Dr Carla Mae Pausta

Domestic wastewaters have a significant concentration of nutrients that can be utilised as alternative sources of phosphorus and nitrogen for agriculture applications. Chemical precipitation is one of the processes found to be an efficient way for nutrient recovery from various wastewater feed-stock. However, not all nutrients are in a form that can be readily recovered. Therefore, a pre-treatment process may be necessary for an efficient recovery of nitrogen and phosphorus. In this research, acid hydrolysis was performed as pre-treatment to release phosphorus from synthetic septage into soluble forms for the subsequent precipitation as struvite (MgNH 4 PO 4 ·6H 2 O) which is known as a slow-release fertiliser for application in agriculture. Results show that acid hydrolysis increases the phosphate concentration (PO 4-P) to 148.07 ± 1.78 from 61.50 ± 0.07 mg/L, showing the potential of hydrolysis as pre-treatment to efficiently recover nutrients in the form of struvite. The result can inform further research to develop efficient processes for the recovery of nutrients from domestic wastewater.

Nutrient recovery technologies have been constantly developed and optimised to address challenges in water and wastewater management, sanitation, and agri-food systems, while promoting sustainable management of resources and circular phosphorous economy. However, these technologies have been rarely explored beyond the laboratory-scale in developing countries where it is mostly needed. In this study, a nutrient recovery batch reactor system was installed at a local farm in the Philippines to process raw septage from an onsite sanitation system, a septic tank, to recover a high-value fertiliser for local crop production. The batch reactor was used for two processes, namely acid hydrolysis for pre-treatment of septage and chemical precipitation for recovered phosphorous fertiliser (RPF). The recovered fertiliser was then applied to produce eggplants and tomatoes, which are the common crops grown in the farm. Results show that an average of 290 g of RPF was produced for every 100 L of raw septage processed. With hydrolysis, 77% of the phosphate concentration were released as phosphates from the solid component of the raw septage. About 98.5% of phosphates were recovered from the hydrolysed septage. The RPF when applied to the farm’s eggplants and tomatoes has yields comparable to that of the commercial fertilisers. This study was able to demonstrate the potential of a resource-oriented sanitation system that promotes nutrient recycling towards sustainable agriculture that further leads to meeting the United Nations sustainable development goals, particularly zero hunger (goal 2), clean water and sanitation (goal 6), sustainable cities and communities (goal 11), and responsible consumption and production (goal 12).

Understanding the resources nexus such as food, energy, water, and land will play a crucial role in our progress towards sustainability and resilience. For example, food production is the main driver behind the excessive global use of mineral fertilisers. Though these fertilisers provide critical nutrients such as nitrogen and phosphorous, they also contribute significantly to the carbon footprint and embodied energy of the agri-food systems. In addition, these nutrients from agricultural runoff and sewage may also pollute and cause dead zones in our water bodies. On the one hand, phosphorous scarcity and food security could also pose an existential risk against the backdrop of feeding ten billion people by 2050. One emerging sustainability pathway is the green circular bioeconomy that encourages nutrient recycling from biowastes such as that agricultural waste, food waste, and domestic wastewater.

Increase in anthropogenic activities proliferated the consumption of resources such as phosphorus; and increase the adverse environmental impacts especially eutrophication on water resources such as lakes. Nutrient recovery from domestic wastewaters to produce a fertiliser has been explored to address these challenges in the context of a sustainable circular nutrient economy. Life cycle assessment (LCA) was performed to holistically assess the impacts of integrating a nutrient recovery system on wastewater and water resource management using Laguna de Bay, Philippines as the geographical boundary. The inventory was developed based on the results of the emerging nutrient recovery reactor operations and the application of the recovered fertiliser on the agricultural crops. The LCA results for the proposed scenario showed environmental benefits of about 83.6% freshwater eutrophication, 102.5% terrestrial ecotoxicity, 26.9% water consumption, 100.7% mineral resource scarcity, while the global warming potential is 95.4% higher than the baseline scenario. Results imply policy review for septage management, system optimisation, and evaluation of alternative methods of wastewater management, in terms of life cycle thinking and sustainability across the globe. The traditional linear supply chains brought about by the industrial revolution and economic development have ensued massive extraction of resources, and significant increase in waste generation resulting in the decline of planetary health 1. This affects transgressions in the global food security and increase in adverse environmental impacts that are interconnected with water-nutrient management and agricultural systems in hotspot regions, mainly in Asia 2. However, the improvement of the quality of water resources and nutrient pathways would require complex problem-solving and collective efforts from scientists, policy makers, and the rest of the society 3. Hence, a paradigm shift from the linear flow model to integrated industrial ecosystem is required, that adapts the circular economy approach and life cycle thinking 4. Nutrient recovery and recycling from waste streams, particularly wastewater, has been considered an efficient driver in closing the loop towards sustainable development and resilience in water-nutrient management 5. This would also particularly address the urgent challenges in phosphorus resource depletion and eutrophication in the context of agri-food systems, clean water, and sustainable sanitation 6. Eutrophication is one of the leading environmental issues, that is as complicated to control and manage as climate change 7,8. Developing countries in Asia, such as Philippines, are greatly affected with eutrophication due to high population density and lack of appropriate sewage and septage treatment systems 9. In fact, the biggest inland water body in the Philippines, Laguna de Bay (Laguna Lake), is already experiencing the effects of eutrophication with regular occurrences of mass fish mortalities 10. This affects 21.4 million people who rely on the lake as their major source of food, water, and livelihood. This prompted the Philippine government to amend its existing policies to update the wastewater effluent quality standards as most of the wastewater treatment plants do not involve nutrient removal yet 11,12. Consequently, about 84% of the households in the Philippines use OPEN