Phenol removal from hypersaline wastewaters in a Membrane Biological Reactor (MBR): operation and microbiological characterisation

Wastewater Treatment Using Membrane Bioreactor Technologies: Removal of Phenolic Contaminants from Oil and Coal Refineries and Pharmaceutical Industries

Huge amounts of noxious chemicals from coal and petrochemical refineries and pharmaceutical industries are released into water bodies. These chemicals are highly toxic and cause adverse effects on both aquatic and terrestrial life. The removal of hazardous contaminants from industrial effluents is expensive and environmentally driven. The majority of the technologies applied nowadays for the removal of phenols and other contaminants are based on physio-chemical processes such as solvent extraction, chemical precipitation, and adsorption. The removal efficiency of toxic chemicals, especially phenols, is low with these technologies when the concentrations are very low. Furthermore, the major drawbacks of these technologies are the high operation costs and inadequate selectivity. To overcome these limitations, researchers are applying biological and membrane technologies together, which are gaining more attention because of their ease of use, high selectivity, and effectiveness. In the present review, the microbial degradation of phenolics in combination with intensified membrane bioreactors (MBRs) has been discussed. Important factors, including the origin and mode of phenols' biodegradation as well as the characteristics of the membrane bioreactors for the optimal removal of phenolic contaminants from industrial effluents are considered. The modifications of MBRs for the removal of phenols from various wastewater sources have also been addressed in this review article. The economic analysis on the cost and benefits of MBR technology compared with conventional wastewater treatments is discussed extensively.

Modeling and assessment of the transfer effectiveness in integrated bioreactor with membrane separation

Integrating a reaction process with membrane separation allows for effective product removal, favorable shifting of the reaction equilibrium, overcoming eventual inhibitory or toxic effects of the products and has the advantage of being energy and space saving. It has found a range of applications in innovative biotechnologies, generating value-added products (exopolysaccharides, antioxidants, carboxylic acids) with high potential for separation/ concentration of thermosensitive bioactive compounds, preserving their biological activity and reducing the amount of solvents and the energy for solvent recovery. Evaluating the effectiveness of such integrated systems is based on fluid dynamics and mass transfer knowledge of flowing matter close to the membrane surface – shear deformation rates and shear stress at the membrane interface, mass transfer coefficients. A Computational Fluid Dynamics (CFD)-based approach for assessing the effectiveness of integrated stirred tank bioreactor with submerged membrane module is compiled. It is related to the hydrodynamic optimization of the selected reactor configuration in two-phase flow, as well as to the concentration profiles and analysis of the reactor conditions in terms of reaction kinetics and mass transfer.

Anaerobic biological treatment of industrial saline wastewater: fixed bed reactor performance and analysis of the microbial community structure and abundance

The purpose of the present work is to treat saline Tuna fish wastewater, with the salt concentration of 43 g L^-1 and total organic carbon (TOC) of 8.3 g L^-1, using an anaerobic fixed bed reactor involving salt-tolerant bacteria from the natural hypersaline environment during 150 days. The highest volatile solids (VS) removal efficiency of 84.1% was recorded for the organic loading rate (OLR) of 1.04 g TOC L^-1.d^-1 and the lowest salinity of 14.6 g NaCl L^-1. In addition, the maximum biogas production of 0.8 L^-1.d^-1 for a working volume of 4 L and an organic loading rate of 2.07 g TOC L^-1.d^-1 correlated with the decrease of Volatile fatty acids (VFA) content. The Polymerase Chain Reaction-Denaturing Gradient Gel Electrophoresis (PCR-DGGE) and the phylogenetic analysis of the bacterial community showed the action of hydrolytic, acidogenic, halotolerant sulfate-reducing and halophilic fermentative bacterium during the processing time. A stable archaeal and methanogenic community's diversity including hydrogenotrophic methanogens was demonstrated with Quantitative-PCR (Q-PCR). The highest bacterial population abundance was detected for 1.45 g TOC L^-1.d^-1 and the important methanogenic community abundance for 2.07 g TOC L^-1.d^-1 may be related to the highest biogas production in this charge for an effluent salinity of 27.7 g NaCl L^-1.

Absence of the nahG-like gene caused the syntrophic interaction between Marinobacter and other microbes in PAH-degrading process

In this study, Marinobacter sp. N4 isolated from the halophilic consortium CY-1 was found to degrade phenanthrene as a sole carbon source with the accumulation of 1-Hydroxy-2-naphthoic acid (1H2N). With the assistance of Halomonas sp. G29, phenanthrene could be completely mineralized. The hpah1 and hpah2 gene cluster was amplified from the genome of strain N4, that were responsible for upstream and downstream of PAH degradation. Strain N4 was predicted for the transformation from phenanthrene to 1H2N, and strain G29 could transform the produced 1H2N into 1,2-dihydroxynaphthalene (1,2-DHN). The produced 1,2-DHN could be further transformed into salicylic acid (SALA) by strain N4. SALA could be catalyzed into catechol by strain G29 and further utilized by strains N4 and G29 via the catechol 2,3-dioxygenase pathway and catechol 1,2-dioxygenase pathway, respectively. NahG, encoding salicylate hydroxylase, was absent from the hpah2 gene cluster and predicted to be the reason for 1H2N accumulation in the PAH-degrading process by pure culture of strain N4. The syntrophic interaction mode among Marinobacter and other microbes was also predicted. According to our knowledge, this is the first report of the PAH-degrading gene cluster in Marinobacter and the syntrophic interaction between Marinobacter and other microbes in the PAH-degrading process.

Performance of Anammox Processes for Wastewater Treatment: A Critical Review on Effects of Operational Conditions and Environmental Stresses

The anaerobic ammonium oxidation (anammox) process is well-known as a low-energy consuming and eco-friendly technology for treating nitrogen-rich wastewater. Although the anammox reaction was widely investigated in terms of its application in many wastewater treatment processes, practical anammox application at the pilot and industrial scales is limited because nitrogen removal efficiency and anammox activity are dependent on many operational factors such as temperature, pH, dissolved oxygen concentration, nitrogen loading, and organic matter content. In practical application, anammox bacteria are possibly vulnerable to non-essential compounds such as sulfides, toxic metal elements, alcohols, phenols, and antibiotics that are potential inhibitors owing to the complexity of the wastewater stream. This review systematically summarizes up-to-date studies on the effect of various operational factors on nitrogen removal performance along with reactor type, mode of operation (batch or continuous), and cultured anammox bacterial species. The effect of potential anammox inhibition factors such as high nitrite concentration, high salinity, sulfides, toxic metal elements, and toxic organic compounds is listed with a thorough interpretation of the synergistic and antagonistic toxicity of these inhibitors. Finally, the strategy for optimization of anammox processes for wastewater treatment is suggested, and the importance of future studies on anammox applications is indicated.

Membrane fouling and performance of anaerobic ceramic membrane bioreactor treating phenol- and quinoline-containing wastewater: granular activated carbon vs polyaluminum chloride

Although anaerobic membrane bioreactor (AnMBR) has been proposed for the treatment of phenolic wastewater, the membrane fouling is still a major obstacle. The effects of dosing of granular activated carbon (GAC) and polyaluminum chloride (PACl) on the treatment performance and membrane fouling of anaerobic ceramic membrane bioreactor were investigated for treating phenol- and quinoline-containing wastewater. The results suggested that the one-off dosing of GAC resulted in a decrease of protein/carbohydrate ratio, which might account for the aggravation of membrane fouling alongside with the decreased flocs size. Nevertheless, the substrate uptake rates (SUR) of phenol and quinoline, and the specific methanogenic activity of sludge at the GAC dosing stage of experimental reactor (R1) were 8.79 ± 0.63 mg phenol g^-1 MLVSS d^-1, 7.01 ± 0.09 mg quinoline g^-1 MLVSS d^-1 and 0.27 ± 0.01 g COD_CH4 g^-1 MLVSS d^-1, which were 1.69, 3.59 and 1.93 times higher than that of the control reactor (R2). The dosing of PACl reduced the membrane fouling rate by changing the floc structure of sludge, as well as the component of SMP and EPS. However, the substrate uptake rate of quinoline was declined. This work provides a comprehensive evaluation on the effect of GAC and PACl dosing on membrane fouling and performance of anaerobic ceramic membrane bioreactor treating phenol-and quinoline-containing wastewater.

Nitrate supply and sulfate-reducing suppression facilitate the removal of pentachlorophenol in a flooded mangrove soil

An anaerobic incubation was launched with varying nitrate (1, 5, 10 and 20 mM exogenous NaNO₃) and molybdate (20 mM Na₂MoO₄, a sulfate-reducing inhibitor) additions to investigate the characteristics of PCP dechlorination, as well as the reduction of natural co-occurring electron acceptors, including NO₃^-, Fe(III) and SO₄^2-, and the responses of microbial community structures under a unique reductive mangrove soil. Regardless of exogenous addition, nitrate was rapidly eliminated in the first 12 days. The reduction process of Fe(III) was inhibited, while that of SO₄^2- reduction depended on addition concentration as compared to the control. PCP was mainly degraded from orth-position, forming the only intermediate 2,3,4,5-TeCP by anaerobic microbes, with the highest PCP removal rate of average 21.9% achieved in 1 and 5 mM NaNO₃ as well as 20 mM Na₂MoO₄ treatments and the lowest of 7.5% in 20 mM NaNO₃ treatment. The effects of nitrate on PCP dechlorination depended on addition concentration, while molybdate promoted PCP attenuation significantly. Analyses of the Illumina sequencing data and the relative abundance of dominant microorganisms indicated that the core functional groups regulated PCP removal at genera level likely included Bacillus, Pesudomonas, Dethiobacter, Desulfoporosinus and Desulfovbrio in the nitrate treatments; while that was likely Sedimentibacter and Geosporobacter_Thermotalea in the molybdate treatment. Nitrate supplement but not over supplement, or addition of molybdate are suggested as alternative strategies for better remediation in the nitrate-deficient and sulfur-accumulated soil ecosystem contaminated by PCP, through regulating the growth of core functional groups and thereby coordinating the interaction between dechlorination and its coupled soil redox processes due to shifts of more available electrons to dechlorination. Our results broadened the knowledge regarding microbial PCP degradation and their interactions with natural soil redox processes under anaerobic soil ecosystems.

Microalgae cultivation for phenolic compounds removal

Microalgae are promising sustainable and renewable sources of oils that can be used for biodiesel production. In addition, they contain important compounds, such as proteins and pigments, which have large applications in the food and pharmaceutical industries. Combining the production of these valuable products with wastewater treatment renders the cultivation of microalgae very attractive and economically feasible. This review paper presents and discusses the current applications of microalgae cultivation for wastewater treatment, particularly for the removal of phenolic compounds. The effects of cultivation conditions on the rate of contaminants removal and biomass productivity, as well as the chemical composition of microalgae cells are also discussed.

Salinity effect on the metabolic pathway and microbial function in phenanthrene degradation by a halophilic consortium

With the close relationship between saline environments and industry, polycyclic aromatic hydrocarbons (PAHs) accumulate in saline/hypersaline environments. Therefore, PAHs degradation by halotolerant/halophilic bacteria has received increasing attention. In this study, the metabolic pathway of phenanthrene degradation by halophilic consortium CY-1 was first studied which showed a single upstream pathway initiated by dioxygenation at the C1 and C2 positions, and at several downstream pathways, including the catechol pathway, gentisic acid pathway and protocatechuic acid pathway. The effects of salinity on the community structure and expression of catabolic genes were further studied by a combination of high-throughput sequencing, catabolic gene clone library and real-time PCR. Pure cultures were also isolated from consortium CY-1 to investigate the contribution made by different microbes in the PAH-degrading process. Marinobacter is the dominant genus that contributed to the upstream degradation of phenanthrene especially in high salt content. Genus Halomonas made a great contribution in transforming intermediates in the subsequent degradation of catechol by using catechol 1,2-dioxygenase (C12O). Other microbes were predicted to be mediating bacteria that were able to utilize intermediates via different downstream pathways. Salinity was investigated to have negative effects on both microbial diversity and activity of consortium CY-1 and consortium CY-1 was found with a high degree of functional redundancy in saline environments.

The problem of fouling in submerged membrane bioreactors – Model validation and experimental evidence

Integrating biological treatment with membrane separation has found a broad area of applications and industrial attention. Submerged membrane bioreactors (SMBRs), based on membrane modules immersed in the bioreactor, or side stream ones connected in recycle have been employed in different biotechnological processes for separation of thermally unstable products. Fouling is one of the most important challenges in the integrated SMBRs. A number of works are devoted to fouling analysis and its treatment, especially exploring the opportunity for enhanced fouling control in SMBRs. The main goal of the review is to provide a comprehensive yet concise overview of modeling the fouling in SMBRs in view of the problematics of model validation, either by real system measurements at different scales or by analysis of the obtained theoretical results. The review is focused on the current state of research applying computational fluid dynamics (CFD) modeling techniques.

Kinetic studies on the removal of phenol by MBBR from saline wastewater

BACKGROUND

Phenols are chemical compounds which are included in the high priority of pollutants by environmental protection agency (USEPA). The presence of high concentrations of phenols in wastewaters like oil refineries, petrochemical plants, olive oil, pesticide production and oil field operations contain high soluble solids (TDS) and in an olive oil plant, wastewater is acidic, high salty and phenol concentrations are in the range of 0.1- 1%.

METHODS

Kinetic parameters were calculated according to Monod, Modified Stover- Kincannon, Hamoda and Haldane models. The influence of different initial phenol concentrations on the biodegradation rate was performed. The concentrations of phenol varied from 0 to 500 mg/l.

RESULTS

The value of K_i in saline phenolic wastewater in attached growth systems was higher than suspended growth systems that represented a higher phenol inhibition in suspended growth systems. It was obvious that the best model fitting the obtained data are Hamoda model and the Modified Stover-Kincannon model, having highest R² values of 0.991 and 1, respectively. The value of K_i in saline phenolic wastewater in attached growth system was higher than suspended growth systems which represented a higher phenol inhibition in suspended growth systems.

CONCLUSIONS

Hamoda model and the Modified Stover-Kincannon model having highest R2 value of 0.991 and 1, respectively, and also predicting reasonable kinetic coefficient values.

Acclimation of aerobic-activated sludge degrading benzene derivatives and co-metabolic degradation activities of trichloroethylene by benzene derivative-grown aerobic sludge

The acclimation of aerobic-activated sludge for degradation of benzene derivatives was investigated in batch experiments. Phenol, benzoic acid, toluene, aniline and chlorobenzene were concurrently added to five different bioreactors which contained the aerobic-activated sludge. After the acclimation process ended, the acclimated phenol-, benzoic acid-, toluene-, aniline- and chlorobenzene-grown aerobic-activated sludge were used to explore the co-metabolic degradation activities of trichloroethylene (TCE). Monod equation was employed to simulate the kinetics of co-metabolic degradation of TCE by benzene derivative-grown sludge. At the end of experiments, the mixed microbial communities grown under different conditions were identified. The results showed that the acclimation periods of microorganisms for different benzene derivatives varied. The maximum degradation rates of TCE for phenol-, benzoic acid-, toluene-, aniline- and chlorobenzene-grown aerobic sludge were 0.020, 0.017, 0.016, 0.0089 and 0.0047 mg g SS(-1) h(-1), respectively. The kinetic of TCE degradation in the absence of benzene derivative followed Monod equation well. Also, eight phyla were observed in the acclimated benzene derivative-grown aerobic sludge. Each of benzene derivative-grown aerobic sludge had different microbial community composition. This study can hopefully add new knowledge to the area of TCE co-metabolic by mixed microbial communities, and further the understanding on the function and applicability of aerobic-activated sludge.

Biodegradation of organic pollutants in saline wastewater by halophilic microorganisms: a review

Agro-food, petroleum, textile, and leather industries generate saline wastewater with a high content of organic pollutants such as aromatic hydrocarbons, phenols, nitroaromatics, and azo dyes. Halophilic microorganisms are of increasing interest in industrial waste treatment, due to their ability to degrade hazardous substances efficiently under high salt conditions. However, their full potential remains unexplored. The isolation and identification of halophilic and halotolerant microorganisms from geographically unrelated and geologically diverse hypersaline sites supports their application in bioremediation processes. Past investigations in this field have mainly focused on the elimination of polycyclic aromatic hydrocarbons and phenols, whereas few studies have investigated N-aromatic compounds, such as nitro-substituted compounds, amines, and azo dyes, in saline wastewater. Information regarding the growth conditions and degradation mechanisms of halophilic microorganisms is also limited. In this review, we discuss recent research on the removal of organic pollutants such as organic matter, in terms of chemical oxygen demand (COD), dyes, hydrocarbons, N-aliphatic and N-aromatic compounds, and phenols, in conditions of high salinity. In addition, some proposal pathways for the degradation of aromatic compounds are presented.

Biological removal of phenol from saline wastewater using a moving bed biofilm reactor containing acclimated mixed consortia

In this study, the performance of an aerobic moving bed biofilm reactor (MBBR) was assessed for the removal of phenol as the sole substrate from saline wastewater. The effect of several parameters namely inlet phenol concentration (200-1200 mg/L), hydraulic retention time (8-24 h), inlet salt content (10-70 g/L), phenol shock loading, hydraulic shock loading and salt shock loading on the performance of the 10 L MBBR inoculated with a mixed culture of active biomass gradually acclimated to phenol and salt were evaluated in terms of phenol and chemical oxygen demand (COD) removal efficiencies. The results indicated that phenol and COD removal efficiencies are affected by HRT, phenol and salt concentration in the bioreactor saline feed. The MBBR could remove up to 99% of phenol and COD from the feed saline wastewater at inlet phenol concentrations up to 800 mg/L, HRT of 18 h and inlet salt contents up to 40 g/L. The reactor could also resist strong shock loads. Furthermore, measuring biological quantitative parameters indicated that the biofilm plays a main role in phenol removal. Overall, the results of this investigation revealed that the developed MBBR system with high concentration of the active mixed biomass can play a prominent role in order to treat saline wastewaters containing phenol in industrial applications as a very efficient and flexible technology.

Performance of a MBR pilot plant treating high strength wastewater subject to salinity increase: analysis of biomass activity and fouling behaviour

Membrane bioreactors produce high quality effluents that could be suitable for reuse. However, when treating high strength wastewater subject to a salinity increase, a modification of biomass characteristics may occur. This circumstance is of importance, since it can have a significant impact in terms of biokinetic as well as fouling behaviour. The aim of the study was to evaluate the performance of a pilot plant MBR, in terms of biomass activity and membrane fouling, fed with high strength synthetic wastewater, when subject to a salinity increase. With normal salinity, the pilot plant showed high removal efficiencies and high biomass respiratory activity. On the other hand, the salinity increase significantly affected the removal efficiency as well as the SMP production. Furthermore, the salinity increase showed a strong effect on biomass activity, reducing in particular the respiration rates of autotrophic populations.

Influence of nutrient mixtures on p-nitrophenol degradation by Stenotrophomonas sp. isolated from groundwater

We isolated strain CERAR5, a Stenotrophomonas sp., from an aquifer contaminated with chlorinated hydrocarbons that utilizes up to 1.0 mM PNP within 62 h in M9 medium as a source of carbon and nitrogen. To assess the potential of this strain for use in bioremediation, we investigated the influence of external sources of carbon and nitrogen on bacterial degradation of PNP following a full factorial design analysis. Glucose, sodium acetate, phenol, sodium nitrate and ammonium chloride were the factors chosen, while per cent removal of PNP, growth of the bacterial strain, and change in pH of the medium were the responses measured. Glucose and acetate had significant positive influence on the removal PNP. In particular, acetate exhibited a significant positive effect on all the three responses measured, clearly suggesting that the addition of acetate greatly contributes to an efficient bioremediation of habitats contaminated with PNP by Stenotrophomonas sp. CERAR5.

Mechanisms of removing pollutants from aqueous solutions by microorganisms and their aggregates: a review

With the public's enhanced awareness of eco-safety, environmentally benign measures based on microorganisms and microbial aggregates have become more accepted as methods of removing pollutants from aquatic systems. In this review, the application of microorganisms and microbial aggregates for removing pollutants from aqueous solutions is introduced and described based on mechanisms such as assimilation, adsorption, and biodegradation. The advantages of and future studies regarding the use of microorganisms and microbial aggregates to remove pollutants are discussed. Due to the limitation of a single microorganism species in adapting to heterogeneous conditions, this review demonstrates that the application of microbial aggregates consisting of multiple photoautotrophic and heterotrophic microorganisms, is a promising method of removing multiple pollutants from complex wastewaters and warrants further research.

A novel 2,3-xylenol-utilizing Pseudomonas isolate capable of degrading multiple phenolic compounds

This work characterized a novel 2,3-xylenol-utilizing Pseudomonas isolate XQ23. From 16S rRNA phylogenetic analysis, XQ23 was found to be a member of the Pseudomonas putida group. Most of its physiological characteristics also shared similarities to P. putida. Phenols were catabolized by the meta-cleavage pathway. The dependence of the specific growth rate on 2,3-xylenol concentration could be well fitted by the Haldane model, with the maximum occurring at the concentration around 180 mg l(-1). Kinetic parameters indicated that XQ23 was sensitive to 2,3-xylenol and had low affinity. Three patterns, i.e. constant, linear decline, and allometric decline, were proposed to describe the biomass yields of phenols during bacterial degradation and XQ23 under 2,3-xylenol culturing conditions followed the allometric pattern. In a mineral-salts medium supplemented with 180 mg l(-1) of 2,3-xylenol as the sole carbon and energy source, over 40% of 2,3-xylenol was turned into CO(2) to provide energy by complete oxidization.