Granular Activated Carbon Particles Research Articles

Removal of N-nitrosopyrrolidine from GAC by a three-dimensional electrochemical reactor: degradation mechanism and degradation path.

Nitrogen-containing disinfection by-products (N-DBPs) produced in the process of drinking water disinfection are widely concerning due to the high cytotoxicity and genotoxicity. It is due to the difficulty of natural degradation of N-DBPs in water and the fact that conventional treatment systems do not effectively treat N-DBPs in drinking water. In this study, N-nitrosopyrrolidine (NPYR) in water was electrocatalytically degraded by a three-dimensional electrode reactor (3DER). This system applied graphite plates as anode and cathode. The granular activated carbon (GAC) was used as third electrode. The degradation of NPYR using a continuous flow three-dimensional electrode reactor was investigated by examining the effects of flow rate, current density, electrolyte concentration, and pollutant concentration on the degradation efficiency, energy consumption, and reaction kinetics of GAC particle electrodes. The results showed that the optimal operating conditions were flow rate = 0.45mL/min, current density = 6mA/cm2, Na2SO4 concentration = 0.28mol/L, and NPYR concentration = 20mg/L. Under optimal conditions, the degradation of NPYR exceeded 58.84%. The main contributor of indirect oxidation was deduced from free radical quenching experiments. NPYR concentration was measured by GC-MS with DB-5 capillary column, operating in full scan monitoring mode for appropriate quantification of NPYR and intermediates. Based on the identification of reaction intermediates, a possible pathway for the electrochemical oxidation of NPYR on GAC particle electrodes was proposed.

Predicting per‐ and polyfluoroalkyl substances removal in pilot‐scale granular activated carbon adsorbers from rapid small‐scale column tests

AbstractPer‐ and polyfluoroalkyl substances (PFAS) occur widely in drinking water, and consumption of contaminated drinking water is an important human exposure route. Granular activated carbon (GAC) adsorption can effectively remove PFAS from water. To support the design of GAC treatment systems, a rapid bench‐scale testing procedure and scale‐up approach are needed to assess the effects of GAC type, background water matrix, and empty bed contact time (EBCT) on GAC use rates. The overarching goal of this study was to predict PFAS breakthrough curves obtained at the pilot‐scale from rapid small‐scale column test (RSSCT) data. The scale‐up protocol was developed for pilot data obtained with coagulated/settled surface water (TOC = 2.3 mg/L), three GACs, and two EBCTs. Between 7 and 11 PFAS breakthrough curves were available for each pilot column. RSSCT designs were investigated that assumed intraparticle diffusivity is independent of GAC particle size (i.e., constant diffusivity [CD]) or linearly dependent on GAC particle size (i.e., proportional diffusivity [PD]). CD‐RSSCTs effectively predicted the bed volumes of water that could be treated at the pilot‐scale to reach 50% breakthrough (BV50%) of individual PFAS. In contrast, PD‐RSSCTs overpredicted BV50% obtained at the pilot‐scale by a factor of ~2–3. The shape of PFAS breakthrough curves obtained with CD‐RSSCTs deviated from those obtained at the pilot‐scale, indicating that intraparticle diffusivity was dependent on GAC particle diameter (dp). Using the pore surface diffusion model (PSDM), intraparticle diffusivity was found to be proportional to (dp)0.25 when considering data up to about 70% PFAS breakthrough. This proportionality factor can be used to design RSSCTs or scale up existing CD‐RSSCT data using the PSDM. Using pilot‐scale data obtained with groundwater and wastewater‐impacted groundwater as well as with additional GACs, the developed RSSCT scale‐up approach was validated for PFAS breakthrough percentages up to 70%. The presented methodology permits the rapid prediction of GAC use rates for PFAS removal.

Polypyrrole Modified Granular Activated Carbon Nanocomposite for Treatment of Wastewater Containing Highly Toxic Hexavalent Chromium

AbstractThis study explored the fabrication of Polypyrrole (PPy) and Granular Activated Carbon (GAC) composites (PPy‐GAC) for effective removal of toxic hexavalent chromium (Cr(VI)) from aqueous solutions. Two synthesis methods are employed: (1) electrostatic deposition of PPy onto pre‐charged GAC paper and (2) in‐situ chemical polymerization of pyrrole monomer with GAC particles. Batch adsorption experiments investigated the impact of various operational parameters on Cr(VI) removal. Compared to pristine GAC (54.64 mg g−1), the PPy‐GAC composite exhibited a remarkable 3‐fold increase in equilibrium adsorption capacity, reaching 175.44 mg g−1. Pseudo‐second‐order kinetic model (R2 > 0.999) accurately described the adsorption kinetics, while the Langmuir isotherm model (R2 > 0.99) provided a good fit for the equilibrium data. Maximum adsorption capacity (qmax) increased with temperature, reaching 204.08, 243.90, and 270.27 mg g−1 at 298, 308, and 318 K, respectively. Furthermore, a fixed‐bed column experiment examined the composite's effectiveness in continuous Cr(VI) removal, demonstrating its suitability for practical applications. Notably, the PPy‐GAC composite successfully removed Cr(VI) from a real wastewater sample containing 68 µg L−1 Cr(VI) obtained from a ferrochrome industry, highlighting its potential for real‐world remediation.

Column-based removal of high concentration microplastics in synthetic wastewater using granular activated carbon

ABSTRACTMicroplastic (MP) is an emerging contaminant of concern due to its abundance in the environment. Wastewater treatment plant (WWTP) can be considered as one of the main sources of microplastics in freshwater due to its inefficiency in the complete removal of small MPs. In this study, a column-based MP removal which could serve as a tertiary treatment in WWTPs is evaluated using granular activated carbon (GAC) as adsorbent/filter media, eliminating clogging problems commonly caused by powder form activated carbon (PAC). The GAC is characterized via N2 adsorption–desorption isotherm, field emission scanning electron microscopy, and contact angle measurement to determine the influence of its properties on MP removal efficiency. MPs (40–48 μm) removal up to 95.5% was observed with 0.2 g/L MP, which is the lowest concentration tested in this work, but still higher than commonly used MP concentration in other studies. The performance is reduced with further increase in MP concentration (up to 1.0 g/L), but increasing the GAC bed length from 7.5 to 17.5 cm could lead to better removal efficiencies. MP particles are immobilized by the GAC predominantly by filtration process by being entangled with small GAC particles/chips or stuck between the GAC particles. MPs are insignificantly removed by adsorption process through entrapment in GAC porous structure or attachment onto the GAC surface.

Effect of mechanical scouring on fouling control in greywater filtration with fluidized bed submerged membrane reactor for decentralized wastewater treatment process

Synthetic greywater was applied into a novel, fluidized submerged membrane reactor (FSMR) to compare membrane fouling with three different types of scouring agents: granular activated carbon (GAC), tubular polyvinylidene fluoride (PVDF) media, and spherical polyethylene terephthalate (PET) beads. Trans-membrane pressure (TMP) was investigated to estimate the extent to the fouling in the FSMR operated at 13 and 40 L/m2.h of permeate flux. The selection of scouring agents affected transient behavior of TMP value significantly to reduce membrane fouling. Fluidization of spherical PET beads driven by recirculating bulk suspension only through the FSMR was a prominent way to mitigate fouling. However, the cake layer was formed on membrane surface extensively as GAC or tubular PVDF media was fluidized over the course of reactor operation. At 13 L/m2.h, the TMP reached 0.74, 0.7, and 0.04 bar after 7 d operation with FSMR added with GAC particles, tubular PVDF media, and spherical PET beads as scouring agent, respectively. For the non-adsorbing PET beads, organic compound such as humic acids and proteins were a main organic fraction in cake layer. The organic removal efficiency was enhanced by complex formation resulting from the concentrated greywater in the reactor operated during extended filtration time. However, small carbon particles produced by the pulverization of GAC particles in the FSMR system disrupted fouling control and led rapid TMP rise.

Membrane fouling, methane production and microbial community under fluidization of biocarrier with conductive surface in anaerobic fluidized bed membrane bioreactor for greywater treatment

A comparative study of organic removal efficiency, fouling control, and methane production from synthetic greywater was performed operating three anaerobic fluidized bed membrane bioreactors (AFMBRs). Granular activated carbon (GAC) particles, polyaniline-coated polyethylene terephthalate (PET) beads, and uncoated PET beads were added as scouring agent to control fouling through each AFMBR. The use of PET spherical beads coated with polyaniline as a fluidized medium improved both fouling reduction and methane production kinetics. Although the GAC particles showed the highest organic removal efficiency in AFMBR due to adsorption capability, their progressive fragmentation reduced the methanogenic population and accelerated fouling rate. Microbial activity was adversely affected when the bulk biomass was exposed to the surfactant in the synthetic greywater. Microbiome analysis showed that the methanogenic archaeal population in the GAC bulk biomass reduced significantly from 10 to 0.5%, which corroborates the decrease in methane production rate. The methanogens on the PET beads shifted gradually from acetoclastic Methanosaeta to hydrogenotrophic Methanospirillum presumably because of the detachment of the biofilm that suppressed the slow-growing Methanosaeta. In addition, the key exoelectrogenic microbes were related to Desulfovibrio and Geobacter, which may be associated with direct interspecies electron transfer with the methanogens.

Gravity-driven membrane reactor for decentralized wastewater treatment: Comparison of reactor configuration and membrane module

Gravity-driven membrane (GDM) filtration is an attractive option for decentralized wastewater treatment due to lower energy consumption. However, insufficient information is available on the design factors of GDM reactor. In this study, we investigated the impacts of membrane aeration, types of membrane modules, and biocarrier deposition onto the membrane on water quality and membrane performance of GDM reactors. In detail, the membrane air diffuser located inside the granular activated carbon (GAC)-biofilm zone had benefit for mass transfer of dissolved oxygen and achieving co-existence of anoxic and aerobic conditions in the reactor, leading to higher removal efficiencies for organics (93.8–94.6 %), nitrogen (38.2–47.2 %) and phosphorus (31.9–57.7 %), compared to the air diffuser located outside the GAC zone (90.3 % for organics, 25.3 % for nitrogen and 7.0 % for phosphorus). In addition, the inside-out ceramic hollow fibre membrane showed ∼150–200 % higher fouling resistance (mainly cake resistance) due to greater biopolymer deposition compared to the outside-in polymeric hollow fibre membrane. However, for the outside-in flat sheet configuration, the ceramic and polymeric membranes showed comparable fouling resistance. The deposition of GAC particles on the membrane surface as secondary layer could improve permeate water quality, but at the expense of an increase in irremovable fouling.

Pilot-scale aerobic granular sludge reactors with granular activated carbon for effective nitrogen and phosphorus removal from domestic wastewater

Aerobic granular sludge (AGS) is a breakthrough biotechnology of 21st century and an innovative alternative to activated sludge for treating wastewater. Concerns on long-start up periods for development of AGS and stability of granules are impeding its widespread implementation for treating low-strength domestic wastewater especially in tropical climate conditions. Addition of nucleating agents have been shown to improve development of AGS while treating low-strength wastewaters. There are no previous studies on AGS development and biological nutrient removal (BNR) in the presence of nucleating agents during treatment of real domestic wastewater. This study investigated AGS formation and BNR pathways while treating real domestic wastewater in a 2 m3 pilot-scale granular sequencing batch reactor (gSBR) operated without and with granular activated carbon (GAC) particles. The gSBRs were operated under tropical climate (T ≈ 30 °C) for >4-years to evaluate the effect of GAC addition on granulation, granular stability and BNR at pilot-scale. Formation of granules was observed within 3 months. MLSS values of 4 and 8 g/L were recorded within 6 months in gSBRs without and with GAC particles, respectively. The granules had an average size of 1.2 mm and SVI5 of 22 mL/g. Ammonium was mainly removed through nitrate formation in the gSBR without GAC. But, ammonium was removed by short-cut nitrification via nitrite due to washout of nitrite oxidizing bacteria in the presence of GAC. Phosphorus removal was much higher in gSBR with GAC due to the establishment of enhanced biological phosphorus removal (EBPR) pathway. After 3 months, the phosphorus removal efficiencies were at 15 % and 75 %, respectively, without and with GAC particles. The addition of GAC led to moderation in bacterial community and enrichment of polyphosphate-accumulating organisms. This is the first ever report on pilot-scale demonstration of AGS technology in the Indian sub-continent and GAC addition on BNR pathways.

Preparation of Granular Activated Carbon Particle Electrode Loaded with Co3O4 and its Effect on Amoxicillin Wastewater Treatment

In this work, granular activated carbon (GAC) loaded with Co3O4 catalyst (Co3O4/GAC) was used as a particle electrode for three-dimensional (3D) electrochemical treatment of amoxicillin (AMX) wastewater. The morphology, crystal structure, surface chemical bonds, specific surface area, and pore structure of the particle electrodes were characterized. Considering AMX and TOC removal rates and electrical energy consumption (EEC), the optimal manufacturing conditions of the Co3O4/GAC were determined as the calcination temperature of 700 °C, the calcination time of 5 h, and the impregnation time of 3 h, respectively. The measurement of electrochemical impedance spectroscopy showed that the interfacial electron transfer property of Co3O4/GAC was much improved compared with GAC. AMX removal rate (96.0%, 40 min), TOC removal rate (84.4%, 2 h), and EEC (87.2 kWh kg−1 TOC) of the 3D-Co3O4/GAC system were all significantly improved compared to the 3D-GAC system (77.9%, 40.3%, 232.9 kWh kg−1 TOC) and the 2D system (66.4%, 3.9%, 2080.3 kWh kg−1 TOC) under the same operating conditions. It was confirmed that Co3O4/GAC catalytically generates ·OH and H · radicals and increases the conductivity inside the reactor. The degradation of AMX was confirmed using ultraviolet-visible spectroscopy and the degradation mechanism of AMX in the 3D-Co3O4/GAC system was proposed.

Nano α-Fe2O3 Self-Assembled Hybrid Biofilm Boosts Hydrogen Autotrophic Denitrification in a Three-Dimensional Biofilm Electrode Reactor

The performance of three-dimensional biofilm electrode reactors (3D-BERs) in hydrogen autotrophic denitrification is determined by electroactive biofilms. Herein, a self-assembled hybrid biofilm (SAHB) is developed on granular activated carbon particle electrodes by incorporating nano α-Fe2O3. The influences of operating parameters such as current, influent concentration, and hydraulic retention time (HRT) on denitrification are investigated as well as the mechanisms of SAHB-improved denitrification. The results indicate that SAHB achieves a high autotrophic denitrification rate of 4.20 mg TN/L/h under 40 mA current, 100 mg/L nitrate, and 26 h HRT, outperforming the naturally formed biofilm by 23.53%. SAHB contains more microorganisms than naturally formed biofilms, revealing that nano α-Fe2O3 is conducive to trapping free microorganisms on particle electrodes. SAHB enriches denitrification-related genes and increases corresponding enzyme activities (particularly nitrite reductase). According to metagenomic sequencing, nano α-Fe2O3 addition at a current level of 40 mA appears to favor denitrification via the nirS-dependent pathway probably due to its high affinity for cytochrome C. Metagenomic binning reveals that the microorganism associated with Zoogloeaceae (Rhodocyclales order) in SAHB may play a pivotal role in hydrogen autotrophic denitrification. This work develops a novel denitrification system, furthering our understanding of hydrogen autotrophic denitrification in 3D-BERs.

De novo granulation of sewage-borne microorganisms: A proof of concept on cultivating aerobic granular sludge without activated sludge and effective enhanced biological phosphorus removal

Long start-up periods for granulating activated sludge and concerns on granular stability are the bottlenecks reported during implementation of novel aerobic granular sludge (AGS) technology in municipal wastewater treatment plants. Here, de novo granulation of sewage-borne microorganisms without using activated sludge (AS) inoculum was investigated in bench-scale sequencing batch reactors (SBR). Data showed that formation of AGS from sewage-borne microorganisms was rapid and first granules appeared within one week. Granulation was indicated by appearance of biomass particles (size >0.12 mm), high biomass levels (∼8 g/L) and superior settling properties (SVI30 min: 30 mL/g). Granulation process involved distinct stages like formation of aggregates, retention of aggregates, and growth of millimetre sized granules. Simultaneous COD, nitrogen and phosphorous removal was established within 10 days of start-up in the SBR without using AS inoculum. However, phosphorus removal became stable after 50 days of start-up. Total nitrogen (TN) and total phosphorus (TP) removals of 92% and 70%, respectively, were achieved from real domestic wastewater. Furthermore, addition of granular activated carbon (GAC) had improved both granulation and biological nutrient removals. Interestingly, phosphorus removal became quite stable within 10 days of start-up in the SBR operated with GAC particles. TN and TP removals were found to be higher at >98% and >94%, respectively, in GAC-augmented SBR. Removal of ammonia and phosphorus were mediated by nitritation-denitritation and enhanced biological phosphorus removal (EBPR) pathways, respectively. The bacterial diversity of AGS was lower than that of sewage. Quantitative PCR indicated enrichment of ammonia oxidizing bacteria, denitrifying bacteria and polyphosphate accumulating organisms during granulation. De novo granulation of sewage-borne microorganisms is a promising approach for rapidly cultivating AGS and establishing biological nutrient removal in sewage treatment plants.

Advanced water treatment process by simultaneous coupling granular activated carbon (GAC) and powdered carbon with ultrafiltration: Role of GAC particle shape and powdered carbon type

In current ultrafiltration systems, limited removal for small-sized contaminants and membrane fouling remain longstanding obstacles to overcome. Herein, a novel process by simultaneous coupling powered carbon (PC) and fluidized granular activated carbon (GAC) with ultrafiltration was proposed aiming to achieve high effluent quality and mitigated membrane fouling. This study conducted mechanistic explorations on the performances of different-shaped GAC particles on fouling control and PC release during fluidization, meanwhile comparing the utilizations of powdered activated carbon (PAC) and biochar in terms of their adsorption, deposition and interactions with aquatic contaminants during filtration. The results showed that the effluent COD of biochar-UF was slightly higher than PAC-UF attributed to lower specific surface area and pore volume present on biochar. Compared with PAC-UF, the biochar-UF without fluidized GAC exhibited higher fouling propensity due to more organics attached on membranes via bridging with Ca2+ released by the biochar. Concurrently, distinct morphologies were found for PAC and biochar depositions, where PAC uniformly dispersed on membranes but biochar tended to agglomerate. Interestingly, fluidized spherical GAC (RGAC) with highest particle momentum and least energy consumption appeared highly effective in reducing fouling associated with biochar, and the overall fouling rate of RGAC-biochar-UF was even lower than RGAC-PAC-UF system. More importantly, substantial amount of small-sized PC was released by two cylindrical-shaped GACs, which were determined to be around 12–16 mg/L in contrast to merely 3.4 mg/L produced from RGAC. Consequently, the RGAC-biochar-UF system achieved commensurate effluent quality but better permeability than RGAC-PAC-UF along with a 20% expenditure saved, which might be a promising water treatment system more suitable for large-scale applications.

Comparison of pyrophyllite- and alumina-coated membrane treating industrial wastewater in aspect of membrane fouling and organic removal

In this study, two ceramic membranes such as coated alumina-based (ACA) and low cost coated pyrophyillite-based (ACP) membranes were compared for elucidating the effect of feed charge on fouling control and fluidization of adsorbent on the treatment of organic solution. The granular activated carbon (GAC) was fluidized along the surface of ceramic membrane to provide physical scouring and adsorption capability. Results revealed that the surface of ACP membrane was rougher than that of ACA membrane showing surface roughness of 81.2 and 61.6 nm, respectively. Furthermore, contact angle of ACP membrane was higher than that of ACA membrane (32° vs. 10°). Without GAC fluidization, the fouling rate resulting from ACP membrane was dependent upon the type of wastewater. With ACP membrane, membrane fouling was higher with cationic dye-based wastewater than that with anionic dye-based one. Regardless of different types of wastewaters, relatively low fouling was observed for ACA membrane. The intrinsic properties of membranes such as surface roughness, surface charge and hydrophilicity played important roles in determining membrane fouling. Low organic rejection efficiency (less than 40 %) was observed during membrane filtration without GAC. However, almost 98 % of organic rejection efficiency was reached within initial 30 min of filtration under the GAC fluidization at 50 % of packing ratio based upon effective reactor volume. Under the 10 % of packing ratio with GAC particles, membrane fouling was controlled successfully during 12 h filtration with almost complete UV removal efficiency within initial 4 h of filtration.

Simultaneous coupling of fluidized granular activated carbon (GAC) and powdered activated carbon (PAC) with ultrafiltration process: A promising synergistic alternative for water treatment

Ultrafiltration (UF) has been extensively employed in current water treatment practice, during which limited removal for soluble contaminants and membrane fouling remain two perennial hurdles to efficient operation. This study proposed a promising approach by simultaneous coupling of fluidized granular activated carbon (GAC) and PAC with UF process, whereby PAC was responsible for improving effluent quality, and fluidized GAC was targeted for mitigating UF fouling and PAC deposition. The operational performance of such integrated GAC-PAC-UF system was systemically evaluated in a lab-scale setup. The results showed that fluidized GAC particles with larger size appeared highly effective in removing PAC deposition and fouling formed by surface water. PAC addition improved the effluent quality mainly by adsorbing humic acid-like substances. More importantly, energy consumption by GAC fluidization was found to be at least an order-of-magnitude lower than conventional fouling control methods employed in UF. Furthermore, redundancy analysis revealed that the key mechanism for UF fouling mitigation was tied to GAC particle momentum, whereas inorganic fouling mitigation was mostly achieved by GAC-induced liquid turbulence. It is expected that such integrated GAC-PAC-UF process proposed should be technically feasible and economically viable, potentially achieving high permeate quality and reducing membrane fouling with limited energy requirement.

Long-term performance of granular activated carbon electrode system for the removal of amoxicillin

Three-dimensional electrode reactor, packed with conductive particles, is more cost-effective than traditional two-dimensional electrode reactor. In this study, granular activated carbon (GAC) was applied as particle electrode, then the long-term performance on amoxicillin (AMX) removal and activated carbon regeneration of the GAC particle electrode oxidation process (GAC EOP) was investigated, and the GAC adsorption process (GAC ADS) was carried out for comparison. Both of them ran continuously to remove AMX. Because of the regeneration effect of electrochemical action, the GAC EOP showed a more stable physisorption capacity than GAC ADS, with less change in micropore volume, pore size distribution and surface morphology of GAC. The result of XPS revealed the AMX chemisorption mechanism: the carbonyl (CO) and phenolic hydroxyl (OH) on activated carbon combined with carboxyl (COOH) and ammonium group (NH3+) on AMX, respectively. Correspondingly, the content of CO and OH on GAC fell significantly during the GAC ADS. However, due to the chemical bond regeneration effect of electrolysis, noticeable declines were not observed in GAC EOP, which ensured the stable chemisorption capacity of this system. It was shown that during the 50 consecutive runs, the AMX removal in GAC EOP was always higher than 60%. Even the removal efficiency showed an upward tendency, with the average value reached 86.1% and 99.1% in the 31–40 and 41–50 run times respectively. It was because of the rising specific surface area of GAC and the effect of electro-polarization, which made it more meaningful to explore the long-term performance of three-dimensional electrode reactor.

Preparation and characterisation of polypyrrole nanoparticles for enhancement of granular activated carbon (GAC) as adsorbent

BackgroundThe adsorption capacity of Granular Activated Carbon (GAC) is being enhanced using various nanoparticles. A special category of nanohybrid materials also called Janus particles have gained huge interest owing to their tunable properties. The purpose of this work is to report on the synthesis and characteristics of a Janus Ppy-GAC nanocomposite with increased functionality to be applied as a robust adsorbent for efficient and simultaneous removal of organic and inorganic pollutants from wastewater. MethodsA novel method for the preparation of Polypyrrole (Ppy) nanoparticles is presented. All materials were characterised using Raman spectroscopy and Atomic Force Microscopy (AFM). Significant findingsRaman spectroscopy of Janus Ppy-GAC nanocomposite depicts peaks for both Ppy and GAC with slight shifts of major peaks denoting a strong interfacial bond between the two phases. Ppy nanoparticles were successfully attached to one side of the GAC surface with relatively strong adhesion forces amounting to 10.8 nN on average. An increase in adhesion forces of 25% was observed when Ppy nanoparticles were deposited on the surface of GAC particles as compared to pristine GAC. This implies that the Janus Ppy-GAC nanocomposite is sufficiently robust to be used as an adsorbent for water treatment.

Improved degradation of diuron herbicide and pesticide wastewater treatment in a three-dimensional electrochemical reactor equipped with PbO2 anodes and granular activated carbon particle electrodes

The electrocatalytic performance of porous carbon felt/PbO2 and planar titanium/PbO2 anodes in a three-dimensional electrochemical reactor (3DER) equipped with granular activated carbon (GAC) particle has been studied for synergistic degradation of diuron herbicide (DIU) and treatment of pesticide wastewater. The results showed that porous carbon felt/PbO2 anode in addition to high stability can provide around three times more surface area than titanium/PbO2 for degradation reactions. Optimization of DIU degradation in 3DER system with carbon felt/PbO2 anode was performed by a five-level rotatable central composite design. The TOC mineralization rate under optimal conditions (pH = 4.7, current density = 13.5 mA cm−2, Na2SO4 concentration = 0.04 M and DIU concentration = 40 mg L−1) for the 3ٍِDER system with carbon felt/PbO2 and titanium/PbO2 anodes after 50 min were 100% and 63.8%, respectively. However, the electrocatalytic efficiency of carbon felt/PbO2 and titanium/PbO2 anodes in the absence of GAC particles to remove TOC was 85.5 and 42.7%, respectively. The energy consumed in the 3DER system equipped with carbon felt/PbO2 anode was 2.28 times less than the 3DER system with titanium/PbO2. The contribution of direct and indirect oxidation of DIU in 3DER degradation systems was determined by radical scavenging technique. The safety of the anodes was evaluated for Pb2+ leakage. The DIU degradation pathway was proposed based on the intermediates identified by LC-MS. The performance of optimized 3DER systems was evaluated for treatment of real pesticide wastewater. The chemical oxygen demand (COD) removal efficiency after 300 min of reaction in the 3DER system with carbon felt/PbO2 and titanium/PbO2 electrodes was 95% and 62.5%, respectively.

Enhanced electrocatalytic degradation of bisphenol A by graphite/β-PbO2 anode in a three-dimensional electrochemical reactor

In this study, the electrocatalytic synergy of the graphite/β-PbO2 anode and granular activated carbon (GAC) particles electrodes for bisphenol A (BPA) degradation are investigated in a three-dimensional electrochemical reactor (3DER). The graphite/β-PbO2 anode was prepared by anodic deposition method and the electrocatalytic properties of lead oxide film were studied by FESEM, XRD, EDX-mapping, linear sweep voltammetry and accelerated lifetime test techniques. The effect of five independent variables including pH, Na2SO4 concentration, current density, GAC amount, and reaction time on the system response was optimized by an orthogonal central composite-genetic algorithm (OCCD-GA). The results showed that β-PbO2 crystals were deposited as completely compact pyramidal clusters on the graphite surface. In addition, the service life and oxygen evolution potential (OEP) for the electrocatalytic layer of β-PbO2 were 90 h and 2 V, respectively. Based on the developed quadratic model (R2 > 0.99 and p-value < 0.0001), the optimal points for pH, Na2SO4 concentration, current density, GAC amount, and reaction time were predicted to be 4.6, 0.074 mol L−1, 35.7 mA cm−2, 25 g, and 80 min, respectively. Under optimal conditions, BPA removal efficiency in 3DER system and separate application of electrocatalytic degradation and GAC were obtained 98.8%, 72.2% and 9.75%, respectively. Thus, the electrocatalytic synergy of 3DER system due to lead oxide layer and GAC particle electrodes in BPA degradation was calculated to be 35.5%. LC-MS analysis was used to identity the intermediates formed during BPA degradation. The final degradation intermediates were short-chain acids including adipic acid, malonic acid and, acetic acid.

Improved performance and cost efficiency by surface area optimization of granular activated carbon in air-cathode microbial fuel cell

Microbial fuel cell (MFC) architectural modification is increasingly becoming an important area of research due to the need to improve energy recovery. This study presents a low-cost modification method of the anode that does not require pre-treatment-step involving hazardous chemicals to improve performance. The modification step involves deposition of granular activated carbon (GAC) which is highly conductive and provides a high specific surface area inside a carbon cloth that acts as an anode and as a supporting material. The GAC particle size of 0.6–1.1 mm resulted in an increase in air-cathode MFC performance due to an increase in available surface area of 879.5 m2 g−1 for attachment of cells based on Brunauer, Emmett, and Teller (BET) results, and an increase in the appropriate surface for attachment of cells which was rough based on the scanning electron microscope (SEM) results. On the other hand, although GAC with size of particles of 0.45–0.6 mm had the highest available surface area for attachment of cells, it lacked the appropriate surface for attachment of cells and reduced MFC performance. This means that particle size optimization of GAC is essential since there is a limit to which the particle diameter can be reduced. The utilization of the GAC with the optimized particle size produced an output voltage of 507.5 mV and maximum power output of 1287.7 mW m−3 at current output of 2537.5 mA m−3. This study also showed that there is an economic benefit in modifying carbon cloth using GAC with optimized particle size.

Combined Effect of Activated Carbon Particles and Non-Adsorptive Spherical Beads as Fluidized Media on Fouling, Organic Removal and Microbial Communities in Anaerobic Membrane Bioreactor.

The combined effect of acrylonitrile butadiene styrene (ABS) spherical beads and granular activated carbon (GAC) particles as fluidized media on the performance of anaerobic fluidized bed membrane bioreactor (AFMBR) was investigated. GAC particles and ABS beads were fluidized together in a single AFMBR to investigate membrane fouling and organic removal efficiency as well as energy consumption. The density difference between these two similarly sized media caused the stratified bed layer where ABS beads are fluidized above the GAC along the membrane. Membrane relaxation was effective to reduce the fouling and trans-membrane pressure (TMP) below 0.25 bar could be achieved at 6 h of hydraulic retention time (HRT). More than 90% of soluble chemical oxygen demand (SCOD) was removed after 80 d operation. Biogas consisting of 65% of methane was produced by AFMBR, suggesting that combined use of GAC and ABS beads did not have any adverse effect on methane production during the operational period. Scanning Electron Microscope (SEM) examinations showed the adherence of microbes to both media. However, 16S rRNA results revealed that fewer microbes attached to ABS beads than GAC. There were also compositional differences between the ABS and GAC microbial communities. The abundance of the syntrophs and exoelectrogens population on ABS beads was relatively low compared to that of GAC. Our result implied that syntrophic synergy and possible occurrence of direct interspecies electron transfer (DIET) might be facilitated in AFMBR by GAC, while traditional methanogenic pathways were dominant in ABS beads. The electrical energy required was 0.02 kWh/m3, and it was only about 13% of that produced by AFMBR.