Effects of Hydraulic Retention Time and Substrate Concentration on Acidification of Synthetic Whey, Yeast and Yolk Wastewaters

Abstract

The acidification of protein wastewaters were investigated under different hydraulic retention times (HRTs) and substrate concentrations without pH adjustment. Synthetic whey, yeast and yolk wastewaters were used as the substrates. Three lab-scale continuously stirred tank reactors (CSTRs), each with a working volume of 2 L, were employed as acidogenic reactors. Firstly, HRTs in the range of 4 to 36 h with a substrate concentration of 2 gCOD/L were applied. The acidification efficiency and acidification rate were affected by HRT. At 4 h HRT of whey and yeast wastewaters, the highest acidification efficiencies and acidification rates were observed at 30.9 and 3.0%, and 3.9 and 0.4 gCOD/L‧d, respectively. For yolk wastewaters, acidification at 24 h HRT had the highest efficiency (12.7%) while maximum acidification rate of 0.4 gCOD/L‧d was observed at 4 and 16 h HRT. The methanogenic activity was totally suppressed at HRT of 8 h or lower. The effect of substrate concentrations in the range of 1 to 8 gCOD/L with 4 h HRT was evaluated. The acidification was not dependent on substrate concentrations for yeast and yolk wastewaters whereas whey wastewater showed an increasing trend on acidification rate along with increasing influent concentration. The substrate concentrations for whey, yeast and, yolk wastewaters to achieve highest acidification efficiencies at 69.0, 6.0 and 6.5%, respectively, were 8.6, 6.4 and 4.3 gCOD/L. The composition of volatile fatty acids (VFA) in the effluent of each protein wastewater was dissimilar due to the difference in substrate structure.