Characterization and performance of carbonaceous materials obtained from exhausted sludges for the anaerobic biodecolorization of the azo dye Acid Orange II

Utilizing sludge-based activated carbon for targeted leachate mitigation in wastewater treatment

Activated carbon (AC) based adsorbents derived from waste sludge were utilized to remediate mixed contaminants in wastewater as an integrated waste-to-resource approach promoting a paradigm shift in management of refuse sludge and wastewater. This review specifically focuses on the remediation of constituents of landfill leachate by sludge-based activated carbon (SBAC). The adsorption effectiveness of SBAC for the exclusion of leachate characters including heavy metals, phenols, dyes, phosphates, and phosphorus were explored with regard to modifiers such as pH, temperature, properties of the adsorbent including functional groups, initial doses of absorbent and adsorbate, and duration of exposure to note the impact of each parameter on the efficiency of adsorption of the sludge adsorbent. Through the works of various researchers, it was noted that the properties of the adsorbent, pH and temperature impact the working of SBACs. The pH of the adsorbent by influencing the functional groups. Temperature was expected to have a paramount effect on the adsorption efficiency of the SBACs. The importance of the regeneration and recycling of the adsorbents as well as their leachability is highlighted. Sludge based activated carbon is recommended as a timely, resource-efficient, and sustainable approach for the remediation of wastewater.

Progress and prospects of applying carbon-based materials (and nanomaterials) to accelerate anaerobic bioprocesses for the removal of micropollutants

Carbon‐based materials (CBM), including activated carbon (AC), activated fibres (ACF), biochar (BC), nanotubes (CNT), carbon xenogels (CX) and graphene nanosheets (GNS), possess unique properties such as high surface area, sorption and catalytic characteristics, making them very versatile for many applications in environmental remediation. They are powerful redox mediators (RM) in anaerobic processes, accelerating the rates and extending the level of the reduction of pollutants and, consequently, affecting positively the global efficiency of their partial or total removal. The extraordinary conductive properties of CBM, and the possibility of tailoring their surface to address specific pollutants, make them promising as catalysts in the treatment of effluents containing diverse pollutants. CBM can be combined with magnetic nanoparticles (MNM) assembling catalytic and magnetic properties in a single composite (C@MNM), allowing their recovery and reuse after the treatment process. Furthermore, these composites have demonstrated extraordinary catalytic properties. Evaluation of the toxicological and environmental impact of direct and indirect exposure to nanomaterials is an important issue that must be considered when nanomaterials are applied. Though the chemical composition, size and physical characteristics may contribute to toxicological effects, the potential toxic impact of using CBM is not completely clear and is not always assessed. This review gives an overview of the current research on the application of CBM and C@MNM in bioremediation and on the possible environmental impact and toxicity.

Adsorption Thermodynamic and Kinetic Studies of Methyl Orange onto Sugar Scum Powder as a Low-Cost Inorganic Adsorbent

In the present study, batch adsorption experiments were carried out to investigate the removal of methyl orange (MO) from aqueous solution using sugar scum powder as an effective inorganic adsorbent which is a cheap precursor and abundant. The characteristics of this material were determined using XRD, SEM/EDX, and FTIR. The adsorption performance of sugar scum powder was evaluated using MO as the model adsorbate. Effects of various parameters such as initial dye concentration, contact time, and adsorbent dose were studied. The adsorption process can be best described by the pseudo-second-order kinetic and Langmuir adsorption isotherm models. Maximum monolayer adsorption capacity for MO removal was found to be 15.24 mg/g at temperature 22°C and pH 7.2. Moreover, thermodynamic parameters suggested that the adsorption of MO onto sugar scum powder was a spontaneous and exothermic process. The results demonstrated that sugar scum is a suitable precursor for the preparation of efficient adsorbent for dye removal from wastewater.

Enhanced Capture Ability of Sludge-Derived Mesoporous Biochar with a Template-like Method

Sewage sludge-derived mesoporous biochars (SS-MBCs) were prepared by using cationic polyacrylamide (PAM⁺) as a template agent through a template-like method under high temperature and employed for getting rid of methylene blue (MB) from water. Textural evolution, mesostructured morphology, thermodynamic properties, and surface chemical groups of SS-MBCs were analyzed. It showed that PAM⁺ not only played an important role in good nucleation that brought well-developed texture and novel pore size distribution to SS-MBCs but also improved the MB adsorption capacities of SS-MBCs by increasing the specific surface area and the content of oxygen functional groups, especially the lactone. Preparation factor analysis indicated that PAM⁺ concentration, dosage of additive sludge, and carbonization temperature had distinct effects on material structure and adsorption performance especially above the pyrolytic temperature of 800 °C. The adsorption kinetics and isotherms were analyzed in detail, and it revealed that the kinetics and equilibrium adsorptions of SS-MBCs could be well-described by the Langmuir isotherm model and pseudo-second-order kinetics, respectively. Remarkably, the SS-MBCs showed higher removal efficiency and adsorption capacity than commercial activated carbon and most reported sludge-based adsorbents.

Development of high quality activated carbon from biological sludge and its application for dyes removal from aqueous solutions

A high quality activated carbon was developed from biological sludge of a beverage wastewater treatment plant (BWTP). The material was characterized and its adsorption potential to remove Allura Red AC and Crystal Violet dyes from aqueous media was verified. The ACBS (activated carbon from beverage sludge) revealed mesoporous features, presenting average pore diameter of 6.32 nm, pore volume of 0.5098 cm³ g^-1 and surface area of 631.8 m² g^-1. Adsorption was adequate using 0.25 g L ^-1 of ACBS, and, the process was favored at pH 2.0 for Allura Red AC and pH 8.0 for Crystal Violet. From the kinetic viewpoint, the data were satisfactorily represented by the pseudo-second order model. Freundlich and Sips models were suitable to represent the adsorption equilibrium of the Allura Red and Crystal Violet, respectively. The maximum values for adsorption capacities were 287.1 mg g^-1 for Allura Red and 640.7 mg g^-1 for Crystal Violet. The adsorption of both dyes was thermodynamically spontaneous, favorable and endothermic. In brief, the residual sludge of a wastewater treatment plant may be used as an eco-friendly precursor for ACBS production. ACBS was an efficient adsorbent material able to uptake dyes from aqueous solutions.

Fast Aqueous Biodegradation of Highly-Volatile Organic Compounds in a Novel Anaerobic Reaction Setup

The present work explores the biodegradation of some emerging pollutants (EPs) in an anaerobic slowly-agitated up-flow packed-bed reactor (USPBR) filled with biological activated carbon (BAC). Chlorobenzene (CB) and 2,4-dichlorophenoxyacetic acid (2,4-D) were selected as volatile organic compounds (VOC) and major constituents of many pesticides. Experiments carried out in continuous operation showed that bioconversion up to 90% was achieved for CB and 2,4-D, at space times below 0.6 h and 1.2 h, respectively, at ambient temperature. Overall, removal rates of 0.89 g L−1 d−1 and 0.46 g L−1 d−1 were obtained for CB and 2,4-D, respectively. These results revealed that the degradation of CB and 2,4-D in this anaerobic configuration of bioreactor is an efficient and fast process. The Michaelis–Menten model properly describes the degradation process for CB. Above initial concentrations of 100 mg L−1, 2,4-D presented a considerable inhibitory effect over the biofilm. For this reason, a substrate inhibition factor was included in the Michaelis–Menten equation; the expanded model presented a good fitting to the experimental data, regardless of the inlet concentration. Therefore, USPBR-BAC combination showed to be a highly efficient system for the biodegradation of such compounds.

High-performance microbial fuel cell anodes obtained from sewage sludge mixed with fly ash

Microbial fuel cells (MFCs) are promising for converting biomass energy into electricity, and have attracted much research interest. However, few inexpensive high-performance anode materials for MFCs exist. In this study, MFC anodes composed of sewage sludge and different contents of fly ash (0%, 20%, 40%, 60%, and 80%) are fabricated via a one-step carbonization method. The maximum current density of 25.5 A m^-2 is achieved using the electrode with 20% fly ash, which is 37.5% higher than that of the electrode without fly ash. The improved anode performance is attributed to its good hydrophilicity, which is indicated by its water contact angle of less than 60°, facile adsorption of exoelectrogens, low electron transfer resistance, and good biocompatibility. In addition, the mechanical strength of the electrode with 20% fly ash is approximately 18 times that of the electrode without fly ash. This study reveals a promising method to fabricate high-performance MFC anodes and sheds light on the future development of MFCs using abundant municipal solid waste products.

Optimization of Preparation Conditions of Novel Adsorbent from Sugar Scum Using Response Surface Methodology for Removal of Methylene Blue

A novel and inexpensive adsorbent was prepared from sugar scum for the removal of methylene blue as an organic pollutant from aqueous solutions. The response surface methodology was used to study the effects of the calcination temperature and time on the yield and the methylene blue adsorption. In order to determine the optimal conditions of the preparation, the Doehlert design and desirability function were applied. The increase in calcination temperature increases the methylene blue adsorption and induces a reduction in yield. The optimal conditions have been identified to be a calcination temperature of 986°C and calcination time of 61 min. The characteristics of the obtained adsorbent were determined using SEM/EDX, and surface functions were obtained based on FTIR and pHpzc. The produced adsorbent had a porous structure and a pHpzc of 12.5. The results showed that the yield was 49.74% and the adsorption of methylene blue was 24.52 mg·g−1 with a contact time of 10 h determined by kinetic test. The sugar scum was found to be an effective material for the preparation of appropriate adsorbent for dye removal from wastewater.

The efficacy of bacterial species to decolourise reactive azo, anthroquinone and triphenylmethane dyes from wastewater: a review

The industrial dye-contaminated wastewater has been considered as the most complex and hazardous in terms of nature and composition of toxicants that can cause severe biotic risk. Reactive azo, anthroquinone and triphenylmethane dyes are mostly used in dyeing industries; thus, the unfixed hydrolysed molecules of these dyes are commonly found in wastewater. In this regard, bacterial species have been proved to be highly effective to treat wastewater containing reactive dyes and heavy metals. The bio-decolourisation of dye occurs either by adsorption or through degradation in bacterial metabolic pathways under optimised environmental conditions. The bacterial dye decolourisation rates vary with the type of bacteria, reactivity of dye and operational parameters such as temperature, pH, co-substrate, electron donor and dissolved oxygen concentration. The present paper reviews the efficiency of bacterial species (individual and consortia) to decolourise wastewater containing reactive azo, anthroquinone and triphenylmethane dyes either individually or mixed or with metal ions. It has been observed that bacteria Pseudomonas spp. are comparatively more effective to treat reactive dyes and metal-contaminated wastewater. In recent studies, either immobilised cell or isolated enzymes are being used to decolourise dye at a large scale of operations. However, it is required to investigate more potent bacterial species or consortia that could be used to treat wastewater containing mixed reactive dyes and heavy metals like chromium ions.

One-step synthesis of silicon carbide foams supported hierarchical porous sludge-derived activated carbon as efficient odor gas adsorbent

Hierarchical porous sludge-derived activated carbon coated on macroporous silicon carbide (SiC) foams substrate has been facilely fabricated via a simple one-step strategy by utilizing sludge as carbon source, and jointly using zinc chloride and hexadecanol as pore forming agents. The sludge-derived carbon has been confirmed to be hierarchical macro-meso-microporous structure based on detailed characterization by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectra and nitrogen adsorption-desorption measurement. The adsorption tests showed that the hierarchical porous sludge-derived activated carbon fabricated by one-step pore-forming (zinc chloride and hexadecanol microemulsion mixture) possesses excellent adsorption capacity (259.9mgg^-1, breakthrough time reach 90min and saturation end-time up to 140min) of methyl mercaptan (CH₃SH). The excellent adsorption performance can be attributed to the macroporous SiC foam skeleton and the mesopores channel formed by nonionic surfactant hexadecanol micelles, as well as the micropores activated by ZnCl₂ as odor capture sites. The proposed pore-forming strategy paves an avenue for the sludge disposal and even the development of bio-derived materials.

Nano-rod Ca-decorated sludge derived carbon for removal of phosphorus

Recovering phosphorus (P) from waste streams takes the unique advantage in simultaneously addressing the crisis of eutrophication and the shortage of P resource. A novel calcium decorated sludge carbon (Ca-SC) was developed from dyeing industry wastewater treatment sludge by decorating calcium (Ca) to effectively adsorb phosphorus from solution. The X-ray diffraction (XRD) and Fourier transform infrared (FTIR) techniques were used to characterize the Ca-SCs, followed by isotherm and kinetic sorption experiments. A preferred design with CaCO₃ to sludge mass ratio of 1:2 was found to have a sorption capacity of 116.82 mg/g for phosphorus. This work reveals the crucial role of well-dispersed nano-rod calcium on the Ca-SC surface for the sorption of phosphorus. Moreover, the decoration of nano-rod calcium was found to further promote the uptake of phosphorus through the formation of hydroxylapatite (Ca₅(PO₄)₃(OH)). Thus, the development of decorated Ca-SC for sorption of phosphorus is very important in solving the P pollution and resource loss.

Utilization of sludge based adsorbents for the removal of various pollutants: A review

Sludge based adsorbents are widely used for the removal of various pollutants from water and wastewater systems and the available data is much diversified. The purpose of this review is to organize and critically review the scattered available information on the potential of use of sludge based adsorbents for the removal of various pollutants. It was observed that performance of the sludge based adsorbents varies depending on the type of pollutants, type of precursor sludge, carbonization time-temperature profile and the type of activation conditions used. The variation in pyrolysis and activation conditions found to directly affect the adsorbent properties, adsorption capacity and the mechanism of pollutant removal by sludge based adsorbents. The interaction mechanisms of pollutants with adsorbent surface found to have a detrimental effect on desorption and regeneration of the adsorbents and its recycling potential. Therefore, desorption and regeneration technique used for recycle of the adsorbents is also discussed in detail. Moreover, life cycle and cost analysis of sludge based adsorbents is assessed to ensure the cost effectiveness of their application in water treatment operations.

Conversion of Fe-rich waste sludge into nano-flake Fe-SC hybrid Fenton-like catalyst for degradation of AOII

Permanently increasing in the amount of sludge resulted in the serious environment burden. This work reports a novel carbothermal process for converting the Fe-rich waste sludge into cleaner nano-flake Fenton-like catalyst to relieve the crisis. The transformation of Fe species at different carbothermal temperature was evaluated by XRD analysis. SEM and XPS analyses were involved to characterize the morphology and chemical bonds of the catalysts. Results shown that the resulted catalyst carbonized at 800 °C (Fe-SC-800) was composed of Fe(0) and Fe3O4, performing nano-flake-like structure. The Fe-SC-800 has the highest catalytic activity in degradation of AOII in C0 = 200 mg/L. The efficiency achieves at 98% within 30 min at neutral pH, which is ascribed to the hydroxyl radical oxidation. Moreover, no iron is leached and the Fe-SC-800 could be recycled for three times at least. Thus, the Fe rich sludge could be reutilized as a valuable source for eco-friendly catalyst production, constituting an ecological way to manage these sludge wastes and eliminate the sludge and organic pollution to environment.

Activated carbon derived from carbon residue from biomass gasification and its application for dye adsorption: Kinetics, isotherms and thermodynamic studies

In this work, activated carbon (AC) as an effective and low-cost adsorbent was successfully prepared from carbon residue (or char, one of the by-products from woody biomass gasification) via physical activation. The surface area of char was significantly increased from 172.24 to 776.46m(2)/g after steam activation at 900°C. The obtained activated carbons were then employed for the adsorption of dye (Rhodamine B) and it was found that activated carbon obtained from steam activation exhibited the highest adsorption capability, which is mainly attributed to the higher surface area and the abundance of hydroxyl (-OH) and carboxyl (-COOH) groups on the activated carbon surface. Moreover, it was also found that the adsorption capability significantly increased under the basic condition, which can be attributed to the increased electrostatic interaction between the deprotonated (negatively charged) activated carbon and dye molecules. Furthermore, the equilibrium data were fitted into different adsorption isotherms and found to fit well with Langmuir model (indicating that dye molecules form monolayer coverage on activated carbon) with a maximum monolayer adsorption capability of 189.83mg/g, whereas the adsorption kinetics followed the pseudo-second-order kinetics.

Enhanced azo dye removal in a continuously operated up-flow anaerobic filter packed with henna plant biomass

Effects of henna plant biomass (stem) packed in an up-flow anaerobic bio-filter (UAF) on an azo dye (AO7) removal were investigated. AO7 removal, sulfanilic acid (SA) formation, and pseudo first-order kinetic constants for these reactions (kAO7 and kSA) were higher in the henna-added UAF (R2) than in the control UAF without henna (R1). The maximum kAO7 in R1 and R2 were 0.0345 and 0.2024 cm(-1), respectively, on day 18; the corresponding molar ratios of SA formation to AO7 removal were 0.582 and 0.990. Adsorption and endogenous bio-reduction were the main AO7 removal pathways in R1, while in R2 bio-reduction was the dominant. Organics in henna could be released and fermented to volatile fatty acids, acting as effective electron donors for AO7 reduction, which was accelerated by soluble and/or fixed lawsone. Afterwards, the removal process weakened over time, indicating the demand of electron donation and lawsone-releasing during the long-term operation of UAF.

Role of surfactant derived intermediates in the efficacy and mechanism for radiation chemical degradation of a hydrophobic azo dye, 1-phenylazo-2-naphthol

A combined methodology involving gamma and pulse radiolysis, product analysis and toxicity studies has been adopted to comprehend the degradation process of a model hydrophobic azo dye, 1-phenylazo-2-naphthol, emphasizing the role of the surfactant, which is an integral part of textile waste. Two new and important findings are underlined in this article. The first is the direct attestation of the hydrazyl radical-parent adduct, formed in the reaction of the dye with e(-)aq followed by protonation and subsequent addition to the unreacted dye molecule. This has been confirmed from concentration dependent studies. Secondly, we have clearly shown that in the reaction of hydroxyl radical with the dye in Triton X-100 media, the initially produced TX radicals cause reductive degradation of the dye. Identification and detailed analysis of HPLC and GCMS data reveals that similar products are formed in both the reactions of e(-)aq and OH radicals. Moreover, the cytotoxicity of 10(-4)moldm(-3) dye was found to be reduced significantly after irradiation. Thus, the present study not only depicts new pathways for the degradation of hydrophobic azo dye, but also demonstrates the role of a surfactant in the entire process.

A potential application of sludge-based catalysts for the anaerobic bio-decolorization of tartrazine dye

Two highly efficient (K2CO3/sludge carbon and ZnCl2/sludge carbon) solids were prepared by chemical addition following carbonization at 800 °C and were tested for anaerobic reduction of tartrazine dye in a continuous upflow packed-bed biological reactor, and their performance was compared to that of commercial activated carbon (CAC). The chemical and structural information of the solids was subjected to various characterizations in order to understand the mechanism for anaerobic decolorization, and efficiency for SBCZN800 and SBCPC800 materials was 87% and 74%, respectively, at a short space time (τ) of 2.0 min. A first-order kinetic model fitted the experimental points and kinetic constants of 0.40, 0.92 and 1.46 min(-1) were obtained for SBCZN800, SBCPC800 and CAC, respectively. The experimental results revealed that performance of solids in the anaerobic reduction of tartrazine dye can depend on several factors including chemical agents, carbonization, microbial population, chemical groups and surface chemistry. The Langmuir and Freundlich models are successfully described in the batch adsorption data. Based on these observations, a cost-effective sludge-based catalyst can be produced from harmful sewage sludge for the treatment of industrial effluents.

Aerobic granular sludge-derived activated carbon: mineral acid modification and superior dye adsorption capacity

A novel aerobic granular sludge-derived activated carbon (AC) was prepared by a zinc chloride activation method and further modified by mineral acid (nitric acid (NA) and sulfuric acid (SA)).

Sorption performance and mechanism of a sludge-derived char as porous carbon-based hybrid adsorbent for benzene derivatives in aqueous solution

A porous sludge-derived char was prepared by a new one-step pyrolytic process with citric acid-ZnCl2 mixed fabricating-pore agents. The sludge-derived char was confirmed to be a hierarchically porous hybrid adsorbent containing-elemental carbon, -highly carbonized organic species and -inorganic ash with a great surface area of 792.4m(2)g(-1). It was used as a carbon-based hybrid adsorbent for four benzene derivatives including 4-chlorophenol, phenol, benzoic acid and 4-hydroxylbenzoic acid in aqueous solution. Results showed that their sorption isotherms were nonlinear at low concentrations and linear at high concentrations. The sorption performance could be described by a multiple sorption model (QT=QA+KPCe). The order of these partition sorption coefficients (KP) of these benzene derivatives was consistent with their octanol-water partition coefficients (logKow), but those saturated amounts (QA) were inconsistent with their logKow. The inconstancy was found to be considerably dependent on the preferential interaction of benzoic acid with SiO2 in the sludge-derived char. Quantum theoretical calculation confirmed that the preferential interaction was attributed to the formation of hydrogen bonds (1.61 and 1.69Å) and new Si-O bonds (1.83 and 1.87Å) between the carboxyl of benzoic acid and the SiO2 surface in the sorption process.

Preparation and adsorption behavior of new hollow-like spherical sludge chars for methylene blue

Hollow-like spherical sludge char (HSC) was prepared to decrease low pressure and increase high surface area to 1008 m² g⁻¹.