| Activated sludge process which acts as a core part of wastewater treatment system, has played a huge role in the treatment of municipal wastewater as well as some industrial wastewater. The biomass of heterotrophic bacteria in activated sludge has a decisive impact on the water treatment effect and operating costs of sewage plants. The ASM working group has suggested to adopt two methods which were respiration incremental method in the phase of microbial logarithmic growth and estimation method of endogenous respiration rate to determine the biomass of heterotrophic bacteria. These methods were more accurate than conventional suspended solids method and simpler than molecular biological technique, thus had strong practicability in sewage plants. However, the time node of endogenous respiration had great impact on the result of these methods. In order to better estimate the time node of endogenous respiration phase of heterotrophic bacteria, this study showed the characteristics of activated sludge during the endogenous respiration phase which focused on traditional municipal activated sludge as well as municipal garbage leachate which represented the industrial waste water.The main results were shown as follows:(1) Endogenous respiration processes of the two kinds of activated sludge were analyzed by using respiration map technology. Results showed that two kinds of activated sludge reached endogenous status at different time, but entered into the period of dormancy simultaneously, which suggested that sludge type and sludge age had effect on the time of entering into endogenous respiration phase, but was irrelevant on the time of entering into dormancy phase. In addition, whether autotrophic and heterotrophic bacteria would reach the endogenous status simultaneously depended on type of the sludge.(2) In terms of the variation of endogenous respiration ratio, three stages could be identified as low endogenous respiration(ratio less than 8%), high active respiration(ratio between 8% and 16%) and high endogenous respiration(ratio higher than 16%). Combined with the water quality analysis in laboratory and practical operation investigation of the sewage plant, high active respiration stage(endogenous respiration ratio between 8% and 16%) was found to be the best operational period of traditional municipal activated sludge. The sludge in high active respiration stages had better growth condition and stronger ability to degrade organic matter, so this stage was defined as the health stage of activated sludge process. Findings in this study gained better understanding of endogenous respiration ratio and might help improving the practical operational effect of WWTPs.(3) Based on the variation of heterotrophic bacteria versus autotrophic bacteria ratio, endogenous respiration process of the microflora presented three stages, which were high platform stage, rapid decline stage and low platform stage. The ratio variation could characterize heterotrophic bacteria and autotrophic bacteria with the ability of hunger resistance and the proportion of recoverable part. Meanwhile, it could also characterize the activity variation of main microflora in the endogenous respiration period.(4) Through comparative study between respiration incremental method and endogenous respiration estimation method, combined with the study of biomass estimation in our research group for years, research suggested that when the endogenous respiration ratio was less than 8% and higher than 16%, the biomass obtained by the two methods was relatively consensus. In the high active respiration stage, the biological specific growth rate was high due to active microbial metabolism, and biomass results gained by the two methods were relatively different. Hence a suitable endogenous respiration time node was suggested in this study for convenient estimation of heterotrophic bacteria biomass using endogenous respiration method in WWTPs. |
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