Optimal conditions and nitrogen removal performance of aerobic denitrifier Comamonas sp. pw-6 and its bioaugmented application in synthetic domestic wastewater treatment

To assess the possibility of using aerobic denitrification (AD) bacteria with high NO2--N accumulation for nitrogen removal in wastewater treatment, conditional optimization, as well as sole and mixed nitrogen source tests involving AD bacterium, Comamonas sp. pw-6 was performed. The results showed that the optimal carbon source, pH, C/N ratio, rotational speed, and salinity for this strain were determined to be succinate, 7, 20, 160 rpm, and 0%, respectively. Further, this strain preferentially utilized NH4+-N, NO3--N, and NO2--N, and when NO3--N was its sole nitrogen source, 92.28% of the NO3--N (150 mg·L-1) was converted to NO2--N. However, when NH4+-N and NO3--N constituted the mixed nitrogen source, NO3--N utilization by this strain was significantly lower (p < 0.05). Therefore, a strategy was proposed to combine pw-6 bacteria with traditional autotrophic nitrification to achieve the application of pw-6 bacteria in NH4+-N-containing wastewater treatment. Bioaugmented application experiments showed significantly higher NH4+-N removal (5.96 ± 0.94 mg·L-1·h-1) and lower NO3--N accumulation (2.52 ± 0.18 mg·L-1·h-1) rates (p < 0.05) than those observed for the control test. Thus, AD bacteria with high NO2--N accumulation can also be used for practical applications, providing a basis for expanding the selection range of AD strains for wastewater treatment.

Extracellular Polymeric Substances Drive Symbiotic Interactions in Bacterial‒Microalgal Consortia

The importance of several factors that drive the symbiotic interactions between bacteria and microalgae in consortia has been well realised. However, the implication of extracellular polymeric substances (EPS) released by the partners remains unclear. Therefore, the present study focused on the influence of EPS in developing consortia of a bacterium, Variovorax paradoxus IS1, with a microalga, Tetradesmus obliquus IS2 or Coelastrella sp. IS3, all isolated from poultry slaughterhouse wastewater. The bacterium increased the specific growth rates of microalgal species significantly in the consortia by enhancing the uptake of nitrate (88‒99%) and phosphate (92‒95%) besides accumulating higher amounts of carbohydrates and proteins. The EPS obtained from exudates, collected from the bacterial or microalgal cultures, contained numerous phytohormones, vitamins, polysaccharides and amino acids that are likely involved in interspecies interactions. The addition of EPS obtained from V. paradoxus IS1 to the culture medium doubled the growth of both the microalgal strains. The EPS collected from T. obliquus IS2 significantly increased the growth of V. paradoxus IS1, but there was no apparent change in bacterial growth when it was cultured in the presence of EPS from Coelastrella sp. IS3. These observations indicate that the interaction between V. paradoxus IS1 and T. obliquus IS2 was mutualism, while commensalism was the interaction between the bacterial strain and Coelastrella sp. IS3. Our present findings thus, for the first time, unveil the EPS-induced symbiotic interactions among the partners involved in bacterial‒microalgal consortia.

Biofilm characterization in removal of total chemical oxygen demand and nitrate from wastewater using draft tube spouted bed reactor

The present paper investigates the effect of dilution rate on the removal of total chemical oxygen demand and nitrate in the draft tube spouted bed reactor and morphological characteristics of biofilms formed by microorganisms of mixed culture on granular activated carbon (GAC). The nitrate and total chemical oxygen demand (COD) decreased from 97 to 81% and 95% to 87% respectively with increase in dilution rate from 0.6/h to 1.5/h showing that residence time in the reactor governs the nitrate and total COD reduction efficiency. Lower dilution rates favor higher production of biomass and extracellular polymeric substances (EPS). It was observed that the nitrate and total COD reduction rate increased with time along with simultaneous increase in EPS production. Thus, the performance of a reactor in terms of dynamic and steady-state biofilm characteristics associated with nitrate and organic reduction is a strong function of dilution rate. Hence these findings indicate that a draft tube spouted bed reactor is capable of simultaneously reducing total organics and nitrogen in industrial/municipal wastewater, as this reactor possesses two distinct regions aerobic and anoxic conditions which can prevail in different parts of a reactor.

Characterization of Thermophilic Lignocellulolytic Microorganisms in Composting

Composting involves the selection of a microbiota capable of resisting the high temperatures generated during the process and degrading the lignocellulose. A deep understanding of the thermophilic microbial community involved in such biotransformation is valuable to improve composting efficiency and to provide thermostable biomass-degrading enzymes for biorefinery. This study investigated the lignocellulose-degrading thermophilic microbial culturome at all the stages of plant waste composting, focusing on the dynamics, enzymes, and thermotolerance of each member of such a community. The results revealed that 58% of holocellulose (cellulose plus hemicellulose) and 7% of lignin were degraded at the end of composting. The whole fungal thermophilic population exhibited lignocellulose-degrading activity, whereas roughly 8-10% of thermophilic bacteria had this trait, although exclusively for hemicellulose degradation (xylan-degrading). Because of the prevalence of both groups, their enzymatic activity, and the wide spectrum of thermotolerance, they play a key role in the breakdown of hemicellulose during the entire process, whereas the degradation of cellulose and lignin is restricted to the activity of a few thermophilic fungi that persists at the end of the process. The xylanolytic bacterial isolates (159 strains) included mostly members of Firmicutes (96%) as well as a few representatives of Actinobacteria (2%) and Proteobacteria (2%). The most prevalent species were Bacillus licheniformis and Aeribacillus pallidus. Thermophilic fungi (27 strains) comprised only four species, namely Thermomyces lanuginosus, Talaromyces thermophilus, Aspergillus fumigatus, and Gibellulopsis nigrescens, of whom A. fumigatus and T. lanuginosus dominated. Several strains of the same species evolved distinctly at the stages of composting showing phenotypes with different thermotolerance and new enzyme expression, even not previously described for the species, as a response to the changing composting environment. Strains of Bacillus thermoamylovorans, Geobacillus thermodenitrificans, T. lanuginosus, and A. fumigatus exhibiting considerable enzyme activities were selected as potential candidates for the production of thermozymes. This study lays a foundation to further investigate the mechanisms of adaptation and acquisition of new traits among thermophilic lignocellulolytic microorganisms during composting as well as their potential utility in biotechnological processing.

Supported Biofilms on Carbon-Oxide Composites for Nitrate Reduction in Agricultural Waste Water

Escherichia coli colonies were grown on different supports for the removal of nitrates from water. A carbon material and different commercial metal oxides, such as SiO₂, TiO₂ and Al₂O₃, and their corresponding carbon–metal oxide composites were studied. The physicochemical properties were analyzed by different techniques and the results were correlated with their performance in the denitrification process. Developed biofilms effectively adhere to the supports and always reach the complete reduction of nitrates to gaseous products. Nevertheless, faster processes occur when the biofilm is supported on mesoporous and non-acid materials (carbon and silica).

The nitrogen removal characterization of a cold-adapted bacterium: Bacillus simplex H-b

The removal efficacy of biological nitrogen removal process is inhibited by low temperatures. Herein, a psychrotrophic bacterium strain, Bacillus simplex H-b, was isolated and identified with the potential to conduct heterotrophic nitrification and aerobic denitrification in the temperature range from 5 to 37 °C. At 10 °C, the removal efficiencies of initial nitrate-N (63 mg/L), nitrite-N (10 mg/L) and ammonium-N (60 mg/L) were 67.29%, 78.69% and 82.16%, with the maximum removal rate of 0.56, 0.18 and 0.74 mg/L/h, respectively. Additionally, both the accumulation level of ATP (adenosine triphosphate) and the formation of extracellular polymeric substances was found to increase with the decrease of temperature from 37 °C to 10 °C, indicating strain H-b might resist low temperature stress through its cellular extreme environment resistant mechanism and further suggesting the newly isolated strain could serve as a promising candidate for nitrogen contaminated wastewater treatment, especially under low-temperature condition.

Spontaneously Fermented Fruiting Bodies of Agaricus bisporus as a Valuable Source of New Isolates of Lactic Acid Bacteria with Functional Potential

The aim of the investigation was the identification and initial study of lactic acid bacteria (LAB) isolated from spontaneously fermented (at 28 °C for 5 days) fruiting bodies of white button mushrooms (Agaricus bisporus). The isolated LAB were preliminarily characterized applying the MALDI-TOF Biotyper. Moreover, further phenotypical, genotypical characteristics as well as some functional and technological properties of the selected microorganisms (including the ability to produce exopolysaccharides, cell hydrophobicity, resistance to low pH, and bile salt) were also analyzed. Among autochthonous LAB (isolated from the tested mushroom raw material), Leuconostoc mesenteroides predominated in spontaneously fermented A. bisporus, while Lactiplantibacillus paraplantarum, Lactiplantibacillus plantarum, and Lactococcus lactis were less abundant. The highest dynamics of acidification of the mushroom material were exhibited by isolates EK55 and EK4 that, after 24 h of incubation, were able to decrease the pH of the raw material up to 5.06 ± 0.021 and 5.17 ± 0.015, respectively. Furthermore, the analysis of bacterial cell hydrophobicity indicated that the highest values of this parameter were noted for L. plantarum isolates EK12 (29.59 ± 0.7%), EK55 (28.75 ± 0.551%), and EK5 (27.33 ± 1.516%). It was revealed some of the analyzed LAB (especially isolates L. plantarum EK55 and L. paraplantarum EK4) exhibited functional and technological potential that might be used in the formulation of novel starter cultures.

Simultaneous nitrate and dissolved organic matter removal from wastewater treatment plant effluent in a solid-phase denitrification biofilm reactor

In the present study, an up-flow solid-phase denitrification biofilm reactor (US-DBR) was established for simultaneous nitrate and dissolved organic matter (DOM) removal from wastewater treatment plant effluent. After 100 days operation, the nitrate and COD removal efficiencies were high of 97% and 80%, respectively. According to EEM-FRI analysis, aromatic and tryptophan protein-like, humic-like and fulvic acid-like substances were identified in DOM. Additionally, protein-like substances in DOM components were much easier transformed as carbon source for denitrification. Moreover, protein secondary structure of DOM changed significantly due to the biodegradation and microorganisms metabolic process. High-throughput sequencing analysis implied that Simplicispira, Diaphorobacter, Hydrogenophaga, Pseudoxanthmonas and Stenotrophomonas were the dominate genera in the whole of US-DBR, that were responsible for the removal of nitrate, organics and degradation of solid carbon source, respectively. This study provided a further biological basis about practical application of solid-phase denitrification for simultaneously remove nitrate and organic matter.

Biodegradation of crude oil by Chelatococcus daeguensis HB-4 and its potential for microbial enhanced oil recovery (MEOR) in heavy oil reservoirs

Biodegradation of crude heavy oil was investigated with Chelatococcus daeguensis HB-4 that was isolated from the produced fluid of Baolige Oilfield in China. Batch growth characterization and crude oil degradation tests confirmed HB-4 to be facultative anaerobic and able to degrade heavy oil. The oil degradation was found to occur through degrading long hydrocarbons chains to shorter ones, resulting in oil viscosity reduction. By mixing crude oil with glucose, or using sole crude oil as carbon source, the content of light fractions (C₈-C₂₂) increased by 4.97% while heavy fractions (C₂₃-C₃₇) decreased by 7.98%. It was also found that bioemulsifiers were produced rather than commonly observed biosurfactants in the fermentation process, which was attributed to the extracellular degradation of hydrocarbons. Core flooding tests demonstrated 20.5% oil recovery by microbial enhancement, and 59.8% viscosity reduction, showing potential of strain HB-4 for application in the oil industry, especially in enhanced heavy oil recovery.

Effects of biomass pyrolysis derived wood vinegar (WVG) on extracellular polymeric substances and performances of activated sludge

The effects of wood vinegar (WVG) on extracellular polymeric substances (EPS), and flocculation, sedimentation and dewatering performances of activated sludge were investigated in sequencing batch reactor (SBR) process. Results showed that polysaccharide (PS) and DNA were accounted for the largest and smallest proportion of EPS, respectively. With WVG injection, productions of soluble EPS (S-EPS), loosely bound EPS (LB-EPS), tightly bound EPS (TB-EPS), protein (PN), PS, and DNA were significantly increased. The optimal WVG concentration was found as 4 μl/l. The effects of WVG on different types of EPS followed an order of LB-EPS > TB-EPS > S-EPS. According to batch and long-term SBR operations, WVG could increase the biomass amount of activated sludge, which was beneficial to improve sewage treatment efficiencies. However, WVG showed negative impact on flocculation, sedimentation, and dewatering performance of activated sludge.