Phosphorus recovery as struvite from hydrothermal carbonization liquor of chemically produced dairy sludge by extraction and precipitation

The work herein reported aimed to the study of phosphorus purification from liquid phase of hydrothermal treatment of dairy sludge by struvite precipitation. The sludge were produced by chemical process using iron salts as coagulants, and  the products had high iron content, which affected the quality of the product. The experiment was done to find process conditions for production of a commercial product (Struvite) with iron content lower than non-declarable value to maximize the purity of the product. The chemical extraction followed by precipitation enabled the phosphorus and iron recovery as struvite  and oxalate salts, respectively. Both products are useful in fertilizer and chemical applications, respectively. Struvite is a source of two primary plant macronutrients (Nitrogen and phosphorus) and one secondary macronutrient (magnesium). In addition, the small iron content (<2%) makes the product a potential source of plant micronutrients. The produced struvite was evaluated and demonstrated good nutrient availability and nutrient use efficiency.