Pissarra de Matos, 21-r/c, 6300-906 Guarda, Portugal; E-Mails: (S.J.A.C.); (A.J.A.) * Author to whom correspondence should be addressed; E-Mail: ; Tel.: +351-253-604720; Fax: +351-253-604721. Received: 4 November 2009 / Accepted: 7 December 2009 / Published: 11 December 2009 Abstract: The impact of arsenic on human health has led its drinking water MCL to be drastically reduced from 50 to 10 ppb. Consequently, arsenic levels in many water supply sources have become critical. This has resulted in technical and operational impacts on many drinking water treatment plants that have required onerous upgrading to meet the new standard. This becomes a very sensitive issue in the context of water scarcity and climate change, given the expected increasing demand on groundwater sources. This work presents a case study that describes the development of low-cost techniques for efficient arsenic control in drinking water. The results obtained at the Manteigas WTP (Portugal) demonstrate the successful implementation of an effective and flexible process of reactive filtration using iron oxide. At real-scale, very high removal efficiencies of over 95% were obtained. Keywords: safe drinking water; public health; arsenic removal; emerging techniques; real-scale removal efficiencies; water sources sustainability; Manteigas WTP (Portugal) Sustainability 2009, 1 1289 1. Introduction Arsenic in drinking water has been reported as the most widespread geogenic contaminant in water sources worldwide. Groundwater contamination is of global concern and arsenic-associated human health problems have now been recognised in many parts of the world, mainly in developing countries [1]. A wide variety of adverse health effects, including severe skin lesions, cardiovascular and haematological effects, and neurological disturbances effects have been attributed to chronic arsenic exposure, primarily from drinking water [2]. Furthermore, several epidemiological studies have confirmed that chronic arsenic poisoning causes skin and internal cancers [3]. Considering the lethal impact of arsenic on human health, environmental authorities have taken a more stringent attitude towards the presence of arsenic in water. In 1993, the World Health Organization (WHO) had recommended a maximum contaminant level (MCL) of arsenic in drinking water of 10 ppb [4]. The WHO recommendation was adopted by the EU in 2003 (Directive 98/83/EC), thereby revoking the previous 50 ppb limit. The new MCL was later transposed to the Portuguese legislation through Law Decree (DL) no. 236/2001. The drastic reduction of the arsenic MCL from 50 to 10 ppb has led many impoundments, which serve small and medium water supply systems, to become critical for this contaminant. Consequently, drinking water facilities are undergoing several technical and operational changes induced by the non-compliance (though seasonal) of raw water arsenic levels with the new quality standard. These changes concern: • many Water Treatment Plants (WTP) that require upgrades to address arsenic removal in order to comply with the new lower limit; • many drinking water supply systems managers that need to build new plants with arsenic removal facilities, since this contaminant has now become a critical parameter. When arsenic contamination is identified and quantified to be above the MCL, managers are confronted with either finding other water sources or implementing arsenic removal operations. When a safer drinking water source is not available or it becomes too expensive to exploit—one that is both low-arsenic or arsenic-free, and exhibits acceptable microbiological quality-treating raw water for arsenic removal is often the sole viable option to explore. In this case, there is ample justification for the development of innovative removal technologies that are more efficient and economically sustainable for small and medium-sized water supply systems. This issue is very sensible in the context of water scarcity and climate change. The work presented herein summarises the major processes (conventional and emerging) that can be used for arsenic removal in drinking water treatment, including an analysis of corresponding efficiencies, in order to establish selection criteria of those technologies as a function of the raw water characteristics and/or treatment schemes for existing WTP. In this context, the authors present a case study describing the rehabilitation of the WTP of Manteigas carried out by the Águas do Zêzere e Côa (AdZC) Company, concerning the development and installation of a suitable arsenic removal facility [5]. Their process decisions and methodological design allowed the managing company to avoid the rash acquisition of an expensive and pre-formatted arsenic removal solution. Sustainability 2009, 1 1290 2. Arsenic Toxicity and Related Health Hazards Arsenic naturally occurs in over 200 different mineral forms. Of these, approximately 60% are arsenates, 20% sulphides and sulphosalts; while the remaining 20% include arsenide, arsenite, oxides, silicates and elemental arsenic [6]. Arsenopyrite is produced by hydrothermal activity associated with the intrusion of granitic magma and orogenesis. Arsenic pollution of natural waters has become an international sanitation problem that currently affects over 40 million people in the World. It was initially reported in Bangladesh and in some countries of Latin America, where groundwater arsenic concentrations surpass 3.4 mg/L (e.g., in Córdoba, Argentina). In New Zealand, Romania, the Russian Federation, Spain and the USA, arsenic levels between 0.4 and 1.4 mg/L have been reported for carbonated water springs. In Taiwan, artesian aquifers display concentrations above 1.8 mg/L. In Portugal, water sources that exhibit higher concentrations of arsenic (approximately 800 ppb for groundwater and 60 ppb for surface waters) are generally located in Trás-os-Montes and Alto Douro [7], where the presence of arsenic-rich quartz-sulphur minerals is very common. Minho, Beiras, Ribatejo and Alentejo are additional locations where the legal contaminant concentration (10 ppb) is now exceeded. This has justified the pertinence of epidemiological studies in exposed populations (over many years) to the ingestion of waters containing arsenic concentrations between 10 and 50 ppb (the new and the old legal limit). These studies would allow the evaluation of the real exposure impacts on public health, thereby providing a valuable contribution and su (...truncated)