Green Synthesis of ZnO and Black TiO2 Materials and Their Application in Photodegradation of Organic Pollutants.

ZnO and black TiO2 have been selected as the most efficient materials for organic pollution abatement due to their increased efficiency when compared to other materials. However, the concept of green chemistry makes it desirable to design green synthesis approaches for their production. In this study, black TiO2 was synthesized using an environmentally safe synthetic technique with glycerol as a reductant. ZnO was prepared by using ionic-liquid-based microwave-assisted extracts of Polygonum minus. To investigate the materials' potential to photodegrade organic pollutants, methylene blue (MB) and phenol were chosen as model organic pollutants. Both materials were found to exhibit spherical morphologies and a mesoporous structure and were efficient absorbers of visible light. ZnO exhibited electron-hole pair recombination lower than that of black TiO2. Black TiO2 was discovered to be an anatase phase, whereas ZnO was found to have a hexagonal wurtzite structure. In contrast to black TiO2, which had a surface area of 239.99 m2/g and a particle size of 28 nm, ZnO had a surface area of 353.11 m2/g and a particle size of 32 nm. With a degradation time of 60 min, ZnO was able to eliminate 97.50% of the 40 mg/L MB. Black TiO2, on the other hand, could reduce 90.0% of the same amount of MB in 60 min. When tested for phenol degradation, ZnO and black TiO2 activities were reduced by nearly 15 and 25%, respectively. A detailed examination of both ZnO and black TiO2 materials revealed that ZnO has more potential and versatility for the degradation of organic pollutants under visible light irradiation.

Environmental implication and cancer risk assessment of residual pollutants in cotton crop: a case study of Multan District, Pakistan.

Pakistan is the fourth largest yarn producer in the world heavily that relies on cotton crop which receives a substantial 62% of all pesticide applications. The present study was conducted to quantify the levels of pesticides such as bifenthrin, spirotetramat, pyriproxyfen, imidacloprid, and diafenthiuron in soil and plants residue at selected cotton fields of Multan District, Pakistan. In addition to pesticides, the assessment of heavy metal concentration was also conducted in order to determine the overall risks that these compounds to both plants and human population. For this analysis, 20 soil samples and 10 plant samples were collected from 10 selected cotton fields. Pesticides and heavy metals in soil and plant samples were analyzed using high-performance liquid chromatography (HPLC) and Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES), respectively. It was observed that all samples collected from selected fields contained pesticide residue in top soil (0-15 cm). However, no pesticides were detected in the lower soil layer (16-30 cm). In case of heavy metals, the highest concentration of Fe, Pb, and Mn was observed in both soil and plant residue samples. The heavy metals were found in the order of Fe > Mn > Pb > Zn > Cu > Cd in the soil. The total carcinogenic risk values for a few pesticides were found to range from 10-6 to 10-2, indicating that residents of the study area have low to higher chances of developing cancer. A positive correlation was observed among the pesticides (r = 0.18-0.95) as well as in metals related parameters (r = 0.49-0.96), where a weak negative correlation was found among metal to pesticide parameters except Pd where the maximum r value was 0.62. In general, the finding of this study encourages the development and adoption of sustainable agricultural practices that lower the dependence on toxic pesticides and endorse environmentally friendly alternatives.

Optimized photodegradation of palm oil agroindustry waste effluent using multivalent manganese-modified black titanium dioxide.

This article presents a methodological approach to use manganese (Mn3+Mn7+)-modified black titanium dioxide (Mn/BTiO2) as a photocatalyst to optimize and improve visible-light-driven photodegradation of treated agro-industrial effluent (TPOME). A modified wet chemical process was used to prepare BTiO2. The BTiO2 was then wet impregnated with Mn and calcined at 300 °C for 1 h to produce Mn/BTiO2. The activity of Mn/BTiO2 was investigated in terms of photo-assisted elimination of chemical oxygen demand (COD), phenolic compounds (PCs), color, and total organic carbon (TOC). Using the design of experiments (DOE), the conditions of the photocatalytic process, including photocatalyst loading, Mn concentration, hydrogen peroxide (H2O2) dose, and irradiation time, were optimized. Under the optimum conditions (0.85 g/L photocatalyst loading, 0.048 mol/L H2O2 dose, 0.301 wt.% Mn concentration, and 204 min irradiation time) COD, PCs, color, and TOC removal efficiencies of 88.87%, 86.04%, 62.8%, and 84.66%, respectively, were obtained. Statistical analysis showed that the response variable's removal from TPOME estimation had high R2 and low RMSE, MSE, MAD, MAE, and MAPE values, indicating high reliability. This study demonstrated the significant potential of the developed photocatalytic system for the treatment of waste effluent generated by the palm oil industry and other agro-industries, with the ability to simultaneously reduce a number of organic pollution indicators (OPIs).

A Recent Progress in the Leachate Pretreatment Methods Coupled with Anaerobic Digestion for Enhanced Biogas Production: Feasibility, Trends, and Techno-Economic Evaluation.

Landfill leachate (LFL) treatment is a severe challenge due to its highly viscous nature and various complex pollutants. Leachate comprises various toxic pollutants, including inorganic macro/nano components, xenobiotics, dissolved organic matter, heavy metals, and microorganisms responsible for severe environmental pollution. Various treatment procedures are available to achieve better effluent quality levels; however, most of these treatments are nondestructive, so pollutants are merely transported from one phase to another, resulting in secondary contamination. Anaerobic digestion is a promising bioconversion technology for treating leachate while producing renewable, cleaner energy. Because of its high toxicity and low biodegradability, biological approaches necessitate employing other techniques to complement and support the primary process. In this regard, pretreatment technologies have recently attracted researchers' interest in addressing leachate treatment concerns through anaerobic digestion. This review summarizes various LFL pretreatment methods, such as electrochemical, ultrasonic, alkaline, coagulation, nanofiltration, air stripping, adsorption, and photocatalysis, before the anaerobic digestion of leachate. The pretreatment could assist in converting biogas (carbon dioxide to methane) and residual volatile fatty acids to valuable chemicals and fuels and even straight to power generation. However, the selection of pretreatment is a vital step. The techno-economic analysis also suggested the high economic feasibility of integrated-anaerobic digestion. Therefore, with the incorporation of pretreatment and anaerobic digestion, the process could have high economic viability attributed to bioenergy production and cost savings through sustainable leachate management options.

Pseudomonas and Curtobacterium Strains from Olive Rhizosphere Characterized and Evaluated for Plant Growth Promoting Traits.

Plant growth promoting (PGP) bacteria are known to enhance plant growth and protect them from environmental stresses through different pathways. The rhizosphere of perennial plants, including olive, may represent a relevant reservoir of PGP bacteria. Here, seven bacterial strains isolated from olive rhizosphere have been characterized taxonomically by 16S sequencing and biochemically, to evaluate their PGP potential. Most strains were identified as Pseudomonas or Bacillus spp., while the most promising ones belonged to genera Pseudomonas and Curtobacterium. Those strains have been tested for their capacity to grow under osmotic or salinity stress and to improve the germination and early development of Triticum durum subjected or not to those stresses. The selected strains had the ability to grow under severe stress, and a positive effect has been observed in non-stressed seedlings inoculated with one of the Pseudomonas strains, which showed promising characteristics that should be further evaluated. The biochemical and taxonomical characterization of bacterial strains isolated from different niches and the evaluation of their interaction with plants under varying conditions will help to increase our knowledge on PGP microorganisms and their use in agriculture.

Hexachlorocyclohexane toxicity in water bodies of Pakistan: challenges and possible reclamation technologies.

Pakistan is an agro-economy country where hexachlorocyclohexane (HCH) pesticides are being used to improve crop productivity, as a result the risk of contamination of soil and sediment has been increased. HCH exhibits all the characteristics of persistent organic pollutants (POP), and was therefore added to the list of 'new POPs' in 2009. This review report revealed that the major rivers of Pakistan such as the Indus Basin, River Ravi, River Chenab and their tributaries all are contaminated with HCH and the highest residual concentration (4,090 ng/g) was detected in a pesticide burial ground in Hyderabad city. Major sources of HCH contamination were identified as agricultural runoff, discharge of untreated industrial effluents and surface runoff. In order to manage HCH pollution, various ex-situ and in-situ remediation techniques along with their merits and demerits are thoroughly reviewed. Among these, microbial bioremediation is a low cost, environment friendly, effective in-situ remediation technique for remediation of HCH. Overall, the information provided in this manuscript will provide a future reference to the scientific community and bridge the knowledge gap between HCH release in the environment and their mitigation through proper treatment methods.

Carbon nitride/titania nanotubes composite for photocatalytic degradation of organics in water and sludge: Pre-treatment of sludge, anaerobic digestion and biogas production.

In this study, carbon nitride/titania nanotubes (C3N4/TiO2 NTs) composites were synthesized for the enhanced visible light mediated photocatalytic degradation and pre-treatment of wastewater sludge for enhanced biogas production. The co-existence of C3N4 and TiO2 NTs and visible light activity was confirmed by XRD, TEM, UV-visible and PL spectroscopy. The photocatalytic performance of TiO2 NTs with 2% of melamine (precursor of C3N4), enhanced the degradation of 2-chlorophenol (2-CP) (k = 0.0176 min-1), where 96.6% removal was achieved at optimum pH 7.0 and 2-CP concentration of 30 mg/L. On the other hand, the application of C3N4/TiO2 NTs for solubilization of the rigid structure of sludge by photocatalysis released the soluble organics showing an improvement in sCOD production (4587 mg/L). Subsequently, anaerobic digestion of solubilized sludge has improved the methane production (723.4 ml kg-1 VS) by 1.37 and 1.6 times compared to that in anaerobic digestion with photolytic and raw sludge, thus showing a promising applicability for biogas production from sludge and wastewater treatment.

Synthesis of Cr2O3/C3N4 composite for enhancement of visible light photocatalysis and anaerobic digestion of wastewater sludge.

Visible light photocatalysts of Cr2O3/C3N4 composites (with different melamine concentrations) were prepared by high temperature calcination method. The composites samples were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy SEM, energy-dispersive X-ray spectroscopy (EDX), UV-visible spectroscopy and particle size analysis, which clearly indicated the coexistence of both Cr2O3 and C3N4 in the composites. The Cr2O3/C3N4 catalysts were tested for photocatalytic degradation of 2-chlorophenol in wastewater and solubilization of sludge in anaerobic digestion process to enhance biomethane production. The co-catalytic performance of Cr2O3, with 6% of melamine (precursor of C3N4), improved the photocatalytic degradation of 2-chlorophenol (k = 0.0156 min-1) under visible light, where up to 94% removal was achieved at optimum pH 5.0, pollutant concentration of 60 mg/L, and time duration of 180 min. On another hand, application of Cr2O3/C3N4 for photocatalytic pretreatment of sludge released the soluble substances in solution in which sCOD was increased from 431 mg/L to 3666 mg/L after 6 h and VS content decrease by only 9.1%, which indicated that the short time pretreatment could avoid the further mineralization of organic to complete degradation. Thereafter, anaerobic digestion of solubilized sludge was achieved after 30 days with production of 634 ml kg-1VS of methane and 46% of organic matter removal efficiency (OMRE), compared with 472 ml kg-1VS and 402 ml kg-1VS of methane, 35 and 31% of OMRE respectively in photolytic and raw sludge (control) reactors. These results can provide a useful base and reference for the multi applications of visible light Cr2O3/C3N4 photocatalyst in enhancement of degradation of toxic pollutant in wastewater and sludge stabilization with bioenergy production in practice.

Visible light photocatalytic disintegration of waste activated sludge for enhancing biogas production.

Biogas production using waste activated sludge (WAS) is one of the most demanding technologies for sludge treatment and generating energy in sustainable manner. The present study deals with the photocatalytic pretreatment of WAS using ZnO-ZnS@polyaniline (ZnO-ZnS@PANI) nanocomposite as means for increasing its degradability for improved biogas production by anaerobic digestion (AD). Photocatalysis accelerated the hydrolysis of WAS and increased the sCOD by 6.7 folds after 6 h and transform tCOD into bioavailable sCOD. After the AD of WAS, a removal of organic matter (60.6%) and tCOD (69.3%) was achieved in photocatalytic pretreated sludge. The biogas production was 1.6 folds higher in photocatalytic sludge with accumulative biogas up to 1645.1 ml L-1vs after 45 days compared with the raw sludge (1022.4 ml L-1VS). Moreover, the photocatalysis decrease the onset of methanogenesis from 25 to 12 days while achieve the maximum conversion rate of reducing sugars into organic acids at that time. These results suggested that photocatalysis is an efficient pretreatment method and ZnO-ZnS@PANI can degrade sludge efficiently for enhance biogas production in anaerobic digestion process.

Synergistic effect of co-digestion to enhance anaerobic degradation of catering waste and orange peel for biogas production.

Catering waste and orange peel were co-digested using an anaerobic digestion process. Orange peel is difficult to degrade anaerobically due to the presence of antimicrobial agents such as limonene. The present study aimed to examine the feasibility of anaerobic co-digestion of catering waste with orange peel to provide the optimum nutrient balance with reduced inhibitory effects of orange peel. Batch experiments were conducted using catering waste as a potential substrate mixed in varying ratios (20-50%) with orange peel. Similar ratios were followed using green vegetable waste as co-substrate. The results showed that the highest organic matter degradation (49%) was achieved with co-digestion of catering waste and orange peel at a 50% mixing ratio (CF4). Similarly, the soluble chemical oxygen demand (sCOD) was increased by 51% and reached its maximum value (9040 mg l-1) due to conversion of organic matter from insoluble to soluble form. Biogas production was increased by 1.5 times in CF4 where accumulative biogas was 89.61 m3 t-1substrate compared with 57.35 m3 t-1substrate in the control after 80 days. The main reason behind the improved biogas production and degradation is the dilution of inhibitory factors (limonene), with subsequent provision of balanced nutrients in the co-digestion system. The tCOD of the final digestate was decreased by 79.9% in CF4, which was quite high as compared with 68.3% for the control. Overall, this study revealed that orange peel waste is a highly feasible co-substrate for anaerobic digestion with catering waste for enhanced biogas production.

The anaerobic digestion of solid organic waste.

The accumulation of solid organic waste is thought to be reaching critical levels in almost all regions of the world. These organic wastes require to be managed in a sustainable way to avoid depletion of natural resources, minimize risk to human health, reduce environmental burdens and maintain an overall balance in the ecosystem. A number of methods are currently applied to the treatment and management of solid organic waste. This review focuses on the process of anaerobic digestion which is considered to be one of the most viable options for recycling the organic fraction of solid waste. This manuscript provides a broad overview of the digestibility and energy production (biogas) yield of a range of substrates and the digester configurations that achieve these yields. The involvement of a diverse array of microorganisms and effects of co-substrates and environmental factors on the efficiency of the process has been comprehensively addressed. The recent literature indicates that anaerobic digestion could be an appealing option for converting raw solid organic wastes into useful products such as biogas and other energy-rich compounds, which may play a critical role in meeting the world's ever-increasing energy requirements in the future.