Latin American experiences in arsenic removal from drinking water and mining effluents

J.L. CORTINA; M.I. LITTER; O. GIBERT; C. VALDERRAMA; A.M. SANCHA FERNÁNDEZ; S. GARRIDO; V.S.T. CIMINELLI

Innovative Materials and Methods for Water Treatment-Separation of Cr and As

CRC-Taylor & Francis

Año: 2016;

Conventional technologies (coagulation/ co-precipitation, adsorption and reverse osmosis) havebeen applied for As removal from centralized water supplies on the large and medium scale inChile, Argentina, Guatemala and Peru. Technologically complex techniques such as adsorptionusing tailored adsorbents or membrane processes may be too expensive for populations withlow economic resources such as those in Latin America. Sometimes, reluctance of consumers inaccepting changes in the organoleptic properties of waters they have been drinking for years isanother problem for the implementation of a removal procedure. In addition, As treatment unitsrequire very sensitive monitoring and maintenance facilities; this is not always feasible in someareas in LA. Furthermore, the volume, handling and final disposal of the wastes generated duringthe treatment processes is becoming a new problem due to the recent regulations, as has beenreported in Chile and in Argentina (CIS, 2006; Sancha, 2003).After decades of experience in Chile andArgentina in the field of coagulation-basedAs removalplants, it was shown that coagulation is a very efficient procedure for removing As from waterin the tested cases, reaching the recommended WHO and national standards (10μgL−1). Thisis a cost-effective technology dealing with low to medium production capacity plants (30 to520 L s−1), which requires moderate capital investment (reactive dosifiers, mixers, filters, etc.),when compared with other technologies like RO. The modified coagulation process (C/F) is asimplified procedure that can be applied to groundwater with low turbidity, with a good correlationbetween residual turbidity (flocs with adsorbed As) and As concentration in the treatedwater. The composition of water and the As oxidation state are the critical factors that regulatethe application of the process, and water has to be preoxidized to assure the total oxidationof As(III). The coagulation/adsorption/filtration processes are low-cost technologies that do notrequire extremely trained personnel or expensive chemicals.In the particular case of the Chilean plants, the optimization of the coagulation step by controlof the pH and the coagulant dose allowed the attainment of a residual concentration of As of10μgL−1, achieving the national regulations since 2008. Although plants built before 2005 hada period to reach the legislation requirement, all the existing plants in Chile began to producewater with As levels of 10μgL−1 since 2004, demonstrating that the coagulation technology wassuitable to reach these requirements.In the case of Argentina, plants developed with the ArCIS-UNR process (coagulation/adsorption/filtration process with PAC or ferric chloride, followed by double filtration), werefound efficient in removing bothAs and F−. The particular use of PAC provides removal capacitiesallowing to reach the value recommended by WHO in a pH range of 6.5 to 8.On the other hand, in the last decades several RO plants have been installed in Argentina toremove As and salinity. However, the high levels of solids, including high silica content obligedthe use of antiscaling reagents. More importantly, water rejection is around 50%, a detrimentalfactor for desert zones, and the lifetime of the membranes used so far in most of the cases is lowdue to a deficient pretreatment design. The experience in Argentina shows that RO has elevatedoperating costs, being not affordable by poor communities. Moreover, there are no systematicsludge environmental impact studies. However, recently, an improved RO plant has been installedin the periphery of Buenos Aires.Other examples of As removal plants have been reported in Peru and in Guatemala. In the firstcase, a technology using coagulation/co-precipitation with FeCl3 has been used, whereas in thesecond case, FeCl3, a flocculant plus ceramic-based filtering media were used.Concerning removal and disposal of As from industrial effluents containing high levels ofthe element in solution (copper and gold mining and metallurgical plants of Chile and Brazil),co-precipitation methods with iron salts either as amorphous (arsenical ferrihydrite) or crystallinearsenates are the predominant technologies.In spite of all the difficulties and problems that had to be faced, the Latin American experiencegives valuable information that could be used to solve this problem in other regions of the world,especially in countries ofAsiawhere the first option is to find otherwater sources not contaminatedwith As.