Combining camelina sativa production with phytodepuration of contaminated effluents obtained in hydrothermal carbonization processes – an opportunistic approach

In recent years, hydrothermal carbonization (HTC) has been considered an alternative thermochemical process that converts high moisture organic feedstock into carbon rich solids. However, during this process toxic organic and inorganic compounds present in the feedstock, such as hydrocarbons, are leached to a liquid phase that needs to be depurated. Phytodepuration is a technology based on the use of plants in the remediation of contaminated effluents, thus it’s a sustainable option that allows to simultaneously clean the contaminated waters obtained in the HTC process and produce biomass that can be used in multiple applications. Camelina sativa is an energy crop that has the potential to produce biofuels, as well as, value added products from its oil. In this work we evaluated the phytodepuration capacity of Camelina sativa (winter and spring varieties) when subjected to the irrigation of contaminated effluents obtained in HTC, as well as, the productivity and quality of biomass. The hydrothermal carbonization effluent used in this study (360 mg/L O₂) was diluted 1:3 (WW1: 120 mg/L O₂), 1:2.4 (WW2: 150 mg/L O₂) and 1:2 (WW3: 180 mg/L O₂) to obtain the chemical oxygen demand (COD) equal to 0.8, 1.0 and 1.2 times the limit value for wastewater discharge established by the Portuguese Decree Law 236/98. Also, the plants were irrigated with tap water as a control treatment. The results obtained led to the conclusion that the soil-biomass system was able to depurate the contaminated waters from the HTC process, decreasing by circa 63-72% for WW1, 69-75% for WW2 and 68-76% for WW3 the initial COD values and thus, avoiding the contamination of groundwater. Regarding biomass productivity, it’s was concluded that the winter variety of Camelina sativa was the least affected by the contaminated waters of the HTC effluent. In addition, the winter variety obtained the highest productivity (loss of siliquae yield: 9-45% for the winter variety; 11-67% for the spring variety). Ash, nitrogen, phosphorus as well as some metals content, in the plant, were also affected by the contaminated effluents from the HTC process. The oil content was also affected by the contaminated HTC effluents, which can compromise its use as a feedstock for biofuels production, as an energy carrier or as a feedstock for chemicals.