Effect of directional switching frequency on toluene degradation in a vapor-phase bioreactor

A potential method to improve biomass distribution and the stability of vapor-phase bioreactors is to operate them in a directionally switching mode such that the contaminant air stream direction is periodically reversed through the reactor. In this study, the effect of switching frequency (SF) on bioreactor performance and biodegradation activity was investigated at 1-, 3- and 7-day SFs using toluene as a model compound. Rapid losses of biodegradation capacity and serious bioreactor instability were observed in the bioreactor operated at a 1-day SF. It is hypothesized that the frequent dynamic loading conditions at the 1-day SF hindered biofilm development and ultimately bioreactor stability. In contrast, bioreactors operated at the 3- and 7-day SFs achieved overall removal efficiencies of greater than 99% for 72 and 59 days of operation, respectively. Following each air-stream reversal, the bioreactor operated at the 7-day SF required 48 h to fully restore biodegradation capacity in the inlet bioreactor section. The 1-day SF bioreactor required no such reacclimation period. The toluene-degrading activity in the inlet section of the 7-day SF bioreactor dropped by 71% during the 7-day cycle, whereas it decreased by only 11% in the inlet of the 3-day SF bioreactor. These declines suggest that continuous or near-continuous exposure to toluene can inhibit microbial activity. Of the three SFs examined, the 3-day SF yielded the most efficient bioreactor performance by balancing reacclimation requirements with biodegradation activity losses.     

Bioaugmentation of a rotating biological contactor for degradation of 2-fluorophenol

The performance of a laboratory scale rotating biological contactor (RBC) towards shock loadings of 2-fluorophenol (2-FP) was investigated. During a period of ca. 2 months organic shock loadings of 25 mg L?1 of 2-FP were applied to the RBC. As no biodegradation of 2-FP was observed, bioaugmentation of the RBC with a 2-FP degrading strain was carried out and, along ca. 6 months, organic shock loadings within a range of 25-200 mg L?1 of 2-FP were applied. Complete biodegradation of 50 mg L?1 of 2-FP was observed during operation of the reactor. The RBC showed to be robust towards starvation periods, as after ca. 1month of non-supply of the target compound, the reactor resumed 2-FP degradation. The inoculated strain was retained within the biofilm in the disks, as the 2-FP degrading strain was recovered from the biofilm by the end of the experiment, thus bioaugmentation was successfully achieved.     

Membrane bioreactor for drinking water denitrification

The aim of this study is to evaluate the performance of a membrane bioreactor with cell recycle to be used for drinking water denitrification, when operated with a high nitrate load (up to 7.68?kgNO₃ ^?/m³?day) and low hydraulic retention time (down to 0.625?h). Nitrate and nitrite were always completely removed for all the operational conditions used. The effluent's nitrite concentration kept below 0.1?mg NO₂ ^?/l with exception of a short period, during the reactor start-up, when it accumulates. The performance of the membrane bioreactor was also evaluated using a groundwater containing 148?mg NO₃ ^?/l. Nitrate and nitrite concentration in the effluent were below the recommended values for drinking water when the reactor was controlled at pH 7.0. The membrane flux decreases during operation as a consequence of membrane fouling. The flux decrease was more severe during operation with synthetic medium than with contaminated groundwater due to the existence of molecular complexes in the synthetic broth. A backshock technique was used to reduce the surface fouling of the membrane. Combining this technique with the use of a reserve asymmetric structured membrane it was found that the membrane flux remains nearly unchanged.     

Long-term effect of weak nitrogen limitation on polyhydroxyalkanoates production of propionate-fed activated sludge operated at long sludge retention time

A sequencing batch reactor (SBR) submitted to aerobic dynamic feeding condition was fed with weakly nitrogen-limited substrate (COD/N ratio of 60?mg/mg, propionate as the sole carbon source), and operated at 15?days sludge retention time (SRT). Then, the nitrogen-limited sludges at different cultivating periods (45th, 120th, 195th and 240th days) were harvested to conduct aerobic batch experiments of PHAs production under various nitrogen concentrations. Experimental results indicated that PHAs accumulating behavior of the propionate-fed sludge declined significantly after long-term cultivation, implying that weak nitrogen limitation and long SRT operation cannot achieve a stable PHAs producing performance of the sludge. Supplementing enough nitrogen was consequently a requisite to guarantee the stability of the propionate-fed PHAs accumulating culture. Besides, the sludge with higher PHAs content in SBR did not ensure a better PHAs producing capability in the batch PHAs production phase. Batch experiments also indicated that the propionate-fed sludge with 0.7?N?mmol/L exhibited a better PHAs producing capability than with other nitrogen concentrations.     

Biodegradation of organic wastes containing surfactants in a biomass recycle reactor.

The microbial biodegradation of simulated graywater, containing 21.5 mg of linear alkylbenzene sulfonate liter-1, was investigated with a continuous-flow bioreactor with 100% biomass recycle. Low concentrations of organic matter in the ultrafiltration eluate were achieved by hydraulic residence times as short as 1.6 h and for periods of up to 74 days at a hydraulic residence time of 6 h. Upon a shift from the chemostat to the biomass recycle mode, the increase in biomass with time approximated a linear rather than an exponential function. Biomass densities as high as 6.8 g of cell protein liter-1 were reached; this was 50-fold higher than the steady-state biomass level in chemostats fed the same medium. We assessed physiological changes in the microbial community after a switch from the chemostat to the biomass recycle mode. Over 150 h, there was a two- to fourfold decrease in the respiratory potential of the microbes. After this decrease, respiratory potentials were relatively constant up to 74 days of operation. A decline in reactivity was also indicated by increasing lag periods before growth in response to organic nutrient inputs and by a decrease in the proportion of cells able to reduce tetrazolium dye. However, the bioreactor system was still capable of rapidly metabolizing inputs of organic matter, because of the very high biomass concentrations. It appears that < 10% of the organic carbon inputs accumulate as biomass.     

反应器进水管生物膜中喹啉降解菌的分离鉴定及降解特性

【背景】喹啉是一类高毒、致癌且难降解的含氮杂环化合物,本实验室建立了一个长期高效运行的反硝化喹啉降解生物反应器。【目的】从反应器进水管富集的生物膜中筛选有氧条件下降解喹啉的菌株。【方法】通过以喹啉为唯一碳源的培养基来富集、分离、纯化菌株;利用16S rRNA基因的序列分析鉴定分离株的系统发育地位;比较不同pH及温度条件下菌株的喹啉降解特性。【结果】经鉴定,4株分离物Q1、Q3、Q7和Q8分别属于Sphingobium、Massilia、Rhodococcus和Dyadobacter属。降解实验表明,以上菌株均能在48 h内实现50 mg/L喹啉的完全去除,但各自表现出不同的降解特性,其中Q1、Q3和Q8在降解过程中都检测到了喹啉降解产物2-羟基喹啉的积累。降解喹啉的Sphingobium、Massilia和Dyadobacter属菌株尚未见报道。【结论】从喹啉降解生物反应器的进水管内分离的4株喹啉降解菌可为设计处理含喹啉工业废水的反应器提供新菌种资源,对于完善喹啉生物降解机理研究具有实际意义。     

Phenol biodegradation in hybrid hollow-fiber membrane bioreactors

Hollow-fiber membrane bioreactors were developed with granular activated carbon (GAC) for the biodegradation of phenol using Pseudomonas putida. Hollow fibers showed similar structure with/without GAC incorporated; while GAC hollow fiber had a stronger phenol adsorption capacity. In batch biotransformation experiments, complete depletion of 1000 mg phenol l⁻¹ (at which concentration free cells cannot grow) was accomplished in the reactor within 18 h in the hybrid bioreactor, comparing with 23 h in the GAC free bioreactor. Desorption and bioregeneration of the hollow-fiber membrane were believed to be the key for the enhancement of bioreactor performance. At continuous running, the GAC bioreactor showed its superiority over the GAC free bioreactor during start-up and elevated loading phase. More than 90% of the phenol was transformed in the GAC bioreactor when the phenol loading was <24 mg h⁻¹. The better bioreactor performance may be due to the enhanced mass transportation and adsorption capacity with the incorporation of GAC.     

Removal of ammonium via simultaneous nitrification-denitrification nitrite-shortcut in a single packed-bed batch reactor

A polyurethane packed-bed-biofilm sequential batch reactor was fed with synthetic substrate simulating the composition of UASB reactor effluents. Two distinct ammonia nitrogen concentrations (125 and 250 mg l(-1)) were supplied during two sequential long-term experiments of 160 days each (320 total). Cycles of 24h under intermittent aeration for periods of 1h were applied, and ethanol was added as a carbon source at the beginning of each anoxic period. Nitrite was the main oxidized nitrogen compound which accumulated only during the aerated phases of the batch cycle. A consistent decrease of nitrite concentration started always immediately after the interruption of oxygen supply and addition of the electron donor. Removal to below detection limits of all nitrogen soluble forms was always observed at the end of the 24h cycles for both initial concentrations. Polyurethane packed-bed matrices and ethanol amendments conferred high process stability. Microbial investigation by cloning suggested that nitrification was carried out by Nitrosomonas-like species whereas denitrification was mediated by unclassified species commonly observed in denitrifying environments. The packed-bed batch bioreactor favored the simultaneous colonization of distinct microbial groups within the immobilized microbial biomass. The biofilm was capable of actively oxidizing ammonium and denitrification at high ratios in intermittent intervals within 24h cycles.     

High efficiency degradation of tetrahydrofuran (THF) using a membrane bioreactor: identification of THF-degrading cultures of<Emphasis Type="Italic"> Pseudonocardia</Emphasis> sp. strain M1 and<Emphasis Type="Italic"> Rhodococcus ruber</Emphasis> isolate M2

A mixed microbial culture capable of growing aerobically on tetrahydrofuran (THF) as a sole carbon and energy source was used as the inoculum in a 10 l working volume membrane bioreactor. Following start-up, the reactor was operated in batch mode for 24 h and then switched to continuous feed with 100% biomass recycle. On average, greater than 96% of THF fed to the reactor was removed during the 8-month study. THF loading rates ranged from 0.62 to 9.07 g l^–1 day^–1 with a hydraulic retention time of 24 h. THF concentrations as high as 800 mg/l were tolerated by the culture. Biomass production averaged 0.28 kg total suspended solids/kg chemical oxygen demand removed, i.e., comparable to a conventional wastewater treatment process. Periodic batch wasting resulted in a solids retention time of 7–14 days. Reactor biomass typically ranged from 4 to 10 g/l volatile suspended solids and the effluent contained no solids. Pure THF-degrading cultures were isolated from the mixed culture based on morphological characteristics, Gram-staining and THF degradation. Based on 16S rDNA analysis the isolates were identified as Pseudonocardia sp. M1 and Rhodococcus ruber M2.     

短程硝化启动运行中功能菌群变化研究

【目的】短程硝化-厌氧氨氧化是可实现的最短生物脱氮工艺,短程硝化是实现该工艺的重要环节和必要条件。【方法】采用序批式反应器(SBR)来实现短程硝化过程的启动和稳定运行,并对该过程中的相关功能菌群变化进行检测分析。【结果】通过控制低DO浓度(<1 mg/L)和逐步提高氨氮进水负荷,可抑制氨氧化细菌(NOB)菌群增殖并促进亚硝酸氧化菌(AOB)菌群规模显著扩大,实现短程硝化过程的启动和稳定运行。在氨氮进水负荷为0.055 kg/(m3.d)时,平均氨氮去除容积负荷和污泥负荷可达到0.043kg/(m3.d)和0.16 kg/(kg.d),平均亚硝酸盐积累率可达到83.4%。在短程硝化启动和稳定运行过程中,NOB菌群密度从2.0×105CFU/mL降至1.5×104CFU/mL,相对丰度从5.51%降至2.14%;AOB菌群密度从4.5×104CFU/mL增加至1.5×107CFU/mL,相对丰度从0.18%增加至7.25%。【结论】AOB菌群规模的扩大是实现短程硝化和氨氮去除能力提高的主要原因,同时较高的进水氨氮浓度和负荷也会造成亚硝化活性的抑制。     

In situ nitrogen removal in phase-separate bioreactor landfill

The feasibility of in situ nitrogen removal in phase-separate bioreactor landfill was investigated. In the experiment, two sets of bioreactor landfill systems, namely conventional two-phase and in situ nitrogen removal bioreactor landfills, were operated. The in situ nitrogen removal bioreactor landfill (NBL) was comprised of a fresh-refuse filled reactor (NBLF), a methanogenic reactor (NBLM) and a nitrifying reactor (NBLN), while the two-phase bioreactor landfill (BL) used as control was comprised of a fresh-refuse filled reactor (BLF) and a methanogenic reactor (BLM). Furthermore, the methanogenic and nitrifying reactors used aged refuse as bulk agents. The results showed that in situ nitrogen removal was viable by phase-separation in the bioreactor landfill. In total 75.8 and 47.5 g of nitrogen were, respectively, removed from the NBL and the BL throughout the experiment. The methanogenic reactor used the aged refuse as medium was highly effective in removing organic matter from the fresh leachate. Furthermore, the aged refuse was also suitable to use as in situ nitrification medium. The degradation of fresh refuse was accelerated by denitrification in the initial stage (namely the initial hydrolyzing stage) despite being delayed by denitrification in a long-term operation.     

Anaerobic treatment of synthetic medium-strength wastewater using a multistage biofilm reactor

A laboratory-scale multistage anaerobic biofilm reactor of three compartments with a working volume of 54-L was used for treating a synthetic medium-strength wastewater containing molasses as a carbon source at different influent conditions. The start-up period, stability and performance of this reactor were assessed at mesophilic temperature (35 °C). During the start-up period, pH fluctuations were observed because there was no microbial selection or zoning, but as the experiment progressed, results showed that phase separation had occurred inside the reactor. COD removal percentages of 91.6, 91.6, 90.0 and 88.3 were achieved at organic loading rates of 3.0, 4.5, 6.75 and 9.0 kg COD/m³ day, respectively. A decrease in HRT from 24 to 16 h had no effect on COD removal efficiency. When HRT decreased to 8 h, COD removal efficiency was still 84.9%. Recirculation ratios of 0.5 and 1.0 had no effect on COD removal but other factors such as the volatile fatty acid (VFA) content were affected. The effect of toxic shock was also investigated and results showed that the main advantage of using this bioreactor lies in its compartmentalized structure.     

Degradation of phenol by Rhodococcus erythropolis UPV-1 immobilized on Biolite in a packed-bed reactor

A strain of Rhodococcus erythropolis has been isolated and identified by 16S rRNA sequencing. Cells acclimated to phenol can be adsorbed on the external surface of beads of the ceramic support Biolite where they grow forming a network of large filaments. Exponentially-growing cells were adsorbed faster than their stationary-phase counterparts. Immobilization resulted in a remarkable enhancement of the respiratory activity of cells and a shorter lag phase preceding the active phenol degradation. Under optimum operation conditions, the immobilized cells in a laboratory-scale column reactor packed with support beads were able to degrade completely phenol in defined mineral medium at a maximum rate of 18 kg phenol m(-3) per day. The performance of the bioreactor in long-term continuous operation was characterized by pumping defined mineral medium which contained different concentrations of phenol at different flow-rates. Once phenol biodegradation in defined mineral medium was well established, an industrial wastewater from a resin manufacturing company, which contained both phenol and formaldehyde, was tested. In this case, after wastewater conditioning (i.e. pH, nitrogen source and micronutrient amendments) the immobilized cells were able to remove completely formaldehyde and to partly biodegrade phenols at a rate of 1 kg phenol m(-3) per day.     

厌氧氨氧化膨胀床反应器的运行性能

试验研究了以竹炭为载体的厌氧氨氧化膨胀床反应器的运行性能.接种反硝化污泥,用模拟废水可成功启动该反应器:运行至144 d时,容积总氮去除率达到3.02 kg N/m3/d.这是国内文献报道的最高水平.动力学分析表明.这种反应器的最大容积总氮去除率可迭12.77 kg N/m3/d.具有很大的脱氮潜能.反应器的启动过程可分为菌体自溶、活性延滞和活性提高三个阶段.与此相应,污泥性状也从黄褐色絮状污泥变为棕灰色颗粒污泥和红色颗粒污泥.红色颗粒污泥以杆茵和球菌为主.厌氧氨氧化活性可达0.56mg TN/(mgprotein)/h,它们是反应器厌氧氨氧化功能的主要承载者.     

对-氯代苯胺(PCA)在填充床生物反应器中的降解作用

以氯代苯胺(PCA)为选择基质,用驯化技术从降解对二氯苯(p-DCB)的富集培养物中得到了以同化PCA为唯一碳源和氮源的混合微生物。将这种固定在填充床反应器中的微生物用于PCA的降解作用研究中。在该反应器里,PCA的生物降解遵循Logistic方程q=q_max/(1+e^α-βU_v).由方程求出了主要的动力学常数,K_s(半速率常数)和q_max(最大比基质降解速率).于PCA降解的同时,释放氯离子到培养基中。在水力停留时间3h, 进水PCA浓度为360mg·L^-1情况下,基质的体积降解率达到125mg·L^-1·h^-1;基质的百分去除率为91%.     

Biofilm population dynamics in a trickle-bed bioreactor used for the biodegradation of aromatic hydrocarbons from waste gas under transient conditions

The dynamics of a multispecies biofilm population in a laboratory-scale trickle-bed bioreactor for the treatment of waste gas was examined. The model pollutant was a VOC-mixture of polyalkylated benzenes called Solvesso 100. Fluorescence in-situ hybridization (FISH) was applied in order to characterise the population composition. The bioreactor was operated under transient conditions by applying pollutant concentration shifts and a starvation phase. Only about 10% of the biofilm mass were cells, the rest consisted of extracellular polymeric substances (EPS). The average fraction of Solvesso 100-degrading cells during pollutant supply periods was less than 10%. About 60% of the cells were saprophytes and about 30% were inactive cells. During pollutant concentration shift experiments, the bioreactor performance adapted within a few hours. The biofilm population exhibited a dependency upon the direction of the shifts. The population reacted within days after a shift-down and within weeks after a shift-up. The pollutant-degraders reacted significantly faster compared to the other cells. During the long-term starvation phase, a shift of the population composition took place. However, this change of composition as well as the degree of metabolic activity was completely reversible. A direct correlation between the biodegradation rate of the bioreactor and the number of pollutant-degrading cells present in the biofilm could not be obtained due to insufficient experimental evidence.     

Activation of an indigenous microbial consortium for bioaugmentation of pentachlorophenol/creosate contaminated soils

Soil activation, a concept based on the cultivation of biomass from a fraction of a comtaminated soil for subsequent use as an inoculum for bioaugmentation of the same soil, was studied as a method for the aerobic biodegradation of pentachlorophenol (PCP) and polycyclic hydrocarbons (PAH) in contaminated soils. A microbial consortium able to degrade PCP and PAH in contaminated soil from wood-preserving facilities was isolated and characterized for PCP degradation and resistance. To obtain an active consortium from the contaminated soil in a fed-batch bioreactor, the presence of soil as a support or source of nutrients was found to be essential. During the 35 days of bioreactor operation, residual PCP in solution remained near zero up to a loading rate of 700mg/l per day. The PCP meneralization rate increased from 70 mg/l per day when no PCP was added to the bioreactor to 700 mg/l per day at the maximum loading rate. The consortium tolerated a PCP concentration of 400 mg/l in batch experiments. Production of a PCP-degrading consortium in a fed-batch slurry bioreactor enhanced the activity of PCP biodegradation by a factor of ten. PAH biodegradation increased, during the same time period, by a factor of 30 and 81 for phenanthrene and pyrene, respectively. Preliminary laboratory-scale results indicated that a significant reduction in the time required for degradation of PCP and PAH in contaminated soil could be achieved using activated soil as an inoculum.Issued as NRC 33861 correspondence to: R. Samson     

A GAC biofilm reactor for the continuous degradation of 4-chlorophenol: treatment efficiency and microbial analysis

Using a continuous enrichment technique, a bacterial consortium capable of degrading 4-chlorophenol (4-CP) was obtained from the rhizosphere of Phragmites australis. A granular activated carbon (GAC) biofilm reactor was established using this consortium, and the degradation of 4-CP was investigated under continuous flow operation using a feed of 20-50 mg l(-1) with a hydraulic residence time of 17 min over a 6-month period. Chloride liberation occurred throughout the operation, and the reactor had 4-CP removal efficiencies of 69-100%. Periods of lower performance were attributed to clogging of the column with biomass and the formation of channels. Subsequently, the immobilized biofilm was subjected to a starvation period of 5 months, after which its degradative capacity was still maintained. The microbial consortium was characterized during the continuous flow experiment and dynamic population changes were observed throughout. One isolate recovered from the biofilm was shown to be capable of degrading 4-CP as a sole carbon and energy source.     

Characteristics and stability of aerobic granules cultivated with different starvation time

The characteristics of aerobic granules at steady state and the effects of starvation time on the stability of aerobic granules during the long-term operation were investigated in three sequencing batch reactors (SBRs R1–R3). The SBRs were operated with a cycle time of 1.5, 4.0, and 8.0 h, respectively, which resulted in a starvation time of 0.8, 3.3, and 7.3 h in three reactors, respectively. Results showed that aerobic granules were successfully cultivated in the three reactors, but the granules in R2 with a starvation time of 3.3 h showed the highest density and the best settleability at steady state. It is obvious that the starvation time has an optimum value in terms of settleability of granules. In addition, it was found that the coexistence of a minority of fluffy granules with smooth granules was the potential unstable factor in R1 with a starvation time of 0.8 h at the steady state. The sudden dominance of fluffy granules in R1 after the 160-day operation led to the operation failure of the reactor R1, whereas the granules in R2 with a starvation time of 3.3 h and R3 with a starvation time of 7.3 h showed good stability during the long-term operation. As short starvation time leads to the instability of granules, and long starvation time is not advisable for practical application due to low efficiency, starvation time should be controlled in a reasonable range.