New municipal sewage sludge treatment process based on pyrolysis, energy recovery and biochar valorisation

Nuevo proceso de tratamiento de fangos de aguas residuales municipales basado en la pirólisis, la recuperación de energía y la valorización del biochar

The Pyrochar project, funded by the european union’s seventh framework programme and coordinated by the french company e.t.i.a., is developing an adapted, energy efficient and affordable solution to manage the sewage sludge produced by the small municipalities of the member states. in addition to E.T.I.A., this project includes 4 small and medium-sized enterprises – Enviro-Pharm ltd (Hungary), Hydro Italia (Italy), Turguc (Turkey) and Biboaqua (Spain) – and 3 research centers – University of Teesside (uk), Tecnologías Avanzadas Inspiralia (Spain) and Messag (Switzerland).

Officially started on the 1st of November 2013, the PYROCHAR project, will demonstrate the technical feasibility and economic viability of a new process to thermo-chemically convert the municipal sewage sludge into useful biochar (charcoal from pyrolysis treatment) and synthesis gas (syngas).

As it uses energy intensive thermal treatments (drying + slow pyrolysis) to reduce the sludge volume by 95% and convert it in small and stabilized by-products (biochar), the PYROCHAR project is based on the recovery and reuse of the energy contained in the sludge to minimize the overall energy consumption. This is made possible by 1/burning the pyrolysis syngas in a gas turbine to generate heat and electricity for the system and 2/using waste heat from the biochar to offset a part of the hot gas requirements of the dryer.

Practically, this process will integrate a flexible control system with specific operating settings for the pyrolysis to ensure that the syngas produced meets the stringent quality requirements for the gas turbine (in terms of flow, calorific energy, impurities [tars, particulates, sulphur/ chlorine compounds, dioxins]). Indeed the produced syngas contains non condensable gases, mainly H2, CO, CH4, CO2 and some hydrocarbons, in varying proportions which depends upon not only the feedstock composition and moisture but also the pyrolysis reactor type and operating parameters (e.g. residency time, and treatment temperature).

Article published in: FuturENVIRO September 2014