Citation: Pausta, C.M.J.; Promentilla, M.A.B.; Longos, A.L., Jr.; Orbecido, A.H.; Beltran, A.B.; Damalerio, R.G.; Suplido, M.E.A.A.; Saroj, D. Resource-Oriented Sanitation: On-Farm Septage Treatment and Nutrient Recycling for Sustainable Agriculture in the Philippines. Sustainability 2023, 15, 9904. https:// doi.org/10.3390/su15139904 Academic Editor: Marko Vincekovi´ c Received: 26 April 2023 Revised: 9 June 2023 Accepted: 19 June 2023 Published: 21 June 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). sustainability Article Resource-Oriented Sanitation: On-Farm Septage Treatment and Nutrient Recycling for Sustainable Agriculture in the Philippines Carla Mae Jabar Pausta 1 , Michael Angelo Baliwag Promentilla 2,3,4 , Alberto Leyes Longos, Jr. 2 , Aileen Huelgas Orbecido 2,3 , Arnel Bas Beltran 2,3 , Regina Gador Damalerio 2,3 , Maria Eda Apple Artesano Suplido 5 and Devendra Saroj 1, * 1 Centre for Environmental Health and Engineering (CEHE), School of Sustainability, Civil and Environmental Engineering, University of Surrey, Guildford GU2 7XH, UK; c.pausta@surrey.ac.uk 2 Center for Engineering and Sustainable Development Research, De La Salle University, 2401 Taft Avenue, Malate, Manila 1004, Philippines; michael.promentilla@dlsu.edu.ph (M.A.B.P.); alberto_longos@dlsu.edu.ph (A.L.L.J.); aileen.orbecido@dlsu.edu.ph (A.H.O.); arnel.beltran@dlsu.edu.ph (A.B.B.); regina_damalerio@dlsu.edu.ph (R.G.D.) 3 Department of Chemical Engineering, De La Salle University, 2401 Taft Avenue, Malate, Manila 1004, Philippines 4 National Research Council of the Philippines, General Santos Avenue Bicutan, Taguig 1630, Philippines 5 Agrivet Sciences Institute, De La Salle Araneta University, Salikneta Farm, Brgy. Upper Ciudad Real, San Jose Del Monte City 1475, Philippines; apple.suplido@dlsau.edu.ph * Correspondence: d.saroj@surrey.ac.uk Abstract: Nutrient recovery technologies have been constantly developed and optimised to address challenges in water and wastewater management, sanitation, and agri-food systems, while pro- moting 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 demon- strate 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). Keywords: circular economy; nutrients; onsite sanitation system; recovered phosphorous fertiliser (RPF); resource-oriented sanitation system; septage 1. Introduction Rapid urbanisation, population growth, and socio-economic development have caused a 3–4% increase in phosphorus (P) demand annually, leading to an accelerated P supply depletion [1,2]. Hence, it is expected that the future global security of agriculture and food (agri-food) systems will be compromised by year 2050 if P extraction continues to increase [3]. Moreover, the P in the agri-food supply chains following a linear pathway Sustainability 2023, 15, 9904. https://doi.org/10.3390/su15139904 https://www.mdpi.com/journal/sustainability