Effect of the bacterial community assembly process on the microbial remediation of petroleum hydrocarbon-contaminated soil.

Introduction: The accumulation of petroleum hydrocarbons (PHs) in the soil can reduce soil porosity, hinder plant growth, and have a serious negative impact on soil ecology. Previously, we developed PH-degrading bacteria and discovered that the interaction between microorganisms may be more important in the degradation of PHs than the ability of exogenous-degrading bacteria. Nevertheless, the role of microbial ecological processes in the remediation process is frequently overlooked. Methods: This study established six different surfactant-enhanced microbial remediation treatments on PH-contaminated soil using a pot experiment. After 30 days, the PHs removal rate was calculated; the bacterial community assembly process was also determined using the R language program, and the assembly process and the PHs removal rate were correlated. Results and discussion: The rhamnolipid-enhanced Bacillus methylotrophicus remediation achieved the highest PHs removal rate, and the bacterial community assembly process was impacted by deterministic factors, whereas the bacterial community assembly process in other treatments with low removal rates was affected by stochastic factors. When compared to the stochastic assembly process and the PHs removal rate, the deterministic assembly process and the PHs removal rate were found to have a significant positive correlation, indicating that the deterministic assembly process of bacterial communities may mediate the efficient removal of PHs. Therefore, this study recommends that when using microorganisms to remediate contaminated soil, care should be taken to avoid strong soil disturbance because directional regulation of bacterial ecological functions can also contribute to efficient removal of pollutants.

Using organo-mineral complex material to prevent the migration of soil Cd and As into crops: An agricultural practice and chemical mechanism study.

The migration and transformations of Cd and As in soil are different, so it is difficult to simultaneously control them. In this study, an organo-mineral complex (OMC) material was prepared using modified palygorskite and chicken manure, the Cd and As adsorption capacities and mechanism of the OMC were explored, and the response of the crop to the OMC was clarified. The results show that the maximum Cd and As adsorption capacities of the OMC under pH values of 6-8 are 12.19 mg·g-1 and 5.07 mg·g-1, respectively. In the OMC system, the modified palygorskite contributed more to the adsorption of the heavy metals than the organic matter. Cd2+ may form CdCO3 and CdFe2O4, and AsO2- may form FeAsO4, As2O3, and As2O5 on the surfaces of the modified palygorskite. Organic functional groups such as hydroxyl, imino, and benzaldehyde groups can participate in the adsorption of Cd and As. The Fe species and carbon vacancy in the OMC system promote the conversion of As3+ into As5+. A laboratory experiment was conducted to compare five commercial remediation agents with OMC. Planting Brassica campestris in the OMC remediated soil with excessive contamination increased the crop biomass and decreased the Cd and As accumulation sufficiently to meet the current national food safety standards. This study emphasizes the effectiveness of OMC in preventing the migration of Cd and As into crops while promoting crop growth, which can provide a feasible soil management strategy for CdAs co-contaminated farmland soil.

Application of KHSO5 for remediation of soils polluted by organochlorides: A comprehensive study on the treatment's efficacy, environmental implications, and phytotoxicity.

Soil pollution caused by complex organochloride mixtures has been increasing in many parts of the world in recent years; as a result, countless numbers of people are exposed to dangerous pollutions; hence, the treatment of organochlorides-polluted soils is gaining considerable attention. In this study, the potential of unactivated peroxymonosulfate (KHSO5) in remediating soil co-contaminated with trichlorophenol, para-dichlorobenzene, and para-chloro-meta-cresol was investigated. In addition, the treatment's collateral effect on critical soil properties was explored. The result revealed that treating 10 g of soil with 20 mL of 5 mM KHSO5 for 60 min could oxidize 70.49% of the total pollutants. The pH of the soil was decreased following the treatment. The significant decrease, (p < 0.05), in the soil organic matter following the remediation has affected cation exchange capacity, and available nitrogen. It was also observed that the treatment reduced the ß-glucosidase, urease, invertase, and cellulase activities significantly, (p < 0.05). The treatment, on the other hand, brought negligible effects on available phosphorus, available potassium, and particle size distribution. The phytotoxicity tests, which included seed germination and root elongation and soil respiration tests revealed that the treatment did not leach toxins into the treated soil. The treatment method was found to be relatively ecofriendly and cost effective.

Organo-mineral complexes alter bacterial composition and induce carbon and nitrogen cycling in the rhizosphere.

It is widely thought that organo-mineral complexes (OMCs) stabilize organic matter via mineral adsorption. Recent studies have demonstrated that root exudates can activate OMCs, but the influence of OMCs on plant rhizosphere, which is among the most active areas for microbes, has not been thoroughly researched. In this study, a pot experiment using Brassica napus was conducted to investigate the effects of OMCs on plant rhizosphere. The result showed that OMC addition significantly promoted the growth of B. napus compared to the prevalent fertilization (PF, chemical fertilizer + chicken compost) treatment. Specifically, OMC addition increased the relative abundance (RA) of nitrogen-fixing bacteria and the bacterial α-diversity, and the operational taxonomic unit (OTU) group with RA > 0.5% in the OMC-treated rhizosphere was the result of a deterministic assembly process with homogeneous selection. Gene abundance related to nitrogen cycling and the soil chemical analysis demonstrated that the OMC-altered bacterial community induced nitrogen fixation and converted nitrate to ammonium. The upregulated carbon sequestration pathway genes and the increased soil microbial biomass carbon (23.68%) demonstrated that the bacterial-induced carbon storage in the rhizosphere was activated. This study shows that the addition of OMCs can influence the biogeochemical carbon and nitrogen cycling via regulating microorganisms in the rhizosphere. The findings provide fresh insights into the effects of OMCs on the biogeochemical cycling of important elements and suggest a promising strategy for improving soil productivity.

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.

Activating soil microbial community using bacillus and rhamnolipid to remediate TPH contaminated soil.

Soil petroleum contamination has become a global environmental problem. In order to develop a new soil remediation technology, this study established bacteria isolation, surfactant toxicity matching and petroleum contaminated soil remediation practice. The simulated field remediation showed that inoculating the soil with Bacillus methylotrophicus and adding 500 mg kg-1 rhamnolipid (N + RL) to soil can remove 80.24% of aged total petroleum hydrocarbons (TPHs) within 30 days. In particular, although the remediated soil has inoculated sufficient bacterial suspension, the microbial abundance of Bacillus was not a significantly dominant genus after remediation, especially in N + RL (0.73% of the total), but the colonies of indigenous petroleum-degrading bacteria (such as Massilia and Streptomyces) increased significantly. The interaction among genera has been further proved to drive soil non-specific oxidases (such as polyphenol oxidase, laccase and catalase) to remove TPHs. This indicates that the interaction among microorganisms, rather than the degradability of exogenous degrading bacteria, plays more critical role in the degradation of organic pollutants, which enriches the traditional understanding of micro-remediation of contaminated soil. It can be concluded from the obtained results that the remediation of pollutants can be achieved by adjusting the purification capacity of the microbial community and the natural environment.

Remediation of trichloroethylene contaminated soil by unactivated peroxymonosulfate: Implication on selected soil characteristics.

The advanced oxidation process (AOP) based on activated Peroxymonosulfate (PMS) has been attracting many people in the field of soil and water remediation in many ways while ignoring the shortcomings. The high cost of activators, and energy input, as well as the expense to separate the catalyst and transition metal reducing agent from the treated soil, were some disadvantages of using activated PMS. Based on the above rationales of problems related to the use of activated PMS, this study aimed to study the performance of using unactivated peroxymonosulfate for the advanced oxidation process to remediate soil contaminated by trichloroethylene (TCE), and to evaluate the synergistic effect on selected soil properties after treatment. The results showed that within 45 min, a single injection of 5 mM PMS at its initial pH value can degrade 86.90% of the total TCE in the soil. However, when PMS was continuously injected, the removal rate was increased to 95.25%. The direct reaction of TCE and PMS was the main cause of degradation. PMS can degrade TCE in a wide pH range (pH 3-11), but the maximum degradation was at pH = 2.9 (the initial pH of PMS). After the treatment, the soil organic matter (SOM) was degraded significantly. In contrast, FTIR, SEM, and hydrometer tests conducted on the soil showed that the treatment had no significant effect on the functional groups and particle size distribution of the treated soil. The study on the effect of the treatment on the concentration of bioavailable heavy metals in the treated soil showed that only manganese and copper metals were significantly increased after the treatment. According to the results obtained in this study, it is more beneficial and feasible to use unactivated peroxymonosulfate in the advanced oxidation process when remediating soil contaminated by chlorinated organic matter.

In situ phytoremediation of polycyclic aromatic hydrocarbon-contaminated agricultural greenhouse soil using celery.

Although celery has been established as an effective plant in the remediation of organic pollutant-contaminated soil, few studies have investigated the associated biological processes in rhizosphere and the effect of celery on agricultural field remediation in situ. In this study, a polycyclic aromatic hydrocarbon (PAH)-contaminated agricultural greenhouse was used as the experimental site, and three celery species (Apium graveolens L., Oenanthe javanica (Blume) DC., Libanotis seseloides (Fisch. & C.A. Mey. ex Turcz.) Turcz.) were applied for in situ remediation. After 90 days, the PAH dissipation rate of the L. seseloides treatment was highest (50.21%), and most of the PAHs were limited to its roots (translocation factor 0.516). This suggested that L. seseloides is a potential species for phytoremediation coupled with agro-production. The culturable microbial population and invertase activity results strongly supported that O. javanica is suitable for the establishment of exogenous bacteria-celery co-remediation techniques. Pearson's correlation analysis showed that the polyphenol oxidase (PPO) activity was highly significantly positively correlated with the PAH dissipation rate (r = 0.984, P < 0.01), and we suggest that PPO can be used as a microecological index during PAH remediation.

Effect of lignin and plant growth-promoting bacteria (Staphylococcus pasteuri) on microbe-plant Co-remediation: A PAHs-DDTs Co-contaminated agricultural greenhouse study.

Due to the ecological toxicity and environmental residues, how to remove the persistent organic pollutants (POPs), especially of polycyclic-aromatic-hydrocarbons (PAHs) and dichloro-diphenyl-trichloroethanes (DDTs), from agricultural soil has captured the attention of scholars for a long time. To develop an effective and low-cost in situ co-remediation technique, five independent but complementary treatments were used on an over-standard PAHs-DDTs co-contaminated soil in an agricultural greenhouse. Experimental results identified that the combination of microbe (Bacillus methylotrophicus) - plant (Brassica rapa) could remove rhamnolipid activated PAHs and DDTs effectively after enhanced by Staphylococcus pasteuri. Also, the Benzoapyrene and total DDTs residue in Brassica rapa was up to the standard of National (China) food safety. The lignin enhanced the removal of high-rings PAHs and p-p' DDE but reduced soil microbial biomass carbon and soil enzymes activity (polyphenol oxidase, invertase and acid phosphatase). Pearson correlation analysis showed that polyphenol oxidase activity was significantly related to the PAHs/DDTs dissipation rate. Our research suggested a new amendment that could remediate PAHs/DDTs co-contaminated agricultural soil without interrupting crop production, and the polyphenol oxidase activity should be considered as a micro-ecological indicator in this process.

[Pollution Characteristics and Source Apportionment of Polycyclic Aromatic Hydrocarbons in Soils of Shenyang North New Area].

Topsoil (0-20 cm) samples (n=101) in 5 different land use types in Shenyang North New Area (SNNA), Shenyang, China were collected using the uniform grid layout method to investigate the spatial distribution characteristics, composition spectrum, and source analysis of 16 polycyclic aromatic hydrocarbons (PAHs) listed as priority pollutants by the Environmental Protection Agency of the United States. Results showed that the total concentration of the 16 PAHs (ΣPAHs) in soils of SNNA ranged from 123.7 µg·kg-1 to 932.5 µg·kg-1. The PAH components were mainly dominated by 3-ring and 4-ring PAHs, of which the proportion of 3-ring PAHs was the highest. The spatial distribution of the ΣPAHs concentration was obvious, showing a decreasing tendency from south to north and from east to west. In the five soil types, the average concentrations of the ΣPAHs were relatively higher in the urban green space and the artificial forest, followed by the vegetable land, while the total PAH concentrations in paddy fields and corn fields were relatively lower and had no obvious spatial distribution differences. Source apportionment results studied using characteristic ratio analysis and factor analysis/multivariate linear regression showed that the main sources of PAHs in the topsoil of SNNA were mixed sources. Industrial coal combustion and motor vehicle exhaust were the main PAH contributors, with a combined contribution rate of 79.6%. The oil spill and coke oven contribution rate was about 16.2%, and the biomass fuel combustion was about 4.2%.

Surfactant-enhanced bioremediation of DDTs and PAHs in contaminated farmland soil.

Field-scale bioremediation of dichlorodiphenyl trichloroethanes (DDTs) and polycyclic aromatic hydrocarbons (PAHs) contaminated farmland soil from the Shenyang North New Area of China was studied using the bacteria Arthrobacter globiformis. The additive effects of different concentrations of biosurfactant rhamnolipids (RLs) and anionic-nonionic mixed surfactant (SDBS-Tween 80) were evaluated. DDT and PAH removal rates by A. globiformis after 150 days of remediation were 52.1% and 21.9%, respectively. At the optimum RL concentration of 5 mg kg-1, DDTs and PAHs had removal rates of 64.3% and 35.6%, respectively, at 150 days. This was 60.7% and 29.3% higher than the control; 36.9% and 19.8% higher than soil with RL-5 alone; and 12.2% and 13.8% higher than the A. globiformis treatment alone. RL-5 can enhance soil enzyme activity and A. globiformis reproduction during the DDT and PAH biodegradation processes. This study illustrates a highly efficient, low-cost in situ soil bioremediation technology that could have practical utility.