| Summary: | 博士 === 國立中央大學 === 環境工程研究所 === 89 === The nutrient could be effective controlled using attached biofilm system. The fundamental approach of removing nutrient in the biofilter process is similar to activated sludge process. Although several researches have investigated factors of nutrient removal in biofilter, little information is available in terms of the metabolism and process arrangement. Therefore, this study of setting up a series of submerged biofilters were investigated the feature of biofilter on TN removal and TP removal.
Whether nitrification is complete or not is the limited process in TN removal. Nitrification is dependent on HRT and residual COD. COD rapidly decreased to lower level in the 0-20cm height. However, nitrification occurred until 40-80cm height. That resulted from distribution of different microorganisms. Heterotrophs distributed in the initial zone of the biofilter and nitrifying bacteria in the middle to upper zone. The growth of nitrifying bacteria has a tendency towards higher zones of the downflow biofilter especially at the longer HRT.
In the dual column system, the recycling NO3-N could be completely eliminated in the anoxic biofilter. TN removal and nitrogen type of the effluent would be dependent on HRT and recycle ratio. The specific rates decomposed pollutant depends to the biological activity and the effective biological VSS. The operation in low recycled ratio would result in worse total nitrogen removal, but the NH3-N of effluent would be lower. The operation in higher recycled ratio would be opposite to low recycled ratio. Compared with the dual column, the single column system was not feature different in TN removal.
Sequential Batch Biofilm Reactor system (SBBR) is effective in removing phosphorus. The storage and release of intracellular inclusions, especially PHAs and poly-P, would be an important factor for phosphorus removal. Under different operating conditions, total phosphorus removal was always determined by accumulation of PHAs and phosphorus release under the anaerobic phase. The PHAs accumulation under the anaerobic phase was always in proportion to the biofilm phosphorus content under the aerobic condition. The result shows PAOs activity was closely related to PHAs accumulation. However, the PHAs accumulation under the anaerobic phase would be dependent on the hydrolysis of the complex carbon source into short chain fatty acids. The effect of the An/Ox time ratio on TP removal was significant. Shorter anaerobic time would result in insufficient phosphorus release and greater time would result in inactive PAOs. The appropriate An/Ox time ratio was suggested as 1/2 and appropriate duration time was suggested as 6-8 hours.
In the anaerobic phase, the main activity of COD uptake occurs in initial 30 minutes. However, activity of phosphorus release occurs in 30-60 minutes and this phenomenon is more significant for initial substrate with higher concentrations due to the delay effect of mass transfer of adsorbed COD. The PHAs accumulation and phosphorus release share a similar trend. Since PHAs'' demand per released phosphorus is independent of the initial COD, the enhancement of PHAs'' accumulation would benefit phosphorus release. In the biofilm''s system, the only requirement is to have sufficient and simple initial substrate and it would result in sufficient PHAs'' accumulation for phosphorus release. In the aerobic phase, because poly-P storage''s capability is always not saturated, PAOs could uptake excess PO43-. In other words, the limitation of TP removal is always caused by anaerobic phase, not the aerobic phase.
|
|---|
