Resource-Oriented Sanitation: On-Farm Septage Treatment and Nutrient Recycling for Sustainable Agriculture in the Philippines

Abstract

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).

Life cycle assessment of nutrient recovery strategies from domestic wastewaters to quantify environmental performance and identification of trade-offs

“…For provinces, the current scenario for septic tanks, where septage are discharged to unauthorised dumpsites, is utilised as there is no current systematic monitoring yet for individual households and communities 13 . Scenario 3 covers the integration of STPs, and septic tanks with nutrient recovery system as proposed in our previous research study 21 . A pilot-scale nutrient recovery reactor was installed in a local university farm being resided by students and faculty, wherein septage was treated through hydrolysis and nitrogen and phosphorus fertiliser was recovered as struvite through chemical precipitation.…”

“…A pilot-scale nutrient recovery reactor was installed in a local university farm being resided by students and faculty, wherein septage was treated through hydrolysis and nitrogen and phosphorus fertiliser was recovered as struvite through chemical precipitation. Acid hydrolysis, in particular, was utilised as a pre-treatment method prior to the chemical precipitation to release the phosphorus and nitrogen into soluble forms and to kill the pathogens 21 . The recovered fertiliser was applied to crops as an alternative to commercial fertiliser.…”

“…The detailed inventories are presented in the Supplementary Information Tables S1 , S2 , S3 , and S4 . The flows and emissions for Scenario 3 were taken from the results of our previous research study on the pilot-scale nutrient recovery reactor that processes both sewage from a centralised wastewater treatment plant and septage from septic tank 21 . The other data for the conventional wastewater and septage treatment were taken from other literatures as cited.…”

“…Nutrient recovery from wastewater could provide new perspectives on lake water management that could stop nutrient pollution at household-level and potentially shift global problem-solving from end-of-pipe to process-integration solutions 20 . Recently, a pilot-scale nutrient recovery reactor has been installed at a local farm to provide a proof-of-concept on the potential of septage for resource recovery in the context of circular economy 21 . Although the technology is established, the application of this system would require further sustainability evaluation, as stakeholders would necessitate systematic and quantitative assessment of the risks and impacts 22 .…”

“…human waste) management at decentralised scale. A pilot-scale nutrient recovery reactor study carried out in the Philippines has produced significant results to provide technical evaluation of the potential of sewage and septage as a nutrient resource 21 . Moreover, utilising septage as resource for nutrient recovery is an opportunity, that is barely explored, to treat the major domestic wastewater discharge while providing an alternative fertiliser that could incur savings to local farmers and avoid further agricultural water run-offs.…”