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Development of a new adsorbent material for efficient and economic removal of Arsenic from potable water

Periodic Report Summary - AQUASZERO (Development of a new adsorbent material for efficient and economic removal of Arsenic from potable water)

Project background and objectives:

Development of granular binary Ferric-Manganese oxy-hydroxide for Arsenic removal from potable water.

The AquAsZero project developed a low-cost material to absorb Arsenic from drinking water. This material will be used as the absorbent media in new water treatment systems or to replace a conventional adsorbent in existing water treatment systems. The project primarily impacts on the chemicals market for Arsenic removal and secondly, on the water treatment systems manufacturers.

Need… Arsenic is a highly poisonous metallic element generated from the processing of a variety of ores, which affects more than 100 million people worldwide. Chronic exposure to high levels of inorganic arsenic in drinking water has been found to result in health effects, such as cancers, and cardiovascular/neurological implications. There are natural sources of exposure, but water consumption is the major source of arsenic exposure for the majority of the citisens.

Legislation… The standards for arsenic in drinking water have been revised; in Europe, through the Directive 98/83/CE and in the US, the new Maximum Contaminant Level is now 10 µgAs/L. Fulfilling these new requirements is therefore urgent and it will be a major challenge for the water supply companies, as existing technologies are only partly capable of meeting these needs.

Costs… The major issue in the new Arsenic limit is the associated costs to the water treatment facilities. The common methods have been found to be cost effective only at a large scale, where labour costs are spread over a larger amount of treated water produced. The water treatment cost using conventional adsorbents ranges from 6. 7-40 EUR €/100m3 (assuming adsorption capacity 1-3g As/kg and adsorbent cost 5-10EUR €/kg). Consequently, the main disadvantage of the available conventional adsorbent treatment technologies for arsenic removal seems to be the high cost of adsorbents. Additionally, Arsenic residuals have varying toxicity and mobility; thus, they require further treatment prior to disposal, which increases the total cost.

Project Objectives

The aim of the AquAsZero project was to reduce material costs (< 2 EUR € per kg of material), improve efficiency (> 99 % As removal) and reduce operating costs. This was accomplished with the use of iron-based adsorptive media FeS04 and Mn+ 2 and 03 as catalysts. As Mn+ 2 accelerates production of iron oxy-hydroxides and increases the adsorption performance. Furthermore, FeS04 is considered as relatively low-cost material, making the proposed technology economically viable. This new adsorbent has low capital cost and the water treatment system in which it will be integrated will have low energy consumption, low maintenance costs and reduced plant size. The AquAsZero projects' impact on the market of chemicals used in water treatment systems to remove Arsenic and on the manufacturers of water treatment units.

Project results:

The AquAsZero project duration coincided with some very difficult times in Europe. The project not only survived, despite having faced severe management challenges and losing one research organisation to the recession, it emerged as technically successful and went on to win national awards for the most innovative research project in the whole of Greece in 2011.

Background research

From a technical point of view, the work progressed largely according to plan. Year 1 dealt with generating the new scientific knowledge and the development of the new Arsenic Adsorbent.

A European Arsenic concentration map, emphasising the project participant countries of Greece, Spain, Romania and Estonia was created to determine the presence of As (V) and As (III) concentration in groundwater in the region.

A patent search on the available processes for As adsorption was conducted and presented with patents classified according to their relativeness to AquAsZero project. The results of this research showed that no available patents outweigh AquAsZero project and the project went on to file patent applications in its second year.

The leaching behaviours of As adsorbents currently used in working arsenic removal plants were examined, collated and published. The results were very encouraging and a Leaching Test procedure was developed for use in the project.

Also a detailed cost analysis renders AquAsZero as one of the most cost effective materials available.

Lab Based Formulation Research and Analysis

Lab-scale reaction-precipitation tests were carried out for the production of single Fe oxyhydroxides and binary Fe-Mn oxy-hydroxides. These results and the study of the influence of various parameters (Fe/Mn ratio, pH, redox, reagents) on the characteristics of the produced solid suspension and the physicochemical properties of the final adsorbent then influence the the optimum reactor design and configuration.

The choice of the reagents was an important procedure for the whole project. Apart from the type and the concentration of iron precursor solution (FeSO4), the optimisation process identified the pH (NaOH, Ca (OH) 2, Na2CO3) and the redox (KMnO4, H2O2, KSHO5) controlling reagents, not only according to the adsorption ability of the solid product but to the economically viability of the method as well.

A variety of characterisation methods were utilised to understand the influence of the material's physical and chemical parameters in the adsorption process. These same methods were used to estimate the possible interferences and optimise the adsorbent yield for scale-up application. In particular, analytical methods were applied to determine the chemical composition of oxy-hydroxides in different stages of use while techniques for structural investigation clarified issues concerning crystalline order, morphology and surface charge. The main objective was the evaluation of the adsorption capacity in batch and column experiments. To study the adsorption efficiency of the produced adsorbents, kinetic and equilibrium isotherm batch tests were performed using fine powder in NSF challenge water spiked with various concentrations of As (III) or As (V). Finally, the disposal of spent adsorbents from column tests was investigated, according to the European and United States regulations for the safe and legal landfilling as inert materials. The results and the conclusions are reported in the project deliverables.

The solid product is received with low humidity after centrifugation/washing cycles and thermal drying to produce a sludge type material. The handling of this sludge is quite involved and a size selection, crushing and sieving process classified the resulting granules. Preliminary observations and evaluation of dewatering/washing, formulation and drying (described in deliverable 2.
1) were evaluated and recommendations were made for the selection of the sludge handling and treatment method in the following stage (WP3) of the project.

Tuning of adsorption capacity and production costs through the variation of critical parameters allowed the optimisation of the precipitation conditions, reagent selection and the sludge treatment process. The pH-value, the redox level and the percentage of incorporated Mn in the solid were examined as the determinants of the reaction yield and the adsorption properties against As. Variations in the final product with the use of and alternative pH adjusting compound (instead of NaOH) were also investigated and a single Fe and a binary Fe/Mn oxy-hydroxide were qualified. Further performance validation was carried out by testing in dynamic columns.

Workshop and Pilot Scale

During the second year of the project, the new knowledge from the laboratory was transferred to small scale system design and upon successful trials, expanded to a pilot scale system. This was fabricated and delivered to Loufakis for the production and trial of the final adsorbent material.

The qualified project adsorbents were produced in large quantities in the laboratory by following the optimised conditions of precipitation. The two samples will be referred as AquAsZero-Fe and AquAsZero-Fe/Mn, respectively.

Along with the commercial adsorbents Commercial-1 and Commercial-2, samples were subjected to rapid small-scale column adsorption tests (RSSCT) with As (V) and As (III) at concentrations 500µg/L to facilitate breakthrough.

The arsenate adsorption capacities of both AquAsZero adsorbents are almost identical (around 11. 5µg/mg) and much higher than that of Commercial-1 (8 µg/mg) and Commercial-2 (2 µg/mg). The adsorbents, saturated with As (V), were found to be non-hazardous according to EN 12457 as well as to TCLP procedure.
• Quantities of arsenic determined by EN 12457 leaching procedure were found to be around one order lower than the European Union regulation limit for landfill disposal as a non-hazardous material.
• Leached arsenic during the TCLP test was almost three orders of magnitude lower than the limit of 5 mg/L.

The breakthrough curves concerning adsorption column tests for As (III, verify the higher As (III) adsorption when manganese is incorporated in ferric oxy-hydroxides. The adsorption capacity of AquAsZero-Fe (q10 = 4. 5µg/mg) is less than half that of AquAsZero-Fe/Mn (q10 = 10µg/mg). The fact that the adsorption capacity of AquAsZero-Fe/Mn is approximately the same for As (V) and As (III) in the RSSCT test, is explained by the occurrence of anarsenite adsorption mechanism onto binary Fe/Mn oxy-hydroxides through its intermediate oxidation to arsenate. The corresponding values for Commercial-1 and Commercial-2 are sometimes lower (3 and 1. 7 µg/mg). Both AquAsZero spent adsorbents after RSSCT experiment with As (III) were proved to be non-hazardous according to EN 12457 and TCLP tests.

The distribution of As after saturation of the two adsorbents in column tests is illustrated in the corresponding SEM images.

Adsorption efficiency is pH sensitive and much higher for As (V) than As (III). The adsorption capacity for As (V) decreases as the adsorption pH rises from 6 to 8 due to the transformation of H2AsO4-to the HAsO42-form.

The maximum adsorption is observed for AquAsZero-Fe and AquAsZero-Fe/Mn at pH 6 when q10 reaches 17 µg As (V)/mg. This value is more than 30 % higher than the studied ferric commercial adsorbents (Commercial-1, Commercial-2).

Although the absolute adsorption capacity is lower at pH 7, the relative difference between AquAsZero and the commercial solids is ever larger (at least 40 %). Only at pH 8, Commercial-1 becomes more efficient than the other compared samples. Apart from their excellence, compared to the common used commercial products, the qualified adsorbents of the AquAsZero project present an identical adsorption yield for As (V).

Only AquAsZero-Fe/Mn can be considered capable of removing As (III) at a significant level. The q10 value is by far the highest presented value for As (III) adsorption. Single Fe adsorbents (AquAsZero-Fe, Commercial-1, Commercial-2) have a limited removal efficiency. Among them, the structural and morphological properties of AquAsZero-Fe enhance its applicability as a low cost As (III) adsorbent due to its improved efficiency than Commercial-1 and Commercial-2. The q10of the single Fe oxy-hydroxides for As (III) was proved less sensitive to pH value in comparison with that of As (V) being proportionally correlated with it. This was attributed to the presence of the neutral form H3AsO3o. In contrast to the case of As (V), the adsorption capacity of AquAsZero-Fe/Mn for As (III) was reversely correlated with pH value of adsorption. This fact is indicative of the mechanism that the AquAsZero-Fe/Mn uptake As (III) through theoxidation of As (III) and which is retained as As (V).

Finally, the disposal of spent adsorbents from column tests was investigated, according to the European and United States regulations for the safe and legal landfill as inert materials.

Potential Impact:

The Laboratory and Pilot scale experiments conducted lead to the establishment of a method for the production of granular adsorbents with their composition ranging from single Fe to binary Fe/Mn oxy-hydroxides. The final products present high arsenic adsorption capacity. Whilst the possibility to obtain a fine adsorbent at laboratory scale was established, it was important that the process was technically feasible, working at the optimum size and the energy consumption of various parts of the reaction-precipitation process. Although there are optimum conditions for the production of the cheapest and most efficient material for an average arsenic containing water, a procedure for the synthesis on demand of a more targeted product was also developed.

For the treatment of a water with high As (III) levels, the best choice is a binary Fe/Mn oxy-hydroxide with high Mn content, while single Fe oxy-hydroxides are sufficient in the case of water mainly containing As (V) species. Through their sophisticated adsorption mechanism, AquAsZero adsorbents proved to be much more efficient compared to commercial adsorbents, especially in treating As (III). In addition, they can be described environmental friendly from the side of their production wastes and their handling as non-hazardous according to EN 12457 and TCLP after their use.

AquAsZero is an opportunity for water treatment system manufacturers to improve their competitive position by developing an innovative product able to reduce Arsenic concentration in potable water to the new Maximum Contaminant Level with minimised capital and operational costs.

The AquAsZero project will be of great relevance to the SME partners in order to improve their competitiveness in the world arena and face the main market trends. Thus, ensuring the dissemination of knowledge and results generated during the project amongst the target SMEs and assuring the successful exploitation of results are of major importance. The dissemination of knowledge will be carried out by scientific publications and partners training while a strategy for the exploitation of the results by the participating SMEs will be designed. Finally, a plan for the commercialisation of AquAsZero adsorbents and related products/technologies will be launched.

Project website:

http://www.aquaszero.com