The Effect of Calcium Peroxide on the Phenol Oxidase and Acid Phosphatase Activity and Removal of Fluoranthene from Soil

Novel enzymes for biodegradation of polycyclic aromatic hydrocarbons identified by metagenomics and functional analysis in short-term soil microcosm experiments

Polycyclic aromatic hydrocarbons (PAHs) are highly toxic, carcinogenic substances. On soils contaminated with PAHs, crop cultivation, animal husbandry and even the survival of microflora in the soil are greatly perturbed, depending on the degree of contamination. Most microorganisms cannot tolerate PAH-contaminated soils, however, some microbial strains can adapt to these harsh conditions and survive on contaminated soils. Analysis of the metagenomes of contaminated environmental samples may lead to discovery of PAH-degrading enzymes suitable for green biotechnology methodologies ranging from biocatalysis to pollution control. In the present study, our goal was to apply a metagenomic data search to identify efficient novel enzymes in remediation of PAH-contaminated soils. The metagenomic hits were further analyzed using a set of bioinformatics tools to select protein sequences predicted to encode well-folded soluble enzymes. Three novel enzymes (two dioxygenases and one peroxidase) were cloned and used in soil remediation microcosms experiments. The experimental design of the present study aimed at evaluating the effectiveness of the novel enzymes on short-term PAH degradation in the soil microcosmos model. The novel enzymes were found to be efficient for degradation of naphthalene and phenanthrene. Adding the inorganic oxidant CaO2 further increased the degrading potential of the novel enzymes for anthracene and pyrene. We conclude that metagenome mining paired with bioinformatic predictions, structural modelling and functional assays constitutes a powerful approach towards novel enzymes for soil remediation.

Mechanisms of benzene and benzo[a]pyrene biodegradation in the individually and mixed contaminated soils

There is a lack of knowledge on the biodegradation mechanisms of benzene and benzo [a]pyrene (BaP), representative compounds of polycyclic aromatic hydrocarbons (PAHs), and benzene, toluene, ethylbenzene, and xylene (BTEX), under individually and mixed contaminated soils. Therefore, a set of microcosm experiments were conducted to explore the influence of benzene and BaP on biodegradation under individual and mixed contaminated condition, and their subsequent influence on native microbial consortium. The results revealed that the total mass loss of benzene was 56.0% under benzene and BaP mixed contamination, which was less than that of individual benzene contamination (78.3%). On the other hand, the mass loss of BaP was slightly boosted to 17.6% under the condition of benzene mixed contamination with BaP from that of individual BaP contamination (14.4%). The significant differences between the microbial and biocide treatments for both benzene and BaP removal demonstrated that microbial degradation played a crucial role in the mass loss for both contaminants. In addition, the microbial analyses revealed that the contamination of benzene played a major role in the fluctuations of microbial compositions under co-contaminated conditions. Rhodococcus, Nocardioides, Gailla, and norank_c_Gitt-GS-136 performed a major role in benzene biodegradation under individual and mixed contaminated conditions while Rhodococcus, Noviherbaspirillum, and Phenylobacterium were highly involved in BaP biodegradation. Moreover, binary benzene and BaP contamination highly reduced the Rhodococcus abundance, indicating the toxic influence of co-contamination on the functional key genus. Enzymatic activities revealed that catalase, lipase, and dehydrogenase activities proliferated while polyphenol oxidase was reduced with contamination compared to the control treatment. These results provided the fundamental information to facilitate the development of more efficient bioremediation strategies, which can be tailored to specific remediation of different contamination scenarios.

Environmental opportunities and challenges of utilizing unactivated calcium peroxide to treat soils co-contaminated with mixed chlorinated organic compounds

Calcium peroxide (CaO₂) has been proven to oxidize various organic pollutants when they exist as a single class of compounds. However, there is a lack of research on the potential of unactivated CaO₂ to treat mixed chlorinated organic pollutants in soils. This study examined the potential of CaO₂ in treating soils co-contaminated with p-dichlorobenzene (p-DCB) and p-chloromethane cresol (PCMC). The effects of CaO₂ dosage and treatment duration on the rate of degradation were investigated. Furthermore, the collateral effects of the treatment on treated soil characteristics were studied. The result showed that unactivated CaO₂ could oxidize mixed chlorinated organic compounds in wet soils. More than 69% of the pollutants in the wet soil were mineralized following 21 days of treatment with 3% (w/w) CaO₂. The hydroxyl radicals played a significant role in the degradation process among the other decomposition products of hydrogen peroxide. Following the oxidation process, the treated soil pH was increased due to the formation of calcium hydroxide. Soil organic matter, cation exchange capacity, soil organic carbon, total nitrogen, and certain soil enzyme activities of the treated soil were decreased. However, the collateral effects of the system on electrical conductivity, available phosphorus, and particle size distribution of the treated soil were not significant. Likewise, since no significant release of heavy metals was seen in the treated soil matrix, the likelihood of metal ions as co-pollutants after treatment was low. Therefore, CaO₂ can be a better alternative for treating industrial sites co-contaminated with chlorinated organic compounds.

Solid Peroxy Compounds as Additives to Organic Waste for Reclamation of Post-Industrial Contaminated Soils

Solid peroxy compounds have been increasingly applied for the removal of organic pollution from contaminated groundwater and soil due to their ability to release oxygen and hydrogen peroxide. The influence of two solid peroxy compounds (sodium percarbonate, 2Na₂CO₃·3H₂O₂ and calcium peroxide, CaO₂) with poultry manure (PM) added to contaminated soil on the growth of the tested plants (Sinapis alba, Lepidium sativum L. and Sorghum bicolor L. Moench) and the quality of soil water leachates was investigated. A series of experiments involving the addition of CaO₂ and 2Na₂CO₃·3H₂O₂ at the dose of 0.075 g/g PM improved the growth of tested plants. The conducted study indicated that the use of peroxy compounds not only removed pathogens from livestock waste, but also improved the quality of plant growth. The calculated factors for the growth of roots (GFR) and growth of shoots (GFS) in soils treated with a mixture of peroxy compounds and PM were higher than in soils treated only with PM. The physicochemical analysis of soil water leachates indicated that solid peroxy compounds may be a promising alternative compared to the currently used hygienizing agent such as calcium hydroxide (Ca(OH)₂). Solid peroxy compounds increased the bioavailability of components necessary for proper seed germination and plant growth (N, P, K, Ca, Mg and S). In most of the studied cases, the obtained plant shoot and root growth rates were higher for soil mixtures containing organic waste deactivated by biocidal compounds, compared to soils that contained only poultry manure.

Use of Phosphatase and Dehydrogenase Activities in the Assessment of Calcium Peroxide and Citric Acid Effects in Soil Contaminated with Petrol

The objective of the study was to compare the effect of calcium peroxide and citric acid on the activity of acid phosphatase (ACP), alkaline phosphatase (ALP), and dehydrogenases (DHA) in uncontaminated soil and soil contaminated with petrol. The experiment was carried out on samples of loamy sand under laboratory conditions. Petrol was introduced to soil samples at a dose of 0 and 50 g·kg 1 DM, as well as calcium peroxide or citric acid at a dose of 0, 50, 100, or 150 mg·kg 1 DM. The humidity of the samples was brought to 60% maximum water holding capacity, and the samples were incubated at 20°C for 8 weeks. Enzyme activity was determined on days 1, 14, 28, and 56. The obtained results demonstrated that the addition of calcium peroxide and citric acid did not result in significant changes in the activity of the determined enzymes in uncontaminated soil. However, it was observed that the application of calcium peroxide, particularly at the dose of 150 mg·kg 1 DM, largely alleviated the impact of petrol on the enzymatic activity of the soil contaminated with petrol. Moreover, among the determined enzymes, the activity of DHA was found to be the best indicator of the effect of calcium peroxide on the soil ecosystem.

Bioremediation of polycyclic aromatic hydrocarbons (PAHs) present in biomass fly ash by co-composting and co-vermicomposting

An experiment was established to compare composting and vermicomposting for decreasing the content of polycyclic aromatic hydrocarbons (PAHs) in biomass fly ash incorporated into organic waste mixtures. PAH removal from the ash-organic waste mixture was compared to the same mixture spiked with PAHs. The removal of 16 individual ash PAHs ranged between 28.7 and 98.5% during the 240 day experiment. Greater dissipation of total PAH content of ash origin was observed at the end of composting (84.5%) than after the vermicomposting (61.6%). Most ash PAHs were removed similarly to spiked PAHs through the composting and vermicomposting processes. Higher manganese peroxidase in composting treatments indicated increased activity of ligninolytic PAH-degrading microorganisms. 3D models of total PAH removal were parametrized using the polarity index and organic matter content, and paraboloid equations for each treatment were estimated (all R² > 0.91). A two-phase model of pseudo-first order kinetics analysis showed faster PAH removal by higher rate constants during the first 120 days of the experiment. The compost and vermicompost produced from the bioremediation treatments are usable as soil organic amendments.

Application of calcium peroxide in water and soil treatment: A review

Calcium peroxide (CP) has been progressively applied in terms of environmental protection due to its certain physical and chemical properties. This review focuses on the latest progresses in the applications of CP in water and soil treatment, including wastewater treatment, surface water restoration and groundwater and soil remediation. The stability of CP makes it an effective solid phase to supply H₂O₂ and O₂ for aerobic biodegradation and chemical degradation of contaminants in water and soil. CP has exerted great performance in the removal of dyes, chlorinated hydrocarbons, petroleum hydrocarbons, pesticides, heavy metals and various other contaminants. The research progress in the encapsulation technologies of CP with other materials and the preparation of CP nanoparticles were also presented in this review. Based on the summarized research progresses, the perspective of CP application in the future was proposed.