温度与负荷对餐厨与果蔬垃圾混合厌氧消化酸化产物的影响

研究了餐厨果蔬生物质垃圾以一定比例混合后,控制不同温度和不同进料负荷条件的厌氧消化反应,观察酸化效果,达到定向产乙醇和乙酸的目的。结果表明,餐厨与果蔬垃圾的配比以可挥发性固体质量4∶1(VS),F/M=4∶1(VS),反应温度为45℃,初始负荷以总固体TS质量浓度为60 g/L时的定向酸化性能最佳,体系的溶解态化学需氧量SCOD最终达到1 100 mg/(g·L),可挥发性有机物浓度VFA达到320 mg/(g·L),相比反应开始时分别增加了50%和150%。厌氧水解和酸化过程基本同步,乙醇和乙酸在所测定的中间产物中比例最大,分别达到56%和42%,并且其产生过程持续进行。35℃条件适合乙醇转化为乙酸,55℃条件会快速进行乙醇型发酵。     

利用OLR和pH调控快速建立生物制氢反应器

以连续流搅拌槽式反应器(CSTR)作为反应装置,以糖蜜废水为底物利用活性污泥制取氢气,着重对有机负荷(OLR)和pH调控下生物制氢反应器乙醇型发酵的快速启动进行了研究.结果表明,在污泥接种量(以 VSS计)为17.74g/L、温度为35℃±1℃、水力停留时间(HRT)为6h的条件下,通过调节进水化学需氧量(COD)质量浓度和系统pH值,约12d就可以快速实现生物制氢反应器中微生物的主要代谢类型为乙醇型发酵,实现稳定的氢气生产.     

木糖厌氧发酵产氢特性研究

以木糖作为厌氧发酵产氢底物,热预处理(100℃,处理20 min)的厌氧颗粒污泥作为接种物,研究了中温条件(37℃)下厌氧发酵产氢特性.结果表明,当反应进行至50 h时,累积产氢量最大,为81.11 mL;乙酸、丁酸和乙醇是液相末端产物中的主要物质,其中乙酸和丁酸的浓度分别为1290 mg/L和1225 mg/L,发酵类型是典型的丁酸型发酵;反应体系的pH值开始降低,最后稳定在4.40左右,形成一个稳定的缓冲体系.     

生物制氢混合培养系统启动与运行的人工操作

采用连续流搅拌槽式反应系统(CSTR)作为反应装置,以糖蜜废水为发酵底物,污水处理厂剩余污泥为反应的启动污泥,着重对pH和氧化还原电位(ORP)调控下生物制氢反应器乙醇型发酵的启动进行了研究.结果表明:在温度为(35±1)℃,水力停留时间(HRT)为6h,进水COD为4000mg/L时,通过调节ORP和系统pH值可在约33d实现生物制氢反应器中微生物的主要代谢类型为乙醇型发酵,并实现稳定产氢.     

餐厨垃圾SBMR-ASBR两相厌氧消化产气性能研究

以学校食堂餐厨垃圾为原料,考察餐厨垃圾在SBMR-ASBR反应器中产酸和产甲烷性能。结果表明:高负荷下启动酸化相有利于系统快速形成稳定的乙醇型发酵,且可以避开丙酸型发酵,在10 g/(L.d)负荷(以VS计)下,稳定状态产酸率平均达到55 000 mg/L,VFA中乙醇和乙酸分别平均稳定在27 000 mg/L和23 000mg/L,两者共占总VFA的91%;甲烷相可以稳定运行的最高负荷为5 g/(L.d)(以VS计),此时,系统整体处理能力为3.3 g/(L.d),单位容积产气率达到2.3 L/(L.d),甲烷含量在65%～70%,TS,VS去除率分别达到77%,83%。在实际工程中可以高负荷启动酸化相,有利于系统形成稳定的乙醇型发酵和高负荷运行的甲烷相。     

餐厨垃圾与市政污泥协同厌氧制氢影响因素研究

以餐厨垃圾和市政污泥为研究对象,采用协同厌氧制氢工艺研究不同温度、物料配比对厌氧产氢潜力和中间代谢产物变化规律的影响。结果表明,55℃高温发酵时,餐厨垃圾单独厌氧发酵产氢效果最佳,产氢潜力、最大产氢速率分别为342.49 mL、41.48 mL/h,是35℃中温发酵的1.2倍。35℃中温发酵,餐厨垃圾与市政污泥配比为5∶1时氢气含量最高为56.4%。相关性分析表明,pH值与氨氮浓度呈正相关,与还原糖含量、累积产氢量呈显著负相关;还原糖含量与累积产氢量呈正相关,氨氮浓度与累积产氢量呈显著负相关。温度、物料配比和pH值的优化调控对协同厌氧制氢工艺的高效稳定运行具有重要意义。     

生物制氢反应系统的启动负荷与乙醇型发酵

采用连续流搅拌槽式反应器(CSTR),以糖蜜废水为底物,研究了COD容积负荷对生物制氢反应系统启动过程中形成的乙醇型发酵产氢能力的影响。研究表明,在污泥接种量不小于6.24 gVSS/L、启动负荷为7.0 kgCOD/m3.d、水力停留时间(HRT)为6 h、系统pH、氧化还原电位(ORP)分别在4.0~4.3、-440~-470mV之间等条件下,可在30 d内完成乙醇型发酵菌群的驯化,实现生物制氢反应系统的快速启动。由不同启动负荷(3.0、7.0、10.0 kgCOD/m3.d)条件下形成的乙醇型发酵菌群,在相同的运行条件下其产氢能力存在着差异。当系统容积负荷为30 kgCOD/m3.d时,由启动负荷为7.0 kgCOD/m3.d条件下驯化形成的乙醇型发酵菌群比由启动负荷为3.0 kgCOD/m3.d条件下驯化形成的乙醇型发酵菌群产氢能力高56%。     

基于UASB反应器的厨余厌氧发酵产氢研究

针对目前厨余连续流发酵产氢处理负荷不高、产氢率较低的难题,采用UASB反应器进行厨余发酵产氢研究。在温度为30℃,进水COD浓度为2 000~10 000 mg/L,水力停留时间为2~6 h条件下,产氢速率最大达到17.04 L/(L.d)。反应器内有颗粒污泥的形成,平均生物量达到6.17 g/L,为氢气的产生提供了有利保障。当出水pH为4.2~4.4,碱度为260~340 mg/L的条件下,乙醇和乙酸占挥发酸总量的89.2%,形成稳定的乙醇型发酵类型,反应器最高处理负荷COD达到60 kg/(m3.d)。试验结果表明,UASB反应器具有更高的产氢效能和更加稳定的产氢效果,能够为厨余发酵产氢提供有利的保障。     

TS对城市有机垃圾和剩余污泥联合厌氧消化的影响

在中温(35℃)条件下,以城市有机垃圾和污水处理厂剩余污泥为发酵原料,其中生活垃圾∶污泥=4∶1(w/w,干重),研究了固形物含量分别为3%,4%,6%,8%,10%对厌氧发酵过程及发酵效率的影响。结果表明:当发酵液TS为4%时厌氧发酵效率最高,发酵过程中pH适宜产甲烷菌生长,产气时间长,累积产气量最大,为11 967 mL,且甲烷含量较高;同时发酵过程中氨氮浓度升高缓慢,不会对甲烷菌造成氨抑制,对原料中有机质的降解效果明显,COD去除率为61.7%,TS去除率为47.19%,VS去除率为55.93%。     

酸化温度对玉米秸秆厌氧水解酸化性能的影响

文章研究了不同酸化温度(35,40,45℃)对玉米秸秆厌氧水解酸化性能的影响。研究结果表明:酸化温度对玉米秸秆水解酸化的程度以及产酸代谢类型有显著影响;当酸化温度为40℃时,玉米秸秆水解酸化产生的可溶性化学需氧量(SCOD)和挥发性脂肪酸(VFAs)的浓度最高,产生的气体以H_2和CO_2为主;酸化相的pH值为5.14～5.51,VFAs中乙酸和丁酸含量之和占VFAs总量的85.2%～91.4%,此时酸化相进行的是有利于甲烷化的丁酸型发酵;     

Hydrogen production potentials and fermentative characteristics of various substrates with different heat-pretreated natural microflora

Batch tests were carried out to investigate the effects of heat-pretreated inocula on the fermentative hydrogen production characteristics of various types of substrates. A total of 8 different inocula and 4 different substrates (starch, glycerol, oil and peptone) were used. Heat pretreatment of the inocula was conducted in order to harvest spore-forming clostridial bacteria. Significant hydrogen production potentials were observed from starch (20.5–174.4 ml H₂/g-COD_starch) and glycerol (11.5–38.1 ml H₂/g-COD_glycerol); however, almost no hydrogen was produced from oil and peptone. When starch was used as a substrate, two different fermentation patterns were observed, according to the inocula: butyric acid-type and ethanol-type fermentation. Polymerase chain reaction combined with denaturing gradient gel electrophoresis (PCR-DGGE) analysis was conducted to compare the bacterial structures cultivated on the starch medium. Different species of clostridial bacteria were observed between the butyric acid-type and ethanol-type fermentation cultures. When glycerol was used as a substrate, 1,3-propanediol was the main by-product with each inoculum. The results of the present study suggest that simultaneous production of ethanol or 1,3-propanediol in addition to hydrogen is a more promising strategy than conventional hydrogen production in acidogenesis.     

Application of rice rhizosphere microflora for hydrogen production from apple pomace

The combination of substrate materials and bacteria is an important factor affecting conversion technology for biological hydrogen production. We performed anaerobic hydrogen fermentation of apple pomace wastes using rhizosphere bacterial microflora of rice as the parent inoculum. In the vial test, the optimal condition for hydrogen fermentation was initial pH 6.0, 35 °C, and 73.4 g pomace per liter of medium (equivalent to 10 g-hexose/L). In the batch experiment (pH 6.0, temperature 35 °C) the hydrogen yield reached 2.3 mol-H₂/mol-hexose. The time course of biogas production and PCR-DGGE analysis suggest that Clostridium spp. decomposed degradable carbohydrates rapidly and a part of the refractory carbohydrate (e.g. pectin) gradually in the apple pomace slurry. In addition to hydrogen, volatile fatty acids (VFAs) were produced in the anaerobic fermentation of apple pomace, which can be a substrate for methane fermentation. The rice rhizosphere can be a promising source of inoculum bacteria for hydrogen fermentation in combination with plant material waste like apple pomace.     

Integrating waste activated sludge (WAS) acidification with denitrification by adding nitrite (NO2−)

Adding nitrite (NO₂⁻) to waste activated sludge (WAS) fermentation systems is an efficient approach to integrate fermentation with denitrification, and utilize volatile fatty acids (VFAs) to achieve a high nitrogen removal rate even at low C/N ratios. In this study, the effect of nitrite on the integrated WAS fermentation and denitrification (termed as WASFD) was investigated under acidic and alkaline conditions. The results indicated that adding nitrite achieved a most reduction of nitrite to N₂ and improved the acidification of WAS with high VFAs production. Under acidic condition (pH = 5), the maximum VFAs produced with nitrite addition was 3.3 times that without nitrite addition. Higher concentration of free nitrous acid (FNA) at the pH of 5 increased WAS particulates, improved the hydrolysis of organic substrates, and finally promoted VFAs yields. Under alkaline condition (pH = 9), adding nitrite only increased the VFAs production by 1.5 times, indicating that acidic condition was preferable for acidification than alkaline condition.     

海带发酵生产乙醇及其影响因素的控制研究

以海带为原料,在实验室条件下,通过微生物发酵过程,建立了海带生产乙醇的工艺流程,并对影响因素及其控制进行了研究。实验结果表明,海带通过发酵过程能使部分碳水化合物转变为乙醇,控制温度30-35℃、pH值为6-7和发酵时间6-7 d,可以获得最大的乙醇产率;酵母培养液磷酸盐和镁离子的最适营养浓度分别为3 g/L和1.5 g/L。这不仅为利用海带发酵生产乙醇提供了重要的技术参数,而且对开辟新的海藻生物能源具有一定的实践意义。     

Production of hydrogen and methane by one and two stage fermentation of food waste

Anaerobic digestion is an attractive process for generation of hydrogen and methane, which involves complex microbial processes on decomposition of organic wastes and subsequent conversion of metabolic intermediates to hydrogen and methane. Comparative performance of a sequential hydrogen and methane fermentation in two stage process and methane fermentation in one stage process were tested in batch reactor at varying ratios of feedstock to microbial inoculum (F/M) under mesophilic incubation. F/M ratios influence biogas yield, production rate, and potential. The highest H₂ and CH₄ yields of 55 and 94 mL g⁻¹ VS were achieved at F/M of 7.5 in two stage process, while the highest CH₄ yield of 82 mL g⁻¹ VS in one stage process was observed at the same F/M. Acetic and butyric acids are the main volatile fatty acids (VFAs) produced in the hydrogen fermentation stage with the concentration range 10–25 mmol L⁻¹. Little concentrations of VFAs were accumulated in methane fermentation in both stage processes. Total energy recovery in two stage process is higher than that in one stage by 18%. This work demonstrated two stage fermentation achieved a better performance than one stage process.     

Bioethanol production from mahula (Madhuca latifolia L.) flowers by solid-state fermentation

There is a growing interest worldwide to find out new and cheap carbohydrate sources for production of bioethanol. In this context, the production of ethanol from mahula (Madhuca latifolia L.) flowers by Saccharomyces cerevisiae in solid-state fermentation was investigated. The moisture level of 70%, pH of 6.0 and temperature of 30 °C were found optimum for maximum ethanol concentration (225.0 ± 4.0 g/kg flower) obtained from mahula flowers after 72 h of fermentation. Concomitant with highest ethanol concentration, the maximum ethanol productivity (3.13 g/kg flower/h), yeast biomass (18.5 × 10⁸ CFU/g flower), the ethanol yield (58.44 g/100 g sugar consumed) and the fermentation efficiency (77.1%) were also obtained at these parametric levels.     

Effect of hydraulic retention time on the hydrogen production in a horizontal and vertical continuous stirred-tank reactor

Hydraulic retention time (HRT) is the main process parameter for biohydrogen production by anaerobic fermentation. This paper investigated the effect of the different HRT on the hydrogen production of the ethanol-type fermentation process in two kinds of CSTR reactors (horizontal continuous stirred-tank reactor and vertical continuous stirred-tank reactor) with molasses as a substrate. Two kinds of CSTR reactors operated with the organic loading rates (OLR) of 12kgCOD/m3•d under the initial HRT of the 8 h condition, and then OLR was adjusted as 6kgCOD/m3•d when the pH drops rapidly. The VCSTR and HCSTR have reached the stable ethanol-type fermentation process within 21 days and 24 days respectively. Among the five HRTs settled in the range of 2–8 h, the maximum hydrogen production rate of 3.7LH₂/Ld and 5.1LH₂/Ld were investigated respectively in the VCSTR and HCSTR. At that time the COD concentration and HRT were 8000 mg/L and 5 h for VCSTR, while 10000 mg/L and 4 h for HCSTR respectively.Through the analysis on the composition of the liquid fermentation product and biomass under the different HRT condition in the two kinds of CSTR, it can found that the ethanol-type fermentation process in the HCSTR is more stable than VCSTR due to enhancing biomass retention of HCSTR at the short HTR.     

Biohydrogen from molasses with ethanol-type fermentation: Effect of hydraulic retention time

Though ethanol-type fermentation has many advantages for improving hydrogen production rate (HPR) in continuously mode hydrogen producing system, information on this fermentation is very deficient. The effect of hydraulic retention time (HRT) on biohydrogen production and operational stability of ethanol-type fermentation was investigated in a continuous stirred tank reactor (CSTR) using molasses as substrate. Five HRTs were examined, ranging from 4 to 10 h. At HRT 5 h, the highest HPR of 12.27 mmol L⁻¹ h⁻¹ was obtained from ethanol-type fermentation in the pH range of 4.3–4.4. During the whole operation process, ethanol, butyrate and acetate were the predominant metabolites. A total COD concentration of ethanol and acetate accounted for above 73.3% of total soluble microbial products. Linear regression showed that HPR and ethanol production rate were proportionately correlated at all HRTs which could be expressed as y = 0.9821x − 3.5151 (r² = 0.9498). It is meaningful that the proposed recovery of both hydrogen and ethanol from fermentation process can improve energy production rate and economic profit. Results demonstrated that the best energy production rate was 15.50 kJ L⁻¹ h⁻¹, occurred at HRT = 5 h.