It has been estimated that about 15 % of the current nitrogen-fertilizer demand could be served by recovering the nitrogen-content in domestic sewage. In most sewage treatment plants employing the activated sludge process, the concentrated liquid stream (referred to as centrate) resulting from anaerobic digestion of the waste sludge offers a good opportunity for recovering nitrogen for use as fertilizer. This paper presents a non-pressurized gas-permeable membrane-based approach capable of recovering 98 % of the ammoniacal-nitrogen in the centrate as high purity fertilizer suitable for crop cultivation. In the proposed approach, ammoniacal-nitrogen in the centrate on the feed-side of the hydrophobic gas-permeable membrane is preferentially separated and absorbed into sulfuric acid on the product-side to yield ammonium sulfate solution. A tubular gas-permeable membrane reactor developed in this study was able to recover 21−133 g N/d per m² of membrane surface area, which is higher than the typical values of 2–62 g N/d per m² reported for more concentrated feeds. The highest yield recorded in this study was 2.1 g of ammonium sulfate per liter of centrate. Scanning electron microscope equipped with an energy dispersive x-ray spectrometer confirmed the presence of nitrogen, oxygen, and sulfur in the recovered fertilizer. Inductively coupled plasma optical emission spectrometer results confirmed that heavy metal levels in the recovered fertilizer were well below the regulatory levels for land application.

据估计，通过回收生活污水中的氮含量，可以满足当前氮肥需求的15％。在大多数采用活性污泥工艺的污水处理厂中，厌氧消化污泥产生的浓缩液流（称为浓缩液）为回收氮肥提供了很好的机会。本文提出了一种基于非加压透气膜的方法，该方法能够回收浓缩液中98％的氨氮作为适合农作物种植的高纯度肥料。在所提出的方法中，在疏水性透气膜的进料侧上的浓缩液中的氨氮被优先分离并在产物侧被吸收到硫酸中以产生硫酸铵溶液。²的膜表面积，高于报道的更浓缩饲料的典型值2–62 g N / d / m ²。在这项研究中记录的最高产量是每升浓缩液中有2.1克硫酸铵。配备有能量色散X射线光谱仪的扫描电子显微镜证实回收的肥料中存在氮，氧和硫。电感耦合等离子体发射光谱仪的结果证实，回收的肥料中的重金属含量远低于土地应用的监管水平。