Redox potential (ORP) regulation of nutrient removal in wastewater treatment processes and the structure-function analysis of activated sludge floc

The overall aims of this research were to investigate the potential of redox potential (ORP) on-line regulation of the operation of aeration tanks, and to analyze the stratification of chemical and microbial profiles in activated sludge floc in order to provide an insight into the activated sludge floc structure and microbial function in the micro-environment.; Using field-scale research, the ORP and COD in the aeration tank effluent were found to follow a good linear relationship. The ΔORP of the influent and effluent and the ORP values of the effluent could be used for an in situ indication of the pollutant removal efficiency and the effluent quality, respectively. ORP values clearly show the COD removal occurring in an aeration tank.{09}Nitrification occurred at higher ORP values than did organic substrate oxidation. The on-site results demonstrated that the ORP values for wastewater also vary with dissolved oxygen, and temperature.; The micro-environment of activated sludge flocs was studied using microelectrodes. For the first time, this study provides direct proof of chemical profile changes inside activated sludge floc under different bulk COD and DO situations. The activated sludge floc microprofiles showed that, due to microbial oxygen utilization, the aerobic region in the activated sludge floc was often limited to the top layer of the sludge aggregate at the Mill Creek Wastewater Treatment Plant, a plant receiving typical COD loadings. At the Muddy Creek Wastewater Treatment Plant, which receives lower wastewater pollutant concentrations, the ORP and DO inside the sludge aggregates were higher than those from the Mill Creek plant.; An integrated model (derived from ASM No. 3) of the microenvironment and boundary layers of the activated sludge floc was developed for dynamic simulation of COD removal in combined biological processes. The model simulation results and measured profiles showed the heterogeneous and gradient-governed microenvironment of activated sludge floc. The presence of a substrate concentration increase zone (COD concentration increases inside floc at the direction of floc center) and of anoxic processes inside sludge floc under aerobic condition were confirmed.; Fluorescent In Situ Hybridization (FISH) with application of oligonucleotide 16S rRNA-targeted probes indicates a clear spatial distribution of nitrifiers inside activated sludge floc. For the first time, we combined chemical profiles measured by micro-electrodes with the microbial profiles to assess the structure-function of microorganisms inside activated sludge floc. Functional microbes concentrate on the floc particle surface, while the populations of microbe decrease inside the floc. In the activated sludge floc from low concentrated wastewaters (Muddy Creek plant), nitrifiers could still be detected at the sludge floc center.; This study provides an enhanced understanding for applying ORP as a real-time monitoring parameter in aeration tanks. The micro-environment study of activated sludge floc with micro-electrodes and FISH validates the spatial distribution of bacteria and nitrifiers inside activated sludge floc from different wastewaters, and provide an insight into the biological characteristics of activated sludge systems at the molecular level.