Anaerobic ammonia oxidation (Anammox) faces challenges in high salinity environments due to inhibited microbial activity, while upflow anaerobic sludge bed (UASB) reactors maintain a higher biomass concentration. To explore how the Anammox-USAB system responds to the high salinity (NaCl) environment, a UASB reactor seeded with heterotrophic nitrification sludge. The salinity was gradually increased from 0 to 40 g NaCl/L. The results show that, when salinity increased from 0 to 15 g NaCl/L, the conversion rate of ammonia nitrogen (NH4+-N) and total nitrogen (TN) decreased by about 25% and 22 %, respectively. At the same time, the ammonium removal load of unit sludge gradually stabilized at about 3.65 mg NH4+-N/g VSS over 10 g NaCl /L. When the salinity gradient increased to 30 g NaCl/L, microorganisms preferentially increased their polysaccharide (PS) content from 5.50 to 8.26 mg/g VSS to resist the high osmotic pressure environment. Notably, extracellular protein increased significantly, from 5.78 to 29.01 mg/g VSS to stabilize the cell structure and maintain metabolic activities at 40 g NaCl/L. With the increase of salinity, some salt-intolerant bacteria were inhibited or killed, resulting in a continuous decline in abundance while the abundance of salt-tolerant bacteria increased. The abundance of dominant species Candidatus Kuenenia and Halomonas increased from 5.97% and 0.53% to 12.29% and 12.17%, respectively. It could be seen that the Anammox-USAB system used the structural adjustment of the microbial itself and community as an adaptive strategy in response to the changes of the high-salinity environment.
Key Words
nanofiltration; membrane; response surface methodology; salt rejection; dye removal.
Address
Zhang Huining, Li Yan, Ji Bixiao, Guo Xingnan, Zhang Kefeng — School of Civil Engineering, NingboTech University, Ningbo, China
Sun Keying, Pan Zhengmin — School of Civil Engineering, NingboTech University, Ningbo, China/ College of Civil Engineering and Architecture, Zhejiang University, Hangzhou, China
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