Full scale expanded bed reactor with overlaid anaerobic and aerobic zones: joint removal of organic matter and nutrients and the study of microbiological biofilm behavior and DO microsensor

Author(s)

Renato Ribeiro Siman

• Document type: Doctoral Thesis
• Press: São Carlos.
• Institution: Universidade de São Paulo (USP). Escola de Engenharia de São Carlos (EESC/SBD)
• Defense date: 2007-06-15

Examining board members

José Roberto Campos; Eugenio Foresti; Antonio Eduardo Giansanti; Marco Antonio Penalva Reali; Adrianus Cornelius Van Haandel

• Advisor: José Roberto Campos

Abstract

The current research aimed the development of a 159 \'M POT.3\' total volume biological reactor, with a expanded and partially aerated granular coal bed (activated and anthracite), to promote organic matter and nutrients (N and P) removal from wastewater due to the maintenance of anaerobic and aerobic environments, stratified throughout the height of the reactor and also all over the biofilm cultivated in its interior. Methods for the analyses of specific nitrifying activities (ENA), denitrifying (EDA) and methanogenic (EMA) were applied to assess the impact of the operational modifications in the biological behavior of microorganisms present in the reactor, based on standard respirometric tests found in literature. The reactional stratification was also studied inside the biological films with the help of DO microsensors in batch tests. Thus, after 451 of operation it was possible to verify mean \'COD IND.F\', TNK and phosphate removal of 78%, 56% and 42%, respectively, when the reactor was operated for 66 days with average hydraulic detention time of 8.8 h, pure oxygen injector which was installed after the aerated recirculation line which was working pressurized (3 to 4 bar) and with mean recirculation ratio equal to 3, when compared to the feeding flow. For the rest of the period where mean volumetric loading rates of 0.74 \'+ OR -\' 0.28 kg\'COD IND.F\'/\'M POT.3\'.day; 0.17 \'+ OR -\' 0.07 kgTNK/\'M POT.3\'.day and 0.05 \'+ OR -\' 0.02 kg\'PO IND.4\'POT.-3\'/\'M POT.3\'.day were applied the system demonstrated average removal of 65 \'+ OR -\' 20% for \'COD IND.F\', 25 \'+ OR -\' 21% for TNK and 48 \'+ OR -\' 18% for total phosphate, even when it operated with mean cellular retention time of 15 \'+ OR -\' 7 days. The respirometric tests were sensible enough to assess the microbial activity from the biological material collected throughout the reactor, and where mean PME of 0.25 mL\'CH IND.4\'/gSVT.h was verified for the samples of biological material collected in the anaerobic region, at the bottom of the reactor; ANE varying between 1.3 to 4.4 mg\'O IND.2\'/gSVT.h, for the samples collected in the aerobic region, reactor\'s intermediary; and ADE varying between 0.024 to 5.20 mg\'N IND.2\'/gSVT.h, for samples collected at the bottom and the top of the reactor, respectively. The analyses of the liquid material also support the idea of stratification of the aerobic environments, at the bottom of the reactor, and micro-aerated, in its superior intermediate region, pointing to the region as a high potential of occurring joint nitrification and denitrification at the top of the reactive zone. The DO amperometric microsensor, with tip between 10 and 30 \'mü\'m of diameter, produced in a special laboratory, is sensible to the determination of dissolved oxygen concentration gradient inside biological film, sufficient for the formation of anaerobic and aerobic regions in its interior, this information can be useful to the improvement of biofilm reactors, projected for the combined removal of organic matter and nutrients. However, when the definition of kinetic parameters or mass transference is intended more strictness must be applied when choosing the locals for microsensor application, where the effects of the microbial aggregate heterogeneity is reduced in the adjustment of the mathematical modeling applied to the experimental points. (AU)