Multi-antibiotics removal under UV-A light using sol-gel prepared TiO2: Central composite design, effect of persulfate addition and degradation pathway study.

The removal of three antibiotics i.e., metronidazole (MNZ), ciprofloxacin (CIP) and tetracycline (TET), from aqueous system via TiO2 photocatalysis under UV-A light was investigated. Photocatalyst(s) were prepared using sol-gel method under different calcination temperatures (400-800 °C) and water-alcohol ratio. The spherical shaped catalyst (mean particle size âˆ¼ 61 nm) was characterized via FTIR, XRD, BET, SEM, Raman, XPS, UV-DRS, and Fluorometry, and point of zero charge was also determined (pHPZC âˆ¼ 6.6). Batch photo-catalytic degradation studies have shown complete degradation of MNZ, CIP and TET after 50, 75 and 20 min with a TOC removal of 37%, 44% and 31%, respectively. The activity of sol-gel prepared TiO2 was comparatively higher than commercially available pure anatase TiO2 nanoparticles due to lesser mean particle size. The ratio of water to alcohol in the preparation of TiO2 catalyst was found to have significant effect on antibiotic removal. Moreover, persulfate (PS) addition of 0.1 g/L amplified the pseudo-first-order removal-rate constant by 2.75, 3.3 and 1.6 times for MNZ, CIP and TET, respectively. The higher initial pH values (8 and 10) have shown the best removal efficiency for all antibiotics. Subsequently, central composite design (CCD) experiments were conducted under multi-antibiotic conditions. Near complete removal of all antibiotics were observed within 120 min. Scavenging studies revealed that hydroxyl and superoxide radicals play major roles in photo-catalytic degradation of MNZ, CIP and TET. During photocatalysis, MNZ degradation was initiated by hydroxylation reaction, CIP by piperazine ring opening by hydroxyl attack and TET by multiple hydroxylation process. Overall, TiO2 showed good efficiency at degrading multiple antibiotics and has the potential for practical application on a larger scale.

New insight on interfacial charge transfer at graphitic carbon nitride/sodium niobate heterojunction under piezoelectric effect for the generation of reactive oxygen species.

Piezocatalytic removal of metronidazole (MET) using graphitic carbon nitride (g-C3N4, GCN)/sodium niobate (NaNbO3) heterojunction was investigated under ultrasonication. Herein, optimized GCN(50)/NaNbO3 heterojunction achieved 87.2% MET removal within 160 min (k = 0.0138 min-1). A new pathway for the generation of reactive oxygen species (ROS) via GCN(50)/NaNbO3 piezocatalytic heterojunction was identified. The type-II heterojunction formulated using optimized GCN(50)/NaNbO3 was found to generate hydroxyl radical (.OH); however, it was thermodynamically not feasible. The main reasons are; (i) piezopotential generated converted type-II to S-scheme heterojunction and resulted in the participation of high oxidizing potential holes in valence band (VB) of NaNbO3, and (ii) formation of depletion region at the GCN-water interface and subsequent improvement in the redox potential of holes, and (iii) piezopotential generated at NaNbO3 provided bias to GCN and established a piezo-electrocatalytic system. The higher screening of piezopotential in presence of external ions was found to reduce the generation of .OH. Overall, self-powered NaNbO3 has great ability to improve interfacial charge transfer at GCN(50)/NaNbO3 to form ROS.

Single and multi-antibiotics removal via peroxymonosulfate activation using molybdenum disulfide (MoS2): Central composite design and degradation pathway.

The efficacy of molybdenum disulfide (MoS2) for the degradation of metronidazole (MET), tetracycline (TET), and ciprofloxacin (CIP) in single and multicomponent systems through peroxymonosulfate (PMS) activation was investigated. Several characterization techniques, such as SEM, XRD, XPS, and EPR were performed to understand the removal mechanism of the three antibiotics in PMS/MoS2 system. In single component system with an initial antibiotic concentration of 10 mg L-1, >95% removal of MET, TET, and CIP were observed within 60 min (PMS = 100 mg L-1; MoS2 = 0.5 g L-1). It was observed that sulfate radical (SO4.-) and reactive ≡Mo- OOSO3- complex played a major role in the removal of antibiotics. Adsorption on MoS2 and direct oxidation by PMS contributed to the removal of TET and CIP in MoS2/PMS system. A Central composite design (CCD) with response surface methodology (RSM) was used to model the removal of MET, TET, and CIP in a multi-antibiotic system. The presence of multiple antibiotics affected the performance of MoS2/PMS system as antibiotics competed for the adsorption sites on MoS2 and the generated reactive species. CIP predominantly deterred the removal of both MET and TET. On the other hand, MET removal was decreased up to 25-40% in the presence of both TET and CIP. Similarly, TET removal decreased up to 15-20% in the presence of MET and CIP. CIP removal decreased up to 15-25% in the presence of MET and TET. In the presence of multiple antibiotics, the deterring effect of one pollutant over another can be overcome by increasing the MoS2 concentration above 1200 mg L-1 and PMS above 200 mg L-1 to obtain 100% removal of all three pollutants. Overall, MoS2 could be an ideal catalyst for the removal of antibiotics through PMS activation.

Application of Chlorella vulgaris for nutrient removal from synthetic wastewater and MBR-treated bio-park secondary effluent: growth kinetics, effects of carbon and phosphate concentrations.

Application of Chlorella vulgaris for polishing secondary effluent of a wastewater treatment (containing C, N and P) was investigated. As a first step, batch experiments were conducted in Bold's Basal Media (BBM) to quantify the effects of orthophosphates (0.1-107 mg/L), organic carbon (0-500 mg/L as acetate) and N/P ratio on the growth of Chlorella vulgaris. The results revealed that the orthophosphate concentration was found to control the removal rates of nitrates and phosphates; however, both were effectively removed (> 90%) when the initial orthophosphate concentration was 4-12 mg/L. The maximum nitrate and orthophosphate removals were observed at an N:P ratio of ~ 11. However, the specific growth rate (µ) was significantly increased (from 0.226 to 0.336 g/g/day) when the initial orthophosphate concentration was 0.1-4.3 mg/L. On the other hand, the presence of acetate had significantly improved the specific growth and specific nitrate removal rates of Chlorella vulgaris. The specific growth rate increased from 0.34 g/g/day in a purely autotrophic culture to 0.70 g/g/day in the presence of acetate. Subsequently, the Chlorella vulgaris (grown in BBM) was acclimated and grown in the membrane bioreactor (MBR)-treated real-time secondary effluent. Under the optimised conditions, 92% nitrate and 98% phosphate removals (with a growth rate of 0.192 g/g/day) were observed in the bio-park MBR effluent. Overall, the results indicate that coupling Chlorella vulgaris as a polishing treatment in existing wastewater treatment units could be beneficial for highest level of water reuse and energy recovery goals.

Photocatalytic and adsorptive performance of polyvinyl alcohol/chitosan/TiO2 composite for antibiotics removal: single- and multi-pollutant conditions.

A polymer-TiO2 macro composite (i.e., PVA-CS-TiO2) was synthesized via chemical precipitation of PVA-CS-TiO2 blend in alkali/solvent medium and applied for the removal of three model antibiotics (i.e., metronidazole (MNZ), ceftiofur (CEF) and tetracycline (TET)), as single compound and multi-compound conditions. The photocatalytic and adsorptive removals of antibiotics (concentrations of 0.1, 1 and 10 mg L-1) by the composite in an UV reactor system (32 W UV-C power, 0.3 g L-1 of composite) was assessed through kinetic models. Antibiotics adsorption followed pseudo-second-order kinetics, and the order of adsorption was MNZ > TET > CEF. On the other hand, the hydrophilic MNZ was degraded faster compared to hydrophobic CEF and TET drugs. Moreover, UV reactor system exhibited antagonistic behavior under multi-compound condition. Micro-toxicity of antibiotics was performed using bioluminescent bacterium Vibrio fischeri and EC50 of CEF, TET and MNZ were found to be 18.25 mg L-1, 173.8 mg L-1, and 668.6 mg L-1, respectively. However, the relative toxicity levels of PVA-CS-TiO2 and treated effluent were well with the limits as inferred from the microtoxicity analysis. Thus, synthesized biocompatible composite exhibited structural stability, consistent performance for three photocatalytic cycles for all antibiotics at a minimal catalyst loading, easily retained using metallic tea strainer and does not exhibit microtoxicity has a scope for real-time applications.

Leachate treatment using sequential microwave and algal photo-bioreactor: Effect of pretreatment on reactor performance and biomass productivity.

The present study aims to design a lab-scale hybrid reactor, primarily focused on the removal of organics, nutrients, heavy metal and other toxic compounds, thereby, minimizing risk associated with the disposal of landfill leachate. The potential of a designed hybrid treatment system (i.e., sequential microwave (MW) with algal bioreactor) with and without pretreatment, i.e., coagulation-flocculation (CF), was evaluated based on several parameters. The CF pretreatment under optimized conditions has resulted in 90% turbidity and 76% COD removals from leachate; furthermore, the MW treatment achieved 91% ammonia removal from raw leachate. As a result, substantial algal growth was observed in the preliminary algal batch experiment conducted with MW and MW-CF treated samples. Subsequently, leachate treatment was carried out using sequencing batch reactor (SBR) systems, i.e., MW-algal SBR and CF-MW-algal SBR. Algal biomass growth and increment in DO level were observed in algal-SBR experiments. Under the optimized reactor conditions, TN and TP removal rates in the algal-SBR were found to be 1.67-20 mg/L/d and 0.6-9.6 mg/L/d, respectively. The majority of heavy metals present in the leachate were removed due to algal-uptake (mainly Zn2+) and bio-sorption (total-Fe, Cu2+ and Pb2+). Meanwhile, some amount of energy can be recovered from algal biomass as inferred from the cost benefit analysis. Overall, the hybrid treatment combining MW and algal-SBR has shown immense potential for sustainable leachate treatment.

Boosted sono-oxidative catalytic degradation of Brilliant green dye by magnetic MgFe2O4 catalyst: Degradation mechanism, assessment of bio-toxicity and cost analysis.

The magnetic MgFe2O4 nanoparticles (NPs) were fabricated via a facile co-precipitation technique and was comprehensively characterized by XRD, FTIR, SEM, EDX and VSM. The prepared NPs were used as catalyst in presence of ultrasound (US) irradiation to activate persulfate (PS) for generation of sulfate radicals (SO4·-) for boosted degradation of toxic Brilliant Green (BG) dye. Preliminary experiments revealed that highest BG dye degradation efficiency of 91.63% was achieved at MgFe2O4 catalyst dose of 1.0 g/L, PS dose of 300 mg/L, and initial dye concentration of 70 ppm within 15 min of US irradiation. However, only US, US in presence of PS oxidation and US in presence of MgFe2O4 catalyst have shown 20.2%, 83.6% and 45.0% of BG dye removal, respectively. Furthermore, response surface methodology (RSM) based central composite design (CCD) was executed to investigate the effect of interaction between independent variables such as MgFe2O4 catalyst dose (0.5-1.5 g/L), PS dose (150-350 mg/L), initial BG dye concentration (50-150 ppm) and US irradiation time (4-12 min). The RSM based quadratic model was used to predict the experimental data, and the prediction accuracy was confirmed by analysis of variance (R2 = 0.98). The established RSM model has predicted the optimum experimental conditions as MgFe2O4 catalyst dose of 0.75 g/L, PS dose of 300 mg/L, initial dye concentration of 75 ppm and sonication time of 10 min. Subsequently, the treatment cost analysis was performed for all thirty experimental runs of CCD, and the RSM predicted response was found to be evidently optimum as this has delivered best economic condition (140 $/kg of BG removed) with respect to relative dye removal (%). COD removal and residual sulfate analysis have demonstrated satisfactory reduction of COD (90.31%) as well as sulfate ions (42.87 ppm) in the dye solution after treatment. Results of degradation pathway analysis portrayed the transformation of BG molecule (M/Z ratio 385) into simpler fractions with M/Z ratio of 193, 161, 73, and 61. Moreover, the toxicity analysis revealed that sono-catalytically activated PS system has efficiently reduced the toxicity level of BG dye from 93.9% to 5.13%.

Facile synthesis of graphitic carbon nitride from acetic acid pretreatment to activate persulfate in presence of blue light for photocatalytic removal of metronidazole.

Activation of persulfate (PS) in presence of blue LED light (λmax ∼454 nm) using acetic acid modified graphitic carbon nitride (ACN) was investigated. Usage of acetic acid had improved the specific surface area (SSA, 21.89 m2 g-1) of ACN compared with pristine graphitic carbon nitride (GCN) and it also reduced interfacial charge transfer resistance in ACN. Subsequently, photocatalytic removal of metronidazole (MET) was investigated using ACN. It was observed that upward shift in the conduction band (CB) in ACN produced the reduction of PS to form sulfate radicals (SO4.-) (CB of ACN (-1.25 V vs normal hydrogen electrode (NHE); Bandgap = 2.77 eV) and GCN (-1.23 V vs NHE; Bandgap = 2.73 eV)), which enhanced the MET removal. Moreover, batch experiments were conducted to quantify the effects of PS dosage (0.08-0.40 g L-1), ACN dosage (0.20-2 g L-1), light intensity (15-45 W), and pH (2-13.50). ACN (1 g L-1) and GCN (1 g L-1) with 0.16 g L-1 of PS have shown 100% and 76.1% MET (Co-10 mg L-1) removal within 300 min, respectively, and the removal followed zero-order kinetics (k ∼2.39 mg L-1 h-1). However, MET mineralization was approximately 30% with ACN. MET removal had decreased with increase in pH and almost complete inhibition was observed at pH ∼12. Overall, it was identified that SO4.- was the major reactive species whereas holes (h+) in the valence band (VB) of ACN (1.52 V vs NHE) played a minor role in MET removal.

Simultaneous removal of antibiotic and nutrients via Prosopis juliflora activated carbon column: Performance evaluation, effect of operational parameters and breakthrough modeling.

In this study, the behavior of mono-component (metronidazole/phosphate/nitrate, MET/PO43-/NO3-) and multi-component (MET+PO43-+NO3-) adsorption in fixed-bed adsorption column was investigated using Prosopis juliflora activated carbon (PJAC). The influence of column operating parameters such as bed depth (H: 5-15 cm), influent flow rate (Q: 0.5-2 L/h) and adsorbate concentration (Co: 25-100 mg/L) on breakthrough curves were evaluated. The experimental data was correlated with breakthrough models viz. Thomas, Adams-Bohart, Yoon-Nelson and bed depth service time (BDST) models. The results showed that the Thomas model fitted the experimental data better than other models in predicting the breakthrough characteristics for the removal of MET, PO43- and NO3- by PJAC. The maximum adsorption capacity found by Thomas model was 9.70, 8.21 and 5.57 mg/g for MET, PO43- and NO3-, respectively. In multi-component systems, antagonistic behavior in sorption of MET, PO43- and NO3- was observed and as a result, adsorption capacity was 1.2-1.5 folds lesser than that observed in mono-component system. In conclusion, results of the present study indicate that the PJAC can be successfully employed for the removal of MET, PO43- and NO3- using fixed-bed adsorption column; however, the column design for multi-component mixture should be based on rapid breakthrough sorbate.

Microbial fuel cell-based biosensor for online monitoring wastewater quality: A critical review.

Recently, the application of the microbial fuel cell (MFC)-based biosensor for rapid and real-time monitoring wastewater quality is very innovative due to its simple compact design, disposability, and cost-effectiveness. This review represents recent advances in this emerging technology for the management of wastewater quality, where the emphasis is on biochemical oxygen demand, toxicity, and other environmental applications. In addition, the main challenges of this technology are discussed, followed by proposing possible solutions to those challenges based on the existing knowledge of detection principles and signal processing. Potential future research of MFC-based biosensor has been demonstrated in this review.

Mature landfill leachate treatment using sonolytic-persulfate/hydrogen peroxide oxidation: Optimization of process parameters.

The suitability of stand-alone ultrasound (US) system, coagulation pre-treatment followed by US, hydrogen peroxide added US system (US-H2O2) and persulfate added US system (US-PS) for the treatment of matured landfill leachate was investigated. With US system, around 67% COD removal and an increase in BOD/COD ratio were observed (from 0.033 to 0.142) after 15 min at 30% US amplitude. However, the energy input required for landfill leachate treatment in US system was found to be very high due to the presence of fixed solids. Coagulation pretreatment using alum was carried out to improve the overall COD removal and reduce the cost of treatment. As a result, the COD removal was increased to 78% (42% in pretreatment and 36% in US) in 15 min. On the other hand, US-H2O2 and US-PS hybrid systems have shown significant improvement in COD removals (93% and 86%, respectively) from raw leachate after 15 min. Subsequently, a three factor (i.e. PS dose (mg/L), H2O2 dose (mol/L), and US amplitude (%)) 5-level design of experiment was used to maximize the COD removal efficiency by response surface methodology (RSM). The RSM model generated a quadratic equation to accurately analyze the influence of input variables on COD removal efficiency (R2 of 0.92). A maximum COD removal of 98.3% was predicted using the model and the corresponding optimal experimental condition were identified as follows: PS dose ∼4700 mg/L, H2O2 dose ∼0.7 mol/L and US amplitude ∼49%. The overall observations reveals that PS and H2O2 coupled with US system has a great prospective to treat mature landfill leachate.

Sequential coagulation/flocculation and microwave-persulfate processes for landfill leachate treatment: Assessment of bio-toxicity, effect of pretreatment and cost-analysis.

The possibility of landfill leachate treatment in a coupled microwave-persulfate (MW-PS) system with and without pretreatment, i.e. coagulation-flocculation (C-F) was investigated. The C-F pretreatment with alum and FeCl3 has reduced the turbidity from 90 NTU to 43 NTU and 10 NTU, respectively, at the optimized coagulant dosage. Moreover, 73% COD and 86% color removal was observed in C-F pretreatment with FeCl3. The application of MW-PS system (at 10 g/L of PS dosage) for pretreated leachate (FeCl3 dosage 1 g/L and pH 5.5) has produced a final COD removal of 89%. Similarly, alum pretreatment (dosage 1.6 g/L, pH 8.2) coupled with MW-PS system has achieved a total COD removal of 62%. In MW-PS system, the ratio of initial PS dosage to initial COD ratio has shown significant effect on leachate treatment. However, slightly lesser ammonia removal was observed in MW-PS (93%) compared to MW alone (97%) owing to reduction in pH of the system. The comparison of bio-toxicity (i.e. inhibition to aliivibrio fischeri) of treated samples from MW-PS and MW alone after pretreatment, i.e. 12.1 mg/L and 6.8 mg/L of equivalent ZnSO4 toxicity, indicated that MW-PS treated sample were found to be more toxic than MW alone treatment and raw leachate (7.6 mg/L and 7.2 mg/L of equivalent ZnSO4 toxicity, respectively) due to sulfate ion. This indicates that C-F followed by MW alone would be an ideal option for leachate treatment. The cost and energy estimation of MW and MW coupled systems well supported the above findings.

Sulfamethoxazole removal in membrane-photocatalytic reactor system - experimentation and modelling.

In this study, the efficacy of membrane-photocatalytic reactor (MPR) in sulfamethoxazole (SMX) removal was explored at a fixed initial SMX concentration, i.e. 100 mg/L. A supported catalyst, i.e. TiO2 on granular activated carbon (GAC-TiO2), was used for MPR experiments. The SMX removal efficiency of the MPR was investigated under a range of hydraulic retention time (i.e. HRT from 51 to 152.5 min) and TiO2 catalyst dosage (55-50 mg/L). A maximum SMX removal efficiency of 83.6% was observed under 220 mg/L catalyst dosage and 80 min HRT. The increase in catalyst dosage from 55 to 550 mg/L has increased the transmembrane pressure of the reactor from 9.8 to 22.2 kPa. A multiple non-linear regression model was developed based on the experimental data and its significance was analyzed using two-way ANOVA. Based on the model, the optimal HRT and catalyst dosage for complete SMX removal (100%) were found out. The comparison of photocatalytic degradation experiments with sorption experiments conducted earlier revealed that SMX removal in the MPR was mainly by photocatalytic degradation and not by adsorption onto GAC-TiO2 catalyst. However, the performance of MPR in removing other emerging pollutants from real-time wastewaters could be explored before its field-scale application.

Photocatalytic-oxidation and photo-persulfate-oxidation of sulfadiazine in a laboratory-scale reactor: Analysis of catalyst support, oxidant dosage, removal-rate and degradation pathway.

The extent of sulfadiazine (SDZ) removal via photo-degradation (UV-C), photocatalysis with TiO2 (UV-C/TiO2) and photo-persulfate-oxidation (UV-C/PS) was investigated in a batch reactor under different UV-C power levels (i.e. 14, 28, 42 and 56 W). Moreover, effects of suspended/immobilized catalyst, i.e. TiO2 slurry/TiO2 supported on granular activated carbon (GAC-TiO2), on SDZ removal and corresponding SDZ degradation kinetics under different catalyst loading (1-6 g/L) were explored. Around 41.7% SDZ removal was observed after 120 min in UV-C system at the highest power level, i.e. 56 W. On the other hand, photocatalysis with TiO2 and GAC-TiO2 has shown better SDZ removal than photo-degradation. In UV-C/TiO2 (4 g/L and 28 W) and UV-C/GAC-TiO2 (5 g/L and 28 W) systems, SDZ removals were 91.8% after 120 min and 100% after 60 min, respectively; however, TOC analysis has revealed that 45.4% and 60.8% SDZ was mineralized in these systems, respectively. In UV-C/PS system, near complete degradation of SDZ (99.8%) was observed within 10 min under 50 mg/L of PS and 28 W UV illumination. On the other hand, complete SDZ removal was observed in PS alone system at a dosage of 1000 mg/L but the formation of SO42- was found to be a drawback. In photolysis and photocatalysis systems, SDZ removal followed pseudo-first-order kinetics whereas the kinetics followed pseudo-second-order in UV-C/PS system. The comparison of electrical energy consumed (EEO) in different systems revealed that UV-C/GAC-TiO2 and UV-C/PS system were energy efficient compared with other systems. The LC-MS analysis has confirmed the cleavage of C-N bonds in the pyrimidine ring followed by S-N bonds in the sulfonyl group, which was found to be the major degradation pathway of SDZ.

Pharmaceutical products as emerging contaminant in water: relevance for developing nations and identification of critical compounds for Indian environment.

Pharmaceuticals and personal care products (PPCPs) are contaminants of emerging concern and have been detected worldwide in water bodies in trace concentrations. Most of these emerging contaminants are not regulated in water quality standards except a few in the developed countries. In the case of developing countries, research in this direction is at a nascent stage. For the effective management of Pharmaceutical contaminants (PC) in developing countries, the relevance of PCs as an emerging contaminant has to be analyzed followed by regular monitoring of the environment. Considering the resource constraints, this could be accomplished by identifying the priority compounds which is again region specific and dependent on consumption behavior and pattern. In this work, relevance of pharmaceutical compound as emerging contaminant in water for a developing country like India is examined by considering the data pertaining to pharmaceutical consumption data. To identify the critical Pharmaceutical Contaminants to be monitored in the Indian environment, priority compounds from selected prioritization methods were screened with the compounds listed in National List of Essential Medicine (NLEM), India. Further, information on the number of publications on the compound as an emerging contaminant, data on monitoring studies in India and the number of brands marketing the compound in India were also analyzed. It is found that out of 195 compounds from different prioritization techniques, only 77 compounds were found relevant to India based on NLEM sorting.

Carbofuran removal in continuous-photocatalytic reactor: Reactor optimization, rate-constant determination and carbofuran degradation pathway analysis.

Carbofuran (CBF) removal in a continuous-flow photocatalytic reactor with granular activated carbon supported titanium dioxide (GAC-TiO2) catalyst was investigated. The effects of feed flow rate, TiO2 concentration and addition of supplementary oxidants on CBF removal were investigated. The central composite design (CCD) was used to design the experiments and to estimate the effects of feed flow rate and TiO2 concentration on CBF removal. The outcome of CCD experiments demonstrated that reactor performance was influenced mainly by feed flow rate compared to TiO2 concentration. A second-order polynomial model developed based on CCD experiments fitted the experimental data with good correlation (R2 ∼ 0.964). The addition of 1 mL min-1 hydrogen peroxide has shown complete CBF degradation and 76% chemical oxygen demand removal under the following operating conditions of CBF ∼50 mg L-1, TiO2 ∼5 mg L-1 and feed flow rate ∼82.5 mL min-1. Rate constant of the photodegradation process was also calculated by applying the kinetic data in pseudo-first-order kinetics. Four major degradation intermediates of CBF were identified using GC-MS analysis. As a whole, the reactor system and GAC-TiO2 catalyst used could be constructive in cost-effective CBF removal with no impact to receiving environment through getaway of photocatalyst.

Photocatalytic degradation of carbofuran by TiO2-coated activated carbon: Model for kinetic, electrical energy per order and economic analysis.

The photocatalytic removal of carbofuran (CBF) from aqueous solution in the presence of granular activated carbon supported TiO2 (GAC-TiO2) catalyst was investigated under batch-mode experiments. The presence of GAC enhanced the photocatalytic efficiency of the TiO2 catalyst. Experiments were conducted at different concentrations of CBF to clarify the dependence of apparent rate constant (kapp) in the pseudo first-order kinetics on CBF photodegradation. The general relationship between the adsorption equilibrium constant (K) and reaction rate constant (kr) were explained by using the modified Langmuir-Hinshelwood (L-H) model. From the observed kinetics, it was observed that the surface reaction was the rate limiting step in the GAC-TiO2 catalyzed photodegradation of CBF. The values of K and kr for this pseudo first-order reaction were found to be 0.1942 L  mg(-1) and 1.51 mg L(-1) min(-1), respectively. In addition, the dependence of kapp on the half-life time was determined by calculating the electrical energy per order experimentally (EEO experimental) and also by modeling (EEO model). The batch-mode experimental outcomes revealed the possibility of 100% CBF removal (under optimized conditions and at an initial concentration of 50 mg L(-1) and 100 mg L(-1)) at a contact time of 90 min and 120 min, respectively. Both L-H kinetic model and EEO model fitted well with the batch-mode experimental data and also elucidated successfully the phenomena of photocatalytic degradation in the presence of GAC-TiO2 catalyst.

Sulfamethoxazole in poultry wastewater: Identification, treatability and degradation pathway determination in a membrane-photocatalytic slurry reactor.

The presence of sulfamethoxazole (SMX) in a real-time poultry wastewater was identified via HPLC analysis. Subsequently, SMX removal from the poultry wastewater was investigated using a continuous-mode membrane-photocatalytic slurry reactor (MPSR). The real-time poultry wastewater was found to have an SMX concentration of 0-2.3 mg L(-1). A granular activated carbon supported TiO2 (GAC-TiO2) was synthesized, characterized and used in MPSR experiments. The optimal MPSR condition, i.e., HRT ∼ 125 min and catalyst dosage 529.3 mg L(-1), for complete SMX removal was found out using unconstrained optimization technique. Under the optimized condition, the effect of SMX concentration on MPSR performance was investigated by synthetic addition of SMX (i.e., 1, 25, 50, 75 and 100 mg L(-1)) into the wastewater. Interestingly, complete removals of total volatile solids (TVS), biochemical oxygen demand (BOD) and SMX were observed under all SMX concentrations investigated. However, a decline in SMX removal rate and proportionate increase in transmembrane-pressure (TMP) were observed when the SMX concentration was increased to higher levels. In the MPSR, the SMX mineralization was through one of the following degradation pathways: (i) fragmentation of the isoxazole ring and (ii) the elimination of methyl and amide moieties followed by the formation of phenyl sulfinate ion. These results show that the continuous-mode MPSR has great potential in the removal for SMX contaminated real-time poultry wastewater and similar organic micropollutants from wastewater.

Effect of supplementary carbon addition in the treatment of low C/N high-technology industrial wastewater by MBR.

The effect of supplementary carbon addition for the treatment of high-technology industrial wastewater in a membrane bioreactor (MBR) was investigated. The MBR was operated for 302 days under different C/N (BOD(L)/NH(4)(+)-N) ratios, i.e. 0.9-1 to 20 days, 1.6-21 to 42 days, 2.9-43 to 82 days, 3.6-83 to 141 days, 4.8-165 to 233 days and 9.3-240 to 302 days. Irrespective of the C/N ratios investigated, SS and BOD(5) removal efficiencies were above 95% and above 80% COD removal efficiency was observed. In addition, complete nitrification was observed throughout the investigation. However, denitrification and total nitrogen removal efficiencies reached their maximum values at the highest C/N ratio (9.3) investigated. Real-time PCR analysis revealed 10 times higher ammonia oxidizing bacteria to total bacteria ratio under the highest C/N ratio condition (9.3) compared to the low C/N ratio condition (1.6).

Influence of organic matter and solute concentration on nitrate sorption in batch and diffusion-cell experiments.

Nitrate sorption potentials of three surface soils (soils-1-3) were evaluated under different solute concentrations, i.e. 1-100 mg L(-1). Batch and diffusion-cell adsorption experiments were conducted to delineate the diffusion property and maximum specific nitrate adsorption capacity (MSNAC) of the soils. Ho's pseudo-second order model well fitted the batch adsorption kinetics data (R(2)>0.99). Subsequently, the MSNAC was estimated using Langmuir and Freundlich isotherms; however, the best-fit was obtained with Langmuir isotherm. Interestingly, the batch adsorption experiments over-estimated the MSNAC of the soils compared with the diffusion-cell tests. On the other hand, a proportionate increase in the MSNAC was observed with the increase in soil organic matter content (OM) under the batch and diffusion-cell tests. Therefore, increasing the soil OM by the application of natural compost could stop nitrate leaching from agricultural fields and also increase the fertility of soil.