Phosphate in wastewater can be recovered in the form of struvite crystals for use as slow-release fertilizer. Currently, struvite recovery often requires supplementing magnesium ions and raising pH with chemicals, making the recovered struvite unfavorable for organic production. In an effort for cleaner production, this study developed a versatile approach employing two mineral products in variable combinations for optimal supplementation of magnesium and elevation of pH. Magnesite, a mineral of MgCO, was ground and calcined without use of any catalysts. The magnesite calcined under the optimum conditions (800 °C for 30 min) can be dissolved in near-neutral filtrate of sludge digestate to supplement magnesium and raise pH for effective struvite formation. The OMRI-listed Epsom salts (MgSO∙7HO), mineral-based water-soluble commercial products, can be used to supplement magnesium without changing pH of alkaline wastewater. Six-hour batch operation of an air-lift crystallizer removed 85.7% and 94.7% of phosphate in hydrolyzed human urine when magnesium was amended to 1.2 × molar concentration of phosphate with calcined magnesite and an OMRI-listed Epsom salt, respectively. More than 98% of phosphate was removed from filtrate of sludge digestate in 3-h batch operation using calcined magnesite to raise pH to 8.5 and the Epsom salt for further magnesium supplementation. Struvite accounted for 85.7%, 90.5%, and 81.5% of the crystals recovered from urine with calcined magnesite, urine with Epsom salt, and filtrate with both mineral products, respectively. The material and energy costs of this green process were estimated to be $0.16/kg struvite from urine with calcined magnesite, $1.37/kg struvite from urine with Epsom salt, and $0.94/kg struvite from filtrate with both mineral products. This study proved the technical and economic feasibility of chemical-free magnesium supplementation and pH elevation, making the recovered struvite potentially certifiable for organic production.

中文翻译：

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回收鸟粪石用于有机生产：矿物质镁补充和 pH 值升高

废水中的磷酸盐可以以鸟粪石晶体的形式回收，用作缓释肥料。目前，鸟粪石回收往往需要补充镁离子并用化学品提高pH值，使得回收的鸟粪石不利于有机生产。为了实现清洁生产，本研究开发了一种多功能方法，采用两种矿物质产品的不同组合，以实现镁的最佳补充和 pH 值的升高。菱镁矿是一种 MgCO 矿物，在不使用任何催化剂的情况下进行研磨和煅烧。在最佳条件（800℃，30分钟）下煅烧的菱镁矿可以溶解在污泥消化液的近中性滤液中，以补充镁并提高pH值，以有效形成鸟粪石。 OMRI 列出的泻盐 (MgSO·7H2O) 是一种矿物基水溶性商业产品，可用于补充镁而不改变碱性废水的 pH 值。当用煅烧菱镁和 OMRI 列出的泻盐将镁分别修正为 1.2 倍磷酸盐摩尔浓度时，气升式结晶器的 6 小时批量操作可去除水解人尿中 85.7% 和 94.7% 的磷酸盐。使用煅烧菱镁矿将 pH 值提高到 8.5，并使用泻盐进一步补充镁，在 3 小时的间歇操作中，从污泥消化滤液中去除了超过 98% 的磷酸盐。在用煅烧菱镁矿的尿液、用泻盐的尿液和用两种矿物产品的滤液中回收的晶体中，鸟粪石分别占85.7%、90.5%和81.5%。据估计，这种绿色工艺的材料和能源成本为 0.16 美元/千克来自含有煅烧菱镁的尿液的鸟粪石，来自含有泻盐的尿液的鸟粪石为 1.37 美元/千克，来自含有两种矿物产品的滤液的鸟粪石为 0.94 美元/千克。这项研究证明了无化学补充镁和提高 pH 值的技术和经济可行性，使回收的鸟粪石有可能用于有机生产。