Innovative treatment system for digester liquor using anammox process

This study demonstrated that partial nitritation using nitrifying activated sludge entrapped in a polyethylene glycol (PEG) gel carrier, as a pretreatment to anammox process, could be successfully applied to digester liquor of biogas plant at a nitrogen loading rate of 3.0 kg-N/m³/d. The nitritation process produced an effluent with a NO₂–N/NH₄–N ratio between 1.0 and 1.4, which was found to be suitable for the subsequent anammox process. A high SS concentration (2000–3000 mg/l) in the digester liquor did not affect partial nitritation treatment performances. Effluent from this partial nitritation reactor was successfully treated in the anammox reactor using anammox sludge entrapped in the PEG gel carrier with T-N removal rates of greater than 4.0 kg-N/m³/d. Influent BOD and SS contents did not inhibit anammox activity of the anammox gel carrier. The combination of partial nitritation and anammox reactors using PEG entrapped nitrifying and anammox bacteria was shown to be effective for the removal of high concentration ammonium in the digester liquor of a biogas plant.     

An innovative combined on-site process for the remote rural solid waste treatment--a pilot scale case study in China

The aim of this study was to find a feasible method for the treatment of solid waste generated in the remote rural, where the transportation costs are prohibitive and the resources to construct and maintain conventional treatment plants are not available. This process, consisted of two types of simulated bioreactor landfill (one was recirculated bioreactor landfill, and the other was comprised of fresh and aged refuse reactor) and a soil infiltration system, was operated in ambient temperature for 180 days all together. After treated by the system of fresh and aged refuse reactor, the refuse and leachate reached a strongly degraded and stable state. The remaining leachate can be treated by the soil infiltration system, and 87.5 ± 2.1%, 98.6 ± 1.0% and 95.7 ± 1.7% were achieved by 60 cm soil depths for organic matter, ammonium nitrogen and total nitrogen removal, respectively.     

Importance of the operating pH in maintaining the stability of anoxic ammonium oxidation (anammox) activity in moving bed biofilm reactors

Two bench-scale parallel moving bed biofilm reactors (MBBR) were operated to assess pH-associated anammox activity changes during long term treatment of anaerobically digested sludge centrate pre-treated in a suspended growth partial nitrification reactor. The pH was maintained at 6.5 in reactor R1, while it was allowed to vary naturally between 7.5 and 8.1 in reactor R2. At high nitrogen loads reactor R2 had a 61% lower volumetric specific nitrogen removal rate than reactor R1. The low pH and the associated low free ammonia (FA) concentrations were found to be critical to stable anammox activity in the MBBR. Nitrite enhanced the nitrogen removal rate in the conditions of low pH, all the way up to the investigated level of 50 mg NO₂-N/L. At low FA levels nitrite concentrations up to 250 mg NO₂-N/L did not cause inactivation of anammox consortia over a 2-days exposure time.     

Sudden failure of biological nitrogen and carbon removal in the full-scale pre-denitrification process treating cokes wastewater

A full-scale pre-denitrification process treating cokes wastewater containing toxic compounds such as phenols, cyanides and thiocyanate has shown good performance in carbon and nitrogen removal. However, field operators have been having trouble with its instability without being able to identify the causes. To clarify the main cause of these sudden failures of the process, comprehensive studies were conducted on the pre-denitrification process using a lab-scale reactor system with real cokes wastewater. First, the shock loading effects of three major pollutants were investigated individually. As the loading amount of phenol increased to 600 mg/L, more COD, TOC and phenol itself were flowed into the aerobic reactor, but phenol itself did not inhibit nitrification and denitrification, owing to the effect of dilution and its rapid biodegradation. Higher loading of ammonia or thiocyanate slightly enhanced the removal efficiency of organic matter, but caused the final discharge concentration of total nitrogen to be above its legal limit of 60 mg-N/L. Meanwhile, continuous inflow of abnormal wastewater collected during unstable operation of the full-scale pre-denitrification process, caused a sudden failure of nitrogen removal in the lab-scale process, like the removal pattern of the full-scale one. This was discovered to be due to the lack of inorganic carbon in the aerobic reactor where autotrophic nitrification occurs.     

Organic nitrogen exports from urban stormwater wetlands in North Carolina

Effluent organic nitrogen concentrations from seven constructed stormwater wetlands in North Carolina were examined to compare background organic nitrogen (ON) concentrations and the fraction of organic nitrogen relative to total nitrogen discharged. Seasonal influences on organic nitrogen concentrations were also examined. The median ON concentration from the stormwater wetlands was 0.78 mg l⁻¹, and despite differences in wetland design and influent ON characteristics, outlet ON concentrations from all but one wetland were not significantly different. ON export from all stormwater wetlands was significantly less than untreated runoff entering the wetlands (p = 0.002). In addition, median organic:total nitrogen (ON:TN) ratios from stormwater wetlands (0.75) were significantly greater than from untreated urban runoff (0.66), comparing more closely to ON:TN ratios collected from a naturally occurring wetland and reported in the literature for natural landscapes. Seasonal differences in organic nitrogen concentrations were identified with significantly lower concentrations during the winter. Though stormwater wetlands will not (and perhaps should not be expected to) completely remove total nitrogen loads from runoff, these results suggest constructed wetlands can play a role in restoring the balance between organic and inorganic nitrogen forms closer to that of an undisturbed landscape. The presence of background organic nitrogen concentrations from stormwater wetlands similar to those from a naturally occurring wetland highlights the importance of choosing appropriate metrics (e.g., effluent concentrations) when assessing treatment performance.     

Start-up and inhibition analysis of the Anammox process seeded with anaerobic granular sludge

The longer start-up period of the Anammox process is due to the very low cellular yield and growth rates of Anammox bacteria. Nitrite inhibition is considered to be the key factor in the instability of the Anammox process during the operation. However, little attention was paid to the inhibitory effect of pH and free ammonia. This paper presents start-up and inhibition analysis of an Anammox biofilm reactor seeded with anaerobic granular sludge. Results showed that the start-up period could be divided into the sludge lysis phase, lag phase, propagation phase, stationary phase and inhibition phase. Optimization control could be implemented correspondingly to accelerate the start-up of Anammox bioreactors. Effluent pH increased to 8.7–9.1 when the nitrogen removal rate was higher than 1,200 mg l⁻¹ day⁻¹. The free ammonia concentration was accompanied with a higher level of 64–73 mg l⁻¹. Inhibitory effects of high pH and free ammonia on Anammox bacteria contributed to the destabilization of the Anammox bioreactor during the first 125 days with influent KHCO₃ of 0.5 g l⁻¹. Increasing the suffering capacity in the inlet by dosing 1.25 g KHCO₃ l⁻¹ effectively reduced the pH variation, and the nitrogen removal performance of the reactor was further developed.     

Experimental simulation of oxygen profiles and their influence on baker's yeast production: II. Two-fermentor system

A reactor configuration consisting of two reactors with an exchange flow was used for the experimental simulation of large-scale conditions. The influence of fluctuations in oxygen concentration on the growth and metabolite production of baker's yeast was investigated by sparging one fermentor with air and one with nitrogen gas. It was found that the biomass yield decreased and the metabolite formation increased with rising circulation time (longer oxygen-unlimited and oxygen-limited periods). Not only was the performance of the oxygen-limited fermentor characterised by (partly) reductive metabolism, but that of the oxygen-unlimited fermentor as well. The results of the experiments in this reactor system were compared with those from the experiments carried out in a one-fermentor system with periodically changing oxygen concentrations. The formation of acetic acid, which is characteristic for transient states, showed a distinct difference between the two reactor systems.     

Fast start-up, performance and microbial community in a pilot-scale anammox reactor seeded with exotic mature granules

The possibility to introduce the exotic anammox sludge to seed the pilot-scale anammox granular reactor and its fast start-up for treating high nitrogen concentration wastewater were evaluated in this study. The reactor was started up successfully in two weeks; in addition, high nitrogen removal was achieved for a long period. Stoichiometry molar ratios of nitrite conversion and nitrate production to ammonium conversion were calculated to be 1.26 ± 0.02:1 and 0.26 ± 0.01:1, respectively. The Stover-Kincannon model which was first applied in granular anammox process indicated that the granular anammox reactor possessed high nitrogen removal potential of 27.8 kg/m³/d. The anammox granules in the reactor were characterized via microscope observation and fluorescence in situ hybridization technique. Moreover, the microbial community of the granules was quantified to be composed of 91.4-92.4% anammox bacteria by real-time polymerase chain reaction. This pilot study can elucidate further information for industrial granular anammox application.     

Development of a simultaneous partial nitrification and anaerobic ammonia oxidation process in a single reactor

Up-flow oxygen-controlled biofilm reactors equipped with a non-woven fabric support were used as a single reactor system for autotrophic nitrogen removal based on a combined partial nitrification and anaerobic ammonium oxidation (anammox) reaction. The up-flow biofilm reactors were initiated as either a partial nitrifying reactor or an anammox reactor, respectively, and simultaneous partial nitrification and anammox was established by careful control of the aeration rate. The combined partial nitrification and anammox reaction was successfully developed in both biofilm reactors without additional biomass inoculation. The reactor initiated as the anammox reactor gave a slightly higher and more stable mean nitrogen removal rate of 0.35 (± 0.19) kg-N m⁻³ d⁻¹ than the reactor initiated as the partial nitrifying reactor (0.23 (± 0.16) kg-N m⁻³ d⁻¹). FISH analysis revealed that the biofilm in the reactor started as the anammox reactor were composed of anammox bacteria located in inner anoxic layers that were surrounded by surface aerobic AOB layers, whereas AOB and anammox bacteria were mixed without a distinguishable niche in the biofilm in the reactor started as the partial nitrifying reactor. However, it was difficult to efficiently maintain the stable partial nitrification owing to inefficient aeration in the reactor, which is a key to development of the combined partial nitrification and anammox reaction in a single biofilm reactor.     

Acetone-butanol-ethanol (ABE) fermentation in an immobilized cell trickle bed reactor

Acetone-butanol-ethanol (ABE) fermentation was successfully carried out in an immobilized cell trickle bed reactor. The reactor was composed of two serial columns packed with Clostridium acetobutylicum ATCC 824 entrapped on the surface of natural sponge segments at a cell loading in the range of 2.03-5.56 g dry cells/g sponge. The average cell loading was 3.58 g dry cells/g sponge. Batch experiments indicated that a critical pH above 4.2 is necessary for the initiation of cell growth. One of the media used during continuous experiments consisted of a salt mixture alone and the other a nutrient medium containing a salt mixture with yeast extract and peptone. Effluent pH was controlled by supplying various fractions of the two different types of media. A nutrient medium fraction above 0.6 was crucial for successful fermentation in a trickle bed reactor. The nutrient medium fraction is the ratio of the volume of the nutrient medium to the total volume of nutrient plus salt medium. Supplying nutrient medium to both columns continuously was an effective way to meet both pH and nutrient requirement. A 257-mL reactor could ferment 45 g/L glucose from an initial concentration of 60 g/L glucose at a rate of 70 mL/h. Butanol, acetone, and ethanol concentrations were 8.82, 5.22, and 1.45 g/L, respectively, with a butanol and total solvent yield of 19.4 and 34.1 wt %. Solvent productivity in an immobilized cell trickle bed reactor was 4.2 g/L h, which was 10 times higher than that obtained in a batch fermentation using free cells and 2.76 times higher than that of an immobilized CSTR. If the nutrient medium fraction was below 0.6 and the pH was below 4.2, the system degenerated. Oxygen also contributed to the system degeneration. Upon degeneration, glucose consumption and solvent yield decreased to 30.9 g/L and 23.0 wt %, respectively. The yield of total liquid product (40.0 wt %) and butanol selectivity (60.0 wt %) remained almost constant. Once the cells were degenerated, they could not be recovered.     

Kinetics of nitrification and denitrification reactions

Nitrification and denitrification are important microbiological reactions of nitrogen. In this work, the kinetics of these reactions have been investigated based on a Monod-type expression involving two growth limiting substrates: ammonium nitrogen and dissolved oxygen for nitrification and nitrate nitrogen and dissolved organic carbon for denitrification. The kinetic constants and yield coefficients were evaluated for both these reactions. Past experimental work was used to determine the constants for the nitrification reaction. For the denitrification reaction, experiments were performed in a stirred tank reactor under conditions such that only one substrate was growth limiting. Steady-state values of the substrate concentrations in the reactor were determined at various dilution rates. These data were analyzed to obtain the kinetic and stoichiometric constants. From these constants it was concluded that in the range of nitrate nitrogen concentrations encountered in waste water, the denitrification reaction can be considered a first-order reaction. It was also found that three times as much organic carbon is required as nitrate nitrogen for complete nitrogen removal.     

Effect of the hydraulic retention time on the anaerobic biofilm reactor efficiency applied to screened cattle waste treatment

Summary It was found that the increase of the hydraulic retention time improved the organic matter removal and the conversion of organic to ammonia nitrogen. Methane concentration in the biogas was not affected by the hydraulic retention time.The reactor in operation during one year was not clogged.     

Treatment of screened dairy manure by upflow anaerobic fixed bed reactors packed with waste tyre rubber and a combination of waste tyre rubber and zeolite: effect of the hydraulic retention time

Two laboratory-scale anaerobic fixed bed reactors were evaluated while treating dairy manure at upflow mode and semicontinuous feeding. One reactor was packed with a combination of waste tyre rubber and zeolite (R1) while the other had only waste tyre rubber as a microorganism immobilization support (R2). Effluent quality improved when the hydraulic retention time (HRT) increased from 1.0 to 5.5 days. Higher COD, BOD5, total and volatile solids removal efficiencies were always achieved in the reactor R1. No clogging was observed during the operation period. Methane yield was also a function of the HRT and of the type of support used, and was 12.5% and 40% higher in reactor R1 than in R2 for HRTs of 5.5 and 1.0 days, respectively. The results obtained demonstrated that this type of reactor is capable of operating with dairy manure at a HRT 5 times lower than that used in a conventional reactor.     

An integrated process for the treatment of CETP wastewater using coagulation, anaerobic and aerobic process

The aim of this study was to treat the wastewater collected from equalization tank of Common Effluent Treatment Plant (CETP), which was a mixture of waste coming from 525 small-scale industries manufacturing textile and dyestuff intermediate, pigments and pharmaceuticals. Initially a pretreatment using ferric chloride and lime was carried out to increase the biodegradability (BOD(5)/COD) of the effluent, which showed color removal of 74% and COD reduction of 75% at a concentration of 10 and 4 g/L. respectively. The biological treatment system using anaerobic fixed film reactor was investigated as secondary treatment. A mixture of bacterial consortium DMAB and cowdung slurry was used for the formation of biofilm. The effect of hydraulic retention time (HRT) and organic loading rate (OLR) on the efficiency of treatment of anaerobic reactor was analysed. Subsequent aerobic treatment after anaerobic step using aerobic culture Pseudomonas aeroginosa helped in further removal of COD and color. Formation of aromatic amines during anaerobic treatment was mineralized by sequential aerobic treatment.     

Characterization of a hydrogen-producing granular sludge

This study demonstrated that hydrogen-producing acidogenic sludge could agglutinate into granules in a well-mixed reactor treating a synthetic sucrose-containing wastewater at 26 degrees C, pH 5.5, with 6 h of hydraulic retention. A typical matured granule is 1.6 mm in diameter, 1.038 g/mL in density, 11% in ash content, and over 50 m/h in settling velocity. Treating a solution containing 12.15 g/L of sucrose at a volumetric loading rate of 48.6 g/(L x d), the reactor containing 20 g/L of granular sludge degraded 97% of sucrose. Effluent comprised 46% acetate and 49% butyrate and the methane-free biogas comprised 63% hydrogen, 35% carbon dioxide, and 2% nitrogen. Hydrogen production rate was 13.0 L/(L x d), and the yield was 0.28 L/g-sucrose. The granule had multiple cracks on the surface and comprised two morphological types of bacteria: fusiform bacilli and a spore-forming bacterium. Phylogenetic analysis showed that 69.1% of the clones were affiliated with four Clostridium species in the family Clostridiaceae, and 13.5% with Sporolactobacillus racemicus in the Bacillus/Staphylococcus group.     

生物膜型污水脱氮系统中膜结构及微生物生态研究进展

生物膜法污水脱氮系统主要利用生物膜中脱氮功能微生物的代谢活动去除氮素,从而达到净化水质的目的,研究脱氮生物膜的微观结构和微生物生态是揭示生物膜脱氮机理从而提高脱氮效率的重要途径.本文综述了生物膜型污水脱氮系统类型、生物膜微观结构特征及其影响因素、生物膜型污水脱氮系统内氮素传质过程、脱氮机理和生物膜数学模型等方面的研究进展.另外,本文介绍了生物膜型污水脱氮系统内生物膜脱氮功能微生物分布特征,不同生物膜脱氮系统、底物、运行条件和时间对功能微生物群落影响,及新型脱氮功能微生物等方面的研究进展,为生物膜脱氮技术的深入研究提供参考.     

Start-up of the Anammox process in a membrane bioreactor

The start-up of an Anammox process was studied in a membrane sequencing batch reactor (MSBR) in which a submerged hollow fibre membrane module was used to retain the biomass. The reactor was seed with Anammox biomass and fed using the Van de Graaf medium. During a first operating stage, salt precipitation was observed and interfered with microbial activity and caused a decrease of the nitrogen removal rate of the reactor from 100 to only 10 mgl(-1) per day. Salt precipitation was avoided by diminishing adequately the Ca and P concentrations of the Van de Graaf medium during the last operating stage. This action increased quickly the activity of the system, and nitrogen removal rate reached up to 710 mgl(-1) per day with almost full nitrite removal. Sporadic flotation of the sludge was observed in the MSBR. The use of the membrane avoided biomass wash-out from the system. Moreover, a surprising fact was that Anammox biomass did not grow in flocs in the MSBR, but in granules. This fact showed that this kind of microorganisms have a trend to grow in aggregates. Results indicated that the use of the MSBR could be a suitable system for nitrogen removal by using the Anammox reaction.     

Lactic acid production by immobilized Lactobacillus casei in recycle batch reactor: a step towards optimization.

Different nutritional and process parameters influencing lactic acid production by Lactobacillus casei, adsorbed to Poraver beads in a recycle batch reactor system, were studied in an attempt to set up a system having a long operational lifetime and permitting use of high substrate concentrations for maximal conversion to the product. The presence of lactose, even as a minor fraction of the total sugar amount, was necessary for complete utilization by the organism for growth and conversion to lactate. Hydrolysed whey protein constituted a richer source of nitrogen compared to yeast extract. Addition of lactate to the medium at the start of the process resulted in severe inhibition compared with the normal process. For a homofermentative process, pH 6.0 was found to be optimal. The overall productivity of the recycle system was higher under all conditions studied in comparison with the batch process using free cells. Enhancement in productivity in the recycle batch reactor was also accompanied by an increase in density of suspended cells. However, the contribution of the suspended cells to the overall reactor productivity was not noticeable. The bead size of the matrix was found to be important for operational stability of the reactor.     

Aerobic treatment of dairy wastewater with sequencing batch reactor systems

Performances of single-stage and two-stage sequencing batch reactor (SBR) systems were investigated for treating dairy wastewater. A single-stage SBR system was tested with 10,000 mg/l chemical oxygen demand (COD) influent at three hydraulic retention times (HRTs) of 1, 2, and 3 days and 20,000 mg/l COD influent at four HRTs of 1, 2, 3, and 4 days. A 1-day HRT was found sufficient for treating 10,000-mg/l COD wastewater, with the removal efficiency of 80.2% COD, 63.4% total solids, 66.2% volatile solids, 75% total Kjeldahl nitrogen, and 38.3% total nitrogen from the liquid effluent. Two-day HRT was believed sufficient for treating 20,000-mg/l COD dairy wastewater if complete ammonia oxidation is not desired. However, 4-day HRT needs to be used for achieving complete ammonia oxidation. A two-stage system consisting of an SBR and a complete-mix biofilm reactor was capable of achieving complete ammonia oxidation and comparable carbon, solids, and nitrogen removal while using at least 1/3 less HRT as compared to the single SBR system.     

Comparison of aerobic and anaerobic degradation of municipal solid waste in bioreactor landfills

Two landfill bioreactors were operated under aerobic and anaerobic conditions in a thermo-insulated room at a constant temperature of 32 °C. Reactors were filled with 19.5 kg of shredded synthetic solid waste prepared according to the average municipal solid waste compositions determined in Istanbul and operated under wet-tomb management strategy by using leachate recirculation. Aerobic conditions in the reactor were developed by using an air compressor. The results of experiments indicated that aerobic reactor had higher organic, nitrogen, phosphorus and alkali metal removal efficiencies than the anaerobic one. Furthermore, stabilization time considerably decreased when using aerobic processes with leachate recirculation compared to the anaerobic system with the same recirculation scheme.