Effect of dissolved oxygen concentration (microaerobic and aerobic) on selective enrichment culture for bioaugmentation of acidic industrial wastewater

Carbon and nitrogen metabolic pathways and interaction of cold-resistant heterotrophic nitrifying bacteria under aerobic and anaerobic conditions

In this study, both the carbon and nitrogen metabolisms of two heterotrophic nitrification bacteria were investigated under aerobic and anaerobic conditions at 2 °C. Similar catabolism and anabolism trends were observed for the two bacteria in stable experimental systems under aerobic and anaerobic conditions. Based on the nitrogen and carbon balance analysis and adenosine triphosphate (ATP) calculation, we proposed the following metabolic pathways: i) aerobic: except for microbial assimilation, the carbon and nitrogen sources were removed through respiration and nitrification, which provided energy for cell synthesis; and ii) anaerobic: the nitrification process almost stopped and most of the carbon sources decomposed into inorganic carbon, which dissolved in the medium. Based on our proposed metabolic pathways, we speculated that the nitrifying process almost stopped under anaerobic conditions and the nitrification bacteria would degrade more carbon contaminants to produce energy and maintain the cell growth. Furthermore, these bacteria may decompose the non-readily biodegradable carbon through anaerobic degradation. To verify these hypotheses, experiments with two types of synthetic wastewater were conducted: i) synthetic wastewater rich in carbon and poor in nitrogen, and higher carbon removal efficiencies of strain J and strain P (∼25%) were obtained under anaerobic conditions compared with aerobic conditions (∼19%); and ii) synthetic wastewater with recalcitrant carbon sources, and carbon removal efficiencies under anaerobic conditions were higher than those under aerobic conditions. The results of the synthetic wastewater experiments were consistent with the hypotheses and thus validated the metabolic pathways proposed for carbon and nitrogen.

A Hierarchically Modified Graphite Cathode with Au Nanoislands, Cysteamine, and Au Nanocolloids for Increased Electricity-Assisted Production of Isobutanol by Engineered Shewanella oneidensis MR-1

It is necessary to understand the surface structural effects of electrodes on the bioalcohol productivity of Shewanella oneidensis MR-1, but this research area has not been deeply explored. Here, we report that the electricity-assisted isobutanol productivity of Shewanella oneidensis MR-1::pJL23 can be enhanced by sequentially modifying a graphite felt (GF) surface with Au nanoislands (Au), cysteamine (NH₂), and Au nanoparticles (Au NPs). After bacteria were incubated for 50 h with the unmodified GF under various electrode potentials (vs Ag/AgCl), the bacterial isobutanol concentrations increased from 2.9 ± 1 mg/L under no electricity supply to a maximum of 5.9 ± 1 mg/L at -0.6 V. At this optimum electrode potential, the concentrations continued increasing to 9.1 ± 1, 14 ± 2, and 27 ± 2 mg/L when the GF electrodes were modified with Au, NH₂-Au, and Au NP-NH₂-Au, respectively. We further studied how each surface structure affected the bacterial adsorptions, current profiles, and biofilms' electrochemical performances. In particular, these modifications induced the adsorption of elongated bacteria, with the amount dependent on the electrode structure. In the presence of electric supply, the amount of elongated bacteria further increased. We also found that the NH₂-Au-GF and Au NP-NH₂-Au-GF electrodes themselves could increase the concentrations to 11 ± 0.3 and 12 ± 2 mg/L, respectively, upon the bacterial incubation without electricity. Among the electrodes tested, the contribution of electricity to the bacterial isobutanol production was the greatest with the Au NP-NH₂-Au-GF electrode. After 96 h of incubation, the concentration increased to 72 ± 2 mg/L, which was 4.7 and 3.7 times the previously reported values obtained without and with electricity, respectively.

Bioaugmentation in a pilot-scale constructed wetland to treat domestic wastewater in summer and autumn

In order to determine whether bioaugmentation is an effective technique in wetlands before the plants were harvested, the nitrogen (N) removal from a constructed wetland (CW) planted with Phragmites was evaluated after inoculating with Paenibacillus sp. XP1 in Northern China. The experiment was loaded with secondary effluent of rural domestic wastewater (RDW) using the batch-loaded method for over a 17-day period in summer and autumn. Chemical oxygen demand (CODcr), ammonia nitrogen (NH3-N), and total nitrogen (TN) decreased significantly in the CW with Phragmites inoculated with Paenibacillus sp. XP1. Four days after treatments were set up, the removal efficiencies were found to be 76.2 % for CODcr, 83 % for NH3-N, and 63.8 % for TN in summer and 69.5 % for CODcr, 76.9 % for NH3-N, and 55.6 % for TN in autumn, which were higher than the control group without inoculation during the entire 17-day experiment. The inoculated bacteria did not have a noticeable effect on total phosphorus (TP) removal in autumn. However, bioaugmentation still keep a low P concentration in the whole CW. First-order kinetic model represented well the CODcr, TN, and TP decay in CWs with bioaugmentation, resulting in very good coefficients of determination, which ranged from 0.97 to 0.99. It indicated that bioaugmentation would be an effective treatment for pollutant removal from RDW in the CWs.

Microaerobic DO-induced microbial mechanisms responsible for enormous energy saving in upflow microaerobic sludge blanket reactor

This study experimentally examined the microaerobic dissolved oxygen (DO)-induced microbial mechanisms that are responsible for enormous energy savings in the upflow microaerobic sludge blanket reactor (UMSB) for domestic wastewater treatment. Phylogenetic and kinetic analyses (as determined by clone library analyses and sludge oxygen affinity analyses) showed that the microaerobic conditions in the UMSB led to the proliferation and dominance of microaerophilic bacteria that have higher oxygen affinities (i.e., lower sludge oxygen half-saturation constant values), which assured efficient COD and NH3-N removals and sludge granulation in the UMSB similar as those achieved in the aerobic control. However, the microaerobic DO level in the UMSB achieved significant short-cut nitrification, a 50-90% reduction in air supply, and an 18-28% reduction in alkali consumption. Furthermore, the disappearance of sludge bulking in the UMSB when it was dominated by "bulking-induced" filamentous bacteria should be attributed to its upflow column-type configuration.

An eco-friendly treatment of tannery wastewater using bioaugmentation with a novel microbial consortium

A novel microbial consortium (BM-S-1) enriched from natural soils was successfully used to treat tannery wastewater from leather manufacturing industries in Korea on a pilot scale. The objective of this study was to determine whether augmentation with a novel microbial consortium BM-S-1could successfully treat the recalcitrant wastewater without chemical pre-treatment in a tannery wastewater treatment system. Chemical oxygen demand (COD), total nitrogen (TN) and total phosphorus (TP) were monitored for water quality. The microbial population dynamics were analyzed using pyrosequencing, and denitrifying bacteria were quantified using real-time PCR (RT-PCR). The removal efficiencies for COD, TN and TP were greater than 91%, 79%, and 90%, respectively. The dominant phyla in the buffering tank (B), primary aeration (PA), secondary aeration (SA) and sludge digestion tank (SD) were Proteobacteria, Firmicutes, Bacteroidetes, Planctomycetes and Deinococcus-Thermus. Cluster analysis based on the UniFrac distance of the species in the different stages showed that the PA is similar to the SA, whereas the B is similar to the SD. qPCR of the nosZ genes showed the highest abundance of denitrifiers in B, which was increased 734-fold compared to the influent (I). It was hypothesized that anaerobic denitrifiers and the diverse microbial community may play important roles in the biological treatment of tannery wastewater. This technology may also contribute to the full-scale treatment of industrial wastewater containing food processing wastewater and marine sediment with high organic content.