Anaerobic Codigestion of Algal Material with Two Different Co-Substrates, Biowaste and Sewage Sludge: Process Yields and Behaviour Comparison

The problem of algae disposing, especially in coastal and lagoon areas where eutrophication occurs in all its gravity, makes necessary to seek appropriate methods for the treatment of this organic material. The anaerobic digestion for the treatment of this biomass is currently of considerable interest, due the low environmental impact and the energy recovery at the same time. After a pre-screening analysis, it is possible to say that algal biomass completely meets the requirements needed for anaerobic digestion process. In this paper are reported the feasibility results of the anaerobic codigestion treatment of algal biomass. Pilot-scale continuous stirred tank reactors with working volumes of 3 and 1 m3 were used, and full-scale digestion operational conditions were applied. Anaerobic digestion process with algae and organic fraction of municipal solid waste was inhibited by high concentration of hydrogen sulfide. This process was feasible if the algae content in the feeding mixture was equal to 10 % (in terms of solids) and with addition of iron powder; on the other hand the co-treatment of sewage sludge appeared very interesting, in fact the biogas production rate increased from 0.4 to 0.8 m3/m3reactord and methane content reached 71 %