Particle Image Velocimetry (PIV) was used to study the settling of activated sludge flocs under turbulent flow conditions. Experimental results showed that a larger particle diameter led to a higher settling velocity while the higher turbulence intensity led to lower settling velocity. Based on the measurements a mathematical relation has been derived which correlates the settling velocity for individual sludge flocs under turbulent conditions through a modified Vesilind equation. Settling velocity shows a power-type relation to sludge particle diameter and an exponential-type relation with turbulence intensity and sludge concentration.

The aim of this paper is to realize fully the hybrid respirometric measurement principle with high accuracy and measuring frequency. Based on the knowledge of the difficulty in implementing “ultimate” hybrid respirometer and the drawbacks of the simpler hybrid respirometer, a novel implementation of the hybrid respirometric measurement principle was developed. It was verified that the new hybrid respirometer possessed the advantage of “ultimate” hybrid respirometer while its DO electrodes suffered no effect of flow rate change. Also the accurate and constant temperature of the whole set-up was solved. For the purpose of enhancing the availability of the respirometer proposed in this paper, software with friendly user interface was developed, in which advanced arithmetic and median filter were adopted. Finally the new hybrid respirometer system was evaluated and the accuracy and reliability were satisfied.

Based on batch settling tests, a model describing the compression settling process of activated sludge was developed and validated by experiments. Furthermore, a theoretical equation for determining the critical point when the compression settling stage commences, and a new velocity function for the compression settling were deduced from the model. By combining the new model and the conservation of mass, it was proved that the Vesilind function was also capable of describing the compression settling velocity on condition that the appropriate parameters were estimated. Dividing the complete settling process of activated sludge into the zone settling and compression settling stages, and describing them by the Vesilind function with different parameter sets was more reasonable for characterizing the complete settling process of activated sludge. The method was applied to predict the sludge blanket height during batch settling tests, and the results showed that the settling processes could be simulated well.

A staged anaerobic and aerobic membrane bioreactor (MBR) was constructed. The membrane module was submerged in the aerobic zone of the reactor, and was operated under the mode of alternative suction and air backwash. Air backwash and aeration around the membrane module served as the cleaning of the membrane, resulted in the steady operation of the reactor at the flux of 5-14lm−2 h−1 for up to 200h without any additional cleaning. The efficiency of COD removal was more than 99% at up to 10.08g CODl−1 per day of the volumetric loading rate (VLR). The efficiency of ammonium removal was 100% at a VLR of 0.18g NH4+-N l−1 per day. Sixty to 80% of COD was anaerobically biodegraded in the anaerobic zone of the reactor and this produced a great amount of methane. Methane passed to the aerobic zone of the reactor and could serve as a carbon source for denitrification. Intermittent aeration allowed nitrification and denitrification to occur simultaneously in the aerobic zone of the reactor. The capacity for ammonium removal reached up to 0.5g NH4+-N l−1 per day. Eighty-four to 94% of the total oxidised nitrogen converted from the oxidisation of ammonium was denitrified.

The integration of methanogenesis with denitrification and anaerobic ammoniumoxidation (ANAMMOX) was studied in an expanded granular sludge bed (EGSB) reactor in this work. Experimental results from the continuous treatment of wastewater with nitrite and ammonium, which lasted for 107 days, emonstrated that wastewater with high nitrite and ammonium could be anaerobically treated in an expanded granular sludge bed reactor. More than 91% to 97% of COD were removed at up to about 3.9g CODP (L