Optimization of hydrogen peroxide-to-hemoglobin ratio for biocatalytic mineralization of polycyclic aromatic hydrocarbons (PAHs)-contaminated soils

Evolution in mitigation approaches for petroleum oil-polluted environment: recent advances and future directions

Increasing petroleum consumption and a rise in incidental oil spillages have become global concerns owing to their aquatic and terrestrial toxicity. Various physicochemical and biological treatment strategies have been studied to tackle them and their impact on environment. One of such approaches in this regard is the use of microbial processes due to their being "green" and also apparent low cost and high effectiveness. This review presents the advancement in the physical and biological remediation methods and their progressive efficacy if employed in combination of hybrid modes. The use of biosurfactants and/or biochar along with microbes seems to be a more effective bioremediation approach as compared to their individual effects. The lacuna in research at community or molecular level has been overcome by the recent introduction of "-omics" technology in hydrocarbon degradation. Thus, the review further focuses on presenting the state-of-art information on the advancement of petroleum bioremediation strategies and identifies the research gaps for achieving total mitigation of petroleum oil.

Recent Developments in Advanced Oxidation Processes for Organics-Polluted Soil Reclamation

Soil pollution has become a substantial environmental problem which is amplified by overpopulation in different regions. In this review, the state of the art regarding the use of Advanced Oxidation Processes (AOPs) for soil remediation is presented. This review aims to provide an outline of recent technologies developed for the decontamination of polluted soils by using AOPs. Depending on the decontamination process, these techniques have been presented in three categories: the Fenton process, sulfate radicals process, and coupled processes. The review presents the achievements of, and includes some reflections on, the status of these emerging technologies, the mechanisms, and influential factors. At the present, more investigation and development actions are still desirable to bring them to real full-scale implementation.

Recent advances in biocatalysis of nitrogen-containing heterocycles

Nitrogen-containing heterocycles (N-heterocycles) are ubiquitous in both organisms and pharmaceutical products. Biocatalysts are providing green approaches for synthesizing various N-heterocycles under mild reaction conditions. This review summarizes the recent advances in the biocatalysis of N-heterocycles through the discovery and engineering of natural N-heterocycle synthetic pathway, and the design of artificial synthetic routes, with an emphasis on biocatalysts applied in retrosynthetic design for preparing complex N-heterocycles. Furthermore, this review discusses the future prospects and challenges of biocatalysts involved in the synthesis of N-heterocycles.

Hemoglobin peroxidase reaction of hemoglobin efficiently catalyzes oxidation of benzo[a]pyrene

Its high molecular weight endows benzo[a]pyrene (BaP) with strong adsorption to soil, causing serious soil contamination. Our previous study has reported that hemoglobin (Hb) is able to oxidize organic pollutants in the presence of H₂O₂. This present study showed that Hb catalytic mechanism for BaP oxidation was similar to that of lignin peroxidase. 2-Methyl-3-vinylmaleimide was confirmed as a major degradation intermediate of BaP by Hb catalysis. In addition, BaP was shown to be degraded by heme (Hm)-catalyzed reaction, suggesting that Hm of Hb is the essential catalytic center. Rate constants (k) for BaP oxidation by Hm-catalyzed reaction were 0.4954 h^-1. The major degradation intermediate by Hm-catalyzed reaction is 3,3',5,5'-tetramethylbiphenyl. While values of K_m and V_max of Hb and Hm are very similar, k_cat values was 100 times higher with Hb than with Hm. But k_cat value for Hb was much lower than that for lignin peroxidase H2. All the results above suggested that Hb-catalyzed reactions efficiently degrade BaP in aqueous condition. Thus, we suggest that Hb for oxygen carrier in blood could be employed as a biocatalyst (i.e., hemoglobin peroxidase) for BaP degradation in the environment, due to the high availability of Hb.

Sequential biowashing-biopile processes for remediation of crude oil contaminated soil in Kuwait

The application of biological processes for remediation of the aged crude oil-contaminated soil of Kuwait can be an inefficient way, thus, this study developed 20 d-sequential biowashing and biopile processes where the biowashing step uses an enrichment culture of the indigenous soil bacterial community and the biopile step includes hemoglobin-catalyzed oxidation (HCO). The residual total petroleum hydrocarbons (TPH) concentrations and CO₂ generation were measured to determine the removal efficiency, and the bacterial community changes were studied to investigate the effect of the sequential processes on the soil indigenous bacterial community. The enrichment culture grown on hemoglobin showed an increased surface activity, and this promoted desorption and emulsification of crude oil from the soil sample in the biowashing step resulting in 75% TPH removal. Potential surfactant-producing bacterial species were observed in the soil sample after biowashing. The HCO in the beginning of the biopile step removed 21% of the residual TPH, and further TPH removal was observed with a longer biopile period. Overall, the sequential biowashing and biopile processes removed 86% TPH. The results show that the developed sequential biowashing and biopile processes can be used to efficiently remediate the aged crude oil-contaminated soil of Kuwait.

Effects of compositions, chemical structures, and microporosity of sedimentary organic matter on degradation of benzo(a)pyrene by hydrogen peroxide

We investigated how the degradation of 7-¹⁴C-BaP aged in sediments by H₂O₂ treatment was influenced by the chemical structures, compositions, and microporosity of sedimentary organic carbon (SOC). Unstable OC (USOC), stable OC (STOC), mineral-protected OC (MOC), and chemically resistant OC (ROC) fractions were fractionated. The chemical structures and microporosity of the ROC fractions were characterized by ¹³C solid-state nuclear magnetic resonance (NMR) and CO₂ adsorption technique, respectively. A first-order, two-compartment kinetics model described the degradation process very well (R² > 0.980). The BaP degradation ratios increased with the increasing USOC contents and decreased with the increasing ROC contents. The BaP parent compound in the aqueous solution was almost completely degraded. The considerable portions of oxidized intermediates were detected in different SOC fractions, which represented either oxidized intermediates or parent compounds. The very good multivariate regressions among the degradation kinetics parameters, SOC structures and micropore volumes demonstrated that ROC-bulk, aliphatic moieties, and microporosity played crucial roles in protecting sorbed BaP from being degraded by H₂O₂. The results showed that ROC, aliphatic moieties, and microporosity played vital roles in Bap degradation process in sediments during H₂O₂ treatment, which is reported for the first time in this study.

Remediation of soil polluted with HMW-PAHs by alfalfa or brome in combination with fungi and starch

High-molecular weight polycyclic aromatic hydrocarbons (HMW-PAHs) are common pollutants in soil of coal mining areas that affect the safety of crops and the environment. In a pot experiment, we compared the remediation potential of alfalfa (Medicago sativa Linn) and brome (Bromus inermis Leyss.) either alone or in combination with starch or Fusarium sp. strain ZH-H2 for a farmland soil contaminated with 4-6-ring PAHs from a coal mine area. The alfalfa and brome alone treatments reduced the concentrations of most HMW-PAHs. However, when starch was added, the removal rates of indeno(1,2,3-cd)pyrene and benzo(ghi)perylene were significantly higher for brome than for alfalfa. When ZH-H2 was combined with brome, benzo(k)fluoranthene, benzo(a)pyrene, indeno(1,2,3-cd)pyrene, and benzo(ghi)perylene degradation rates were significantly enhanced compared with brome alone. In contrast, an antagonistic effect was observed between alfalfa and Fusarium. The brome, starch and ZH-H2 combination resulted in far better removal rates than the alfalfa combination. Maximum removal rates were obtained with the brome + starch + ZH-H2 combination for benzo(k)fluoranthene (42.64%), benzo(a)pyrene (51.01%), indeno(1,2,3-cd)pyrene (62.29%), and benzo(ghi)perylene (74.85%). These removal rates were 829.78%, 182.34%, 46.13%, and 70.94% higher than the equivalent alfalfa combination treatments. The lignin peroxidase activity was significantly increased in the presence of starch, ZH-H2 and brome, consistent with the increased removal rates of HMW-PAHs.