OZONOLYSIS IN ANAEROBIC DIGESTION: A REAL-SCALE AND LABORATORY-SCALE CASE STUDY

Abstract

As part of the PerFORM WATER 2030 project, funded by the Lombardy Region, a full-scale and laboratory-scale study was carried out for the application of ozonolysis process as pre-treatment of the sludge fed to anaerobic digestion to optimize the biogas production. The ozonolysis process makes the treated sludge more bioavailable for anaerobic processes, increasing degradation efficiencies and the consequent biogas production. The study, conducted at a 30.000 PE WWTP in northern Italy, allowed to highlight an increase in biogas production at full scale of 20% for dosages of about 10 gO₃/kgVS and at laboratory scale from 38% to 74% for dosages of 20 - 140 gO₃/KgVS. The full-scale ozonolysis treatment resulted in an improvement of the biogas quality with the abatement of about 50% of the H₂S content, originally equal to 2.800 ppm. The action of ozonolysis is expressed in the solubilisation of the sludge with a reduction of the total suspended solids concentration of the order of 7-13% depending on the dosage tested.

During the laboratory-scale tests, the digestate treatment was also tested to evaluate the effectiveness of ozonolysis in increasing the residual methane capacity of the digested sludge. The tests gave positive results, highlighting the possibility of increasing the residual biogas production, equal to 30 mlCH₄/gVS, from 100% to 500% for dosages from 130 to 300 gO₃/kgVS.

All results obtained during the experimentation give the indication that ozonolysis process does not express inhibitory effects respect to the anaerobic digestion process for the dosages tested.

An initial economic-environmental assessment of the process confirms its sustainability if combined with efficient thermal/electrical recovery systems of the biogas produced or biomethane up-grading and in a context with sludge disposal costs greater than 150 €/t.