With the increase in human population and activities, there has also been an increase in wastewater being produced. Currently, wastewater volumes exceed 300 billion tons per year globally. While several factors contribute to the problem, human waste is now a key component in global nitrogen (N) and phosphorus (P) cycles. This excess of nutrients is bad for aquatic systems, as it causes eutrophication—the dense growth of harmful plants. The presence of these organisms alters the amount of oxygen and other nutrients in the sea, harming the entire ecosystem.
Eutrophication and algae blooms in the aquatic environment.
Fortunately, significant investments have been made in the wastewater industry to meet the regulations restricting point-source nutrient discharge. Wastewater management infrastructure are retrofitting to enhance the treatment levels and to remove more nutrients. However, the use of energy- and chemicals-intensive technologies in any intervention could have other environmental impacts. With this in mind, we constructed an integrated assessment model and performed the broad-scale examination of nutrient discharge in wastewater in 173 countries from 1990 to 2050, over three different time periods. This was evaluated along with a series of environmental impacts that ranged from the N and P cycles to climate change, stratospheric ozone depletion, atmospheric aerosol lading, chemical pollution, biodiversity loss and freshwater use, and integrated with socio-economic drivers such as population, urbanization, food- and water (consumption)-related factors, to understand the changing hotspots of impacts.
Results show that even though universal wastewater management would have an immediate positive effect on aquatic environments, the effect would be almost unnoticeable by 2030 given the ever-rising population and other negative factors. In fact, population growth, especially in developing countries, as well as the increase in dietary protein are the main contributing factors. With increasing populations, increasing daily protein consumption, and increasing urbanization with inadequate sanitary practices, the areas of concern, or impact hotspots, are predicted to transition from Asia to Africa by 2050. Africa alone is predicted to contribute to half of the global total N input from human waste by 2050. These combined trends can lead to significant environmental impacts in African countries, with less capacity to fund major investments in sanitation infrastructure.
Insufficient and inadequate sanitation facilities and poor management in most African countries.
Overall, while improving the wastewater infrastructure could significantly reduce the nutrient input to surface waters, it may have irreversible effects on the atmosphere and the broader environment. Emphasis on nutrient recycling, rather than nutrient removal, may be a potential solution to this problem. Examples include urine diversion and nutrient recovery, which also offer the opportunity to decrease the use of commercial fertilizers and thus offset the unwanted impacts.
Traditional wastewater treatment approaches require a paradigm shift to enhance resource efficiency and maximise sustainability.
Reducing consumption of high-protein human diets would also reduce this environmental impact, although interestingly, the wastewater-related impacts were more sensitive for plant-based proteins, as they usually contain twice as much P. Nonetheless, despite this interesting fact, plant-based diets are considered more environmentally sustainable compared with meat-rich diets because of the lower depletion of resources and reduced carbon emissions. Furthermore, environmental sustainability has to correspond to maintaining health nutrient. Interesting studies could therefore be conducted on the connections between dietary habits and waste management in the broad context of sustainability.
Waste management requires a systems-based approach, as various human and natural components interact across space and time. This study provides a useful insight into the complex dynamics of waste management. Understanding how to meet the growing needs of a growing population on a finite planet requires the collaboration of multiple agencies at various levels. Reducing nutrient discharge and tackling the potential trade-offs require the engagement of consumers, researchers, policymakers, and institutions.