Effects of low temperature on sludge settleability and nutrients removal performance treating domestic wastewater

In order to investigate the effect of temperature on activated sludge systems,sludge settleability,nitrogen and phosphorus removal processes were investigated by changing temperature variation patterns using 4 sequencing batch reactors (SBR).The results showed that no matter temperature changes in the range of 15-22 ℃ (decrease or increase) gradually or sharply,it has little effect on nitrogen and phosphorus removal processes.But when temperature decreases to 12 ℃,biochemical reactions will be inhibitted obviously.At least 1 sludge retention time (SRT) is needed for nitrification adapt to new temperature envirionment,and more time is necessary for phosphorus removal process.When temperature increases from 12 ℃ to 22 ℃ sharply,nitrification process deteriorates seriously,but phosphorus removal process shows no change.In addition,sludge settleability deteriorates when temperature changes sharply (decrease or increase),but the reasons are different.Under temperature decrease condition,it is mainly caused by the increase of accumulated extracellular polymeric substances (EPS).Under temperature increase condition,the loosing sludge flocs' configuration is the main reason.It should be pointed out that the filamentous bacteria content during the entire experiment keeps almost constant,and the sludge settleability variations are the reflection of the change of sludge physicochemical characteristics.

Relationship between sludge settleability and membrane fouling in a membrane bioreactor

The evolution of activated sludge settleability and its relationship to membrane fouling in a submerged mem-brane bioreactor were studied at a lab-scale equipment fed with synthetic wastewater.It was found that sludge volume index(SVI)gradually increased and the sludge settleability was reduced,which was caused by the propagation of filamentous bacteria.With increasing SVI,the average increasing rate of trans-membrane pressure increased,the stable filtration period was shortened,and the two stages(smooth stage and accelerating stage)of the trans-membrane pressure were more obvious.At the same time,the increasing rate of trans-membrane pressure at the smooth stage decreased and the rate at the accelerating stage increased with SVI,respectively.The observation by using scanning electronic microscopes showed the cake layer with loose structure and large thickness formed on the membrane surface due to the appearance of filamentous bacteria and high SVI in sludge.Influence of the sludge settleability on the trans-membrane pressure was related to the structure and thickness of the cake layer on the membrane.

Control of sludge settleability and nitrogen removal under low dissolved oxygen condition

Low dissolved oxygen （DO） is an energy- saving condition in activated sludge process. To investi- gate the possible application of limited filamentous bulking （LFB） in sequencing batch reactor （SBR）, two lab-scale SBRs were used to treat synthetic domestic wastewater and real municipal wastewater, respectively. The results showed that prolonging low DO aeration duration and setting pre-anoxic （anaerobic） phase were effective strategies to induce and inhibit filamentous sludge bulking, respectively. According to the sludge settleability, LFB could be maintained steadily by adjusting operation patterns. Filamentous bacteria content and sludge volume index （SVI） were likely correlated. SVI fluctuated dramatically within a few cycles when around 200 mL-g~, where altering operation pattern could change sludge settleability in spite of the unstable status of activated sludge system. Energy consumption by aeration reduced under low DO LFB condition, whereas the nitrification performance deteriorated. However, short-cut nitrification and simultaneous nitrification denitrification （SND） were prone to take place under such conditions. When the cycle time kept constant, the anoxic （anaerobic） to aerobic time ratio was determining factor to the SND efficiency. Similarity keeping aerobic time as constant, the variation trends of SND efficiency and specific SND rate were uniform. SBR is a promising reactor to apply the LFB process in practice.

Innovative method of culturing bdelloid rotifers for the application of wastewater biological treatment

This study aims to establish a simple and efficient method for the mass culture of bdelloid rotifers,which is the basis for the application of bdelloid rotifers as biological manipulators to improve wastewater biological treatment performance.A common bdelloid rotifer,Habrotrocha sp.,in a wastewater biological treatment system was selected as the culture target.Rotifers fed on flour could reproduce faster than those fed traditional food such as Chlorella vulgaris or mixed bacteria.As a rotifer food,flour has the advantages of simple preparation,effortless preservation,and low cost compared to live Chlorella vulgaris or mixed bacteria,so it is more suitable for the mass culture of rotifers.The optimal rotifer culture conditions using flour as food were also studied.According to the experimental results,the recommended rotifer culture conditions arc a flour particle size of 1 a flour concentration of 6×10^(6) cell/mL,a temperature of 28℃,a pH level of 6.5 and salinity of 100-500 mg/L.In addition,the sludge volume index in the sequencing batch reactor(SBR)with the addition of cultured rotifers was 59.9 mL/g at the end of operation and decreased by 18.2%compared to SBR without rotifer,which indicates that the cultured rotifers still retained the ftinction of helping to improve sludge settling.This function may be related to the rotifer's role in inhibiting bacteria from producing loosely bound extracellular polymeric substances in the SBR.