Abstract. Accumulation, processing and disposal of organic waste, in particular, vegetable waste, is considered an urgent problem today for Ukraine and the EU countries. Currently, one of the promising ways to solve the problematic issue is the application of modern biotechnologies of organic waste processing with the use of a specific consortium of microorganisms, which allow in the process of bioconversion of beet, carrot and potato waste to obtain digestate and biohydrogen in 6 days of fermentation at a temperature of 37 ⁰C. The effectiveness of using additional substrates, such as expired bread and probiotic lactulose, to activate the fermentation process of organic waste has been proven. The experiments confirmed the absence of pathogenic cultures in the digestate, which is explained by the high titer of viable cultures of antagonistic microorganisms (lactic acid bacteria, Bacillus subtilis, Paenibacillus polymyxa). The obtained research results show that in all samples (1–7) there is an intensification of the fermentation process on the 2nd, 3rd, and 4th day of fermentation, which is evidenced by changes in the redox potential index, which ranges for samples (1–7) from -100 to – 200 mV. The release of biohydrogen intensively began on the 2nd day of fermentation and lasted for 6 days of the experiment. In order to intensify the process of transformation of plant waste, the expediency of using additional sources of carbon, namely expired bread in the amount of 10% and lactulose in the amount of 2 and 4% of the mass of waste, was substantiated for the first time.