Wastewater treatment plants (WWTPs) are no longer considered pollution removal systems but rather resources (nutrients and energy) recovery plants. Legislation imposing more stringent effluent ...requirements and the need energy self-sufficient or even energy-positive plants are the main drivers for the research and development of new WWTP configurations. While a lot of effort has been focused on developing new processes for nutrient recovery, limited efforts have been allocated to maximizing energy recovery from the organic load. Within this context, high-rate activated sludge (HRAS) is the most promising alternative technology to redirect carbon (organic compounds) towards energy as biogas. This is a critical review of the last decade's development of new alternatives for carbon redirection to improve the energy balance of WWTPs on both the laboratory and the industrial scale.
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•C redirection technologies challenges are reviewed.•Bio-sorption/HRAS processes demonstrated high organic matter removal efficiencies.•Bio-sorption/HRAS systems are beneficial in terms of a global energy balance.•60% of C is expected to be redirected to the sludge during the bio-sorption step.•The main challenge of Bio-sorption/HRAS is focused on sludge settling properties.
Acidic mine Drainage (AMD) is still considered one of the greatest mining sustainability challenges due to the large volumes of wastes generated and the high associated treatment cost. New regulation ...initiatives on sustainable development, circular economy and the need for strategic elements as Rare Earth Elements (REE) may overcome the traditional research initiatives directed to developing low cost treatment options and to develop research initiatives to identify the potential benefit of considering such AMD as a potential secondary resource. As an example, this study develops the integration of a three-stage process where REE are selectively separated from base metals (e.g. Fe, Al, Mn, Ca, Mg, Cd, Pb) and then concentrate to produce a rich REE by-product recovered as REE-phosphates. Selective separation of Fe (>99%) was achieved by total oxidation to Fe(III) and subsequent precipitation as schwertmannite at pH 3,6 ± 0.2. REE were then extracted from AMD using a sulfonic ion-exchange resin to produce concentrated REE sulfuric solutions up to 0.25 gREE/L. In a final stage selective separation of REE from Al(III), Ca(II) and Mg(II) and transitions elements (Cu, Zn, Ni) was achieved by precipitation with phosphate solutions under optimized pH control and total phosphate concentration. XRD analysis identified low-crystalline minerals. By using a thermal treatment the presence of PrPO4(s) and Cheralite (CePO4(s)) where Ce is substituted by La and Ca and Xenotime (YPO4(s)) were found as main minerals AlPO4(s) Ca,MgYPO4(s) were also identified.
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•Rare earth recovery from acid mine drainage•Effective process to treat acid mine drainage to concentrate and recover rare earth elements•Integration of selective phosphate precipitation with ion-exchange concentration•Selective separation of rare earth elements from transition elements
Electrodialysis (ED) is a separation process that uses an electric field to selectively transport ions through ion exchange membranes. To further advance the technology and bring it to an industrial ...scale, modeling ED and associated research on transport phenomena have become critical. Nowadays, most of the models present in literature are semi-empirical, which imply a large experimental campaign to properly predict the performance of ED systems. Contrary, a few models are based on Computational Fluid Dynamics to couple the hydrodynamics inside the stack and Nernst-Planck equations to model properly the ED performance. This work aims to provide further understanding of the transport of species in ED focused in the analysis of concentration profiles and fluxes, by building a 2-D computational time-dependent model. Moreover, the analysis of the concentration profiles was conducted at several positions within the stack, revealing that the ion concentration values varied depending on the location. In addition, simulations were contrasted with experimental data from a lab-scale unit. Theoretical data showed a reasonable agreement with experiments, with some discrepancies attributed to the presence of water transport.
•2-D time dependent model using CFD•Ion-concentration profiles and fluxes at several positions within the ED stack•Experimental validation evaluating the voltage drop over a single-cell pair
Electrodialysis with bipolar membranes (EDBM) has drawn attention motivated by their application in generating reagents from salts. Due to the water splitting (WS) occurring at the junction of the ...bipolar membranes (BPMs), where the anion and cation layers are in strict contact, H+ and OH- are released from the BPM producing acid and alkali on the respective compartment. Considering this application, the interest of this work is to provide further understanding of the mechanisms of WS and transport of species in EDBM. This work develops and utilizes, for the first time, an experimentally validated two-dimensional (2-D) computational model, in which the Navier-Stokes and Nernst-Planck equations are coupled with the description of WS given by the Second Wien effect. In addition, a 1-D geometry is also proposed to perform a comparison between electroneutrality and Poisson charge conservation. The model is computationally solved using COMSOL Multiphysics. According to simulations, electroneutrality is valid for 2-D geometries. Moreover, the semipermeable characteristics of the membranes are assessed by means of evidencing a polarization effect resulting in a double-electric layer. The model proposed predicts a significant proton leakage, and facilitates the study of WS within the BPMs.
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•Reagent generation using EDBM.•Water splitting and ion transfer mechanisms.•1-D & 2-D models using CFD.
The accumulation of ammonia in water bodies can cause eutrophication and reduce water quality. Furthermore, 80% of the ammonia in the world is consumed as fertilizer, which makes it a resource that ...can be recovered under the circular economy concept. Then, ammonia from wastewater can be valorised for agricultural applications. Liquid-liquid membrane contactors (LLMCs) have been postulated as a novel and eco-friendly technology for ammonia recovery, because they can convert dissolved ammonia into ammonium salts by an acid stripping solution. The concentration of the ammonium salt produced is limited by the co-transport of water in LLMC. Further concentration by electrodialysis (ED) is presented as a solution to overcome this problem. In this work, ammonia streams with different initial ammonia concentrations (1.7–4.0 g/L) were treated by LLMCs to produce liquid ammonium salt fertilizers (as NH4NO3 and NH4H2PO4). Then, these ammonium solutions were concentrated by ED in order to achieve the nitrogen content required for direct application in agriculture for fertigation. After the LLMC process, the fertilizer obtained was composed of approximately 5.1% or 10.1% (w/w) nitrogen, depending on the initial ammonia concentration. After that, it was possible to concentrate these ammonium salts by a factor of 1.6 ± 0.3 using ED with an optimal energy consumption of 0.21 ± 0.08 kWh/kg ammonium salt and 93.1 ± 4.2% of faradaic yield. This gave a liquid fertilizer composed of 15.6% (w/w) nitrogen as NH4NO3. Overall, it was possible to integrate two innovative membrane technologies for the valorisation and concentration of nutrients from ammonia wastewater streams.
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•Ammonia is a non-environmental friendly specie since it could cause eutrophication.•LLMC can convert ammonia into ammonium salts by using an acid stripping solution.•Ammonium salts can be used as liquid fertilizers due to its N content.•Ammonium salts were concentrated by ED to achieve N fertilizers requirements.•LLMC + ED integration was used to valorize and concentrate nutrients from wastewater.
Nitrogen (N) is a macronutrient that, together with P and K, is vital for improving agricultural yields, but its excessive use in crop fertilisation and presence in treated wastewater and sludge are ...generating emissions both into the atmosphere and into natural water bodies, which leads to eutrophication events. The Haber–Bosch process is energy-intensive and it is the main chemical route to produce reactive nitrogen for the production of fertilisers. Furthermore, there is a strong dependence on imports of reactive nitrogen in Spain and Europe. For these reasons, it is necessary to propose sustainable alternatives that allow solving environmental and supply problems, in addition to proposing efficient management schemes that fit into the circular economy approach. In this context, a nitrogen flow analysis (NFA) was carried out for Spain with the year 2016 as reference. To assess some interactions and flows of N, specific sub-models were also considered for the agriculture and waste management systems. For the food and non-food flow systems, country-specific data were considered. The sectors covered were crop production (CP), animal production (AP), food processing (FP), non-food production (NF) and human consumption (HC). The results reveal a total annual import of 2142 kt N/y, of which 43 % accumulated in stocks of soils and water bodies (913 kt N/y). The largest proportion of losses was associated with emissions from agriculture (724 kt N/y to water bodies and 132 kt N/y accumulated in soils), followed by industry emissions to the atmosphere (122 kt N/y). Wastewater treatment plants (WWTPs) received around 67 kt N/y, of which 26 % was removed as biosolids and 20 % of these biosolids were recovered to be used for fertilising applications. The 49 kt N/y discharged in the final treated effluent represented 79 % of the total loss of reactive nitrogen to water bodies. In addition, an analysis of N-use efficiency and the actions required for its improvement in Spain, as well as the impact of the current diet on the N cycle, was carried out.
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•A nitrogen flow analysis was carried out for Spain with the year 2016 as reference.•The largest proportion of losses was associated with air emissions from agriculture and industry.•Results highlight the dependence on products with high N content from third markets.•The efficiency of N use and the impact of current diet on N cycling have been evaluated.•A circular strategy involves recovering the nutrients present in WW and transforming them into fertilisers.
Nanofiltration (NF), as a selective Mg(II) and Ca(II) separation and concentration treatment, and electrodialysis with bipolar membranes (EDBM) were evaluated for the valorization of seawater ...desalination reverse osmosis brines (60NaCl/L) to produce both rich Mg(II) and Ca(II) brines for phosphate recovery and HCl and NaOH as chemicals for desalination treatments.
A NF pilot plant, using NF270 membranes at 20bar, provided a rich Mg(II) (8.3gMg(II)/L) and Ca(II) (2.1gCa(II)/L) brine on the concentrated stream with enrichment factors of 3.2 for Mg(II) and 2.5 for Ca(II). The NF permeate stream containing 50±2gNaCl/L was treated to remove residual Mg(II) (760mg/L) and Ca(II) (415mg/L) by chemical precipitation with Na2CO3 and NaOH before the EDBM unit. Divalent cations free brine containing NaCl (50gNaCl/L) were fed into the EDBM stack in order to produce NaOH and HCl under recirculation configuration. Constant voltage and acid and base concentrations at different initial conditions were evaluated to obtain the maximum acid and base concentration (approximately 1M NaOH/HCl) at 9V. No substantial effect of initial acid and base concentrations on the overall performance was observed. An energy consumption of 2.6kWh/kg NaOH and current efficiency of 77±3% were calculated.
•NF was used to concentrate and separate Ca–Mg from RO brine for phosphate recovery.•NF permeate stream precipitation treatment was done to remove residual Ca and Mg.•EDBM was applied to produce HCl and NaOH as chemicals for desalination treatments.•Rich Mg and Ca concentrate stream and rich NaCl permeate stream were obtained by NF.•NaOH and HCl up to 1M were obtained at 9V by EDBM using RO divalent free brines.
•A biogas deep treatment was installed and operated at pilot-scale in a WWTP in Spain.•The H2S adsorption mechanism on the iron adsorbent was oriented to oxidation to S(s).•Siloxane D4 was ...responsible of the adsorption breakthrough on the activated carbon.•The integration of biogas treatment and fuel cell systems is technically possible.•Cascade configuration reduces operation cost compared to stand alone sorption systems.
Biogas from anaerobic digestion is a powerful renewable fuel that can be used as a feedstock for fuel cell systems. A biogas deep treatment was installed and operated at pilot plant level in a Waste Water Treatment Plant (WWTP) in Spain in order to demonstrate the integration opportunities with Solid Oxide Fuel Cell (SOFC) technologies. The three-stage polishing system based on adsorption consisted of: (i) a regenerable iron-based adsorbent unit to remove H2S, (ii) a biogas drying unit to remove moisture and (iii) an activated carbon unit to remove the remaining trace components (siloxanes, linear and aromatic hydrocarbons). The biogas entering the polishing system was previously treated in a biotrickling filter for primary H2S abatement. Removal efficiencies on the iron-based adsorbent were over 99% and adsorption capacity was calculated to be of 21%wt. An adsorption mechanism for H2S chemisorption oriented to oxidation to elemental sulphur rather than to crystalline FeS(s) was proposed and could explain the low efficiency of the regeneration process. The remaining contaminant traces were efficiently removed in the drying and activated carbon unit and concentration levels below 0.1mg/Nm3 were obtained. A roll-up phenomenon with siloxane D4, which was responsible of adsorption breakthrough on the activated carbon filters, was postulated; and leaded to an overall adsorption capacity of 2%wt. The economic assessment concluded that the cascade configuration of an upstream H2S abatement followed by downstream adsorption technologies, compared to stand-alone adsorption systems, divides the overall treatment cost by three; increasing the profitability of biogas-powered fuel cell projects.
Granular activated carbon (GAC) was evaluated as a suitable sorbent for polycyclic aromatic hydrocarbons (PAHs) removal from aqueous solutions. For this purpose, kinetic measurements on the ...extraction of a family of six PAHs were taken. A morphology study was performed by means of a scanning electron microscopy (SEM) analysis of GAC samples. Analyses of the batch rate data for each PAH were carried out using two kinetic models: the homogenous particle diffusion model (HPDM) and the shell progressive model (SPM). The process was controlled by diffusion rate the solutes (PAHs) that penetrated the reacted layer at PAH concentrations in the range of 0.2–10
mg
L
−1. The effective particle diffusion coefficients (
D
eff) derived from the two models were determined from the batch rate data. The Weber and Morris intraparticle diffusion model made a double contribution to the surface and pore diffusivities in the sorption process. The
D
eff values derived from both the HPMD and SPM equations varied from 1.1
×
10
−13 to 6.0
×
10
−14
m
2
s
−1.
The simplest model, the pore diffusion model, was applied first for data analysis. The model of the next level of complexity, the surface diffusion model, was applied in order to gain a deeper understanding of the diffusion process. This model is able to explain the data, and the apparent surface diffusivities are in the same order of magnitude as the values for the sorption of functionalized aromatic hydrocarbons (phenols and sulphonates) that are described in the literature.
Acid mine waters (AMWs), generated in the processing of polymetallic sulphides, contain copper and zinc as the main valuable transition metal ions, which are typically removed by liming, due to their ...great environmental impact. In this context, this work proposes the integration of selective precipitation (SP) and ion-exchange (IX) processes for the separation and recovery of both valuable metals to encourage on-site and off-site management options promoting valorisation routes. Thus, the main objectives of this work were (i) the selective removal of Fe(III) and Al(III), using NaOH under pH control (pH < 5) to avoid the precipitation of Cu(II) and Zn(II) and (ii) the evaluation of a solvent-impregnated resin (Lewatit VP OC 1026, named VP1026) and a cation IX resin (Lewatit TP 207, named TP207) for the sequential extraction of both metal ions from AMW (batch and column experiments).
Results indicated that the metallic pollution load was mostly removed during the SP process of Fe(III) (>99%) and Al(III) (>90%) as hydroxylsulphates (e.g., schwertmannite and basaluminite). The metal extraction profiles were determined for both metals from pH 1 to pH 5 by batch experiments, and indicated that the best extraction of Zn(II) was obtained using VP1026, being higher than 96% (pH = 2.6–2.8), whereas TP207 extraction performance was optimal for Cu(II) extraction (>99%) at pH = 3–4. Moreover, in dynamic experiments using a fixed-bed configuration, it was possible to separate and concentrate Zn(II) (concentration factor = 10) and Cu(II) (concentration factor = 40) using VP1026 and TP207, respectively.
Overall, the integration of SP and IX processes showed a great potential in the separation and recovery of valuable metals from mine waters to promote a circular economy, based on the management proposal for non-ferrous metallurgical industries. The recovered Zn-rich and Cu-rich sulphuric concentrated streams were theoretically evaluated for further on-site or off-site re-use treatments (e.g., electrowinning, precipitation, crystallization).
•Selective precipitation and ion-exchange process integration for Zn and Cu recovery.•Fe (>99%) and Al (>90%) were removed as hydroxylsulphates in the precipitation step.•Zn separation by Lewatit VP 1026 resin (>96% extraction, CF = 10) at pH > 2.5•Lewatit TP 207 resin was used for Cu separation (>99% extraction, CF = 40) at pH > 3.•On-site/off-site managements were proposed for non-ferrous metallurgical plants.
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