【作者】 陈祥；

【导师】 盛奎川；

【作者基本信息】 浙江大学 ， 生物系统工程， 2014， 博士

【摘要】 餐厨垃圾以有机组分为主,通过厌氧发酵工艺将其转化为氢气、甲烷是能源化处置的重要方式之一。餐厨垃圾厌氧发酵中氮的控制有其重要的特殊性,发酵时有机氮不断氨化,控制对象不稳定,且反应体系内产氢菌和产烷菌特性殊异,协同控制难。本文对餐厨垃圾厌氧发酵独立产氢、独立产烷以及两相联产氢气和甲烷过程中的氨氮抑促特性进行研究,并针对餐厨垃圾厌氧发酵氮抑促特性,研究适于两相厌氧发酵的氨氮调控方法。主要结论如下：1)获取了氨氮控制水平与餐厨垃圾厌氧发酵氢气生产之间的相关关系。通过联合控制餐厨垃圾与接种污泥配比(Feedstock/Inoculum, F/I)及氨氮水平,可有效抑制产甲烷菌同时促进产氢菌,成功实现厌氧发酵生物制氢。低浓度氨氮对餐厨垃圾厌氧发酵产氢有促进作用。在产氢效果最佳的F/I (F/I=3.9)下,0.5-6.0g/L氨氮添加浓度对氢气生产具有促进作用,氨氮添加浓度为3.5g/L时获得最高氢气产量(121.4mL/gVS),相比未添加氨氮时提高57.3%。高浓度氨氮对餐厨垃圾厌氧发酵产氢有显著的抑制作用。氨氮添加浓度超过6.0g/L开始呈现抑制产氢,7.5和10.0g/L的氨氮添加浓度分别引起氢气产量减少14.3%和58.7%。2)获取了氨氮以及硝氮联合氨氮控制水平与餐厨垃圾厌氧发酵甲烷生产之间的相关关系。低浓度氨氮对产烷有一定的促进作用,高浓度氨氮对产烷有显著的抑制作用。在6.7g VS/L有机负荷下,氨氮添加浓度为0.5g/L时,甲烷产量提高5.1%；1.54g/L总氨氮浓度(氨氮添加浓度1.0g/L)被认定为氨抑制浓度阈值,氨氮浓度高于该阈值时,甲烷生产呈现受抑制状态,批式产烷过程中需调控总氨氮浓度≤1.54g/L。在产烷氨氮抑促特性研究基础上,试验评估了应用硝化工艺脱除循环厌氧发酵系统中高浓度氨氮的可行性。通过向厌氧发酵系统投加硝氮和氨氮,模拟发酵余液经硝化处理后回流至发酵系统以稀释氨氮浓度至特定水平。试验发现,在氨氮添加浓度为1.0g/L条件下,100-750mg/L硝氮可提高甲烷产量,但硝氮添加浓度高于1.0g/L时,甲烷生产受到抑制。在带有发酵余液回流的循环厌氧发酵系统中,硝化工艺具有很大的潜力,可用于脱除总氨氮浓度小于2.29g/L餐厨垃圾发酵余液中的氨氮。但当发酵余液中总氨氮浓度高于2.29g/L时,硝化工艺将不再适用于脱除系统中的氨氮,因为氨氮将被硝氮／亚硝氮所替代,而硝氮／亚硝氮在达到一定浓度时同样对产甲烷菌具有抑制作用。3)比较研究了餐厨垃圾与园林垃圾混合干湿发酵的产气性能及氨氮抑促特性。餐厨垃圾与园林垃圾混合发酵确认具有协同效应,增加原料中餐厨垃圾的百分比可提高甲烷产量,而增加原料中园林垃圾的百分比可缩短发酵保留时间。15%和20%TS干式发酵试验组的甲烷产量高于湿式发酵(5%和10%TS),而当TS含量增至25%时,甲烷产量显著下降。干式发酵反应体系内总氨氮浓度远高于湿式发酵,具有更大的潜力发生氨抑制现象。25%TS干式发酵下总氨氮浓度高达4.2g/L,引发了对产甲烷菌的初始抑制。餐厨垃圾与园林垃圾混合批式发酵试验中,不同混合配比下最终总氨氮浓度无显著差异。连续发酵试验中,以餐厨垃圾为单一原料发酵系统内的总氨氮浓度远高于以餐厨垃圾混合园林垃圾为原料的试验组,且当总氨氮浓度累积至高于1912mg/L时,甲烷生产受到抑制。在高有机负荷率下,餐厨垃圾与园林垃圾混合发酵相比于餐厨垃圾单一发酵具有更高的稳定性和氨氮耐受性。4)获取了氨氮控制水平与餐厨垃圾两相厌氧发酵氢烷生产之间的相关关系。控制产氢相有机负荷率为9.4g VS/(L·d),水力停留时间为4d,回流比为1.0,产烷相水力停留时间为20d,成功实现两相联产氢气和甲烷。产氢相氢气产量为47.7mL/g VS,产烷相甲烷产量达335.0mL/g VS.低浓度氨氮(<4044mg/L)对产氢相中的氢气生产有一定的促进作用,高浓度氨氮(>4044mg/L)对产氢有显著的抑制作用。总氨氮浓度为4256mg/L时,氢气产量减少51.8%,总氨氮浓度为4972mg/L时,氢气生产完全停止,且在高浓度氨氮下,产氢和产酸微生物均遭受严重的氨抑制作用。产烷相在经受总氨氮浓度低于5800mg/L的急性抑制作用后,可恢复到与受抑制前相当的产气水平。总氨氮浓度高于6200mg/L时,甲烷生产性能只能恢复至低于正常产气的水平。产烷相在长期经受高浓度氨氮(>6200mg/L)慢性抑制作用时,甲烷生产受到显著抑制,总氨氮浓度为9836mg/L时,甲烷产量减少53.2%。利用扩展的Monod方程可较好的模拟氨氮对甲烷生产的影响(R2=0.959)。联合调整水力停留时间、回流比以及利用稳定产气阶段留存的产烷相发酵余液置换发酵内容物,可有效调控两相系统中的总氨氮浓度降低至与氨抑制浓度阈值相当或以下的水平。经总氨氮浓度调控后,产氢相成功恢复氢气生产性能,产烷相在经受氨氮的慢性抑制作用后未能随总氨氮浓度的降低而恢复产气性能。更多还原

【Abstract】 Food waste is a biodegradable waste which has high organic contents. Bioenergy recovery through anaerobic digestion (AD) process is considered to be a sustainable food waste treatment practice, with hydrogen or methane rich biogas as the main product. Nitrogen control plays a vital role in the performance and stability of AD of food waste. Organic nitrogen in food waste is hydrolyzed to ammonia, and ammonia accumulation is potentially encountered during AD of food waste. The different characteristics and functions of microbial consortium during hydrogenogenesis and methanogenesis result in the hard synergetic control of microbial consortium. The ammonia characteristics of independent production of hydrogen or methane via one-phase AD, and co-production of hydrogen and methane via two-phase AD were investigated in this study. To optimize recovery of AD process following ammonia inhibition, ammonia control strategies were further explored. The main results are as follows:1) Effect of ammonia on hydrogen production from food waste via AD was studied. Successful hydrogen production from food waste was achieved by controlling feedstock to inoculum ratios (F/I), and ammonia concentrations at appropriate ranges. Hydrogen production could be enhanced by keeping ammonia at suitable levels. The proper range of total ammonia nitrogen (TAN) concentrations is0.5-6.0g/L at F/I3.9. The highest hydrogen yield (121.4mL/g VS) was achieved at the added TAN concentration of3.5g/L with an increase of57.3%compared to the control group without added ammonia. High concentration ammonia had negative effect on hydrogen production. The inhibition of ammonia on hydrogen production started to appear when the added TAN concentration was higher than6.0g/L. The addition of7.5and10.0g/L TAN resulted in14.3%and58.7%reduction of hydrogen yields, respectively.2) Effect of ammonia and nitrate on methane production from food waste via AD was investigated. At a VS loading of6.7g VS/L, lower added TAN concentrations (<1.0g/L) were beneficial to AD process, while higher TAN concentrations (>1.5g/L) caused an excessive inhibition of methanogenesis. Methane yield at the added TAN concentration of0.5g/L was increased by5.1%in comparison with the control group without added ammonia. TAN concentration of1.54g/L (with1.0g/L added TAN) corresponded to a threshold concentration for ammonia inhibition effect, above which ammonia would initiate inhibition of methanogenesis.Based on the study of ammonia effect on methane production, the suitability of nitrification process for ammonia removal from food waste digestate in the recirculated AD system was evaluated. In an attempt to simulate conditions of recycling digestate after nitrification treatment into the digestion system for ammonia dilution, the impact of nitrification products on AD performance was investigated by employing the nitrate as a variable compound with an added TAN concentration of1.0g/L. Results showed that added NO3-N concentrations in the range of100-750mg/L enhanced the methane production, while nitrate started to inhibit the methane production at added NO3-N concentrations higher than1.0g/L. Nitrification process can be potentially suitable for ammonia removal from food waste digestate with lower TAN concentrations (<2.29g/L). However, nitrification process would no longer be an appropriate technology for the digestate with higher TAN concentrations (>2.29g/L), since the ammonia was replaced by nitrate/nitrite that also had inhibitory effects on methanogenesis at certain concentrations.3) Comparison of high-solids to liquid anaerobic co-digestion of food waste and green waste was evaluated. Synergistic effects were found in co-digestion of food waste and green waste. Increasing the food waste percentage in the feedstock resulted in an increased methane yield, while shorter retention time was achieved by increasing the green waste percentage. Methane yields from high-solids AD (15-20%TS) were higher than the output of liquid AD (5-10%TS), while methanogenesis was inhibited by further increasing the TS content to25%. The high-solids AD system had much higher final TAN concentrations than that of the liquid AD system. Ammonia inhibition was more likely to be encountered in high-solids AD. A higher TAN concentration of4.2g/L at25%TS initiated inhibition of methanogenesis, leading to lower methane yields.During batch anaerobic co-digestion of food waste and green waste, no significant differences were observed in the final TAN concentrations at different mixing ratios. In the continuous AD trials, the TAN concentration in the digestion system with food waste as the single feedstock was much higher than that in the system with food waste and green waste as co-substrates. Higher TAN concentrations (>1912mg/L) caused an inhibition of methane production. Under high organic loading rates (OLR), higher process stability and ammonia tolerance capacity were achieved in co-digestion of food waste and green waste with respect to mono-digestion of food waste.4) Effect of ammonia on hydrogen and methane co-production from food waste by two-phase AD was investigated. A two-phase process with OLR9.4g VS/(Ld), hydraulic retention time (HRT)4d, recirculation ratio1.0for hydrogen reactor, and HRT20d for methane reactor, successfully achieved co-production of hydrogen and methane. The hydrogen yield in the hydrogen reactor was47.7mL/g VS, and the methane yield in the methane reactor was335.0mL/g VS. Lower TAN concentrations (<4044mg/L) improved hydrogen production in the hydrogen reactor, while higher TAN concentrations (>4044mg/L) caused an obvious inhibition of hydrogenogenesis. TAN concentrations of4256and4972mg/L caused51.8%and100%reduction in hydrogen production, respectively. Under higher TAN concentrations, both acid formers and hydrogen formers were subjected to severe inhibition of ammonia.Complete recovery was achieved in the methane reactor after acute inhibitory effects of lower TAN concentrations (<5800mg/L) on methanogenesis. Nevertheless, incomplete recovery to a level lower than the stable methane yield was followed after being subjected to higher TAN concentrations (>6200mg/L). The methane reactor long subjected to higher TAN concentrations (>6200mg/L) revealed chronic inhibition of methanogens. TAN concentration of9836mg/L caused53.2%drop in methane production. Effect of ammonia on the methane production was well simulated using the extended Monod equation (R2=0.959).An approach by adjusting HRT and recirculation ratio, and replacing reactor contents with the methane phase digestate retained at the steady stage was explored for controlling the ammonia inhibition. The approach was shown to effectively reduce the TAN concentrations in the two-phase system to levels comparable or lower than the ammonia inhibition threshold. Successful recovery was achieved in the hydrogen reactor after TAN reduction, while after chronic ammonia inhibition, the TAN reduction was still followed by a failed recovery in the methane reactor.更多还原