Biofilm architecture in a novel pressurized biofilm reactor

Abstract

A novel pure-oxygen pressurized biofilm reactor was operated at different organic loading, mechanical shear and hydrodynamic conditions to understand the relationships between biofilm architecture and its operation. The ultimate goal was to improve the performance of the biofilm reactor. The biofilm was labeled with seven stains and observed with confocal laser scanning microscopy. Unusual biofilm architecture of a ribbon embedded between two surfaces with very few points of attachment was observed. As organic loading increased, the biofilm morphology changed from a moderately rough layer into a locally smoother biomass with significant bulging protuberances, although the chemical oxygen demand (COD) removal efficiency remained unchanged at about 75%. At higher organic loadings, biofilms contained a larger fraction of active cells distributed uniformly within a proteinaceous matrix with decreasing polysaccharide content. Higher hydrodynamic shear in combination with high organic loading resulted in the collapse of biofilm structure and a substantial decrease in reactor performance (a COD removal of 16%). Moreover, the important role of proteins for the spatial distribution of active cells was demonstrated quantitatively.

Keywords:

• biofilm architecture
• CLSM
• wastewater treatment
• novel biofilm reactor with mechanical control
• shear stress

Abbreviations:

• ASP, activated sludge process
• Con A, concanavalin A
• COD, chemical oxygen demand
• CLSM, confocal laser scanning microscopy
• CTC, 5-cyano-2,3-ditolyl tetrazolium chloride
• CTF, CTC–formazan
• DAPI, 4,6-diamidino-2-phenylindole
• DI water, deionized water
• DO, dissolved oxygen
• EPS, extracellular polymeric substances
• HRT, hydraulic retention time
• OLR, organic loading rate
• PBR, pressurized biofilm reactor
• PLC, programmable logic controller
• SRT, solids retention time
• SS, suspended solids
• VSS, volatile suspended solids

Acknowledgements

The Wawona Frozen Foods Company and Matt Trout are thanked for their assistance with the experiments. Wei Jiang acknowledges the scholarship supported by the China Scholarship Council (CSC).

Conflict of interest disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was funded by Grundfos Corporation, National Water Pollution Control Program [2009ZX07317-008-5]; 111 Project, Shanghai Shuguang Tracking Program [10GG12]; and the National Natural Science Foundation of China [51108437, 21306180].