Estudio cinético de biorreactores de membrana con y sin lecho móvil aplicados al tratamiento de aguas residuales urbanas

Resumen

New technologies regarding wastewater treatment have been developed. Among these technologies, the moving bed biofilm reactor-membrane bioreactor (MBBR-MBR) is a recent alternative solution to conventional processes. Seven different systems for municipal wastewater treatment were studied regarding the removal of organic matter and nutrients. The wastewater treatment plants (WWTPs), which were designed for organic matter and nitrogen removal, consisted of a membrane bioreactor (MBR), a hybrid MBBR-MBR system containing carriers both in the anoxic and aerobic zones of the bioreactor (hybrid MBBR-MBRa), a hybrid MBBR-MBR which contained carriers only in the aerobic zone of the bioreactor (hybrid MBBR-MBRb) and a pure MBBR-MBR which also contained carriers only in the aerobic zone of the biological reactor. The WWTPs, which were designed for organic matter, nitrogen and phosphorus removal, consisted of an MBRp, a hybrid MBBR-MBR containing carriers in the anaerobic, anoxic and aerobic zones of the bioreactor (hybrid MBBR-MBRap) and a hybrid MBBR-MBR which contained carriers only in the anaerobic and anoxic zones of the bioreactor (hybrid MBBR-MBRbp). The WWTPs operated under different hydraulic retention times (HRTs), 30.4 h, 26.5 h, 18 h, 9.5 h and 6 h, and different biomass concentrations, which were grouped in low biomass concentrations around an average value of 2,700 mg L-1, intermediate biomass concentrations around an average value of 3,700 mg L-1 and high biomass concentrations around an average value of 6,500 mg L-1. A study of the microbial kinetics concerning the heterotrophic and autotrophic biomass, mainly ammonium-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB), was carried out to explain the removal of organic matter and nutrients. The microbial communities of AOB, NOB and denitrifying bacteria (DeNB) of each wastewater treatment plant (WWTP) were analyzed by 454 pyrosequencing methods to detect and quantify the contribution of nitrifying bacteria in the total bacterial community. Additionally, the evolution of the enzymatic activities of ¿-glucosidase and acid and alkaline phosphatase was studied, the bacterial diversity was evaluated by temperature gradient gel electrophoresis (TGGE) fingerprints and the bacterial community structure was analyzed throughout the scanning electron microscopy (SEM). The hybrid MBBR-MBRb had the highest efficiency regarding the chemical oxygen demand (COD) removal for HRTs lower than 9.5 h, with values of 87.39±6.01% and 84.10±2.25% for 9.5 h and 6 h, respectively. There were not statistically significant differences regarding the COD removal between the different configurations for HRTs higher than 18 h. The efficiency concerning the total nitrogen (TN) removal was slightly higher in the hybrid MBBR-MBRb for HRTs higher than 9.5 h. The pure MBBR-MBR had the highest percentages of TN removal for HRTs lower than 9.5 h. Therefore, an anoxic zone without carriers provided better contact between nitrate and the microorganisms. The removal of carrier from the anoxic zone of the bioreactor (hybrid MBBR-MBRb) involved an increase of the enzymatic activities studied, as well as the capacity to remove TN. The results concerning the organic matter and nitrogen removal were in accordance with the kinetic study for heterotrophic and autotrophic biomass, respectively. The introduction of an anaerobic zone in the bioreactor improved the total phosphorus (TP) removal, with a value of 81.42±3.85% for the hybrid MBBR-MBRap, which showed the highest performance. Kinetic modeling and microbiological study enhanced the basic ASM3 model by introducing two-step nitrification. The MBR and MBRp had usually the best kinetic behavior regarding the NOB kinetics. The hybrid MBBR-MBRb and hybrid MBBR-MBRbp under a hydraulic retention time (HRT) of 18 h and the pure MBBR-MBR with the HRTs of 9.5 h and 6 h could have a better kinetic behavior regarding the AOB because, as a whole, the kinetics of autotrophic biomass was more effective in these systems.