Abstract
In this study, the long-term effects of different salinities on the performance, sludge morphology and shifts in microbial communities were studied in a simultaneous anammox and denitrification (SAD) process at a C/N ratio of 0.5. Stable nitrogen removal efficiencies of 86.96 and 84.58% and nitrogen removal rates of 0.95 and 0.93 kg (m3 d)−1 could be achieved under low (25 mmol l−1) and moderate (50 mmol l−1) salinity, respectively. However, the performance collapsed when the system was exposed to high salinity (100 mmol l−1). The content of extracellular polymeric substances increased as salinity increased, which resulted in larger sizes of granular sludge under low and moderate salinities. Nevertheless, high salinity shock disintegrated granular sludge, thereby decreasing the average granule size. The Illumina-Miseq sequencing results revealed that Candidatus Jettenia was the sole salinity-tolerant AnAOB genus during the entire operation, whereas the main denitrification bacterial genera shifted from Denitrisoma under low salinity to Denitrisoma, Thauera and Ignavibacterium under high salinity. The results of this study provide a comprehensive and practical evaluation of the SAD process for organic nitrogen-rich saline wastewater treatment.
Highlights
The eutrophication of slow-flowing water bodies resulting from excessive nitrogen discharge has attracted much attention [1,2]
Anammox is an autotrophic nitrogen removal process occurring under anaerobic conditions that is dependent on a class of anaerobic ammonia-oxidizing bacteria (AnAOB) belonging to the phylum Planctomycetes, which is known to include five functional genera: Candidatus Brocadia, Ca
chemical oxygen demand (COD), NH4þÀN, NO3ÀÀN, NO2ÀÀN, total nitrogen (TN), mixed liquor suspended solids (MLSS) and mixed liquor volatile suspended solids were measured according to standard methods [26], and TN concentration was the sum of the NH4þÀN, NO2ÀÀN and NO3ÀÀN concentrations
Summary
The eutrophication of slow-flowing water bodies resulting from excessive nitrogen discharge has attracted much attention [1,2]. The conventional biological nitrogen removal process primarily relies on aerobic ammonia-oxidizing bacteria (AerAOB) and nitriteoxidizing bacteria (NOB) to complete the nitrification bioreaction under oxic conditions and denitrifying bacteria (DNB) to complete the denitrification bioreaction under anoxic conditions and convert nitrogen in water bodies into dinitrogen [3]. The anaerobic ammonia oxidation (anammox) process has become increasingly favoured for biological nitrogen removal in the wastewater treatment field. Anammox is an autotrophic nitrogen removal process occurring under anaerobic conditions that is dependent on a class of anaerobic ammonia-oxidizing bacteria (AnAOB) belonging to the phylum Planctomycetes, which is known to include five functional genera: Candidatus Brocadia, Ca. Kuenenia, Ca. Scalindua, Ca. Anammoxoglobus and Ca. Jettenia [5,6]. The principal bioreactions involved in the SAD process are depicted in equations (1.1)–(1.3): Anammox: NH4þ þ 1:32NO2À þ 0:066HCO3À þ 0:13Hþ ! 1:02N2 þ 0:26NO3À þ 0:066CH2O2:5N2:5 þ 2:03H2O: ð1:1Þ
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