Petroleum refining industries produce large amounts of toxic effluents, causing environmental pollution. Iran is an oil-rich country that encounters oil pollution in its soil and water. Bioremediation of these pollutants is an appropriate solution to tackle them, compared to physical and chemical remediation methods. There are some factors that increase the rate of biodegradation; therefore, this study aims to determine the rate of gasoil bioremediation by two indigenous bacterial isolates (from oil-contaminated soils of an oil refinery south of Tehran) in two different media, namely soil and soil-sawdust mixture. The two superior indigenous bacteria has been isolated through three steps with results indicating that in an optimal environmental condition (temperature= 27±2 °C, humidity of 60%, water holding capacity, and daily manual aeration), bacterial isolates are able to degrade about 78.87% and 93.53% of gasoil during 45 days in soil and soil-sawdust mixture media, respectively. These results imply the role of sawdust in improving aeration, water holding capacity, and-consequently- increasing bioavailability of gasoil to bacteria.

Sawdusts of hardwood - oak and black locust, modified with formaldehyde and/or alkali solution, were used as adsorbents zinc ions from model water. The influence of concentration of alkali solution for modification, on zinc ions adsorption efficiency were investigated. Batch adsorption tests were conducted on ambient temperature. Langmuir and Freundlich adsorption isotherm equations were determinated for some adsorbents investigated. Good improvement of adsorption characteristics is achieved by modification of sawdust with alkali. Modification of sawdusts only with formaldehyde results with good prevention of leaching of organic substances as well as poor increase of adsorption efficiency.

Biodegradation of microplastics (MPs) in contaminated biowastes has received big scientific attention during the past few years. The aim here is to study the impacts of livestock manure biochar (LMBC) on the biodegradation of polyhydroxyalkanoate microplastics (PHA-MPs) during composting, which have not yet been verified. LMBC (10% wt/wt) and PHA-MPs (0.5% wt/wt) were added to a mixture of pristine cow manure and sawdust for composting, whereas a mixture without LMBC served as the control (CK). The maximum degradation rate of PHA-MPs (22–31%) was observed in the thermophilic composting stage in both mixtures. LMBC addition significantly (P < 0.05) promoted PHA-MPs degradation and increased the carbon loss and oxygen loading of PHA-MPs compared to CK. Adding LMBC accelerated the cleavage of C–H bonds and oxidation of PHA-MPs, and increased the O–H, CO and C–O functional groups on MPs. Also, LMBC addition increased the relative abundance of dominant microorganisms (Firmicutes, Proteobacteria, Deinococcus-Thermus, Bacteroidetes, Ascomycota and Basidiomycota) and promoted the enrichment of MP-degrading microbial biomarkers (e.g., Bacillus, Thermobacillus, Luteimonas, Chryseolinea, Aspergillus and Mycothermus). LMBC addition further increased the complexity and connectivity between dominant microbial biomarkers and PHA-MPs degradation characteristics, strengthened their positive relationship, thereby accelerated PHA-MPs biodegradation, and mitigated the potential environmental and human health risk. These findings provide a reference point for reducing PHA-MPs in compost and safe recycling of MPs contaminated organic wastes. However, these results should be validated with other composting matrices and conditions.

Batch sorption of metformin hydrochloride (MET) onto a specially designed biochar mix consisting of both macro (MAC) and micro (MIC) algae, rice husk and pine sawdust was conducted. Pyrolysis of both MAC and MIC algae mixture was done followed by chemical activation with hydrogen-peroxide. Additionally, sorption of MET under the influence of pH was separately investigated. Batch studies of isotherms were well described by Freundlich model with high non-linearity and Freundlich exponent values ranged anywhere from 0.12 to 1.54. Heterogeneity of MET adsorption to the bonding sites was attributed to the surface functional groups of the modified biochar. Amongst the four biochars, the activated macroalgae biochar (MACAC) and microalgae biochar (MICAC) depicted favourable adsorption of MET with maximum adsorption at pH 7. Up to 76% of MET removal from the environment was obatained using the MACAC biochar. Scanning electron micrographs coupled with energy dispersive X-ray, as well as elemental analyses confirmed formation of oxygen containing surface functional groups due to activation strengthening chemisorption as the main sorption mechanism. Further, Fourier transform infra-red spectroscopy and other surface functional group analyses along with Zeta potential measurements reinforced our proposed sorption mechanism. Lowest zeta potential observed at pH 7 enhanced the electrostatic force of attraction for both the biochars. Negative zeta potential value of the biochars under different pH indicated potential of the biochars to adsorb other positively charged contaminants. From a techno-economic perspective, capital expenditure cost is not readily available, however, it is envisaged that production of pyrolyzed biochar from algal biomass could make the process economically attractive especially when the biochar could be utilised for high-end applications.

This study investigated catalytic ozone oxidation using a sawdust char (SDW) catalyst to remove hazardous toluene emitted from the chemical industry. The catalyst properties were analyzed by proximate, ultimate, nitrogen adsorption-desorption isotherms, Fourier-transform infrared, and X-ray photoelectron spectroscopy analyses. In addition, hydrogen-temperature programmed reduction experiments were conducted to analyze the catalyst properties. The specific area and formation of micropores of SDC were improved by applying KOH treatment. MnOx/SDC-K3 exhibited a higher toluene removal efficiency of 89.7% after 100 min than MnOx supported on activated carbon (MnOx/AC) with a removal efficiency of 6.6%. The higher (Oₐdₛ (adsorbed oxygen)+Oᵥ(vacancy oxygen))/OL (lattice oxygen) and Mn³⁺/Mn⁴⁺ ratios of MnOx/SDC-K3 than those of MnOx/AC seemed to be important for the catalytic oxidation of toluene.

The spread of antibiotic resistance genes (ARGs) is a global environmental issue. Dissolved biochar is more likely to contact bacteria in water, producing ecological risks. This study explored the effects of dissolved biochar on ARGs transfer in bacteria. Conjugative transfer efficiency was significantly different following treatment with different types of dissolved biochar. Typically, humic acid-like substance in dissolved biochar can significantly improve the transfer efficiency of ARGs between bacteria. When the concentration of dissolved biochar was ≤10 mg biochar/mL, humic acid-like substance substantially promoted ARGs transfer. An increase in dissolved biochar concentration weakened the ARGs transfer from humic acid-like substance. The inhibitory effects of small-molecule matters dominated, decreasing conjugative transfer frequency. At a concentration of 100 mg biochar/mL, the conjugative transfer efficiency of all treatments was lower than that of control. Compared with corn straw dissolved biochar, there were more transconjugants in pine sawdust dissolved biochar. Following treatment with 10 mg biochar/mL pine sawdust dissolved biochar, the number of transconjugants was at its maximum; approximately 7.3 folds higher than the control. We also explored mechanisms by which dissolved biochar impacts conjugative transfer. Due to the complex composition of dissolved biochar, its effects on the expression of conjugative transfer-related genes were also dynamic. This study investigates the ecological risk of biochar and guides its scientific application.

Nitrate is the most common contaminant in groundwater in Korea, as well as across the world. Reduction of nitrate to ammonia is one of the options available to remediate groundwater. In this study, nitrate in groundwater was removed using a zero-valent iron (ZVI) containing biochar synthesized by co-pyrolyzing iron oxide and sawdust biomass. Among the various biogases generated during the pyrolysis of biomass, CO and H₂ act as reducing agents to transform iron oxides to ZVI. Approximately 71% of nitrate was reduced to ammonium by ZVI-biochar at initial pH 2.0, and the reduction decreased sharply by the increase in pH. The mass of nitrate-N decreased is exactly same with the mass of ammonia-N formed. However, ammonium remained in the aqueous phase after reduction by ZVI-biochar, and the total nitrogen was not lowered. Acid-washed zeolite adsorbed most ammonium reduced by the ZVI-biochar and maintained the pH to acidic condition to facilitate the reduction of nitrate. The results of this study imply that nitrate-contaminated groundwater can be properly treated within the guidelines of water quality by synthesized ZVI-containing biochar.

Effective and economically viable method to remove elevated metal(loid)s from farm and industrial lands remains a major challenge. In this study, magnetic biochar-based adsorbents with Fe₃O₄ particles embedded in a porous biochar matrix was synthesized via iron (Fe) treated biochar or thermal pyrolysis of Fe treated cedar sawdust. Application and separation of the adsorbent to a multi-contaminated soil slurry simultaneously removed 20–30% of arsenic, cadmium and lead within 24 h. Fast removal of multi-metal(loid)s result from the decrease in all operationally defined fractions of metal(loid)s, not limited to the exchangeable fraction. The direct removal of arsenic-enriched soil particles was observed via micro X-ray fluorescence maps. Furthermore, through comparison of biochars with different production methods, it has been found that magnetization after pyrolysis treatment leads to stronger metals/metalloids adsorption with a higher qₑ (bound sorbate) than other treatments but pyrolysis after magnetization stabilized Fe oxides on the biochar surface, indicating a higher biochar recovery rate (∼65%), and thus a higher metal(loid)s removal efficiency. The stability of Fe oxides on the surface of biochar is the determining factor for the removal efficiency of metal(loid)s from soil.

Leaching of herbicides in cropping soils not only impacts the groundwater sources but also reduces their effect in controlling weeds. Leaching studies were carried out in two cropping soils and two forestry biowaste media, wood pulp and sawdust with two herbicides, atrazine and bromacil in a packed lysimeter with simulated rainfall. The hypothesis was that high organic matter forestry biowaste soil amendments reduce the leaching of herbicides through the soil profile. Results from the experimental setups varied due to the impact of the simulated rainfall on the surface structure of the media. Organic carbon content, pH and structure of the media were all factors which affected the leaching of the two herbicides. The hypothesis was true for wood pulp, but for sawdust, organic matter content had less bearing on the leaching of the herbicides than other over-riding factors, such as pH, that were media specific. In sawdust, its large particle size and related pore volume allowed preferential flow of herbicides. Overall, the data indicated that both forestry biowastes were retentive to herbicide leaching, but the effect was more pronounced with wood pulp than sawdust.

Properly increasing mobility of heavy metals could promote phytoremediation of contaminated soil. Fe₁₋ₓS/biochar was successfully prepared from sawdust with loading pyrrhotite (Fe₁₋ₓS) at a pyrolysis temperature of 550 °C. Thiobacillus were successfully adsorbed and enriched on the surface of Fe₁₋ₓS/biochar. Microbial growth for 36 d supported by bio-oxidization of Fe₁₋ₓS decreased the system pH from 4.32 to 3.50, increased the ORP from 298 to 487 mV, and the Fe³⁺ release reached 25.48 mg/g, enhancing the oxidation and leaching of soil Pb. Finally, Fe₁₋ₓS/biochar and Thiobacillus were simultaneously applied into Pb-contaminated soil for 60 d, the soil pH decreased from 7.83 to 6.72, and the exchangeable fraction of soil Pb increased from 22.86% to 37.19%. Ryegrass planting for 60 d in Pb-contaminated soil with Fe₁₋ₓS/biochar and Thiobacillus showed that the Pb content in shoot and root of ryegrass increased by 55.65% and 73.43%, respectively, confirming an obvious increase of phytoavailability of soil Pb. The relative abundance of Thiobacillus in remediated soil significantly increased from 0.06% to 34.55% due to the addition of Fe₁₋ₓS/biochar and Thiobacillus. This study provides a novel approach for regulating the Pb phytoavailability for phytoremediation of Pb-contaminated soil.