Beizhen Xie

Using low intensity ultrasound to improve the efficiency of biological phosphorus removal

Low intensity ultrasound can produce various effects on biological materials, such as stimulating enzyme activity, cell growth, biosynthesis, etc., which may improve the efficiency of enhanced biological phosphorus removal (EBPR). We adopt total phosphorus (TP) and dehydrogenase activity (DHA) as indicators to confirm the feasibility of applying low intensity ultrasound in EBPR. Single-factor experiments and orthogonal test were conducted in batch anaerobic/oxic (A/O) process simulation to study the influence of ultrasonic intensity and exposure time in the EBPR process. The results showed that the optimal ultrasonic parameters were 0.2 W/cm2 and 10 min under which condition the TP concentration in the effluent was 35-50% lower than that of the control (without ultrasonic irradiation). Changes of sludge activities after ultrasonic irradiation were examined. The improvement of sludge activity by ultrasound took 4 h after irradiation to reach the peak level, when an increase above 50% of DHA has been achieved by ultrasonic irradiation, and the enhancing effects induced by ultrasound disappeared in 16 h after irradiation. A tentative mechanism of biological phosphorus removal enhancement stimulated by ultrasound was discussed based on these phenomena.

Continuous flowing membraneless microbial fuel cells with separated electrode chambers

Microbial fuel cell (MFC) is an emerging technology in the energy and environment field. Its application is limited due to its high cost caused by the utilization of membranes and noble metal catalysts. In this paper, a membraneless MFC, with separated electrode chambers, was designed. The two separated chambers are connected via a channel and the continuous electrolyte flow from anode to cathode drives proton transfer. The proton mass transfer coefficiency in this MFC is 0.9086 cm/s, which is higher than reported MFCs with membranes, such as J-cloth and glass fiber. The maximum output voltage is 160.7 mV, with 1000 Ω resistor. Its peak power density is 24.33 mW/m³. SCOD removal efficiency can reach 90.45% via this MFC. If the connection between the two electrode chambers is blocked, the performance of MFC will decrease severely. All the above results prove the feasibility and advantages of this special MFC model.

Microbiological mechanism of the improved nitrogen and phosphorus removal by embedding microbial fuel cell in Anaerobic–Anoxic–Oxic wastewater treatment process

Anaerobic-Anoxic-Oxic (AA/O) wastewater treatment process is a widely used wastewater treatment process for simultaneous nitrogen and phosphorus removal. Microbial fuel cell (MFC) can generate electricity and treat the organic wastewater simultaneously. Our previous research showed that embedding MFC in AA/O wastewater treatment process could enhance the pollutants removal efficiency. However, the mechanism was not clear. In this study, a lab-scale corridor-style AA/O reactor with MFC embedded was operated and both the total nitrogen and total phosphorus removal efficiencies were enhanced. DGGE and Illumina Miseq results demonstrated that both the microbial community structures on the surface of the cathode and in the suspensions of cathode chamber have been changed. The percentage of Thauera and Emticicia, identified as denitrifying bacteria, increased significantly in the suspension liquid when the MFC was embedded in the AA/O reactor. Moreover, the genus Rheinheimera were significantly enriched on the cathode surface, which might contribute to both the nitrogen removal enhancement and electricity generation.

Photosynthetic characteristics, antioxidant capacity and biomass yield of wheat exposed to intermittent light irradiation with millisecond-scale periods

Energy consumption and output are two very important standards for evaluating the reliability of electric light sources when plants are grown in a controlled environment. As a primary source of energy, light is one of the most important environmental factors for wheat growth. The objective of this study was to investigate the influences of light/dark cycle operation with millisecond-scale period on the growth of wheat, photosynthetic characteristics, antioxidant capacity and biomass yield and quality during their life cycle. Four types of intermittent lighting with the same intensity were employed: a light/dark (0.5/0.5 ms) light (50%), a light/dark (0.7/0.3 ms) light (70%), a light/dark (0.8/0.2 ms) light (80%) and a continuous light (100%). The results showed that the wheat cultivated in the 80% light was characterized by highest photosynthetic rate and lowest lignin in inedible biomass, which was more beneficial to recycle substances in the processes of the environment regeneration. The data were comparable to those under continuous light condition in terms of chlorophyll concentration, antioxidant capacity, harvest index (HI) and thousand kernel weight (TKW). Wheat was sensitive to intermittent illumination which significantly affected those indices of growth and physiology, especially at heading and flowering stages.

Increased power density from a spiral wound microbial fuel cell

Using Microbial fuel cell (MFC) to convert organic and inorganic matter into electricity is of great interest for powering portable devices, which is now still limited by the output of MFC. In this study, a spiral wound MFC (SWMFC) with relatively large volume normalized surface area of separator (4.2 cm(2)/ml) was fabricated to enhance power generation. Compared with double-membrane MFC (DMMFC) and conventional double chamber MFC (DCMFC), the power density of SWMFC increased by 42% and 99% resulted from its lower internal resistance. Besides larger separator area, the better performance of SWMFC benefited from its structure sandwiching the cathodes between two separators. This point was proved again by a comparison of another DCMFC and a triple chamber MFC (TCMFC) as well as a simulation using finite element method. Moreover, the feature of SWMFC was more convenient and compact to scale up. Therefore, SWMFC provides a promising configuration for high power output as a portable power source.

Gut microbes in correlation with mood: case study in a closed experimental human life support system

Gut microbial community, which may influence our mood, can be shaped by modulating the gut ecosystem through dietary strategies. Understanding the gut–brain correlationship in healthy people is important for maintenance of mental health and prevention of mental illnesses.

Rearing Tenebrio molitor L. (Coleptera: Tenebrionidae) in the “Lunar Palace 1” during a 105-day multi-crew closed integrative BLSS experiment

Yellow mealworm (Tenebrio molitor L.) is one of the animal candidates for space bioregenerative life support systems. In this study, T. molitor was involved in a 105-day multi-crew closed integrative BLSS experiment for a tentative rearing study. The results showed that the overall bioconversion rate (ratio of T. molitor gained to the total feed consumed) of T. molitor reared in the closed system was 8.13%, while 78.43% of the feed was excreted as frass. T. molitor reared in the closed system had a good nutritional composition. The eight essential amino acids (EAAs) in T. molitor larvae accounted for 41.30% of its total amino acids, and most EAA contents were higher than the suggested amino acid pattern recommended by the FAO/WHO. T. molitor sample obtained in this work was high in polyunsaturated fatty acids, and low in saturated fatty acids, indicating that the composition of fatty acids was beneficial to human health. In the open environment outside the experimental system, we simultaneously reared three parallel groups of larval T. molitor using the same feeding regime and temperature condition. Compared with T. molitor reared in the open environment, larvae reared in the closed system grew slower. With the course of time t, the growth rate of T. molitor in the open environment was 0.839e(0.017t) times that of larvae in the closed system. This paper can provide data for future design and improvement of BLSS containing a T. molitor rearing unit.

Can bicarbonate replace phosphate to improve the sustainability of bioelectrochemical systems for H2 production

Phosphate is generally used as an effective electrolyte buffer in bioelectrochemical systems, but it is not sustainable. Bicarbonate, if it can replace phosphate as an alternative buffer, may improve the overall economic feasibility of microbial electrolysis cells (MEC) for its application in wastewater treatment and H2 production. In this study, the performance of single-chamber MECs with combo buffers with different PO43− to HCO3− (P/C) ratios was investigated. The results demonstrate that large (about 80%) but not complete replacement of PO43− with HCO3− is feasible, indicating phosphate is necessary to maintain the electric current and the stability of MECs. The current density of MEC with P/C at 20/80 (in mol%) was comparable to that with a full phosphate buffer, and can be kept stable for as long as 1800 h, under 0.5 to 0.9 V applied voltages. Analysis by using molecular approaches, including denaturing gradient gel electrophoresis and DNA sequencing, shows that P/C ratios affect the microbial community structure of the bioanode biofilm, especially on the population of Geobacter, which is a predominant and key exoelectrogenic bacteria to produce an electric current in MEC. The results of this study will broaden the knowledge of the buffer effect and promote the potential applicability of MECs for H2 production.

Kinetics and gene diversity of denitrifying biocathode in biological electrochemical systems

Cathodic denitrification using a bioelectrochemical system removes nitrogen at a low C/N ratio, and also harvests energy as electricity. Denitrifying biocathodes were cultured using three electrode systems with nitrate (NO3−) and/or nitrite (NO2−) as electron acceptors. Results showed that denitrification of NOx− in biocathodes exhibit typical enzymatic reaction kinetics and denitrification rate follows the Monod equation, with rmax = 1.33 kg N m−3 d−1, Ks = 5.52 g L−1 for NO3− and rmax = 1.76 kg N m−3 d−1, Ks = 8.09 g L−1 for NO2−, respectively. Optimal cathodic efficiency was obtained at an initial substrate concentration of 0.5 g L−1. A high-throughput sequencing analysis of 16S rRNA gene showed high biodiversity in a denitrifying biocathode and nitrite contributed more to the formation of cathodic microbial community structure. Denitrification functional gene analysis revealed Pseudomonas are effective denitrifiers in a biocathode.

Effect of external resistance on the sensitivity of microbial fuel cell biosensor for detection of different types of pollutants

The relatively poor sensitivity is the main bottleneck restricting the application of microbial fuel cell biosensor (MFC-biosensor) for toxicity monitoring. Previous studies have shown that external resistance (Rext) had an obvious effect on sensor sensitivity. However, these studies reported different results and the reason of this discrepancy was not clear. The objective of this research was to observe the effect of Rext on sensor sensitivity when detecting different types of pollutants and reveal its microbiological mechanism. Results demonstrated that the optimal Rext of MFC-biosensor varied with the type of pollutants. The optimal values for detecting avermectins, tetracyclines and heavy metals were 100 Ω, 330 Ω and 680 Ω, respectively. This discrepancy was mainly due to the visible differences in anodic microbial communities at different Rext settings. Both Azospirillum and Acinetobacter were susceptible to Cd and Pb, occuping 19.20% of the anodic microbial population in 680 Ω MFC-biosensor. Pseudomonas accounted for 10.73% in 330 Ω MFC-biosensor and possessed the sensitivity to tetracyclines. As for 100 Ω MFC-biosensor, the avermectin-intolerant Ocillibacter made up 2.55% of the anodic microbial community. This study indicated that the Rext of MFC-biosensor should be optimized according to the potential pollutants.