Respirometric Approach For Quantitative Analysis Of Microbial Process And Its Optimization

Improving treatment effect and reducing the energy consumption of the wastewatertreatment plants （WWTPs） has been the core issue of concern in the water treatmentindustry. With the development of water treatment technology, sewage treatment systemdevelops gradually from single simple form into complex huge system. Efficientreliable design and operation of the sewage treatment system become the newchallenges of the water treatment industry. On the one hand with the gradual deepeningof the understanding of biological processes, the process parameters of the ASM getmore and more, on the other hand, the full-scale operating is difficult to apply thesetheoretical achievements. As a typical case, designs and operations of domestic WWTPsstill use the static model-based parameters, like hydraulic retention time （HRT）, this is afar cry from the development of the activated sludge model technology. The cause ofthe problem lies in the activated sludge model parameter identification and componentmeasurement is too complex, time-consuming, and high cost of model application.Respirometer is an important useful tool for ASM parameters quantification, buttraditional respirometry didn’t overcome the above bottlenecks. It is necessary tooptimize and simplify the operation difficulty and complexity, thus providing ascientific and quantitative basis for design and operation of WWTPs.On this basis, test conditions are discussed in order to optimize the respirometer inorder to optimize the respirometer, including temperature, pH, F/M, MLSS, etc. Basedon these theoretical achievements, an improved respirometer is designed for quantitative analysis of operating WWTPs.Specifically, the theoretical results obtained in this paper are as follows:1. Measurements of oxygen mass transfer coefficient （k_La） and saturated dissolvedoxygen concentration （C^∞） in activated sludge were investigated. Good results could beobtained with the flowing conditions: sludge with endogenous respiration, test timespan of approximately5/k_La⁶/k_La, and nonlinear curve fitting methods for data process.Additionally, neither high nor low initial oxygen concentration should be used for datafitting, and approximately25%of the measured maximum concentration should be usedfor it.2. Combined with activated sludge model and in situ respirometry, the oxygentransfer coefficient of two different bench scale aerobic units is measured. The relativeerror of the obtained results with the standard method’s is within10%.3.Methodology was developed to characterize the effect of high ammonia, nitrite,and nitrate concentrations, alkalinity and pH on nitrification activity by oxygen uptakerate （OURA）, maximum oxygen uptake rate （OURN,max）, oxygen half-saturationcoefficient（KO,A） and the maximum specific growth rate (μ_A,max). The results show thatOURAis applicable to characterize effect of pH on nitrification activity. OURN,maxcanquantitatively characterize the inhibition effect of ammonia and nitrite, KO,Acanquantitatively characterize the inhibition effect of ammonia and nitrite. OURAand μ_A,maxboth show alkalinity influence nitrification activity. As operation control indicator,OURAshould be only applied in the short-term situation. For the short-term operationsystems which need maintain a certain amount of nitrifying bacteria, μ_A,maxis moreapplicable.4. Explored the method to characterize sludge activity with endogenous respiration,the result indicate that the commonly used special endogenous respiration rate,SOURen,SSand SOURen,VSS, are associated with heterotrophic active biomass, but itmakes little sense to tell sludge activity. While stability of advantage of endogenousrespiration was notice, based on this endogenous respiration ratio among totalrespiration （η） is proposed to be an indicator of biological activity. By contrastingendogenous respiration ratios under different pH and growth stage and ratios ofdifferent sludge, results show η is valuable to quantify sludge activity. 5. Method used for measuring kinetic parameters for autotrophic bacteria withopening respirometry is investigate, the result shows opening respirometry is low F/Mand short-term, reads OUR more frequently, and require accurate and stable k_La. Underthis low F/M and short-term situation, μ_A,maxand X_Acan’t be estimated independently.However in this short test procedure ammonia is fully utilized, opening respirometry isuseful to measure ammonia half-saturation coefficient （KNH） and yield for autotrophicbiomass （YA）.6. Optimized the experiment to estimate maximum specific growth rate forautotrophic biomass (μ_A,max) and active autotrophic biomass （X_A）. In the end, the testperiod is shorten to4～5hours from above15hours.7. On the basis of summarizing the respirometry experimental process to improvethe respirometer, temperature is controlled by semiconductor chilling plate, and microperistaltic pumps control liquid flow, such as activated sludge, matrix, acid and alkalinesolution for pH maintain. The respirometer links to the PC and PLC to achieveautomation.With the practical, accurate respirometer developed in this study, the experimentand calculation methods are optimized, by shortening the testing time, improving thecalculation accuracy, making sense of the significance of parameters, putting forwardnew characterization indicators. These make the quantitative analysis of microbialprocesses more rapid, and the quantitative indicators more practical value in themanagement of WWTPs.