Recent developments in hazardous pollutants removal from wastewater and water reuse within a circular economy

Data availability: The authors declare that the data supporting the findings of this study are available within the manuscript. Further data can be requested (if need be) by contacting the corresponding author.Copyright © The Author(s) 2022. Recent advances in wastewater treatment processes have resulted in high removal efficiencies for various hazardous pollutants. Nevertheless, some technologies are more suitable for targeting specific contaminants than others. We comprehensively reviewed the recent advances in removing hazardous pollutants from industrial wastewater through membrane technologies, adsorption, Fenton-based processes, advanced oxidation processes (AOP), and hybrid systems such as electrically-enhanced membrane bioreactors (eMBRs), and integrated eMBR-adsorption system. Each technology’s key features are compared, and recent modifications to the conventional treatment approaches and limitations of advanced treatment systems are highlighted. The removal of emerging contaminants such as pharmaceuticals from wastewater is also discussed.Khalifa University through the Center for Membranes and Advanced Water Technology (CMAT), under grant number RC2-2018-009

Assessment and rationalization of water quality monitoring network: a multivariate statistical approach to the Kabbini River (India)

The establishment of an efficient surface water quality monitoring (WQM) network is a critical component in the assessment, restoration and protection of river water quality. A periodic evaluation of monitoring network is mandatory to ensure effective data collection and possible redesigning of existing network in a river catchment. In this study, the efficacy and appropriateness of existing water quality monitoring network in the Kabbini River basin of Kerala, India is presented. Significant multivariate statistical techniques like principal component analysis (PCA) and principal factor analysis (PFA) have been employed to evaluate the efficiency of the surface water quality monitoring network with monitoring stations as the evaluated variables for the interpretation of complex data matrix of the river basin. The main objective is to identify significant monitoring stations that must essentially be included in assessing annual and seasonal variations of river water quality. Moreover, the significance of seasonal redesign of the monitoring network was also investigated to capture valuable information on water quality from the network. Results identified few monitoring stations as insignificant in explaining the annual variance of the dataset. Moreover, the seasonal redesign of the monitoring network through a multivariate statistical framework was found to capture valuable information from the system, thus making the network more efficient. Cluster analysis (CA) classified the sampling sites into different groups based on similarity in water quality characteristics. The PCA/PFA identified significant latent factors standing for different pollution sources such as organic pollution, industrial pollution, diffuse pollution and faecal contamination. Thus, the present study illustrates that various multivariate statistical techniques can be effectively employed in sustainable management of water resources. Highlights The effectiveness of existing river water quality monitoring network is assessed Significance of seasonal redesign of the monitoring network is demonstrated Rationalization of water quality parameters is performed in a statistical framework

Understanding wetting phenomena in membrane distillation and how operational parameters can affect it

Direct contact membrane distillation experiments were carried out under this work to study the influence of operational variables on membrane wetting. In the first part of this work, experiments were designed according to a Box-Behnken methodology and results were analyzed statistically using Pearson correlation coefficients, principal component/factor analysis and cluster analysis. The independent operational parameters were the temperatures of both the hot and cold streams (Tf, Tc) and their flow rates (Ff, Fc). The analyzed responses were the time and rate of wetting along with distillate flux. Statistical analysis showed strong evidence of a relationship between the selected variables and the wetting patterns. In general, parameters enhancing flux production led to suppression of wetting (both delayed wetting and reduced wetting rate). The second part of the work focused on reversing the wetting with minimal operation disruption by varying the operational parameters. The data generated helped in understanding the salt passage and wetting mechanisms. The wetting hypothesis developed herein is based on water bridging as a consequence of the weak hydrophobicity of the PVDF membrane and a net absolute transmembrane pressure. Data were analyzed through the Peclet number, the Poiseuille flow and a mass balance in order to understand the interplay between diffusion and convection/advection. High transmembrane temperature (¿T) (¿T=Tf-Tc) counteracts the build-up of a net absolute transmembrane pressure and reduces the viscous liquid flux. In this case, the diffusion of salt through the stagnant water layer in the membrane pores (a much slower mechanism) becomes more important and the wetting rate can be reduced and further reversed.Peer ReviewedPostprint (author's final draft

Synergistic effect of humic acid on alkali pretreatment of sugarcane bagasse for the recovery of lignin with phenomenal properties

Lignin forms a recalcitrant structure in lignocellulosic biomass and hence huge amount of enzymes are required for disintegrating it into their subsequent components, like glucose and other by-products. Thus, the pretreatment is an ineluctable step in the bioethanol scheme for the delignification of biomass and also the recovery of lignin, an emerging value added polymer in many industrial applications. A green facile method was developed wherein humic acid (HA) acts as a catalyst and surfactant in the alkali pretreatment of sugarcane bagasse for the step reduction in lignin recovery scheme with phenomenal properties and enhanced enzymatic-hydrolysis. HA assisted experiments were performed with and without calcium chloride (CaCl2). Effective disintegration of lignocellulose by the cleavage of β-O-4 moieties resulted in forming lignin and hydrolyzable biomaterial via two pathways. Possible covalent linkages between the HA and lignin resulted in the release of esters as a byproduct. Thus, the delignified biomass, the isolated lignin and a variety of esters, could be valorised in various industrial applications. The biomass was characterized by XRD and SEM analysis. The isolated lignin was characterized using FTIR, NMR, GPC, SEM, and TGA – DTA studies. The yield of recovered pure lignin for the two process was 90–100%, as measured through gravimetric analysis. The produced esters were confirmed using FTIR studies. Batch enzymatic hydrolysis was performed for the HA assisted de-lignified bagasse (without CaCl2), which demonstrated a 19% increase in glucose yield compared to the alkali treated bagasse. The produced hydrolysates were subjected to fermentation for the production of ethanol

Thin film deposition techniques for polymeric membranes– A review

Thin film deposition (TFD) allows for precise tuning of the chemical and physical properties of a membrane to improve performance, including the selectivity, flux, chemical resistance, and antifouling and antimicrobial properties. TFD techniques have a unique advantage over other traditional surface modification methods (e.g., grafting) vis-à-vis their applicability to low-surface energy polymers, which usually resist modification through other techniques. TFD is also an economical approach to surface modification as inexpensive base materials can be functionalized with small amounts of more expensive active chemistries. Here, we review a range of TFD techniques and their applicability for the modification of polymeric membranes to improve durability and performance across water treatment applications. The discussed techniques include sputtering, thermal evaporation, chemical vapor deposition, atomic layer deposition, electrochemical deposition, electron beam deposition, Langmuir-Blodgett deposition, and colloidal deposition. We review how recent developments in TFD techniques have made these methods a competitive alternative to other methods of membrane modification and discuss how modified membranes lead to improved performance for water applications, including microfiltration, nanofiltration, reverse osmosis, and membrane distillation. Relative advantages of each coating process are discussed. We also discuss how process parameters for the various TFD techniques (deposition speed, versatility, conformality, thickness, bonding strength, temperature, etc.) influence the final chemical and physical properties of modified membranes. We conclude with an outlook for how further developments in TFD techniques will continue to introduce new possibilities for unique membrane properties and applications

Polydopamine-coated graphene oxide nanosheets embedded in sulfonated poly (ether sulfone) hybrid UF membranes with superior antifouling properties for water treatment

A novel high-performance hybrid ultrafiltration (UF) membrane was fabricated by blending polydopamine-coated graphene oxide (PDGO) nanosheets with sulfonated poly(ether sulfone) (SPES) via phase inversion method and tested for the removal of natural organic matter (humic acid; HA) from aqueous solution. The PDGO nanosheets were synthesized via self-polymerization of dopamine with GO nanosheets in alkaline tris-buffer solution at room temperature for 24 h and were fully characterized. Hybrid SPES membranes were prepared by incorporating 1–10 wt% of PDGO, which were further characterized by Raman spectroscopy, surface zeta potential, and field emission scanning electron microscopy to confirm membrane stability without any defects even by adding up to 10 wt%, of PDGO nanosheets. The membranes demonstrated a significant increase in hydrophilicity, water flux, and retention rate for HA (RHA). For instance, water permeability with 5 wt% PDGO (M5) (680.7 L m−2 h−1 bar−1) was ca. 1.8-folds that of the pristine SPES membrane (380.8 L m−2 h−1 bar−1), while maintaining an HA rejection (RHA) of 91.7% for a 50 ppm HA feed solution. This was accompanied by a distinct increase in surface hydrophilicity of M5, which showed a water contact angle of 27.8°, well below that of pristine SPES membrane (59.1°). The hybrid UF membranes also demonstrated a significant reduction in HA adhesion onto the membrane surface along with a superior antifouling performance for the membrane containing 10 wt% PDGO, giving irreversible fouling ratio (Rir) of only 6.9% compared to 32.7% for the pristine membrane

Recent developments in hazardous pollutants removal from wastewater and water reuse within a circular economy

Recent advances in wastewater treatment processes have resulted in high removal efficiencies for various hazardous pollutants. Nevertheless, some technologies are more suitable for targeting specific contaminants than others. We comprehensively reviewed the recent advances in removing hazardous pollutants from industrial wastewater through membrane technologies, adsorption, Fenton-based processes, advanced oxidation processes (AOP), and hybrid systems such as electrically-enhanced membrane bioreactors (eMBRs), and integrated eMBR-adsorption system. Each technology's key features are compared, and recent modifications to the conventional treatment approaches and limitations of advanced treatment systems are highlighted. The removal of emerging contaminants such as pharmaceuticals from wastewater is also discussed

Synthesis of polydopamine coated tungsten oxide@ poly(vinylidene fluoride-co-hexafluoropropylene) electrospun nanofibers as multifunctional membranes for water applications

In this work, electrospun poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) nanofiber membranes were loaded with tungsten oxide (WO3) nanoparticles, surface coated with polydopamine (PDA) hierarchical structures, and tested in oil/water separation, photothermal water evaporation, and degradation of ampicillin. The electrospun nanofiber membranes (ENMs) consisted of three layers and the WO3 nanoparticles were incorporated into the top layer to increase their surface exposure. These layers were then heat-pressed for dimensional stability and surface coated with PDA hierarchical structures. Characterization was conducted using microscopic, goniometric, gravimetric, and spectroscopic methods. All ENMs displayed randomly oriented, smooth microporous structure and EDS mapping revealed a uniform distribution of WO3 nanoparticles on the nanofiber matrix. WO3-blended ENMs showed improved mechanical strength, higher UV/Vis absorption, and similar thickness as pristine ENM. PDA deposition has reduced the water contact angle of pristine PVDF-HFP membrane from 130.3 to 0 degrees, whereas, the underwater oil contact angle has increased from 55.8 to 159.7 degrees. The PDA-coated ENMs exhibited enhanced oil/water separation with 384.3 L m 2h- 1 (LMH) of flux and 97.6% oil rejection when filtered under gravity. Photothermal interfacial evaporation and ampicillin degradation tests also demonstrated the multifunctionality and exciting features of the fabricated membranes for a wide range of applications

Reversing membrane wetting in membrane distillation: comparing dryout to backwashing with pressurized air

The critical failure mode for membrane distillation (MD) desalination is wetting through the pores of the hydrophobic membrane, which allows the saline solution to leak through and contaminate the permeate. The standard practice for reversing membrane wetting is to dry out the membrane for several hours before resuming the desalination process. An alternative method for mitigating MD membrane wetting is examined in this study, wherein pressurized air is pushed through the membrane from the permeate side for several seconds, forcing trapped water out before it can evaporate. To compare the wetting reversal methods, the liquid entry pressure (LEP) was surpassed with saline water at varied salinity. Then, either a 24+ hour dryout, a 10 second pressurized air treatment, or both were applied, followed by remeasuring the LEP. Pressurized air backwashing restored the LEP to 75% of the original value for lower salinity feeds. The backwashing method is hypothesized to achieve this superior result because it removes saline solution from the membrane without separating water and salts by vaporization, whereas the dryout method causes seawater within the membrane to evaporate, leaving crystalline solutes trapped within the membrane. Such trapped particles may act as a path for rewetting, and also impair permeate flux and system energy efficiency. For all three methods, membranes tested with higher salinity water had lower LEP restoration irrespective of the restoration technique used. A method for testing LEP with more accuracy was also developed, using stepwise pressure increases. SEM images showed that the restoration methods did not alter the membranes themselves, although there remains a possibility that the air backwashing can cause superficial tears. Keywords: membrane distillation, wetting, dryout, air backwash, cleaning, crystallizationMIT Masdar Program (Reference 02/MI/MI/CP/11/07633/GEN/G/00