Characteristics of volatile fatty acids production and microbial succession under acid fermentation via anaerobic membrane bioreactor treating kitchen waste slurry

In this study, two anaerobic membrane bioreactors (AnMBRs) were proceeded to produce volatile fatty acids (VFAs) from kitchen waste slurry under acidic conditions of pH 5 and pH 6. Higher fermentation potential and VFAs quality were obtained at pH 6, with VFAs production, yield and CODVFAs/CODeffluent ratios of 42.0 g/L, 0.35 g/g-CODinfluent and 80% respectively. The alkali dosages at pH 5 and pH 6 were 0.028 g-NaOH/g-VFAs and 0.081 g-NaOH/g-VFAs respectively, far lower than that of pH 9 (0.4 g-NaOH/g-VFAs). The microbial community presented marked differences between pH 5 and pH 6. In addition, chemical cleaning and sludge discharge could alleviate membrane fouling and ensure the stable membrane operation at pH 6, while these control strategies had no obvious improvement for fouling at pH 5 due to higher H+ toxicity.In summary, this study indicates that under acidic conditions, pH 6 is more suitable for VFA production using AnMBR and is associated with lower alkali consumption.