pH值和产甲烷抑制剂对两相耦合系统污泥发酵定向产乙酸的影响

采用产氢产乙酸/同型产乙酸两相耦合工艺对剩余污泥进行了半连续式厌氧发酵,主要研究了pH值和产甲烷抑制剂2-bromoethanesulphonate(BES)对耦合系统定向产乙酸的影响.结果表明:碱性pH(pH=10.0)和添加BES都能促进A相乙酸的积累,提高乙酸的产率,同时碱性pH比添加BES更有利于污泥的水解.当...     

Biogas generation apple pulp

In view of the pressing problem that appears in our region (Asturias, north of Spain) with the residues from the cider production, it was decided to test this kind of material as a co-substrate joint with slaughterhouse waste in a laboratory unit.     

Biodegradation performance of an anaerobic hybrid reactor treating olive mill effluent under various organic loading rates

The primary objective of this study was to evaluate the performance of a 20 l lab scale anaerobic hybrid reactor (AHR) combining sludge blanket in the lower part and filter in the upper part under varying organic loading rates (OLRs) in order to study biodegradation of olive mill effluent (OME). For this purpose, some parameters, such as total phenols, effluent chemical oxygen demand (COD), suspended solids (SS), volatile fatty acids (VFAs), and pH in the influent and effluent, and removal efficiencies for those parameters (except pH) were continuously monitored throughout the experimental period of 477 days. Eleven different organic loadings between 0.45 and 32 kg COD m⁻³ day⁻¹ were imposed by either varying influent COD or hydraulic retention time (HRT). The results demonstrated that the AHR reactor could tolerate high influent COD concentrations. Removal efficiencies for the studied pollution parameters were found to be as follows: COD, 50–94%; total phenol, 39–80%; color, 0–54%; and suspended solids, 19–87%. The levels of VFAs in the effluent, which was principally acetate, butyrate, iso-butyrate, and propionate, varied between 10 and 2005 mg l⁻¹ depending upon OLRs. A COD removal efficiency of 90% could be achieved as long as OLR is kept at a level of less than 10 kg COD m⁻³ day⁻¹. However, a secondary treatment unit for polishing purposes is necessary to comply with receiving media discharge standards.     

VFAs bioproduction from waste activated sludge by coupling pretreatments with Agaricus bisporus substrates conditioning

A novel strategy for improving volatile fatty acids (VFAs) bioproduction from waste activated sludge (WAS) was developed by coupling pretreatments with conditioning (CPC). Agaricus bisporus substrate (ABS) was used as external carbohydrate additive source of conditioning step. Pretreatment was studied in three ways: alkaline, alkaline-thermal and ultrasonic. WAS hydrolysis and protein degradation was distinctly improved by CPC treatments, resulting in a considerable enhancement of VFAs yield. The maximal VFAs yield was 614 ± 71, 712 ± 49 and 598 ± 19 mg COD/g VSS at pre-optimized alkaline, alkaline-thermal and ultrasonic CPC treatments, respectively, with an increase of 35%, 50% and 38% compared to the yields of pretreated WAS fermentation. Fourier transformed infrared spectroscopy and three-dimensional excitation-emission matrix fluorescence spectroscopy indicated that a synergistic effect occurred in co-digesting WAS and ABS. The conditioning of carbohydrate with feasible pretreatment provided large room for the digestibility improvement and the operation cost reduction in the whole WAS treatment system.     

Bacterial community dynamics during reduction of odorous compounds in aerated pig manure slurry

Aims:  To study the microbial community responsible for the reduction of the polluting load during aerobic digestion of pig slurry.
Methods and Results:  We analysed bacterial succession by nonculture-based methods and determined the physicochemical parameters and polluting substances during 6 days of aerobic digestion. The bacterial subpopulations evolved by aeration, predominantly Bacillus spp., degraded organic matter and vigorously consumed oxygen, as indicated by low oxidation–reduction potential (ORP). In this phase, the volatile fatty acid (VFA) levels drastically decreased, and VFAs were almost depleted on day 4. Simultaneously, the ammonia concentration decreased to its lowest level on day 4; thereafter, it increased until the end of the process. After the decrease in the total organic carbon content in the supernatant of the decomposed slurry, the ORP increased (∼0 mV), and the microbial community showed an abundance of lineages belonging to the phylum Proteobacteria.
Conclusions:  Bacillus was the predominant member of the bacterial community driving the VFA-removal process. Their predominance was related to the presence of available carbon, including VFAs and changes in ORP.
Significance and Impact of the Study:  Information on the relationships among the involved microbes, polluting materials and physicochemical parameters will aid process design and retrofitting of the process.     

Anaerobic hydrolysis and acidification of organic substrates: determination of anaerobic hydrolytic potential

This study aimed to develop a biochemical-test mainly to evaluate the hydrolytic-potential of different substrates and to apply this test to characterize various organic substrates. Outcome of this study can be used for optimization of the WWTPs through enhancement of N/P removal or anaerobic digestion. Out of four series of batch experiments, the first two tests were conducted to determine the optimal operating conditions (test duration, inoculum-ratio etc.) for the hydrolytic-potential test using secondary and synthetically-prepared sludges. Based on the results (generation of CODs, pH and VFA), test duration was fixed between 6 and 7 d allowing to attain maximum hydrolysis and to avoid methanogenesis. Effect of inoculum-ratios on acid fermentation of sludge was not significantly noticed. Using this methodology, third and fourth tests were performed to characterize various organic substrates namely secondary, pre-treated sludge, pig and two different cattle slurries. VFA production was shown to be substantially dependent on substrates types.     

Volatile fatty acids productivity by anaerobic co-digesting waste activated sludge and corn straw: Effect of feedstock proportion

Volatile fatty acids (VFAs) are the most suitable and biodegradable carbon substrates for many bioprocesses. This study explored a new approach to improve the VFAs production from anaerobic co-digesting waste activated sludge (WAS) with corn straw (CS). The effect of feedstock proportion on the acidification efficiency was investigated. The maximum VFAs yield (corresponding fermentation time) was substantially increased 69% (96 h), 45% (72 h), 13% (120 h) and 12% (120 h) with 50%, 35%, 25% and 20% CS proportion of feedstock, respectively. HAc (acetic acid) was consistently the most abundant, followed by HPr (propionic acid) and n-HBu (butyric acid) in the co-digesting tests. The increase of CS in feedstock led to more production of HAc and HPr. Moreover, the consumption of protein and carbohydrate were also improved remarkably from 2955 and 249 mg COD/L (individual WAS fermentation) to 6575 and 815 mg COD/L (50%_WAS:50%_CS co-digestion) from 120 onward, respectively. The highest contribution of CS to additional VFAs production was1113 mg VFAs (as COD)/g CS/L in the 65%_WAS:35%_CS co-digesting test. Our study indicated a valuable method to improve VFAs production from anaerobic co-digesting WAS and CS.     

Comparative study of the effect of ultrasonication on the anaerobic biodegradability of food waste in single and two-stage systems

Five different mesophilic systems were evaluated in this study for the anaerobic treatment of food waste. Systems A and B were one stage methane with unsonicated and sonicated feeds, respectively, while, systems C and D were two-stage hydrogen and methane with unsonicated and sonicated feeds, respectively. System E comprised a novel sonicated biological hydrogen reactor (SBHR) followed by methane reactor. The results showed that sonication inside the reactor in the first stage (system E) showed superior results compared to all other systems. Overall VSS removal efficiencies of 67%, 59%, 51%, 44%, and 36% were achieved in systems E, D, C, B, and A, respectively. Volumetric hydrogen production rates of 4.8, 3.3, and 2.6 L H₂/L_reactor d were achieved in the SBHR, CSTR with and without sonicated feed, respectively, while, methane production rates of 1.6, 2.1, 2.3, 2.6, and 3.2 L CH₄/L_reactor d were achieved in systems A-E, respectively.     

Fate of organic carbon in UAFB treating raw sewage: impact of moderate to low temperature

The anaerobic biological treatment of raw sewage under low ambient temperatures was investigated in an up-flow anaerobic fixed bed (UAFB) reactor, over a 220-day trial period. The operating temperature was lowered stepwisely from 35 to 25, 20 and 15 °C. Obvious accumulation of acetic acid was observed in the effluent as the temperature dropped, which almost tripled at 15 °C compared to that at 35 °C. An interesting psychrophilic-forward-shift trend of methane production rate following the decrease of temperature was discovered. The methane yield at each trial was 169, 201, 256 and 269 L_STP CH₄/kg COD_removed. For each temperature trial, about 32.6%, 28.3%, 34.4% and 34.9% were removed in form of methane. Based on PCR-DGGE results, the band corresponded to Methanosphaera spp. only showed up on 15 °C profile. Analysis of both methane production and DGGE results indicated that psychro-tolerant microorganisms dominated the archaeal populations in the UAFB under low-temperature.     

The effect of volatile fatty acids as a sole carbon source on lipid accumulation by Cryptococcus albidus for biodiesel production

The use of volatile fatty acids (VFAs) for microbial lipid accumulation was investigated in flask cultures of Cryptococcus albidus. The optimum culture temperature and pH were 25 °C and pH 6.0, respectively, and the highest lipid content (27.8%) was obtained with ammonia chloride as a nitrogen source. The lipid yield coefficient on VFAs was 0.167 g/g of C. albidus with a VFAs (acetic, propionic, butyric acids) ratio of 8:1:1, which was in good agreement with a theoretically predicted lipid yield coefficient of the VFAs as a carbon source. The major fatty acids of the lipids accumulated by C. albidus were similar to those of soybean oil and jatropha oil. A preliminary cost analysis shows that VFAs-based biodiesel production is competitive with current palm and soybean based biodiesels. Further process development for lower aeration cost and higher lipid yield will make this process more economical.