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.

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.

Optimal river monitoring network using optimal partition analysis: a case study of Hun River, Northeast China.

River monitoring networks play an important role in water environmental management and assessment, and it is critical to develop an appropriate method to optimize the monitoring network. In this study, an effective method was proposed based on the attainment rate of National Grade III water quality, optimal partition analysis and Euclidean distance, and Hun River was taken as a method validation case. There were 7 sampling sites in the monitoring network of the Hun River, and 17 monitoring items were analyzed once a month during January 2009 to December 2010. The results showed that the main monitoring items in the surface water of Hun River were ammonia nitrogen (NH4+-N), chemical oxygen demand, and biochemical oxygen demand. After optimization, the required number of monitoring sites was reduced from seven to three, and 57% of the cost was saved. In addition, there were no significant differences between non-optimized and optimized monitoring networks, and the optimized monitoring networks could correctly represent the original monitoring network. The duplicate setting degree of monitoring sites decreased after optimization, and the rationality of the monitoring network was improved. Therefore, the optimal method was identified as feasible, efficient, and economic.