Valorization of algal biomass to synthesize heterogeneous gC3N4-Biochar photocatalyst for the treatment of industrial wastewater using photocatalysis-persulfate oxidation process.

Textile wastewater, heavily contaminated with organic dyes, is generating severe problems to environment and human health. The implementation of gC3N4 with biochar (gC3N4-BC) for the treatment of textile wastewater is less effective due to the limited adsorption capacity and slower degradation kinetics. To tackle these problems, peroxydisulfate (PDS) is integrated with gC3N4-BC photocatalyst to enhance the process efficiency and kinetics. The synthesized gC3N4-BC-5 composite shows higher separation of charge carriers, light absorbance, and lower energy bandgap (2.62 eV). The results of photocatalytic degradation and rate constant are enhanced up to 99.9 % and 0.041 min-1 using gC3N4-BC-5 with PDS as compared to without PDS (96.8 % and 0.028 min-1, respectively). The radicals (SO4-•,O2-•, and OH•) are responsible to improve the degradation process efficiency and kinetics. The reusability of optimized sample indicates that gC3N4-BC-5 is stable and effective up to five cycles. The gC3N4-BC-5 composite attains highest adsorption (70.9 %) when compared to BC (62.3 %) and pure gC3N4 (27.1 %). The well-fitted models of adsorption (Pseudo-Second-Order and Freundlich) confirm the favorable, chemical, and multilayered adsorption process. The coupling of gC3N4-BC-5 with PDS is effective, efficient, and stable process to enhance the kinetics and degradation of textile wastewater.

Macroalgal biochar synthesis and its implication on membrane fouling mitigation in fluidized bed membrane bioreactor for wastewater treatment.

The intensification of biochar into fluidized bed membrane bioreactor was investigated to mitigate membrane fouling. Different biochars from algal biomass were produced and used as biomaterials for wastewater treatment. In this study, different macroalgal biochar was synthesized at different pyrolysis temperatures and characterized using Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Brunauer Emmett-Teller (BET) and Fourier transform infrared spectroscopy (FTIR) techniques to implicate their effect on membrane fouling reduction in fluidized bed membrane bioreactor. The combined effect of macroalgal biochars and biocarriers with gas sparging was evaluated for fouling mitigation. Macroalgal biochar curtailed membrane fouling effectively at low gas sparging rate. Transmembrane pressure (TMP) was reduced to 0.053 bar; under the fluidization of biochar-650 and biocarriers with gas sparging; from 0.27 bar (gas sparging only). Combined effect of gas sparging, biocarriers and biochar-650 instigated 92.1% fouling reduction in comparative to gas sparging alone. Mechanical scouring driven by biocarriers could reduce fouling due to removing surface deposit of foulants from membrane surface effectively and biochar can efficiently adsorb foulants because of its active functional groups resulting in reduction of colloidal fouling. The addition of divalent ions (Ca2+) further enhanced the fouling reduction in fluidized bed membrane bioreactor.

Removal of ceftriaxone sodium antibiotic from pharmaceutical wastewater using an activated carbon based TiO2 composite: Adsorption and photocatalytic degradation evaluation.

The water pollution becomes a serious concern for the sustainability of ecosystems due to the existence of pharmaceutical products (ceftriaxone (CEF) antibiotic). Even in low concentration of CEF has lethal effects on ecosystem and human health. To remove CEF, TiO2 is considered as an effective and efficient nanoparticles, however its performance is reduced due to wider energy gap and rapid recombination of charge carriers. In this study, activated carbon based TiO2 (ACT-X) heterogeneous nanocomposites were synthesized to improve the intrinsic properties of TiO2 and their adsorption-photocatalytic performance for the removal of CEF. The characterization results revealed that ACT-X composites have slower recombination of charge carriers, lower energy band gap (3.05 eV), and better light absorption under visible region of light. From ACT-X composites, the ACT-4 photocatalyst has achieved highest photocatalytic degradation (99.6%) and COD removal up (99.2%). The results of radical scavengers showed that photocatalytic degradation of CEF is mainly occurred due to superoxide and hydroxyl radicals. Meanwhile, the reusability of ACT-4 up to five cycles shows more than 80% photocatalytic degradation, which make the process more economical. The highest experimental adsorption capacity is achieved up to 844.8 mg g-1 using ACT-4. The favorable and multilayer heterogeneous adsorption is carried out according to the well-fitted data with pseudo-second-order and Freundlich models, respectively. These results indicate that the carbon-based TiO2 composites can be used as a green, stable, efficient, effective, reusable, renewable, and sustainable photocatalyst to eliminate the pharmaceutical pollutants (antibiotics) via adsorption and photocatalytic degradation processes.

Integrating bioremediation of textile wastewater with biodiesel production using microalgae (Chlorella vulgaris).

Microalgae-led wastewater treatment is a promising biorefinery approach to promote environmental and economical sustainability. In this study, Chlorella vulgaris (C. vulgaris) was employed for the bioremediation of textile wastewater (TWW) and biodiesel production. C. vulgaris is cultivated in undiluted and diluted TWW (50%). Cultivation in freshwater containing BG11 medium was set as a control. Results show the highest growth (1.62 ± 0.12 OD680) in diluted TWW followed by BG11 medium (1.56 ± 0.15 OD680) and undiluted TWW (0.89 ± 0.11 OD680). The highest methylene blue decolorization of 99.7% was observed in diluted TWW as compared to 98.5% in undiluted TWW. Morever, COD removal efficiency was also higher (99.7 ± 4.2%) in diluted TWW than BG11 medium (94.4 ± 3.5%) and undiluted TWW (76.3 ± 2.8%). For all treatment, more than 80% nitrogen and phosphorous removal were achieved. Otther than this, fatty acids methyl ester (FAME) yield in diluted TWW was higher (11.07 mg g-1) than the undiluted TWW (9.12 mg L-1). Major FAME were palmitic acid (C16:0) and linolenoic acid (C18:3) which are suitable for biodiesel production. All these results suggest that C. vulgaris can be cultivated in both diluted and undiluted TWW for biodiesel production. However, cultivation in undiluted TWW is more favorable as it displaces the need for freshwater addition in the growth medium.

Integrating adsorption and photocatalysis: A cost effective strategy for textile wastewater treatment using hybrid biochar-TiO2 composite.

TiO2 based photocatalysts are extensively used for textile wastewater treatment as they are ecofriendly, inexpensive, easily available, nontoxic and have higher photostabililty. However, their wider band gap, charge carrier's recombination, and utilization of light absorbance limits their performance. In the present work, a hybrid biochar-TiO2 composite (BCT) has been synthesized by a facile synthesis strategy to overcome these problems. These photocatalysts are characterized using X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), Fourier Transform Infrared (FTIR), UV-vis diffuse reflectance spectra (DRS), and photoluminescence (PL) to evaluate their crystallinity, morphology, functional groups, bandgap energy and charge separation properties, respectively. The photodegradation of simulated textile wastewater is analyzed using hybrid composites. The hybrid biochar-TiO2 composite showed higher charge separation, slow recombination of electron-hole pairs, and enhanced light absorption as compared to control (pure TiO2 and BC alone). 99.20 % photodegradation efficiency of dye-simulated wastewater is achieved employing optimum hybrid composite, while the pure biochar and TiO2 samples exhibits 85.20 % and 42.60 % efficiencies, respectively. The maximum adsorption capacity is obtained for hybrid biochar-TiO2 sample, 74.30 mgg-1 in comparison to biochar (30.40 mgg-1) and pure TiO2 (1.50 mgg-1). The results show that hybrid biochar-TiO2 composites can perform in the target application of organic industrial pollutant removal.