Supporting data for "Production of Polyhydroxyalkanoates (PHAs) from urban food waste with mixed microbial culture"

As urban areas expand and economies advance, municipal solid waste accumulation becomes a pressing concern world wild. Among various urban wastes, food waste (FW) is a major component. The typical Chinese FW is predominantly starch-based, offering rich resources including carbon, nitrogen, and phosphorus. This makes it an optimal candidate for anaerobic fermentation (AF), wherein the wasted carbon is transformed into volatile fatty acids (VFA) and subsequently used to produce PHA. In light of this, this study delves into an innovative biological process that integrates FW fermentation with a PHA mixed microbial culture (MMC) to accomplish waste reduction and simultaneous resource recovery.In the combination of FW fermentation and single-stage PHA MMC, a substantial CODVFA/g VS0 of 0.51 ± 0.07 g was gained with a CODVFA/COD of 0.7 during FW fermentation for effective PHA accumulation. Across a 198-day span, overall 80% CODVFA was removed, and a maximum PHA content rate of 39.1 ± 7.7 g/g VSS with a yield of 0.17 ± 0.06 g/g CODVFA was achieved. An overall yield of 8.0% wt PHA/CODVFA was estimated based on the mass balance calculation. Bioinformatics analysis results revealed that Xanthobacter was the most dedicated contributor to PHA producing with an abundance remaining at almost 60% regardless of changes in carbon source, loading rate, or nutrients amount.Despite FW, the wasted activated sludge (AS) generated by wastewater treatment plants (WWTPs), also constitutes a significant portion of urban waste. The co-fermentation of FW and AS enhanced VFA production, yielding a CODVFA/g VS0 of 0.43 ± 0.06 g and a high CODVFA/COD of 78.5%. Over the 186 days of operation, the PHA MMC achieved a peak PHA% of 40.0 ± 4.2 g/g VSS, with a yield of 0.14 ± 0.07 g/g CODVFA, and an overall PHA yield of 12.5% wt PHA/ CODVFA daily. The incorporation of AS for fermentation notably elevated the proportion of propionate in VFAs, leading to a transition from polyhydroxybutyrate (PHB)-dominant to polyhydroxyvalerate (PHV)-dominant PHA composition. The 16S rRNA analysis revealed the genus Mesorhizobium crucially contributed to PHA generation, maintaining dominance throughout the whole operation period.To address the distinct kinetics for biomass growth and PHA accumulation, and to mitigate the adverse effects of PHA production-related sludge bulking, a novel waste conversion system which comprised of an FW fermenter and a 2-stage PHA MMC was studied. The FW fermentation yielded a CODVFA/g VS0 of 0.53 g and a CODVFA/COD of 73.2%, which served as feedstock for the 2-scale system spanning 120 days. Throughout this period, a PHA accumulation of 46.4% was achieved, with a PHA yield of 0.16, ultimately attaining a maximum daily PHA production yield of 12.1% wt PHA/ CODVFA. 16S rRNA analysis revealed consistent trends in the functional microbial community of the 2-stage MMC that the initially dominated Leucobacter and Xanthobacter were gradually instead of. the coexistence of diverse functional microorganisms. Overall, the findings of this study suggested the combination of FW-based fermentation and PHA MMC holds promise as an appropriate technology for urban waste reduction and resource recovery.

随着城市扩张与经济发展，城市生活垃圾堆积已成为全球亟待解决的严峻问题。在各类城市生活垃圾中，餐厨垃圾（food waste, FW）占比颇高。典型中国餐厨垃圾以淀粉类物质为主，富含碳、氮、磷等营养元素，使其成为厌氧发酵（anaerobic fermentation, AF）的理想底物：餐厨垃圾中的废弃碳源可经厌氧发酵转化为挥发性脂肪酸（volatile fatty acids, VFA），进而用于合成聚羟基脂肪酸酯（polyhydroxyalkanoates, PHA）。鉴于此，本研究聚焦于一种创新生物工艺，将餐厨垃圾发酵与聚羟基脂肪酸酯混合微生物培养（mixed microbial culture, MMC）体系相结合，以实现垃圾减量化与资源同步回收。

在餐厨垃圾发酵与单级聚羟基脂肪酸酯混合微生物培养体系中，餐厨垃圾发酵阶段的挥发性脂肪酸化学需氧量/初始挥发性固体（CODVFA/g VS₀）可达0.51±0.07 g，挥发性脂肪酸化学需氧量/总化学需氧量（CODVFA/COD）为0.7，可实现高效的聚羟基脂肪酸酯合成。在198天的运行周期内，挥发性脂肪酸化学需氧量整体去除率达80%，最高聚羟基脂肪酸酯含量可达39.1±7.7 g/g挥发性悬浮固体（VSS），产率为0.17±0.06 g/g CODVFA；通过物料衡算估算，整体聚羟基脂肪酸酯产率为8.0%（质量占比，PHA/CODVFA）。生物信息学分析结果显示，黄色杆菌属（Xanthobacter）是聚羟基脂肪酸酯合成的核心功能菌，无论碳源、负荷率或营养盐水平如何变化，其相对丰度始终维持在约60%。

除餐厨垃圾外，污水处理厂（wastewater treatment plants, WWTPs）产生的剩余活性污泥（activated sludge, AS）也是城市生活垃圾的重要组成部分。餐厨垃圾与剩余活性污泥的混合发酵可提升挥发性脂肪酸产量，其挥发性脂肪酸化学需氧量/初始挥发性固体可达0.43±0.06 g，挥发性脂肪酸化学需氧量/总化学需氧量高达78.5%。在186天的运行周期内，聚羟基脂肪酸酯混合微生物培养体系的最高聚羟基脂肪酸酯含量可达40.0±4.2 g/g挥发性悬浮固体，产率为0.14±0.07 g/g CODVFA，整体日度聚羟基脂肪酸酯产率达12.5%（质量占比，PHA/CODVFA）。添加剩余活性污泥进行混合发酵可显著提升挥发性脂肪酸中丙酸的占比，使聚羟基脂肪酸酯的组成从以聚羟基丁酸酯（polyhydroxybutyrate, PHB）为主转变为以聚羟基戊酸酯（polyhydroxyvalerate, PHV）为主。16S rRNA基因测序分析显示，中慢生根瘤菌属（Mesorhizobium）在聚羟基脂肪酸酯合成中发挥关键作用，且在整个运行周期内始终占据菌群优势地位。

为解决微生物生长与聚羟基脂肪酸酯合成的动力学差异问题，并缓解聚羟基脂肪酸酯生产过程中伴生的污泥膨胀负面影响，本研究开发了一种新型垃圾转化系统，该系统由餐厨垃圾发酵罐与两级聚羟基脂肪酸酯混合微生物培养体系组成。该系统中的餐厨垃圾发酵阶段可实现挥发性脂肪酸化学需氧量/初始挥发性固体为0.53 g，挥发性脂肪酸化学需氧量/总化学需氧量为73.2%，以此作为两级体系的底物，运行周期达120天。在该运行周期内，聚羟基脂肪酸酯合成率可达46.4%，产率为0.16，最终最高日度聚羟基脂肪酸酯产率达12.1%（质量占比，PHA/CODVFA）。16S rRNA基因测序分析显示，两级聚羟基脂肪酸酯混合微生物培养体系的功能菌群呈现一致的演替趋势：初始占优势的勒克菌属（Leucobacter）与黄色杆菌属（Xanthobacter）逐渐被多种功能微生物的共存群落所取代。

综上，本研究结果表明，餐厨垃圾发酵与聚羟基脂肪酸酯混合微生物培养体系的结合技术，在城市垃圾减量化与资源回收领域具有良好的应用前景。