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厌氧发酵是一种能够有效实现有机废物资源化和能源化的生物反应过程[1]。在我国,餐厨垃圾(FW)每年的产生量约为6×107 t,占城市固体废弃物总量的40%以上[2]。FW主要由易于降解的碳水化合物、蛋白质和脂质组成,具有较高的产甲烷潜力[3-4]。但是,单独发酵FW时,由于FW水解速度较快会积累挥发性脂肪酸(VFA),易发生系统抑制崩溃的后果[5]。已经有研究证明将剩余活性污泥(WAS)添加到FW厌氧发酵系统提高混合发酵运行性能的可行性[6]。与单独FW或WAS厌氧发酵相比,将2者进行厌氧混合发酵能够促使微生物发挥协同作用,稳定厌氧发酵性能。
目前,有关FW和WAS厌氧混合发酵系统的构型主要采用间歇进料的连续搅拌反应器(CSTR)[7-8]。然而,CSTR不能实现污泥停留时间(SRT)和水力停留时间(HRT)的有效分离,使得微生物难以持留,难以保障微生物的持续生长,而且CSTR的间歇式进料方式容易引起负荷冲击。动态膜生物反应器(DMBR)使用在膜基材表面上沉积/吸附形成的滤饼层作为过滤层,能有效防止生长缓慢的厌氧微生物尤其是产甲烷菌的流失,提供了较长SRT来维持大量微生物种群生长[9]。已有研究利用板框内置式膜组件,采用连续流运行模式,在2.8 g·L−1·d−1的负荷下,实现了基于DMBR进行玉米秸秆和FW的混合发酵[10]。连续流进料方式可以有效缓解间歇式进料方式引起的基质冲击,增加系统的缓冲能力。目前,有关连续流动态膜厌氧混合发酵系统的稳定运行的解析鲜见报道。
在厌氧混合发酵系统中,基质的混合比例是影响厌氧发酵的关键参数,李浩等[11]的研究结果表明,在FW和WAS厌氧混合发酵过程中,FW所占比例影响混合发酵的反应速率。同时,厌氧发酵系统的最优基质混合比也会随着系统的长期运行和菌群结构的驯化改变而变化[12]。食微比(F/M)是衡量有机负荷的重要参数[13],F/M与基质种类和接种物中微生物菌群密切相关,不同的F/M会影响系统的效能潜力。截至目前,很少有研究考虑基质混合比(FW/WAS)和F/M对厌氧混合发酵系统长期运行的影响。
本研究构建了FW和WAS的外置式动态膜厌氧混合发酵系统。在连续流条件下启动动态膜厌氧混合发酵系统,以实现系统的稳定运行;同时,对DMBR运行过程中动态膜的形成和固液分离的效果进行解析。通过FW/WAS的产甲烷潜能和动力学实验,优化连续流厌氧混合发酵系统的因素,结合F/M 动力学实验,评价FW/WAS与F/M对连续流厌氧混合发酵系统运行效能的影响。
连续流动态膜餐厨垃圾和剩余污泥厌氧混合发酵系统的运行效能
Operational efficiency of continuous anaerobic dynamic membrane co-digestion system with food waste and waste activated sludge
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摘要: 为探究厌氧动态膜生物反应器(DMBR)在典型城市有机废弃物厌氧发酵领域应用的可行性,以餐厨垃圾(FW)和剩余污泥(WAS)为处理对象,在连续流条件下探究动态膜FW和WAS厌氧混合发酵系统的运行效能,并优化基质混合比(FW/WAS)和食微比(F/M)。结果表明,以水力停留时间(HRT)和有机负荷(OLR)分别为62.5 d和(1.84±0.45) g·L−1·d−1为初始条件,在连续流下启动FW和WAS厌氧混合发酵系统,经过72 d的运行,系统pH稳定在7.6~8.0,平均甲烷产量达到(0.41±0.08) L·L−1·d−1,无短链挥发性脂肪酸(VFA)累积且TVFA/碱度最大比值仅为0.024,表明系统启动成功且运行稳定。通过对动态膜的特性分析可知,动态膜形成快速,可在较短时间内实现低浊度(<50 NTU)出料,动态膜截留效果显著。通过FW/WAS和F/M的批次优化实验可知,厌氧混合发酵系统最优FW/WAS为4.4∶1 (基于VS),定期调整优化FW/WAS有望取得更高的系统甲烷产率;相应的系统能够耐受的最大F/M为0.944,为后续充分发挥连续流动态膜FW和WAS混合发酵系统的最大效能提供依据。本研究结果可为典型城市有机废物厌氧发酵产甲烷系统的低碳高效稳定运行提供参考。Abstract: To explore the feasibility of anaerobic dynamic membrane bioreactor (DMBR) in the field of anaerobic digestion with typical urban organic wastes, the operating efficiency of the continuous anaerobic dynamic membrane co-digestion system with food waste (FW) and waste activated sludge (WAS) was investigated, and the substrate mixing ratio (FW/WAS) and the food to microorganism (F/M) ratio of the co-digestion system were also optimized. The results showed that the continuous anaerobic co-digestion with FW and WAS can be start-up under hydraulic retention time (HRT) of 62.5 days and organic loading rate (OLR) of (1.84±0.45) g·L−1·d−1. After 72 days of long-term operation, the system pH and average methane production were stable realized at 7.6-8.0 and (0.41±0.08) L·L−1·d−1, respectively without volatile fatty acids (VFA) accumulated and maximum TVFA/Alkalinity less than 0.024, which indicated that the stable system was realized. Through analysis of the dynamic membrane characteristics, the dynamic membrane can be formed rapidly with a low permeate turbidity (<50 NTU), indicated that the dynamic membrane interception effect was remarkable to achieve good permeate. Through the batch experiments to optimize the FW/WAS and F/M ratios, the optimal FW/WAS ratio of the co-digestion system was 4.4∶1 (based on VS) after long-term operation. Thus, a higher methane yield can be achieved through adjust FW/WAS ratio regularly. Moreover, the corresponding maximum F/M ratio was 0.944, which can be used to guide the subsequent operation of the continuous dynamic membrane co-digestion system with FW and WAS. This study can provide a reference for the low-carbon, high-rate and stable operation of anaerobic digestion system with typical urban organic wastes.
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表 1 基质和接种污泥的理化特性
Table 1. Physicochemical properties of substrate and seed sludge
供试对象 TS/
(g·L−1)VS/
(g·L−1)TCOD/
(g·L−1)SCOD/
(g·L−1)pH 乙酸/
(g·L−1)蛋白质/
(g·L−1)多糖/
(g·L−1)NH4+-N/
(g·L−1)FW 140.0±15.3 134.0±13.2 220.0±18.5 104.0±8.3 4.4 1.730 2.74±0.03 85.30±4.10 0.31±0.01 WAS 56.0±8.3 30.4±4.2 52.2±7.3 — — — — — — 混合基质 124.0±0.6 115.0±0.5 181.0±2.3 74.5±1.4 3.9 0.001±0.000 8.20±0.12 2.71±0.03 0.10±0.01 接种污泥 39.1±0.6 19.7±1.5 27.2±0.3 3.1±0.0 7.9 0.003±0.000 0.81±0.03 0.27±0.02 2.62±0.17 注:“—”表示未测定。 表 2 批次实验的运行设置
Table 2. Operating characteristics of the batch experiments
实验项目 FW/WAS F/M 接种物/mL FW/mL WAS/mL 混合基质/mL 蒸馏水/mL FW单发酵 1∶0 0.206 30 0.905 0 — 3.095 WAS单发酵 0∶1 0.206 30 0 4.000 0 FW/WAS混合发酵 3∶1 0.206 30 0.680 1.000 — 2.320 FW/WAS混合发酵 4∶1 0.206 30 0.725 0.800 2.475 FW/WAS混合发酵 4.4∶1 0.206 30 0.740 0.740 2.520 FW/WAS混合发酵 5∶1 0.206 30 0.755 0.670 2.575 FW/WAS混合发酵 6∶1 0.206 30 0.775 0.575 2.650 F/M混合发酵 4.4∶1 0.090 30 — 0.960 14.040 F/M混合发酵 4.4∶1 0.176 30 1.865 13.135 F/M混合发酵 4.4∶1 0.354 30 3.750 11.250 F/M混合发酵 4.4∶1
4.4∶10.472
0.56730
305.000
6.00010.000
9.000F/M混合发酵 F/M混合发酵 4.4∶1 0.708 30 7.500 7.500 F/M混合发酵 4.4∶1 0.944 30 10.000 5.000 F/M混合发酵 4.4∶1 1.417 30 15.000 0 注:“—”表示不适用。 表 3 不同FW/WAS和F/M通过修正Gompertz模型和一级动力学模型拟合后产甲烷性能参数
Table 3. Kinetic parameters of CH4 production with respect to different FW/WAS and F/M obtained from the modified Gompertz model and first-order model
实验项目 FW/WAS F/M 修正的Gompertz模型 一级动力学模型 P0/mL Rmax/mL t0/d R2 P0/mL k/d-1 R2 FW单发酵 1∶0 0.206 16 4 0.2 0.975 17 0.287 0.971 WAS单发酵 0∶1 0.206 325 22 0.7 0.984 344 0.022 0.988 FW/WAS混合发酵 3∶1 0.206 70 6 0 0.984 74 0.160 0.993 FW/WAS混合发酵 4∶1 0.206 78 10 0 0.982 86 0.169 0.989 FW/WAS混合发酵 4.4∶1 0.206 82 11 0 0.985 88 0.172 0.994 FW/WAS混合发酵 5∶1 0.206 67 9 0 0.987 74 0.179 0.990 FW/WAS混合发酵 6∶1 0.206 63 8 0 0.985 68 0.181 0.991 F/M混合发酵 4.4∶1 0.090 51 105 0 0.985 51 2.610 0.977 F/M混合发酵 4.4∶1 0.176 91 85 0 0.979 91 1.610 0.989 F/M混合发酵 4.4∶1 0.354 166 99 0 0.969 169 0.968 0.981 F/M混合发酵 4.4∶1 0.472 219 126 0 0.980 223 0.874 0.987 F/M混合发酵 4.4∶1 0.567 240 118 0 0.982 246 0.751 0.990 F/M混合发酵 4.4∶1 0.708 277 106 0 0.989 286 0.575 0.996 F/M混合发酵 4.4∶1 0.944 325 43 0.02 0.994 402 0.135 0.984 F/M混合发酵 4.4∶1 1.417 0 0 2.0 0.902 0 0 0 -
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