Anode-biofilm electron transfer behavior and wastewater treatment under different operational modes of bioelectrochemical system

Buffer capacity regulates the stratification of anode-respiring biofilm during brewery wastewater treatment

Improving the buffer capacity of the electrolyte can enhance the anode performance in bioelectrochemical systems (BESs). To elucidate the mechanism underlying the facilitated BESs performance, this study used three different anode biofilms cultured with different concentrations of phosphate buffer (5, 50 and 100 mM) to investigate the biofilm response, in terms of the spatial structure of metabolic activity and microbial community, to different buffer capacities. Results showed that the electrochemical activities of the anode biofilms positively correlated with the buffer concentration. The spatial stratification of metabolic activity and microbial community of the anode biofilms were regulated by the buffer capacity, and the spatial microbial heterogeneity of the anode biofilm decreased as the buffer concentration increased. With increasing buffer capacity, Geobacter spp. were enriched in both the inner and outer layers of the biofilm, and the inhibition of methanogens growth improved the COD removal attributed to anode respiration. Additionally, the stimulation of EPS production in biofilms played a role in increasing the electrochemical performance of biofilms by buffer improvement. This study first revealed the regulation of buffer capacity on the stratification of anode biofilm during brewery wastewater treatment, which provided a deep insight into the relation of biofilm structure to its electrochemical properties.

Dual detection of biochemical oxygen demand and nitrate in water based on bidirectional Shewanella loihica electron transfer

This study for the first time proposed a method for simultaneously measuring BOD and nitrate in water using electrochemically active bacteria. Firstly, the bidirectional extracellular electron transfer (EET) capability of a model electricigen Shewanella loihica PV-4 was revealed. Then, based on the respective outward and inward EET, S. loihica PV-4 was utilized to detection BOD and nitrate. The results demonstrated a positive correlation between the outward EET and BOD (from 0 mg/L to 435 mg/L) while a negative correlation between the inward EET and nitrate (from 0 mg/L to 7 mg/L); both the relationships were well fitted by the combination of traditional linear model and Michaelis-Menten model (R²>0.96). Finally, a dual detection method for BOD and nitrate measurements was established based on the ano-cathodophilic capability of S. loihica PV-4 biofilm, and exhibited the characteristics of high accuracy (>80%) and fast analysis (<1h), suggesting a promising prospect in water monitoring.

Enhanced anaerobic dechlorination of polychlorinated biphenyl in sediments by bioanode stimulation

The application of a low-voltage electric field as an electron donor or acceptor to promote the bioremediation of chlorinated organic compounds represents a promising technology meeting the demand of developing an efficient and cost-effective strategy for in situ treatment of PCB-contaminated sediments. Here, we reported that bioanode stimulation with an anodic potential markedly enhanced dechlorination of 2,3,4,5-tetrachlorobiphenyl (PCB 61) contained in the sediment at an electronic waste recycling site of Qingyuan, Guangdong, China. The 110-day incubation of the bioanode with a potential poised at 0.2 V relative to saturated calomel electrode enabled 58% transformation of the total PCB 61 at the initial concentration of 100 μmol kg(-1), while only 23% was reduced in the open-circuit reference experiment. The introduction of acetate to the bioelectrochemical reactor (BER) further improved PCB 61 transformation to 82%. Analysis of the bacterial composition showed significant community shifts in response to variations in treatment. At phylum level, the bioanode stimulation resulted in substantially increased abundance of Actinobacteria, Bacteroidetes, and Chloroflexi either capable of PCB dechlorination, or detected in the PCB-contaminated environment. At genus level, the BER contained two types of microorganisms: electrochemically active bacteria (EAB) represented by Geobacter, Ignavibacterium, and Dysgonomonas, and dechlorinating bacteria including Hydrogenophaga, Alcanivorax, Sedimentibacter, Dehalogenimonas, Comamonas and Vibrio. These results suggest that the presence of EAB can promote the population of dechlorinating bacteria which are responsible for PCB 61 transformation.

Simultaneous phenol removal, nitrification and denitrification using microbial fuel cell technology

Here we show that concomitant removal of phenol and nitrogen can be accomplished in a single dual-chamber microbial fuel cell (MFC) reactor, in which the two chambers are separated with an anion-exchange membrane. A series of experiments were performed with ammonium (230 NH4(+)-N mg L(-1)) and phenol (with concentrations varying from 0 to 1400 mg L(-1)) fed to the aerobic cathode chamber of the MFC. Experimental results demonstrated that no apparent inhibitory effect of phenol on the nitrifying reaction was noted even at the phenol concentration up to 600 mg L(-1). For all the experiments, simultaneous nitrification and denitrification was achieved in the MFC. In comparison to the traditional aerobic bioreactor (ABR) and the same MFC run under the open-circuit condition, the MFC reactor allowed less inhibition of nitrification to phenol exposure and higher rate of nitrogen removal. The data of bacterial analysis revealed that electrochemically active bacteria and denitrifiers in the anaerobic chamber play a significant role in electricity generation and anaerobic denitrification, respectively, while phenol-degrading bacteria, nitrifiers, and denitrifiers in the aerobic cathode chamber are responsible for phenol oxidation, aerobic nitrification and aerobic denitrification, respectively. These results imply that the MFC holds potential for simultaneous removal of phenolic compounds and nitrogen contained in some particular industrial wastewaters.

Estimation of the adhesive force distribution for the flagellar adhesion of Escherichia coli on a glass surface

The effects of the presence or absence of microbial flagella and the microbial motility on the colloidal behaviors of microbial cells were quantitatively evaluated. The microbial cell attachment and detachment processes on a glass surface were observed directly using a parallel-plate flow chamber. Wild-type, flagellar paralyzed, and nonflagellated Escherichia coli strains were used as model microbial cells. In the cell attachment tests, the microbial adhesion rate in a 160mM NaCl solution was approximately 10 times higher than that in a 10mM solution, for all E. coli strains. The colloidal behavior of the microbial cells agreed well with the predictions of the DLVO theory. In addition, the microbial flagella and motility did not significantly affect the cell attachment, regardless of the existence of a potential barrier between the cell and the glass substratum. In the cell detachment tests, the cumulative number of microbial cells detached from the glass substratum with increasing flow rate was fit well with the Weibull distribution function. The list of strains arranged in order of increasing median drag force required to remove them was nonflagellated strain, flagellar paralyzed strain, and wild-type strain. These results indicated that the flagella and the flagellar motility inhibited the cell detachment from the glass substratum. Furthermore, a large external force would likely be required to inhibit the microbial adhesion in the early stage of the biofilm formation.

Measurement of microbial adhesive forces with a parallel plate flow chamber

HYPOTHESIS

It was predicted that the colloidal behaviors of archaea and bacteria with disparate surface structure were different. In this study, the effects of the physicochemical properties of microbial cell surfaces on colloidal behavior were analyzed with Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, thermodynamics, and powder technology.

EXPERIMENTS

Cell attachment and detachment from model substrates were directly observed using a parallel plate flow chamber. Gram-negative Escherichia coli and archaeal Methanosarcina barkeri were used as model microbial cells, and positively and negatively charged glass slides were used as model substrates.

FINDINGS

Microbial adhesion on both substrates agreed well with predictions calculated from DLVO theory, using experimental parameters. The total number of cells detached from the substrates as a function of flow rate was fit with the Weibull distribution function. In addition, the drag force required for detachment, which was estimated from the hydrodynamic forces, had a wide distribution; however, the forces became smaller with increasing ionic strength because of reduced electrostatic interactions between the cells and the substrate. M. barkeri could not be detached from positively charged substrates because it would entail a negative change in the interfacial energy of interaction. Thus adhesion was thermodynamically favored in this case.