Biological treatments for olive mill waste cleanup using bacterial strains have proven to be effective and environmentally friendly. Three phenol-degrading bacterial strains identified as Lysinibacillus macroides, Lysinibacillus boronitolerans, and Brevundimonas olei were isolated from olive mill wastewater (OMWW) have high efficacy in degrading polyphenols. These strains exhibited both enzymes, catechol 1,2-dioxygenase and catechol 2,3-dioxygenase, responsible for degradation of phenolic compounds to varying degrees. Lysinibacillus macroides, rather than Lysinibacillus boronitolerans or Brevundimonas olei, have the highest catechol-dioxygenase enzyme activities. Various factors were optimized during the OMWW fermentation process to maximize the phenol degradation process. Maximum degradation rates were reached after 35 days at 20% dilution and pH ranged from 6 to 7 with starch and yeast reaching 1 g/l when added as carbon and nitrogen sources. In greenhouse experiments, the final fermentation product was evaluated as an organic biofertilizer. Bioassay data showed that the application of fermented OMWW significantly increases barley height, fresh and dry weight, nitrogen, potassium, and phosphorus contents compared to non-fermented barley, regardless of the type of bacteria used. The results of this study demonstrate that biologically fermented OMWW is proved to be economically beneficial to be used as an organic biofertilizer.