Tomoki Kawagishi

Comparative experiment on treating digested piggery wastewater with a biofilm MBR and conventional MBR: simultaneous removal of nitrogen and antibiotics

A biofilm membrane bioreactor (BF-MBR) and a conventional membrane bioreactor (MBR) were parallelly operated for treating digested piggery wastewater. The removal performance of COD, TN, NH4+-N, TP as well as antibiotics were simultaneously studied when the hydraulic retention time (HRT) was gradually shortened from 9 d to 1 d and when the ratio of influent COD to TN was changed. The results showed that the effluent quality in both reactors was poor and unstable at an influent COD/TN ratio of 1.0±0.2. The effluent quality was significantly improved as the influent COD/TN ratio was increased to 2.3±0.5. The averaged removal rates of COD, NH4+-N, TN and TP were 92.1%, 97.1%, 35.6% and 54.2%, respectively, in the BF-MBR, significantly higher than the corresponding values of 91.7%, 90.9%, 17.4% and 31.9% in the MBR. Analysis of 11 typical veterinary antibiotics (from the tetracycline, sulfonamide, quinolone, and macrolide families) revealed that the BF-MBR removed more antibiotics than the MBR. Although the antibiotics removal decreased with a shortened HRT, high antibiotics removals of 86.8%, 80.2% and 45.3% were observed in the BF-MBR at HRTof 5–4 d, 3–2 d and 1 d, respectively, while the corresponding values were only 83.8%, 57.0% and 25.5% in the MBR. Moreover, the BF-MBR showed a 15% higher retention rate of antibiotics and consumed 40% less alkalinity than the MBR. Results above suggest that the BF-MBR was more suitable for digested piggery wastewater treatment.

Advantages of intermittently aerated SBR over conventional SBR on nitrogen removal for the treatment of digested piggery wastewater

An intermittently aerated sequencing batch reactor (IASBR) and a traditional sequencing batch reactor (SBR) were parallelly constructed to treat digested piggery wastewater, which was in high NH4+-N concentration but in a low COD/TN ratio. Their pollutant removal performance was compared under COD/TN ratios of 1.6–3.4 d and hydraulic retention times of 5–3 d. The results showed that the IASBR removed TN, NH4+-N and TOC more efficiently than the SBR. The average removal rates of TN, NH4+-N and TOC were 83.1%, 96.5%, and 89.0%, respectively, in the IASBR, significantly higher than the corresponding values of 74.8%, 82.0%, and 86.2% in the SBR. Mass balance of organic carbon revealed that the higher TN removal in the IASBR might be attributed to its efficient utilization of the organic carbon for denitrification, since that 48.7%–52.2% of COD was used for denitrification in the IASBR, higher than the corresponding proportion of 43.1%–47.4% in the SBR. A pre-anoxic process in the IASBR would enhance the ammonium oxidation while restrict the nitrite oxidation. Anoxic duration of 40–80 min should be beneficial for achieving stable nitritation.