Functional consortia for cresol-degrading activated sludges: toxicity-to-extinction approach

Bioaugmentation of Soil with Pseudomonas monteilii Strain Eliminates Inhibition of Okra (Abelmoschus esculentus) Seed Germination by m-Cresol

Cresols are ubiquitous in nature due to their bulk production and end uses in various industrial processes as well as due to their natural presence. They are highly toxic to both fauna and flora and are included in the list of priority pollutants. In the present study, the effect of m-cresol on germination of ten different crop seeds was tested and the seeds of okra and eggplant were found to be very sensitive, okra being the most vulnerable. Okra seeds lost its viability in the presence of m-cresol, which was proportionate to its concentration as indicated by the standard 2,3,5-tetrazoliumtrichloride (TTC) test. Marked decrease in protease and amylase activities was observed in germinating seeds exposed to the compound. The inhibitory effect of m-cresol on germination was eliminated effectively by bioaugmentation of the soil with the cresol-degrading Pseudomonas monteilii S-CSR-0014. Normal germination and seedling vigor were obtained when the seeds were sown four and eight days after the soil inoculation with the bacterial cells, whereas the seeds sown immediately did not show proper germination. The inoculated bacterium degraded m-cresol efficiently from the spiked soil and exhibited concomitant growth. It can be concluded that m-cresol-contaminated soils could be effectively bioremediated to render the soil suitable for normal seed germination and healthy seedling growth of sensitive crops.

Adaptation of granular sludge microbial communities to nitrate, sulfide, and/or p-cresol removal

Effluents from petroleum refineries contain a toxic mixture of sulfide, nitrogen, and phenolic compounds that require adequate treatment for their removal. Biological denitrification processes are a cost-effective option for the treatment of these effluents, but the knowledge on the microbial interactions in simultaneous sulfide and phenol oxidation in denitrifying reactors is still very limited. In this work, microbial community structure and macrostructure of granular biomass were studied in three denitrifying reactors treating a mixture of inorganic (sulfide) and organic (p-cresol) electron donors for their simultaneous removal. The differences in the available substrates resulted in different community assemblies that supported high removal efficiencies, indicating the community adaptation capacity to the fluctuating compositions of industrial effluents. The three reactors were dominated by nitrate reducing and denitrifying bacteria where Thiobacillus spp. were the prevalent denitrifying organisms. The toxicity and lack of adequate substrates caused the endogenous decay of the biomass, leading to release of organic matter that maintained a diverse although not very abundant group of heterotrophs. The endogenous digestion of the granules caused the degradation of its macrostructure, which should be considered to further develop the denitrification process in sulfur-based granular reactors for treatment of industrial wastewater with toxic compounds.

Simultaneous oxidation of ammonium and cresol isomers in a sequencing batch reactor: physiological and kinetic study

The aim of this study was to evaluate the physiological and kinetic capacities of a nitrifying consortium to simultaneously oxidize ammonium (138 mg N/L day), m-cresol, o-cresol, and p-cresol (180 mg C/L day in mixture) in a sequencing batch reactor (SBR). A 1-L SBR was firstly operated without cresol addition (phase I) for stabilizing the nitrification respiratory process with ammonium consumption efficiencies close to 100 % and obtaining nitrate as the main end product. When cresols were added (phase II m-cresol (10, 20, and 30 mg C/L); phase III m-cresol (30 mg C/L) and o-cresol (10, 20, and 30 mg C/L); phase IV a mixture of three isomers (30 mg C/L each one)), inhibitory effects were evidenced by decreased values of the specific rates of nitrification compared with values from phase I. However, the inhibition diminished throughout the operation cycles, and the overall nitrifying physiological activity of the sludge was not altered in terms of efficiency and nitrate yield. The different cresols were totally consumed, being o-cresol the most recalcitrant. The use of SBR allowed a metabolic adaptation of the consortium to oxidize the cresols as the specific rates of consumption increased throughout the cycles, showing that this type of reactor can be a good alternative for treating industrial effluents in a unique reactor.

Nitrogen removal from coal gasification wastewater by activated carbon technologies combined with short-cut nitrogen removal process

A system combining granular activated carbon and powdered activated carbon technologies along with shortcut biological nitrogen removal (GAC-PACT-SBNR) was developed to enhance total nitrogen (TN) removal for anaerobically treated coal gasification wastewater with less need for external carbon resources. The TN removal efficiency in SBNR was significantly improved by introducing the effluent from the GAC process into SBNR during the anoxic stage, with removal percentage increasing from 43.8%-49.6% to 68.8%-75.8%. However, the TN removal rate decreased with the progressive deterioration of GAC adsorption. After adding activated sludge to the GAC compartment, the granular carbon had a longer service-life and the demand for external carbon resources became lower. Eventually, the TN removal rate in SBNR was almost constant at approx. 43.3%, as compared to approx. 20.0% before seeding with sludge. In addition, the production of some alkalinity during the denitrification resulted in a net savings in alkalinity requirements for the nitrification reaction and refractory chemical oxygen demand (COD) degradation by autotrophic bacteria in SBNR under oxic conditions. PACT showed excellent resilience to increasing organic loadings. The microbial community analysis revealed that the PACT had a greater variety of bacterial taxons and the dominant species associated with the three compartments were in good agreement with the removal of typical pollutants. The study demonstrated that pre-adsorption by the GAC-sludge process could be a technically and economically feasible method to enhance TN removal in coal gasification wastewater (CGW).

p-Cresol mineralization and bacterial population dynamics in a nitrifying sequential batch reactor

The ability of a nitrifying sludge to oxidize p-cresol was evaluated in a sequential batch reactor (SBR). p-Cresol was first transformed to p-hydroxybenzaldehyde and p-hydroxybenzoate, which were later mineralized. The specific rates of p-cresol consumption increased throughout the cycles. The bacterial population dynamics were monitored by using denaturing gradient gel electrophoresis (DGGE) and sequencing of DGGE fragments. The ability of the sludge to consume p-cresol and intermediates might be related to the presence of species such as Variovorax paradoxus and Thauera mechernichensis. p-Cresol (25 to 200mgC/L) did not affect the nitrifying SBR performance (ammonium consumption efficiency and nitrate production yield were close to 100% and 1, respectively). This may be related to the high stability observed in the nitrifying communities. It was shown that a nitrifying SBR may be a good alternative to eliminate simultaneously ammonium and p-cresol, maintaining stable the respiratory process as the bacterial community.

Unconventional approaches to isolation and enrichment of functional microbial consortium--a review

Studies on how different functional strains interact in a microflora may include isolation of pure strains using conventional plating technique and then mix a few of the isolates before observing their growth in specific medium. As isolating pure strains that take part in the key function of industrial effluent purification via conventional method is impractical, convenient alternative approaches to screen essential microbial group that maintains desired function of a mixed population is desired. Such approaches can be employed to allow the selection and enrichment of so-called functional consortium with user-defined attributes for specific functions. This manuscript provides a review of various approaches to isolation and enrichment of microbial functional consortium in several biological processes. Consideration for the isolation and enrichment approaches and their applications are delineated. Challenges to the applications and further work are also outlined.

Biodegradation of m-cresol by aerobic granules in a sequencing batch reactor

The present study was aimed at the development of aerobic granules in a sequencing batch reactor for the biodegradation of m-cresol. The reactor was started with 100 mg L(-1)of m-cresol. Aerobic granules first appeared within 1 month of the start-up of the reactor. The granules were large and strong and had a compact structure. The diameter of stable granules on day 200 was in the range of 1.5 - 5 mm. The integrity coefficient and density of the granules was found to be 98% and 1046 kg m(-3), respectively. The settling velocity of the granules was found to be in the range of 2-6 x 10(-2) m s(-1). The aerobic granules were able to degrade m-cresol up to 800 mg L(-1) at a removal efficiency of 87%. UV and GC/MS studies confirmed that the biodegradation ofm-cresol occurred via catechol via the ortho-cleavage pathway. The specific m-cresol degradation rate in aerobic granules followed the Haldane model for substrate inhibition. A high specific m-cresol degradation rate of up to 0.718 g m-cresol g(-1)VSS(-1)d(-1) was sustained up to an m-cresol concentration of 400 mgL(-1). The higher removal efficiency and good settling characteristics of aerobic granules make the sequencing batch reactor method suitable for enhancing the microorganism potential for biodegradation of inhibitory compounds.

Interspecific interactions in mixed microbial cultures in a biodegradation perspective

In recent works, microbial consortia consisting of various bacteria and fungi exhibited a biodegradation performance superior to single microbial strains. A highly efficient biodegradation of synthetic dyes, polycyclic aromatic hydrocarbons, polychlorinated biphenyls, and other organic pollutants can be achieved by mixed microbial cultures that combine degradative enzyme activities inherent to individual consortium members. This review summarizes biodegradation results obtained with defined microbial cocultures and real microbial consortia. The necessity of using a proper strategy for the microbial consortium development and optimization was clearly demonstrated. Molecular genetic and proteomic techniques have revolutionized the study of microbial communities, and techniques such as the denaturing gradient gel electrophoresis, rRNA sequencing, and metaproteomics have been used to identify consortium members and to study microbial population dynamics. These analyses could help to further enhance and optimize the natural activities of mixed microbial cultures.

Kinetics of aerobic biodegradation of dihydroxybenzenes by a p-nitrophenol-degrading activated sludge

The aerobic biodegradation of the three dihydroxybenzene isomers (catechol, resorcinol and hydroquinone) by an activated sludge acclimated to consume p-nitrophenol (PNP) was studied through batch respirometric tests. The PNP-degrading biomass was able to consume each isomer as the sole organic carbon source, as well as, mixtures of two or three dihydroxybenzenes. However, the biodegradation rates were significantly different for each isomer and were highly influenced by the simultaneous presence of the other dihydroxybenzenes in binary or ternary mixtures. In general, hydroquinone was the isomer consumed at the fastest rate while the consumption rate of resorcinol was the slowest one. The kinetics of aerobic biodegradation of hydroquinone and catechol were successfully described by a Haldane model. The values of the kinetic coefficients showed that the affinity of PNP-degrading biomass for both isomers was low while catechol caused less substrate inhibition than hydroquinone.

Phenol degradation activity and reusability of Corynebacterium glutamicum coated with NH(2)-functionalized silica-encapsulated Fe3O4 nanoparticles

In this study, a novel method to immobilize and separate Corynebacterium glutamicum for phenol degradation was developed using Fe(3)O(4) nanoparticles (NPs). The Fe(3)O(4) NPs were encapsulated with silica and functionalized with NH(2) groups to enhance their capacity to adsorb on the cell surface. The results showed that the NH(2)-functionalized silica-encapsulated Fe(3)O(4) NPs strongly adsorbed on the cell surface of C. glutamicum during 32 d culture without any interruptions of their normal cell growth. The coated C. glutamicum were easily separated from the culture broth within 2 min by applying an external magnetic field Also, the coated C.glutamicum were able to completely degrade 50 ppm phenol in the culture broth after 8d culture at 30 °C. Concerning reusability, the coated cells could completely degrade phenol during the first 2 cycles, and retain ~60% activity of phenol degradation for the third and four cycles.

Assessment of denitrifying bacterial composition in activated sludge

The abundance and structure of denitrifying bacterial community in different activated sludge samples were assessed, where the abundance of denitrifying functional genes showed nirS in the range of 10(4)-10(5), nosZ with 10(4)-10(6) and 16S rRNA gene in the range 10(9)-10(10) copy number per ml of sludge. The culturable approach revealed Pseudomonas sp. and Alcaligenes sp. to be numerically high, whereas culture independent method showed betaproteobacteria to dominate the sludge samples. Comamonas sp. and Pseudomonas fluorescens isolates showed efficient denitrification, while Pseudomonas mendocina, Pseudomonas stutzeri and Brevundimonas diminuta accumulated nitrite during denitrification. Numerically dominant RFLP OTUs of the nosZ gene from the fertilizer factory sludge samples clustered with the known isolates of betaproteobacteria. The data also suggests the presence of different truncated denitrifiers with high numbers in sludge habitat.