Petroleum industry generates large volumes of hydrocarbon-containing wastewater, that may be treated and
valorized by anaerobic conversion to methane. This process is performed by complex microbial communities
and is only thermodynamically feasible at low hydrogen partial pressure, which is generally accomplished by
the activity of hydrogenotrophic methanogens. However, alkanes, polyaromatic hydrocarbons and BTEX
were shown to inhibit methanogenesis in mixed microbial cultures. This may be due to a direct inhibition of
the methanogens, or may result from indirect inhibition, by disrupting the microbial relationships in the
complex communities. To get more insights on this topic, the toxicity of aliphatic hydrocarbons towards pure
cultures of hydrogenotrophic methanogens was assessed in this work. Aliphatic hydrocarbons represent the
largest fraction of crude oil or petroleum-derived products, and hexadecane (HC) was chosen as model
compound. Methane production from H2/CO2 (80:20%, 1.7x105 Pa) by Methanobacterium formicicum and
Methanospirillum hungatei was measured in the presence of increasing HC concentrations (1, 5, 15 and 30
mM), and was compared with the controls without HC. For both methanogens, the methane production rate
was significantly lower (p30 mM could be estimated for M. formicicum and M. hungatei, respectively.
Therefore, M. hungatei is more tolerant to the presence of HC than M. formicicum, possibly due to the
differences in cell wall structure and membrane lipid composition of the two species. Moreover, the relatively
high IC50 values obtained are most likely related with the low HC solubility. Considering the typical range of
hydrocarbon concentrations in wastewater from the petroleum industry, toxic effects from aliphatic
hydrocarbons towards hydrogenotrophic methanogens will not be expected to occur during the anaerobic
treatment of these type of wastewater.This study was supported by FCT under the scope of project MORE (PTDC/AAGTEC/3500/2014; POCI-01-0145-FEDER-016575), of the strategic funding of UID/BIO/04469/2019 unit and
BioTecNorte operation (NORTE-01-0145-FEDER-000004) funded by the European Regional Development
Fund under the scope of Norte2020 - Programa Operacional Regional do Norte.info:eu-repo/semantics/publishedVersio
