Organic residue treatment

A treatment system for organic residues has been launched by CST Wastewater Solutions, promising to convert almost any organic residue or energy crop into biogas, valuable electricity or heat.

CST Wastewater Solutions has partnered with Global Water Engineering (GWE) to supply the Raptor system, which stands for Rapid Treatment of Organic Residues. It’s a powerful liquid-state anaerobic digestion process that consists of enhanced pre-treatment followed by multi-step biological fermentation.

The plant is suitable for handling: food waste; agro-industry residues, like starch and sugar pulps, vegetable or potato waste; industrial residues, such as brewery waste (spent grain), fruit processing waste and paper mill sludge; and energy crops, for example corn (silage), various grasses and algae.

A range of different pre-treatments is available. The pre-treated and blended substrate slurry is transferred into a mixed digester. The digester tank comes in sizes up to 12,000 m³. Optional extras include a foam breaker fan, a scum buster system and a bottom grit trap.

The digester tank is fully insulated, heated by recycling the digester content through a heat exchanger.

Loading rates of up to 10-15 kg COD/m³ per day, and biogas production rates of up to 6.3 Nm³ per digester per day, can be obtained in Raptor plants, depending on the nature of the substrate.

The digestate from the digester is usually treated in a centrifuge for removal and disposal of non-digestible solids in the form of wet sludge cake, suitable for use as an agricultural fertiliser. Sludge cake drying and pelletising systems are available.

The liquid concentrate from the digester is added to the fresh solid waste in the slurry-making stage, or recycled to a TAR treatment, or ultimately disposed of in a conventional wastewater treatment plant.

Biogas generated in the Raptor process is desulfurised and partially dried, using GWE’s Sulphurix and Gasodrix systems, and consequently used for green power generation.

Alternatively, it can be used in a steam boiler for steam production, in which case desulfurisation and drying are typically not needed.