Showing papers in "Journal of water process engineering in 2020"

Role of nanomaterials as adsorbents in heavy metal ion removal from waste water: A review

Abstract: This review presents a holistic analysis of the synthesis and efficacy of nanosorbents towards the waste water purification by the removal of selected heavy metal ions, with special emphasis on the effect of functionalization of nanoadsorbents on certain key properties such as surface area, separation and adsorption capacity. We have compiled enormous data based on the characteristic properties of nanomaterials and their selective affinity towards certain heavy metal ions. The experimental factors like pH, adsorbent dosage, contact time, temperature, initial ion concentration and ionic strength affecting metal ion removal have also been explored. Besides, the different adsorption kinetics and adsorption isotherm models are discussed with the help of various illustrations to have an insight into the adsorption procedure.

Removal of heavy metals from aqueous solution using carbon-based adsorbents: A review

Abstract: Heavy metal contamination has been a serious threat to environment and human health Carbon-based materials, from biochar/activated carbon to modified materials (ie carbon nanotubes-based materials, and graphene-based materials), have been widely studied as efficient adsorbents for the heavy metal removal from aqueous solutions This review discussed the recent achievements in adsorption isotherms, adsorption kinetics and adsorption mechanism according to the existing forms of heavy metals in water The effect of process conditions, such as temperature, pH value, and coexisting ions, on adsorption performance are combed, and the universal guidance law is obtained The physical adsorption, electrostatic interaction, ion exchange, surface complexation, and precipitation/coprecipitation play important roles in heavy metals adsorption process In addition to the common activated carbon(AC), biochar(BC) and the emerging carbon nanotubes(CNTs) and graphene(GN) adsorbent show good development potentials Meanwhile, though the modified carbonaceous materials can achieve high adsorption capacity and removal efficiency of heavy metals, the modification operation is complex, especially chemical modification Acid and alkali solution are often used to regenerate spent materials in desorption, however, further studies of other desorption reagent are really needed This review highlights the removal of heavy metal ions from aqueous solution using carbon-based materials as adsorbents, and discusses the existing deficiencies and suggestions on further study

Development of synthetic zeolites from bio-slag for cesium adsorption: Kinetic, isotherm and thermodynamic studies

Abstract: This study reported a novel synthetic zeolite based adsorbent developed from the municipal wastewater sludge molten slag (bio-slag) through the hydrothermal modification process for removal of cesium (Cs) from simulated wastewater. The artificial zeolites were produced from the raw bio-slag which was identified by the several physicochemical experimental procedures such as the surface area analysis (the BET technique), the FESEM, the XRF and the XRD. The Cs adsorption process of modified bio-slag was exmined by the linear pseudo-first order, pseudo-second order and intra-particles diffusion models whilst the second order kinetic model confirmed a better agreement with the correlation coefficient, R2 = 0.999-1.000 for 20-400 mg/L Cs solution. The Langmuir, Freundlich and the Temkin isotherm model were investigated using the adsorption isotherm data. A satisfactory correlation coefficient value (R2= >0.980) proved that the isotherm parameters were perfectly fitted to the Langmuir and Freundlich model and the highest Cs adsorption ability of modified bio-slag were 51.02, 51.02 and 49.51 mg/g at 288, 298 and 308 K, respectively. The better agreement of adsorption data with the second order kinetic model and the Langmuir model proved the adsorption mechanism was controlled by the chemical reaction (ion-exchange). Thermodynamic studies under the different temperatures proved that the adsorption reaction was endothermic ( Δ H =20.53 kJ/mol) and Δ S = 0.021 kJ/mol/K) and non-spontaneous ( Δ G > 0 ). Moreover, the modified bio-slag effectively removed Cs even in the co-existence of Na+ and K+ as competitive ions at their wide range of concentrations (upto 300 mM) although the higher concentration slightly affected the Cs adsorption.

Engineered nanomaterials and their surface functionalization for the removal of heavy metals: A review

Abstract: Water is polluted by various harmful toxic chemical substances, precisely heavy metals, dyes, and pathogens, which have a disastrous effect on the ecological balance of human as well as animal life. Therefore, there is an urgent need for new technologies to remove these noxious pollutants from water/wastewater. Adsorption is one of the predominant method among all the reported techniques for the removal of heavy metals. Nano technological applications in this direction, i.e. development of nano-sized materials, tubes and composites as adsorbents have engrossed rapidly. In this review, current trends of nanomaterials for the removal of heavy metals from water/wastewater are concisely discussed. Applications of different engineered nanomaterials based on iron oxide, titanium oxide, silica, carbon, graphene oxide, and bio-nanomaterials are largely focused. Different strategies and surface modifiers have been used for the surface modifications/functionalization of these nanomaterials, which in turn enhanced the adsorption capacities by many folds. Toxic effects of various nanoparticles are also discussed, and various strategies like embedding, encapsulation to prevent their releases into the environment are deliberated. In addition, the selection of NPs for the removal of various metals has also been discussed in the respective sections. This review will provide an insight into the latest researches, which is expected to offer worthy implications to academicians and industry professionals working in environmental engineering domain for the removal of heavy metals from water/wastewater.

Waterworks sludge-filter sand permeable reactive barrier for removal of toxic lead ions from contaminated groundwater

Abstract: This study aims to use of inexpensive and available byproduct waterworks sludge resulted in huge quantities from the activities of water supply treatment system in the remediation of groundwater contaminated with lead ions as an application of sustainability principles. Results revealed that this material can be used effectively in the permeable reactive barrier technology. The best operational conditions for initial pH, contact time, and sorbent dosage in the batch tests were 5, 1 h, and 0.3 g/50 mL, respectively at agitation speed of 200 rpm and initial concentration of 50 mg/L to achieve the maximum removal efficiency (97 %). Langmuir isotherm model was introduced a fair description for sorption measurements with maximum capacity of 20.41 mg/g. Also, the precipitation/co-precipitation processes were found the predominant mechanisms in the sorption process under consideration based on Fourier-transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) images in combination with final pH values. The developed model for continuous tests solved by COMSOL Multiphysics 3.5a to plot the contaminant transport under the effects of initial concentration, flowrate and bed depth. It is recognized that the model predictions can be simulated the experimental values with satisfactory concurrence where the coefficient of determination (R2) ≥ 0.983. The breakthrough point in the continuous transport was appeared earlier by decreasing the bed depth, and increasing both the initial concentration as well as the flow rate.

A review of biological drinking water treatment technologies for contaminants removal from polluted water resources

Abstract: This paper is the first critical review of the technology of water treatment via biological process for contaminants removal from water resources. The biological process is considered the future for drinking water treatment, especially for developing countries. The main focus of the review is on single and integrated treatment technologies that have been studied for all types of drinking water resources, including surface water and ground water. These treatment technologies have the capability to treat contaminants in polluted drinking water resources, such as heavy metals, natural organic matter, inorganic non-metallic matter, disinfection by-products, endocrine disrupting chemicals and microbial contaminants. The potential threats and challenges of using the biological process for safe drinking water production also have been discussed, as this technology is a relatively new concept for safe drinking water production, and there have been very limited studies performed in developing countries.

Hybrid ozonation process for industrial wastewater treatment: Principles and applications: A review

Abstract: Ozone is a strong oxidant and have been effectively used for the degradation and mineralization of organic pollutants. However, the increase in the toxicity and disposal of the recalcitrant organics standalone ozonation process is not effective and sustainable solution for the treatment of industrial wastewater containing recalcitrant. It is therefore necessary to provide a summary of success of hybrid ozonation process for industrial wastewater treatment along with the reaction mechanism for enhancing the molecular ozone reactivity. The paper presents a detailed review of hybrid ozonation process as a combination of two different techniques to enhance the hydroxyl radical formation thereby increasing the process efficiency. An extensive review on the mechanism and application of these hybrid ozonation processes for degradation, mineralization, detoxification of different organic pollutants present in the industrial wastewater is reported.

Role of electrocoagulation in wastewater treatment: A developmental review

Abstract: Electrocoagulation (EC) is a popular wastewater treatment alternative that had been studied extensively for a wide range of wastewater types, due to its versatility, ease of setup, low footprint and eco-friendly nature The recent studies on EC advancements on various wastewater types had been reviewed in this paper The operational variables that are vital to EC and the fundamental relationship of EC with conventional chemical coagulation had been assessed as they are the primary factors that govern the pollutant removal mechanism of the process Hence, EC needs further studies for optimisation of its process parameters and modelling for scale up in the industrial level Moreover, this paper reviews the current emerging hybrid technologies of EC with integrated separation technologies and their limitations for enhanced wastewater treatment systems for cleaner effluents, water reclamation and recycle The current prominent hybrid EC processes under research include: EC-adsorption, EC-peroxidation, EC-chemical coagulation (CC), photovoltaic EC and EC-membrane Due to the overall low footprint requirement, environmental sustainability and strong potential of constant operation without needing extensive control, hybrid EC-membrane process undeniably stands out to be the future of wastewater treatment

Ultrafiltration membranes for wastewater and water process engineering: A comprehensive statistical review over the past decade

Abstract: The primary intention of this review is to showcase and quantify the level of research interest and current research trends concerning UF membrane applications and processes within the past decade (2009–2018). Detected statistics revealed a resurgent interest in the UF technology on a yearly basis. "Journal of Membrane Science" and "Desalination and Water Treatment" were the primary journals dominating the size of the annual publication output among more than 120 journals, with 854 and 683 papers, respectively. Based on the ScienceDirect research platform, fouling (27 %), modelling (17 %) and wastewater (12 %) were the dominant research topics and accounted for more than half of the total scientific articles published (4547 articles) within the specified period of the research. Unsurprisingly, topics like UF membrane fabrication and modification, food processing, and hybrid membrane process have revealed a growing trend in terms of annual publications. The current review revealed the present-day significance of UF membranes along with their prospective opportunities for attaining sustainability in water industries and materializing the efforts of future researchers in the right direction.

Multivariate optimisation of Cr (VI), Co (III) and Cu (II) adsorption onto nanobentonite incorporated nanocellulose/chitosan aerogel using response surface methodology

Abstract: In this study, tailor made Nanobentonite incorporated Nanocellulose/Chitosan aerogel (NCNB) has been used to study its metal adsorption capacity from simulated wastewater. The aerogel was characterised with FESEM, AFM, EDX, XRD, FTIR, Raman spectroscopy and found the successful conversion to the desired adsorbent in nano dimension. This NCNB was used for optimisation of Chromium, Cobalt and Copper adsorption. Response Surface Methodology (RSM) was implemented to derive the binary correlation between various experimental parameters such as initial metal concentration, pH, adsorbent mass and temperature using Central Composite Design (CCD). The regression coefficients were evaluated which validated second order polynomial equation for the remediation of Cr, Co and Cu with NCNB. The maximum adsorption efficiencies under the optimum condition of the process parameters for Cr, Co and Cu removal were found to be 98.90, 97.45 and 99.01 % respectively. Co efficient of determination, R2 for Cr, Co and Cu were 0.9796, 0.8973 and 0.9321 respectively. Halsey isotherm and pseudo-second-order kinetic model agreed well with the experimental data for all the three metals. Thermodynamics study showed the metal adsorption was spontaneous, endothermic and feasible in nature. These data imperatively show that use of this aerogel can be a good alternative to the expensive methods of heavy metal remediation.

Poly‐and perfluoroalkyl substances in water and wastewater: A comprehensive review from sources to remediation

Abstract: Per- and polyfluoroalkyl substances (PFAS) are pollutants have attracted major concern due to their high persistence and bioaccumulation. They are causing increasingly serious epidemiological problems in many communities globally due to consuming PFAS-contaminated water sources. Necessarily, the behavior of PFAS in water and wastewater needs to be understood better. This study attempts to comprehensively review, analyze and discuss PFAS based on the following key aspects: (i) sources, (ii) occurrence in water and wastewater, (iii) transformation, fate and migration, and (iv) remediation technologies. Studies indicated that modern water and wastewater treatment plants cannot deal completely with PFAS and in some cases, the removal efficiency is minus -3500-fold. The main reasons are the high hydrophobicity of PFAS and presence of PFAS precursors. Precursors can account for 33–63% of total PFAS concentration in water and wastewater. Detection and identification of precursors are challenging due to the requirement of advanced analytical instrument and standard chemicals. Several technologies have been developed for PFAS remediation involving two main mechanisms: separation-concentration and destruction. The most widespread in-use technology is adsorption because it is reasonably affordable. Anion exchange resin and synthesized materials are the most effective sorbents having a sorption capacity of 100–2000 mg PFAS/g sorbent, effective within a few hours. The destruction technology such as plasma can also be a promising one for degrading PFAS to below health-based standard in 1 min. However, plasma is costly and not yet ready for full scale application.

Energy efficient electrocoagulation using baffle-plates electrodes for efficient Escherichia Coli removal from Wastewater

Abstract: A new electrocoagulation reactor (EC), which utilises the concepts of baffle-plates, has been applied to remove Escherichia coli (E. coli) from wastewater. This new aluminium-based EC reactor utilises perforated baffle-plates electrodes to mix water, which reduces the need for mechanical or magnetic mixers that require extra power to work. This new reactor has been used to treat E. coli containing wastewater samples, considering the effects of different parameters such as treatment time (TT), inter-electrode distance (IED), and current density (CD). A statistical analysis has also been commenced to evaluate the influence of each parameter on the removal of E. coli. Additionally, an economic study has been conducted to assess the operating cost of the new reactor. The outcomes of the experimental work confirmed that the new reactor removes as high as 96 % of the E. coli within 20 min of electrolysis at IED of 0.5 cm, and CD of 1.5 m A / c m 2 . Additionally, it has been found that the operating cost of the new reactor is 0.11 US $/m3 (for E. coli removal), which is less than operating cost of traditional reactors. Finally, it has been found that the effect of the studied parameters on E. coli removal followed the order: T T > C D > I E D .

Removal mechanism of heavy metal (Cu, Ni, Zn, and Cr) in the presence of cyanide during electrocoagulation using Fe and Al electrodes

Abstract: Heavy metals have frequently been detected in metal plating wastewater. In this study, electrocoagulation method using iron (Fe) and aluminum (Al) electrodes was applied to simultaneously remove four heavy metals (Cu, Ni, Zn, Cr) in artificial metal plating wastewater. The Fe electrode showed greater removal efficiency for especially Cr than did the Al electrode due to the reduction of Cr6+ ion by Fe2+ ions produced from electrode. Alkaline pH favored electrocoagulation because of the abundance of hydroxide (OH−) ions; thus, metal hydroxides can be formed readily under alkaline pH. The metal removal increased with current density, as Fe2+ ion was generated more effectively at high current. However, the electrolyte concentration did not significantly affect metal removal efficiency. In electrocoagulation experiments using Fe electrodes, the mass of sludge formed was 0.68–2.50 kg/m3 and the amount of energy consumed was 0.37–2.78 kW h/m3, respectively, during the treatment of artificial metal plating wastewater containing four heavy metals in the absence of cyanide, which increased to 3.64–4.74 kg/m3 and 4.80–5.04 kW h/m3 for artificial wastewater in the presence of cyanide. The FTIR spectra of the sludge samples generated when using Fe and Al electrodes showed that all four metals exhibited OH stretching peaks, implying that main removal mechanism of metals during electrocoagulation is the precipitation with metal hydroxide. Iron sludge was composed mainly of Fe3O4 and FeO(OH), and Al sludge was mostly AlO(OH). When using Fe electrode in the presence of cyanide, cyanide was also adsorbed onto iron sludge via Fe-CN bonding.

Bioremediation of dyes: Current status and prospects

Abstract: Environmental pollution associated with the discharge of textile industries is becoming a global concern. There is an imperative need for developing efficient, environmentally friendly, and cost-effective techniques for treating the wastewater containing dyes. Bioremediation of dyes is a fascinating approach to treat the textile effluents as it offers many advantages over the conventional treatment techniques. This review critically evaluates the latest advancements in applications of bioremediation techniques for the removal of various dyes from wastewater. The applications of various microorganisms such as bacteria, algae, fungi, yeast, and enzymes for the uptake of dyes are portrayed in detail. The current advancements in the bioremediation of textile effluents, research opportunities, challenges, and future outlook are emphasized. It also highlights the progress in bioremediation of dyes using bioreactors and microbial fuel cells. This review is beneficial in understanding the current status of bioremediation in water purification and accelerating the research focusing the role of bioremediation in water purification applications in future.

Review on discharge Plasma for water treatment: mechanism, reactor geometries, active species and combined processes

Abstract: Owing to the water crisis, the development of innovative and clean advanced oxidation processes to decompose a variety of harmful organic compounds in wastewater becomes the main challenge for many research teams. Cold discharge plasma is one of the most widely studied and developed processes, owing to its low energy cost and easy to operate. The impact of different factors on the decontamination effectiveness of discharge plasma are detailed in this review. The generation and reaction mechanisms of reactive species in discharge plasma systems have also gained a significant interest and hence discussed. Several potentials and laboratory-scale reactor design recently reported are discussed and schematically presented. The recent combination of discharge plasma decontamination and other processes in both post and pre-treatment configuration are reported. Some applications of water treatment based on discharge plasma at the pilot scale have been addressing.

Adsorption of pollutants by plant bark derived adsorbents: An empirical review

Abstract: Plant barks are among the most widely applied low-cost biomass materials in the study of pollutant removal from aqueous media. This paper extensively reviews the experimental findings presented in open literature with much focus on the last 15 years. This study classified plant bark adsorbents into 5 broad groups (based on their preparation technique): unmodified biosorbent, pre-modified biosorbent, chemically modified biosorbent, physically modified biosorbent and bio-based activated carbon. It was observed that eucalyptus, pine, neem, acacia and mango are the most explored source species in tree bark adsorption studies. About two-third of target impurities reported on the subject in open literature have been on heavy metals. The review elucidated the excellent adsorption capacities of plant bark based adsorbents and biosorbents for the uptake of heavy metals, dyes, pesticides and other pollutants. Adsorption was majorly best-fit to either the Langmuir or Freundlich isotherm models and the pseudo-second order kinetic model. The thermodynamics findings revealed that the adsorption is highly spontaneous and is by a physical mechanism in most cases. It was also observed that plant barks have high reusability potential thereby underlying their usefulness for industrial application. Knowledge gaps in the research area were also discussed in line with future perspectives.

Application of Magnetic Graphene Oxide for Water Purification: Heavy Metals Removal and Disinfection

Abstract: Water pollutant like heavy metals is one of the major hazards due to rapid urbanization and industrialization. In this study, a simple, fast and facile method was applied for the synthesis of magnetic graphene oxide (MGO) by fabricating the surface of graphene oxide (GO) with iron particles (Fe3+). Characterization of MGO was done by UV-VIS, FT-IR, SEM, XRD and VSM. Efficient removal of toxic heavy metal ions (Pb+2, Cr+3, Cu+2, Zn+2 and Ni+2) were studied using Atomic Absorption Spectroscopy (AAS). The adsorption performance of MGO was evaluated by investigating the effect of different parameters such as pH (3-9), temperature (25-55 °C), contact time (10-65 mins) and adsorbent dose (0.002 – 0.016 g). The maximum adsorption capacities at pH 5.0 for Pb (II), pH 6 for Cr (III), pH 6 for Cu (II), pH 7 for Zn (II) and pH 8 for Ni (II), ions were 200, 24.330, 62.893, 63.694 and 51.020 mg/g respectively. The adsorption processes was spontaneous and endothermic, followed the Langmuir adsorption isotherm and pseudo-second-order kinetics model. MGO action against microbial activity of E-Coli, Yersina Ruckeri and Antobacter Agglomerans was also studied. The results exhibited that MGO is a competent adsorbent and disinfectant for safe drinking water.

A review of oily wastewater treatment using ultrafiltration membrane: A parametric study to enhance the membrane performance

Abstract: The industries like petroleum refining, petrochemicals, metallurgical, oil & gas, etc., generate a substantial volume of oily wastewater, and it is recognized as a potential threat to the environment. The topic of oily wastewater treatment is very topical and important to major industry developments such as shale oil and gas. Among the techniques employed, the treatment of oily wastewater using polymeric ultrafiltration membrane (UFM) has emerged as a cost-effective technique with ease of operation as well as high separation efficiency over the conventional oily wastewater treatment methods. The major limitation of the UFM technique is mainly due to the fouling of membranes because of the accumulation of tiny oil droplets on the surface and blockage of membrane pores. Therefore, the enhanced wettability (i.e., hydrophilicity) and the antifouling behavior of membranes are the key parameters to improve the performance of UFMs. In this review, we briefly highlight the parametric effects on the performance of UFM performance, which includes the (i) composition of the membrane related to the blend-ratio of several additives (namely, polymeric, inorganic, grafted polymers, etc.) (ii) operating conditions (pH, temperature, salinity, oil concentration, and cross-flow velocity of feed, the viscosity of casting solution and salinity of the coagulation bath, etc.) and (iii) process optimization. The review further provides an insight into the fouling of membranes using oily wastewater. Finally, the present review emphasizes the challenges faced for commercial applications of UFM, economic aspects as well as the range of strategies for the researchers to follow.

Utilization of alum sludge as adsorbent for phosphorus removal in municipal wastewater: A review

Abstract: Aluminium sulphate is the commonest and most widely used coagulant for water treatment worldwide. Aluminium is a well-known adsorbent for phosphorous (P), a nutrient highly associated with eutrophication in most water bodies. Thus, this paper provides a review on P adsorption from aqueous media using alum sludge waste material generated by water treatment plants that use aluminium sulphate as sole coagulant. A meta-analysis of data on characteristics of various alum sludges was done. The hindrance factors and adsorption capacities, under varying operating conditions are presented, including future direction. It is evident from literature survey that there is the emerging shift from reuse and recycling of raw alum sludge towards synthesis of value-added alum sludge based adsorbents. Possibilities to improve efficacy as both filter media and adsorbent but at the same time reducing metal leaching are highlighted. Value-added products may also offer an added advantage of acting as source of phosphorous for possible reuse in agricultural soils.

Experimental and molecular dynamics study on dye removal from water by a graphene oxide-copper-metal organic framework nanocomposite

Abstract: In this study, a novel copper-based metal-organic framework (Cu-MOF), immobilized on graphene oxide (GO), was fabricated via ultrasonication method. The synthesized GO-Cu-MOF was used as an adsorbent, and the kinetics data for the removal of dye molecules investigated along with the molecular dynamics simulations. Various parameters such as solution temperatures and pH, dye, and adsorbent concentrations were studied to evaluate the performance of the adsorbent in removing a model contaminant based on the real-world water treatment conditions. The synthesized adsorbent was characterized using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDX), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Ultraviolet-visible spectroscopy (UV–vis), Brunauer–Emmett–Teller (BET) analysis, and Zeta Potential. The characterization results showed full exfoliation of GO in Cu-MOF. The adsorption kinetic results followed the rapid adsorption process with a pseudo-second-order characteristic. The GO-Cu-MOF exhibited higher adsorption capacity of 173, 251, and 262 mg/g at 25 °C, 45 °C and 65 °C compared to 106, 117 and 142 mg/g adsorption capacity of Cu-MOF at the same temperature. The dye removal experiments suggest that the acidic condition and the higher temperature (65 °C) favors the adsorption of Methylene blue (MB) on GO-Cu-MOF compound. The molecular dynamics simulation performed to calculate the adsorption energy for Cu-MOF and GO-Cu-MOF. The calculated adsorption energy of -323 (kCal/mol), and -119 (kCal/mol) for GO-Cu-MOF and Cu-MOF was in agreement with the experimental data.

A review on the synthesis of hydroxyapatite, its composites and adsorptive removal of pollutants from wastewater

Abstract: In the current study, the synthesis of hydroxyapatite (HAP) and its composite by various techniques, are abridged highlighting the eco-friendly technique – a green synthesis that involves the use of eco-friendly solvents like water and precursor substitution by waste resources. Magnetic HAP plays a major role in the HAP composites because of the ease of recovery and reuse. This study also emphasizes the prowess of the adsorption technique for the removal of various pollutants such as heavy metals, dyes, and emerging pollutants. A detailed adsorption mechanism is explained to understand the possible reactions taking place between the adsorbent and the adsorbate. Recent literature regarding the adsorption of various environmental pollutants by HAP and its composites are reported to support the efficiency of the adsorption process.

Moving towards practical applications of microbial fuel cells for sanitation and resource recovery

Abstract: Sanitation is the basic quality index of life and proper sanitation practices play a vital role in maintaining the hygienic conditions. Use of human waste (urine and faeces) as a substrate for microbial oxidation is found to be sustainable approach towards improving the sanitation facilities. Advancement in microbial fuel cell (MFC) system towards field-scale application for treatment of human waste is restricted by several technological, social, economical, material science and bio-electrochemical limitations. However, recently developed Pee-power urinal and Bioelectric toilet demonstrated the field-scale applicability of MFC for human waste treatment and simultaneous electricity generation for onsite use. This review mainly focuses on suitability and applicability of human waste as a substrate in MFC to improve the sanitation facilities and also the challenges faced while scaling-up of this system for field applications are being discussed along with possible solutions. Recent advancement towards field-scale application of MFC demonstrated that this technology is getting ready for the commercialization in sanitation infrastructure.

Implications of advanced wastewater treatment: Electrocoagulation and electroflocculation of effluent discharged from a wastewater treatment plant

Abstract: In this research, wastewater treatment was inspected on a pilot-scale wastewater treatment plant by electrochemical techniques, electrocoagulation (EC), electroflotation (EF) and electrophoretic deposition (EPD). The wastewater samples have been characterised by applying different parameters to determine optimum working conditions of the electrocoagulation reactor. Two electrodes have been tested separately with an outflow coming from primary and secondary sedimentation tank. The outflows from these tanks are introduced in EC reactor then EC reactor efficacy is determined for the removal of chemical oxygen demand (COD), suspended solids, micropollutants and amount of coagulants in agglomerates at different current densities. The amounts of suspended solids (SS) in influent and effluent streams were determined by the membrane filtration technique. The operational applied current values range from 1–4 A in the case of COD removal by Fe and Al. While for SS aggregation the applied current ranges from 0.5–3 A and inflow rate was tested from 250 to 500 L/h. The pH of outflows increased by increasing applied current and both of these parameters were found a positive increase in the amount of SS aggregations after EC treatment. Furthermore, the COD removal efficiency was found to be 56–57 % and 12–18 % in case Fe and Al electrode respectively after EC treatment. The results showed that applied current is the most effective parameter, whereas the aluminium electrodes have produced more amounts of flocs and bubbles in comparison to iron electrodes at similar amount of current density.

Latest trends in heavy metal removal from wastewater by biochar based sorbents

Abstract: Biochar, a solid carbon-rich residue is derived from wide variety of abundantly available raw materials like forest and agricultural waste, industrial by products and waste, and municipal solid waste through pyrolysis. Besides enhancing soil fertility thereby agricultural productivity and reducing greenhouse gas emissions, biochar based sorbents are widely being employed in waste water treatment owing to their attributes viz., high porosity, large surface area, affinity towards metals, surface modifications, stability, recyclability and even safe disposal. In this comprehensive review, latest trends w.r.t. synthesis protocols, modifications, mechanisms, metal removal comparison, thermo-kinetics, mechanisms, regeneration and safe disposal methods have been presented and discussed. Synthesis through slow pyrolysis (300−700 °C, 0.01−2 °C/s), nanoscale modifications with metal oxides especially based on iron to magnetise the biochar, regeneration through acids and complexation agents are found to be highly promising. While ion exchange and electrostatic interactions are found to be common mechanisms of metal removal which in turn depends on nature of biomass, process conditions and metal, it is found that modifications and mechanisms are strongly interrelated. From our studies, biochar based sorbents gave heavy metal adsorption capacities in mg/g of 1217 (Ag), 560 (Pb), 288 (Cu), 216 (Cd), 204 (As), 130 (Cr), 58 (Ni), 48 (Hg) etc under optimal conditions. Though the nature of kinetic models and isotherms do depend on the material and process conditions, pseudo kinetic models (first and second order) along with Langmuir and Fruendlich isotherms were most widely reported. Disposal of spent biochar could be using it in construction (cement and bricks) and electronic (super-capacitors) industries besides phytoremediation.

A review on valorization of biomass in heavy metal removal from wastewater

Abstract: This review summarizes the progress made, in the field of low-cost biosorption of heavy metal ions, over the past few years. It gives a comprehensive summary of the synthesis, performance, modification and regeneration of biosorbent. The review also focused upon optimum operating parameters, isotherm and kinetic studies. Moreover, from an industrial application point of view, fixed-bed column studies have been discussed in this paper. Methods like chemical pretreatment, grafting, immobilization, etc., which improve the biosorbent properties, have been summarized. Operating parameters that affect the biosorption process such as temperature, pH, contact time, agitation speed, etc. have been studied to understand the relationship between factors and removal efficiency. For most of the studies, biosorption process was found to be endothermic, with room temperature being optimum for the process. Grafting was observed to enhance the adsorption capacity of biosorbent enormously. Biosorption process generally followed Langmuir or Freundlich isotherm, whereas mostly the best fit for kinetic model was pseudo-second-order. Desorption process was mostly carried out via acidic eluent. The performance of biosorbents was observed to be appreciable when they were packed into fixed-bed columns.

Alternative techniques for caffeine removal from wastewater: An overview of opportunities and challenges

Abstract: Water contaminants have attracted considerable research attention owing to the safety risks they pose when present in drinking water consumed by humans and animals, where their high toxicity and bioaccumulation characteristics in biological tissues can cause severe health problems. Caffeine is an emerging contaminant due to its high consumption by the general population, and it can be used to track pollution caused by humans. Approximately 5% of ingested caffeine is excreted through the urine as it cannot be completely metabolized. The caffeine removal efficiency of conventional wastewater treatment methods varies with the system. In addition, studies have reported higher caffeine concentrations in water resources than in water treated in wastewater treatment plants, indicating that effluents are being illegally discharged into rivers. Therefore, alternative caffeine treatment methods have been studied, including adsorption, advanced oxidative processes, bioremediation, and membrane separation. This paper presents a literature review of methods for caffeine removal from aqueous solutions and real effluents, and it covers the main results and limitations of each method. The Scopus database was used to identify relevant articles on caffeine removal. Through the review, it is concluded that even with promising application trends, the current methods developed for caffeine removal present several limitations, often include the complexity of the mechanisms of action, quantification of the contaminants in real effluents, and low sustainability of the technique.

A critical review of antibiotic removal strategies: Performance and mechanisms

Abstract: Environmental pollution by antibiotics has severely affected human health and development. Antibiotic resistance genes (ARGs) have also been recognized as emerging pollutants because of their persistence and adverse impacts in aquatic ecosystems, even at low concentrations. For the alleviation and elimination of antibiotics stress, several approaches have been proposed, some of which have been applied in practice. This review systematically summarizes the removal strategies for various antibiotics and their corresponding mechanisms, including chemical, physical, biological, condition-based and combined strategies. Moreover, a comparison among these methods is made with a focus on the performance and efficiency. Further research needs are also proposed, which provides a guidance for the establishment of a control strategy to achieve simultaneous removal of nitrogen, antibiotics and ARGs.

Peroxymonosulfate-assisted photocatalytic degradation of sulfadiazine using self-assembled multi-layered CoAl-LDH/g-C3N4 heterostructures: Performance, mechanism and eco-toxicity evaluation

Abstract: CoAl-LDH/g-C3N4 (CoAl-LDH/CN) heterostructures was prepared through self-assembly method using exfoliated CoAl-LDH and g-C3N4 nanosheets via electrostatic attraction force. The morphology and physicochemical properties characterization verified the success synthesis of layer-by-layer structure of CoAl-LDH/CN. Heterogeneous catalytic degradation of sulfadiazine (SDZ) was assessed using CoAl-LDH/CN combined with peroxymonosulfate (PMS) and visible light irradiation. A remarkable synergistic effect was obtained in SDZ removal. After 15 min, 10 μM SDZ could be removed by 87.1 % at conditions of 0.1 g/L CoAl-LDH/CN, 0.5 mM PMS, and pH = 6.0. The reusability tests signified the excellent reusing potential of CoAl-LDH/CN. Mechanism study suggested that CoAl-LDH in the heterostructures activated PMS to produce SO4 – and OH, while g-C3N4 acted as dual roles: electron acceptor and PMS activator. Additionally, density functional theory (DFT) calculations successfully disclosed that the sites with high Fukin index (f0) on SDZ molecule were more vulnerable to radicals attack. Eco-toxicity evaluation signified the generation of less toxic intermediates compared to SDZ after photocatalysis. Our findings demonstrate the integration of CoAl-LDH/CN, visible light and PMS can be applied as a promising approach for efficient degradation of organic compound polluted water.

The role of wastewater treatment plants as tools for SARS-CoV-2 early detection and removal

Abstract: The world is facing the third coronavirus caused pandemic in less than twenty years. The SARS-CoV-2 virus not only affects the human respiratory system, but also the gastrointestinal tract. The virus has been found in human feces, in sewage and in wastewater treatment plants. It has the potential to become a panzootic disease, as it is now proven that several mammalian species become infected. Since it has been shown that the virus can be detected in sewage even before the onset of symptoms in the local population, Wastewater Based Epidemiology should be developed not only to localize infection clusters of the primary wave but also to detect a potential second, or subsequent, wave. To prevent a panzootic, virus removal techniques from wastewater need to be implemented to prevent the virus dissemination into the environment. In that context, this review presents recent improvements in all the fields of wastewater treatment from treatment ponds to the use of algae or nanomaterials with a particular emphasis on membrane-based techniques.

Stabilized nanofibers of polyvinyl alcohol (PVA) crosslinked by unique method for efficient removal of heavy metal ions

Abstract: Removal of heavy metal ions is vital in water purification system. In this report we designed a unique method to crosslink polyvinyl alcohol (PVA) nanofiber to enhance its adsorption capacity against metal ions like Copper (Cu2+) and Lead (Pb2+). PVA nanofibers were crosslinked by conventional method using glutaraldehyde vapors and also by solution method (self-designed). Morphological properties were examined by scanning electron microscope (SEM) which confirmed uniform morphology of nanofiber membranes. Thermal degradation analysis was done using thermogravimetric analyzer (TGA). Mechanical properties were also improved significantly in case of solution crosslinked PVA nanofibers. X-Ray diffraction results showed that crystallinity was also increased when nanofibers were crosslinked using solution method. Fourier transform infrared spectroscopy (FTIR) was performed to check bonding of hydroxyl group in the result of crosslinking and it was confirmed that more hydroxyl groups were bound in case of solution crosslinked PVA nanofibers. Adsorption capacity for copper and lead ions was measured using inductively coupled plasma (ICP) atomic emission spectrometer and it was concluded from adsorption data that solution crosslinked PVA nanofibers were far efficient as compared to that of uncrosslinked and vapor crosslinked nanofibers. Equilibrium time was decreased significantly which gives credibility of process with efficient removal of metal ions in shorter time.