Clean Conversion of Biomass Energy by Bio-electrochemical System

Biomass energy is an important constituent of the world＇s future sustainable energy source system, but current biomass energy conversion techniques have low efficiency and cause secondary pollution to environment easily. Bio-eleetrochemical system （BES） appeared in recent years could realize the clean efficient con- version of biomass energy, and has become a research hotspot in the biomass energy field. In this study, the research and application of BES in biomass energy con- version were overviewed, and the existing problems were analyzed.

Study on Influencing Factors of Bio-electrochemical System for Water Softening

Bio-electrochemical system( BES) was used to soften hard water,and effects of ion species,electrode area and influent concentration on the performance of BES to soften hard water were analyzed. The results showed that it was more easy to remove Mg^(2+) from the hard water than Ca^(2+). Increasing electrode area could enhance the performance of BES to soften hard water. When the amount of added graphite at the anode was 150 g,the removal efficiency of Ca^(2+) increased by 18. 1%. The increase of influent concentration at the anode and the cathode could improve the softening efficiency of hard water by BES. As COD concentration at the anode and NO_3^--N concentration at the cathode increased to 2000 and 300 mg/L,the removal efficiency of Ca^(2+) rose by 36. 1% and 9. 4% respectively.

Suppression of Methane Gas Emissions and Analysis of the Electrode Microbial Community in a Sediment-Based Bio-Electrochemical System

The effects of bioelectrochemical systems (BESs) for the suppression of methane gas emissions from sediment were examined using a laboratory-scale reactor system. Methane gas emissions from acetate were suppressed by approximately 36% from control based on the installation of a BES in which carbon-graphite electrodes were buried in sediment and arbitrarily set at certain oxidative potentials (+300 mV vs Ag/AgCl) using a potentiostat. Meanwhile, methane gas emissions increased in the BES reactor where the electrode potential was set at -200 mV. Results obtained from pyrotag sequencing analysis of the microbial community on the surface of the buried electrodes targeting 16S rRNA genes demonstrated that the genusGeobacterhad drastically propagated in a sample from the reactor where the electrodes were buried. Quantitative analysis of 16S rRNA genes of archaea also revealed that the archaeal population had decreased to approximately 1/6 of its original level on the electrode of the BES set at +300 mV. This implied that the oxidation-reduction potential (ORP) in the sediment was raised to the inhibition level for methanogenesis in the vicinity of the buried electrode. Analysis of electron flux in the experiment revealed that electrons intrinsically used for methanogenesis were recovered via current generation in the sediment where a potential of +300 mV was set for the electrode, although most electrons donated from acetate were captured by oxygen respiration and other electron-accepting reactions. These results imply that BES technology is suitable for use as a tool for controlling re-dox-dependent reactions in natural environments, and that it also brought about changes in the microbial population structure and methanogenic activity in sediment.

Experimental Study on Denitrification Using Coated Electrode of Immobilized Denitrifying Bacteria

Objective To develop a coated electrode of immobilized denitrificants and to evaluate the performance of a bioelectrochemical reactor to enhance and control denitrification, Methods Denitrifying bacteria were developed by batch incubation and immobilized with polyvinyl alcohol （PVA） on the surface of activated carbon fiber （ACF） to make a coated electrode. Then the coated electrode （cathode） and graphite electrode （anode） were transferred to the reactor to reduce nitrate. Results After acclimated to the mixtrophic and autotrophic denitrification stages, the denitrifying bacteria could use hydrogen as an electron donor to reduce nitrate, When the initial nitrate concentration was 30.2 mg NO3-N/L, the denitrification efficiency was 57.3% at an applied electric current of 15 mA and a hydraulic retention time （HRT） of 12 hours. Correspondingly, the current density was 0.083 mA / cm^2. The nitrate removal rate of the reactor was 34,4 g NO3-N / m^3,d, and the surface area loading was 1.34 g NO3-N / m^2.d. Conclusion The coated electrode may keep high quantity of blomass, thus achieving a high denitrification rate. Denitrification efficiencies are related to HRT, current density, oxidation reduction potential （ORP）, dissolved oxygen （DO）, pH value, and temperature,

Electrochemistry-stimulated environmental bioremediation:Development of applicable modular electrode and system scale-up

Bioelectrochemical systems(BESs)have been studied extensively during the past decades owing primarily to their versatility and potential in addressing the water-energy-resource nexus.In stark contrast to the significant advancements that have been made in developing innovative processes for pollution control and bioresource/bioenergy recovery,minimal progress has been achieved in demonstrating the feasibility of BESs in scaled-up applications.This lack of scaled-up demonstration could be ascribed to the absence of suitable electrode modules(EMs)engineered for large-scale application.In this study,we report a scalable composite-engineered EM(total volume of 1 m^(3)),fabricated using graphite-coated stainless steel and carbon felt,that allows integrating BESs into mainstream wastewater treatment technologies.The cost-effectiveness and easy scalability of this EM provides a viable and clear path to facilitate the transition between the success of the lab studies and applications of BESs to solve multiple pressing environmental issues at full-scale.

The plant-enhanced bio-cathode:Root exudates and microbial community for nitrogen removal

A plant bio-electrochemical system(PBES) was constructed for organic pollutant removal and power generation. The bio-cathode, composed of granular activated carbon(GAC), stainless wire mesh and a plant species(Triticum aestivum L.), was able to catalyze cathodic reactions without any requirement for aeration or power input. During the 60-day-long operation, an average voltage of 516 m V(1000 Ω) and maximum power density(Pmax) of 0.83 W/m^3 were obtained in the PBES. The total nitrogen removal and total organic carbon removal in the PBES were 85% and 97%, respectively. Microbial community analyses indicated that bacteria associated with power generation and organic removal were the predominant species in the bio-cathode, and plant-growth-promoting rhizobacteria were also found in the PBES. The results suggested that the coupling of plants with the GAC cathode may enhance the organicmatter degradation and energy generation from wastewater and therefore provide a new method for bio-cathode design and promote energy efficiency.