Agro-industrial residues as a unique support in a sand filter to enhance the bioactivity to remove microcystin-Leucine aRginine and organics

Formulation of synthetic bacteria consortia for enzymatic biodegradation of polyaromatic hydrocarbons contaminated soil: soil column study

As an efficient method to remove contaminants from highly polluted sites, enzyme biodegradation addresses unresolved issues such as bioremediation inefficiency. In this study, the key enzymes involved in PAH degradation were brought together from different arctic strains for the biodegradation of highly contaminated soil. These enzymes were produced via a multi-culture of psychrophilic Pseudomonas and Rhodococcus strains. As a result of biosurfactant production, the removal of pyrene was sufficiently prompted by Alcanivorax borkumensis. The key enzymes (e.g., naphthalene dioxygenase, pyrene dioxygenase, catechol-2,3 dioxygenase, 1-hydroxy-2-naphthoate hydroxylase, protocatechuic acid 3,4-dioxygenase) obtained via multi-culture were characterized by tandem LC-MS/MS and kinetic studies. To simulate in situ application of produced enzyme solutions, pyrene- and dilbit-contaminated soil was bioremediated in soil columns and flask tests by injecting enzyme cocktails from the most promising consortia. The enzyme cocktail contained about 35.2 U/mg protein pyrene dioxygenase, 61.4 U/mg protein naphthalene dioxygenase, 56.5 U/mg protein catechol-2,3-dioxygenase, 6.1 U/mg protein 1-hydroxy-2-naphthoate hydroxylase, and 33.5 U/mg protein protocatechuic acid (P3,4D) 3,4-dioxygenase enzymes. It was found that after 6 weeks, the average pyrene removal values showed that the enzyme solution could be effective in the soil column system (80-85% degradation of pyrene).

Visible light-driven photocatalytic degradation of Microcystin-LR by Bi2WO6/Reduced graphene oxide heterojunctions: Mechanistic insight, DFT calculation and degradation pathways

Developing heterostructure photocatalysts for removing Microcystin-LR (MC-LR) under visible light was of positive significance to control the risk of Microcystins and ensure the safety of water quality. Herein, the Bi₂WO₆/Reduced graphene oxide (RGO) nanocomposites were prepared via a simple one-spot hydrothermal method for the first time to degrade MC-LR. The optimized Bi₂WO₆/RGO (Bi₂WO₆/RGO_3%) achieved a removal efficiency of 82.3% toward MC-LR, with 1.9-fold higher efficiencies than Bi₂WO₆, and it showed superior reusability and high stability after 5 cycles. The degradation efficiency of MC-LR demonstrated a negative trend with the initial concentration of MC-LR, fulvic acid, and initial algal density increased, while MC-LR removal rate for the presence of anions was in the order of Cl^- > CO₃^-2 > NO₃^- > H₂PO₄^-. The degradation efficiency of MC-LR could reach up to 82.3% within 180 min in the neutral condition. The active species detection experiments and EPR measurements demonstrated that the holes (h⁺), hydroxide radicals (∙OH), and superoxide radicals (∙O₂^-) participated in the degradation of MC-LR. The DFT calculations showed that 0.56 of electron transferred from Bi₂WO₆ to RGO, indicating RGO introduction could prevent the recombination of photoelectrons and holes and was beneficial for MC-LR degradation. Finally, the possible intermediate products and degradation pathways were also proposed by the LC-MS/MS analysis.

Immobilization of Microbes for Biodegradation of Microcystins: A Mini Review

Harmful cyanobacterial blooms (HCBs) frequently occur in eutrophic freshwater ecosystems worldwide. Microcystins (MCs) are considered to be the most prominent and toxic metabolites during HCBs. MCs may be harmful to human and animal health through drinking water and recreational water. Biodegradation is eco-friendly, cost-effective and one of the most effective methods to remove MCs. Many novel MC-degrading bacteria and their potential for MCs degradation have been documented. However, it is a challenge to apply the free MC-degrading bacterial cells in natural environments due to the long-term operational instability and difficult recycling. Immobilization is the process of restricting the mobility of bacteria using carriers, which has several advantages as biocatalysts compared to free bacterial cells. Biological water treatment systems with microbial immobilization technology can potentially be utilized to treat MC-polluted wastewater. In this review article, various types of supporting materials and methods for microbial immobilization and the application of bacterial immobilization technology for the treatment of MCs-contaminated water are discussed. This article may further broaden the application of microbial immobilization technology to the bioremediation of MC-polluted environments.

Multi-Soil-Layering Technology: A New Approach to Remove Microcystis aeruginosa and Microcystins from Water

Eutrophication of surface waters caused by toxic cyanobacteria such as Microcystis aeruginosa leads to the release of secondary metabolites called Microcystins (MCs), which are heptapeptides with adverse effects on soil microbiota, plants, animals, and human health. Therefore, to avoid succumbing to the negative effects of these cyanotoxins, various remediation approaches have been considered. These techniques involve expensive physico-chemical processes because of the specialized equipment and facilities required. Thus, implementing eco-technologies capable of handling this problem has become necessary. Indeed, multi-soil-layering (MSL) technology can essentially meet this requirement. This system requires little space, needs simple maintenance, and has energy-free operation and high durability (20 years). The performance of the system is such that it can remove 1.16 to 4.47 log10 units of fecal contamination from the water, 98% of suspended solids (SS), 92% of biological oxygen demand (BOD), 98% of chemical oxygen demand (COD), 92% of total nitrogen (TN), and 100% of total phosphorus (TP). The only reported use of the system to remove cyanotoxins has shown a 99% removal rate of MC-LR. However, the mechanisms involved in removing this toxin from the water are not fully understood. This paper proposes reviewing the principal methods employed in conventional water treatment and other technologies to eliminate MCs from the water. We also describe the principles of operation of MSL systems and compare the performance of this technology with others, highlighting some advantages of this technology in removing MCs. Overall, the combination of multiple processes (physico-chemical and biological) makes MSL technology a good choice of cyanobacterial contamination treatment system that is applicable in real-life conditions, especially in rural areas.

Hazardous wastes treatment technologies

A review of the literature published in 2019 on topics related to hazardous waste management in water, soils, sediments, and air. The review covered treatment technologies applying physical, chemical, and biological principles for the remediation of contaminated water, soils, sediments, and air. PRACTICAL POINTS: This report provides a review of technologies for the management of waters, wastewaters, air, sediments, and soils contaminated by various hazardous chemicals including inorganic (e.g., oxyanions, salts, and heavy metals), organic (e.g., halogenated, pharmaceuticals and personal care products, pesticides, and persistent organic chemicals) in three scientific areas of physical, chemical, and biological methods. Physical methods for the management of hazardous wastes including general adsorption, sand filtration, coagulation/flocculation, electrodialysis, electrokinetics, electro-sorption ( capacitive deionization, CDI), membrane (RO, NF, MF), photocatalysis, photoelectrochemical oxidation, sonochemical, non-thermal plasma, supercritical fluid, electrochemical oxidation, and electrochemical reduction processes were reviewed. Chemical methods including ozone-based, hydrogen peroxide-based, potassium permanganate processes, and Fenton and Fenton-like process were reviewed. Biological methods such as aerobic, anoxic, anaerobic, bioreactors, constructed wetlands, soil bioremediation and biofilter processes for the management of hazardous wastes, in mode of consortium and pure culture were reviewed. Case histories were reviewed in four areas including contaminated sediments, contaminated soils, mixed industrial solid wastes and radioactive wastes.

Physical and biological removal of Microcystin-LR and other water contaminants in a biofilter using Manganese Dioxide coated sand and Graphene sand composites

Sand as a filter media is often challenged by the presence of organics in the form of natural organic matter, metal ions, and various micropollutants in the source water. It is mainly due to the presence of limited active adsorption sites and low surface area that governs an ineffective adsorption potential of the sand material. Herein, graphitized sand was synthesized to tackle the above limitations using two sugar solution sources: a) brewery effluent (as a low-cost solution) (GS1) and; b) sucrose solution (GS2). GS1 showed 68%, 60%, and 99% higher maximum adsorption constant (q_max) for divalent metal ions: iron, copper, and manganese, respectively as compared to raw sand (RS). Coating of MnO₂ over the graphitized sand (GSMs: GS1M and GS2M) further helped in Microcystin-LR (MC-LR) removal (3%-9%) when inoculated with MC-LR-degraders, but was not as effective in removing metals, organic carbon and nitrogen when compared to just graphitized sand (GS1 or GS2). Inoculating GS and GSMs (for both sugar sources) not only helped in higher MC-LR removal (10%-15% more) but also enhanced the removal of other water contaminants including metals, organic nitrogen, and carbon. GS1 showed 20% and 50% more MC-LR removal than the sand material when tested at a low and high initial concentration of MC-LR (5 µg/L and 50 µg/L). The highest breakthrough period was obtained for GS1 filter using 1 mg/L Rhodamine-B dye, which was 12 times (48 min) more than the raw sand filter and almost 2.5 times (second best, 21 min) than GS1M. After three cycles of regeneration and reuse of GS1 filter, a decrease of just 14% in saturation adsorption capacity indicated its high reusability aspects.

Insight Into the Molecular Mechanisms for Microcystin Biodegradation in Lake Erie and Lake Taihu

Microcystins are potent hepatotoxins that are frequently detected in fresh water lakes plagued by toxic cyanobacteria. Microbial biodegradation has been referred to as the most important avenue for removal of microcystin from aquatic environments. The biochemical pathway most commonly associated with the degradation of microcystin is encoded by the mlrABCD (mlr) cassette. The ecological significance of this pathway remains unclear as no studies have examined the expression of these genes in natural environments. Six metatranscriptomes were generated from microcystin-producing Microcystis blooms and analyzed to assess the activity of this pathway in environmental samples. Seventy-eight samples were collected from Lake Erie, United States/Canada and Lake Tai (Taihu), China, and screened for the presence of mlr gene transcripts. Read mapping to the mlr cassette indicated transcripts for these genes were absent, with only 77 of the collective 3.7 billion reads mapping to any part of the mlr cassette. Analysis of the assembled metatranscriptomes supported this, with only distantly related sequences identified as mlrABC-like. These observations were made despite the presence of microcystin and over 500,000 reads mapping to the mcy cassette for microcystin production. Glutathione S-transferases and alkaline proteases have been previously hypothesized to be alternative pathways for microcystin biodegradation, and expression of these genes was detected across space and time in both lakes. While the activity of these alternative pathways needs to be experimentally confirmed, they may be individually or collectively more important than mlr genes in the natural environment. Importantly, the lack of mlr expression could indicate microcystin biodegradation was not occurring in the analyzed samples. This study raises interesting questions about the ubiquity, specificity and locality of microcystin biodegradation, and highlights the need for the characterization of relevant mechanisms in natural communities to understand the fate of microcystin in the environment and risk to public health.