Partial Nitrification In An Intermittently Aerated SBR For Digested Piggery Wastewater Treatment

In this study, the intermittent aeration sequencing batch reactor (IASBR) technology was applied for the shortcut nitrification and denitrification investigation on digested piggery wastewater, which had the characteristics of high concentrations of ammonia nitrogen and low ratio of carbon and nitrogen. The IASBR is an improved technology based on the traditional SBR, which achieved an aerobic and hypoxic environment allematively in a SBR operation cycle through the automatic control process innovatively. The iASBR could inhibit the growth of nitrite oxidizing bacteria (NOB) to realize the shortcut nitrification and save25%of the aeration quantity. This paper compares the nitrification effects of IASBR reactor in three operating modes, aiming at optimizing the IASBR operation parameters of digested piggery wastewater treatment and ultimately providing basical data for the realization of the swine wastewater shortcut nitrification and dentrification treatment by IASBR technology. The results are as follows:(1)0#IASBR achieved the shortcut nitrification in the start-up period with the non-aeration and aeration time ratio of0,4, FA initial concentration of0.6～2.1mg/L at low temperature of17.5～22.1℃and sufficient aeration environment, which might be due to the selective inhibition of high concentrations of FA on nitrification bacteria with no sludge discharge condition. However, the nitrite accumulation rate decreased and ultimately the shortcut nitrification was destroyed. The reasons might be the difficulty of maintaining an appropriate FA concentration to inhibit mitrite oxidizing bacteria when the ammonia nitrogen load reduced and aeration time extended.(2)1#,2#IASBR started on parallel with different non aeration and aeration time radios of respectively0.6and1at higher temperature of20～30.7℃.1#and2#IASBR didn’t immediately appear nitrite accumulation when the initial FA concentration was higher than0.6mg/L while began to accumulate slowly after a period of time, which showed that the nitrite oxidizing bacteria had a high activity and the FA tolerance activity enhanced under higher temperature. However,1#,2#presented a rapid nitrite accumulation after a high influent loading shock so as to realize the transition from the complete nitrification to the shortcut nitrification. In the subsequent113d long run, the lowest nitrite accumulation rate could reach up to about70%though the ammonia nitrogen load greatly reduced. However, high concentrations of nitrite accumulation and temperature change in the reactor made a significant effect on the stable nitrification of ammonia nitrogen.1#,2#IASBR have no significant difference.(3) The fluorescence quantitative PCR was also applied to count the total bacteria, ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) in1#and2#system. The results showed that there were almost no changes of the total bacteria concentration with sludge retention time (SRT) of30d,but the nitrifying bacteria were enriched. The AOB enrichment degree was greater than that of NOB1#,2#IASBR had a radio of AOB and NOB number of respectively2.25,3,02on the run day of74, which showed the AOB growth rate was greater than NOB in a high temperature. Moreover, the FA concentration presented an inhibition on NOB while no inhibition on AOB, accelerating the expansion of the AOB and NOB number d ratio.(4) Meanwhile, the pH, DO and ORP changes within the1#,2#IASBR in one operation cycle was monitored in this study to investigate the operation characteristics. The results showed that the aerobic nitrification process was excellent while the anoxic denitrification was very weak. Moreover, there was hardly pH increase observed in anoxic stage in operation late periods with the continuous acclimation of activated sludge.