Effect Of Salinity On Partial Nitrification And Denitrification Using SBR And SBBR

The effect of salinity on pollutants removal and stability of partial nitrification and denitrification in sequencing batch reactor (SBR) and sequencing batch biofilm reactor (SBBR) was investigated.(1) The full nitrification sludge was cultured by the SBR and SBBR. The stable partial nitrification and denitrification in SBR and SBBR were successfully achieved and maintained at the salinity of 0.6% by controlling the aeration rate (360 mL/min) and temperature (30℃) after three months. When the salinity increased from 1.0% to 5.0%, the COD removal was not inhibited by the increasing salinity. When the salinity increased from 1.0% to 4.5%, the effluent NH4+-N, NO2--N and N03--N concentration of the two systems was less than 1.0,0.5,0.5 mg/L, respectively. The nitrification and denitrification was not inhibited by the increasing salinity. Nitrite accumulation rate (NAR) was more than 97.00% in the SBR and was more than 95.00% in the SBBR with salinity increasing from 1.0% to 4.5%. When the salinity increased to 5.0%, the partial nitrification of the two reactors was completely destroyed after 9 d, 7 d, respectively. The oxidation of NH4+-N was significantly inhibited by salinity.(2) The sludge volume index (SVI) increased at the beginning, and then decreased with the increasing salinity from 0.6% to 5.0% in the SBR and SBBR. When the salinity increased from 1.0% to 3.0%, the specific oxygen uptake rate (SOUR) of SBR activated sludge, SBBR suspended sludge and biofilm decreased with the increasing salinity. When the salinity increased from 1.0% to 5.0%, the specific ammonia oxidation rate (SAOR), specific nitrite reduction rate (SNIRR) and specific nitrate reduction rate (SNARR) of the three kinds of microorganisms in the SBR and SBBR decreased with increasing salinity. The inceresing salinity had more significant effect on SAOR than SNIRR and SNARR in the three kinds of microorganisms, which indicated that the salt-tolerant ability of nitrite and nitrate-reducing bacteria were much larger than nitrifying bacteria. The specific nitrite oxidation rate (SNIOR) of the three kinds of microorganisms was not detected, which because the stability of partial nitrification was not destroyed at the salinity of 1.0%-3.0% and the nitrification was completed damaged when the salinity reached to 5.0%. At every salinity level, the microbial activity of suspended sludge was greater than biofilm (SOUR, SAOR, SNIOR, SNIRR, SNARR).(3) In the SBR and SBBR, the protein (PN) and polysaccharide (PS) of soluble microbial products (SMP), loosely bound extracellular polymeric substances (LB-EPS) and tightly bound EPS (TB-EPS) increased at the beginning, and then decreased with the increasing of salinity, and attained the maximum value at the salinity of 2.0%. The four peaks identified by three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectroscopy in SMP, LB-EPS and TB-EPS were attributed to protein-like and humic acid-like substances with salinity increasing from 0.6% to 5.0%. The humic acid-like fluorescence peaks in LB-EPS of the three kinds of microorganisms in SBR and SBBR varied significantly, which indicated that salinity had obvious effect on humic acid-like substances. The humic acid-like fluorescence peaks in LB-EPS of suspended sludge changed more significantly than biofilm. With the salinity increasing from 0.6% to 5.0%, the absorption peaks of fourier transform infrared (FTIR) spectra in SMP, LB-EPS and TB-EPS were similar, but the intensity changed with the increasing salinity.