Development Of Hybrid Respirometer And Research On Influent COD Characterization Of Activated Sludge Models

Research, development and application of activated sludge models (ASMs) are new aspects of international water science and technology field. However, the COD characterization, which is the basis of ASMs and the essential requirement for the application of ASMs, has been an unfathomed and important scientific problem in present. Recently, some researchers in China start elementary work on this aspect. In this thesis a novel hybrid respirometer is developed based on the principle of pollutants biochemical degradation, and the methods of ASMs influent COD characterization are studied systematically using the respirometer and the other routine analytical methods. Through these researches the following conclusions are obtained:(1) Measurement chambers are introduced into the novel hybrid respirometer and the operational pattern of positive pressure up-flow is adopted, in which the liquid flows at intense onflow and makes the renewal rate of the liquid near the membrane of DO probes high enough to eliminate the influence of flow rate on DO readings even at low flow rate. The two measurement chambers are located at the inlet and outlet of the respiration chamber, so the DO concentration of the liquid flowing in and out of the respiration chamber can be measured. There is no influence on DO readings resulting from the difference of flow pattern because the two measurement chambers are identical. All the reactors are located in the same constant temperature water tank and so the constant temperature of the whole system is achieved.(2) Owing to the respirometric software developed on LabView the automatic level of the novel hybrid respirometer is improved and its operation is simplified. The 7-rank median filter is adopted to eliminate signal noise, linear regression is used to replace differential arithmetic and a method called"soft calibration"is proposed to calibrate the drift from each other of the two DO probes in the software. Taking advantage of all these means the measure precision of the respirometer is improved.(3) The stability, accuracy and reproducibility of the novel hybrid respirometer are evaluated through experiments and the results showed that: the CV (Coefficient of Variation) and 95% confidence zone width of the peak height and peak area of the oxygen utility rate (OUR) profiles obtained from the long time run of the respirometer are below 3% and 6%, respectively. The recovery efficiency of added substrate was in the range of 89% and 108%, and its CV is below 4%. The CV of model parameter estimation and toxicity evaluation are below 12% and 10%, respectively. From all these results it can be concluded that the novel hybrid respirometer developed in this paper is stable under long time run and its measurement possesses good accuracy and reproducibility.(4) The research on the four physical-chemical methods (0.45μm filter, 0.1μm filter, flocculation and flocculation +0.45μm filter) of COD characterization showed that: the"COD release"of some kind of filter membrane is obvious. The reproducibility of the four methods is good and there is no remarkable difference between them. The biodegradable COD (BCOD) of the filtrates of the four methods contained COD fractions whose biodegradation rate is different, in which the percentage of readily biodegradable COD (RBCOD) is only 35%-45%. The concentration of RBCOD of the four filtrates is approximate to that of the raw wastewater.(5) The results of the two methods (batch respirometry and model fitting) determining the active heterotrophic biomass (XH) in wastewater are correlative and the latter was 78% of the former. It is necessary for the method of model fitting to measure the exponential growth phase of XH and therefore the results are unsatisfied for the raw wastewater with high XH and low RBCOD. The modification by adding extra substrate and/or diluting the wastewater is feasible. Due to the simplicity and much less interferential factors, the batch respirometry is more practical for the determination of XH in wastewater.(6) The BCOD measured by short-time BOD (BODst) test (respirometry) are lower than those of long-time BOD (BODlt) test because the active biomass COD is included in the latter. The sum of BCOD of BODst test and XH measured through batch respirometer is consistent with the BCOD of BODlt test and the ratio between them was in the range of 0.88-1.02 with average 0.94. The BODlt test is time-consuming and the microorganisms'population and their metabolic characteristic are different from that of the actual activated sludge process. So the respirometry has the advantage of time-validity and representation for the actual activated sludge system.(7) The method that determinates the RBCOD and SBCOD in municipal wastewater through respirometry directly and simultaneously is investigated experimentally and the results show that the optimal ratio of initial substrate concentration S(0) (calculated as total COD) and initial biomass concentration X(0) (calculated as MLVSS) for the respirometric experiments is 0.20-0.60gCOD/gMLVSS. Under this optimal S(0)/X(0) the standard deviation and CV of the measuring results of RBCOD and SBCOD are below 5mg/l and 8%, respectively, which validates that the method proposed here is practically feasible.(8) A new method is proposed to characterize SI: first the raw wastewater is treated physical-chemically and the total COD of filtrate is measured; then the biodegradable COD (BCOD) of filtrate is measured through respirometry and the difference between the total COD and BCOD is equal to SI of raw wastewater. Flocculation+0.45μm filter is selected as the pretreatment of the method proposed here.(9) A set of standard methods for ASMs COD characterization is suggested in the thesis and it advantages are:①Respirometry is adopted to measure RBCOD and SBCOD;②SI is determined from raw wastewater and so there is no influence of inert products;③Heterotrophic biomass in wastewater is measured;④The key instrument used in the standard methods-hybrid respirometer, has high automatic level and friendly user interface which simplifies the respirometry. So the suggested standard methods are practical.(10) According to the suggested standard methods, the influent COD of a wastewater treatment plant in Chongqing, China, is characterized. The results show that:①The RBCOD and the total COD (COD_tot) are correlative well and corresponding R2 is 0.9. The ratio between them is 8.25%～10.34% with average 9.35%, which is about 50% of the values reported in literature.②The percentage of XH in the COD_tot is 23%～46% with average 31%.③The SBCOD accounts for 26.85%～39.75% of the COD_tot with average 33.96%, which is less than those reported in literature.④The percentage of soluble inert COD fraction (SI) in the COD_tot is 1.40%～4.28% with average 2.92%. The results reported in literature are as 2～5 times more as those listed here.⑤The particle inert COD fraction (XI) in the COD_tot is 14.17%～36.31% with average 22.43%, which is greater that those reported in literature.