Micro-structure And Mass Transfer Kinetics Of SRB Biofilm In Wastewater Treatment

Sulfate-reducing Bacteria biofilm applied in heavy metal sulfate wastewater treatment is a new and well accepted technology. The main research about this technology is focusing on process optimization and effect checking at present, while little about the SRB biofilm inner structure and mass transfer were mentioned. This thesis investigated the SRB biofilm inner structure via Confocal Scanning Laser Microscopy and mass transfer kinetics based on experiments, and finally an appropriate mass transfer mathematical model was adopted.It was found that, SRB biofilm generally shaped flat and smooth on the surface, but respectively heterogeneous in inner structure. The SRB aggregated together to form biofilm in flowing medium condition, while SRB connected to chains twisting together to form biofilm in static medium condition. Certain liquid flow can lead to a denser and more compact biofilm. SRB biofilm growth process can be divided into 5 stages: adhesive period, acclimated period, growing period, mature period and sloughing period, of which the adhesive period and growing period are the key stages for SRB biofilm forming. SRB biofilm adhesive kinetics can be described by , and SRB biofilm growth kinetics fit Monod model very well. Substrate concentration and liquid flow velocity had important influence on SRB biofilm mass transfer. Under steady state, the removal rate of substrate increased with improving substrate concentration; the specific removal rate of substrate decayed exponentially with increase of HRT and increased linearly with surface liquid flow velocity. Based on the SRB biofilm structure and compared with other biofilm models, it was concluded that 1D diffusion-reaction theory model is sufficient and suitable for engineering demand. Therefore we deduced the calculation method of the SRB biofilm average mass transfer coefficient and raised a bidirectional mass transfer concept model.