Performance of a packed-bed anode bio-electrochemical reactor for power generation and for removal of gaseous acetone

Enhanced nitrogen removal from secondary effluent of municipal wastewater using denitrification filter: Feasibility of refractory organics as a carbon source

Conventional advanced nitrogen removal in municipal wastewater is hindered by the limited availability of carbon sources in the secondary effluent. However, refractory organics present in it had the potential to serve as intrinsic carbon sources after hydrolysis for nitrogen removal via simultaneous denitrification and partial-denitrification anammox (PDA) processes. To assess this potential, a denitrification filter was set up in this study to evaluate its feasibility of concurrent processes. Results showed that increasing influent ammonium (NH4+-N) from 1.0 to 7.0 mg/L increased total nitrogen (TN) removal from 52.4 % to 89.9 %. Simultaneous occurrence of PDA and denitrification process were confirmed by the actual chemical oxygen demand (COD) consumption (0.8-1.2 mg/mg TN removal) from non-fluorescent organics. The presence of the anammox, hydrolytic and denitrifying bacteria further supported the achievement of nitrogen removal through PDA and denitrification processes by utilizing hydrolytic products biodegraded from refractory organics.

Influence of temperature on performance and mechanism of advanced synergistic nitrogen removal in lab-scale denitrifying filter with biogenic manganese oxides

Temperature is a significant operational parameter of denitrifying filter (DF), which affects the microbial activity and the pollutants removal efficiency. This study investigated the influence of temperature on performance of advanced synergistic nitrogen removal (ASNR) of partial-denitrification anammox (PDA) and denitrification, consuming the hydrolytic and oxidation products of refractory organics in the actual secondary effluent (SE) as carbon source. When the test water temperature (TWT) was around 25, 20, 15 and 10 °C, the filtered effluent total nitrogen (TN) was 1.47, 1.70, 2.79 and 5.52 mg/L with the removal rate of 93.38%, 92.25%, 87.33% and 74.87%, and the effluent CODcr was 8.12, 8.45, 10.86 and 12.29 mg/L with the removal rate of 72.41%, 66.17%, 57.35% and 51.87%, respectively. The contribution rate of PDA to TN removal was 60.44%∼66.48%, and 0.77-0.96 mg chemical oxygen demand (CODcr) was actually consumed to remove 1 mg TN. The identified functional bacteria, such as anammox bacteria, manganese oxidizing bacteria (MnOB), hydrolytic bacteria and denitrifying bacteria, demonstrated that TN was removed by the ASNR, and the variation of the functional bacteria along the DF layer revealed the mechanism of the TWT affecting the efficiency of the ASNR. This technique presented a strong adaptability to the variation of the TWT, therefore, it has broad application prospect and superlative application value in advanced nitrogen removal of municipal wastewater.

Biofilms for Production of Chemicals and Energy

The twenty-first century will be the century of biology. This is not only because of breakthrough advances in molecular biology tools but also because we need to reinvent our economy based on the biological principles of energy efficiency and sustainability. Consequently, new tools for production routines must be developed to help produce platform chemicals and energy sources based on sustainable resources. In this context, biofilm-based processes have the potential to impact future production processes, because they can be carried out continuously and with robust stationary biocatalysts embedded in an extracellular matrix with different properties. We review productive biofilm systems used for heterotrophic and lithoautotrophic production and attempt to identify fundamental reasons why they may be particularly suitable as future production systems.

Comparison study on enhancement of phosphorus recovery from low-strength wastewater treated with different magnesium-based electrochemical constructed wetland

Phosphorus (P) recovery from wastewaters treated with constructed wetlands (CWs) could alleviate the current global P crisis but has not received sufficient attention. In this study, P transformation in different magnesium-based electrochemical CWs, including micro-electrolysis CW (M-CW), primary battery CW (P-CW), and electrolysis CW (E-CW), was thoroughly examined. The results revealed that the P removal efficiency was 53.0%, 75.8%, and 61.9% in the M-CW, E-CW, and P-CW, respectively. P mass balance analysis showed that P electrode deposition was the main reason for the higher P removal in the E-CW and P-CW. Significant differences were found between the E-CW and P-CW, P was distributed primarily on the magnesium plate in the P-CW but was distributed on the carbon plate in the E-CW. The E-CW had excellent P recovery capacity, and struvite was the major P recovery product. More intense magnesium plate corrosion and alkaline environment increased struvite precipitation in the E-CW, with the proportion of 61.6%. The results of functional microbial community analysis revealed that the abundance of electroactive bacteria was positively correlated with the deposition of struvite. This study provided an essential reference for the targeted electrochemical regulation of electric field processes and microorganisms in CWs to enhance P recovery.

Advanced synergetic nitrogen removal of municipal wastewater using oxidation products of refractory organic matters in secondary effluent by biogenic manganese oxides as carbon source

Due to the high operational cost and secondary pollution of the conventional advanced nitrogen removal of municipal wastewater, a novel concept and technique of advanced synergetic nitrogen removal of partial-denitrification anammox and denitrification was proposed, which used the oxidation products of refractory organic matters in the secondary effluent of municipal wastewater treatment plant (MWWTP) by biogenic manganese oxides (BMOs) as carbon source. When the influent NH₄⁺-N in the denitrifying filter was about 1.0, 2.0, 3.0, 4.0, 5.0 and 7.0 mg/L, total nitrogen (TN) in the effluent decreased from about 22 mg/L to 11.00, 7.85, 6.85, 5.20, 4.15 and 2.09 mg/L, and the corresponding removal rate was 49.15, 64.82, 69.40, 76.70, 81.36 and 90.58%, respectively. The proportional contribution of the partial-denitrification anammox pathway to the TN removal was 12.00, 26.45, 39.70, 46.04, 54.97 and 64.01%, and the actual COD_cr consumption of removing 1 mg TN was 0.75, 1.43, 1.26, 1.17, 1.08 and 0.99 mg, respectively, which was much lower than the theoretical COD_cr consumption of denitrification. Furthermore, COD_cr in the effluent decreased to 8.12 mg/L with a removal rate of 72.40%, and the removed organic matters were mainly non-fluorescent organic matters. Kinds of denitrifying bacteria, anammox bacteria, hydrolytic bacteria and manganese oxidizing bacteria (MnOB) were identified in the denitrifying filter, which demonstrated that the advanced synergetic nitrogen removal was achieved. This novel technology presented the advantages of high efficiency of TN and COD_cr removal, low operational cost and no secondary pollution.

Advanced nitrogen removal performance and microbial community structure of a lab-scale denitrifying filter with in-situ formation of biogenic manganese oxides

Advanced nitrogen removal faces the challenges of high operational cost resulted from the additional carbon source and secondary pollution caused by inaccurate carbon source dosage in municipal wastewater. To address these problems, a novel carbon source was developed, which was the oxidation products of refractory organic matters in the secondary effluent of municipal wastewater treatment plant (MWWTP) by in-situ generated biogenic manganese oxides (BMOs) in the denitrifying filter. In the steady phase, the effluent chemical oxygen demand (COD_cr), NO₃^--N and total nitrogen (TN) in the denitrifying filter 2^# with BMOs was 11.27, 9.03 and 10.36 mg/L, and the corresponding removal efficiency was 54.79%, 51.85% and 48.03%, respectively, which was significantly higher than those in the control denitrifying filter 1^# that the removal efficiency of COD_cr, NO₃^--N and TN was only 32.30%, 28.58% and 29.36%, respectively. Kinds of denitrifying bacteria (Candidatus Competibacter, Defluviicoccus, Dechloromonas, Candidatus Competibacter, Dechloromonas, Pseudomonas, Thauera, Acinetobacter, Denitratisoma, Anaerolineae and Denitratisoma) and anammox bacteria (Pirellula, Gemmata, Anammoximicrobium and Brocadia) were identified in the denitrifying filters 1^# and 2^#, which explained why the actual COD_cr consumption (1.55 and 1.44 mg) of reducing 1 mg NO₃^--N was much lower than the theoretical COD_cr consumption. While manganese oxidizing bacteria (MnOB, Bacillus, Crenothrix and Pedomicrobium) was only identified in the denitrifying filter 2^#. This novel technology presented the advantages of no additional carbon source, low operational cost and no secondary pollution. Therefore, the novel technology has superlative application value and broad application prospect.

Insight into the temporal dynamics of microbial succession and ecology mechanisms in biological activated carbon tanks

Biological activated carbon (BAC) has long been applied in China to guarantee water quality and to achieve drinking water regulations. However, a knowledge gap remains regarding the temporal dynamics of microbial communities, particularly microbe-based assembly and co-occurrence patterns. Accordingly, this study investigated the evolution of BAC microbial communities using a pilot-scale system and examined by multivariate ecological combined with high-throughput Illumina sequencing and statistical methods. The results showed that BAC microbial diversity reached its peak in 2 years and declined thereafter. Microbial communities composition was accompanied by significant temporal evolution in the BAC biofilm. Deterministic processes gained in importance along with time, especially homogeneous selection which contributed 59.09 %-75.63 % to the community assembly in 8-yr, 9-yr, and 10-yr BAC. According to co-occurrence network analysis, microbial networks have more unstable structures over time, as evidenced by higher modularity, heightened connectivity, and fewer keystones. Moreover, the interaction between microbial taxa tended to have a higher proportion of competitive relationships during the operation of the BAC tank, ranging from 13.51 % to 76.35 %. Based on these dynamic ecological processes, microbial community succession in BAC biofilm might undergo four phases: community establishment (Years 0-2); community stability (Years 2-5); community quasi-degradation (Years 5-8); community degradation (Years 8-10). The performance of BAC was greatly influenced by community development, and contaminant removal gradually decreased as community succession proceeded. These results add to our knowledge of microbial ecology and provide the basis for further research into microbial communities' regulation strategies in BAC tanks.

Performance of bioelectrochemical systems in treating exhaust gas with power generation: Effects of shock-load, shut-down episodes and microbial community

A diffusive packed anode-bioelectrochemical (Dpa-Bes) system was constructed by feeding waste gas from the cathode to the anode tank in DPa-Bes through a proton exchange membrane (PEM). The high removal of oxygen by the PEM and the effective combination of the two packing materials reduced the electron loss and enhanced the proton transfer capacity, promoting the removal of acetone from the exhaust gas and increasing the output power. The maximum acetone removal efficiency of the modified Dpa-Bes reached ∼99 % after seven days of closed-circuit operation, with a 3.2-fold increase in maximum power density and a 2.27-fold increase in closed-circuit voltage relative to those of the unmodified Dpa-Bes. When the acetone concentration was 2400 ppm, the removal efficiency was 73.22 % and the elimination capacity was at its highest value of 290.21 g/m³/h. Microbial analysis revealed that the conductive filter contained abundant facultative and anaerobic bacteria, whereas the non-conductive filter was rich in aerobic bacteria. The abundance of anaerobic and facultative microorganisms in Dpa-Bes was much higher than in the unmodified Dpa-Bes, and the dominant bacteria were Flavobacterium and Ferruginibacter.