Precipitation of struvite by sustainable waste materials and use as slow release fertilizer – A circular economy approach

Abstract

The increased concern on the quantity of wastewater generation subsequent degradation in the quality of surface water sources, especially through eutrophication has urged many researchers to find sustainable ways to recover the nutrients and reuse as a natural fertilizer. Precipitation and simultaneous removal of struvite, otherwise called as magnesium ammonium phosphate hexahydrate (MgNH4PO4.6H2O), from the wastewater using natural coagulants will be a better alternative. In the present study, the wastewater rich in ammonia was treated using sustainable modus operandi and nutrient-rich struvite was recovered. The objective of the research was to (i) optimize the quantity and struvite precipitation rate and study the effect of pH and (ii) germinate the seed (cereals) with optimal struvite dosage. Initially, the wastewater obtained from the hostel was characterized and subsequently coagulated using natural coagulants like pumpkin seeds and fish bones to precipitate the struvite. The raw wastewater found to have a pH of 6.64±0.32, the turbidity 304±28 NTU, ammoniacal nitrogen 32±3.9 mg/L, total solids 2240±72 mg/L and total alkalinity as 950±25 mg/L. The struvite with varied dosages in the order of 0.25 to 1.5 grams per 500 grams of soil was used for seed germination. At an optimal dosage of 0.5 grams per 500 grams of soil showed an effective plant growth and increased yield. Additionally, the wastewater after recovering struvite can be treated with a reed-bed system providing a circular economical solution for the modern agriculture industry.