Combination of coagulation-flocculation and heterogeneous photocatalysis for improving the removal of humic substances in real treated water from Agbô River (Ivory-Coast)

Designing a cercosporin-bioinspired bifunctional algicide with flocculation and photocatalysis for efficiently controlling harmful cyanobacterial blooms

Harmful cyanobacterial blooms (HCBs) are spreading in freshwater ecosystems worldwide, adversely affecting drinking water supplies, aquatic production, recreational and tourism activities. Therefore, the efficient and environmentally friendly method is still of interest to be developed to effectively control HCBs. Inspired by the excellent algicidal activity of cercosporin (CP), a novel metal-free algaecide SiO2@EDU@CP (EDU, N-ethyl-N'-(3-dimethylaminopropyl)urea) with flocculation and photoremoval functions, was successfully designed and prepared in one-step to simultaneously introduce CP and EDU on SiO2 nanoparticles. It could rapidly form algae flocs in 20 min with 97.1% flocculation rate, and remove Microcystis aeruginosa within 12 h with 91.0% algicidal rate under 23 W compact fluorescent light irradiation without any leaked CP detected. Additionally, odorant β-cyclocitral and toxin microcystin-LR were both photodegraded after treatment of SiO2@EDU@CP. Further mechanistic studies showed that the introduction of EDU significantly reversed the zeta potential of SiO2-COOH to achieve the flocculation through neutral charge, and the photophysical characterization of SiO2@EDU@CP revealed the improved charge separation ability to generate reactive oxygen species. More importantly, the utility of SiO2@EDU@CP was well demonstrated by its effectiveness for algae from Taihu Lake under natural sunlight and inability to regrow after treatment. This study not only establishes a bifunctional algicide SiO2@EDU@CP to efficiently control HCBs, but also provides design possibilities to develop more novel and efficient algicides for the better control of practical HCBs.

Metal Oxides Nanoparticles: General Structural Description, Chemical, Physical, and Biological Synthesis Methods, Role in Pesticides and Heavy Metal Removal through Wastewater Treatment

Nanotechnology (NT) is now firmly established in both the private home and commercial markets. Due to its unique properties, NT has been fully applied within multiple sectors like pharmacy and medicine, as well as industries like chemical, electrical, food manufacturing, and military, besides other economic sectors. With the growing demand for environmental resources from an ever-growing world population, NT application is a very advanced new area in the environmental sector and offers several advantages. A novel template synthesis approach is being used for the promising metal oxide nanostructures preparation. Synthesis of template-assisted nanomaterials promotes a greener and more promising protocol compared to traditional synthesis methods such as sol-gel and hydrothermal synthesis, and endows products with desirable properties and applications. It provides a comprehensive general view of current developments in the areas of drinking water treatment, wastewater treatment, agriculture, and remediation. In the field of wastewater treatment, we focus on the adsorption of heavy metals and persistent substances and the improved photocatalytic decomposition of the most common wastewater pollutants. The drinking water treatment section covers enhanced pathogen disinfection and heavy metal removal, point-of-use treatment, and organic removal applications, including the latest advances in pesticide removal.

Hybrid carbonaceous adsorbents based on clay and cellulose for cadmium recovery from aqueous solution

The current work describes the synthesis of carbonaceous composites via pyrolysis, based on CMF, extracted from Alfa fibers, and Moroccan clay ghassoul (Gh), for potential use in heavy metal removal from wastewater. Following synthesis, the carbonaceous ghassoul (ca-Gh) material was characterized using X-ray fluorescence (XRF), Scanning Electron Microscopy coupled with Energy Dispersive X-ray (SEM-EDX), zeta-potential and Brunauer-Emmett-Teller (BET). The material was then used as an adsorbent for the removal of cadmium (Cd²⁺) from aqueous solutions. Studies were conducted into the effect of adsorbent dosage, kinetic time, initial concentration of Cd²⁺, temperature and also pH effect. Thermodynamic and kinetic tests demonstrated that the adsorption equilibrium was attained within 60 min allowing the determination of the adsorption capacity of the studied materials. The investigation of the adsorption kinetics also reveals that all the data could be fit by the pseudo-second-order model. The Langmuir isotherm model might fully describe the adsorption isotherms. The experimental maximum adsorption capacity was found to be 20.6 mg g^-1 and 261.9 mg g^-1 for Gh and ca-Gh, respectively. The thermodynamic parameters show that the adsorption of Cd²⁺ onto the investigated material is spontaneous and endothermic.

A comprehensive appraisal on status and management of remediation of DBPs by TiO2 based-photocatalysts: Insights of technology, performance and energy efficiency

Disinfection has been acknowledged as an inevitable technique in water treatment. However, an inadvertent consequence of generation of carcinogenic and mutagenic disinfection byproducts (DBPs) is associated with the reaction of disinfectants and natural organic matter (NOM) present in water. More than 700 DBPs have been identified in drinking water. The conventional processes carried out in WTPs do not optimally ensure NOM elimination, which evokes the need for the incorporation of other processes. In this context, several physicochemical and advanced oxidation processes (AOP), such as adsorption, membrane techniques, photocatalysis, etc., have been studied for the removal of NOM from water. Photocatalysis using semiconductors has been one of the most proficient technologies, which utilizes light energy for the degradation of recalcitrant organics. The present study aims to provide a comprehensive appraisal on the performance of titanium dioxide (TiO₂) based photocatalysts in the remediation of DBPs concerning the efficacy and energy requirements of the system. Furthermore, the effect of process parameters, such as pH, catalyst dose, light intensity, etc. on the efficacy of the process was also studied. It was observed that conventional P25-TiO₂ powders were efficient in the degradation of dissolved organic carbon (DOC) (up to 90%). However, low photocatalytic activity under visible light activation is one of its significant downsides. Several modifications on the catalyst surface in many studies exhibited advantages, such as high humic acid (HA) degradation under visible light. Furthermore, doped TiO₂ catalysts have shown high total organic carbon (TOC) degradation. The photocatalytic systems have achieved a better decrease in trihalomethane formation potential (THMFP) when compared to haloacetic acid formation potential (HAAFP). The energy requirements of the photocatalytic systems are determined by electrical energy per order (EE/O), which has been observed to be lesser for doped TiO₂ and engineered TiO₂ catalysts when compared with P25-TiO₂ powders. Carbon, iron, silver, etc., based catalysts can be a promising alternative to TiO₂-based photocatalysts for the degradation of NOM, although further research is required in this direction. The present review provides critical highlights on the uses, opportunities, and challenges of TiO₂-based photocatalytic techniques for the management of DBPs and their precursors pertaining to an emerging area of water treatment.

Seasonal variations of natural organic matter (NOM) in surface water supplied to two coal-fired power stations

Global issues such as pollution and global warming have resulted in changes in water characteristics over the past 20 years. Natural organic matter (NOM) which is a major component in water systems has shown an increase globally. This increase in NOM concentration has negatively affected both water treatment processes and drinking water quality. It is subsequently critical to understand the seasonal variations and composition of NOM to be able to address issues related to NOM. In this study, techniques such as ultraviolet-visible spectroscopy, total organic carbon and liquid chromatography-organic carbon detection (LC-OCD) were used for characterisation and quantification of NOM. Two coal-fired power stations were selected for this study with each power station receiving water from a different source, i.e. power station A receives water from the Vaal River and power station B from the Nkomati River. Results from this study demonstrated that composition and concentration of NOM from these two water sources varied seasonally. Characterisation of NOM using the LC-OCD indicated that the different fractions of NOM, i.e. low molecular weight neutrals, low molecular weight acids, building blocks, humic substances and biopolymers, varied seasonally. The dissolved organic carbon concentration and specific ultraviolet absorbance values of the raw water at both power stations showed an increment amid the wet seasons and a decrease amid the dry seasons.

Prospects for humic acids treatment and recovery in wastewater: A review

Clean water shortages require the reuse of wastewater. The presence of organic substances such as humic acids in wastewater makes the water treatment process more difficult. Humic acids can significantly affect the removal of heavy metals and other such toxins. Humic acids is formed by the decomposition and transformation of animal and plant remains by microorganisms, and naturally exists in soil and water. It is necessary to degrade and remove humic acids from wastewater. As it seriously human health, effective technologies for removing humic acids from wastewater have attracted great interest over the past decades. This study compared existing techniques for removing humic acids from wastewater, as well as their limitations. Physicochemical treatments including filtration and oxidation are basic and key approaches to removing humic acids. Biological treatments including enzyme and fungi-mediated humic acids degradation are economically feasible but require some scalability. In conclusion, the integrated treatment processes are more significant options for the effective removal of humic acids from wastewater. In addition, humic acids have rich utilization values. It can improve the soil, increase crop yields, and promote the removal of pollutants.

Synergy of photocatalysis and fuel cells: A chronological review on efficient designs, potential materials and emerging applications

The rising demand of energy and lack of clean water are two major concerns of modern world. Renewable energy sources are the only way out in order to provide energy in a sustainable manner for the ever-increasing demands of the society. A renewable energy source which can also provide clean water will be of immense interest and that is where Photocatalytic Fuel Cells (PFCs) exactly fit in. PFCs hold the ability to produce electric power with simultaneous photocatalytic degradation of pollutants on exposure to light. Different strategies, including conventional Photoelectrochemical cell design, have been technically upgraded to exploit the advantage of PFCs and to widen their applicability. Parallel to the research on design, researchers have put an immense effort into developing materials/composites for electrodes and their unique properties. The efficient strategies and potential materials have opened up a new horizon of applications for PFCs. Recent research reports reveal this persistently broadening arena which includes hydrogen and hydrogen peroxide generation, carbon dioxide and heavy metal reduction and even sensor applications. The review reported here consolidates all the aspects of various design strategies, materials and applications of PFCs. The review provides an overall understanding of PFC systems, which possess the potential to be a marvellous renewable source of energy with a handful of simultaneous applications. The review is a read to the scientific community and early researchers interested in working on PFC systems.

Adsorption and Photocatalytic Degradation of Pesticides into Nanocomposites: A Review

The extensive use of pesticides in agriculture has significantly impacted the environment and human health, as these pollutants are inadequately disposed of into water bodies. In addition, pesticides can cause adverse effects on humans and aquatic animals due to their incomplete removal from the aqueous medium by conventional wastewater treatments. Therefore, processes such as heterogeneous photocatalysis and adsorption by nanocomposites have received special attention in the scientific community due to their unique properties and ability to degrade and remove several organic pollutants, including pesticides. This report reviews the use of nanocomposites in pesticide adsorption and photocatalytic degradation from aqueous solutions. A bibliographic search was performed using the ScienceDirect, American Chemical Society (ACS), and Royal Society of Chemistry (RSC) indexes, using Boolean logic and the following descriptors: "pesticide degradation" AND "photocatalysis" AND "nanocomposites"; "nanocomposites" AND "pesticides" AND "adsorption". The search was limited to research article documents in the last ten years (from January 2012 to June 2022). The results made it possible to verify that the most dangerous pesticides are not the most commonly degraded/removed from wastewater. At the same time, the potential of the supported nanocatalysts and nanoadsorbents in the decontamination of wastewater-containing pesticides is confirmed once they present reduced bandgap energy, which occurs over a wide range of wavelengths. Moreover, due to the great affinity of the supported nanocatalysts with pesticides, better charge separation, high removal, and degradation values are reported for these organic compounds. Thus, the class of the nanocomposites investigated in this work, magnetic or not, can be characterized as suitable nanomaterials with potential and unique properties useful in heterogeneous photocatalysts and the adsorption of pesticides.

Color removal from secondary treated pulp & paper industry effluent using waste driven Fe-TiO2 composite

In the present study, the concurrent fixed-bed dual technology (photocatalysis and photo-Fenton) was performed as a polishing step for the color removal of tertiary treated agro-based paper & pulp industry effluent. For this purpose, the cheap and visibly dynamic Fe-TiO₂ composite was prepared using industrial waste materials which also promoted the idea of the circular economy. The effectiveness of the prepared composite and the dual process was evaluated in terms of color removal efficiency and rate constant along with optimizing the process factors. Various kinetic models namely Log-linear, Weibull, and Biphasic with shoulder were used for the comparative study of three different processes i.e. photocatalysis, photo-Fenton, and dual process. Several parameters such as pH (4.5), % surface area covered (100%), and H₂O₂ dose (525 mgL^-1) were optimized which gave the best output using dual-process i.e. 91.6% of color reduction along with good R² values i.e. 0.874, 0.981 and, 0.998 for Log-linear, Weibull and, Biphasic with Shoulder model respectively. The proposed composite was durable enough to retain its dual catalytic ability with minor activity reduction of 5-10% even after 50 recycles. Thus, this innovative technology with the dual effect of photocatalysis and photo-Fenton can be a potential bet as a tertiary treatment option in the existing industrial wastewater treatment system for removing color from the final treated effluent.

The comparison of Fenton and photo-Fenton oxidation as a primary unit process for the treatment of raw textile wastewaters

The Fenton and photo-Fenton oxidation processes (FOP and PFOP) are usually applied as a secondary unit process, and direct usage of both processes is critical in textile wastewater treatment. There is seldom study on the direct application of the FOP or PFOP showing the treatment of raw textile industry wastewaters. This study demonstrates the application and comparison of both FOP and PFOP as single units separately for the treatment of wastewater in a textile industry producing woven fabrics. In both processes, the highest treatment efficiency was achieved at pH 3. Chemical oxygen demand (COD), suspended solids (SS), and color parameters in FOP reduced from 1341 to 254 mg/L, 99.5 to 19.9 mg/L, and 1396 to 97.7 Pt-Co, respectively. Separately, in the PFOP, 365-nm wavelength UV radiation sources have been used. In PFOP, the same parameters were reduced from 715 to 42.9 mg/L, 90 to 9 mg/L, and 2080 to 83.2 Pt-Co, respectively. These results were obtained at 0.7 g Fe2+ /L and 2 mM H2 O2 concentrations in both studies. PFOP can meet the textile industry receiving environment discharge standards of many countries, especially in Turkey. The use of PFOP as a single unit is possible in the treatment of textile industry wastewater without primary precipitation. The findings in this study may be practical for the adaptation of the processes on the field scale. PRACTITIONER POINTS: There is seldom study on the direct application of Fenton or photo-Fenton processes as a single unit to raw textile wastewaters This study shows the application of the Fenton or photo-Fenton processes as single units for the treatment of raw wastewater in a textile industry Results of both processes in this study meet the discharge standards of many countries Evaluations of efficiencies of both processes were achieved This study may be the focus of attention of treatment plant operators and researchers.

Copper cable doped with tin oxide and its application to photodegrade natural organic matters

Natural organic matters are of particular importance in drinking water treatment due to their reaction with chlorine, and formation of disinfection byproducts that cause cancer in humans. Photocatalysis can remove natural organic matters from water but usually powdery photocatalysts are used which should be separated from water by filtration due to their toxic effects. In this work, a piece of copper cable used in electric industries was doped with tin oxide and applied as a photocatalyst to remove natural organic matters, humic acid and humate liquid fertilizer, from water. Tin (II) chloride was used as precursor, and deposited on the copper cable by dip coating method. Then the coated cable was calcinated at 300 °C. The prepared SnO₂/CuO/Cu photocatalyst was characterized by ICP, SEM, DRS, XRD, and ASAP techniques. The results of XRD confirmed the existence of copper oxide, and tin oxides. DRS showed that doping with tin oxide caused the photocatalytic property to improve, and the catalyst was active under irradiation of UV-Vis light. Effects of humic acid concentration, photocatalyst length, and time were studied. The kinetic of humic acid photodegradation by the SnO₂/CuO/Cu photocatalyst was investigated, which obeyed the first order model. The photocatalyst regeneration and reuse were investigated in five cycles, and the results indicated that photocatalytic activity was remained nearly constant. The cable form SnO₂/CuO/Cu photocatalyst with the main advantage of easy separation from water without the need to filtration, has excellent photocatalytic activity.

Three-Phase Three-Dimensional Electrochemical Process for Efficient Treatment of Greywater

Water shortages around the world have intensified the search for substitute sources. Greywater can serve as a solution for water requirements. Compared to two-dimensional electrochemical processes for water treatment, the addition of particle activated carbon enhances the conductivity and mass transfer or the adsorption of pollutants in a three-dimensional (3D) electrochemical process. The large specific surface areas of these particles can provide more reactive sites, resulting in a higher removal efficiency. In this study, the treatment of greywater by the electro-Fenton (E-Fenton) method was carried out in a 3D electrolytic reactor. The effects of the operating conditions, such as electrode spacing, applied voltage, treatment time, and activated carbon loading, on the efficacy of the E-Fenton process were investigated, and the corresponding optimum conditions were found to be 7 cm, 9 V, 2 h, and 10 g. The results showed that CODCr removal of greywater treated using the 3D electrochemical process was 85%. With the help of the Box–Behnken experiment design and the response surface methodology, the parameters were optimized to determine the optimal conditions. The results of the response surface analysis were consistent with the experimental results. The above findings illustrate that the proposed three-phase 3D electrochemical process is feasible for the efficient treatment of greywater.

Occurrence, toxic effects, and mitigation of pesticides as emerging environmental pollutants using robust nanomaterials - A review

Increasing demand of food and agriculture is leading us towards the increasing use and introduction of pesticides to the environment. The upright increase of pesticides in water and associated adverse effects have become a great point of concern to develop proficient methods for their mitigation from water. Various different methods have been traditionally employed for this purpose. Recently, nanotechnology has turned out to be the field of prodigious interest for this purpose, and various specific methods were developed and employed to remove pesticides from water. In this study, nanotechnological methods such as adsorption and degradation have been thoroughly discussed along with their applications and limitations where different types of nanoparticles, nanocomposites, nanotubes, and nanomembranes have played a vital role. However, in this study the most commonly adopted method of adsorption is considered to be the better technique due to its low cost, efficiency, and ease of operation. The adsorption kinetic models were described to explain the efficiency of the nano-adrsorbants in order to evaluate the mass transfer processes. However, various degradation methodologies including photocatalysis and catalytic reduction have also been elaborated. Numerous robust metal, metal oxide and functionalized magnetic nanomaterials have been emphasized, categorized, and compared for the removal of pesticides from water. Additionally, current challenges faced by researchers and future directions have also been provided.

Reduction of nitrates in a photocatalytic membrane reactor in the presence of organic acids

The present study explores the capability of the Photocatalytic Membrane Reactor (PMR) technology to remove nitrates from drinking water sources in the presence of organic electron donors. A systematic investigation was performed in a laboratory-pilot PMR, employing a hybrid TiO₂/UV-A catalysis-ultrafiltration process, using formic acid as the most favorable hole scavenger for nitrate reduction. The naturally occurring humic acid as well as the cheaper and harmless acetic acid were also tested as sacrificial electron donors. The performance of the PMR system was evaluated in respect of nitrate and Total Organic Carbon (TOC) percentage removal. The results demonstrate the superiority of formic acid regarding nitrate reduction, followed by acetic acid and humic acid, as well as the negligible effect of nitrates on organic mineralization. Formic acid was further used to assess the effects of molar organic/nitrate ratio, catalyst dosage and power of irradiation per unit volume (P_R) on nitrate reduction. With the present laboratory-pilot, the near optimum nitrate removal was ~60 % and the TOC reduction ~85 %; selectivity to dinitrogen was in the range 65-90 %. Key issues for improving this synergistic process and related R&D directions are discussed.

Magnetic photocatalysts from δ-FeOOH and TiO2 and application in reactions for degradation of methylene blue and paracetamol with UV-C and sunlight

Water contamination is a common problem, especially considering dyes and drugs disposal. A possible and effective treatment method to remove these organic pollutants from water is photocatalytic reaction. This study aimed to improve the photocatalytic properties of TiO₂ using iron oxides (Ti/Fe composite). Different magnetic photocatalysts based on commercial TiO₂ were obtained with 30, 50, and 80% (wt./wt.) of TiO₂ supported on maghemite. X-ray diffraction with Rietveld refinement confirms the presence of γ-Fe₂O₃, α-Fe₂O₃, anatase, and rutile, as well as the relative percentages of the phases present in each photocatalyst. The magnetic properties were certified by VSM and sedimentation kinetics in the presence of a magnetic field. Besides their magnetic properties, UV-vis DRS shows that the obtained photocatalysts presented lower bandgap values when compared with TiO₂. These factors allowed the materials to absorb radiation in the visible-light region and the separation from the reaction medium by the application of magnetic field. It was observed an enhancement of photodegradation reaction of methylene blue (MB) and paracetamol (PC). For example, when the content of TiO₂ increased from 30 to 80% (wt./wt.), the efficiency increased from 58 to 99% (for MB) and 39 for 80% (for PC) under UV (λ = 254 nm). The reactions carried out with solar radiation showed 56 to 95% efficiency to discolor MB. In addition, the results of sedimentation kinetics and characterization confirmed the goals of the synthesis.

Porous Silicon Carbide (SiC): A Chance for Improving Catalysts or Just Another Active-Phase Carrier?

There is an obvious gap between efforts dedicated to the control of chemicophysical and morphological properties of catalyst active phases and the attention paid to the search of new materials to be employed as functional carriers in the upgrading of heterogeneous catalysts. Economic constraints and common habits in preparing heterogeneous catalysts have narrowed the selection of active-phase carriers to a handful of materials: oxide-based ceramics (e.g. Al₂O₃, SiO₂, TiO₂, and aluminosilicates-zeolites) and carbon. However, these carriers occasionally face chemicophysical constraints that limit their application in catalysis. For instance, oxides are easily corroded by acids or bases, and carbon is not resistant to oxidation. Therefore, these carriers cannot be recycled. Moreover, the poor thermal conductivity of metal oxide carriers often translates into permanent alterations of the catalyst active sites (i.e. metal active-phase sintering) that compromise the catalyst performance and its lifetime on run. Therefore, the development of new carriers for the design and synthesis of advanced functional catalytic materials and processes is an urgent priority for the heterogeneous catalysis of the future. Silicon carbide (SiC) is a non-oxide semiconductor with unique chemicophysical properties that make it highly attractive in several branches of catalysis. Accordingly, the past decade has witnessed a large increase of reports dedicated to the design of SiC-based catalysts, also in light of a steadily growing portfolio of porous SiC materials covering a wide range of well-controlled pore structure and surface properties. This review article provides a comprehensive overview on the synthesis and use of macro/mesoporous SiC materials in catalysis, stressing their unique features for the design of efficient, cost-effective, and easy to scale-up heterogeneous catalysts, outlining their success where other and more classical oxide-based supports failed. All applications of SiC in catalysis will be reviewed from the perspective of a given chemical reaction, highlighting all improvements rising from the use of SiC in terms of activity, selectivity, and process sustainability. We feel that the experienced viewpoint of SiC-based catalyst producers and end users (these authors) and their critical presentation of a comprehensive overview on the applications of SiC in catalysis will help the readership to create its own opinion on the central role of SiC for the future of heterogeneous catalysis.

Magnetic ZnO Crystal Nanoparticle Growth on Reduced Graphene Oxide for Enhanced Photocatalytic Performance under Visible Light Irradiation

Magnetite zinc oxide (MZ) (Fe₃O₄/ZnO) with different ratios of reduced graphene oxide (rGO) was synthesized using the solid-state method. The structural and optical properties of the nanocomposites were analyzed using transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, Fourier-transform infrared spectroscopy (FTIR), ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis/DRS), and photoluminescence (PL) spectrophotometry. In particular, the analyses show higher photocatalytic movement for crystalline nanocomposite (MZG) than MZ and ZnO nanoparticles. The photocatalytic degradation of methylene blue (MB) with crystalline ZnO for 1.5 h under visible light was 12%. By contrast, the photocatalytic activity for MZG was more than 98.5%. The superior photocatalytic activity of the crystalline nanocomposite was detected to be due to the synergistic effect between magnetite and zinc oxide in the presence of reduced graphene oxide. Moreover, the fabricated nanocomposite had high electron-hole stability. The crystalline nanocomposite was stable when the material was used several times.

Fate and effects of microplastics in wastewater treatment processes

Microplastics (MPs) have garnered growing attention of researchers, as they are proved to be hazardous to the environment and humans. Wastewater treatment plants (WWTPs) are deemed as an important releasing source of MPs to the environment, and thus it is of significance to study the behavior of MPs in WWTPs. In this review, the fate of MPs in WWTPs and their effects on different wastewater treatment processes have been comprehensively discussed. Studies have shown that the secondary treatment is the most efficient process to remove MPs from wastewaters with a removal rate around 98%. The presence of MPs can increase reagent addition dosage, inhibit nitrogen conversion rate, and cause membrane fouling in wastewater treatment processes. Besides, the influences of MPs on activated sludge mainly exert on nitrification and denitrification processes, sludge digestion, and microbial communities. However, it is worth noting that different methods have been employed to determine the concentrations of MPs in WWTPs. As a result, the removal performance on MPs in WWTPs is difficult to be accurately assessed. Moreover, complicated interaction among MPs and other environmental pollutants may expand the impacts of MPs on wastewater treatment processes, which still remains insufficiently investigated. Therefore, this review has also proposed some knowledge gaps existing in present MP studies in WWTPs, and would provide reference to alleviate the adverse effects of MPs for future research.

Enhanced Photocatalytic Activity of ZnO-Graphene Oxide Nanocomposite by Electron Scavenging

Advances in nanotechnology have opened new doors to overcome the problems related to contaminated water by introducing photocatalytic nanomaterials. These materials can effectively degrade toxic contaminants, such as dyes and other organic pollutants, into harmless by-products such as carbon dioxide and water. Consequently, these photocatalytic nanomaterials have the potential to provide low-cost and environment-friendly alternatives to conventional water and wastewater treatment techniques. In this study, a nanocomposite of zinc oxide and graphene oxide was developed and evaluated for photocatalysis. This nanocomposite was characterized by XRD, FTIR, FESEM, Diffuse Reflectance Spectroscopy (DRS), TEM and UV-Vis spectrophotometer. The photocatalytic behavior of the nanocomposite was studied through the degradation of methyl orange under ultraviolet light. It is reported that the weight ratios of zinc oxide and graphene oxide do not considerably affect the photocatalytic performance, which gives this process more compositional flexibility. Moreover, hydrogen peroxide was used as an electron scavenger to increase the time-efficiency of the process. The photodegradation rate can be significantly improved (up to 24 times) with the addition of hydrogen peroxide, which increases the number of trapped electrons and generates more oxidizing species, consequently increasing the reaction rate.

Photocatalytic Oxidation of Natural Organic Matter in Water

Increased concentrations of natural organic matter (NOM), a complex mixture of organic substances found in most surface waters, have recently emerged as a substantial environmental issue. NOM has a significant variety of molecular and chemical properties, which in combination with its varying concentrations both geographically and seasonally, introduce the opportunity for an array of interactions with the environment. Due to an observable increase in amounts of NOM in water treatment supply sources, an improved effort to remove naturally-occurring organics from drinking water supplies, as well as from municipal wastewater effluents, is required to continue the development of highly efficient and versatile water treatment technologies. Photocatalysis has received increasing interest from around the world, especially during the last decade, as several investigated processes have been regularly reported to be amongst the best performing water treatment technologies to remove NOM from drinking water supplies and mitigate the formation of disinfection by products. Consequently, this overview highlights recent research and developments on the application of photocatalysis to degrade NOM by means of TiO2-based heterogeneous and homogeneous photocatalysts. Analytical techniques to quantify NOM in water and hybrid photocatalytic processes are also reviewed and discussed.

Pilot Tests on the Treatment of Bath Wastewater by a Membrane Bioreactor

In order to save water and reduce the cost of water in public areas, we studied the feasibility of recycling bath wastewater by a membrane bioreactor (MBR) at a college campus scale. The results showed that the treatment of bath wastewater by the MBR could achieve a chemical oxygen demand (COD) <50 mg/L with an average removal rate of 83%, a final NH₃–N concentration of <10 mg/L with an average removal rate of 72%, and a turbidity of <0.5 ntu, with an average value of chromaticity of 26.4 tu. The treated water could meet or exceed the urban miscellaneous water standard of China (GB/T 18920-2002), and the processing cost is 1.70 CNY/m³ or 0.25 USD/m³, which is below the price of tap water. The results demonstrated both the economic benefit and the conservation of natural resources.

Synthesis and characterization of an α-Fe2O3/ZnTe heterostructure for photocatalytic degradation of Congo red, methyl orange and methylene blue

The leading challenge towards environmental protection is untreated textile dyes. Tailoring photocatalytic materials is one of the sustainable remediation strategies for dye treatment. Hematite (α-Fe2O3), due to its favorable visible light active band gap (i.e. 2.1 eV), has turned out to be a robust material of interest. However, impoverished photocatalytic efficiency of α-Fe2O3 is ascribable to the short life span of the charge carriers. Consequently, the former synthesized heterostructures possess low degradation efficiency. The aim of the proposed endeavor is the synthesis of a novel zinc telluride-modified hematite (α-Fe2O3/ZnTe) heterostructure, its characterization and demonstration of its enhanced photocatalytic response. The promising heterostructure as well as bare photocatalysts were synthesized via a hydrothermal approach. All photocatalysts were characterized by the X-ray diffraction technique (XRD), scanning electron microscopy (SEM), and electron diffraction spectroscopy (EDX). Moreover, the selectivity and activity of the photocatalyst are closely related to the alignment of its band energy levels, which were estimated by UV-Vis diffuse reflectance spectroscopy (DRS) and X-ray photoelectron spectroscopy (XPS). Nanomaterials, specifically α-Fe2O3 and α-Fe2O3/ZnTe, were used for the degradation of Congo red (97.9%), methyl orange (84%) and methylene blue (73%) under light irradiation (>200 nm) for 60 min. The results suggested that with the aforementioned optimized fabricated heterostructure, the degradation efficiency was improved in comparison to bare hematite (α-Fe2O3). The key rationale towards such improved photocatalytic response is the establishment of a type-II configuration in the α-Fe2O3/ZnTe heterostructure.

Challenges and Opportunities of Biocoagulant/Bioflocculant Application for Drinking Water and Wastewater Treatment and Its Potential for Sludge Recovery

The utilization of metal-based conventional coagulants/flocculants to remove suspended solids from drinking water and wastewater is currently leading to new concerns. Alarming issues related to the prolonged effects on human health and further pollution to aquatic environments from the generated nonbiodegradable sludge are becoming trending topics. The utilization of biocoagulants/bioflocculants does not produce chemical residue in the effluent and creates nonharmful, biodegradable sludge. The conventional coagulation-flocculation processes in drinking water and wastewater treatment, including the health and environmental issues related to the utilization of metal-based coagulants/flocculants during the processes, are discussed in this paper. As a counterpoint, the development of biocoagulants/bioflocculants for drinking water and wastewater treatment is intensively reviewed. The characterization, origin, potential sources, and application of this green technology are critically reviewed. This review paper also provides a thorough discussion on the challenges and opportunities regarding the further utilization and application of biocoagulants/bioflocculants in water and wastewater treatment, including the importance of the selection of raw materials, the simplification of extraction processes, the application to different water and wastewater characteristics, the scaling up of this technology to a real industrial scale, and also the potential for sludge recovery by utilizing biocoagulants/bioflocculants in water/wastewater treatment.

Hybrid System of Flocculation-Photocatalysis for the Decolorization of Crystal Violet, Reactive Red X-3B, and Acid Orange II Dye

A hybrid system of flocculation-photocatalysis (HSFP) was applied to evaluate the color removal from simulative dye wastewater. The decolorization performance of HSFP was investigated considering four key factors: flocculant dosage, pH, turbidity, and ionic strength. Compared with flocculation alone, HSFP showed better decolorization effectiveness for simulative Crystal Violet-Reactive Red X-3B dye wastewater (CV-RR) and simulative Crystal Violet-Acid Orange II dye wastewater (CV-AO). The dosage of flocculant was determined by the molecular structure of target dyes. A higher dosage was required for the color removal of dyes with a lower molecular weight and less sulfonic acid groups. The dominant decolorization mechanism was different with different initial pH values of simulative dye wastewater, which influenced the decolorization efficiency of flocculation and photocatalysis. For dyes with a lower molecular weight and less sulfonic acid groups, better decolorization performance was achieved under neutral conditions, mainly depending on strong charge neutralization and adsorption bridging capacity. For dyes with a higher molecular weight and more sulfonic acid groups, decolorization efficiency was improved with an increase in pH, due to stronger deprotonation. An increase of turbidity reduced the dye removal efficiency of flocculation alone and HSFP. The presence of NaCl, CuCl₂, and CrCl₃ led to a different decrease in the flocculation efficiency and photodegradation efficiency.

Dye removal from water and wastewater by nanosized metal oxides - modified activated carbon: a review on recent researches

The conventional water and wastewater treatment methods are unable to provide up-to-data organized standards for drinking water and discharging effluents into natural ecosystems. Therefore, developing advanced and cost-effective methods to achieve published standards for water and wastewater and population needs are nowadays necessity. The important parts of this article are providing literature information about dyes and their effects on the environment and human health, adsorption properties and mechanism, adsorbent characteristics, and recent information on various aspects of modified activated carbons with nanosized metal oxides (AC- NMOs) in the removal of dyes. This review also summarized the effect of main environmental and operational parameters such as adsorbent dosage, pH, initial dye concentration, contact time, and temperature on the dye adsorption using AC-NMOs. Furthermore, the applied isotherm and kinetic models have been discussed.

Study on the removal of humic acid by ultraviolet/persulfate advanced oxidation technology

Humic acid (HA) in water is the main precursor of disinfection by-products in the chlorination process of drinking water. In this study, an ultraviolet/persulfate (UV/PS) process, in a laboratory-scale system, is successful in the degradation of HA. The results showed that HA was significantly degraded (UV₂₅₄ removal rate of ~ 89%) and partially mineralized (~ 62.5%) by UV/PS treatment at a PS dose of 0.4 mM, pH of 7.12, and UV irradiation time of 160 min. The trihalomethane formation potential (THMFP) was also significantly reduced (THMFP reduction of ~ 85.4%). A strong linear relationship was observed between UV₂₅₄ and dissolved organic carbon. The removal rate of HA at low pH was better than that at high pH conditions, and the inhibition by Cl^- slowed down after an initial increase, and the inhibition was weaker than HCO₃^-. By analyzing the fluorescence spectrum of two humic-like substances, the fluorescent compounds C1 and C2 in HA were significantly degraded, and the change in C1 and C2 concentration was correlated with the decrease of THMFP. The degradation of different fractions of natural organic matter in real-world water samples indicated that UV/PS has significant potential to decrease HA in water.

Disinfection mechanism of E. coli by CNT-TiO2 composites: Photocatalytic inactivation vs. physical separation

Magnetic carbon nanotube (MCNT) composites with titanium dioxide (TiO₂) have an enhanced photocatalytic disinfection efficiency (i.e. higher disinfection rate) and better applicability (i.e. solar light applicability and catalyst separation using its magnetic property) than bare TiO₂ and/or MCNT. However, the role and mechanism of MCNT in the disinfection process are still unclear. Therefore, this study aimed at investigating the disinfection mechanism of Escherichia coli using MCNT-TiO₂ nanocomposites under various conditions (i.e. the presence and absence of light and reactive oxygen species scavengers, and different MCNT-TiO₂ ratio) and photocatalytic disinfection models. The results showed that (i) MCNT and its nanocomposites with TiO₂ had much higher disinfection efficiencies than bare TiO₂, (ii) the physical bacterial capture was the dominant disinfection mechanism, (iii) the higher disinfection rate was found at an optimum MCNT:TiO₂ ratio of 5:1 under the tested experimental conditions, (iv) hydroxyl radical (OH) was the influencing reactive oxygen species on the photocatalytic disinfection using MCNT-TiO₂, and (v) good correlation between experimental parameters (i.e. carbon contents, surface area and concentration of MCNT-TiO₂) and the contribution rate of physical and photocatalysis reactions. The finding from this study and the methods proposed herein are essential for understanding the photocatalytic disinfection processes using TiO₂ and its carbonaceous nanocomposites, which can promote the application of photocatalytic disinfection process.

Adsorption of 2,4-dichlorophenoxyacetic acid in an aqueous medium on nanoscale MIL-53(Al) type materials

MIL-53(Al) type materials were prepared using MW-activation. They show high adsorption capacities in the adsorption of 2,4-dichlorophenoxyacetic acid in an aqueous medium and demonstrate faster adsorption rates as compared to an activated carbon.

Pre-disinfection columns to improve the performance of the direct electro-disinfection of highly faecal-polluted surface water

This work presents the design and evaluation of a new concept of pre-disinfection treatment that is especially suited for highly polluted surface water and is based on the combination of coagulation-flocculation, lamellar sedimentation and filtration into a single-column unit, in which the interconnection between treatments is an important part of the overall process. The new system, the so-called PREDICO (PRE-DIsinfection Column) system, was built with low-cost consumables from hardware stores (in order to promote in-house construction of the system in poor countries) and was tested with a mixture of 20% raw wastewater and 80% surface water (in order to simulate an extremely bad situation). The results confirmed that the PREDICO system helps to avoid fouling in later electro-disinfection processes and attains a remarkable degree of disinfection (3-4 log units), which supplements the removal of pathogens attained by the electrolytic cell (more than 4 log units). The most important sizing parameters for the PREDICO system are the surface loading rate (SLR) and the hydraulic residence time (HRT); SLR values under 20 cm min^-1 and HRT values over 13.6 min in the PREDICO system are suitable to warrant efficient performance of the system.

Heterogeneous photocatalysis and its potential applications in water and wastewater treatment: a review

There has been a considerable amount of research in the development of sustainable water treatment techniques capable of improving the quality of water. Unavailability of drinkable water is a crucial issue especially in regions where conventional drinking water treatment systems fail to eradicate aquatic pathogens, toxic metal ions and industrial waste. The research and development in this area have given rise to a new class of processes called advanced oxidation processes, particularly in the form of heterogeneous photocatalysis, which converts photon energy into chemical energy. Advances in nanotechnology have improved the ability to develop and specifically tailor the properties of photocatalytic materials used in this area. This paper discusses many of those photocatalytic nanomaterials, both metal-based and metal-free, which have been studied for water and waste water purification and treatment in recent years. It also discusses the design and performance of the recently studied photocatalytic reactors, along with the recent advancements in the visible-light photocatalysis. Additionally, the effects of the fundamental parameters such as temperature, pH, catalyst-loading and reaction time have also been reviewed. Moreover, different techniques that can increase the photocatalytic efficiency as well as recyclability have been systematically presented, followed by a discussion on the photocatalytic treatment of actual wastewater samples and the future challenges associated with it.

Ultrafiltration membrane fouling induced by humic acid with typical inorganic salts

Severe ultrafiltration (UF) membrane fouling is always induced by humic acid (HA). However, little attention has been paid to the influence of inorganic salts, and even the studies related have been limited to only a single kind of salt. In addition, the concentration of the inorganic salts reported in previous studies is much high. Herein, the effect of HA on UF membrane performance was investigated in the presence of typical inorganic salts, with concentrations similar to those in natural waters or actually used in most current water plants. The results showed that membrane performance was influenced little by monovalent inorganic salts (NaCl and KCl), while divalent inorganic salts (CaCl₂ and MgCl₂) could exacerbate the membrane fouling. For trivalent inorganic salts (AlCl₃·6H₂O and FeCl₃·6H₂O), floc adsorption was the dominant HA removing mechanism, and AlCl₃·6H₂O behaved better than FeCl₃·6H₂O. Relating to the floc properties, severe membrane fouling occurred with low dosage, while it was mitigated with high dosage. Compared with the trivalent inorganic salts, more severe membrane fouling was caused by divalent inorganic salts. Additionally, little synergistic or inhibitory effect occurred with mixtures of divalent inorganic salts and trivalent inorganic salts. Furthermore, analysis with the classical fouling models showed that cake filtration was the main fouling mechanism with/without inorganic salts. Based on the findings, we believe these different HA behaviors exhibited during coagulation process with inorganic salts will have a large potential application in UF membrane fouling alleviation in water treatment.

Advanced oxidation processes for the removal of natural organic matter from drinking water sources: A comprehensive review

Natural organic matter (NOM), a key component in aquatic environments, is a complex matrix of organic substances characterized by its fluctuating amounts in water and variable molecular and chemical properties, leading to various interaction schemes with the biogeosphere and hydrologic cycle. These factors, along with the increasing amounts of NOM in surface and ground waters, make the effort of removing naturally-occurring organics from drinking water supplies, and also from municipal wastewater effluents, a challenging task requiring the development of highly efficient and versatile water treatment technologies. Advanced oxidation processes (AOPs) received an increasing amount of attention from researchers around the world, especially during the last decade. The related processes were frequently reported to be among the most suitable water treatment technologies to remove NOM from drinking water supplies and mitigate the formation of disinfection by products (DBPs). Thus, the present work overviews recent research and development studies conducted on the application of AOPs to degrade NOM including UV and/or ozone-based applications, different Fenton processes and various heterogeneous catalytic and photocatalytic oxidative processes. Other non-conventional AOPs such as ultrasonication, ionizing radiation and plasma technologies were also reported. Furthermore, since AOPs are unlikely to achieve complete oxidation of NOM, integration schemes with other water treatment technologies were presented including membrane filtration, adsorption and others processes.

Removal of natural organic matter in drinking water treatment by coagulation: A comprehensive review

Natural organic matter (NOM) is a complex matrix of organic substances produced in (or channeled to) aquatic ecosystems via various biological, geological and hydrological cycles. Such variability is posing a serious challenge to most water treatment technologies, especially the ones designed to treat drinking water supplies. Lately, in addition to the fluctuating composition of NOM, a substantial increase of its concentration in fresh waters, and also municipal wastewater effluents, has been reported worldwide, which justifies the urgent need to develop highly efficient and versatile water treatment processes. Coagulation is among the most applied processes for water and wastewater treatment. The application of coagulation to remove NOM from drinking water supplies has received a great deal of attention from researchers around the world because it was efficient and helped avoiding the formation of disinfection by products (DBPs). Nonetheless, with the increased fluctuation of NOM in water (concentration and composition), the efficiency of conventional coagulation was substantially reduced, hence the need to develop enhanced coagulation processes by optimizing the operating conditions (mainly the amount coagulants and pH), developing more efficient inorganic or organic coagulants, as well as coupling coagulation with other water treatment technologies. In the present review, recent research studies dealing with the application of coagulation for NOM removal from drinking water supplies are presented and compared. In addition, integration schemes combining coagulation and other water treatment processes are presented, including membrane filtration, oxidation, adsorption and others processes.

Investigation of Coagulation Activity of Cactus Powder in Water Treatment

This paper is focused on the comparative study of cactus powder, Alum, and their combination of physiochemical analyses of water sample such as TDS, pH, conductivity, salinity, and turbidity using jar test. The result indicated that percentage removal of turbidity from turbid water sample increased from 23.9% to 54% and 28.46% to 58.2% as dose increased from 0.50 to 3.50 g for both cactus powder and Alum, respectively. Cactus powder also has a marginal effect on pH value (7.33 at 0.50 g, 7.49 at 1.50 g, 7.57 at 2.50 g, and 7.57 at 3.50 g) as compared to the usage of chemical coagulants (Alum). The salinity was increased from 0.4% to 0.69 % and 0.39% to 0.98% as the dose of cactus powder and Alum increased from 0.50 g to 3.50 g, respectively. The result revealed that cactus powder is more effective in pH upholding, TDS maintenance, and salinity removal than Alum, but their combination is the most effective in terms of turbidity removal, reduction of salinity, reduction of conductivity, and reduction of TDS and has a marginal effect on dissolved oxygen (DO) value. In conclusion, the combination of Alum and cactus powder is more effective for turbidity removal, salinity removal, and pH and conductivity upholding than either of them used individually.