The PIKO project uses two types of ‘biochar’ produced using different methods: hydrochar and plant charcoal.

Hydrochar is produced using the hydrothermal carbonisation (HTC) process. In this process, the (moist) biomass is mixed with water and heated to around 180 to 240°C in a pressure-tight vessel, where it is ‘cooked’ for several hours. Simple filtration allows the liquid and solid phases to be separated. The peat- to coal-like product exhibits properties similar to those of peat: it has a low pH value (around pH 5), has low nutrient and salt contents depending on the biomass used, and contains many chemical compounds on its surface, making nutrients and water available to plants. Hydrocarbons are generally mineralised after a few years (broken down by bacteria and fungi into CO₂ and nutrients) and thus serve only as a short-term store of carbon. The feedstocks for the hydrocarbons in the project are to consist primarily of residual materials. These include, for example, vegetation from paludiculture (reeds, cattails, sedges) or grass-like vegetation from wet meadows.

Biochar is usually produced by pyrolysis. Biomass (primarily wood or wood-like material) with a low water content is ‘partially combusted’ in a pyrolysis furnace at temperatures between 500 and 900 °C, i.e. part of the biomass carbon is burnt, generating the high process temperatures. The remaining biomass carbon is converted into charcoal under high temperature and in the absence of oxygen. Pyrolysis charcoal differs significantly from hydrochar: its pH value is well above pH 7, its nutrient and salt content is high, and the biochar is highly resistant to degradation by bacteria and fungi, thereby contributing to the long-term storage (over centuries) of carbon.

The PIKO project is primarily investigating the extent to which grass-like vegetation from paludiculture can be pyrolysed. Findings from the literature suggest that biochar derived from grass-like vegetation has high ash contents (due to the high ash contents of the source biomass), meaning that the carbon content of at least 80 per cent required by the German Fertiliser Ordinance (DüMV) cannot be met.