Effect of hydraulic retention time on lactic acid production and granulation in an up-flow anaerobic sludge blanket reactor

Unveiling methane oxidation dynamics, microbial community, and function of Fe(III)-driven anaerobic methane oxidation inside landfill

Trivalent iron (Fe3+) could participate in methane (CH4) oxidation as an electron acceptor under anaerobic conditions, but the kinetic process remains unknown in landfills, and the understanding of metabolic pathway of Fe3+-dependent anaerobic methane oxidation (Fe-DAMO) is still limited. In this study, the dual-substrate (CH4-Fe3+) kinetic model of CH4 oxidation is obtained with Vmax (7.35 ± 0.4184)μmol/(kg d), half-saturation constant K m , CH 4 (16.6699 ± 2.3940)ppmv, and K m , Fe 3 + (0.00107 ± 0.0002g/g). Microbial community analysis shows that Methanobacteriales and Clostridia are dominant microorganisms of Fe-DAMO. PICRUSt analysis confirms that the metabolic pathway of AMO is the reverse CH4 production pathway. The results provide a new perspective for CH4 biodegradation in landfills and offer a better understanding of Fe-DAMO process.

Electrical voltage application as a novel approach for facilitating methanogenic granulation

Despite having high-rate methanogenic performance, up-flow anaerobic sludge blanket reactor still has challenges regarding long-start up period (3-8 months) for granulation. In this study, "electrical voltage (EV, 0.3 V) application" was attempted for facilitating granulation in the continuous operation with increased organic loading rates (0.5-11.0 kg COD/m³/d). Up to 11.0 kg COD/m³/d, EV-reactor exhibited the stable performance, while the control failed. After 49 days of operation (at 7 kg COD/m³/d), the granules collected from EV-reactor had larger diameter (2.3 vs 1.6 mm), higher settling velocity (2.6 vs 1.9 cm/s), and higher hydrophobicity (52.1 % vs 34.5 %), compared to the control. EV application also increased the specific methanogenic activity for propionate and hydrogen almost by two times. The relative abundance of Pseudomonas sp. (quorum sensing (QS)-related microbe) in EV-reactor was 17 % higher than that in the control. In addition, EV application increased the expression of QS genes significantly by 27 times.

Decomposition process of cefotaxime sodium from antibiotic wastewater by Up-flow Blanket Filter (UBF) reactor: Reactor performance, sludge characteristics and microbial community structure analysis

In this study, a novel Up-flow Blanket Filter (UBF) reactor was applied to the degradation of antibiotic wastewater. The experiments showed that when the hydraulic retention time (HRT) was 24 h and the ratio of volatile fatty acids (VFA) to alkalinity (ALK) was 0.3, the best removal efficiency was achieved in the combined packing UBF reactor, and the COD removal efficiency reached 80.1%-84.6%, exhibiting a significant difference in reaction performance from the other two reactors (P < 0.05) and a good efficiency of cefotaxime sodium removal. Moreover, the microstructure and surface characteristics of the reactor fillers were studied through scanning electron microscope (SEM) analysis, which showed that three fillers all had biofilm adhesion, but the combined packing gave best performance. Energy dispersive spectrometer (EDS) tests indicated abundant element components in the combined packing. The particle size distribution of sludge was also considered in the experiment, and the result showed the particle size of sludge increased with the operation of the reactor. In addition, microbial community structures of sludge and biofilm with the combined packing were analyzed. High-throughput sequencing confirmed the existence of Pseudomonas, which had good adaptability to antibiotic wastewater and became the dominant bacteria. Decomposition process of cefotaxime sodium after hydrolysis and anaerobic treatment was analyzed through Fourier transform infrared spectroscopy (FTIR). The reactor, which is economical, exhibited favorable performance in degrading the pollutions in the antibiotic wastewater.

Growth and Break-Up of Methanogenic Granules Suggests Mechanisms for Biofilm and Community Development

Methanogenic sludge granules are densely packed, small, spherical biofilms found in anaerobic digesters used to treat industrial wastewaters, where they underpin efficient organic waste conversion and biogas production. Each granule theoretically houses representative microorganisms from all of the trophic groups implicated in the successive and interdependent reactions of the anaerobic digestion (AD) process. Information on exactly how methanogenic granules develop, and their eventual fate will be important for precision management of environmental biotechnologies. Granules from a full-scale bioreactor were size-separated into small (0.6-1 mm), medium (1-1.4 mm), and large (1.4-1.8 mm) size fractions. Twelve laboratory-scale bioreactors were operated using either small, medium, or large granules, or unfractionated sludge. After >50 days of operation, the granule size distribution in each of the small, medium, and large bioreactor sets had diversified beyond-to both bigger and smaller than-the size fraction used for inoculation. Interestingly, extra-small (XS; <0.6 mm) granules were observed, and retained in all of the bioreactors, suggesting the continuous nature of granulation, and/or the breakage of larger granules into XS bits. Moreover, evidence suggested that even granules with small diameters could break. "New" granules from each emerging size were analyzed by studying community structure based on high-throughput 16S rRNA gene sequencing. Methanobacterium, Aminobacterium, Propionibacteriaceae, and Desulfovibrio represented the majority of the community in new granules. H2-using, and not acetoclastic, methanogens appeared more important, and were associated with abundant syntrophic bacteria. Multivariate integration (MINT) analyses identified distinct discriminant taxa responsible for shaping the microbial communities in different-sized granules.

Anaerobic treatment of glutamate-rich wastewater in a continuous UASB reactor: Effect of hydraulic retention time and methanogenic degradation pathway

To investigate the anaerobic treatment efficiency and degradation pathways of glutamate-rich wastewater under various hydraulic retention times (HRTs), a lab-scale upflow anaerobic sludge blanket (UASB) reactor was operated continuously for 180 days. Results showed that high chemical oxygen demand (COD) removal efficiencies of 95.5%-96.5% were achieved at HRTs of 4.5 h-6 h with a maximum methane yield of 0.31 L-CH₄/g-COD. When the HRT was shortened to less than 3 h, the removal performance of the reactor declined. There also was an excessive accumulation of volatile fatty acids, which implies that an appropriately small HRT is applicable to the UASB reactor treating glutamate-rich wastewater. Methanogenic degradation of glutamate in the UASB reactor depended on the HRT applied, and the typical methane-producing capability of the sludge at an HRT of 3 h, in descending order, was acetate > glutamate > butyrate > H₂/CO₂ > valerate > propionate. Clostridium and Methanosaeta were predominant in the glutamate-degrading sludge. At least three degradation pathways most likely existed in the UASB reactor, and the pathway via 3-methlaspartate by Clostridium pascui was expected to be dominant.

Strategies of anaerobic sludge granulation in an EGSB reactor

Anaerobic sludge granulation was evaluated in an expanded granular sludge bed (EGSB) reactor based on the increases in the specific organic loading rate (SOLR). The effect of precursor substances (calcium chloride, sodium chloride, and tannin) on the development of granular sludge was also investigated in batch reactors. The reactors were fed with synthetic sewage and operated in mesophilic conditions. The EGSB was operated with a variable hydraulic retention time (HRT) and the batch reactors, with cycles of 8 h and 16 h. The increase of SOLR from 17.4 ± 7.4 to 104.6 ± 66.7 mgCOD gVSS^-1 d^-1 in the EGSB resulted in an increase on the average granules diameter from 344.3 to 1583.3 μm. These conditions also favored the reduction rates of chemical oxygen demand (COD) and volatile fatty acids (VFAs) concentration in the reactor. When the upflow velocity suffered an abrupt increase (from 0.06 L h^-1 to 0.25 L h^-1), the granules size began to decrease and lose their settleability characteristics. Considering this, it is proposed to start the biomass granulation process without effluent recirculation, and, after the granules reach the desired size and settleability capacity, the normal operation of EGSB reactor starts. The results showed that calcium chloride was more efficient for granulation. CaCl₂ addition can be performed only during the reactor's start-up, improving granulation and reducing start-up time. Thus, these results have practical implications as granules maintenance is the key to the proper EGSB operation.

Addition of iron materials for improving the removal efficiencies of multiple contaminants from wastewater with a low C/N ratio in constructed wetlands at low temperatures

Constructed wetlands (CWs) are widely used in wastewater treatment. Wastewater generally contains multiple contaminants. In this study, CWs were applied to treat wastewater with a low COD/TN ratio and containing heavy metals. Iron-based material was added in CWs to enhance the treatment efficiency. The contaminant removal efficiency was positively correlated with the dosage of iron-based material. Considering the operation cost, we added 1 g of iron-based material in CW and realized the multi-contaminant removal efficiency after 4-day treatment at low temperature: 99.51% of Cu(II), 87.22% of Cr(VI), 65.62% of TN, and 60.23% of COD. Microbial community analysis and kinetic analysis predicted that the removal mechanism involved ion exchange and microbial denitrification. Specific bacteria were found in CWs with iron-based material, such as Thiobacillus spp. and Thauera spp., indicating that the nitrate removal in the denitrification process was triggered by carbon sources and that Fe²⁺ worked as both the electron donor and the adjuster of the abundances of specific bacteria. The addition of iron-based material into CWs was a green option to improve the pollutant removal performance.

Effects of iron and calcium carbonate on contaminant removal efficiencies and microbial communities in integrated wastewater treatment systems

In the paper, we explored the influences of different dosages of iron and calcium carbonate on contaminant removal efficiencies and microbial communities in algal ponds combined with constructed wetlands. After 1-year operation of treatment systems, based on the high-throughput pyrosequencing analysis of microbial communities, the optimal operating conditions were obtained as follows: the ACW10 system with Fe³⁺ (5.6 mg L^-1), iron powder (2.8 mg L^-1), and CaCO₃ powder (0.2 mg L^-1) in influent as the adjusting agents, initial phosphorus source (PO₄^3-) in influent, the ratio of nitrogen to phosphorus (N/P) of 30 in influent, and hydraulic retention time (HRT) of 1 day. Total nitrogen (TN) removal efficiency and total phosphorus (TP) removal efficiency were improved significantly. The hydrolysis of CaCO₃ promoted the physicochemical precipitation in contaminant removal. Meanwhile, Fe³⁺ and iron powder produced Fe²⁺, which improved contaminant removal. Iron ion improved the diversity, distribution, and metabolic functions of microbial communities in integrated treatment systems. In the treatment ACW10, the dominant phylum in the microbial community was PLANCTOMYCETES, which positively promoted nitrogen removal. After 5 consecutive treatments in ACW10, contaminant removal efficiencies for TN and TP respectively reached 80.6% and 57.3% and total iron concentration in effluent was 0.042 mg L^-1.

Performance of an anaerobic membrane bioreactor in which granular sludge and dynamic filtration are integrated

To alleviate the fouling of a filter, simple substrates, dynamic filtration, and granular sludge were applied in an anaerobic membrane bioreactor (AnMBR). The results showed that under a transmembrane pressure < 20 kPa, the filter flux ranged between 15 and 20 l (m^-2 h)^-1 for a period of 30 days. The flux was higher than the typical flux of AnMBRs with conventional membranes and most current dynamic filters. In addition, the low cost of the filter avoided the need for a higher flux. Moreover, a stable granular sludge bed, which consumed all volatile fatty acids, was maintained. A compact fouling/filtration layer formed on the filter, which contributed to low effluent chemical oxygen demand concentrations and turbidity. In addition, substrate scarcity in the filtration zone resulted in the evolution of diverse bacteria on the filter.

Performance of a full-scale modified anaerobic/anoxic/oxic process: High-throughput sequence analysis of its microbial structures and their community functions

The average COD, TN, TP, and NH4(+)-N elimination rates in a new wastewater treatment plant (WWTP) based on a modified A2/O process were 83%, 72.4%, 93.5%, and 98.6%, respectively, even under conditions of a low C/N ratio and low temperature. Among the four potential denitrifying units, the post-anoxic unit was the least efficient with respect to the removal efficiency. However, the structures of the bacterial community among samples obtained from the treatment units were similar, as demonstrated using Illumina Miseq high-throughput sequencing. Genera with nitrifying, denitrifying, hydrolyzing, and glycogen-accumulating activities were identified in all units, indicating that functional groups were highly enriched in the active sludges and thus enabled nitrogen removal. The key functional microorganisms responsible for nitrification-denitrification in the WWTP were species belonging to the genera Nitrospira, Hydrogenophilaceae, Comamonas, Dechloromonas, Thauera, Haliangium, and Halomonas.

Influence of two-phase anaerobic digestion on fate of selected antibiotic resistance genes and class I integrons in municipal wastewater sludge

The response of representative antibiotic resistance genes (ARGs) to lab-scale two-phase (acidogenic/methanogenic phase) anaerobic digestion processes under thermophilic and mesophilic conditions was explored. The associated microbial communities and bacterial pathogens were characterized by 16S rRNA gene sequencing. A two-phase thermophilic digestion reduced the presence of tetA, tetG, tetX, sul1, ermB, dfrA1, dfrA12 and intI1 exhibiting 0.1-0.72 log unit removal; in contrast, tetO, tetW, sul3, ermF and blaTEM even increased relative to the feed, and sul2 showed no significant decrease. The acidogenic phase of thermophilic digestion was primarily responsible for reducing the quantity of these genes, while the subsequent methanogenic phase caused a rebound in their quantity. In contrast, a two-phase mesophilic digestion process did not result in reducing the quantity of all ARGs and intI1 except for ermB and blaTEM. ARGs patterns were correlated with Proteobacteria and Actinobacteria during the two-phase anaerobic digestion.

Microbial structures and community functions of anaerobic sludge in six full-scale wastewater treatment plants as revealed by 454 high-throughput pyrosequencing

The microbial communities and abundance in anaerobic sludge from 4 industrial and 2 municipal wastewater treatment plants were investigated using 454 pyrosequencing technology in this study. A total of 5482-8692 high-quality reads of 16S rRNA V3-V5 regions were obtained. Taxonomic analysis using QIIME and RDP classifier found that Proteobacteria, Bacteroidetes, Chloroflexi and Firmicutes were the most abundant phyla in these samples. Furthermore, real-time PCR was used to validate the absolute abundance of these 16S rRNAs and some functional genes, including total bacteria, anammox bacteria, NOB (Nitrobacter, Nitrospira), AOA amoA, AOB amoA, nosZ, nirS, nirK, narG, napA, nrfA, mcrA and dsrA. Multivariate linear regression analysis indicated that AOA might be mixotrophic. Finally, redundancy analysis was used to reveal the relationships between operation parameters and microbial communities. Results showed that the coexistence of anammox, denitrification and DNRA could be useful for the simultaneous removal of nitrogen and organic matter.

Effect of the accuracy of pH control on hydrogen fermentation

pH, known as the most important parameter in H2 fermentation, cannot be precisely controlled in a scaled-up fermenter as in a lab fermenter. In the preset work, to assess the effect of pH control accuracy on H2 fermentation, the pH was controlled at 6.0±0.1, 6.0±0.3, 6.0±0.5, 6.0±0.7, and 6.0±0.9 during batch fermentation of food waste. Up to deviation of ±0.3, a high H2 yield of 1.67-1.73 mol H2/mol hexose(added) was attained with producing butyrate as a major metabolite (>70% of total organic acids produced). A huge drop of H2 production, however, was observed at deviation >±0.5 with lowered substrate utilization and increased production of lactate. Next generation sequencing results showed that Clostridium was found to be the dominant genus (76.4% of total number of sequences) at deviation of ±0.1, whereas the dominant genus was changed to lactic acid bacteria such as Streptococcus and Lactobacillus with increase of deviation value.