Display omitted •The highest total VFAs concentration at RT=5days was achieved at acidic environment.•Alkaline environment was favorable at long RT due to WAS disintegration.•Acetate dominated all of the VFAs most likely due to WAS disintegration.•Caproate concentration doubled with prolonging RT from 5 to 15days. Mixed culture fermentation consists of stable microbial population hence waste could be potentially used as a substrates. The aim of the work was to investigate the impact of pH and retention time on the anaerobic mixed culture fermentation. Trials at different pH (4–12) in unbuffered systems were conducted for 5, 10 and 15days. The highest VFAs concentration was achieved after 15days at pH 10 (0.62g/gVSadded), promising results were also achieved for pH 11 (0.54g/gVSadded). For pH 4 and short retention time propionic acid was the major product instead of acetic acid. For batches run at 15days (besides pH 6) caproic acid presence was noticed whereas at pH 11 occurrence of succinic was quantified. Significant correlation between operational factors and fermentation’s effluents was proved. Throughout changing simple operating parameters one could design process to produce desirable concentration and composition of VFAs.