Effects of ferric chloride (FeCl3) concentration on the product distribution of acidogenic fermentation of sludge

expressed by propionic acid ratio

was investigated in sequencing batch reactor with semi-continuous operation mode.The results show that under these conditions: temperature 32℃

HRT 6.6 d

feed VS 20.43 g·L-1

pH 5.5—6.0

ORP of fermentation liquid increases gradually while propionic acid ratio in fermentation products changes a little

although FeCl3 concentration varying from 0 to 232 mg·L-1.When the concentration of FeCl3 is at 464—928 mg·L-1range

ORP increases significantly and at the same time propionic acid ratio goes up from 25.82% to 49.57%.One feasible start-up modes are proposed with aerobic activated sludge for sludge acid-type fermentation using conditions of temperature 32℃

HRT 6.6 d

pH 5.5—6.0

FeCl3 464 mg·L-1.With this start-up mode

acid-type fermentation can run smoothly after 6 day and propionic acid ratio can reach 50%.