Ionic liquids as a potential solvent for lipase-catalysed reactions: a review

Ionic liquids (ILs) - as environmentally friendly “green” solvents- have been progressively used in various reactions as reagents, solvents and co-solvents including lipase-catalysed reactions. In fact, lipase-catalysed reactions in ILs are considered as a “green”-reaction and are more advantageous than chemical methods owing to the easy recovery of the product and the mild conditions of the reactions. The use of lipase in ILs provides many technological advantages compared to conventionally used solvents, such as selectivity enhancement, enzyme stability improvement, higher conversion rate, and better recyclability and recovery system. Nevertheless, in some cases, especially in hydrophilic ILs, lipase exhibits activity reduction when compared with organic solvents. Currently, various attempts have been made to enhance the performance of lipases in ILs. The main objective of this review is to demonstrate recent developments in the technology of using ILs as reaction media for lipase. It is expected that this review might be an inspiration in ILs assisted lipase-catalysed reactions to produce value-added materials including biofuels as well as biodiesel

Isolation and characterisation of copper leaching microbes from sanitary landfill for e-waste bioleaching

Electronic waste has been the fastest increasing waste generated globally and is predicted to surpass 111 million tons per year by 2050. This trend is concerning, not just due to the growing volume but also due to its high composition of heavy metal elements, leading to potential environmental pollution if not managed properly. However, this issue opens a new prospect in material acquisition through the concept of urban mining via the metal extraction from electronic waste. A conventional method of extraction, i.e., chemical leaching, possesses harmful environmental impact with the production of its residual leachate. Thus, an alternative extraction technique is proposed, known as bioleaching, in which the microbial activity from bacteria mobilized metal into a more soluble form. In this study, bacterial strains were isolated from Malaysia sanitary landfill for bioleaching of copper from waste printed circuit boards (wPCB) with minimal mechanical pre-processing procedure. They were grown in low pH media to utilize their activity for copper bioleaching from the wPCB. Four bacterial strains were successfully isolated. Using 16S rRNA gene sequencing, the isolates were identified as Bacillus sp. strain SE, Bacillus sp. strain SC, Lysinibacillus sp. strain SE2, and Oryzobacter terrae strain S1A. All the isolates showed appropriate bioleaching ability, with strain SC demonstrated the highest copper extraction with up to 23.36 ppm through the two-step bioleaching process. This strain was further evaluated using a copper strip to observe the actual copper extraction and demonstrated a total of 0.80 ±0.02 mg/g copper recovery. These results suggest that copper bioleaching of wPCB is viable as a standalone process

Bioconversion of lignin by oxidative enzymes for lignin depolymerization from tropical bacteria isolates

The conversion of lignocellulosic biomass into bioethanol or biochemical products requires a crucial pre-treatment process to break down the recalcitrant lignin structure. Biological pre-treatment using microbial enzymes appears to be the most promising alternative to depolymerize the lignin fragment, which can simultaneously facilitate conversion into valuable chemical products. Thus, this research focuses on bioconversion of Alkali Lignin (AL) for lignin depolymerization, using several enzymes from bacterial isolates. Two bacteria isolates, Streptomyces sp. strain S6 and Bacillus subtilis strain S11y, were selected as the potential strains for the source of candidate enzymes responsible for lignin depolymerization. Sequencing of the genomic DNA of these strains revealed four successful candidate genes with lignin depolymerizing ability, in which two genes were identified as dye-decolorizing peroxidase (DyP2, ~41 kDa) and multicopper oxidase (CuO1, ~44 kDa) from Streptomyces sp. strain S6, and also two genes identified as Cu/Zn superoxide dismutase (SOD2, ~22 kDa) and monofunctional heme catalase (Kat2, ~55 kDa) from Bacillus subtilis strain S11y. These genes were successfully expressed as recombinant enzymes and confirmed to have the ability to degrade AL polymer. Differential UV-vis spectrum (Δε-spectrum) of AL treated with the candidate enzymes demonstrated increased absorbance at ~295 nm and 350 nm after treatment, indicating increased free and conjugated phenol structure due to depolymerization. These enzymes also showed activity for oxidation of AL, reducing ~100-240 Da of the high-molecular-weight fraction of AL within 24 h treatment. Analysis of reaction components of all enzymes with AL by ultra-high-pressure liquid chromatography-mass spectrometry and gas chromatography-mass spectrometry showed that the enzymes generated various low-molecular-weight products of diverse groups, such as vanillyl alcohol, vanillin, dihydro-ferulic acid, salicylic acid, benzoic acid, 2,4-dimethyl-benzaldehyde, and oxalic acid. Based on the depolymerization products, the reaction mechanisms performed by each enzyme were also successfully elucidated, which involved several types of reactions, including β−O−4, Cα-Cβ, Cβ-Cγ, Aryl-Cα bond cleavages, O-demethylation, polymerization, decarboxylation, benzylic oxidation, and aromatic ring oxidative cleavage. Each enzyme appeared to generate radicals formed on the lignin surface, leading to several bond cleavages and structural modification in AL after enzymatic treatment, proving their ability to depolymerize polymer lignin. Successful evaluation of lignin depolymerizing enzymes can be applicable for lignin pre-treatment process in green energy production as well as generation of valuable chemicals in bio-refinery

Screening of thermostable and organic solvent tolerant lipase producing fungi in solid state bioconversion of palm kernel cake

Special consideration has been focused on the utilization of lipase enzyme as a suitable alternative method for biodiesel production, which is expected to be more stable and practical. However, the high production costs as well as low productivity have hindered the marketable production of biodiesel using the commercial lipase. Isolation of lipases from filamentous fungi, particularly found in agricultural wastes has attracted special interest due to their potential towards developing more sustainable and economical applications. Only lipase possessing thermal stability and organic solvent tolerant can distinctively enhance the biodiesel production. Therefore, in the present study, isolation of thermostable- organic solvent tolerant fungal strains from palm kernel cake (PKC) were conducted based on their ability to grow at 45oC on YpSs (yeast extract + starch + agar) media and in the presence of organic solvent. The isolates were screened based on the clearing zone methods on phenol red as well as on tween 80 agar media. Four isolates were screened for potential lipase production. These isolates were incubated under Solid State Fermentation (SSF) at 45oC for 7 days with PKC as substrate. The most promising strain with the potential to produce lipase was PKC12B2, which showed satisfactory enzyme activity

Optimization of thermostable organic solvent-tolerant lipase production by thermotolerant Rhizopus sp. using solid-state fermentation of palm kernel cake

This study enhanced the production of thermostable organic solvent-tolerant (TS-OST) lipase by locally isolated thermotolerant Rhizopus sp. strain using solid-state fermentation (SSF) of palm kernel cake (PKC). The optimum conditions were achieved using a series of statistical approaches. The cultivation parameters, which include fermentation time, moisture content, temperature, pH, inoculum size, various carbon and nitrogen sources, as well as other supplements, were initially screened by the definitive screening design, and one-factor-at-a-time using PKC as the basal medium. Three significant factors (olive oil concentration, pH, and inoculum size) were further optimized using face-centred central composite design. The results indicated a successful and significant improvement of lipase activity by almost two-fold compared to the initial screening production. The findings showed that the optimal conditions were 2% (v/w) inoculum size, 2% (v/w) olive oil, 0.6% (w/w) peptone, 2% (v/w) ethanol, 70% moisture content at initial pH 10.0 and 45 °C within 72 h of fermentation. Process optimization resulted in maximum lipase activity of 58.63 U/gram dry solids (gds). The analysis of variance showed that the statistical model was significant (p value <0.0001) and reliable with a high value of R2 (0.98) and adjusted R2 (0.96). This indicates a better correlation between the actual and predicted responses of lipase production. By considering this study, the low-cost PKC through SSF appears to be promising in the utilization of agro-industrial waste for TS-OST lipase production. This is because satisfactory enzyme activity could be attained that promises industrial application

Development of enzymatic pretreatment of palm oil mill effluent for monomers towards biogas production

In anaerobic digestion for enhancement of biogas production, various types of pre-treatment method have been used with some limitations in terms of sustainable environmental management. Although acid and alkali pretreatment have a significant effect on the degradation of biomass, these methods have some negative impacts on the environment due to their hazardous nature, while the enzymatic pre-treatment is more environmentally friendly. One of the constraints of using the enzyme in pretreatment process for biogas production is a high cost which is currently focused to reduce cost through using a locally produced enzyme. The hydrolytic enzymes, cellulase and lipase were applied to evaluate the pretreatment and hydrolysis process for POME based biogas production. The results showed that about 66.67% more free fatty acid (FFA) was obtained in this study in compared to untreated sample as the control (POME) by using 15 U/ml lipase at the pH of 4.5. About 3 fold higher reducing sugar was recorded at the loading of 2.4 FPU/ml cellulase enzyme as compared to the control at the pH range 4. Both enzymes were effective in the pretreatment process in conversion of complex substances in the POME into monomars towards biogas production

Recent Applications of the Electrocoagulation Process on Agro-Based Industrial Wastewater: A Review

Agro-based final discharge is one of the major contributors to wastewater in the world. It creates high demand for efficient treatment. The electrocoagulation process can be used for agro-based wastewater treatment. The performance of the electrocoagulation process is based on several parameters, including the electrode materials, electrolysis time, current density, and electrolyte support. Agro-based industrial wastewater (AIW) treatment processes depend on the characteristics of the wastewater. The removal of organic content from various sources of AIW can reach up to more than 80%. Some studies show that the performance of the electrochemical process can be increased using a combination with other methods. Those other methods include biological and physical treatment. The results of previous research show that organic content and color can be degraded completely. The relationship between the energy consumption and operating cost was analyzed in order to show the efficiency of electrocoagulation treatment

Recent Applications of the Electrocoagulation Process on Agro-Based Industrial Wastewater: A Review

Agro-based final discharge is one of the major contributors to wastewater in the world. It creates high demand for efficient treatment. The electrocoagulation process can be used for agro-based wastewater treatment. The performance of the electrocoagulation process is based on several parameters, including the electrode materials, electrolysis time, current density, and electrolyte support. Agro-based industrial wastewater (AIW) treatment processes depend on the characteristics of the wastewater. The removal of organic content from various sources of AIW can reach up to more than 80%. Some studies show that the performance of the electrochemical process can be increased using a combination with other methods. Those other methods include biological and physical treatment. The results of previous research show that organic content and color can be degraded completely. The relationship between the energy consumption and operating cost was analyzed in order to show the efficiency of electrocoagulation treatment

A review of the biological treatment of leachate: Available technologies and future requirements for the circular economy implementation

Leachate, which refers to dark-colored toxic wastewater generated from landfills, has become an issue of environmental concern, posing a threat to soil, surface water, and groundwater quality, thereby negatively affecting humans’ health. Therefore, it is necessary to select the most appropriate leachate treatment methods considering its complex properties. Among several treatment processes available for this purpose, the biological treatment process is notably effective at removing pollutants and also relatively affordable to operate. Its application to leachate treatment has received much attention in recent years. This study summarizes the leachate characteristics and the methods of leachate treatment with a focus on biological approaches, either aerobic or anaerobic. In addition, this paper concisely discusses the effectiveness and the factors influencing the performance of each treatment technology in case of organics, nutrients, and other pollutants removal. The findings of this paper are expected to provide a deeper insight into the future research and development of leachate treatment, especially the biological treatments concerning the circular economy

Paracetamol degradation in a dual-chamber rectangular membrane bioreactor using microbial fuel cell system with a microbial consortium from sewage sludge

The public widely uses Paracetamol (PCT) as an analgesic drug to reduce pain and fever symptoms in the human body. The COVID-19 pandemic has led to an increase in PCT consumption, resulting in its presence in water bodies and establishing it as a common aquatic environmental pollutant. Conventional methods for PCT removal rely on chemical treatments, which necessitate harsh reaction conditions and incur high operational costs. This study aims to investigate the potential for PCT degradation within the anode environment of the Microbial Fuel Cell (MFC) system, using a consortium of bacteria isolated from sewage sludge. The initial PCT concentration and the pH of the anode environment were varied. The results showed that PCT degradation occurred within 72 hours. The highest PCT removal rate was achieved at elevated concentrations, specifically 28.54 ± 18.84% for an initial PCT concentration of 31.45 mg/L. Furthermore, the pH levels of the anode environment were observed to influence PCT degradation, with the highest degradation rate recorded at 48.69 ± 0.86% at a pH of 8.2. In this study, the highest average power density reached was 1174.42 mW/m2 with an external resistance of 1000 Ω at an initial PCT concentration of 31.45 mg/L. Microbial community analysis was conducted, revealing that Burkholderia sp. dominated the reactor containing PCT. These findings offer valuable insights for the development of more efficient technologies for the removal of PCT from pharmaceutical wastewater using natural microbial communities