Characterization of novel solar based nitrogen doped titanium dioxide photocatalytic membrane for wastewater treatment.

The increasing presence of microbial and emerging organic contaminants pose detrimental effects on the environment and ecosystem such as diseases, pandemics and toxicity. Most of these synthetic pollutants are biorecalcitrant and therefore persist in the environment. Conventional water treatment methods are not effective thereby necessitating the development of advanced techniques such as photocatalysis and membrane processes. In this study, visible light-driven photocatalytic membrane was synthesized through the immobilization of nitrogen-doped nanoparticles onto the polyvinylidene fluoride (PVDF) membrane and performance evaluated with E.coli microbial contaminant removal. Characterization was done using Fourier transform infrared spectra, X-ray diffraction (XRD), water contact angle, Scanning Electron Microscopy-Energy Dispersive X-ray (SEM-EDX). The Nitrogen-doping of titanium dioxide red-shifted the light absorption to a visible range of 440 nm from 400 nm. Nitrogen dopant was detected at 1420 cm-1and 1170 cm-1 for nitrogen doped nanoparticles and 1346-1417 cm-1 for nitrogen doped titanium dioxide PVDF membrane. SEM-EDX confirmed presences of nitrogen in nitrogen doped titanium dioxide nanoparticles on membrane surface with nitrogen elemental composition of 0.01 % wt. The water contact angle reduced by 81.39o from 120.14o to 38.75o because of PVA immobilization of nitrogen-doped titanium dioxide and glutaraldehyde crosslinking. Nitrogen doping resulted in visible light active photocatalytic membranes with better hydrophilicity and fouling resistance. 8.42 E.coli log removal and a relative flux of 0.35 was obtained within 75 min. The developed photocatalytic membrane enables the use of sunlight hence a less costly method for decontamination of wastewater.

Effect of TiO2/Fe2O3 nanopowder synthesis method on visible light photocatalytic degradation of reactive blue dye.

Water pollution and scarcity of clean water are major issues of concern globally. In this study, titanium dioxide (TiO2) photocatalyst doped with ferric oxide (Fe2O3) was used to degrade reactive blue dye (171) using sunlight irradiation. Two approaches were employed to synthesize the photocatalyst: synthesis of ferric oxide and titanium precursor through ultrasonic-assisted sol-gel method and using iron (III) nitrate nonahydrate with commercial titanium dioxide. The photocatalysts were characterized using FTIR Spectroscopy, SEM, XRD analyses, and UVDRS to determine their chemical composition, morphology, crystallinity, and light absorption, respectively. The effect of contaminant concentration (1-3 ppm), solution pH and photocatalyst type on the degradation efficiency was studied. Doping enabled visible light absorption as confirmed by the UVDRS analysis. Solar photocatalytic degradation resulted in complete (100 % removal) of the dye within 2 h under solar irradiation for all concentrations of the dye studied. Furthermore, the photocatalysts exhibited superior performance in both neutral and acidic solutions compared to basic ones. After four cycles, the dye removal efficiency has decreased by less than 15 % for all the photocatalysts confirming the significant activity and high stability of the nanocomposite. The increased dye photodegradation efficacy of Fe2O3 doped TiO2 under sunlight irradiation is attributed to the narrowing of the photocatalyst's bandgap from 3.76 eV (in pure TiO2) to 2.83 eV. This narrowing of the bandgap enhances the absorption of visible light from sunlight, thus making this photocatalyst effective under sunlight and eliminating the use of electricity which is a requirement for ultraviolet photocatalysis.

Current trends in palm oil waste management: A comparative review of Cameroon and Malaysia.

This paper carried out a comparative review on the current trends in the conversion of palm oil waste into value-adding products by the Cameroonian and Malaysian palm sectors/researchers. Trends like composting, composite, pulping, mushroom cultivation, pyrolysis, aerobic and anaerobic digestion of palm biomass were studied as means to reduce the bulk, and to curb emissions of Greenhouse gas while producing value. Base on this research, limited works has been done on the conversion of palm biomass into value in Cameroon, whereas Malaysian palm researchers have employed all of these techniques and producing values from them. It was discovered that the various conversion process have different degree of feasibility and sustainability, and the end-products have different applications. Conversion process like pyrolysis is relatively faster, it could take just a few minute and the end-product which is biofuel have a wide range of applications; in contrast to composting which could take up to 180 days to mature and the end-product is limited to fertilizer. This research aims to sensitize the palm sector in Cameroon to the various processes that can be applied to sustainably manage palm waste. A priority table was also developed based on the feasibility and sustainability of the various conversion processes to serve as a guide towards sustainable waste management in the agro-industrial palm sector in Cameroon and a step towards industrialization.

Characterization of kitchen and municipal organic waste for biogas production: Effect of parameters.

Globally, the production of municipal solid waste is rising annually because of consumerism and the urbanization process. In the past few years, different researchers have explored strategies for generating biogas from various organic wastes. In this study, kitchen waste and municipal solid waste were characterized by several physical-chemical parameters. Ten of these substrates were mono-digested for biogas production in batch reactors where cabbage showed a 96.36 ± 1.73% volatile solid and biogas yield of 800 ± 8.8 mL within 10 days, while cooked rice had an 83.00 ± 1.49% volatile solid, and a biogas yield of 2821 ± 31.03 mL within 28 days. The CN ratio for cabbage and cooked rice waste was 13.9 and 30.9 respectively, whereas their pH values were 6.2 and 7.2. Based on the characterization and biogas yields attained, cooked rice waste could be mono-digested for biogas production and no published work showed a high yield as the current study while the other substrates require co-digestion to improve the biogas yield.

Versatile Silver-Nanoparticle-Impregnated Membranes for Water Treatment: A Review.

Increased affordability, smaller footprint, and high permeability quality that meets stringent water quality standards have accelerated the uptake of membranes in water treatment. Moreover, low pressure, gravity-based microfiltration (MF) and ultrafiltration (UF) membranes eliminate the use of electricity and pumps. However, MF and UF processes remove contaminants by size exclusion, based on membrane pore size. This limits their application in the removal of smaller matter or even harmful microorganisms. There is a need to enhance the membrane properties to meet needs such as adequate disinfection, flux amelioration, and reduced membrane fouling. To achieve these, the incorporation of nanoparticles with unique properties in membranes has potential. Herein, we review recent developments in the impregnation of polymeric and ceramic microfiltration and ultrafiltration membranes with silver nanoparticles that are applied in water treatment. We critically evaluated the potential of these membranes in enhanced antifouling, increased permeability quality and flux compared to uncoated membranes. Despite the intensive research in this area, most studies have been performed at laboratory scale for short periods of time. There is a need for studies that assess the long-term stability of the nanoparticles and the impact on disinfection and antifouling performance. These challenges are addressed in this study and future directions.

Ultraviolet and solar photocatalytic ozonation of municipal wastewater: Catalyst reuse, energy requirements and toxicity assessment.

The present study evaluated the treatment of municipal wastewater containing phenol using solar and ultraviolet (UV) light photocatalytic ozonation processes to explore comparative performance. Important aspects such as catalyst reuse, mineralization of pollutants, energy requirements, and toxicity of treated wastewater which are crucial for practical implementation of the processes were explored. The activity of the photocatalysts did not change significantly even after three consecutive uses despite approximately 2% of the initial quantity of catalyst being lost in each run. Analysis of the change in average oxidation state (AOS) demonstrated the formation of more oxidized degradation products (ΔAOS values of 1.0-1.7) due to mineralization. The energy requirements were determined in terms of electrical energy per order (EEO) and the collector area per order (ACO). The EEO (kWh m-3 Order-1) values were 26.2 for ozonation, 38-47 for UV photocatalysis and 7-22 for UV photocatalytic ozonation processes. On the other hand, ACO (m2 m-3 order-1) values were 31-69 for solar photocatalysis and 8-13 for solar photocatalytic ozonation. Thus photocatalytic ozonation processes required less energy input compared to the individual processes. The cytotoxicity of the wastewater was analysed using the 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay with Vero cells. The cell viability increased from 28.7% in untreated wastewater to 80% in treated wastewater; thus showing that the treated wastewater was less toxic. The effectiveness of photocatalytic ozonation, recovery and reusability of the photocatalysts, as well as detoxification of the wastewater make this low energy consumption process attractive for wastewater remediation.

Evaluation of synergy and bacterial regrowth in photocatalytic ozonation disinfection of municipal wastewater.

The use of solar and ultraviolet titanium dioxide photocatalytic ozonation processes to inactivate waterborne pathogens (Escherichia coli, Salmonella species, Shigella species and Vibrio cholerae) in synthetic water and secondary municipal wastewater effluent is presented. The performance indicators were bacterial inactivation efficiency, post-disinfection regrowth and synergy effects (collaboration) between ozonation and photocatalysis (photocatalytic ozonation). Photocatalytic ozonation effectively inactivated the target bacteria and positive synergistic interactions were observed, leading to synergy indices (SI) of up to 1.86 indicating a performance much higher than that of ozonation and photocatalysis individually (SI≤1, no synergy; SI>1 shows synergy between the two processes). Furthermore, there was a substantial reduction in contact time required for complete bacterial inactivation by 50-75% compared to the individual unit processes of ozonation and photocatalysis. Moreover, no post-treatment bacterial regrowth after 24 and 48h in the dark was observed. Therefore, the combined processes overcame the limitations of the individual unit processes in terms of the suppression of bacterial reactivation and regrowth owing to the fact that bacterial cells were irreparably damaged. The treated wastewater satisfied the bacteriological requirements in treated wastewater for South Africa.

Impact of ozonation in removing organic micro-pollutants in primary and secondary municipal wastewater: effect of process parameters.

The study investigates the influence of process parameters on the effectiveness of ozonation in the removal of organic micro-pollutants from wastewater. Primary and secondary municipal wastewater containing phenol was treated. The effect of operating parameters such as initial pH, ozone dosage, and initial contaminant concentration was studied. An increase in contaminant decomposition with pH (3-11) was observed. The contaminant removal efficiencies increased with an increase in ozone dose rate (5.5-36.17 mg L(-1) min(-1)). Furthermore, the ultraviolet absorbance (UV 254 nm) of the wastewater decreased during ozonation indicating the breakdown of complex organic compounds into low molecular weight organics. Along the reaction, the pH of wastewater decreased from 11 to around 8.5 due to the formation of intermediate acidic species. Moreover, the biodegradability of wastewaters, measured as biological and chemical oxygen demand (BOD5/COD), increased from 0.22 to 0.53. High ozone utilization efficiencies of up to 95% were attained thereby increasing the process efficiency; and they were dependent on the ozone dosage and pH of solution. Ozonation of secondary wastewater attained the South African water standards in terms of COD required for wastewater discharge and dissolved organic carbon in drinking water and increased significantly the biodegradability of primary wastewater.