2004 chen et al agro environmental protection 20 2003 424 428 the experimental device utilized in this example was sequencing batch reactor srs see agro environmental protection pages 329 332 no 5 2001 consisting of elevated tank water storage tank pump solenoid valve logo time controller and aeration equipment the quantitative volume of elevated tank was 2 l and the volume of sbr solvent was about 5 l additional acetic acid was added as carbon source artificial wastewater was prepared with cod of about 1000 mg l by using acetic acid as substrate during the preparation of wastewater ammonium chloride potassium dihydrogen phosphate magnesium sulfate heptahydrate potassium hydrogen phosphate and calcium chloride the above chemicals were produced by beijing chemical plant analytical grade were added at 5 mg l as nutrients in order to balance the nutrition ph value was kept at 6 8 u02dc 7 1 sludge used in the experiments was mainly the active sludge collected from the anaerobic aerobic active sludge process ebpr see chen et al agro environmental protection 20 2003 424 428 the collected active sludge from sewage treatment station siming yantang milk corp guangzhou was filtered washed by physiological saline and aerated for 4 hrs to degrade the suspended or gel matter and then was disposed into the reactor every experimental cycle was 8 hrs three cycles per day every cycle was arranged as follows water injection 2 min aeration 240 min precipitation 180 min supernatant.