The challenge of removing waste from wastewater: let technology use nature!

Access to clean and safe drinking water is a basic human right. Since ancient times, engineers, scientists, and government authorities have contributed to protecting and enhancing water sources’ quality. One key concern has been the management of human excreta and domestic wastes that significantly contribute to the quality degradation of drinking water sources. This has led to the construction of sewage drainage systems, especially in the cities and urban areas. To date, sewage drainage systems remain an integral part of the infrastructure, playing a key role in protecting water sources from pollution. With the industrial and urban agglomerations, wastewater production has tremendously continued to grow. Therefore, the development of robust and cost-effective wastewater treatment technologies is inevitable.

Wastewater treatment is less prioritized than other industrial activities, especially in low-income earning countries, mainly due to their low-profit margins. On the other hand, most global urban wastewater treatment plants (UWWTPs) depend on low-cost biological-based technologies such as the commonly used conventional activated sludge (CAS). Despite the effectiveness of CAS-based treatment systems in reducing pathogens and degradable organic matter in sewage, they are less effective in removing chemical micropollutants and biological contaminants. Moreover, the development of effective technologies for removing biological and chemical contaminants is compromised by emerging issues such as climate change. This further results in the scarcity of drinking water and deterioration of water quality. Therefore, using UWWTPs as recycling units for producing safe and reusable effluents is a promising method for enhancing sustainability and efficient utilization of the available water sources.

Even though the current UWWTP technologies can remove nitrogen and phosphorus from wastewaters with high efficiency, the biological removal of chemical micropollutants is still a challenge. Herein, Dr. Olga Nunes from the Universidade do Porto discussed the challenges of treating wastewaters. In particular, she explored the efficacy of using nature-based wastewater treatment technologies. The work is currently published in the research journal, Microbial Biotechnology.

The author noted that even though a wide range of microorganisms can degrade a vast number of micropollutants, they exhibit low bioavailability in biological reactions mainly due to the low concentration of such compounds in wastewaters. Consequently, final effluents produced from CAS-based UWWTPs contain high micropollutants at worrying concentrations. Advanced oxidation technologies (AOT) such as ozonation are among the best solutions for treating secondary effluents from CAS-based UWWTPs before discharge into water bodies. Besides degradation of unwanted chemical pollutants, AOTs can disinfect water and reduce the microbial load of wastewaters.

Unfortunately, using AOTs to recycle urban water may require additional treatment to remove toxic degradation productions, an overall expensive and time-consuming process. Consistently, the author, based on previous research findings, noted that some microbiota such as ARBs & ARGs can survive the AOT treatments and re-grow during the storage periods. The regrowth is characterized by the disturbance of the microbial community and a decrease in biodiversity. And similar phenomenon has been observed with other wastewater treatment technologies. This presents another challenge because the microorganisms can re-grow to a high level, thus compromising the treated water quality. Furthermore, cleaning of built environments, where disinfectants are frequently used, using aggressive agents also seems to favor microbiomes encoding functions leading to their growth.

In summary, Dr. Olga explored the treatment of wastewaters, the challenges involved, and possible remedies. Based on the findings, the author argued that upgrading UWWTPs to include the final disinfection step may not be adequate to transform the facilities into feasible and efficient wastewater recycling units. This calls for further research focusing on the design and implementation of storage systems capable of balancing the bacterial community before the stored, treated wastewater can be reused. For instance, measures like inoculation of disinfected wastewater with balanced natural microbial communities would restore the biodiversity and microbial richness of the wastewaters; thus, preventing the overgrowth of hazardous microorganisms. Therefore, the study provides critical expert opinions that would lead to a better understanding of the biotic relations in treated wastewaters and the technological implementation of advanced systems for high-quality wastewater treatment.