Use of aerobic granular sludge (AGS) to remove antibiotics from hospital wastewater

Hospitals are a leading source of effluents with high concentrations of antibiotics. The final disposal of hospital effluents without prior treatment directly into sewage systems poses a significant risk to the environment and public health and contributes significantly to the spread of antimicrobial resistance to the most widely used antibiotics in routine clinical practice.

The project proposed the use of aerobic granular sludge (AGS) to remove antibiotics and antimicrobial-resistant genes, especially beta-lactamase-encoding genes, from hospital wastewater. AGS is a low-cost technology, defined as a type of biofilm that does not require support material to grow. The technology features low energy consumption and operates without the need for aeration and decantation tanks, commonly used in wastewater treatment plants.

The project was conducted by a multidisciplinary team of expert engineers, pharmacists, chemists, and microbiologists.

The project's first stage focused on the collection and initial analysis of characteristics of the raw hospital effluent from the National Institute of Traumatology and Orthopedics (INTO). 

AGS was then adapted to initial proportions of 5%, 10%, 15%, and 20% of hospital effluent. This step aimed to evaluate changes in the granule´s physical properties, such as sedimentation capacity, changes in granular structure, and the ability to remove chemical oxygen demand, ammonia, and phosphorus. The third stage, extending beyond the above-mentioned analyses, assessed the ability to remove antimicrobial resistance genes, mainly genes encoding beta-lactamases, at concentrations of 25%, 50%, 75%, and 100%. This step was performed in the Laboratory of Medical Microbiology at the Paulo de Góes Institute of Microbiology in the Federal University of Rio de Janeiro (UFRJ) under the coordination of Professor Renata Cristina Picão. The next step assessed the raw effluent´s impact on the granular microbial community and the risk of environmental spread of antimicrobial resistance, based on an analysis of the raw effluent, AGS, and treated effluent.

The study showed that AGS is able to adapt to hospital sewage and is effective in removing nutrients, mainly ammonia. Continuous exposure to hospital effluent considerably impacted the AGS microbial community, but the system proved resilient and capable of removing the beta-lactamase-encoding genes, especially at a concentration of 25% of hospital sewage. The study concluded that AGS is an economically feasible and environmentally adequate alternative for treatment of effluents from public health units and can considerably reduce sewage treatment plants´ operating costs. The reduction lies in the decrease in the operational area, about 75% less than the activated sludge system, since different biological processes take place inside the granule. In addition, the ability to withstand high concentrations of organic load and to remove beta-lactamase-encoding genes makes AGS a good alternative for removing antimicrobial resistance genes from different aquatic matrices.

Aerobic granular sludge has produced excellent results in different effluents but had not been applied previously to treatment of hospital effluents. The current project is an innovative, low-cost, sustainable, and promising opportunity for removing antibiotics.

Due to the scarcity of financial resources in developing countries' hospital settings, the choice of an economically feasible and environmentally adequate treatment is paramount. The treatment must comply with the pertinent legislation and demonstrate efficiency in removing antibiotics, bacteria, and antimicrobial-resistant genes.

The future plan is to form AGS using sludge from a hospital wastewater treatment plant and feed it through the combination of hospital effluent and synthetic effluent. The following step is to scale up the initiative to a hospital unit.