Effects of the internal recycling rate on biological nutrient removal and microbial community structure in a sequential anoxic/anaerobic membrane bioreactor

This study investigated the effects of the internal recycling rate on nutrients removal in a sequential anoxic/anaerobic membrane bioreactor (SAM). Microbial community structure in sludge from the SAM was studied using quinone profile method. Above 98% COD, 68% nitrogen, and 55% phosphorus removal efficiencies were achieved when the internal recycling rate was 2.5 times influent flow. At that rate, the optimum specific nitrate loading rate and COD/NO(3)-N ratio were found to be 2.24 mgNO(3)-N g(-1) MLSS h(-1) and 9.13, respectively. Batch tests demonstrated that anoxic condition suppressed phosphorus release, and that denitrification was also influenced by initial substrate concentration. Denitrification appeared to have some priority over phosphorus release for substrate uptake. Microbial community analysis revealed a predominance of the subclass beta-Proteobacteria. Furthermore, it was found that Rhodocyclus-related bacteria were efficient at phosphorus removal than Actinobacteria.     

Effect of pH change on the performance and microbial community of enhanced biological phosphate removal process

An acetate-rich wastewater, containing 170 mg/L of total organic carbon (TOC), 13 mg/L of N, and 15 mg/L of P, was treated using the enhanced biological phosphate removal (EBPR) process operated in a sequencing batch reactor. A slight change of pH of the mixed liquor from 7.0 to 6.5 led to a complete loss of phosphate-removing capability and a drastic change of microbial populations. The process steadily removed 94% of TOC and 99.9% of P from the wastewater at pH 7.0, but only 93% TOC and 17% of P 14 days after the pH was lowered to pH 6.5. The sludge contained 8.8% P at pH 7.0, but only 1.9% at pH 6.5. Based on 16S rDNA analysis, 64.8% of the clones obtained from the sludge at pH 7.0 were absent in the pH 6.5 sludge. The missing microbes, some of which were likely responsible for the phosphate removal at pH 7.0, included beta-Proteobacteria, Actinobacteria, Bacteriodetes/Chlorobi group, plus photosynthetic bacteria and Defluvicoccus of the alpha-Proteobacteria. Among them, the last two groups, which represented 9.3% and 10.1% of the EBPR sludge at pH 7.0, have rarely been reported in an EBPR system.     

Effects of temperature and temperature shock on the performance and microbial community structure of a submerged anaerobic membrane bioreactor

Effects of temperature and temperature shock on the performance and microbial community structure of a submerged anaerobic membrane bioreactor (SAnMBR) treating thermomechanical pulping pressate were studied for 416 days. The results showed that the SAnMBR system were highly resilient to temperature variations in terms of chemical oxygen demand (COD) removal. The residual COD in treated effluent was slightly higher at 55 °C than that at 37 and 45 °C. There were no significant changes in biogas production rate and biogas composition. However, temperature shocks resulted in an increase in biogas production temporarily. The SAnMBR could tolerate the 5 and 10 °C temperature shocks at 37 °C and the temperature variations from 37 to 45 °C. The temperature shock of 5 and 10 °C at 45 °C led to slight and significant disturbance of the performance, respectively. Temperature affected the richness and diversity of microbial populations.     

Novel MBR_based main stream biological nutrient removal process: high performance and microbial community

For municipal wastewater treatment, main stream biological nutrient removal (BNR) process is becoming more and more important. This lab-scale study, novel MBR_based BNR processes (named A₂N-MBR and A₂NO-MBR) were built. Comparison of the COD removal, results obtained demonstrated that COD removal efficiencies were almost the same in three processes, with effluent concentration all bellowed 30 mg L^?1. However, the two-sludge systems (A₂N-MBR and A₂NO-MBR) had an obvious advantage over the A²/O for denitrification and phosphorus removal, with the average TP removal rates of 91.20, 98.05% and TN removal rates of 73.00, 79.49%, respectively, higher than that of 86.45 and 61.60% in A²/O process. Illumina Miseq sequencing revealed that Candidatus_Accumulibacter, which is capable of using nitrate as an electron acceptor for phosphorus and nitrogen removal simultaneously, was the dominant phylum in both A₂N-MBR and A₂NO-MBR process, accounting for 28.74 and 23.98%, respectively. Distinguishingly, major organism groups related to nitrogen and phosphorus removal in A²/O system were Anaerolineaceae_uncultured, Saprospiraceae_uncultured and Thauera, with proportions of 11.31, 8.56 and 5.00%, respectively. Hence, the diversity of dominant PAOs group was likely responsible for the difference in nitrogen and phosphorus removal in the three processes.     

Effect of aspartate and glutamate on the fate of enhanced biological phosphorus removal process and microbial community structure

This study investigated the fate of enhanced biological phosphorus removal (EBPR) and changes in microbial speciation in a sequencing batch reactor (SBR) fed with aspartate and glutamate. It involved SBR operation for 288 days, batch tests for observation of metabolic functions together with microscopic and phylogenetic analyses. Polyphosphate accumulating organisms (PAOs) were observed in abundance with complete removal of phosphorus. Fluorescence in situ hybridization (FISH) combined with 4′,6-dia-midino-2-phenylindole (DAPI) staining confirmed the accumulation of polyphosphate by Rhodocyclus-related and Actinobacterial PAOs. Aspartate seemed to favor the competitive growth of Rhodocyclus-related PAOs since EBPR population used the common biochemical pathways followed by Rhodocyclus-related PAOs in the aspartate fed batch tests. In the glutamate fed batch reactors, however, Actinobacterial PAOs appeared to be competitively selected which explains the lower levels of PHA generation. Even though operational conditions did not change, effective EBPR could not be maintained during the latter part of the study.     

Degradation of chlorophenols by a defined mixed microbial community

Synthetic sewage containing phenol, acetone, and alkanols plus 4-chlorophenol or a mixture of isomeric chlorophenols is completely degraded by a defined mixed culture with Pseudomonas sp. strain B13 as a chlorocatechol-dissimilating member of the community. Total degradation of the organic carbon was indicated by release of stoichiometric amounts of chloride and low content of dissolved organic carbon in the cell-free effluents. During adaptation to high loads of chlorophenols the initial meta-cleavage activity was completely replaced by ortho-cleavage activity of type I and II. In the fully acclimated culture, hybrid strains such as Alcaligenes sp. strain A7-2 were detected, which are more competitive than Pseudomonas sp. strain B13 with respect to chlorophenol degradation.     

Laccase variation during dye decolourisation in a 200 L packed-bed bioreactor

Summary The white-rot fungus, Pycnoporus cinnabarinus, was grown in a 200 L packed-bed bioreactor. The dye, Remazol Brilliant Blue R, was added to the reactor and was rapidly decolourised. The phenoloxidase, laccase, catalysed this process. Laccases isolated from different days in the bioreactor cycle indicated variations in charge to size characteristics. Purified laccase from different days was isoelectrically focused and showed variations in intensities and numbers of bands whilst catalytic activity was retained.     

Degradation of chlorophenols by a defined mixed microbial community.

Synthetic sewage containing phenol, acetone, and alkanols plus 4-chlorophenol or a mixture of isomeric chlorophenols is completely degraded by a defined mixed culture with Pseudomonas sp. strain B13 as a chlorocatechol-dissimilating member of the community. Total degradation of the organic carbon was indicated by release of stoichiometric amounts of chloride and low content of dissolved organic carbon in the cell-free effluents. During adaptation to high loads of chlorophenols the initial meta-cleavage activity was completely replaced by ortho-cleavage activity of type I and II. In the fully acclimated culture, hybrid strains such as Alcaligenes sp. strain A7-2 were detected, which are more competitive than Pseudomonas sp. strain B13 with respect to chlorophenol degradation.     

Analysis of the microbial community structure in a membrane bioreactor during initial stages of filtration

Membrane biofouling was investigated during the early stages of filtration in a laboratory-scale membrane bioreactor operated on molasses wastewater. The bacterial diversity and composition of the membrane biofilm and activated sludge were analyzed using terminal restriction fragment length polymorphism coupled with 16S rRNA clone library construction and sequencing. The amount of extracellular polymeric substances produced by bacteria was investigated using spectroscopic methods. The results reveal that the bacterial community of activated sludge differs significantly from that of the membrane biofilm, especially at the initial phase. Phylogenetic analysis based on 16S rRNA gene sequences identified 25 pioneer OTUs responsible for membrane surface colonization. Also, the relationship between the identified bacterial strains and the system specifications was explored.     

Optimization of biological sulfide removal in a CSTR bioreactor

In this study, biological sulfide removal from natural gas in a continuous bioreactor is investigated for estimation of the optimal operational parameters. According to the carried out reactions, sulfide can be converted to elemental sulfur, sulfate, thiosulfate, and polysulfide, of which elemental sulfur is the desired product. A mathematical model is developed and was used for investigation of the effect of various parameters on elemental sulfur selectivity. The results of the simulation show that elemental sulfur selectivity is a function of dissolved oxygen, sulfide load, pH, and concentration of bacteria. Optimal parameter values are calculated for maximum elemental sulfur selectivity by using genetic algorithm as an adaptive heuristic search. In the optimal conditions, 87.76% of sulfide loaded to the bioreactor is converted to elemental sulfur.     

Modeling the microbial growth and temperature profile in a fixed-bed bioreactor

Aiming to scale up and apply control and optimization strategies, currently is required the development of accurate plant models to forecast the process nonlinear dynamics. In this work, a mathematical model to predict the growth of the Kluyveromyces marxianus and temperature profile in a fixed-bed bioreactor for solid-state fermentation using sugarcane bagasse as substrate was built up. A parameter estimation technique was performed to fit the mathematical model to the experimental data. The estimated parameters and the model fitness were evaluated with statistical analyses. The results have shown the estimated parameters significance, with 95 % confidence intervals, and the good quality of process model to reproduce the experimental data.     

A metagenome of a full-scale microbial community carrying out enhanced biological phosphorus removal

Enhanced biological phosphorus removal (EBPR) is widely used for removal of phosphorus from wastewater. In this study, a metagenome (18.2 Gb) was generated using Illumina sequencing from a full-scale EBPR plant to study the community structure and genetic potential. Quantitative fluorescence in situ hybridization (qFISH) was applied as an independent method to evaluate the community structure. The results were in qualitative agreement, but a DNA extraction bias against gram positive bacteria using standard extraction protocols was identified, which would not have been identified without the use of qFISH. The genetic potential for community function showed enrichment of genes involved in phosphate metabolism and biofilm formation, reflecting the selective pressure of the EBPR process. Most contigs in the assembled metagenome had low similarity to genes from currently sequenced genomes, underlining the need for more reference genomes of key EBPR species. Only the genome of ‘Candidatus Accumulibacter'', a genus of phosphorus-removing organisms, was closely enough related to the species present in the metagenome to allow for detailed investigations. Accumulibacter accounted for only 4.8% of all bacteria by qFISH, but the depth of sequencing enabled detailed insight into their microdiversity in the full-scale plant. Only 15% of the reads matching Accumulibacter had a high similarity (>95%) to the sequenced Accumulibacter clade IIA strain UW-1 genome, indicating the presence of some microdiversity. The differences in gene complement between the Accumulibacter clades were limited to genes for extracellular polymeric substances and phage-related genes, suggesting a selective pressure from phages on the Accumulibacter diversity.     

Biodegradation of nonylphenol in a continuous packed-bed bioreactor

A packed bed bioreactor, with 170 ml glass bead carriers and 130 ml medium, was tested for the removal of the endocrine disrupter, nonylphenol, with a Sphingomonas sp. The bioreactor was first continuously fed with medium saturated with nonylphenol in an attempt to simulate groundwater pollution. At best, nonylphenol was degraded by 99.5% at a feeding rate of 69 ml h^–1 and a removal rate of 4.3 mg nonylphenol day^–1, resulting in a 7.5-fold decrease in effluent toxicity according to the Microtox. The bioreactor was then fed with soil leachates at 69 ml h^–1 from artificially contaminated soil (1 g nonylphenol kg^–1 soil) and a real contaminated soil (0.19 g nonylphenol kg^–1 soil). Nonylphenol was always completely removed from the leachates of the two soils. It was removed by 99% from the artificial soil but only 62% from real contaminated soil after 18 and 20 d of treatment, respectively, showing limitation due to nonylphenol adsorption.     

Influence of the liquid-phase mass transfer on the performance of a packed-bed bioreactor for wastewater treatment

This paper reports on the influence of the liquid-phase mass transfer on the performance of a horizontal-flow, anaerobic, immobilized-biomass (HAIB) reactor treating low-strength wastewater. The HAIB reactor was subjected to liquid superficial velocities (vs) ranging from 10 to 50 cm h(-1), corresponding to hydraulic detention time (theta h) of 10-2 h. The best performance was achieved at an overall theta h of 3.3 h due to the interdependence of biochemical reactions and mass transfer mechanisms for process optimization. The HAIB reactor was provided with four intermediate sampling ports, and the values of v(s) were fixed to permit sampling at different ports corresponding to thetah of 2 h as vs increased. The chemical oxygen demand removal (COD) efficiencies increased from 68% to 82% with the increase of v(s) from 10 to 50 cm h(-1). It could be concluded that the performance of the HAIB reactor was improved significantly by increasing vs, thus decreasing the liquid-phase mass transfer resistance.     

Denitrification performance and microbial diversity in a packed-bed bioreactor using PCL as carbon source and biofilm carrier

Polycaprolactone (PCL) was used as both carbon source and biofilm support for denitrifying bacteria in a packed-bed bioreactor. The denitrification performance and microbial diversity were investigated. The microbial community of biofilm developed on the surface of PCL in the reactor was analyzed by pyrosequencing method. The experimental results showed the average nitrate removal efficiency reached 93 % at stable operation. ESEM observation and FTIR analysis were conducted to characterize the PCL structure before and after microbial utilization. For the microbial community, Betaproteobacteria predominated, and most of the PCL-degrading denitrifying bacteria assigned to the family of Comamonadacea. Denitrifying bacteria accounted for more than 20 % in the total population, indicating that PCL is a good carrier and carbon source for biological denitrification.     

Metabolic resistance of a psychrotolerant VFA-oxidizing microbial community from an anaerobic bioreactor to changes in the cultivation temperature

A psychrotolerant microbial consortium from a low-temperature anaerobic EGSB bioreactor was grown separately on acetate, propionate, butyrate, and H₂/CO₂ at 30 and 10°C in glass flasks. In the course of the experiments, the cultivation temperature was changed at different time intervals. The initial rates of substrate utilization were higher at 30 than at 10°C. However, the microbial consortium was found to be well adapted to low temperatures; when grown at 10°C for 1.5–5 months, the rates of butyrate, propionate, and H₂/CO₂ utilization increased steadily. When grown at 30°C for 1.5–2.5 months, this consortium retained its ability to degrade VFA and H₂/CO₂ at 10°C. However, after long-term (150 days) cultivation at 10°C, its ability to utilize the substrates at 30°C decreased. In the consortium grown in the acetate-containing medium, a Methanosaeta-like methanogen was predominant; in media with propionate and butyrate, besides VFA-degrading bacteria, acetoclastic Methanosaeta-like and hydrogenotrophic Methanospirillum-like methanogenic archaea prevailed. A Methanospirillum-like strain predominated in the H₂/CO₂-containing medium. The Methanospirillum strain of this microbial community was presumably psychrotolerant. A method based on changes in the cultivation temperature is of practical interest and can be used to start up new bioreactors.     

Analysis of the microbial community structure and function of a laboratory scale enhanced biological phosphorus removal reactor

A laboratory scale sequencing batch reactor (SBR) operating for enhanced biological phosphorus removal (EBPR) and fed with a mixture of volatile fatty acids (VFAs) showed stable and efficient EBPR capacity over a four-year-period. Phosphorus (P), poly-beta-hydroxyalkanoate (PHA) and glycogen cycling consistent with classical anaerobic/aerobic EBPR were demonstrated with the order of anaerobic VFA uptake being propionate, acetate then butyrate. The SBR was operated without pH control and 63.67 +/- 13.86 mg P l-1 was released anaerobically. The P% of the sludge fluctuated between 6% and 10% over the operating period (average of 8.04 +/- 1.31%). Four main morphological types of floc-forming bacteria were observed in the sludge during one year of in-tensive microscopic observation. Two of them were mainly responsible for anaerobic/aerobic P and PHA transformations. Fluorescence in situ hybridization (FISH) and post-FISH chemical staining for intracellular polyphosphate and PHA were used to determine that 'Candidatus Accumulibacter phosphatis' was the most abundant polyphosphate accumulating organism (PAO), forming large clusters of coccobacilli (1.0-1.5 micro m) and comprising 53% of the sludge bacteria. Also by these methods, large coccobacillus-shaped gammaproteobacteria (2.5-3.5 micro m) from a recently described novel cluster were glycogen-accumulating organisms (GAOs) comprising 13% of the bacteria. Tetrad-forming organisms (TFOs) consistent with the 'G bacterium' morphotype were alphaproteobacteria, but not Amaricoccus spp., and comprised 25% of all bacteria. According to chemical staining, TFOs were occasionally able to store PHA anaerobically and utilize it aerobically.     

Biotreatment of phenol-contaminated wastewater in a spiral packed-bed bioreactor

A spiral packed-bed bioreactor inoculated with microorganisms obtained from activated sludge was used to conduct a feasibility study for phenol removal. The reactor was operated continuously at various phenol loadings ranging from 53 to 201.4 g m⁻³ h⁻¹, and at different hydraulic retention times (HRT) in the range of 20–180 min to estimate the performance of the device. The results indicated that phenol removal efficiency ranging from 82.9 to 100% can be reached when the reactor is operated at an HRT of 1 h and a phenol loading of less than 111.9 g m⁻³ h⁻¹. At an influent phenol concentration of 201.4 g m⁻³, the removal efficiency increased from 18.6 to 76.9% with an increase in the HRT (20–120 min). For treatment of phenol in the reactor, the maximum biodegradation rate (V _m) was 1.82 mg l⁻¹ min⁻¹; the half-saturation constant (K _s), 34.95 mg l⁻¹.     

Effects of short solids retention time on microbial community in a membrane bioreactor

Effects of operating lab-scale nitrifying membrane bioreactors (MBR) at short solids retention times (SRT = 3, 5 and 10d) were presented with focus on reactor performance and microbial community composition. The process was capable of achieving over 87% removal of ammonia and 95% removal of chemical oxygen demand (COD), almost regardless of SRT. The denaturing gradient gel electrophoresis (DGGE) analysis shown that bacterial communities evolved in time in a similar way at different SRT. The results of clone library analysis indicated that Betaproteobacteria was the dominant bacterial group in all the reactors but there were significant difference of species for different SRT with higher species diversity at longer SRT. Ammonia and COD removal efficiencies were not correlated with the number of bacterial species or their diversity.     

Mathematical modeling of biological sulfide removal in a fed batch bioreactor

In this study, biological sulfide removal is investigated in a fed batch bioreactor. In this process, sulfide is converted into elemental sulfur particles as an intermediate in the oxidation of hydrogen sulfide to sulfate. The main product is sulfur at low dissolved oxygen or at high sulfide concentrations and also more sulfates are produced at high dissolved oxygen. According to the carried out reactions, a mathematical model is developed. The model parameters are estimated and the model is validated by comparing with some experimental data. The results show that, the proposed model is in a good agreement with experimental data. According to the experimental result and mathematical model, sulfate and sulfur selectivity are sensitive to the concentration of dissolved oxygen. For sulfide concentration 0.2 (mM) in the bioreactor and dissolved oxygen of 0.5 ppm, only 10% of sulfide load is converted to sulfate, while it is 60% at the same sulfide concentration and dissolved oxygen of 4.5 ppm. At high sulfide load to the bioreactor, the concentration of uneliminated sulfide increases; it leads to more sulfur particle selectivity and consequently, less sulfate selectivity.