Among the various techniques used to reduce hydrogene sulfide in biogaz avoiding harmfull effects on engines, the chemical and biological treatment appears particularly promising. The main objective of this article is to develop this new process to reduce the harmful effect of hydrogen sulphide (H2S), contained in the biogas resulting from methanization, on the equipment of the wastewater treatment plant (WWTP) of FES city in particular the two cogeneration units. A multiple regime technique for biogas desulfuration, based on the chemical and biological treatment and internal micro-aeration of the digester is developped. The results found are very interesting especially in terms of : • Reducing the concentration of H2S in biogas and improving methane production (biogas production increased from 3,6 M Nm3 in 2018 to 3,8 M Nm3 in 2019, a saving of about 300,000 MAD). • Reduction of desulphurization tower downtime from 4 times / year to 1 time / year. • Increasing operating time of generating sets from 8800 in 2018 to 14 400h in 2019. • Electricity production goes from 5.9 GWh in 2018 to 7.2 GWh in 2019. To improve this process, microbial and molecular analyzes as well as mathematical modeling are necessary. Automatic control of the anaerobic fermentation and microaeration process of the digesters will then be possible.