Comparison of the application of unmodified and modified biochar and microorganisms on some microbial and ecophysiological indicators of soil contaminated with crude oil

Due to the presence of refineries and oil-rich areas in our country, the need for cost-effective and environmentally friendly methods is strongly felt. Biochar is a soil conditioner produced from the pyrolysis of organic residues. In addition to improving the quality of contaminated soils, it also improves the biological conditions of microorganisms involved in bioremediation. Using biochar in biological processes is both economical and affordable. Another point is that this material, compared to other similar products, is more economical and generally creates more tolerance in microorganisms against toxic compounds based on this, a study was implemented to compare the changes in the properties of biochar obtained from sugarcane bagasse and date palm through surface chemical activation with hydrogen peroxide (modified biochar) and unmodified biochar focusing on metabolic, enzymatic activities and the amount of microbial biomass in a saline calcareous soil. Contaminated with crude oil was implemented.

In this research, an experiment was carried out in the form of repeated measurements in time intervals. In the middle and at the end of the experimental period (60 and 120 days), the effect of different levels of unmodified and modified biochar of sugarcane and unmodified palm bagasse (one and two percent) along with microorganisms (with biochar and without biochar and a total of 57 test samples at two times) some biological characteristics and eco-physiological indicators of soil including basic microbial respiration, substrate-induced respiration, microbial carbon dioxide, dehydrogenase enzyme, microbial contribution and metabolic contribution were investigated. The biochar used was prepared from sugarcane bagasse and date palm waste. The wastes were prepared, dried, and pounded. Then they were heat treated at 400 °C for four hours. Then kept for a while to cool. Then they were modified with 10% hydrogen peroxide and kept at room temperature for 24 to 48 hrs. After that, they were placed in the oven at a temperature of 80 °C for 24 hrs and then they were ready to use. To measure basic microbial respiration using the method of Anderson et al. (2011) substrate-induced respiration using the method of Alef and Nannipieri (1995) microbial carbon dioxide using the fumigation method, dehydrogenase enzyme activity using the method of Cassida et al. (1964) and the microbial contribution was obtained by dividing the microbial biomass carbon by the organic carbon, and the metabolic contribution was obtained by dividing the basal respiration by the microbial biomass carbon.

The analysis of the variance table of repeated measurement of the effect of unmodified and modified biochar and microorganisms on the examined traits in the soil showed that in the outgroup effects, all treatments have significant differences with each other at the one percent level. In the intragroup effects, time had a similar status in all the investigated treatments. The interaction of time and treatments also showed a significant difference except in microbial biomass carbon and substrate-induced respiration in the rest of the treatments. The best results in dehydrogenase enzyme, microbial carbon dioxide, basal, and substrate-induced respiration were observed in the treatment of mixture four (a mixture of modified bagasse two percent and bacterial consortium two percent) for 60 days, showing an increase in these traits by 70.98, 8.96, 53.97, and 53.54 %, respectively compared to the control treatment. The highest amount of microbial contribution was found in the control treatment of 120 days and the highest amount of metabolic contribution also was found in the treatment of a mixture three (mixture of unmodified bagasse one percent and bacterial consortium one percent) for 120 days, which has increase of this trait by 76.70% compared to the control treatment of 120 days.

In this research, all the microbial indicators measured in the soil showed a significant difference compared to the control treatment. Also, the results of this research showed that the addition of organic matter in soils contaminated with crude oil, such as unmodified and modified biochar, either alone or in interaction with microorganisms, can partially reduce the destructive effect of the stress caused by the pollutant (crude oil) and the microbial community. Biochar modification using hydrogen peroxide, as a relatively cheap and environmentally friendly modifying agent, increased the effect of biochar on the studied biological and ecophysiological properties, with the best results observed in the modified treatments. Sugarcane bagasse biochar had better results than date palm waste. This improvement was even greater when combined with microorganisms. It should be noted that biochar is not only effective in remediation but also stabilizes and neutralizes toxins. By using the results of this research, we can propose suitable solutions for their biological restoration according to the type of soil. Sugarcane bagasse biochar compared to date palm waste and the presence of microorganisms improved soil biological indicators. Therefore, biochar modification using hydrogen peroxide, as a relatively cheap and environmentally friendly modification agent, increased the effect of biochar on the studied biological and ecophysiological characteristics.