Ping Du

Extraction and structural characteristics of extracellular polymeric substances (EPS), pellets in autotrophic nitrifying biofilm and activated sludge.

The composition and the distribution of extracellular polymeric substances (EPS) and pellets of autotrophic nitrifying biofilm and activated sludge were investigated in this work. Fourier-transform Infrared Spectroscopy, fluorescent in situ hybridization and fluorescence staining were used to examine proteins, carbohydrates, humic substances and DNA being present in the biofilms and the sludge samples. To investigate extraction efficiency and its effect on characterization of tightly bounded EPS, four extraction methods (ethylenediamine tetraacetic acid (EDTA), NaOH, cationic exchange resin (CER), ultrasound) were compared. EDTA and ultrasound showed more effective extraction ability than NaOH and CER. NaOH and ultrasound extraction led to high activity of glucose-6-phosphate dehydrogenase from cell lysis, which was confirmed by fluorescence staining analysis. Ultrasound and NaOH extraction yielded 18% and 11% of dead cells in biofilm, respectively, whereas they obtained 11% and 9% of dead cells in activated sludge, respectively. Four layers of extractible products were separated from autotrophic nitrifiering flocs. The extraction results indicated that extraction yield in different layers varied in a wide range: 3-6% of soluble EPS, 5-10% of loosely bound EPS, 34-67% of tightly bound EPS and 30-60% of pellets.

A control strategy of partial nitritation in a fixed bed bioflim reactor

To achieve an appropriate mixture of ammonium and nitrite for anaerobic ammonium oxidation (ANAMMOX), 50% partial nitritation was optimized in a fixed bed biofilm reactor treating synthetic wastewater. Results suggested that 50% partial nitritation could be achieved by stepwise increases of influent NH4+-N at pH of 7.8±0.2, temperature of 30±1°C and dissolved oxygen (DO) of 0.5-0.8 mg l(-1). Hydraulic retention time (HRT) and influent alkalinity did significantly affect partial nitritation. At HRT 12 h, 50% partial nitritation could be kept stable, regardless of influent NH4+-N variation, by controlling the influent HCO3-/NH4+ molar ratio at 1:1. The fluorescent in situ hybridization (FISH) results indicated the abundance of evolution of ammonia-oxidizing bacteria (AOB) and the nitrite-oxidizing bacteria (NOB) coincided well with the performance of partial nitritation. Furthermore, the AOB were highly affiliated with Nitrosomonas spp. and Nitrosospira spp. dominated (64.1%) in the biofilm with a compact structure during the stable 50% partial nitritation period.

Performance and membrane fouling characteristics of a combined biofilm and membrane bioreactor for treatment of fluorescent whitening agent wastewater

A full-scale system, composed of one anoxic fixed biofilm reactor, four oxic fixed biofilm reactors and an activated sludge membrane bioreactor, was used to treat heavily organic loaded, high toxic and saline fluorescent whitening agent wastewater. This system was running steady during the experimental period of three months. Treatment performance and membrane fouling characteristics were investigated. The concentrations of chemical oxygen demand (COD), , and total nitrogen (TN) in effluent were 447, 27, 14 and 114 mg L−1, corresponding to the removal rates of 89%, 76%, 68% and 64%, respectively. A series of analyses, including Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, confocal laser scanning microscopy, scanning electron microscopy and protein and polysaccharide concentration measurements, represented that the sludge layer formed on the membrane surface contained both organic and inorganic foulants. Polysaccharides in bound extracellullar polymeric substances in mixed liquor were the main contributor to membrane fouling. Off-line tap water rinsing was proved to be a cost-effective method of fouling control.