The VFA concentration was then increased in acidogenic system showing hydrolysis and acetogenic mechanisms when OLR was too high in regards with population present in the reactor and VFA concentration rapidly increased in methanogenic system proving a beginning of methanogen population inhibition. This could be attributed to two reasons, including, the rapid increase of the high VFA concentration when loading rate increasing and the biomass washout from the reactor with the increase of the flow rate. The system then necessitated 50 days to be stabilized again including operational control of pH by soda addition.