Treatment of landfill leachate using photocatalytic based advanced oxidation process - a critical review.

Landfill leachate is a discrete volumetric component of municipal solid waste; hence, researchers and professionals are more concerned about it because of its obscurity. Innovative treatment and emerging technologies are being scrutinized to address the treatment of landfill leachate challenges. The leading target of this review was to examine the possibility of removing recalcitrant organic pollutants from landfill leachate by photocatalytic-based advanced oxidation processes. A summary of the systematic applicability of conventional treatment for landfill leachate is provided, with a focus on physico-chemical and biological processes. The biological treatment, such as aerobic and anaerobic digestion, is an excellent technique for treating highly concentrated organic pollutants in the wastewater. However, Leachate can scarcely be treated using conventional techniques since it is enriched with refractory organics and inorganic ions. It is clear from the literature review that none of the available combinations of physico-chemical and biological treatments are entirely relevant for the removal of recalcitrant organic pollutants from leachate. Recently, the photo-assisted TiO2/ZnO oxidation has shown an excessively potential and feasible way to treat landfill leachate. TiO2/ZnO photocatalysis is currently developing to treat recalcitrant organic pollutants from landfill leachate. The effect of operating parameters reveals that pH and temperature affect the reaction rate. The addition of oxidant H2O2 to the TiO2/ZnO suspension suggests that TiO2 leads to an increase in the rate of reaction when compared to ZnO. Photocatalytic remediation technique of landfill leachate would support the goal of environmental sustainability by greatly enhancing the effectiveness of treated leachate reutilization. In this review, the selection of the best photocatalytic treatment for leachate based on its systematic relevance and potential conditions, characteristics, cost-effectiveness, essential controlling, discharge limit, long-term environmental effects, and its future study perspectives are emphasized and discussed.

A Comprehensive Review on Hot Ambient Temperature and its Impacts on Adverse Pregnancy Outcomes.

INTRODUCTION: High workplace/ambient temperatures have been associated with Adverse Pregnancy Outcomes (APO). Millions of women working in developing nations suffer due to the rising temperatures caused by climate change. There are few pieces of research linking occupational heat stress to APO, and fresh evidence is required. METHODOLOGY: We used databases including PubMed, Google Scholar, and Science Direct to search for research on high ambient/workplace temperatures and their effects. Original articles, newsletters, and book chapters were examined. The literature we analysed was categorised as follows: Heat, strain, and physical activity harming both mother and fetus. After categorising the literature, it was examined to identify the major results. RESULTS: We found a definite association between heat stress and APOs such as miscarriages, premature birth, stillbirth, low birthweight, and congenital abnormalities in 23 research articles. Our work provides important information for future research into the biological mechanisms that create APOs and various prevention measures. CONCLUSION: Our data suggest that temperature has long-term and short-term effects on maternal and fetal health. Though small in number, this study stressed the need for bigger cohort studies in tropical developing countries to create evidence for coordinated policies to safeguard pregnant women.

Status of disinfection byproducts research in India.

India faces high incidents of waterborne disease outbreaks owing to their limited access to safe drinking water. In many ways, the effort to improve the quality of drinking water is performed, and it has been keenly monitored. Among those, the disinfection of drinking water is considered a necessary and important step as it controls the microbial population. Chlorination is the most practiced (greater than 80%) disinfection process in India, and it is known to generate various disinfection byproducts (DBPs). Although the toxicity and trend of DBPs are regularly monitored and investigated in most countries, still in India, the research is at the toddler level. This review summarizes i) the status of drinking water disinfection in India, ii) types of disinfection processes in centralized water treatment plants, iii) concentrations and occurrence patterns of DBPs in a different region of India, iv) a literature survey on the toxicity of DBPs, and v) removal methodologies or alternative technologies to mitigate the DBPs formation. Overall, this review may act as a roadmap to understand the trend of disinfection practices in India and their impacts on securing the goal of safe drinking water for all.

Efficacy of simultaneous advanced oxidation and adsorption for treating municipal wastewater for indirect potable reuse.

The main scope of this study was to compare the efficacy of different advanced oxidation processes (AOPs) combined with adsorption for treating secondary treated effluent of municipal wastewater in a continuous-lab-scale reactor. The results revealed enhanced removal of biological oxygen demand (BOD: C0: 14.1 and Ct: 0 mg L-1 (100%)), chemical oxygen demand (COD: C0: 40.5 and Ct: 4 mg L-1 (≤90%)), and total organic carbon (TOC: C0: 15.2 and Ct: 3.02-3.63 mg L-1 (∼80%)) by UV/PMS, O3/PMS, UV/O3/H2O2, and UV/O3/MnO2 processes followed by glass packed bed reactor (GPBR). Complete inactivation of the bacterial count was observed for all the studied processes. The GPBR showed the additional advantage of termination in the regrowth of bacterial count on the filtering medium. The gas-chromatography and mass spectrometry (GC-MS) analysis showed that AOP followed by adsorption reduced the concentrations of the by-products in the treated effluent. Overall, the synergy between AOP and adsorption improved the effluent quality to meet various indirect potable reuse (IPR) applications.

A review on the applicability of adsorption techniques for remediation of recalcitrant pesticides.

Pesticide has revolutionised the agricultural industry by reducing yield losses and by enhancing productivity. But indiscriminate usage of such chemicals can negatively impact human health and ecosystem balance as certain pesticides can be recalcitrant in nature. Out of some of the suggested sustainable techniques to remove the pesticide load from the environment, adsorption is found to be highly efficient and can also be implemented on a large scale. It has been observed that natural adsorption that takes place after the application of the pesticide is not enough to reduce the pesticide load, hence, adsorbents like activated carbon, plant-based adsorbents, agricultural by-products, silica materials, polymeric adsorbents, metal organic framework etc are being experimented upon. It is becoming increasingly important to choose adsorbents which will not leave any secondary pollutant after treatment and the cost of production of such adsorbent should be feasible. In this review paper, it has been established that certain adsorbent like biochar, hydrochar, resin, metal organic framework etc can efficiently remove pesticides namely chlorpyrifos, diazinon, 2,4-Dichlorophenoxyacetic Acid, atrazine, fipronil, imidacloprid etc. The mechanism of adsorption, thermodynamics and kinetic part have been discussed in detail with respect to the pesticide and adsorbent under discussion. The reason behind choosing an adsorbent for the removal of a particular pesticide have also been explained. It is further highly recommended to carry out a cost analysis before implementing an absorbent because inspite of its efficacy, it might not be cost effective to use it for a particular type of pesticide or contaminant.

Removal of persistent organic pollutants and disinfection of pathogens from secondary treated municipal wastewater using advanced oxidation processes.

An affordable and sustainable tertiary treatment is imperative to solve the secondary contamination issues related to wastewater reuse. To decontaminate and disinfect the actual secondary treated wastewater, various types of advanced oxidation processes (AOPs) have been studied. The optimization of the oxidant and catalyst is carried out to identify the best-performing system. Under selected experimental conditions, UV/peroxymonosulfate (PMS), O3/PMS, UV/MnO2, O3/MnO2, UV/O3/H2O2, O3/MnO2/H2O2, UV/MnO2/H2O2, and UV/O3/MnO2 has been identified as an efficient treatment option for simultaneous decontamination (>90% COD removal) and disinfection (100% inactivation of the total viable count of bacteria). The techno-economic assessment revealed that UV/MnO2 (23.5 $ kg-1 of COD) UV/O3/MnO2 (37.4 $ kg-1 of COD), UV/H2O2/MnO2 (36.4 $ kg-1 of COD), and O3/MnO2/H2O2 (32.5 $ kg-1 of COD) are comparatively low-cost treatment processes. Overall, UV/MnO2, UV/H2O2/MnO2, and O3/MnO2/H2O2 are the three best treatments. Nevertheless, further investigation on by-product and catalyst toxicity/recovery is needed. The results showed that AOPs are a technologically feasible treatment for simultaneously removing persistent organic pollutants and pathogens from secondary treated wastewater.

Effect of image transformation on EfficientNet model for COVID-19 CT image classification.

The Novel Corona Virus 2019 has drastically affected millions of people all around the world and was a huge threat to the human race since its evolution in 2019. Chest CT images are considered to be one of the indicative sources for diagnosis of COVID-19 by most of the researchers in the research community. Several researchers have proposed various models for the prediction of COVID-19 using CT images using Artificial Intelligence based algorithms (Alimadadi e al., 2020 [19], Srinivasa Rao and Vazquez, 2020 [20], Vaishya et al., 2020 [21]). EfficientNet is one of the powerful Convolutional Neural Network models proposed by Tan and Le (2019). The objective of this study is to explore the effect of image enhancement algorithms such as Laplace transform, Wavelet transforms, Adaptive gamma correction and Contrast limited adaptive histogram equalization (CLAHE) on Chest CT images for the classification of Covid-19 using the EfficientNet algorithm. SARS- COV-2 (Soares et al., 2020) dataset is used in this study. The images were preprocessed and brightness augmented. The EfficientNet algorithm is implemented and the performance is evaluated by adding the four image enhancement algorithms. The CLAHE based EfficientNet model yielded an accuracy of 94.56%, precision of 95%, recall of 91%, and F1 of 93%. This study shows that adding a CLAHE image enhancement to the EfficientNet model improves the performance of the powerful Convolutional Neural Network model in classifying the CT images for Covid-19.

Analysis of DNA Sequence Classification Using CNN and Hybrid Models.

In a general computational context for biomedical data analysis, DNA sequence classification is a crucial challenge. Several machine learning techniques have used to complete this task in recent years successfully. Identification and classification of viruses are essential to avoid an outbreak like COVID-19. Regardless, the feature selection process remains the most challenging aspect of the issue. The most commonly used representations worsen the case of high dimensionality, and sequences lack explicit features. It also helps in detecting the effect of viruses and drug design. In recent days, deep learning (DL) models can automatically extract the features from the input. In this work, we employed CNN, CNN-LSTM, and CNN-Bidirectional LSTM architectures using Label and K-mer encoding for DNA sequence classification. The models are evaluated on different classification metrics. From the experimental results, the CNN and CNN-Bidirectional LSTM with K-mer encoding offers high accuracy with 93.16% and 93.13%, respectively, on testing data.

ZnO nanoparticles as efficient sunlight driven photocatalyst prepared by solution combustion method involved lime juice as biofuel.

We have prepared high purity Zinc oxide (ZnO) nanoparticles (NPs) by solution combustion synthesis (SCS) method with the aid of lime juice extract. From powder X-ray diffraction (XRD) spectra, it is observed that the ZnO NPs possess single phase, hexagonal wurzite structure with sharp intense peak at (101) plane, agrees with the planes of SAED pattern. Further, the crystallite size is found to be around 18 nm. UV-Vis analysis shows strong UV absorbance band at 381 nm and PL measurements reveals the presence of strong UV emission at 347 nm along with few weak visible emissions. Optical studies infer the existence of lower recombination rate of electron-hole pair, influence the photocatalytic activity of ZnO. From XPS measurements, presence of oxygen rich states on surface are also confirmed (O 1 s states). The degradation performance and reusability of four different dyes (methylene blue (MB), methyl orange (MO), rhodamine B (RhB), Pararosaniline (PRA)) under UV and sunlight irradiations are carried out to illustrate the photo-catalytic activity in presence of a catalyst like ZnO NPs. Comparatively, about 98.8% of PRA and MB dyes are photodegraded at 90 and 75 min of sunlight irradiation, respectively. Among these two, PRA dye shows maximum degradation performance with shorter irradiation time along with good stability, which can be extend very well to minimize the pollution issues happening in society especially, industrial wastes.

Treatment of high-strength sewage by textile fibers-based sequencing batch biofilm reactor for simultaneous removal of organics and nutrients.

This study investigates the effectiveness of SBBR with low-cost textile fibers-based bio-carrier namely polypropylene fibers for the treatment of real sewage. The influent loading rates of COD, TN, and TP were averaged at 0.2780, 0.0170, and 0.0077 kg/m3.d, respectively. The removal efficiencies of BOD, COD, TN, and TP recorded in SBBR were 98%, 93%, 82%, and 44%, respectively at an aeration time of 4 h. The TN and TP removal achieved in SBBR were 2.05 and 2.75 times, respectively higher than SBR. The COD removal efficiency was more than 90% under all SRT conditions (10, 14, 18, 22, and 26 d) in SBBR, and the highest efficiency of 93% was obtained at an SRT of 22 days. As the SRT increased, the nitrogen and phosphorus removal decreased, because the denitrification rate and phosphorus release and uptake rate decreased at longer SRT. Simultaneous nitrification and denitrification (SND) efficiency was 85% in SBBR and 44% in SBR, indicating the co-existence of aerobic nitrifiers and anoxic denitrifiers in the biofilm reactor. In SBBR, the nitrogen mass balance showed 74% of nitrogen removed by denitrification, 9% was removed through sludge wasting process, and 13% was removed in effluent at an SRT of 22 days and DO concentration of 3 mg/L. The t-test results suggest that the performance of SBBR was better than SBR in nitrogen and phosphorus removal at a 95% confidence interval.

Optimization of operating parameters for gas-phase photocatalytic splitting of H2S by novel vermiculate packed tubular reactor.

Hydrogen production by gas-phase photocatalytic splitting of Hydrogen Sulphide (H2S) was investigated on four semiconductor photocatalysts including CuGa1.6Fe0.4O2, ZnFe2O3, (CdS + ZnS)/Fe2O3 and Ce/TiO2. The CdS and ZnS coated core shell particles (CdS + ZnS)/Fe2O3 shows the highest rate of hydrogen (H2) production under optimized conditions. Packed bed tubular reactor was used to study the performance of prepared photocatalysts. Selection of the best packing material is a key for maximum removal efficiency. Cheap, lightweight and easily adsorbing vermiculate materials were used as a novel packing material and were found to be effective in splitting H2S. Effect of various operating parameters like flow rate, sulphide concentration, catalyst dosage, light irradiation were tested and optimized for maximum H2 conversion of 92% from industrial waste H2S.

Textile dye degradation using nano zero valent iron: A review.

Water soluble unfixed dyes and inorganic salts are the major pollutants in textile dyeing industry wastewater. Existing treatment methods fail to degrade textile dyes and have limitations too. The inadequate treatment of textile dyeing wastewater is a major concern when effluent is directly discharged into the nearby environment. Long term disposal threatens the environment, which needs reclamation. This article reviews the current knowledge of nano zero valent iron (nZVI) technique in the degradation of textile dyes. The application of nZVI on textile dye degradation is receiving great attention in the recent years because nZVI particles are highly reactive towards the pollutant, less toxic, and economical. The nZVI particles aggregate quickly with respect to time and the addition of supports such as resin, nickel, zinc, bentonite, biopolymer, kaolin, rectorite, nickel-montmorillonite, bamboo, cellulose, biochar, graphene, and clinoptilolite enhanced the stability of iron nanoparticles. Inclusion of supports may in turn introduce additional toxic pollutants, hence green supports are recommended. The majority of investigations concluded dye color removal as textile dye compound removal, which is not factual. Very few studies monitored the removal of total organic carbon and observed the products formed. The results revealed that partial mineralization of the textile dye compound was achieved. Instead of stand alone technique, nZVI can be integrated with other suitable technique to achieve complete degradation of textile dye and also to treat multiple pollutants in the real textile dyeing wastewater. It is highly recommended to perform more bench-scale and pilot-scale studies to apply this technique to the textile effluent contaminated sites.

Design of pilot-scale solar photocatalytic reactor for the generation of hydrogen from alkaline sulfide wastewater of sewage treatment plant.

Experiments were conducted for photocatalytic generation of renewable fuel hydrogen from sulphide wastewater from the sewage treatment plant. In this study, pilot-scale solar photocatalytic reactor was designed for treating 1 m3 of sulphide wastewater and also for the simultaneous generation of hydrogen. Bench-scale studies were conducted both in the batch recycle and continuous modes under solar irradiation at similar experimental conditions. The maximum of 89.7% conversion was achieved in the continuous mode. The length of the pilot-scale solar photocatalytic reactor was arrived using the design parameters such as volumetric flow rate (Q) (11 x 10(-2) m3/s), inlet concentration of sulphide ion (C(in)) (28 mol/m3), conversion (89.7%) and average mass flow destruction rate (3.488 x 10(-6) mol/m2 s). The treatment cost of the process was estimated to be 6 US$/m3. This process would be suitable for India like sub-tropical country where sunlight is abundantly available throughout the year.

A study on polypropylene encapsulation and solidification of textile sludge.

The textile sludge is an inevitable solid waste from the textile wastewater process and is categorised under toxic substances by statutory authorities. In this study, an attempt has been made to encapsulate and solidify heavy metals and dyes present in textile sludge using polypropylene and Portland cement. Sludge samples (2 Nos.) were characterized for pH (8.5, 9.5), moisture content (1.5%, 1.96%) and chlorides (245mg/L, 425.4mg/L). Sludge samples were encapsulated into polypropylene with calcium carbonate (additive) and solidified with cement at four different proportions (20, 30, 40, 50%) of sludge. Encapsulated and solidified cubes were made and then tested for compressive strength. Maximum compressive strength of cubes (size, 7.06cm) containing sludge (50%) for encapsulation (16.72 N/mm2) and solidification (18.84 N/mm2) was more than that of standard M15 mortar cubes. The leachability of copper, nickel and chromium has been effectively reduced from 0.58 mg/L, 0.53 mg/L and 0.07 mg/L to 0.28mg/L, 0.26mg/L and BDL respectively in encapsulated products and to 0.24mg/L, BDL and BDL respectively in solidified products. This study has shown that the solidification process is slightly more effective than encapsulation process. Both the products were recommended for use in the construction of non-load bearing walls.

Tertiary treatment of pulp and paper industrial wastewater by electro-Fenton process.

The feasibility of decolourisation/degradation of secondary treated pulp and paper industrial wastewater was investigated by Electro-Fenton process. The wastewater was dark brown in colour, toxic odorous, having high COD (34,800 mg/L), BOD3 (4900 mg/L) and non-biodegradable (0.14--BOD3/COD ratio). The study was carried out to evaluate the effects of the operating variables, viz. pH, dosage of Fe2+, concentration of hydrogen peroxide, current efficiency and contact time. The kinetic results show pseudo-first order degradation, with a rate constant of reaction between CODt/COD0. The maximum colour removal up to 95% and COD removal upto 90% were obtained at pH 3, Fe2+ dosage 125 mg/L, concentration of H2O2, 1500 mg/L, applied current 2.2 A for 120 minutes of contact time. This feasibility study has proved that Electro-Fenton process could be an appropriate tertiary treatment for secondary treated pulp and paper industrial wastewater.

Bioremediation of chromium contaminated soil by Pseudomonas fluorescens and indigenous microorganisms.

Chromium is one of the toxic and hazardous pollutants in industrial wastewaters leading to soil contamination. In this study, the feasibility of remediating chromium contaminated soil using indigenous microorganisms and Pseudomonas fluorescens was evaluated. The contaminated soil sample was collected from Vellore and the pH, moisture content and chromium content were found to be 8.4, 22.5% and 5.1 mg/kg respectively. The effect of chromium on engineering properties showed decrease in permeability by 45.15%. For Pseudomonas fluorescens, the optimum pH, moisture content, biomass concentration and carbon source were found as 6.5, 20%, 10 mL and 10 mL/100 g respectively and for isolated mixed culture, the optimum parameters were found as 8.4, 25%, 15 mL and 15mL / 100 g respectively. Under optimum conditions, the reactor study showed 71.7% chromium reduction after 20 days. From the study, the bioremediation of chromium-contaminated soil by indigenous microorganisms was found to be a promising solution and after bioremediation, the engineering properties of the soil were found to be improved.

Treatment of textile dyeing wastewater using UV/solar photofenton oxidation processes.

Colour removal of effluent from textile dyeing and finishing industry is becoming important because of aesthetic as well as environmental concerns. Conventional treatment methods have several limitations. Hence emerging technologies like advanced oxidation processes which were based on generation of hydroxyl free radicals (OH) were investigated. In the present work, photofenton oxidation process was used to treat textile dyeing wastewater and the study was carried out at different Fenton molar ratio's (H2O2/Fe2+) like 25:1, 50:1, 75:1, 100:1. It was found that maximum decolourisation occurred at a fenton molar ration of 50:1 and pH 3. A maximum colour removal of 97% was achieved after a contact time of 30 minutes and 70% COD reduction was observed after a contact time of 60 minutes in UV photofenton oxidation process. Whereas 80% colour removal and 50-55% COD reduction was observed after a contact time of 2 hrs in solar photofenton oxidation process.