| On-line monitoring is crucial for the modern biological wastewater treatment process control and model simulation. Automatic titrimeter is thought to be an excellent online measuring instrument in the field of biological wastewater treatment, but its development or application was rarely reported in our country. A set of automatically titrimetric system to monitor the hydrogen ion variation during biological wastewater treatment process was developed, and it was integrated with the hybrid respirometer which has been patented in China. The accuracy of measurement for the automatically titrimetric system was adequately evaluated through various experiments, then the titrimetric system was applied for monitoring and controlling a lab SBR to realize shortcut biological nitrogen removal. Through these researchs the following conclusions were obtained:(1)The automatically titrimetric system mainly consists of reactor system, data acquisition and storage system and titrant auto-dosing unit. The automatically titrimetric system has two implementations. The one is to titrate to keep the pH at a fixed value, measuring the system pH with 1 pH electrode in the reactor. The other is to titrate to keep the influent pH and the effluent pH consistent, for which there are 2 pH electrode applied to measure the influent and effluent pH of the small reactor respectively. The second implementation has been evidently improved on the basis of the first one, and it has much greater practical significance. Two kind of application program was developed on the LabVIEW according to the two approaches respectively, with the same hardware system.(2) Owing to the respirometric-titrimetric software developed on LabVIEW the automatical level of the instrument is improved and its operation is simplified. The 7-rank median filter is adopted to eliminate signal noise, and 5-rank sliding average filter is used for measured data smooth treatment. The pH reading delay processing was applied which made the second titrimetric technology feasible. Taking advantage of all these means the measuring precision of the instrument is improved.(3)Firstly the basic performance of the instrument was investigated in the tap water, which didn't contain activated sludge. The quantitative reagent was added in the water to simulate the hydrogen ion variation which was measured by the automatically titrimetric system, and then the accuracy and precision of the instruments was evaluated from both the"total amount"consistent and the"rate"consistent experiments. The results of the"total amount"consistent experiment in a 1L bioreactor showed that the average titration errors with the pHst of 7.93±0.03, 7.5±0.03, 7.0±0.03, 6.5±0.03 and 6.0±0.03 were among 7.26 ~ 11.25% respectively, and the CVs of the repeated experiments were among 2.41% ~ 4.69% respectively. The average titration errors in bioreactors of 1, 2, 3 and 4L with pHst of 7.0±0.03 were 0.52%,3.18%,-5.08% and -9.16% accordingly, and the CVs of the repeated experiments were among 3.86%~5.4%. The test results showed that bigger bioreactor would influence the measuring accuracy because of its significant dynamic effects, while in the smaller bioreactor titration accuracy and precision are higher.(4)The "rate" consistent experiments included two micro pumps mutual tracking tests and using peristaltic pump simulation tests. The two micro pumps mutual tracking tests results showed that the residual error between the two micro pumps'cumulative titrate fluctuated near 0, the titration errors were among -4.16% ~ 2.51% with an average error of -0.68%, and the average titrate rate error was 0. the results of the using peristaltic pump simulation tests showed that the average relative errors between titration rate and dosing rate with the pHst of 6.5, 7, 7.5, 8 and 8.5 were -2.29%,-2.34%,-2.31%,-1.53% and -0.86% respectively. These results proved that the automatically titrimetric instrument could measure the system's hydrogen ion variation rate timely and accurately.(5)The automatic titrimetric system was developed aiming to monitor the dynamic process of biological wastewater treatment. The accuracy of measurement for both the two titrimetric systems was evaluated by monitoring the activated sludge nitrification process. For the first implementation two groups of experiments called stoichiometric relation tests and dynamic process tests separately were made, and for the other one nitrification batch experiments were conducted.In the stoichiometric relation tests, the ratios measured in a 1L bioreactor with NH4+-N concentrations of 1.67, 3.33, 8.33, 16.66 and 30.00 mg/L as N respectively were very close to the theoretical value, and the relative errors were among 2.09% ~ 6.34%. However, the relative errors in bioreactors of 1, 2, 3 and 4L with NH4+-N concentration of 16.66mg/L as N were among 2.09% ~ -18.57%, and increased significantly with accretion of the volume of bioreactor. The buffers of bicarbonate and the ammonium, especially the titrimetric dynamic effects in a larger bioreactor are the primarily factors resulting in errors. Timely sampling and measuring the NH4+-N concentration in the nitrifying process, the accuracy of the system for monitoring dynamic process of nitrification was evaluated by comparing the consistency between the measured NH4+-N concentration and the predicted concentration based on OUR and HPR respectively. For the batch experiments process with initial NH4+-N concentrations of 20 and 25 mg/L respectively, the correlation coefficients between the measured value and the predicted value based on OUR were 0.9967 and 0.9972, 0.9991 and 0.9992 between the measured value and the predicted value based on HPR, that showed that the dynamic process of nitrification could be timely and accurately presented with measuring OUR and HPR in the process.(6)In the tests for the new titrimetric system with initial NH4+-N concentrations of 3, 4.5, 6, 7.5, 9 and 10.5 mg/L respectively, the correlation coefficients between the measured value and the predicted value based on OUR were 0.9982, 0.9968 between the measured value and the predicted value based on HPR, that showed there was good stoichiometric relations between OUR/HPR and NH4+-N substrate. Comparing and analyzing all the signals in one certain batch test, it showed that pH, DO, OUR and HPR all could indicate nitrification ending point, but OUR and HPR were more sensitive than pH signal.(7)The automatically respirometric-titrimetric instrument was applied to real-time control the aeration period of a SBR in our laboratory to achieve shortcut nitrification. Firstly the feasibility of the HPR measurement using the second implementation with 2 pH electrode was investigated, and the results showed that HPR could be used to nitrification process control and nitrogen concentration estimation. Then with pH and HPR as main control parameter, SBR was real-time controlled strictly in order to realize shortcut nitrification. After running about 20 days, the nitrite accumulation rate (NAR) in the SBR has increased to 50%, which indicating that SBR has entered into the shortcut nitrification state. In the following cycles NAR was increasing consistently, and at about 40d NAR has increased to 88% and then stabilized, that improved that short-cut nitrification was achieved.(8)Sludge bulking occurred when the SBR shortcut nitrification process ran stably for almost 4 months. At the beginning sludge bulking was slight bulking, so none measures were taken. After several days, sludge bulking aggravated and serious filamentous bulking occurred, and the ammonia nitrogen removal efficiency was influenced significantly. Sludge bulking was inhibited effectively by taking a series of measures including adding new sludge, increasing aeration rate, altering volumetric exchange ratio and maintaining a constant temperature strictly in the system. After about 10 days later, the NAR raised over 80% again, and then in the following 30 days, the sludge sedimentation characteristic did not aggravate. The SBR system achieved stable shortcut nitrification renewedly.
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