Critical Review : Bioremediation of petroleum hydrocarbon-contaminated soil by petroleum-degrading bacteria immobilized on biochar

Alonzo Bell

Critical Review Report

Article : Bioremediation of petroleum hydrocarbon-contaminated soil by petroleum-degrading bacteria immobilized on biochar 

Authors : Bofan Zhang, Liang Zhang, Xiuxia Zhang ;

Journal : The Royal Society of Chemistry

1. Comments to the Authors    

The major contribution to the paper is that it provides a model of the effectiveness of using immobilized bacteria and biochar to degrade large chains of hydrocarbons. The paper introduces bio-char which is a spent mushroom substrate; and makes great points regarding increasing enzymatic activity and accelerated remediation of carbon, nitrogen and phosphorus substances. The authors did a sound job in conveying the methods of bioaugmentation and biostimulation, and the role which it can play in promoting factors that influence thriving microorganisms. With the combination of bioaugmentation and biostimulation; it makes it possible for native organisms to thrive and for introduced bacteria species to metabolize at fast rates, with the presence of beneficial nutrients and wavelength absorption patterns. Carriers are definitely a significant part of this study, and I think there should have been more detail explaining the dynamics and specifics of the carrier. This study provides conclusions and data which can help with remediation research and innovation in China and around the world. Characteristics of spent mushroom bio-char are clearly illustrated to convey the different properties of the initial soil and the bio-char substrate. In Table 1, Physicochemical properties of soil and biochar, the table shows that the soil before remediation had a pH of 7.39 , organic matter of 9.85 (g kg-¹) and electrical conductivity of 1.45 (mS cm-¹) . The biochar compound appears to have a pH of 11.3, organic matter of 33.5 (g kg-¹), and electrical conductivity of 6.13 (mS cm-¹). The properties of the introduced biochar does have a higher electric conductivity which will allow for more ionic interactions and more possibilities of carbon accumulation and metabolism. With higher pH conditions, higher organic matter content and higher electrical conductivity ; the biochar introduces many organic chemicals, increases ability to take up ions and presents an environment with more favorable growing conditions, than the initial contaminated soil. A strong point of this article is that it shows the distinction between methods of remediation. The authors constantly reiterate the main point and support claims with data in graphs, tables, figures and illustrations. Another strength is that authors utilized methods which allowed them to monitor the microbial activity in the treatments studied. It’s strong point is that it shows how small alkanes can be easily degraded over time, with presence of different microorganisms. Longer alkanes usually take longer to break down , but they are also oxidized over time by bacteria, anaerobic microbes and biochar. By using a soluble membrane, bacteria are able to be immobilized in between pores of hydrocarbon. There are many strengths in this study but a weakness would be that the study didn’t dive deep into depth of soil before remediation. An overall more concise description of the native qualities of the contaminated soil would have strengthened the study. Taking a deeper dive into the post remediation of soil may help to solidify the role in which each organism plays. The method of soil extraction seems clear but it may be unclear in understanding how soils were obtained. In the methods it may be hard to interpret whether samples were collected randomly or in a controlled manner.   

  

2. General   

Bioremediation with micro organisms is definitely a growing field and sparking the interests of people who want to study microbiology. Oil spills and petroleum contamination are significant topics which affect the health ecosystems worldwide. The authors have initiated their research of bioremediation with immobilized bacteria and biochar, in the soil samples of the ShengLi Oil Field, China. The scientific soundness is solid and this article acknowledges many known science concepts such as ; photosynthesis, electromagnetic spectrum, alkalinity, available nutrients, soil parameters, porosity, microbial respiration and total petroleum hydrocarbons. There is a lot of emerging research regarding bioremediation with bacteria and biochar. The authors used methods for treatments which could be replicated such as; 60 day incubation periods with 60% moisture content. The work was very original and uniquely shown data from 5 treatments, to see which process was the most effective. In the article, the authors use science jargon which is widely respected in the science field and related to hydrophobic environments. The organization was very well thought out and outlined the sections in an appropriate order. The abstract and introduction gives a clear and brief overview of how biochar individually, free bacteria and petroleum-degrading bacteria immobilized on biochar, can all have effects in remediation of soils after 60 days. It further establishes the idea that immobilization of oil degrading bacteria coupled with biochar can increase carbon storage and also be able to degrade hydrocarbon C₁₂-₁₈ which sits in hydrophobic plumes. The objective is clear that these methods of remediation can cause an increase in microbial activity and that there should be more exploration on this topic. The argument is cohesive and often expressed throughout the article. The cohesiveness of this article flows into the next subject and fits right in place. The conclusion; that petroleum degrading bacteria coupled with biochar has shown some of the highest efficiency in degrading alkanes and aromatic hydrocarbons, has been supported by data. The removal efficiency was the most effective 58.08% in the BIM treatment and caused the biggest decrease in alkanes and large insoluble hydrocarbon soils. The length of the article is relative to the number of ideas and information, because it expands on the five treatments which were studied and goes into detail about specific methods. The writing, in addition to the graphs and illustrations, presents an appropriate length for the content to be covered along with supporting data backing the main argument. The writing was concise and used scientific jargon which is typically seen when studying microbiology and petroleum in the environment. Some abbreviations were hard to understand, but overall the article is very precise and informational for people wanting to learn more about remediation of petroleum in microbiology. 

3. Specific

1. Presentation 

The presentation does tell a cohesive story. The authors often reiterate throughout the entire article, that biochar with the immobilization of bacteria can increase the rate at which large hydrocarbons, aromatic hydrocarbons, organic material and also inorganic material breaks down due to increased metabolism. The argument is tightly reasoned and evident throughout the paper. The article focused on 5 different treatments with a controlled time of 60 days. The 5 treatments focused on monitoring free bacteria, controlled contaminated soil (without bacteria or biochar), biochar alone, bacteria alone, and a combination of bacteria immobilized on biochar. These treatments were they’re main focus, in understanding how microbes can remediate soils within 60 days; based on important influential factors. The treatments are started with 500 grams of unfertilized soil in flower pot reactors. The article does a good job of presenting how an experiment with bioremediation can give us beneficial solutions for these types of environmental concerns. The abstract, key words, and conclusions accurately and consistently reflect the major points of the paper. The writing is concise and constantly emphasizes that TPHs are a huge problem and the use of spent mushroom substrate biochar and petroleum degrading bacteria can potentially help combat this environmental issue. The paper is easy to follow but there is a lot of information and readers may need to pay close attention to detail.   

2. Length 

The paper has an appropriate length for the amount of information that is compiled within the study. The article would be more sound by expanding on the original state of the contaminated soil in Sheng Li Oil Field, China. Learning more about the ecosystem in this particular soil, would have further strengthened the background knowledge of this specific ecosystem. Overall, the length was appropriate and covered the magnitude of the study.

3. Methods  

The methods in this presentation are appropriate. The methods are complicated and an extensive process which can be repeated by a competent person with some science background. The methods may be harder to understand for someone who is not aware of major concepts in microbiology. Illustrations are clear and easy to understand. Tables, images and graphs are correctly illustrated and correlate with the arguments that are being made in this article. The authors explain that for 60 days the five treatments were facilitated in 3 replicates at 30 degrees celsius with the relative humidity of 60%. They used 500 grams of contaminated soil as the source to conduct the experiment. 

4. Data Presentation  

Data is represented through the illustrations, tables, figures, constants and formulas. The data is consistent with the information and content of the article. Data is clearly labeled and detailed. Some tables and figures seemed very complex but overall they gave a strong representation of the main points in correlation with data. Tables, figures, constants and equations are labeled and thoroughly planned. The results of the 5 treatments are shown in section 3 of the article and figure 2. Results found that after 60 days of incubation the rate at which petroleum hydrocarbon were degraded are reported ; Control group treatment : 3.98 g kg-¹, BIM treatment : 26.85 g kg-¹, BMF treatments : 20.74 g kg-¹ , BF treatments : 17.68 g kg-¹ , BC treatment : 13.66 g kg-¹. The data is supported with the reasoning that immobilized bacteria contributed to the largest decrease in large hydrocarbon plumes. The reasoning explains that immobilized bacteria were more favorable to adapt in the hydrocarbon enriched environment. The biochar substrate - free bacteria treatment resulted in the second largest decrease of petroleum hydrocarbons. In the conclusion of the article, the results are reported and TPHs removal efficiency were ; BIM treatment : 58.08% , BMF treatment : 45.31% , BC treatment : 29.85% , BF treatment : 38.63% and Control group treatment 8.69%.  

5. Statistical Design and Analysis   

The paper was articulated in a way in which you'd be able to discern the measurements and observations. The authors convey the comparisons of the soil’s characteristics and biochar’s characteristics. The writing in combination with Table 1, explains the differences Physicochemical properties of soil and biochar. The reading directs your attention towards Table 1, which compares the organic matter, pH, available nitrogen, electric conductivity of biochar individually and soil sample individually. These factors are essential and influence the abiotic and biotic factors of the soil in ShengLi Oil Field, China. The immobilization of bacteria and biochar can cause higher efficiencies of degradation than original microbes in the soil; and the study supports it with data and statistics.   

 

6. Errors    

I noticed that some of the headings and subheadings weren't capitalized. Capitalizing the headings and subheadings creates consistency and grammatically strong writing. Another error that I noticed; is when the author’s use numbers, not all of the numbers are associated with a metric value which could confuse readers. 

7. Citations    

All of the citations are pertinent and cited appropriately. The sources are cited correctly using the CBE Style Manual. 

8. Overlap 

Many articles have been published regarding the efficiency of degrading petroleum oil spills with specific types of bacteria. Bioremediation is becoming a popular topic, and the authors did a good job of isolating different microorganisms and determining the effectiveness of heterotrophic and autotrophic organisms when metabolizing and breaking down long hydrocarbon chains. The authors developed a unique article regarding biochar and using different factors to determine its effectiveness in bioremediation. This study is unique and original because it reports data and conclusions which have not been published yet.