Wastewater treatment by adsorption and/or ion-exchange processes for resource recovery

Nowadays, resource recovery is a trending topic following the circular economy schemes proposed by the European UnionPostprint (published version

Trace ions rejection tunning in NF by selecting solution composition: Ion permeances estimation

Nanofiltration (NF) is suggested to selectively remove ionic species in aqueous process streams taking benefit of both membrane and aqueous solution composition. The importance of predicting and optimizing selective ion rejections by NF not only of major compounds (e.g. NaCl, Na2SO4, MgCl2, MgSO4) but also of minor ones such as ammonium (NH4+), nitrate (NO3-), bromide (Br-), iodide (I-) typically present in natural and industrial process streams is crucial. The current work explores ion rejection patterns and membrane ion permeances using the phenomenological Solution-Electro-Diffusion-Film (SEDF) model. It makes possible rapid calculations that account for the effects of spontaneously arising electric fields on rejections. Experimental ion rejection data of several inorganic ions species at various transmembrane pressures and at fixed cross-flow velocity have been obtained with NF270 membrane. A number of trace ions (Na+, K+, Cl-, Ca2+, Mg2+, SO42-, NO3-, NH4+, Br-and I-) have been used in combination with various dominant salts (NaCl, MgCl2, MgSO4) as model feed solutions. Results showed that dominant salts were moderately (NaCl) and highly (MgCl2, MgSO4) rejected when some ions are divalent, while trace ions exhibited quite variable rejection, including negative ones mainly at low transmembrane volume flows. The electric field of membrane potential can accelerate or retard the ion flows to the permeate, so negative or unexpectedly high rejections could be observed. Ions transport was shown to be affected by the membrane chemistry (e.g. acid-base properties of the un-crosslinked carboxylic and amine groups) and the dielectric exclusion phenomena. From the modelling procedure, ionic membrane permeances were determined for various multi-ion systems studied. Results showed that nature of dominant salt composition can be used to control the rejection of minor components.Peer ReviewedPostprint (author's final draft

Selectrodialysis and bipolar membrane electrodialysis combination for industrial process brines treatment: Monovalent-divalent ions separation and acid and base production

Chemical industries generate large amounts of wastewater rich in different chemical constituents. Amongst these, salts at high concentrations are of major concern, making necessary the treatment of saline effluents before discharge. Because most of these rejected streams comprise a combination of more than one salt at high concentration, it is reasonable to try to separate and revalorize them to promote circular economy at industry site level. For this reason, ion-exchange membranes based technologies were integrated in this study: selectrodialysis (SED) and electrodialysis with bipolar membranes (EDBM). Different process brines composed by Na2SO4 and NaCl at different concentrations were treated first by SED to separate each salt, and then by EDBM to produce base (NaOH) and acids (HCl and H2SO4) from each salt. The optimum of both electrolyte nature and concentration of the SED stack streams was evaluated. Results indicated that it was possible to separate Cl- and SO42- depending on the anionic membrane, initial electrolytes and concentrations of each stream. Pure NaOH and a mixture of HCl and H2SO4 with different purities could be obtained. Energy consumption evolutions were plotted and an optimal zone work was found where the consumption values were acceptable.Peer ReviewedPostprint (author's final draft

Integration of monopolar and bipolar electrodialysis for valorization of seawater reverse osmosis desalination brines: Production of strong acid and base

Water scarcity in the Mediterranean basin has been solved by using seawater desalination reverse osmosis technology (SWD-RO). This technology produces brine which is discharged back into the sea resulting in an environmental impact on marine ecosystems. Under the circular economy approach, the aim of this work is to recover resources from NaCl-rich brine (~60-70 g/L), e.g. in the form of NaOH and HCl, by integration of two ion exchange-based membrane technologies and quantify the electrical energy consumption. Electrodialysis (ED) incorporating monovalent selective cation exchange membranes as divalent ions purification and concentration of the NaCl present in the SWD-RO brine, was integrated with bipolar membrane ED (EDBM) to produce NaOH and HCl. Current densities of 0.30–0.40 kA/m2 at two temperature ranges simulating different seawater temperature regimes (15-18 ºC and 22-28ºC) were tested and a pure NaCl solution was used as starting concentrate stream. NaCl-rich brines with 100 or 200 gNaCl/L were obtained by ED and then introduced in the EDBM stack producing HCl and NaOH up to 2 M, depending on the initial concentrations. A minimum energy consumption of 1.7 kWh/kgNaOH was calculated when working by EDBM with initial concentrations of 104 g NaCl/L and 0.24 M HCl and NaOH.Peer ReviewedPostprint (author's final draft

Coagulation and flocculation optimization process applied to the sidestream of an urban wastewater treatment plant

Ammonium (NH4+) recirculation from the streams generated in the dehydration stage of the sludge generated in the anaerobic digestion of urban wastewater treatment plants (WWTPs), known as centrate or sidestream, produces a reduction in the efficiency of WWTPs. Given this scenario and the formulation that a WWTP should be considered a by-product generating facility (biofactory), solutions for ammonia/ammonium recovery are being promoted. These include a nitrogen source that reduces the need for ammonia production through the Haber–Bosch process. Therefore, the recovery of nutrients from urban cycles is a potential and promising line of research. In the case of nitrogen, this has been aimed at recovering NH4+ to produce high-quality fertilizers through membrane or ion exchange processes. However, these techniques usually require a pretreatment, which could include an ultrafiltration stage, to eliminate suspended solids and organic matter. In this case, the coagulation/flocculation (C/F) process is an economical alternative for this purpose. In this work, the sidestream from Vilanova i la Geltrú WWTP (Barcelona, Spain) was characterized to optimize a C/F process before being treated by other processes for ammonium recovery. The optimization was performed considering a bibliographic and experimental analysis of several operating parameters: coagulant and flocculant agents, mixing velocity, and operation time, among others. Then, the removal efficiency of control parameters such as turbidity, chemical oxygen demand (COD), and total suspended solids (TSS) was calculated. This optimization resulted in the use of 25 mg/L of ferric chloride (FeCl3) combined with 25 mg/L of a flocculant composed of silicon (SiO2 3%), aluminum (Al2SO4 64.5%), and iron salts (Fe2O3 32.5%), into a 1 min rapid mixing process at 200 rpm and a slow mixing for 30 min at 30 rpm, followed by a final 30 min settling process. The numerical and statistical results of the process optimization reached 91.5%, 59.1%, and 95.2% removal efficiency for turbidity, COD, and TSS, respectively. These efficiencies theoretically support the enhanced coagulation/flocculation process as a pretreatment for a higher NH4+ recovery rate, achieving 570.6 mgNH4+/L, and a reduction in the dimensioning or substitution of other membrane processes process due to its high TSS removal value.Peer ReviewedPostprint (published version

Advanced hybrid system for ammonium valorization as liquid fertilizer from treated urban wastewaters: validation of natural zeolites pretreatment and liquid-liquid membrane contactors at pilot plant scale

This study evaluates a hybrid system combining zeolites as a sorption stage and a hollow fiber membrane contactor (HFMC) for ammonia (NH3) recovery from treated urban wastewater. Ion exchange with zeolites was selected as an advanced pretreatment and concentration step before the HFMC. The system was tested with wastewater treatment plant (WWTP) effluent (mainstream, 50 mg N-NH4/L) and anaerobic digestion centrates (sidestream, 600–800 mg N-NH4/L) from another WWTP. Natural zeolite, primarily clinoptilolite, demonstrated effective desorption of retained ammonium using a 2% NaOH solution in a closed-loop configuration, resulting in an ammonia-rich brine that enabled over 95% NH3 recovery using polypropylene HFMCs. A 1 m3/h demonstration plant processed both urban wastewaters, which were pretreated by ultrafiltration, removing over 90% of suspended solids and 60–65% of COD. The 2% NaOH regeneration brines (2.4–5.6 g N-NH4/L) were treated in a closed-loop HFMC pilot system, producing 10–15% N streams with potential use as liquid fertilizers. The resulting ammonium nitrate was free of heavy metals and organic micropollutants, making it suitable for use as liquid fertilizer. This comprehensive N management solution for urban wastewater applications can contribute to local economies while achieving reduced N discharge and circularity goals.LIFE ENRICH | Ref. LIFE16 ENV/ES/000375Ministerio de Ciencia e Innovación | Ref. PID2020-114401RB-C21Ministerio de Economía y Competitividad | Ref. CTM2017-85346-RGeneralitat de Cataluña | Ref. 2017-SGR-312Ministerio de Ciencia e Innovación | Ref. RYC2021-030966-

Increasing sustainability on the metallurgical industry by integration of membrane nanofiltration processes: acid recovery

The metallurgical industry generates large volumes of toxic effluents characterised, generally, by high acidity and a noticeable content of metals (Fe, Cu and Zn) and non-metals (As, Sb, Bi). The toxicity of these streams makes necessary treatment before its discharge to the environment or reuse. Sustainable management of these effluents must be focused on the recovery of low added valuable by-products (e.g. strong acids) to reduce the wastes generated along with the treatment (e.g. sludge). Nanofiltration offers clear advantages for acid recovery instead of the conventional treatments such as neutralisation and precipitation, due to the high membrane transport ratios of single charged ions and high rejection of multi-charged ions. The performance of a semi-aromatic poly(piperazineamide) membrane (NF270) was evaluated for the treatment of effluents from copper metallurgical process streams of off-gases treatment trains. These streams are characterised by a high acidity (pH¿<¿1) due to a mixture of strong (H2SO4, HCl) and weak (H3AsO4) acids and the presence of metallic species (Fe, Cu, Zn). The membrane performance was evaluated in terms of acid recovery and metal ions rejection taking into account their aqueous speciation in strong acid media. The transport of the species across the membrane was characterised according to the Solution-Electro-Diffusion model. The membrane permeances to aqueous species (both charged and non-charged) in strongly acidic solutions were calculated. NF270 showed good results for strong acid recovery, exhibiting high rejections of the metallic impurities. The implications of the presence of large amounts of As present as H3AsO4 should involve a selective removal stage using H2S or Na2S2O3.Peer ReviewedPostprint (author's final draft

Valorization of bottom ash from municipal solid waste incineration: recovery of copper by electrowinning

Postprint (published version

Potential of nanofiltration and reverse osmosis processes for the recovery of high-concentrated furfural streams

Furfural is an interesting compound that can be produced from renewable and sustainable resources and is used in platform chemicals for the synthesis of biofuels and other chemicals. However, a recovery step is required to separate furfural from lignocellulosic hydrolysates when cellulose-based raw materials are used. In this work, nanofiltration (NF) and reverse osmosis (RO) processes have been evaluated to purify or concentrate synthetic furfural solutions.Postprint (author's final draft

Integration of ion exchange resins and membrane technology for purification of boron from seawater desalination brines

Boron is considered a critical raw material (CRM) to the European Union (EU) due to its economic importance and supply risk. To ensure the sustainable supply of boron and other CRMs to EU industry in a circular economy approach the H2020 Sea4value project proposes the recovery of valuable minerals/metals from seawater desalination brines. Brines can cause damage to marine ecosystems when discharged into the sea. Sea4value aims to reduce the environmental impact of desalination plants while generating value from a waste stream. The project proposes a multi-mineral brine mining process divided in 3 stages: pre-treatment, concentration, and extraction/purification. This work investigates the extraction/purification of boron using nanofiltration as pre-treatment followed by an ion-exchange column for concentration and electrodialysis with bipolar membranes (EDBM) for boric acid production. The nanofiltration permeate (monovalent-rich stream) fed a column packed with the commercial boron selective resin CRB03 (Mitsubishi Chemical). After elution, a concentration factor of 17 was obtained for boron. Sorption of major elements present in the brine (sodium, chloride, magnesium, …) was not observed. However, besides boron, the resin sorbed indium and vanadium. Initial EDBM tests using borax solutions at different pHs showed a concentration factor of 2 for boric acid, at pH 12.Peer ReviewedObjectius de Desenvolupament Sostenible::14 - Vida SubmarinaObjectius de Desenvolupament Sostenible::6 - Aigua Neta i SanejamentPostprint (published version