Characteristics of granular methanogenic sludge grown on phenol synthetic medium and methanogenic fermentation of phenolic wastewater in a UASB reactor

Anaerobic membrane bioreactor coupled with polyaluminum chloride for high-strength phenolic wastewater treatment: Robust performance and potential mechanisms

Anaerobic digestion of phenolic wastewater by anaerobic membrane bioreactor (AnMBR) has revealed increasing attractiveness, but the application of AnMBRs for treating high-strength phenolic wastewater faces challenges related to elevated phenol stress and membrane fouling. In this study, the coupling of AnMBR and polyaluminum chloride (PAC) was developed for efficient treatment of high-strength phenolic wastewater. The system achieved robust removal efficiencies of phenol (99%) and quinoline (98%) at a gradual increase of phenol concentration from 1000 to 5000 mg/L and a constant quinoline concentration of 100 mg/L. The dosing of PAC could effectively control the membrane fouling rate with the transmembrane pressure (TMP) increasing rate as low as 0.17 kPa/d. The robust performances were mainly attributed to the favorable retention of functional microbes through membrane interception, while pulse cross flow buffered against phenol stress and facilitated cake layer removal. Meanwhile, the enriched core functional microbes, such as Syntrophorhabdus, Syntrophus, Mesotoga and Methanolinea, played a crucial role in further reduction of phenol stress. Notably, the significant presence of biomacromolecule degrader, such as Levilinea, contributed to membrane fouling mitigation through extracellular polymer degradation. Moreover, the enlargement of particle size distribution (PSD) by PAC was expected to mitigate membrane fouling. This study provided a promising avenue for sustainable treatment of high-strength phenolic wastewater.

Enhancing Phenol Conversion Rates in Saline Anaerobic Membrane Bioreactor Using Acetate and Butyrate as Additional Carbon and Energy Sources

Phenolic industrial wastewater, such as those from coal gasification, are considered a challenge for conventional anaerobic wastewater treatment systems because of its extreme characteristics such as presence of recalcitrant compounds, high toxicity, and salinity. However, anaerobic membrane bioreactors (AnMBRs) are considered of potential interest since they retain all micro-organism that are required for conversion of the complex organics. In this study, the degradation of phenol as main carbon and energy source (CES) in AnMBRs at high salinity (8.0 g Na⁺⋅L^–1) was evaluated, as well as the effect of acetate and an acetate-butyrate mixture as additional CES on the specific phenol conversion rate and microbial community structure. Three different experiments in two lab-scale (6.5 L) AnMBRs (35°C) were conducted. The first reactor (R1) was fed with phenol as the main CES, the second reactor was fed with phenol and either acetate [2 g COD⋅L^–1], or a 2:1 acetate-butyrate [2 g COD⋅L^–1] mixture as additional CES. Results showed that phenol conversion could not be sustained when phenol was the sole CES. In contrast, when the reactor was fed with acetate or an acetate-butyrate mixture, specific phenol conversion rates of 115 and 210 mgPh⋅gVSS^–1 d^–1, were found, respectively. The syntrophic phenol degrader Syntrophorhabdus sp. and the acetoclastic methanogen Methanosaeta sp. were the dominant bacteria and archaea, respectively, with corresponding relative abundances of up to 63 and 26%. The findings showed that dosage of additional CES allowed the development of a highly active phenol-degrading biomass, potentially improving the treatment of industrial and chemical wastewaters.

Influence of particle size distribution on anaerobic degradation of phenol and analysis of methanogenic microbial community

Sludge morphology considerably affects the mechanism underlying microbial anaerobic degradation of phenol. Here, we assessed the phenol degradation rate, specific methanogenic activity, electron transport activity, coenzyme F₄₂₀ concentration, and microbial community structure of five phenol-degrading sludge of varying particle sizes (i.e., < 20, 20-50, 50-100, 100-200, and > 200 μm). The results indicated an increase in phenol degradation rate and microbial community structure that distinctly correlated with an increase in sludge particle size. Although the sludge with the smallest particle size (< 20 μm) showed the lowest phenol degradation rate (9.3 mg COD·gVSS^-1 day^-1), its methanogenic activity with propionic acid, butyric acid, and H₂/CO₂ as substrates was the best, and the concentration of coenzyme F₄₂₀ was the highest. The small particle size sludge did not contain abundant syntrophic bacteria or hydrogenotrophic methanogens, but contained abundant acetoclastic methanogens. Moreover, the floc sizes of the different sludge varied in important phenol-degrading bacteria and archaea, which may dominate the synergistic mechanism. This study provides a new perspective on the role of sludge floc size on the anaerobic digestion of phenol.

Turf soil enhances treatment efficiency and performance of phenolic wastewater in an up-flow anaerobic sludge blanket reactor

Phenols are industrially generated intermediate chemicals found in wastewaters that are considered a class of environmental priority pollutants. Up-flow anaerobic sludge blanket (UASB) reactors are used for phenolic wastewater treatment and exhibit high volume loading capability, favorable granule settling, and tolerance to impact loads. Use of support materials can promote biological productivity and accelerate start-up period of UASB. In the present study, turf soil was used as a support material in a mesophilic UASB reactor for the removal of phenols in wastewater. During sludge acclimatization (45-96 days), COD and phenols in the treatments were both reduced by 97%, whereas these contents in the controls were decreased by 81% and 75%, respectively. The phenol load threshold for the turf soil UASB reactor was greater (1200 mg/L, the equivalent of COD 3000 mg/L) in comparison with the control UASB reactor (900 mg/L, the equivalent of COD 2250 mg/L) and the turf soil UASB reactor was also more resistant to shock loading. Improved sludge settling, shear resistance, and higher biological activity occurred with the turf soil UASB reactor due to the formation of large granular sludge (0.6 mm or larger) in higher relative percentages. Granular sludge size was further enhanced by the colonization of filamentous bacteria on the irregular surface of the turf soil.

Relationship between phenol degradation efficiency and microbial community structure in an anaerobic SBR

Phenol is a common wastewater contaminant from various industrial processes, including petrochemical refineries and chemical compounds production. Due to its toxicity to microbial activity, it can affect the efficiency of biological wastewater treatment processes. In this study, the efficiency of an Anaerobic Sequencing Batch Reactor (ASBR) fed with increasing phenol concentrations (from 120 to 1200 mg L(-1)) was assessed and the relationship between phenol degradation capacity and the microbial community structure was evaluated. Up to a feeding concentration of 800 mg L(-1), the initial degradation rate steadily increased with phenol concentration (up to 180 mg L(-1) d(-1)) and the elimination capacity remained relatively constant around 27 mg phenol removed∙gVSS(-1) d(-1). Operation at higher concentrations (1200 mg L(-1)) resulted in a still efficient but slower process: the elimination capacity and the initial degradation rate decreased to, respectively, 11 mg phenol removed∙gVSS(-1) d(-1) and 154 mg L(-1) d(-1). As revealed by Denaturing Gradient Gel Electrophoresis (DGGE) analysis, the increase of phenol concentration induced level-dependent structural modifications of the community composition which suggest an adaptation process. The increase of phenol concentration from 120 to 800 mg L(-1) had little effect on the community structure, while it involved drastic structural changes when increasing from 800 to 1200 mg L(-1), including a strong community structure shift, suggesting the specialization of the community through the emergence and selection of most adapted phylotypes. The thresholds of structural and functional disturbances were similar, suggesting the correlation of degradation performance and community structure. The Canonical Correspondence Analysis (CCA) confirmed that the ASBR functional performance was essentially driven by specific community traits. Under the highest feeding concentration, the most abundant ribotype probably involved in successful phenol degradation at 1200 mg L(-1) was affiliated to the Anaerolineaceae family.

Comparative performance of UASB and anaerobic hybrid reactors for the treatment of complex phenolic wastewater

The performance of an upflow anaerobic sludge blanket (UASB) reactor and an anaerobic hybrid reactor (AHR) was investigated for the treatment of simulated coal wastewater containing toxic phenolics at different hydraulic retention times (0.75-0.33d). Fast start-up and granulation of biomass could be achieved in an AHR (45d) than UASB (58d) reactor. Reduction of HRT from 1.5 to 0.33d resulted in a decline in phenolics removal efficiency from 99% to 77% in AHR and 95% to 68% in UASB reactor respectively. AHR could withstand 2.5 times the selected phenolics loading compared to UASB reactor that could not withstand even 1.2 times the selected phenolics loading. Residence time distribution (RTD) study revealed a plug flow regime in the AHR and completely mixed regime in UASB reactor respectively. Energy economics of the reactors revealed that 12,159MJd(-1) more energy can be generated using AHR than UASB reactor.

Characterization of active microbes in a full-scale anaerobic fluidized bed reactor treating phenolic wastewater

This study investigated the active microbial community in a full-scale granular activated carbon-anaerobic fluidized bed (GAC-AFB) reactor treating wastewater from the manufacturing of phenolic resin, using 16S rRNA-based molecular analyses. The results of cDNA from 16S rRNA revealed that Methanosaeta-related (83.9% of archaeal clones) and Syntrophorhabdaceae (formerly named Deltaproteobacteria group TA)-related (68.9% of bacterial clones) microorganisms were as the most predominant populations in the phenol-degrading GAC-AFB reactor. The high abundance of Syntrophorhabdaceae was supported by a terminal restriction fragment length polymorphism (T-RFLP) analysis, which showed that a Syntrophorhabdaceae-like fragment of 119 bp (~80% of total fragments) was the most predominant phylotype. Furthermore, fluorescence in situ hybridization (FISH) analyses suggested that Syntrophus- and Chloroflexi-like cells were also in high abundance in the GAC biofilm. A non-layered structure of microorganisms was found in the GAC biofilm, where Methanosaeta (thick filamentous), Syntrophorhabdaceae (oval-shaped), Syntrophus (small rods) and Chloroflexi (thin-filamentous) were randomly distributed with high abundance. These findings greatly improve our understanding of the diversity and distribution of microbial populations in a full-scale mesophilic bioreactor treating an actual phenol-containing waste stream.

Treatment of phenol in an anaerobic fluidized bed reactor (AFBR): continuous and batch regime

Results of this study describe the feasibility of anaerobic treatment of highly concentrated phenol synthetic wastewater using an anaerobic fluidized bed reactor (AFBR) in both continuous and batch modes. Wastewater with a maximum load of 2,100 mg C.l(-1) was prepared using phenol (maximum concentration of 1,600 mg C.l(-1)) as substrate and a mixture of acetic, propionic and butyric acids (500 mg C.l(-1)) as co-substrate. AFBR reached total organic carbon (TOC) and phenol removal efficiency over 95% treating the highest organic loading rate (OLR) containing phenol studied for this kind of reactor (5.03 g C.l(-1).d(-1)). The phenol loading rate rise caused volumetric biogas rate increase up to 4.4 l.l(-1).d(-1) (average yield of 0.28 l CH(4).g(-1) COD(removed)) as well as variation in the biogas composition; the CO(2) percentage increased while the CH(4) percentage decreased. Morphological examination of the bioparticles at 4.10 g C.l(-1).d(-1), revealed significant differences in the biofilm structure, microbial colonization and bacterial morphological type development. The five batch assays showed that phenol degradation may be favoured by the presence of volatile fatty acids (VFAs) (co-metabolism), whereas VFAs degradation may be inhibited by phenol. AFBR reached initial phenol degradation velocity of 0.25 mg C.l(-1).min(-1).

Treatment of catechol bearing wastewater in an upflow anaerobic sludge blanket (UASB) reactor: sludge characteristics

This paper deals with the characteristics of anaerobic microbial granules grown in an UASB reactor treating catechol bearing synthetic wastewater (SWW). The specific methanogenic activity of the sludge showed an increase in trend with an increase in the organic loading rate and the catechol concentration in the SWW. The settling velocity of individual granules in the size range of 0.5-2.5mm was found to be in the range of 30-75mh(-1). The ash content in the sludge was 11.7% with a sludge volume index of 18-20mlg(-1). The inorganic elemental distribution within the granules showed a decrease except that for phosphorous and cobalt, which increased by approximately 12% and 18%, respectively, after the treatment of SWW. Scanning electron microscopy (SEM) coupled with electron disperse X-ray analysis showed an increase in the sulphur content by approximately 300% after the treatment of SWW. Surface mineral composition of the granules determined by XRD analysis indicated the existence of vuagnatite (CaAlSiO(4)(OH)). SEM observation of the granules showed the predominance of Methanosaeta and Methanobacterium type of species on the surface along with a variety of other species.

Treatment of phenolic wastewater in UASB reactor: effect of nitrogen and phosphorous

Phenolic wastewater representing an industrial wastewater was supplemented with varying amount of nitrogen (N) and phosphorous (P) and treated in upflow anaerobic sludge blanket reactor (UASBR). The variation of COD:N:P from 300:10:1 to 300:1:0.1, did not influence the conversion of phenol COD to methane COD. The concentration of N and P in the influent was reduced from 25.5mgl(-1) to 2.5mgl(-1) and 2.5 to 0.25mgl(-1), respectively. However, on further reducing the nutrients in the feed from 300:1:0.1 to 300:0:0 the (i) CH(4)-COD decreased from 90% to 40%, and (ii) cell yield reduced to 25-50%. The average cell yield was 3.5%. Percent N and P in cells varied from 10% to 14% and 0.6% to 2.4%, respectively. The activity of the sludge assessed as specific methanogenic activity (SMA) was found in the range from 0.15 to 0.66g CH4-CODg(-1) VSSd(-1). The optimum COD:N:P for phenolic wastewater has been estimated to be 300:1:0.1.

Effect of effluent recycling and shock loading on the biodegradation of complex phenolic mixture in hybrid UASB reactors

This study describes the feasibility of anaerobic treatment of synthetic coal wastewater using four identical 13.5L (effective volume) bench scale hybrid up flow anaerobic sludge blanket (HUASB) reactors (R1, R2, R3 and R4) under mesophilic (27+/-5 degrees C) conditions. Synthetic coal wastewater with an average chemical oxygen demand (COD) of 2240 mg/L and phenolics concentration of 752 mg/L was used as substrate. Effluent recirculation was employed at four different effluent to feed recirculation ratios (R/F) of 0.5, 1.0, 1.5 and 2.0 for 100 days to study the effect of recirculation on the performance of the reactors. Phenolics and COD removal was found to improve with increase in effluent recirculation. An effluent to feed recycle ratio of 1.0 resulted in maximum removal of phenolics and COD. Phenolics and COD removal improved from 88% and 92% to 95% each, respectively. The concentration of volatile fatty acids in the effluent was lower than the influent when effluent to feed recirculation was employed. Effect of shock loading on the reactors revealed that phenolics shock load up to 2.5 times increase in the normal input phenolics concentration in the form of continuous shock load for 4days did not affect the reactors performance irreversibly.

Identification of important microbial populations in the mesophilic and thermophilic phenol-degrading methanogenic consortia

Active mesophilic and thermophilic phenol-degrading methanogenic consortia were obtained after an 18-month acclimation and enriching process in the serum bottles, and characterized using the rRNA-based molecular approach. As revealed by cloning, fluorescence in situ hybridization (FISH) and terminal restriction fragment length polymorphism (T-RFLP), these two enrichments differed greatly in the community structures. The results for the first time suggest that group TA in the Deltaproteobacteria (88.0% of EUBmix FISH-detectable bacterial cell area) and Pelotomaculum spp. in the Desulfotomaculum family (81.2%) were the predominant fermentative bacteria under mesophilic (37 degrees C) and thermophilic (55 degrees C) conditions, respectively. These populations closely associated with mesophilic and thermophilic members of Methanosaetaceae, Methanobacteriaceae and Methanomicrobiales to mineralize phenol as the sole carbon substrate to carbon dioxide and methane. Moreover, these two enrichments could mineralize terephthalate and benzoate. During benzoate degradation in the mesophilic enrichment, a shift in the predominant bacterial population from Deltaproteobacteria group TA to Syntrophus spp. was observed, suggesting Syntrophus-related spp. could have a higher substrate affinity for benzoate. FISH further revealed that member of the Deltaproteobacteria group TA represented more than 68.3% of EUBmix FISH-detectable bacterial cell area in a full-scale mesophilic bioreactor treating phenol-containing wastewaters.

Anaerobic biological treatment of phenol at 9.5-15 degrees C in an expanded granular sludge bed (EGSB)-based bioreactor

The aims of this study were to demonstrate the (1) feasibility of psychrophilic, or low-temperature, anaerobic digestion (PAD) of phenolic wastewaters at 10-15 degrees C; (2) economic attractiveness of PAD for the treatment of phenol as measured by daily biogas yields and (3) impact on bioreactor performance of phenol loading rates (PLRs) in excess of those previously documented (1.2 kg phenol m(-3)d(-1)). Two expanded granular sludge bed (EGSB)-based bioreactors, R1 and R2, were employed to mineralise a volatile fatty acid-based wastewater. R2 influent wastewater was supplemented with phenol at an initial concentration of 500 mgl(-1) (PLR, 1 kgm(-3)d(-1)). Reactor performance was measured by chemical oxygen demand (COD) removal efficiency, CH(4) composition of biogas and phenol removal (R2 only). Specific methanogenic activity, biodegradability and toxicity assays were employed to monitor the physiological capacity of reactor biomass samples. The applied PLR was increased to 2 kgm(-3)d(-1) on day 147 and phenol removal by day 415 was 99% efficient, with 4 mgl(-1) present in R2 effluent. The operational temperature of R1 (control) and R2 was reduced by stepwise decrements from 15 degrees C through to a final operating temperature of 9.5 degrees C. COD removal efficiencies of c. 90% were recorded in both bioreactors at the conclusion of the trial (day 673), when the phenol concentration in R2 effluent was below 30 mgl(-1). Daily biogas yields were determined during the final (9.5 degrees C) operating period, when typical daily R2 CH4 yields of c. 3.3lCH4g(-1) COD(removed) d(-1) were recorded. The rate of phenol depletion and methanation by R2 biomass by day 673 were 68 mg phenol gVSS(-1)d(-1) and 12-20 ml CH(4) gVSS(-1)d(-1), respectively.

Anaerobic biogranulation in a hybrid reactor treating phenolic waste

Granulation was examined in four similar anaerobic hybrid reactors 15.5L volume (with an effective volume of 13.5L) during the treatment of synthetic coal wastewater at the mesophilic temperature of 27+/-5 degrees C. The hybrid reactors are a combination of UASB unit at the lower part and an anaerobic filter at the upper end. Synthetic wastewater with an average chemical oxygen demand (COD) of 2,240 mg/L, phenolics concentration of 752 mg/L and a mixture of volatile fatty acids was fed to three hybrid reactors. The fourth reactor, control system, was fed with a wastewater containing sodium acetate and mineral nutrients. Coal waste water contained phenol (490 mg/L); m-, o-, p-cresols (123.0, 58.6, 42 mg/L); 2,4-, 2,5-, 3,4- and 3,5-dimethyl phenols (6.3, 6.3, 4.4 and 21.3mg/L) as major phenolic compounds. A mixture of anaerobic digester sludge and partially granulated sludge (3:1) were used as seed materials for the start up of the reactors. Granules were observed after 45 days of operation of the systems. The granules ranged from 0.4 to 1.2 mm in diameter with good settling characteristics with an SVI of 12 mL/gSS. After granulation, the hybrid reactor performed steadily with phenolics and COD removal efficiencies of 93% and 88%, respectively at volumetric loading rate of 2.24 g COD/Ld and hydraulic retention time of 24 h. The removal efficiencies for phenol and m/p-cresols reached 92% and 93% (corresponding to 450.8 and 153 mg/L), while o-cresol was degraded to 88% (corresponding to 51.04 mg/L). Dimethyl phenols could be removed completely at all the organic loadings and did not contribute much to the residual organics. Biodegradation of o-cresol was obtained in the hybrid-UASB reactors.

Treatment of phenol and cresols in upflow anaerobic sludge blanket (UASB) process: a review

Upflow anaerobic sludge blanket (UASB) process has been successfully applied in the treatment of municipal and industrial wastewaters. Several researchers have investigated the suitability of the process for the treatment of phenols and phenolic wastewaters. The anaerobic treatment of phenols is still at an investigative stage. With increasing recognition of the UASB process, feasibility studies on the treatment of wastewater containing phenol and cresols (o-, m- and p- isomers) in UASB have been reviewed. It is reported that phenol concentration up to a range of 500-750 mg/L is generally not inhibitory to the UASB process. Phenol concentrations greater than 500 mg/L can be effectively treated with acclimatization of inocula, recirculation of the treated effluent and/or supplementing with co-substrates such as glucose, VFA and dilute molasses. The degradability of phenol is more than p-cresol, which in turn is more than m- and o-cresol.

The influence of substrate kinetics on the microbial community structure in granular anaerobic biomass

The development of a strong, active granular sludge bed is necessary for optimal operation of upflow anaerobic sludge blanket reactors. The microbial and mechanical structure of the granules may have a strong influence on desirable properties such as growth rate, settling velocity and shear strength. Theories have been proposed for granule microbial structure based on the relative kinetics of substrate degradation, but contradict some observations from both modelling and microscopic studies. In this paper, the structures of four granule types were examined from full-scale UASB reactors, treating wastewater from a cannery, a slaughterhouse, and two breweries. Microbial structure was determined using fluorescence in situ hybridisation probing with 16S rRNA-directed oligonucleotide probes, and superficial structure and microbial density (volume occupied by cells and microbial debris) assessed using scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The granules were also modelled using a distributed parameter biofilm model, with a previously published biochemical model structure, biofilm modelling approach, and model parameters. The model results reflected the trophic structures observed, indicating that the structures were possibly determined by kinetics. Of particular interest were results from simulations of the protein grown granules, which were predicted to have slow growth rates, low microbial density, and no trophic layers, the last two of which were reflected by microscopic observations. The primary cause of this structure, as assessed by modelling, was the particulate nature of the wastewater, and the slow rate of particulate hydrolysis, rather than the presence of proteins in the wastewater. Because solids hydrolysis was rate limiting, soluble substrate concentrations were very low (below Monod half saturation concentration), which caused low growth rates.

Simultaneous removal of phenol, ortho- and para-cresol by mixed anaerobic consortia

Two different anerobic consortia, one removing phenol and ortho- (o-) cresol and the other removing para- (p-) cresol, were cultivated in serum bottles using whey as cosubstrate substitute for proteose peptone. Phenol and p-cresol removal with the phenol-removing consortium were the same with 0.0125% (w/v) whey as with 0.05% proteose peptone. For the other consortium, 8 days were required to decrease the p-cresol concentration from 35 to 2 mg/L with 0.025% whey, while 35 days were required to achieve a similar removal with 0.5% proteose peptone. The two consortia were mixed and cultivated with 0.025% whey. Phenolic compound removal with the mixed consortia was as good as that achieved by each of the two initial consortia against their respective substrates. This removal activity was maintained after several transfers. In a continuous upflow fixed-film reactor, the mixed consortia removed over 98% of 150 mg/L of phenol and 35 mg/L of each o- and p-cresol in the influent at 29°C, with 0.025% whey as cosubstrate. The hydraulic retention time (HRT) was 0.25 day, corresponding to a phenolic compound volumic loading rate of 880 mg/(L of reactor × day). Once the continuous flow reactor achieved constant phenolic compound removal, no intermediates were found in the effluent, while in serum bottles, m-toluic acid, an o-cresol intermediate, accumulated. Measurements of the specific activity for the uptake of different substrates demonstrated the presence of all trophic groups involved in methanogenic fermentation. These activities were, in mg of substrate/(g of volatile suspended solids × day), as follows: 849 ± 25 for the acidogens; 554 ± 15 for the acetogens; 934 ± 37 for the aceticlastic methanogens; and 135 ± 15 for the hydrogenophilic methanogens. Electron micrographs of the mixed consortia showed seven different morphological bacterial types, including Methanotrix-like bacteria.Key words: anaerobic degradation, fixed-film reactor, proteose peptone, whey, phenolic compounds.