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The Structured Bed Reactor with Recirculation and Intermittent Aeration (SBRRIA) is a reactor configuration that presents high efficiency of organic matter and nitrogen removal, besides low sludge production. However, operational parameters, as the recirculation rate, aeration time, and airflow, are not fully established. A bench-scale structured bed reactor with intermittent aeration was fed with synthetic effluent simulating the characteristics of sanitary sewage. The reactor was operated for 280 days with an operational hydraulic retention time (HRT) of 10 h. The reactor was operated without effluent recirculation for the first time since this approach was not yet reported, and was named Structured Bed Reactor with Intermittent Aeration (SBRIA). The COD removal was higher than 81% for all operational conditions, and the total nitrogen removal ranged from 10 to 80%. The highest efficiencies were obtained with an aeration time of 1 h 45 min (total cycle of 3 h) and an airflow rate of 4.5 L.min

Simultaneous nitrification and denitrification (SND) is a process that can remove both nitrogen and organic matter in a single unit. Several bench-scale studies show that the structured bed reactors (STBR) subjected to recirculation and intermittent aeration have achieved a good performance for SND treating different types of wastewater. Thus, this study took a step forward and evaluated the efficiency and stability of treating domestic sewage in a pilot-scale STBR. COD removal efficiencies higher than 87% were achieved in the whole experimental period. The highest Total-N removal efficiency was approximately 74 ± 7% by adopting a hydraulic retention time (HRT) of 47.2 h and intermittent aeration (2 h aerated and 1 h non-aerated). The setup of the aeration system was an important mechanism to ensure the optimal balance between nitrification and denitrification in a pilot-scale system. El proceso de nitrificación y desnitrificación simultánea (SND) permite alcanzar la eliminación combinada de nitrógeno e de la materia orgánica en una sola unidad. Varios estudios en escala de banco muestran que los reactores de lecho estructurado (STBR) con recirculación y aireación intermitente han logrado un buen desempeño para NDS, tratando diferentes tipos de aguas residuales. El propósito de este estudio fue evaluar la eficiencia y estabilidad del STBR a escala piloto tratando aguas residuales domésticas. Se lograron eficiencias de remoción de DQO superiores al 87% a lo largo del experimento. La mejor eficiencia de remoción de N-total fue aproximadamente 74 ± 7%, con un tiempo de retención hidráulica (HRT) de 47.2 h y aireación intermitente (2h airadas y 1 h no airada). La configuración del sistema de aireación fue un mecanismo importante para garantizar el equilibrio óptimo entre la nitrificación y la desnitrificación en un sistema a escala piloto. A remoção concomitante de matéria orgânica e nitrogênio em uma única unidade pode ser obtida a partir do processo de nitrificação e desnitrificação simultânea (SND). Diversos trabalhos em escala laboratorial mostram que os reatores de leito estruturado (STBR) submetidos à recirculação e aeração intermitente têm atingido desempenho satisfatório no tratamento de diversos tipos de águas residuárias, via processo SND. Desta forma, este trabalho teve como principal objetivo avaliar a eficiência e estabilidade do processo SND para o tratamento de esgoto doméstico em reator STBR em escala piloto. Eficiências de remoção de DQO superiores a 87% foram observadas ao longo de todo o período experimental. A máxima eficiência de remoção de N-total foi de, aproximadamente, 74 ± 7%, com tempo de detenção hidráulica (TDH) de 47.2 h e ciclo de aeração intermitente de 2h com aeração ligada e 1h sem aeração. A configuração do sistema de aeração se mostrou como um mecanismo fundamental para garantir o equilíbrio na ocorrência dos processos de nitrificação e desnitrificação na unidade piloto.

Among the novel system configurations that remove organic matter and nitrogen simultaneously, the structured bed reactor with recirculation and intermittent aeration (SBRRIA) can be mentioned. Studies addressing the SBRRIA have shown high efficiency of organic matter and nitrogen removal, as well as low sludge production. However, operational parameters such as the recirculation rate, intermittent aeration time, and airflow are not fully established. Therefore, this research aimed to evaluate the effect of these three parameters on the mixing characteristics of an SBRRIA adopting established hydrodynamic models, also proposing a new flow model for the reactor. Hydrodynamic tests were performed using sodium chloride as a tracer, and the variables were the recirculation rate, intermittent aeration time, and airflow. Results showed that the reactor presented a plug-flow behavior when the aeration was turned off and behaved as a completely stirred reactor when the aeration was turned on. Traditional models were not sufficient to explain the flow of the SBRRIA, resulting in the development of a simplified programming pseudo-code to adequately represent the flow in the reactor. The tested airflow and recirculation rates did not affect the mixing behavior in the SBRRIA. These observations represent a significant advance in SBRRIA studies as they show that energy consumption could be optimized, making the system even more advantageous by saving electrical energy up to 75% due to pumping.

The present study evaluated the efficiency of a structured-bed reactor subjected to recirculation and intermittent aeration (SBRRIA) to promote nitrogen and carbon removal from domestic sewage. The intermittent aeration and the recycling rate of 3 keeps the desired mixing degree inside the SBRRIA. Four different operational conditions were tested by varying the hydraulic retention time (HRT) from 12 to 8 h and aerated and non-aerated periods (A/NA) from 2 h/1 h and 3 h/1 h. At the THD of 8 h and A/NA of 2 h/1 h there was a decrease in the nitrification process (77.5%) due to the increase of organic matter availability, affecting the total-N removal performance. However, by increasing the aerated period from 2 h to 3 h, the nitrification efficiency rose to 91.1%, reaching a total-N removal efficiency of 79%. The system reached a maximum total-N loading removed of 0.117 kgN.m−3.d−1 by applying an HRT of 8 h and an intermittent aeration cycle of 3 h, aerated and 1 h non-aerated. The simultaneous nitrification and denitrification (SND) process was related to a complex interplay among microorganisms affiliated mostly to Acidovorax sp., Comamonas sp., Dechloromonas sp., Hydrogenophaga sp., Mycobacterium sp., Rhodobacter sp., and Steroidobacter sp.

This study aimed to evaluate the influence of COD/N ratio and carbon source on simultaneous nitrogen and carbon removal processes. A continuous up-flow structured-bed reactor subjected to recirculation and intermittent aeration (SBRRIA) was operated with hydraulic retention time (HRT) of 11.2 ± 0.6 h. The carbon sources were meat peptone and sucrose. The COD/N ratio varied by maintaining the organic loading rate fixed at 1.07 kg COD m(-3) d(-1) and changing the total-N concentration. The COD/N ratios tested were 9.7 ± 1 (sucrose); 7.6 ± 1 (meat peptone); 2.9 ± 1 (meat peptone) and 2.9 ± 0.4 (sucrose). COD removal efficiencies remained above 90% in all experimental phases. At lower COD/N ratios, NH4(+)-N oxidation efficiencies were higher than 90%. An autotrophic metabolism by anammox process was observed in Phases III and IV, which was responsible for 35% and 27% of total-N loading removal rates, respectively. Therefore, the system achieved total nitrogen removal efficiencies of 84.6 ± 10.1 and 81.5 ± 5.3%, under low availability of organic electron donors.

The removal of nitrogen and organic matter using a single reactor has been a common focus of investigation, and reactors operated in batch mode and under intermittent aeration have attracted special attention. This study aimed to evaluate the application of a new reactor configuration consisting of a fixed-bed reactor that was operated under conditions of continuous feeding and intermittent aeration. The reactor was built using acrylic, with a working volume of 6.1 L. The fixed bed used for biomass support was composed of polyurethane foam cylinders vertically oriented inside the reaction zone. The reactor was operated under intermittent aeration (2 h aerated and 1 h non-aerated) and a recirculation ratio Q r / Q = 5. Three different operating conditions (Phase I, Phase II, and Phase III) corresponding to hydraulic retention times (HRT) of 12 h, 8 h, and 10 h, respectively, were tested. In Phase I, the system achieved total nitrogen (TN) and chemical oxygen demand (COD) removal efficiencies of 82% and 89%, respectively. At HRTs of 8 h and 10 h, the reactor was unstable with respect to TN removal, and the average resultant removal efficiencies were 49% and 45%, respectively. However, COD removal efficiencies remained high with mean values of 85% and 88% for Phases II and III, respectively. Based on these results, it can be concluded that this new reactor configuration constitutes an alternative method for effective removal of organic matter and nitrogen from wastewater.

This work aimed at evaluating the effect of recirculation ratio on the degree of mixing in the flow of a structured bed reactor. Stimulus-response assays were carried out with hydraulic retention times of 6 h and 12 h, subjected to recirculation ratios of 0, 1, 2, 3, and 4. The assays were undertaken with dextran blue as a tracer and without aeration. The results fitted a compartment model, allowing the determination of the mixed-flow and plug-flow volumes inside the reactor. The model application showed that recirculation ratios between 1 and 3 do not increase the mixed-flow volume of the reactor. Higher mixed-flow volumes were obtained at recirculation rates higher than 4 for both 6 h and 12 h of hydraulic retention times. The results obtained in this research are important for future applications of this reactor configuration, promoting a mixed flow in the reactor with a minimum recirculation ratio.