This study is to evaluate the utility of a strategy of stepwise increased selection pressure for cultivating aerobic granules. Three sequencing batch reactors (SBR; R1-R3) were used. Substrate ammonium-nitrogen (NH4+-N) concentration was a microbial selection pressure for selecting nitrifying bacteria. It was stepwise increased from 50 to 200mg l−1 in R2 and fixed at 50mg l−1 in R1 and 200mg l−1 in R3. Results showed that aerobic granules failed to be developed in R3 due to free ammonia (FA) inhibition, while they formed quickly in both R1 and R2. Filamentous dominated granules in R1 exhibited poor performance and started to disintegrate from day 131. Stepwise increased selection pressure in R2 selected slow-growing nitrifying bacteria gradually, and this suppressed filamentous growth and improved the stability of aerobic granules. During the 283 days operation, R2 produced aerobic granules with incrementally higher biomass concentration, better settleability, and larger granule size. Larger granules further favored denitrification and the optimal granule size is suggested to be controlled within 2-3mm. This study demonstrates the successful application of the strategy of stepwise increased selection pressure for avoiding the failure of aerobic granulation and improving the stability and performance of aerobic granules.

Cake layer formed on membrane surface presents a major challenge to membrane permeation, and it can be considered as a porous media. Determination of the cake layer permeability is critical for an accurate analysis and design of membrane filtration. A permeation model, based on fractal theory and Darcy's law, for evaluating cake layer permeability in microfiltration of activated sludge wastewater was developed. The cake layer permeability was derived and found to be a function of the pore-area fractal dimension and microstructural parameters. The validity of the model was studied systematically in this paper. The permeation model was applied to study the effect of mixed liquid suspended solids (MLSS) concentration, particle size distribution (PSD) and extracelluler polymeric substance (EPS) on cake layer permeability in a submerged membrane bioreactor. Results showed that the permeation model was a useful tool to study the micromechanism of membrane fouling. There was a close correlation between MLSS concentration and cake layer permeability. There were a slight and a distinct decrease of the cake layer permeation as MLSS increased less and larger than 10,000mg/L, respectively. PSD and EPS are two significant factors affecting cake layer permeability in membrane bioreactor. Effect of activated sludge on cake layer permeability was mainly caused by EPS and small particles attached on membrane surface.

The membrane bioreactor (MBR) is an important process widely used in wastewater treatment. However, membrane flux declines rapidly due to membrane fouling, which limits the application of MBR. In order to alleviate membrane fouling, a precoated dynamic membrane (PDM) was studied systematically. The membrane module consisted of of 56-µm terylene filter cloth as the support membrane and powder-activated carbon (PAC) as the precoating reagent. The precoated dynamic membrane bioreactor (PDMBR) was used in municipal wastewater treatment practice. Meanwhile, from the viewpoint of retention capacity, flux recovery and alleviating membrane fouling, the suitable thickness of the PAC dynamic membrane was also investigated. The experimental results showed that the formation of PDM from PAC on a support membrane belonged to the cake filtering model, and the relationship of PDM resistance (Ra) and its thickness (D) was in accord with log-function; the suitable thickness was controlled around 0.3 mm. It was found that while the flux of PDM was kept at a high value, the operating pressure of PDM rose to 42 kPa after 43 days of stable operation of the PDMBR, and the removal efficiency of effluent COD and NH4+-N were as good as traditional hollow membrane bioreactors. Furthermore, the flux of the fouled membrane could be totally recovered just after being cleaned by brushing, and it did not consume any chemical reagents. Moreover, it was also found that the PDM could prevent biomass contaminations diffusing from the surface inwards by scanning electron microscopy (SEM).

采用孔径56μm的工业滤布制作膜组件，以PAC作为预涂剂，组成预涂动态膜-生物反应器。对比预涂膜、未预涂膜和014μm中空纤维膜的污染物去除效果和膜污染状况。试验结果发现，预涂动态膜2生物反应器不仅污染物质去除效果更好，而且预涂膜可以防止污染物质与微生物向膜材料表面和内部扩散，从而减轻膜污染，运行1128h后，操作压力仅上升至6kPa，并且只需刷洗，膜通量就可以恢复，无须消耗化学试剂。

对序批式运行方式强化膜生物反应器脱氮除磷效果进行了研究。在试验过程中逐渐降低进水CODPTN值，提高总氮负荷，比较序批式膜生物反应器和传统膜生物反应器的脱氮除磷性能与膜污染状况。试验结果表明，进水CODPTN降至318～813，总氮负荷提高至0122kg·m-3·d-1时，传统膜生物反应器无法脱氮，而序批式膜生物反应器通过改变周期、提高交换比等方式，TN和氨氮去除率分别保持在6716%和9311%.序批式的运行方式还可以减轻膜污染.