Eawag, Swiss Federal Institute of Aquatic Science and Technology, 8600 Dübendorf, Switzerland; ETH Zürich, Institute of Environmental Engineering, 8093 Zürich, Switzerland.
Central Environmental Laboratory, School of Architecture, Civil and Environmental Engineering, Ecole Polytechnique Fédérale de Lausanne Lausanne, Switzerland.
Sci Total Environ. 2022 Apr 1;815:152762. doi: 10.1016/j.scitotenv.2021.152762. Epub 2022 Jan 3.
The production of volatile fatty acids (VFAs) represents a relevant option to valorize municipal wastewater (MWW). In this context, different capture technologies can be used to recover organic carbon from wastewater in form of solids, while pre-treatment of those solids has the potential to increase VFA production during subsequent fermentation. Our study investigates how VFA composition produced by fermentation is influenced (i) by the choice of the capture technology, as well as (ii) by the use of thermal alkaline pre-treatment (TAP). Therefore, the fermentation of solids originating from a primary settler, a micro-sieve, and a high-rate activated sludge (HRAS) system was investigated in continuous lab-scale fermenters, with and without TAP. Our study demonstrates that the capture technology strongly influences the composition of the produced solids, which in turn drives the complexity of the fermenter's microbial community and ultimately, of the VFA composition. Solids captured with the primary settler or micro-sieve consisted primarily of polysaccharides, and led to the establishment of a microbial community specialized in the degradation of complex carbohydrates. The produced VFA composition was relatively simple, with acetate and propionate accounting for >90% of the VFAs. In contrast, the HRAS system produced biomass-rich solids associated with higher protein contents. The microbial community which then developed in the fermenter was therefore more diversified and capable of converting a wider range of substrates (polysaccharides, proteins, amino acids). Ultimately, the produced VFA composition was more complex, with equal fractions of isoacids and propionate (both 20%), while acetate remained the dominant acid (50%). Finally, TAP did not significantly modify the VFA composition while increasing VFA yields on HRAS and sieved material by 35% and 20%, respectively. Overall, we demonstrated that the selection of the technology used to capture organic substrates from MWW governs the composition of the VFA cocktail, ultimately with implications for their further utilization.
挥发性脂肪酸（VFAs）的生产是一种有价值的方法，可以利用城市废水（MWW）。在这种情况下，可以使用不同的捕获技术将废水中的有机碳以固体的形式回收，而这些固体的预处理有可能在随后的发酵过程中增加 VFA 的产量。我们的研究调查了发酵过程中 VFA 组成的变化，这些变化受到以下因素的影响：（i）捕获技术的选择，以及（ii）使用热碱性预处理（TAP）。因此，在连续实验室规模的发酵器中，研究了源自初沉池、微筛和高负荷活性污泥（HRAS）系统的固体的发酵情况，同时使用和不使用 TAP。我们的研究表明，捕获技术强烈影响产生的固体的组成，这反过来又驱动了发酵器微生物群落的复杂性，最终影响了 VFA 的组成。用初沉池或微筛捕获的固体主要由多糖组成，导致了专门降解复杂碳水化合物的微生物群落的建立。产生的 VFA 组成相对简单，其中乙酸和丙酸占 VFAs 的>90%。相比之下，HRAS 系统产生的富含生物质的固体与较高的蛋白质含量相关。然后在发酵器中发展的微生物群落因此更加多样化，能够转化更广泛的底物（多糖、蛋白质、氨基酸）。最终，产生的 VFA 组成更加复杂，异丁酸和丙酸的比例相等（均约为 20%），而乙酸仍然是主要的酸（约 50%）。最后，TAP 并没有显著改变 VFA 的组成，而是分别将 HRAS 和筛选材料的 VFA 产量提高了 35%和 20%。总的来说，我们证明了用于从 MWW 中捕获有机底物的技术的选择控制着 VFA 混合物的组成，最终对其进一步利用产生影响。
