Producing fertilizer from wastewater
Utilizing wastewater from a fertilizer factory, an author group at Ho Chi Minh City University of Technology recovered struvite (MgNH4PO4.6H2O) to produce slow-release fertilizer for agricultural use.
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NPK fertilizers are produced from struvite. Photo: NNC
Depending on input materials and production technologies, each chemical fertilizer plant produces different types of wastewater. Pollutants present in chemical fertilizer factory wastewater, such as NH, inorganic acids H2SO4, H3PO4, soluble salts, suspended solids, etc. In particular, chemical fertilizer factory wastewater also contain large amounts of nutrients Nitrogen (N), Phosphorus (P). These substances in large concentrations can cause an excess of nutrients in rivers and lakes, affecting the ecosystem.
To treat this wastewater to meet environmental standards, most factories are applying physico-chemical technology to treat the above wastewater, especially wastewater containing a lot of N and P. According to this method, enterprises must consume a large amount of chemicals and energy to process, in addition, cause secondary pollution.
Wastewater sources were collected by the authors from fertilizer plants in Binh Dien, the Netherlands, and Ca Mau Fertilizer to analyze and evaluate the content of substances in wastewater, such as N, P2O5, K2O, pH, etc. , the authors give parameters to perform the recovery of Struvite (Magnesium ammonium phosphate hydrate - MgNH4PO4.6H2O) from wastewater with high concentrations of N and P.
According to Assoc. Prof. Dr. Le Minh Vien, be in charge of research, struvite is a common crystal in nature, in the form of insoluble (very little soluble). Struvite is slightly soluble in water and solutions, so the slow release of struvite has created an effective source of N, P and Mg for foliar or soil application. Using fertilizers from slow-release struvite can reduce 20-30%, or even more, compared to conventional fertilizers and still have the same yield.
Research results at the laboratory scale show that technological parameters, such as pH, molar ratio of Mg (Magnesium)/P, N/P, and reaction time affect the struvite precipitation efficiency. In which, the most influential parameters are pH, molar ratio Mg/P, N/P.
With the technological parameters to achieve recovery efficiency above 80%, the molar ratio Mg/P=1.0 and N/P= 1.2; pH=8.3, time is 60 minutes at ambient temperature. By precipitation method, the product obtained is struvite powder with particle size from 13-22 micrometers, nutrient content (Mg, N and P) suitable for making slow-dissolving fertilizer for agricultural production.
The author's project has been accepted by Ho Chi Minh city Department of Science and Technology, and the results are satisfactory.