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The recent literature indicates that, depending on the feedstocks and pyrolysis temperature, biochar can be a good source of nutrients. On the contrary, some biochars are not good sources of available carbon and other nutrients, but their porous structure seems to be a suitable microenvironment for microbial colonization. We investigated the response of soil biological parameters, microbial biomass carbon and nitrogen (MBC and MBN), in relation to mobile N species. Five different biochars were produced at different temperatures (300, 350, 400, 450, and 500 °C) from the same feedstock (woodchips). The physicochemical and morphological characteristics of the individual biochar samples were described, and incubation was carried out with the application of 2% biochar to two different soil types (luvisol and fluvisol). The addition of 2% biochar did not change the pH in the slightly acid soils used in the experiment, in spite of the alkaline character of biochar. The increasing amounts of total and nitrate-available nitrogen during the experiment are probably related to changes in soil microbial activity. The amount of soluble carbon was constant during the experiment, confirming its stability in the soil, most likely because of the high amount of lignin in the feedstock. The influence of biochar on the soil microbiome was determined on the basis of the concentrations of MBC and MBN. Microbial biomass was increased in both soils treated with biochar produced at lower temperatures. The physicochemical characteristics of the biochar as well as the sorption behavior of N-NO3− and N-NH4+ indicate that at a pyrolysis temperature of 400 °C, biochar properties change substantially. However, these findings are only valid for biochar produced from woodchips, and the long-term effects of biochar application on soil properties need to be investigated in further studies.

Biostimulation of the activity of degrading autochthonous microbiota constitutes one of the most accepted bioremediation tools for oil-polluted soils. Applications of nutrients such as nitrogen fertilizers, oleophilic fertilizers or surfactants are some of the strategies employed. Soil microcosm experiments were performed in open glass containers to compare the biological activity of two types of soils: a sandy soil with low nutrient content and low biological activity and a clay loam soil with high nutrient content and high biological activity. Arabian crude oil was used as the contaminant, applied at 10,000 mg kg−1 and 20,000 mg kg−1. Different treatments were used including natural attenuation, used as a control, and the application of different biostimulation products. The results showed that for sandy soil at high hydrocarbon pollution, amendment with oleophilic fertilizer combined with a surfactant was the best treatment, whereas at low hydrocarbon pollution no significant differences were found among the treatments. In clay loam soil, at 10,000 mg kg−1 of hydrocarbon pollution, surfactant application was the most efficient treatment for total petroleum hydrocarbons removal. However, when Arabian crude oil was supplied at 20,000 mg kg−1, nitrogen, phosphorous, and potassium treatment and the oleophilic fertilizer S200C in combination with surfactant treatment presented the highest rate of total petroleum hydrocarbons removal. Thus, the suitability of biostimulation treatments was strongly influenced by the initial physicochemical and biological characteristics of the soil.

This study describes the capacity of different sorbents to form stable biofilms under highly hydrocarbon-polluted conditions and the degrading capacity of the microbiota present in the biofilm. With this aim, microcosms were designed in a 1 L beaker with 400 mL of culture medium or polluted wastewater and an amount equivalent of 200 mL of the selected sorbent carrier, made of cork and/or polypropylene meltblown. The culturable bacteria adhered to the sorbent carrier were quantified, and the time course of the hydrocarbon concentration was studied together with the formation of a biofilm on the carrier’s surface. The results revealed a different performance of the carriers in terms of bacterial adhesion, significantly reduction in the hydrocarbon content in water at the end of the assays, and a biofilm tolerance to high hydrocarbon concentration in the polluted water. From these results, it was concluded that the use of a sorbent, hydrophobic cork, or meltblown polypropylene, together with indigenous microbiota, constitutes a promising technology for the treatment of hydrocarbon-polluted water.