Biomass Attachment Research Articles

Membrane fouling in a membrane bioreactor (MBR): Sludge cake formation and fouling characteristics

A submerged membrane bioreactor (MBR) with a working volume of 1.4 L and a hollow fiber microfiltration membrane was used to treat a contaminated raw water supply at a short hydraulic retention time (HRT) of approximately 1 h. Filtration flux tests were conducted regularly on the membrane to determine various fouling resistances, and confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM) were employed to characterize the biofouling development and sludge cake formation on the membrane. The experimental results demonstrate that the MBR is highly effective in drinking water treatment for the removal of organic pollutants, ammonia, and UV absorbance. During the MBR operation, the fouling materials were not uniformly distributed on the entire surface of all of the membrane fibers. The membrane was covered partially by a static sludge cake that could not be removed by the shear force of aeration, and partially by a thin sludge film that was frequently washed away by aeration turbulence. The filtration resistance coefficients were 308.4 x 10(11) m(-1) on average for the sludge cake, 32.5 x 10(11) m(-1) on average for the dynamic sludge film, and increased from 10.5 x 10(11) to 59.7 x 10(11) m(-1) for the membrane pore fouling after 10 weeks of MBR operation at a filtration flux of 0.5 m3/m2 x d. Polysaccharides and other biopolymers were found to accumulate on the membrane, and hence decreased membrane permeability. More important, the adsorption of biopolymers on the membrane modified its surface property and led to easier biomass attachment and tighter sludge cake deposition, which resulted in a progressive sludge cake growth and serious membrane fouling. The sludge cake coverage on the membrane can be minimized by the separation, with adequate space, of the membrane filters, to which sufficient aeration turbulence can then be applied.

Detachment of multi species biofilm in circulating fluidized bed bioreactor

In this study, the detachment rates of various microbial species from the aerobic and anoxic biofilms in a circulating fluidized bed bioreactor (CFBB) with two entirely separate aerobic and anoxic beds were investigated. Overall detachment rate coefficients for biomass, determined on the basis of volatile suspended solids (VSS), glucose and protein as well as for specific microbial groups, i.e., for nitrifiers, denitrifiers, and phosphorous accumulating organisms (PAOs), were established. Biomass detachment rates were found to increase with biomass attachment on carrier media in both beds. The detachment rate coefficients based on VSS were significantly affected by shear stress, whereas for protein, glucose and specific microbial groups, no significant effect of shear stress was observed. High detachment rates were observed for the more porous biofilm structure. The presence of nitrifiers in the anoxic biofilm and denitrifiers in the aerobic biofilm was established by the specific activity measurements. Detachment rates of PAOs in aerobic and anoxic biofilms were evaluated.

Startup of an Anaerobic Fluidized Bed Reactor for Landfill Leachate Treatment

Anaerobic treatment of the young landfill leachate in a pilot-scale fluidized bed reactor was performed to observe the effects of startup on COD removal, biogas production and biomass attachment. During the experiments, the organic loading rate (OLR) was increased gradually from 2.5 to 27 g COD l -1 day -1 with varying the feed rate and the hydraulic retention time in the range of 5.5-13 l day -1 and 1-2.35 days, respectively. The anaerobic fluidized bed reactor (AFBR) showed an excellent performance and attained steady state conditions with COD removal of 90% after 80 days. Biogas production in the reactor continuously increased and its average yield (Ygas) was defined as 0.53 l biogas g-1 CODrem -1 with a correlation of 99%. Greater microbial attachment was found at the increased loading rates and the attached biomass concentration (Xattach) consisted of about 90% of the total biomass concentration. In addition, the substrate utilization rate indicated a linear increase as a function of time during the process.

生物膜付着担体としての転炉スラグの特性

Slag has been considered to be a useful biofilm support because of the continual release of minerals in water environments. In this study, the characteristics of a converter slag as a biofilm support were examined from aspects of mineral sources and surface microstructure. Four types of support material: converter slag, the slag melted at 1700°C, basalt, and limestone, were prepared for comparative experiments. The highest density of biomass was found in the converter slag, followed by the melted slag, basalt, and limestone. From the observation of support surface by a scanning electron microscope, it was found that the slag had an intricate microstructure, and basalt and limestone were rather flat. The melting process of slag destroyed the surface microstructure and decreased the adherence of biofilm. However, the process did not change amounts of mineral released from the slag. Results suggest that the surface microstructure of slag, rather than release of mineral from slag, has an important role for the attachment of high-density biomass.

Microbial activity of biofilm during start-up period of anaerobic hybrid reactor at low and high upflow feeding velocity

With an aim to shorten start-up time of an Anaerobic Hybrid Reactor (AHR), initial biofilm development was studied, particularly at different upflow feeding velocities. At a low (0.01 m x h(-1)) upflow velocity, initial biofilm was found to develop via the attachment of suspended biomass in the packed zone, while microbial growth on the film was insignificant. Contrarily, with higher (1.0 m x h(-1)) upflow velocity, initial biofilm development was from both microbial attachment and growth on supporting media. Biofilm thickness was determined using confocal laser scanning microscopy (CLSM), which indicated that the biofilm developed faster with the higher velocity, due to the contribution of the microbial growth on supporting media. When operated beyond the initial biofilm development with the lower velocity, both the activity of acetogens and the methanogens increased, although there was a lower amount of attached biomass on the supporting media. Whereas, both groups were found to decrease with higher upflow velocity, but acidogenic activity increased. It can be concluded that higher upflow velocity positively affected the initial stage of biofilm development and has the potential to accelerate attached biomass on supporting media during the initial phase. Subsequently, the upflow velocity should be reduced to the normal rate to enhance the methanogenic activity.

Application of a low density support material as an alternative to prevent clogging in a three‐phase fluidized‐bed reactor

A low density support material was evaluated to determine its effect on biofilm growth dynamics when treating synthetic wastewater in a three‐phase fluidized‐bed reactor. After two 40‐day experimental runs, the results showed significant microbial activity from the very beginning of the study. The highest biofilm growth was observed during the first 10 days of operation. Biofilm kept gradually growing after the 11th day and reached a steady‐state at day 21, defined by a consistent biomass attached to the particles. As an indicator of biofilm detachment, effluent suspended biomass decreased as biofilm attachment increased, tending also to stabilize around day 21. During the first 10 days, chemical oxygen demand removal averaged 100 mg 1−1 representing 48% of the influent chemical oxygen demand concentration. The highest chemical oxygen demand removal efficiency (78%) was achieved between days 23 and 29, when influent chemical oxygen demand was 280 mg 1−1. The support material evaluated proved to be effective at allowing attachment of microorganisms. Due to its low density, bed fluidization was achieved under recirculation rates lower than those required to fluidize beds of higher density. The physical properties of the proposed support material allowed an appropriate equilibrium to be achieved between biomass attachment and detachment, eliminating the need for bed backwashing

Mass Cultivation of Anaerobic Ammonium-Oxidizing Sludge Using a Novel Nonwoven Biomass Carrier

Biological conversions of nitrogenous compounds closely resembling the chemistry of the anammox reaction were developed and maintained for approximately two years in fixed-bed, continuous-flow unit processes. Using a novel nonwoven matrix for biomass attachment, the anaerobic, autotrophic biofilm cultures were robust enough to survive occasional operational anomalies and to rebound quickly from temporary setbacks. Using a 2.7-l reactor with a hydraulic retention time of 7.5 hours, influent ammonium (NH 4 +) and nitrite (NO 2 -) concentrations of approximately 250 mg N/l, each, were successfully treated with a total nitrogen (T-N) removal efficiency of 60%. T-N and NH 4 + volumetric removal rates of 40 and 20 mg N/l.h, respectively, were maintained for a one-year period of operation, which are in a suitable range for industrial applications. Using the nonwoven material of the 2.7-l reactor as a seed for a larger 14-l reactor, a fast transition to a stable, relatively high T-N mass removal rate of approximately 300 mg/h (NH 4 -N removal, 150 mg/h) was possible. These results suggest that attached-growth processes such as employed here, with a nonwoven matrix, could serve well not only as a means of nitrogen abatement but also for mass cultivation of the slowly growing anaerobic ammonium-oxidizing cultures for use in development of new reactors.

Comparison of suspended growth and hybrid systems for nitrogen removal in ammonium bisulfite pulp mill wastewater

A series of bench‐scale nitrification/denitrification tests were carried out with both suspended growth and hybrid bioreactors. The hybrid reactor was fined with plastic (polyethylene) media to evaluate the effects of biofilm. Two types of reactor configurations were tested; 4‐compartment and 6‐compartment modes. The experiments were initiated with a half‐strength pulp and paper wastewater and its strength increased stepwise to the raw wastewater. Solid retention time was fixed at 10 days after a start‐up period while hydraulic retention time was extensively varied from 3.5 to OS days. The results from each type of reactor were compared in terms of nitrification/denitrification efficiency and stability. Experimental results demonstrate that the hybrid system showed greater stability in nitrification and higher denitrification efficiency than the suspended growth system. In the hybrid system, attached volatile solids formed 61 — 72% of total volatile solids in the reactor and the amount of attached volatile solids insignificantly varied with the organic loading rate (037 ‐ 2.76 kg COD m‐3 d‐1) after initial biomass attachment. Under the conditions tested (0.1 ‐ 2.8 kg COD m3 d‐1), organic loading rate insignificantly influenced the nitrification. Better performance was obtained in denitrification when the anoxic zone was better isolated from the aerobic compartments (6‐compartment mode). Overall, the hybrid system with fixed‐film growth had better resistance to upset caused by transients such as changes in influent composition or hydraulic retention time.

Methane yield as a monitoring parameter for the start-up of anaerobic fixed film reactors

This paper describes the variation of the methane yield during the start-up period of an anaerobic fluidized bed reactor. After a lag phase, with acclimatized sludge, the methane yield increased with time during biofilm development up to the theoretical steady yield value, reported to be around 0.35l CH4/g CODdeg. The establishment of the biofilm required a high consumption of organic material through the microbial synthesis (anabolism), thereby reducing the proportion of substrate converted to methane. As a result, this yield could be an indirect metabolic parameter for evaluating a start-up operation. It could provide vital information about bacterial fixation processes and is easy to be applied to any biofilm reactor, such as anaerobic filters, where biomass sampling is impracticable. Monitoring this parameter could also give useful dynamic information about the different steps of colonization and biomass attachment, which could be used to improve the start-up performance.

Anaerobic Thermophilic (55°C) Treatment of TMP Whitewater in Reactors Based on Biomass Attachment and Entrapment

Thermomechanical pulping (TMP) whitewater was treated in thermophilic (55°C) anaerobic laboratory-scale reactors using three different reactor configurations. In all reactors up to 70% COD removals were achieved. The anaerobic hybrid reactor, composed of an upflow anaerobic sludge blanket (UASB) and a filter, gave degradation rates up to 10 kg COD/m3d at loading rates of 15 kg COD/m3d and hydraulic retention time (HRT) of 3.1 hours. The anaerobic multi-stage reactor, consisting of three compartments, each packed with granular sludge and carrier elements, gave degradation rates up to 9 kg COD/m3d at loading rates of 15-16 kg COD/m3d, and HRT down to 2.6 hours. Clogging and short circuiting eventually became a problem in the multi-stage reactor, probably caused by too high packing of the carriers. The anaerobic moving bed biofilm reactor performed similar to the other reactors at loading rates below 1.4 kg COD/m3d, which was the highest loading rate applied. The use of carriers in the anaerobic reactors allowed short HRT with good treatment efficiencies for TMP whitewater.

Anaerobic thermophilic (55°C) treatment of TMP whitewater in reactors based on biomass attachment and entrapment

Abstract Thermomechanical pulping (TMP) whitewater was treated in thermophilic (55°C) anaerobic laboratory-scale reactors using three different reactor configurations. In all reactors up to 70 % COD removals were achieved. The anaerobic hybrid reactor, composed of an upflow anaerobic sludge blanket (UASB) and a filter, gave degradation rates up to 10 kg COD/m 3 d at loading rates of 15 kg COD/m 3 d and hydraulic retention time (HRT) of 3.1 hours. The anaerobic multi-stage reactor, consisting of three compartments, each packed with granular sludge and carrier elements, gave degradation rates up to 9 kg COD/m 3 d at loading rates of 15–16 kg COD/m 3 d, and HRT down to 2.6 hours. Clogging and short circuiting eventually became a problem in the multi-stage reactor, probably caused by too high packing of the carriers. The anaerobic moving bed biofilm reactor performed similar to the other reactors at loading rates below 1.4 kg COD/m 3 d, which was the highest loading rate applied. The use of carriers in the anaerobic reactors allowed short HRT with good treatment efficiencies for TMP whitewater.

Nitrification of synthetic wastewater in a cross flow medium trickling filter

The nitrification performance of a synthetic wastewater was investigated in a cross flow medium trickling filter. The attachment of biomass on packing medium was studied. The reactor was operated continuously for three different hydraulic loading rates 5, 9 and 13␣m3/m2 · d under various influent ammonium concentrations. The maximum specific surface nitrification rate was about 1.21 g/m2 · d. There was a good agreement between actual and predicted alkalinity consumption. The ammonium conversion along the filter depth was also investigated. The external surface of the nitrifying biofilm was captured by scanning electron microscope. The results are found to be satisfactory.

Biodegradation of p-toluenesulphonic acid by comamonas testosteroni in an aerobic counter-current structured packing biofilm reactor

p-Toluenesulphonic acid degradation by Comamonas testosteroni was studied in a continuously operated fixed-bed biofilm reactor. Static mixer elements (Sulzer Chemtech, Switzerland) were used as a support matrix for biofilm formation. Degradation of p-toluenesulfonate was investigated at several aeration (0.5–4 L min−1) and dilution (0.15–0.4 h−1) rates under septic conditions. The maximum observed pollutant degradation rate was 198 mg of C L−1 h−1. In spite of nonsterile conditions, a very limited range of microbial species was present in the reactor. The system was operated for over 3 months and Comamonas testosteroni used as inoculum was largely present in the biofilm (about 60% of the total microbial population) during the whole cultivation period. Two other aerobic bacterial strains detected in the biofilm were not able to degrade p-toluenesulphonic acid. High biomass attachment was observed on polypropylene static mixers. Immobilised biomass reached the level of 10.4 g of dry weight per m2 of the support and 23% of its structure was active biomass.

Nitrification of Fertilizer Wastewaters in a Biofilm Reactor

The nitrification characteristics of fertilizer wastes were investigated in a biofilm system using a submerged aerated filter. The attachment of biomass on packing media was studied. Supplement of organic carbon in the form of glucose and yeast extract enhanced biofilm formation although the nitrifiers did not require organic carbon for growth. After an attachment period, continuous operation of the reactor at different loading rates and dissolved oxygen levels was investigated. The maximum achievable nitrification rate was strongly dependent on the dissolved oxygen. In the dissolved oxygen range of 3.2-3.5 mg dm -3 , the maximum ammonia removal rate was about 0.17 kg NH 4 -N m -3 day -1 . When the dissolved oxygen was increased to 4.9 mg dm -3 , removal rates as high as 0.41 kg NH 4 -N m -3 day -1 could be obtained. Nitrite accumulation depended on the bulk nitrogen and dissolved oxygen concentrations.

Biodegradation of p-toluenesulphonic acid by Comamonas testosteroni in an aerobic counter-current structured packing biofilm reactor

p-Toluenesulphonic acid degradation by Comamonas testosteroni was studied in a continuously operated fixed-bed biofilm reactor. Static mixer elements (Sulzer Chemtech, Switzerland) were used as a support matrix for biofilm formation. Degradation of p-toluenesulfonate was investigated at several aeration (0.5–4 L min−1) and dilution (0.15–0.4 h−1) rates under septic conditions. The maximum observed pollutant degradation rate was 198 mg of C L−1 h−1. In spite of nonsterile conditions, a very limited range of microbial species was present in the reactor. The system was operated for over 3 months and Comamonas testosteroni used as inoculum was largely present in the biofilm (about 60% of the total microbial population) during the whole cultivation period. Two other aerobic bacterial strains detected in the biofilm were not able to degrade p-toluenesulphonic acid. High biomass attachment was observed on polypropylene static mixers. Immobilised biomass reached the level of 10.4 g of dry weight per m2 of the support and 23% of its structure was active biomass.

Comparison of porous and non-porous media in upflow anaerobic filters when treating dairy wastewater

The performance of porous and non-porous media in two mesophilic anaerobic upflow filters treating a wastewater from a milk bottling factory was investigated. The results indicated that at higher OLRs the porous media had a much better performance. The reactor with non-porous packing showed instability above an OLR of 4 kg COD/m 3 ·d whereas the reactor with the porous packing was still stable at OLRs of up to 21 kg COD/m 3 ·d. The behaviour of the media and biomass wash-out were observed at high upflow velocities (UV) and results demonstrated that porous media was not as susceptible to shear stresses as non-porous media. At the end of the investigation, attachment studies were carried out and the results showed a heavy biomass attachment in the porous media, whereas mainly unattached biomass was retained in the voids of the non-porous media.

A systematic scanning electron microscopy technique for evaluating combined biological/granular activated carbon treatment processes

Abstract A systematic scanning electron microscope analytical technique has been developed to examine granular activated carbon used as a medium for biomass attachment in liquid waste treatment. The procedure allows for the objective monitoring, comparing, and trouble shooting of combined processes by direct visual examination of the biomass's attachment characteristics and rating key criteria that have been found to have the greatest effect on the process's performance. These criteria include the surface characteristics of the carbon; the quantity, type, and position of the biomass; and the amount of unidentifiable material. A set of instructions along with a set of reference photographs that illustrate the rating scale of each criteria were developed as was a standard data recording form. Several investigators rated samples from a variety of bioreactors to verify the practicality and quality of the technique. A comparison of the individual ratings indicated a significant correlation with each other as well as with the reactor's operating status.

Biological sulfuric acid transformation: Reactor design and process optimization

As an alternative to the current disposal technologies for waste sulfuric acid, a new combination of recycling processes was developed. The strong acid (H(2)SO(4)) is biologically converted with the weak acid (CH(3)COOH) into two volatile weak acids (H(2)S, H(2)CO(3)) by sulfate-reducing bacteria. The transformation is possible without prior neutralization of the sulfuric acid. The microbially mediated transformation can be followed by physiochemical processes for the further conversion of the H(2)S.The reduction of sulfate to H(2)S is carried out under carbon-limited conditions at pH 7.5 to 8.5. A fixed-bed biofilm column reactor is used in conjunction with a separate gas-stripping column which was installed in the recycle stream. Sulfate, total sulfide, and the carbon substrate (in most cases acetate) were determined quantitatively. H(2)S and CO(2) are continually removed by stripping with N(2). Optimal removal is achieved under pH conditions which are adjusted to values below the pK(a)-values of the acids. The H(2)S concentration in the stripped gas was 2% to 8% (v/v) if H(2)SO(4) and CH(3)COOH are fed to the recycle stream just before the stripping column.Microbiol conversion rates of 65 g of sulfate reduced per liter of bioreactor volume per day are achieved and bacterial conversion efficiencies for sulfate of more than 95% can be maintained if the concentration of undissociated H(2)S is kept below 40 to 50 mg/L. Porous glass spheres, lava beads, and polyurethane pellets are useful matrices for the attachment of the bacterial biomass. Theoretical aspects and the dependence of the overall conversion performance on selected process parameters are illustrated in the Appendix to this article.

Attachment and Growth of Biomass on Surface-Modified Activated Carbon Fibers

Activated carbon fiber (ACF) was used as a model of commercial activated carbons to examine the effect of surface chemistry on the attachment behavior of bacterial biomass. Surface acidity was found to enhance the biomass-ACF interaction. When ACFs were applied as biomass support media in a continuous stirred tank reactor, surface acidity of the carbon resulted in faster biomass growth in the start-up phase. The start-up phase was simulated by a simple biomass attachment kinetics model. Experimental and calculated data show a reasonable agreement, with the exception of the hydrogenated specimen, which was interpreted by assuming that the hydrogen-reduced surface is highly reactive and then may undergo oxidation in the initial phase of operation so that the adsorption characteristics are altered.

Factors affecting biomass attachment during startup and operation of anaerobic fluidized beds

Three anaerobic fluidized bed reactors at 37 degrees C were utilized to observe the effects of startup and operational procedures on biomass attachment. Using a meat-based synthetic waste and stepped-loading regime, the influences of synthetic polymer addition and maintenance of anaerobiosis during startup were investigated. Subsequently, increasing bed expansions were applied to assess shear effects. Synthetic polymer addition enhanced biomass retention but did not improve process performance. Maintenance of a reduced environment ameliorated fluctuating process parameters during start up and aided biomass retention and substrate removal. A bed expansion of 5% was detrimental to biomass attachment and COD removal but system stability was maintained at expansions between 10% and 30%. Startup was achieved in 56 days. Anaerobiosis appeared to enhance the initial evolution of a stable, well-adapted microbial population, whereas polymer addition interfered with this. Moderate bed expansions had negligible effects on attachment and performance.