Hybrid process for the purification of water contaminated with nitrites: Ion exchange plus catalytic reduction
Graphical abstract
Introduction
In recent years, a significant amount of surface water sources, mainly from groundwater, with high concentrations of nitrates have been detected, due to excessive use of fertilizers in intensive agriculture, leaking of septic tanks and waste disposal in breeding farms (Rupert, 2008). Chronic and excessive intake of nitrate through water can cause serious health problems in adults, such as ovarian or prostate cancer, as well as growth problems or diseases such as methemoglobinemia (blue baby syndrome) in infants (Arbuckle et al., 1988, Comly, 1987, Dorsch et al., 1984, Fan and Steinberg, 1996).
Numerous processes for the removal of nitrates and nitrites from water have been developed. Among them are the ion exchange, biological denitrification, reverse osmosis, electrodialysis and catalytic reduction. The World Health Organization (WHO) recommends the biological denitrification and ion exchange as the most appropriate methods developed to date for the removal of nitrates from drinking water (World Health Organization, 1992). The biological denitrification is a very specific and selective process. However, it has as disadvantage the risk of contaminating the water with bacteria and metabolic substances. Therefore, it is necessary the filtration and disinfection with germicides of the treated water, which increases the process costs (Mizuta et al., 2004). Meanwhile, technologies using ion exchange are more suitable for water decontamination, due to its simplicity, efficiency, selectivity, reusability, and relatively low cost (Darbi et al., 2003). The main disadvantage of this technology is the disposal of the effluent rich in nitrates or nitrites, which means that the problem is only transferred but not completely solved.
Catalytic reduction of nitrates or nitrites using heterogeneous catalysts is an alternative to remove these species from polluted streams. In these technologies, nitrates or nitrites are reduced to nitrogen using a reducing agent, which is usually hydrogen (Barbosa et al., 2013, Gao et al., 2015, Pintar and Batista, 2007, Zhao et al., 2014). However, this technology presents a major constraint, which is the catalyst selectivity. Over-reduction of nitrate or nitrite leads to the formation of ammonia, being the maximum concentration allowed by the WHO 0.5 mg/L. For this reason, it is necessary to develop catalysts displaying not only good activity but also a very good selectivity to N2.
Recently, polymers have being used as supports, with the purpose of stabilizing the bimetallic particles. Polymers such as poly(N-vinylpyrrolidone) (PVP) or poly(vinylalcohol) (PVA) were used to increase the stability and controlling the size and composition of the bimetallic particles (Guy et al., 2009; Prüsse et al., 2000). A third type of polymers, such as functionalized resins or ion exchange resins have been successfully used in the synthesis of Pd–Cu and Pd–In bimetallic catalysts for their use in the catalytic reduction of nitrates (Barbosa et al., 2013, Gašparoviĉová et al., 2006, Gašparoviĉová et al., 2007, Neyertz et al., 2010). These resins are constituted by a copolymer of styrene- divinylbenzene containing exchange functional groups such as –N(CH3)3+ Cl− or –SO3–H+, known as anionic or cationic resins respectively. The use of acid cationic resins as support for bimetallic catalysts was studied by different authors. Such resins are very attractive because they provide protons that can neutralize the OH− generated during the nitrate reduction, maintaining the pH of the aqueous solution at acceptable values, thus increasing the N2 selectivity (Gašparoviĉová et al., 2006; Kralik et al., 2006; Roveda et al., 2003).
No reports have been found about nitrite removal using monometallic catalysts supported on anionic resins. On the other hand, the effect of competing ions such as sulfates, chlorides and bicarbonates on the exchange capacity and catalytic activity of the resins, were addressed only in few studies (Hekmatzadeh et al., 2012, Samatya et al., 2006, Song et al., 2012, Stefan et al., 2014), in spite of being a key issue in order to properly determine the real catalytic behaviour (Bergquist et al., 2016).
Pintar and Batista (2007) proposed a process in which the nitrates were eliminated from the water using an ion-exchange resin. Once the resin was saturated, it was regenerated by eluting the nitrates using a sodium chloride solution (5%w/w). This stream containing high concentrations of nitrates and chlorides was them fed to a two-reactor system. In the first one, the nitrates were reduced to nitrites in a basic media (pH = 12.5) using a Pd–Cu/Al2O3 catalyst. Then, in a second reactor, the nitrites were selectively converted to nitrogen in an acid media. In the present work, a catalytic process that can be applied to the second reactor of this purification strategy is studied. According to Pintar and Batista (2007) the presence of chlorides decreased the catalyst performance and induced ammonium formation. Also, they found that in the second reactor, the selectivity to ammonium was too high, due to pH gradient inside the catalyst pores.
Catalysts containing metals supported on ion exchange resins have the advantage of being bifunctional. On one hand, the palladium deposited on the resin is capable of reducing nitrites in the presence of H2, and on the other hand, the support may adsorb nitrites by an ion exchange mechanism (IE). Thus, the decrease in the nitrites concentration observed at the reactor outlet is due to the sum of two contributions, the reaction and the ion exchange.
This work presents studies of the catalytic process performance for nitrite reduction of monometallic Pd catalyst, supported on a macroporous anionic resin using the process named as RIE: Reaction + Ion Exchange. The efficiency of this process is compared with that of the conventional ion exchange (IE) using the same catalytic resin.
In addition, the resin regeneration is studied and the process was scaled up to pilot plant level. The overall performance of the process developed showed an excellent performance. Initial adsorption and reaction rates were also determined in a batch reactor, in order to have quantitative information regarding the contribution of each mechanism in the nitrites removal. In addition, the effects of competing anions on nitrites adsorption and reduction were also addressed.
Section snippets
Catalyst preparation
The WA30 (Mitsubishi) resin used as catalytic support is a styrene divinylbenzene polymer matrix with tertiary amine functional groups. It is a weak macroporous anionic exchange resin, with an exchange capacity of 1.6 equivalent/L. Before metal impregnation, the resin was washed with HCl 5 wt.% for 1 h, filtered and washed with distilled water. The palladium was fixed on the resin by addition of a solution containing [PdCl4]2−, obtained by dissolution of PdCl2 in an acidic media (HCl 0.01 wt.%).
Effect of particle size
Fig. 1 shows the variation of nitrite concentration with time for different particle sizes (Ps) of the catalytic resin, obtained in experiments carried out as described in Section 2.4. It can be seen that the rate of nitrites exchange increases with decreasing particle size. Therefore, the internal diffusive effects have a non-negligible effect on the adsorption rate. The commercial particle diameter of WA30 resin is in the 20–40 mesh (841–420 μm) range, which presented the lowest exchange rate.
Conclusions
Important diffusive effects were observed during the ion exchange process. However, decreasing the particle size would bring about problems of fine particles dragging and over-increase the pressure drop throughout the reactor. Taking into account the results obtained in the breakthrough and batch ion exchange experiments, it is concluded that sulfate is the competing ion which causes the larger alterations in the ion exchange ability. The selectivity and activity for nitrite reduction decrease
Acknowledgements
The authors wish to acknowledge the financial support received from UNL (CAID PACT 96) and ANPCyT (PICT 2013).
References (37)
- et al.
The use of a cation exchange resin for palladium–tin and palladium–indium catalysts for nitrate removal in water
Mol. Catal.
(2013) - et al.
Kinetic and equilibrium studies in removing lead ions from aqueous solutions by natural sepiolite
J. Hazard. Mater.
(2004) - et al.
Evaluation of a hybrid ion exchange-catalyst treatment technology for nitrate removal from drinking water
Water Res.
(2016) - et al.
Kinetic modelling of the adsorption of nitrates by ion exchange resin
Chem. Eng. J.
(2006) - et al.
Kinetics of nitrates adsorption on Amberlite IRA 400 resin
Desalination
(2007) - et al.
Health implications of nitrate and nitrite in drinking water: an update on methemoglobinemia occurrence and reproductive and developmental toxicity
Regul. Toxicol. Pharmacol.
(1996) - et al.
Reduction of nitrates dissolved in water over palladium-copper catalysts supported on a strong cationic resin
J. Mol. Catal.
(2006) - et al.
Supported Pd–Cu catalysts in the water phase reduction of nitrates: functional resin versus alumina
J. Mol. Catal.
(2007) - et al.
Highly active Pd–In/mesoporous alumina catalyst for nitrate reduction
J. Hazard. Mater.
(2015) - et al.
Modeling of nitrate removal for ion exchange resin in batch and fixed bed experiments
Desalination
(2012)
Review of second-order models for adsorption systems
J. Hazard. Mater.
Kinetic, isotherm and thermodynamic study of nitrate adsorption from aqueous solution using modified rice husk
J. Ind. Eng. Chem.
Adsorption characteristics of antibiotics trimethoprim on powdered and granular activated carbon
J. Ind. Eng. Chem.
Removal of nitrate-nitrogen from drinking water using bamboo powder charcoal
Bioresour. Technol.
Adsorption of chromium(VI) by a low cost adsorbent: biogas residual slurry
Chemosphere
Catalytic reduction of nitrate in water: promoted palladium catalysts supported in resin
Appl. Catal. A
Catalytic stepwise nitrate hydrogenation in batch-recycle fixed-bed reactors
J. Hazard. Mater.
Improving the catalytic nitrate reduction
Catal. Today
Cited by (14)
Pd and Pd-Cu supported on different carbon materials and immobilized as flow-through catalytic membranes for the chemical reduction of NO<inf>3</inf><sup>-</sup>, NO<inf>2</inf><sup>-</sup> and BrO<inf>3</inf><sup>-</sup> in drinking water treatment
2023, Journal of Environmental Chemical EngineeringDevelopment of Pd-based catalysts for hydrogenation of nitrite and nitrate in water: A review
2023, Journal of Hazardous MaterialsDesign of macrostructured bimetallic MWCNT catalysts for multi-phasic hydrogenation in water treatment with pre- and post-coating metal phase impregnation
2022, Applied Catalysis A: GeneralCitation Excerpt :Among the different techniques that have been developed over the past few years, heterogeneous catalytic reduction emerges as an efficient and sustainable mechanism to perform the conversion of NO3- into less toxic species (namely N2) [7]. The most significant advantage associated with this technology is related to the possibility of converting NO3- in less toxic species while avoiding the trapping of the main pollutant as it happens in the most common techniques applied for the removal of this type of species (namely in ion exchange or membrane separation) [8,9]. This conversion can already be achieved through biological denitrification; however, the process is still very slow, requiring very large infrastructures and multistage processes in order to achieve good results in NO3- conversion and N2 selectivity [10,11].
Hybrid process for nitrates elimination in water
2022, Catalysis TodayCitation Excerpt :These results prove that the promoter metal plays a key role, and therefore, further study should be carried out in this subject in order to maximize the catalytic performance for nitrate reduction using the hybrid process presented in this work. The regeneration mechanism that occurs in this process is similar (but not the same) to the mechanisms described in previous works [20,26]. The process is schematized in Fig. 2.
Mathematical modelling and simulation of nitrite hydrogenation in a membrane microreactor
2020, International Journal of Hydrogen EnergyCitation Excerpt :Catalytic hydrogenation of nitrite can be used for separation of nitrate from water [9], and synthesis of hydroxylamine [10]. Mendow et al. [11] used palladium supported on macroporous anionic exchange resin in order to reduce nitrite and it was proved that the hybrid reaction and ion exchange improves the system performance. Moreover, water purification can be performed using photocatalytic activating molecular oxygen to superoxide radical (-O2−) and hydrogen peroxide [12,13].