Study of emerging aerobic biotechnologies for sewage treatment and resource recovery

Abstract

Activated sludge (AS) technology is the most used in sewage treatment plants (STPs) worldwide. However, with the population growth of recent decades, industrial advances, and changes in consumption patterns, the generation and complexity of effluents have also increased. Thus, STPs face the challenge of increasing treatment efficiency, often to comply with legal requirements for water bodies discharge increasingly restrictive. The search for improvements resulted in the emergence of new technologies such as MBBR (Moving Bed Biofilm Reactor), IFAS (Integrated Fixed FilmActivated Sludge), and AGS (Aerobic Granular Sludge). Therefore, this study was carried out to compare the above emerging aerobic technologies in sanitary sewage treatment to contribute to decision-making in designing future ETEs. In addition, several ways of recovering resources were pointed out to assist in introducing the circular economy within sewage treatment. The first investigation evaluated the influence of including a biofilter layer in a sequential batch reactor with AGS. This study observed that theAGS-BF (R2) system provided a high-quality effluent in terms of total suspended solids and turbidity, in addition to obtaining Total Nitrogen removals above 80% throughout the experimental period. Another fact observed was that the sludge production was evaluated, and the yield coefficient (Y, gVSS/gCODrem) and sludge concentration were higher in the AGS-BF reactor than in the conventional AGS reactor. The new reactor configuration proved to be an alternative to improve some aspects of conventional AGS reactors, such as denitrification and nitrite accumulation, the concentration of TSS in the effluent, and increased system reliability during periods of instability and granule breakage. The second investigation compared four emerging aerobic technologies (MBBR - R1, IFAS - R2, AGS - R3, and AGS-BF - R4) for sanitary sewage treatment and resource recovery. In this study, COD removal and nitrification were high for all reactors. However, total nitrogen removal was moderate for reactors R1 (48%) and R2 (54%), but values above 70% were observed for R3 and R4. Phosphorous removal was also possible, reaching values below 52% for the MBBR (R1) and IFAS (R2) systems but with values above 80% in the aerobic granulation systems R3 and R4. The concentration of volatile solids in the effluent was also higher in R1 and R2 (6.1 and 6.7 mg/L, respectively) when compared to R3 (4.2 mg/L) and R4 (5.4 mg/L). The third study consisted of a systematic review of the recovery of resources such as water, energy, chemicals, raw materials, and nutrients in AGS systems. In this study, several ways of recovering resources were shown, such as water reuse, the use of sludge as inoculum in AGS WWTPs, recovery of phosphorus, recovery of alginate, tryptophan, polyhydroxyalkanoates, biogas, and other compounds found in AGS. Finally, this study highlighted that the recovery of resources inAGS systems could be a solution to reduce treatment costs, making the technology more viable and decentralized.