Environ Technol. 2014 May-Jun;35(9-12):1378-88. doi: 10.1080/09593330.2013.868531.
The freshwater microalga Chlorella vulgaris was harvested by autoflocculation resulting from the precipitation of magnesium or calcium compounds induced by a slow increase in pH in the absence of CO2 input. Autoflocculation was tested in two culture media with, respectively, ammonium (NH4+) and nitrate (NO3-) ions as nitrogen source. The culture pH increased because of photosynthesis and CO2 stripping. pH rose to 11 after 8 h in the NO3- medium, but did not exceed 9 in the NH4+ medium. No flocculation took place in any of the media. Autoflocculation tests were repeated in the NO(3-)-based culture medium by progressively increasing the concentrations of Ca2+ and Mg2+ until inorganic compounds precipitated and flocculated microalgae. The minimal concentrations for flocculation were found to be 120 mg Ca2 L(-1) and 1000 mg Mg2+ L(-1). These values were, respectively, 3.5 times and 20 times higher than those allowing flocculation by NaOH addition. Energy-dispersive X-ray spectroscopy, zeta potential measurement, and ionic chromatography suggest that the mechanisms involved are different. The rate of cell removal was close to 90% in both cases, but cells were more concentrated in the aggregates obtained by magnesium compound precipitation, with an estimated concentration close to 33 g (dry matter) L(-1), against 19 g L(-1) for calcium phosphates.
淡水微藻小球藻通过自絮凝进行收获，这是由于在没有 CO2 输入的情况下，pH 值的缓慢增加导致镁或钙化合物的沉淀。在没有 CO2 输入的情况下，自絮凝在分别以铵（NH4+）和硝酸盐（NO3-）作为氮源的两种培养基中进行了测试。由于光合作用和 CO2 吹脱，培养物的 pH 值增加。在 NO3- 培养基中，8 小时后 pH 上升到 11，但在 NH4+ 培养基中不超过 9。在任何一种培养基中都没有发生絮凝。在基于 NO3-的培养基中通过逐渐增加 Ca2+和 Mg2+的浓度重复进行自絮凝测试，直到无机化合物沉淀并絮凝微藻。发现絮凝的最小浓度分别为 120 mg Ca2 L-1和 1000 mg Mg2+ L-1。这些值分别是通过添加 NaOH 进行絮凝的 3.5 倍和 20 倍。能谱、动电电位测量和离子色谱表明，所涉及的机制不同。在这两种情况下，细胞去除率都接近 90%，但在通过镁化合物沉淀获得的聚集体中，细胞更集中，估计浓度接近 33 g（干物质）L-1，而磷酸钙为 19 g L-1。
