Bioelectrochemical Denitrification System Research Articles

Development of a New Hydrogel Anion Exchange Membrane for Swine Wastewater Treatment.

We developed a proprietary anion exchange membrane (AEM) for wastewater treatment as an alternative to commercial products. Following the successful development of a hydrogel cation exchange membrane on a porous ceramic support, we used the same approach to fabricate an AEM. Different positively charged monomers and conditions were tested, and all AEMs were tested for nitrate and phosphate anion removal from buffers by electrodialysis. The best AEM was tested further with real swine wastewater for phosphate removal by electrodialysis and nitrate removal in a bioelectrochemical denitrification system (BEDS). Our new AEM showed better phosphate removal compared with a commercial membrane; however, due to its low permselectivity, the migration of cations was detected while operating a two-chambered biocathode BEDS in which the membrane was utilized as a separator. After improving the permselectivity of the membrane, the performance of our proprietary AEM was comparable to that of a commercial membrane. Because of the usage of a porous ceramic support, our AEM is self-supporting, sturdy, and easy to attach to various frames, which makes the membrane better suited for harsh and corrosive environments, such as swine and other animal farms and domestic wastewater.

Continuous autotrophic denitrification process for treating ammonium-rich leachate wastewater in bioelectrochemical denitrification system (BEDS)

The reduction of nitrogen compounds in aqueous solution is extremely important for sustainable management of ecosystem and human health. An autotrophic bioelectrochemical denitrification (BED) process was evaluated at various conditions for enhanced treatment of synthetic wastewater (SW) and ammonium-rich leachate. With SW, a decrease in hydraulic retention time (HRT: 41.6 to 8.3 h) resulted in a 370% increase in denitrification rate from 0.026 to 0.096 kg NO3−N/m3. D. An increase in applied voltage (0.7 to 2 V) enhanced nitrate removal (81 to 97% removal), but coulombic efficiency decreased from 74% to 19%. With doubled cathode electrodes, the nitrate removal rate was doubled from 0.056 to 0.114 kg NO3−N/m3. D. Moreover, leachate wastewater was successfully denitrified with the maximum removal rate of 0.121 kg NO3−N/m3. D. These results point towards the practical potential for the combination of nitrification systems with BEDS for reduction of nitrogen for discharge purposes.

Microbial community and metabolism activity in a bioelectrochemical denitrification system under long-term presence of p-nitrophenol

Bioelectrochemical denitrification system (BEDS) is a promising technology for nitrate removal from wastewaters. The hazards and effects concerning p-nitrophenol (PNP) towards BEDS lack enough investigations and possess great research prospects. This study investigated how PNP affected the nitrate removal efficiency, microbial communities, functional denitrifying genes abundances, nitrate and nitrite reductase activities, diffusible signal factors (DSF) release, and extracellular polymeric substances (EPS) production in the BEDS. Results indicated that nitrate removal efficiency decreased with initial PNP concentration increased from 0 to 100mg/L. Phylum Firmicutes and class Clostridia were the main contributors for denitrification process in this BEDS. The abundances of the denitrifying genes nirS, nirK, napA, and narG all presented decreased trends with increasing PNP. In addition, the concentrations of nitrate reductase (NR), nitrite reductase (NIR), and EPS obviously decreased, while the concentration of DSF increased with increasing PNP, which demonstrated that higher PNP would inhibit the biofilm formation.

Response of a three dimensional bioelectrochemical denitrification system to the long-term presence of graphene oxide

In this study, a three dimensional bioelectrochemical denitrification system (3D-BEDS) was operated under long-term graphene oxide (GO) condition to treat high nitrate polluted water. When GO concentration increased from 0 to 100mgL−1, nitrate removal efficiency slightly decreased from 99.52% to 94.81%. However, when GO concentration was further increased to 150mgL−1, the denitrification efficiency dramatically decreased to 74.95%. Increasing GO concentration in this BEDS resulted in decreased community richness, and the abundances of the dominant bacterial communities presented obvious shift. The abundances of denitrifying genes napA, nirS, and nirK showed no obvious changes with GO concentration lower than 50mgL−1. However, the abundances of the three genes decreased when GO concentration was further increased to higher than 100mgL−1. The increased lactate dehydrogenase (LDH) release and reactive oxygen species (ROS) production demonstrated that long-term presence of GO caused chronic impacts onto microorganisms in this BEDS.

Bacterial communities in a novel three-dimensional bioelectrochemical denitrification system: the effects of pH.

Influence of pH on the dominant microbial community structure in bioelectrochemical system (BES) for nitrate removal is poorly understood. Here, the dynamics and variations of microbial communities were investigated with pH varied from 6.0 to 9.0 in a novel three-dimensional BES (3D-BES). The maximum nitrate removal efficiencies 97.58 and 96.36% were obtained at pH 7.0 and 8.0, due to the main contributions of bacterial phylum Firmicutes and class Clostridia. The abundances of dominant phyla and classes tended to decrease under pH 6.0 and 9.0 conditions. Additionally, phylum Proteobacteria and class Gammaproteobacteria preferred acid environment in the BES, while phylum Chloroflexi and class Bacilli and Betaproteobacteria preferred alkaline environment. Furthermore, the excellent nitrate removal ability of the 3D-BES was ascribed to the presences of genera Exiguobacterium, Proteiniclasticum, Pseudomonas, Planococcus, Thauera, Azoarcus, Thiobacillus, etc. These genera facilitated the combined autotrophic denitrification process so that this system achieved excellent nitrate degradation efficiency.

Bacterial communities in a bioelectrochemical denitrification system: The effects of supplemental electron acceptors

Electrochemical treatment of nitrate (NO3−), nitrite (NO2−) and mixtures of nitrate and nitrite was evaluated with microbial catalysts on a cathode in three different bioelectrochemical denitrification systems (BEDS). The removal rates and removal percentage of nitrogen (N) compounds varied during biotic and abiotic operations. The biotic cathode using NO3−-N as an electron acceptor showed enhanced removal percentages (88%) compared to the operation with NO2−-N (85%). The simultaneous reduction of NO3−-N and NO2−-N occurred in the operation with a mixture of N compounds. The bacterial diversity from the initial inoculum (return sludge) changed at the end of bioelectrochemical denitrification operation after 55 days. The microbial community composition was different depending on the type of electron acceptor. BEDS operation with NO3−-N and NO2−-N was enriched with Proteobacteria and Firmicutes respectively. BEDS with a mixture of N electron acceptors showed enrichment with Proteobacteria. There was no clear, distinct microbial community between the cathode biofilm and suspended biomass.

Enrichment of Clostridia during the operation of an external-powered bio-electrochemical denitrification system

Bacterial community composition was investigated in a biocathode of an external-powered bio-electrochemical denitrifying system (BEDS), by analyzing 16S rRNA gene sequences determined from a high-throughput 454 pyrosequencing technology. The bacterial community of the inoculum sludge was mainly composed of Proteobacteria, Bacteroidetes, and Acidobacteria. Over 45 days of the BEDS, Bacteroidetes and Firmicutes were enriched on the biocathode. Putative denitrifying Clostridia belonging to the Firmicutes were distinctively detected on the biocathode via phylogenetic analysis and appeared to be ubiquitous in various autotrophic, heterotrophic, and BEDSs. Elucidation of the bacterial community composition in the denitrification system deepens our knowledge about the bacteria involved in bio-electrochemical denitrification.

Nitrate reduction with biotic and abiotic cathodes at various cell voltages in bioelectrochemical denitrification system

Electrochemical treatment of nitrate ions was attempted using different catalysts on the cathode in bioelectrochemical denitrification systems. The carbon cathode coated by biofilm (biocathode) could remove 91 % of nitrate ions at 1.0 V, which was almost same as the Pt-coated electrode (90 %). The exchange current density of biocathode was 0.0083 A/m(2), which was almost 22 times higher than with an abiotic plain carbon cathode. The formation of intermediate products in nitrate reduction varied depending on the cell voltage. At 0.5 V, a large portion of nitrate was converted to ammonia, but at more increased cell voltage (0.7 and 1 V) a high amount of nitrite ions was found with little ammonia formation in cathodic solution. The maximum nitrate removal rate was 0.204 mg NO(3)-N/cm(2)d by biocathode, while plain carbon paper showed only 0.176 mg NO(3)-N/cm(2)d. Electrochemical analysis of chronoamperometry showed a higher stable current generation for biocathode (3.1 mA) and Pt-coated cathode (2.8 mA) as compared to plain carbon (0.6 mA) at 0.7 V of poised voltage.