The removal of pathogenic bacteria and dissolved organic matter from freshwater using microporous membranes: insights into biofilm formation and fouling reversibility.

Pathogenic bacteria in drinking-water pose a health risk to consumers, as they compromise the quality of portable water. Chemical disinfection of water containing dissolved organic matter (DOM) causes harmful disinfection by-products. In this work, 4-hydroxybenzoic acid (4-HBA) blended polyethersulfone membranes were fabricated and characterised using microscopic and spectroscopic techniques. The membranes were evaluated for the removal of bacteria and DOM from synthetic and environmental water. Permeate flux increased from 287.30 to 374.60 l m-2 h-1 at 3 bars when 4-HBA increased from 0 to 1.5 wt.%, suggesting that 4-HBA influenced the membrane's affinity for water. Furthermore, 4-HBA demonstrated antimicrobial properties by inhibiting bacterial growth. The membrane with 1 wt.% 4-HBA recorded 99.4 and 100% bacteria removal in synthetic and environmental water, respectively. Additionally, DOM removal of 55-73% was achieved. A flux recovery ratio (FRR) of 94.6% was obtained when a mixture of bacteria and humic acid was filtered, implying better fouling layer reversibility during cleaning. Furthermore, 100% FRR was achieved when a multimedia granular filtration step was installed prior to membrane filtration. The results illustrated that the membranes had a high permeate flux with low irreversible fouling. This indicated the potential of the membranes in treating complex feed streams using simple cleaning protocols.

Utilization of biochar for remediation of heavy metals in aqueous environments: A review and bibliometric analysis.

Biochar usage for removing heavy metals from aqueous environments has emerged as a promising research area with significant environmental and economic benefits. Using the PICO approach, the research question aimed to explore using biochar to remove heavy metals from aqueous media. We merged the data from Scopus and the Web of Science Core Collection databases to acquire a comprehensive perspective of the subject. The PRISMA guidelines were applied to establish the search parameters, identify the appropriate articles, and collect the bibliographic information from the publications between 2010 and 2022. The bibliometric analysis showed that biochar-based heavy metal remediation is a research field with increasing scholarly attention. The removal of Cr(VI), Pb(II), Cd(II), and Cu(II) was the most studied among the heavy metals. We identified five main clusters centered on adsorption, water treatment, adsorption models, analytical techniques, and hydrothermal carbonization by performing keyword co-occurrence analysis. Trending topics include biochar reusability, modification, acid mine drainage (AMD), wastewater treatment, and hydrochar. The reutilization of heavy metal-loaded spent biochar includes transforming it into electrodes for supercapacitors or stable catalyst materials. This study provides a comprehensive overview of biochar-based heavy metal remediation in aquatic environments and highlights knowledge gaps and future research directions.

Electrocatalytic oxidation of pyrrole on a quasi-reversible silver nanodumbbell particle surface for supramolecular porphyrin production.

Photoactive supramolecular porphyrin assemblies are attractive molecules for light-harvesting applications. This is due to their relatively non-toxicity, biological activities and charge and energy exchange characteristics. However, the extreme cost associated with their synthesis and requirements for toxic organic solvents during purification pose a challenge to the sustainability characteristics of their applications. This work presents the first report on the sustainable synthesis, spectroscopic and photophysical characterizations of a near-infrared (NIR) absorbing Ca(II)-meso-tetrakis (4-hydroxyphenyl)porphyrin using an electrolyzed pyrrole solution. The latter was obtained by cycling the pyrrole solution across the silver nanodumbbell particle surface at room temperature. The electrolyzed solution condensed readily with acidified p-hydroxybenzaldehyde, producing the targeted purple porphyrin. The non-electrolyzed pyrrole solution formed a green substance with significantly different optical properties. Remarkable differences were observed in the voltammograms of the silver nanodumbbell particles and those of the conventional gold electrode during the pyrrole cycling, suggesting different routes of porphyrin formation. The rationale behind these formations and the associated mechanisms were extensively discussed. Metalation with aqueous Ca2+ ion caused a Stokes shift of 38.75 eV. The current study shows the advantage of the electrochemical method towards obtaining sustainable light-harvesting porphyrin at room temperature without the need for high-energy-dependent conventional processes.

Detection and Quantification of Bisphenol A in Surface Water Using Absorbance-Transmittance and Fluorescence Excitation-Emission Matrices (A-TEEM) Coupled with Multiway Techniques.

In the present protocol, we determined the presence and concentrations of bisphenol A (BPA) spiked in surface water samples using EEM fluorescence spectroscopy in conjunction with modelling using partial least squares (PLS) and parallel factor (PARAFAC). PARAFAC modelling of the EEM fluorescence data obtained from surface water samples contaminated with BPA unraveled four fluorophores including BPA. The best outcomes were obtained for BPA concentration (R2 = 0.996; standard deviation to prediction error's root mean square ratio (RPD) = 3.41; and a Pearson's r value of 0.998). With these values of R2 and Pearson's r, the PLS model showed a strong correlation between the predicted and measured BPA concentrations. The detection and quantification limits of the method were 3.512 and 11.708 micro molar (µM), respectively. In conclusion, BPA can be precisely detected and its concentration in surface water predicted using the PARAFAC and PLS models developed in this study and fluorescence EEM data collected from BPA-contaminated water. It is necessary to spatially relate surface water contamination data with other datasets in order to connect drinking water quality issues with health, environmental restoration, and environmental justice concerns.

Adsorptive removal of malachite green dye from aqueous solution using Rumex abyssinicus derived activated carbon.

The potential for malachite green dye saturated effluent to severely affect the environment and human health has prompted the search for effective treatment technologies. Thus, this study was conducted with the goal of developing activated carbon from Rumex abyssinicus for the adsorptive removal of malachite green dye from an aqueous solution. Unit operations such as drying, size reduction, impregnation with H3PO4, and thermal activation were used during the preparation of the activated carbon. An experiment was designed considering four main variables at their respective three levels: initial dye concentration (50, 100, and 150 mg/L), pH (3, 6, and 9), contact period (20, 40, and 60 min), and adsorbent dosage (0.05, 0.01, and 0.15 g/100 mL). Optimization of the batch adsorption process was carried out using the Response Surface methodology's Box Behnken approach. The characterization of the activated carbon was described by SEM for surface morphology with cracks and highly porous morphology, FTIR for multi-functional groups O-H at 3506.74 cm-1 and 3290.70 cm-1, carbonyl group stretching from aldehyde and ketone (1900-1700 cm-1), stretching motion of aromatic ring C=C (1543.12 cm-1), stretching motion of -C-H (1500-1200 cm-1), vibrational and stretching motion of -OH (1250.79 cm-1), and vibrational motion of C-O-C (1049.32 cm-1), pHpzc of 5.1, BET for the specific surface area of 962.3 m2/g, and XRD for the presence of amorphous structure. The maximum and minimum dye removal efficiencies of 99.9% and 62.4% were observed at their respective experimental conditions of (100 mg/L, 0.10 mg/100 mL, pH 6, and 40 min) and (100 mg/L, 0.15 mg/100 mL, pH 3, and 20 min), respectively. Langmuir, Freundlich, Toth, and Koble-Corrigan models were used to evaluate the experimental data, in which Koble-Corrigan model was found to be the best fit with the highest value of R2 0.998. In addition to this, the kinetic studies were undertaken using pseudo-first-order, pseudo-second-order, intraparticle diffusion, and Boyd models, and as a result, the pseudo-second-order model proved to have a better fit among the kinetic models. The kinetics and isotherm analysis revealed that the nature of the adsorption to be homogenous and monolayer surfaces driven by chemosorption. Furthermore, the thermodynamics study revealed the nature of adsorption to be feasible, spontaneous, and endothermic. On the other hand, the reusability study depicted the fact that the adsorbent can be utilized for five cycles with a negligible drop in the removal efficiencies from 99.9 to 95.2%. Finally, the low-cost, environmentally benign, and high adsorption capacity of the adsorbent material derived from Rumex abyssinicus stem could be used to treat industrial effluents.

Electrochemical, surface morphological and computational evaluation on carbohydrazide Schiff bases as corrosion inhibitor for mild steel in acidic medium.

Anticorrosion and adsorption behaviour of synthesized carbohydrazide Schiff bases, namely (Z)-N'-(4-hydroxy-3-methoxybenzylidene)-6-methyl-2-oxo-4-phenyl-1,2,3,4-tetrahydropyrimidine-5-carbohydrazide(MBTC) and (Z)-N'-(3,4-dichlorobenzylidene)-6-methyl-2-oxo-4-phenyl-1,2,3,4-tetrahydropyrimidine-5-carbohydrazide (CBTC) was examined for mild steel (MS) in 15% HCl medium. The corrosion inhibition study was performed by using gravimetric, thermodynamic, electrochemical and theoretical studies including density functional theory (DFT), molecular dynamic simulation (MDS) and Monte Carlo simulations (MCS). The outcomes in terms of corrosion inhibition efficiency using electrochemical impedance spectroscopy (EIS) method at 303 K and 150 ppm concentration were 96.75% for MBTC and 95.14% for CBTC. Both inhibitors adsorbed on the MS surface through physical as well as chemical adsorption and followed the Langmuir isotherm. The mixed-type nature of both inhibitors was identified by polarization results. Surface analysis was done using FESEM, EDX, AFM and XPS studies and results showed that a protective layer of inhibitor molecules was developed over the surface of MS. The results of DFT, MCS and MDS are in accordance with experimental results obtained by weight loss and electrochemical methods.

Adsorption of chromium from electroplating wastewater using activated carbon developed from water hyacinth.

Industrial wastewater polluted with high concentrations of Cr is commonly discharged into water resources without proper treatment. This gives rise to the deterioration of water quality and imposes adverse effects on public health. Therefore, this study is aimed at removing Cr from electroplating wastewater using activated carbon produced from water hyacinth under a full factorial experimental design with three factors and three levels (pH,2,5 and 8, adsorbent dose 0.5,1and1.5 in 100 mL and contact time 30, 60 and120 min). A phosphoric acid solution of 37% was used to activate the carbon, which was then subjected to thermal decomposition for 15 min at 500 °C. The activated carbon was characterized by the presence of a high surface area (203.83 m2/g) of BET, cracking of adsorbent beads of SEM morphology, amorphous nature of XRD, and many functional groups of FTIR such as hydroxyl (3283 cm-1), alkane (2920 cm-1), nitrile (2114 cm-1) and aromatics (1613 cm-1). The minimum Cr adsorption performance of 15.6% was obtained whereas maximum removal of 90.4% was recorded at the experimental condition of pH 2, adsorbent dose of 1.5 g/100 mL, and contact time of 120 min at a fixed value of initial Cr concentration of 100 mg/L. Similarly, the maximum Cr removal from real electroplating wastewater was 81.2% at this optimum point. Langmuir's model best described the experimental value at R2 0.96 which implies the adsorption is chemically bonded, homogeneous, and monolayer. Pseudo-second-order model best fits with the experimental data with R2 value of 0.99. The adsorbent was regenerated for seven cycles and the removal efficiency decreased from 93.25% to 21.35%. Finally, this technology is promising to be scaled up to an industrial level.

Isotherms and Kinetic Studies of Copper Removal from Textile Wastewater and Aqueous Solution Using Powdered Banana Peel Waste as an Adsorbent in Batch Adsorption Systems.

Heavy metals that are present in surface water and wastewater are becoming a severe environmental problem. Because of its toxicity, heavy metal removal has become the main priority for environmental concerns. Banana peels are low-cost agricultural waste that could be used for heavy metal adsorption in wastewater. The main objective of this study is to evaluate the effective powdered banana peel for the removal of copper (II) from aqueous solutions and real wastewater. The banana peels were collected from domestic waste and ground to get a particle size of 150 µm. Powdered banana peel waste adsorbent (PBPWA) contained moisture content, ash content, volatile matter, and bulk density of 3.8%, 3.5%, 37.5%, and 0.02 g/cm3, respectively. The Fourier-transform infrared spectroscopy (FTIR) results showed that the alkyne, aldehyde, and amide functional groups were dominant in the powdered banana peel surface, and the scanning electron microscope showed the morphology of the adsorbent. Physicochemical characteristics of the raw wastewater revealed that the concentration of Cu (II), Pb (II), COD, BOD5, and Cd (II) were 2.75 mg/L, 2.02 mg/L, 612.16 mg/L, 185.35 mg/L, and 0.01 mg/L, respectively. At pH 5, adsorbent dose of 2g/100 mL, initial copper (II) concentration of 80 mg/L, and contact time of 90 min, the maximum removal efficiency of synthetic wastewater was 96.8% and textile wastewater was 69.0%. The adsorption isotherm fitted well with the Langmuir isotherm model at R2 = 0.99. The kinetics of copper (II) adsorption followed the second-order kinetic model better. Finally, these studies showed that banana peel bio-adsorbent is a potential adsorbent for heavy metal removal from synthetic and textile wastewater.

Adsorption of methylene blue from textile industrial wastewater using activated carbon developed from Rumex abyssinicus plant.

Methylene blue (MB) is abundantly found in textile industrial effluent which can cause severe health problems for public and environmental ecology. Therefore, this study aimed to remove MB from textile wastewater using the activated carbon developed from Rumex abyssinicus. The adsorbent was activated using chemical and thermal methods, and then it was characterized by SEM, FTIR, BET, XRD, and pH zero-point charge (pHpzc). The adsorption isotherm and kinetics were also investigated. The experimental design was composed of four factors at three levels (pH (3, 6, and 9), initial MB concentration (100, 150, and 200 mg/L), adsorbent dosage (20, 40, and 60 mg/100 mL), and contact time (20, 40, and 60 min)). The adsorption interaction was evaluated using response surface methodology. The characterization of a Rumex abyssinicus activated carbon was found to have multiple functional groups (FTIR), an amorphous structure (XRD), crack with ups and down morphology (SEM), pHpzc of 5.03 and a high BET-specific surface area of 2522 m2/g. The optimization of MB dye removal was carried out using the Response Surface methodology coupled with the Box Behnken approach. The maximum removal efficiency of 99.9% was recorded at optimum conditions of pH 9, MB concentration of 100 mg/L, the adsorbent dosage of 60 mg/100 mL, and contact time of 60 min. Among the three adsorption isotherm models, the Freundlich isotherm model was the best fit with an experimental value at R2 0.99 showing the adsorption process was heterogeneous and multilayer whereas the kinetics study revealed that pseudo-second-order at R2 0.88. Finally, this adsorption process is quite promising to be used at an industrial level.

Optimization of Cr (VI) removal from aqueous solution with activated carbon derived from Eichhornia crassipes under response surface methodology.

Tannery industries' effluent contains a high concentration of Cr (VI) which has the potential to affect the environment and public health. Therefore, this study aimed to investigate the optimization of Cr (VI) adsorption by activated carbon (AC) derived from Eichhornia crassipes from an aqueous solution. The adsorbent was activated with dilute sulfuric acid followed by thermal activation. AC was characterized using proximate analysis, SEM, FTIR, X-ray diffraction, and the BET method. The Cr (VI) removal optimization process was performed using a central composite design under the response surface methodology. The proximate analysis showed that the moisture content, volatile matter, ash content, and fixed carbon of the activated carbon were 5.6%, 18.2%, 14.4%, and 61.8% respectively. The surface areas of the Eichhornia crassipes before activation, after activation, and after adsorption were 60.6 g/m2, 794.2 g/m2, and 412.6 g/m2 respectively. A highly porous structure with heterogeneous and irregular shapes was observed in the SEM micrograph. In the FTIR analysis, different peaks are indicated with various functional groups. The intensity of XRD peaks decreased as 2 theta values increased, which indicates the presence of an amorphous carbon arrangement. The point of zero charge (pHpzc) of the activated carbon was found to be 5.20. A maximum Cr (VI) removal of 98.4% was achieved at pH 5, contact time 90 min, adsorbent dose 2 g, and initial Cr (VI) concentration of 2.25 mg/L. Statistically significant interactions (P < 0.05) were observed between the initial Cr (VI) concentration and adsorbent dose as well as the initial Cr (VI) concentration and contact time. Langmuir adsorption isotherm fitted the experimental data best, with an R2 value of 0.99. The separation constant (RL) indicates that the adsorption process is favorable. The kinetic experimental data were best fitted with the pseudo-second-order model with an R2 value of 0.99 whereas the adsorption rate is controlled by intraparticle and extragranular diffusion processes. Generally, the AC has the potential to be a strong adsorbent candidate for wastewater treatment at the industrial level.

Understanding the Principles and Applications of Dual Z-Scheme Heterojunctions: How Far Can We Go?

In the past seven years, dual Z-scheme heterojunctions evolved as favorable approaches for enhanced charge carrier separation through direct or indirect charge transfer transportation mechanisms. The dynamics of the charge transfer is the major strategy for understanding their photoactivity and stability through the formation of distinctive redox centers. The understanding of currently recognized principles for successful fabrication and classification in different energy and pollution remediation strategies is discussed, and a universal charge transfer-type-based classification of dual Z-schemes that can be adopted for Z-scheme and S-scheme heterojunctions is proposed. Methods used for determining the charge transfer as proof of dual Z-scheme existence are outlined. Most importantly, a new macroscopic N-scheme and a triple Z-scheme that can also be adopted as triple S-scheme heterostructures composed of four semiconductors are proposed for generating both oxidatively and reductively empowered systems. The proposed systems are expected to possess properties that enable them to harvest solar light to drive important chemical reactions for different applications.

Porphyrins developed for photoinactivation of microbes in wastewater.

Photodynamic antimicrobial chemotherapy (PACT) is extensively studied as a strategic method to inactivate pathogenic microbes in wastewater for addressing the limitations associated with chlorination, ozonation, and ultraviolet irradiation as disinfection methods, which generally promote the development of resistant genes and harmful by-products such as trihalomethanes. PACT is dependent on photons, oxygen, and a photosensitizer to induce cytotoxic effects on various microbes by generating reactive oxygen species. Photosensitizers such as porphyrins have demonstrated significant microbial inactivation through PACT, hence now explored for wastewater phototreatment. This review aims to evaluate the efficacy of porphyrins and porphyrin-conjugates as photosensitizers for wastewater photoinactivation. Concerns relating to the application of photosensitizers in water treatment are also evaluated. This includes recovery and reuse of the photosensitizer when immobilized on solid supports.

Advances in polymer-based detection of environmental ibuprofen in wastewater.

Globally, ibuprofen is the third most consumed drug and its presence in the environment is a concern because little is known about its adverse effects on humans and aquatic life. Environmentalists have made monitoring and the detection of ibuprofen in biological and environmental matrices a priority. For the detection and monitoring of ibuprofen, sensors and biosensors have provided rapid analysis time, sensitivity, high-throughput screening, and real-time analysis. Researchers are increasingly seeking eco-friendly technology, and this has led to an interest in developing biodegradable, bioavailable, and non-toxic sensors, or biosensors. The integration of polymers into sensor systems has proven to significantly improve sensitivity, selectivity, and stability and minimize sample preparation using bioavailable and biodegradable polymers. This review provides a general overview of perspectives and trends of polymer-based sensors and biosensors for the detection of ibuprofen compared to non-polymer-based sensors.

Modulation of Z-scheme photocatalysts for pharmaceuticals remediation and pathogen inactivation: Design devotion, concept examination, and developments.

The recent outbreak of Covid-19 guarantees overconsumption of different drugs as a necessity to reduce the symptoms caused by this pandemic. This triggers the proliferation of pharmaceuticals into drinking water systems. Is there any hope for access to safe drinking water? Photocatalytic degradation using artificial Z-scheme photocatalysts that has been employed for over a decade conveys a prospect for sustainable clean water supply. It is compelling to comprehensively summarise the state-of-the-art effects of Z-scheme photocatalytic systems towards the removal of pharmaceuticals in water. The principle of Z-scheme and the techniques used to validate the Z-scheme interfacial charge transfer are explored in detail. The application of the Z-scheme photocatalysts towards the degradation of antibiotics, NSAIDs, and bacterial/viral inactivation is deliberated. Conclusions and stimulating standpoints on the challenges of this emergent research direction are presented. The insights and up-to-date information will prompt the up-scaling of Z- scheme photocatalytic systems for commercialization.

Synthesis of biochar-CoFe2O4 nanocomposite for adsorption of methylparaben from wastewater under full factorial experimental design.

The presence of endocrine-disrupting chemicals in municipal wastewater has emerged as a threat to human health and the environment. Therefore, this study aimed to develop biochar-cobalt ferrite (BCF) nanocomposite for the removal of methylparaben from water under the full factorial experimental design of 4 factors with 3 levels (34). The biochar-CoFe2O4 nanocomposite was developed by co-precipitation method from cobalt ferrite and biochar of Eucalyptus tree bark. Adsorbent surface morphology and functional and elemental composition were carried out by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and energy-dispersive X-ray spectroscopy (EDS) techniques which showed the presence of cracks with a rough surface, reasonable surface chemical composition, and many chemical functional groups, respectively. The experimental and predicted adsorption efficiencies ranged from 25.3 to 85.6% and 21.8 to 80.3%, respectively. The maximum adsorption performance (85.6%) reduced the methylparaben concentration from 27.5 to 4.0 mg/L at the optimum condition of adsorbent dose of 55 mg/100 mL, pH 6, contact time 90 min, and the initial methylparaben concentration of 27.5 mg/L. However, the adsorbent dose was the most influential main factor whereas the least influential was the interaction between solution pH and contact time under the regression model. The model also showed that 69% methylparaben removal was described by the regression model. The experimental data best fitted with the Freundlich model indicate multilayer adsorption which is the implication of physisorption. The sorption mechanism is attributed to Vander Waals forces, H-bonding, and dipole interaction. This BCF nanocomposite adsorbent appears to be promising for the removal of methylparaben from wastewater, but a further optimization process is essential to boost the treatment performance.

Modeling the antifouling properties of atomic layer deposition surface-modified ceramic nanofiltration membranes.

This work investigates the enhancement of antifouling properties of ceramic nanofiltration membranes by surface modification via atomic layer deposition (ALD) of TiO2. Feed solutions containing bovine serum albumin (BSA), humic acid (HA) and sodium alginate (SA) were used as model foulants. The classic fouling mechanism models and the modified fouling indices (MFI) were deduced from the flux decline profiles. Surface roughness values of the ALD coated and uncoated membranes were 63 and 71 nm, respectively, while the contact angles were 34.2 and 59.5°, respectively. Thus, coating increased the water affinity of the membrane surfaces and consequently improved the anti-fouling properties. The MFI values and the classic fouling mechanism correlation coefficients for cake filtration for the ALD coated and the uncoated membrane upon SA fouling were 42,963 (R2 = 0.82) and 143,365 sL-2 (R2 = 0.98), respectively, whereas the correlation coefficients for the combined foulants (SA + BSA + HA) were 267,185 (R2 = 0.99) and 9569 sL-2 (R2 = 0.37), respectively. The study showed that ALD can effectively enhance the antifouling properties of ceramic membranes.

Toxicity assessment of TiO2-conjugated Carbon-based nanohybrid material on a freshwater bioindicator cladoceran, Daphnia magna.

The application of nanocomposite materials fabricated from titanium dioxide nanoparticles (TiO2 NPs) and different carbon (C) allotropes have gained popularity in water treatment applications due to their synergistic properties. Studies to date have focused on simple forms of nanomaterials (NMs), however, with the technology development, there is a dramatic increase in production and application of these complex NMs which could result in toxicological impacts on organisms when released into aquatic environments. This raises serious concerns about their safety and the need to ascertain their potential adverse effects on aquatic organisms. While conjugated TiO2 NPs/carbon-based nanohybrids (TiO2/C-NHs) may exhibit enhanced photocatalytic activity, there is no research in the scientific community regarding their toxicological effects on D. magna, which are indicators of freshwater pollution. In this study, two under-represented TiO2/C-NHs (i.e., TiO2- conjugated carbon nanofiber (CNF), and TiO2-conjugated multi-walled carbon nanotube (CNT)) were investigated for their toxic effects on D. magna, through a series of acute toxicity tests with a set of sublethal biochemical biomarkers of oxidative stress. The lethal toxicity and oxidative stress formation of TiO2/C-NHs over 48 h revealed a concentration-dependant increase in D. magna mortality. The primary mechanism identified was the generation of ROS, which was in line with toxicity results. Light microscopy and CytoViva® images visualized D. magna interaction with the NPs, which accumulated and appeared as dark materials in the lines of the gut tract. The collective results indicate that TiO2/C-NHs have the potential to cause an effect on freshwater organisms when released into the environment. However, the relevance of TiO2/C-NHs effects needs further chronic toxicity studies since they show promise to be used in nano-bioremediation materials to treat wastewaters.

The potential of biochar-photocatalytic nanocomposites for removal of organic micropollutants from wastewater.

Biochar (BC)-photocatalyst nanocomposites have emerged as appealing water and wastewater treatment technology. Such nanocomposite materials benefit from the synergistic effect of adsorption and photocatalysis to attain improved removal of pollutants from water and wastewater. Under this review, three BC-based nanocomposite photocatalysts such as BC-TiO2, BC-ZnO, and BC-spinel ferrites were considered. These nanocomposites acquire intrinsic properties to improve the practical limitations of the pristine BC and photocatalysts. The BC-based nanocomposites attained high photocatalytic activity, mechanical hardness, thermal stability, chemically non-reactive, magnetically permeable, reduced energy band gaps, improved reusability, and simplified recovery. Moreover, BC-based photocatalytic nanocomposites showed reduced recombination rates of the electron-hole pairs which are desirable for photocatalytic applications. However, the surface areas of the composites are usually smaller than that of the BC but higher than those of the pristine photocatalysts. Practically, the performances of the nanocomposites are much superior to those of the corresponding pristine components. This hybrid treatment technology is an emerging field and its industrial application is still at an early stage of the investigation. Therefore, exploring the full potential and practical applications of this technology is highly encouraging. Hence, this review focused on the critical evaluation of the most recent research on the synthesis, characterization, and photocatalytic treatment efficiency of the BC photocatalyst nanocomposites towards emerging pollutants in the aqueous medium. Moreover, the influence of various sources of BC feedstocks and their limitations on adsorption and photodegradation activities are discussed in detail. Finally, concluding remarks and future research directions are given to assist and shape the exploration of BC-based nanocomposite photocatalysts in water treatment.

Emerging remediation potentiality of struvite developed from municipal wastewater for the treatment of acid mine drainage.

The valorisation of wastewaters for minerals recovery and their potential beneficiation has gained enormous attention recently. In this study the removal of phosphate and ammonia from municipal wastewater using activated magnesite resulted in the formation of struvite. The optimum conditions for the synthesis of struvite were 60 min of mixing, 300 rpm mixing speed, 1 g of activated magnesite and room temperature, whilst optimum conditions for the treatment of acid mine drainage (AMD) using the synthesized struvite were 45 min of mixing, 20 g of struvite dosage, 1000 mL, and 300 rpm mixing speed. The efficacy of struvite for neutralisation of AMD and attenuation of inorganic contaminants were ≥98.99% for metals (Al3+, Fe3+, and Mn2+) and ≥30% for SO42-. Traces of other metals such as Zn, Cu, Ni, Pb, and Cr were significantly attenuated. Phosphate was fully attenuated from the aqua-sphere. PHREEQC predicted the removal of minerals as oxy-(hydro)-sulphates, oxy-(hydro)-phosphate, metals hydroxides, and other complexes. FE-SEM equipped with FIB and an EDX, XRD, XRF, and FTIR confirmed the synthesis of struvite and fate of chemical species after treatment. This study confirmed the feasibility of recovering phosphate and ammonia as struvite which can be employed for the treatment of AMD.

Characterization of natural organic matter in South African drinking water treatment plants: Towards integrating ceramic membrane filtration.

This work presents the first comprehensive investigation of natural organic matter (NOM) fraction removal using ceramic membranes in South Africa. The rate of removal of bulk NOM (measured as UV254 and DOC % removal), the biodegradable dissolved organic carbon (BDOC) fraction, polarity-based fractions, and fluorescent dissolved organic carbon (FDOM) fractions was investigated from water abstracted from drinking water treatment plants (WTPs) in South Africa. Further, mechanisms of ceramic membrane fouling by waters of South Africa were studied. Ceramic membranes removed more than 80% DOC from samples from coastal WTPs, whereas for inland plants, the removal was between 60% and 75% of DOC. FDOM was removed to at least 80% regardless of the site of the plant. The BDOC removal by the ceramic membranes was above 85%. The hydrophobic fraction was the most amenable to removal by ceramic membranes regardless of the site of sample abstraction (above 60% for all sites). The freshness index (ß:α) correlated strongly to UV254 removal (R2 = 0.96), thus UV254 removal can serve as a proxy for the susceptibility to removal of such class of NOM by ceramic membranes. This investigation demonstrated that ceramic membranes could be a valuable technology if integrated into the existing WTPs. PRACTITIONER POINTS: The removal of bulk parameters by ceramic membrane was greater than unit conventional processes used in all the sampled water treatment plants. The hydrophobic polarity-based fraction of NOM was the most amenable to removal by ceramic membranes regardless of the site of the WTP. Polarity-based fractions, aromaticity, and initial DOC had a combined influence on the removal of organic matter by ceramic membranes as explained by principal component three.