| CIBR (Continuous-flow Integrated Biological Reactor) was a novel continuous-flow integrated biological process adopted for simultaneous nitrogen and phosphorus removal in urban wastewater treatment. CIBR with continuous flow-intermittent aeration could create strict aerobic/anoxic/anaerobic environment by the cycle of aeration/stirring/stirring in a single pool. Owing to simple structure, high effectiveness, stable operation and easy control, CIBR had obvious advantages in solving the problems encountered in the treatment of municipal wastewater with low C/N ratio in south China. CIBR process has been widely applied in urban wastewater treatment. However, less research has been conducted on the process mechanism, the process optimization and the control strategy in the past. Therefore, the main research contents included the characterization of treatment process and mechanisms of nitrogen and phosphorus removal, the design and implementation of online controlling system, the enhanced control strategy and the process optimization.A serial experimental research has been done in a pilot-scale CIBR system with treatment capacities of 0.6 m3/d, combined with batch experiments in 5 L reactors. After the experimental study and numerical analysis in one and a half years, The four results were obtained as follows:(1)The control system with DO (Dissolved Oxygen), ORP (Oxidation-Reduction Potential) and pH as the control parameters was established by method of three-layer distributing-network. The real-time monitor and process control of a pilot-scale CIBR system were realized by using this control software and control system. Characteristic points on the profiles of DO, ORP and pH could exactly reflect the process of nitrogen and phosphorus removal. Based the feedback control algorithm, the corresponding control strategy was designed and applied on the real-time control of the CIBR process.(2) Simultaneous nitrogen and phosphorus removal was realized in CIBR, based on the traditional nitrification-denitrification pathway and enhanced biological phosphorus removal pathway. Moreover, part of nitrogen could be removed via simultaneous nitrification and denitrification (SND) and ammonia adsorption by anoxic activated sludge. The nitrogen forms transformation, the nitrogen balance, the total nitrogen (TN) loss, and the pathways of nitrogen removal were investigated. The TN loss was found during aerobic and anoxic stages. The possible pathways of the TN loss at the aerobic and anoxic stages were SND and ammonia adsorption by anoxic activated sludge. The fractions of nitrogen removal by nitrification-denitrification, aerobic nitrogen loss, anoxic nitrogen loss and effluent were 63.79%,10.5%,2.75% and 22.97%, respectively. A better efficiency of SND could be obtained under a lower aeration rate, and the TN loss was up to 9.76 mg/L at the aeration rate of 0.3 m3/h, while the traditional nitrification method assumed a dominant position under a higher aeration rate.(3) Denitrification was more sensitive to temperature, compared with nitrification. Temperature had a stronger temperature effect on anaerobic P-release than aerobic P-uptake in winter. These two findings were beneficial to SNPR (simultaneous nitrogen and phosphorus removal) in CIBR at low temperature. A high temperature and short anaerobic duration were found to have the positive impact on the effluent quality. Simultaneous nitrogen and phosphorus removal efficiency in CIBR was also significantly affected by influent C/N ratios. Phosphorus release occurred after nitrate depletion when influent C/N ratios were lower than 400:30. At influent C/N ratios of 800:30 and 1200:30, denitrification and phosphorus release occurred simultaneously. Whether or not denitrification and phosphorus release occurred simultaneously, the peak point on pH curve could indicate the completion of denitrification. It was suggested that pH could be used as the main control parameter to optimize the operation cycle of CIBR. The order of the carbon source competitiveness among heterotrophs was:denitrifiers> polyphosphate accumulating organisms (PAOs)> other heterotrophic organisms. At influent C/N ratios of 800:30 and 1200:30, the activity of PAOs was inhibited by denitrification intermediates. Competition mechanisms among heterotrophs included the competition for carbon source, as well as the inhibition of denitrification intermediates. Low influent C/N ratio and nitrite accumulation during denitrification were beneficial to improve the efficiency of carbon utilization.(4) By means of flow form analysis, the law of pollutant migration and diffusion and difficulty analysis of controlling the effluent, the step-feed strategy was proposed. The process is "Aeration without feeding→Aeration with continuous feeding→Stirring with continuous feeding→2 Settling with continuous feeding→Stirring without feeding". The step-feed CIBR process has the significant superiority in the treatment of wastewater with COD concentration of 160-250mg/L, which has great advantages in treating low C/N ratio wastewater by using the step-feed CIBR process. If the COD concentration in wastewater was beyond this range, the influent flow rate of each phase should be adjusted to cope with water quality change. In another word, the hydraulic residence time (HRT) of each phase was different. |
PDF Full Text Request