Abstract
Fate of biofilm sloughing was assessed in a laboratory-scale (LS) integrated fixed-film sequencing batch reactor (IF-SBR) treating synthetic wastewater and in a full-scale (FS) integrated fixed-film activated sludge (IFAS) system treating municipal wastewater. It was observed that the properties of biofilms and flocs, including sludge volume index (SVI), mixed liquor suspended solids (MLSS), effluent suspended solids (ESS), relative hydrophobicity, and composition of extracellular polymeric substance (EPS) were associated with biofilm sloughing and formation of large granular flocs in the LS IF–SBR. In the FS IFAS system, the changes were studied at the molecular level. For example, the extracted EPS content results (the protein to polysaccharide ratio decreased in the flocs and increased in the biofilms, with biofilm sloughing) were complemented with the confocal laser scanning microscopy (CLSM) coupled with molecular specific staining. CLSM analyses revealed that micro-colonies rich in polysaccharides readily sloughed from the carriers. Live-dead staining revealed areas of the biofilm where the viability of biomass was a contributing factor associated with areas of the biofilm susceptible to sloughing. 16S rRNA gene sequencing (Illumina) of FS IFAS samples revealed greater diversity (α-diversity) in biofilms compared to flocs. Biofilm sloughing resulted in a decrease in diversity in biofilms and a corresponding increase in the flocs during sloughing. Microbial population dynamics revealed that bacteria known for denitrification (for example, Comamonadaceae) detached from the biofilms during sloughing, readily associated with the suspended biomass, and were retained in the bioreactors.
Highlights
The first full-scale installation of the integrated fixed-film activated sludge (IFAS) technology was reported in the mid-1990s [1]
During LS integrated fixed-film sequencing batch reactor (IF-SBR) operation, chemical oxygen demand (COD) removal was 99 ±1%, and dissolved oxygen (DO) concentration was maintained at 3–5 mg/L
This paper reports on a study of a laboratory-scale IF-SBR treating synthetic wastewater and a full-scale IFAS system treating municipal wastewater
Summary
The first full-scale installation of the IFAS technology was reported in the mid-1990s [1]. The application of the IFAS technology is an easy option to upgrade the existing conventional wastewater treatment facilities [2,3,4]. Several case studies have shown year-round stability and improvement in capacity and efficiency of BNR when a conventional activated sludge system was upgraded to an IFAS system [5,6,7]. The hybrid nature of IFAS takes advantage of the differential features of biofilms and flocs that contribute differently to biological nutrient removal. Biofilm sloughing in integrated fixed-film system (BNR) [8, 9]. The relative abundance of denitrifying bacteria is higher in biofilms; whereas, the abundance of nitrifying bacteria is relatively higher in the flocs of a hybrid IF-SBR [10]
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