Performance optimization of scintillator neutron detectors for EMD in CSNS

Chinese Spallation Neutron Source(CSNS) has successfully produced its first neutron beam in 28th August 2017. It has been running steadily from March, 2018. According to the construction plan, the engineering materials diffractometer(EMD) will be installed between 2019–2023. This instrument requires the neutron detectors with the cover area near3 m2in two 90° neutron diffraction angle positions, the neutron detecting efficiency is better than 40%@1A, and the spatial resolution is better than 4 mm×200 mm in horizontal and vertical directions respectively. We have developed a onedimensional position-sensitive neutron detector based on the oblique6Li F/Zn S(Ag) scintillators, wavelength shifting fibers,and Si PMs(silicon photomultipliers) readout. The inhomogeneity of the neutron detection efficiency between each pixel and each detector module, which caused by the inconsistency of the wave-length shifting fibers in collecting scintillation photons, needs to be mitigated before the installation. A performance optimization experiment of the detector modules was carried out on the BL20(beam line 20) of CSNS. Using water sample, the neutron beam with Φ5 mm exit hole was dispersed related evenly into the forward space. According to the neutron counts of each pixel of the detector module, the readout electronics threshold of each pixel is adjusted. Compared with the unadjusted detector module, the inhomogeneity of the detection efficiency for the adjusted one has been improved from 69% to 90%. The test result of the diffraction peak of the standard sample Si showed that the adjusted detector module works well.

Simultaneous heterotrophic nitrification and aerobic denitrification at high initial phenol concentration by isolated bacterium Diaphorobacter sp. PD-7

A strain capable of phenol degradation, heterotrophic nitrification and aerobic denitrification was isolated from activated sludge of coking-plant wastewater ponds under aerobic condition. Based on its morphology, physiology,biochemical analysis and phylogenetic characteristics, the isolate was identified as Diaphorobacter sp. PD-7.Biodegradation tests of phenol showed that the maximum phenol degradation occurred at the late phase of exponential growth stages, with 1400 mg·L-1phenol completely degraded within 85 h. Diaphorobacter sp. PD-7accumulated a vast quantity of phenol hydroxylase in this physiological phase, ensuring that the cells quickly utilize phenol as a sole carbon and energy source. The kinetic behavior of Diaphorobacter sp. PD-7 in batch cultures was investigated over a wide range of initial phenol concentrations(0–1400 mg·L-1) by using the Haldane model,which adequately describes the dynamic behavior of phenol biodegradation by strain Diaphorobacter sp. PD-7. At initial phenol concentration of 1400 mg·L-1, batch experiments(0.25 L flask) of nitrogen removal under aerobic condition gave almost entirely removal of 120.69 mg·L-1ammonium nitrogen within 75 h, while nitrate nitrogen removal reached 91% within 65 h. Moreover, hydroxylamine oxidase, periplasmic nitrate reductase and nitrite reductase were successfully expressed in the isolate.

用于中子位置灵敏探测器的SiPM性能研究

为满足中国散裂中子源(China Spallation Neutron Source,CSNS)工程材料衍射谱仪的探测器需求,CSNS探测器组设计并研制了基于硅光电倍增管(Silicon Photomultiplier,SiPM)读出的闪烁体探测器。本工作针对该探测器,选取了Sensl MicroFJ-30035-TSV和Hamamatsu S13363-3050NE-16两种型号的SiPM,开展了其击穿电压、增益、温度特性、暗计数率等关键性能的测试。测试结果显示,两者单光子分辨能力,增益、暗计数率等性能均可满足当前闪烁体探测器需求,相同过偏压下,前者增益高于后者,且Hamamatsu SiPM增益对温度更敏感。测试了两SiPM的温度补偿系数分别为22.0 mV/ºC(Sensl)和53.6 mV/℃(Hamamatsu),为后续SiPM温度补偿电路设计奠定了基础。利用研制的探测器工程样机,在CSNS BL09下测试了两种SiPM读出的探测器对2.8Å中子探测效率分别为76%和68%,为目标探测器及同类型探测器的SiPM选型提供了参考。

Efficient degradation of Rhodamine B by magnetically recoverable Fe_(3)O_(4)-modified ternary CoFeCu-layered double hydroxides via activating peroxymonosulfate

Environment-friendly nano-catalysts capable of activating peroxymonosulfate(PMS)have received increasing attention recently.Nevertheless,traditional nano-catalysts are generally well dispersed and difficult to be separated from reaction system,so it is particularly important to develop nano-catalysts with both good catalytic activity and excellent recycling efficiency.In this work,magnetically recoverable Fe_(3)O_(4)-modified ternary CoFeCu-layered double hydroxides(Fe_(3)O_(4)/CoFeCu-LDHs)was prepared by a simple co-precipitation method and initially applied to activate PMS for the degradation of Rhodamine B(Rh B).X-ray diffraction(XRD),fourier transform infrared spectrometer(FT-IR),scanning electron microscope(SEM),transmission electron microscopy(TEM),Brunauer-Emmett-Teller method(BET),and vibrating sample magnetometer(VSM)were applied to characterize morphology,structure,specific surface area and magnetism.In addition,the effects of several key parameters were evaluated.The Fe_(3)O_(4)/CoFeCu-LDHs exhibited high catalytic activity,and Rh B degradation efficiency could reach 100%within 20 min by adding 0.2 g/L of catalyst and 1 mmol/L of PMS into 50 mg/L of Rh B solution under a wide pH condition(3.0-7.0).Notably,the Fe_(3)O_(4)/CoFeCu-LDHs showed good super-paramagnetism and excellent stability,which could be effectively and quickly recovered under magnetic condition,and the degradation efficiency after ten cycles could still maintain 98.95%.Both radicals quenching tests and electron spin resonance(ESR)identified both HO·and SO_(4)^(·-) were involved and SO_(4)^(·-) played a dominant role on the RhB degradation.Finally,the chemical states of the sample’s surface elements were measured by X-ray photoelectron spectroscopy(XPS),and the possible activation mechanism in Fe_(3)O_(4)/CoFeCu-LDHs/PMS system was proposed according to comprehensive analysis.

Upgrading VFAs bioproduction from waste activated sludge via co-fermentation with soy sauce residue

Conditioning of extra carbon sources has been widely reported to facilitate fermentation of waste activated sludge (WAS). Soy sauce residue (SSR) was a relatively untapped carbon source for sludge conditioning. This batch study aimed to evaluate the possible implementation of SSR for volatile fatty acids (VFAs) production from WAS. To upgrade the bioavailability of feedstock, three typical pretreatment methods were conducted, i.e., ammonium hydroxide (AH), sulfuric acids (SA) and thermal assisted alkaline (TA). AH pretreated test (AH-PT) outperformed due to a relatively strong structure decomposition of cellulosic materials as revealed by infrared spectroscopic analysis and crystal index. As a result, performed a high hydrolysis rate of 4449 mg COD/d, 1.12-1.23-fold higher than that in TA and SA pretreated tests (TA-PT and SA-PT), and 7.8-fold higher than that in the Control test. Meanwhile, a volatile fatty acids (VFAs) contribution of 401.2 mg COD/g SSR L and a maximum acidification rate of 3.59 d was recorded, with a high sum proportion of mall molecular acetic and propionic 82.2%, 11%-70% increase over the other three tests. Besides, speciation process characterized with functional genus differentiation was identified by microbial diversity and distribution investigation and canonical correspondence analysis (CCA). Finally, a potential market value of 0.49-0.65 Billion €/year was preliminary estimated, showing promise of resource recovery from both WAS and SSR instead of extensive disposal.

Reutilize tire in microbial fuel cell for enhancing the nitrogen removal of the anammox process coupled with iron-carbon micro-electrolysis

In this study,microbial fuel cells(MFCs)were explored to promote the nitrogen removal performance of combined anaerobic ammonium oxidation(anammox)and Fe-C micro-electrolysis(CAE)systems.The average total nitrogen(TN)removal efficiency of the modified MFC system was 85.00%,while that of the anammox system was 62.16%.Additionally,the effective operation time of this system increased from six(CAE system alone)to over 50 days,significantly promoting TN removal.The enhanced performance could be attributed to the electron transferred from the anode to the cathode,which aided in reducing nitrate/nitrite in denitrification.The H+released through the proton exchange membrane caused a decrease in the pH,facilitating Fe corrosion.The pyrolyzed waste tire used as the cathode could immobilize microorganisms,enhance electron transport,and produce a natural Fe-C micro-electrolysis system.According to the microbial community analysis,Candidatus kuenenia was the major genus involved in the anammox process.Furthermore,the SM1A02 genus exhibited the highest abundance and was enriched the fastest,and could be a novel potential strain that aids the anammox process.

Acceleration of the particulate organic matter hydrolysis by start-up stage recovery and its original microbial mechanism

To address the availability of carbon sources for denitrification,the accelerated hydrolysis of the most abundant but low-availability fraction of particulate organic matter(POM)was investigated.Mesh sieves with different pore sizes were used as primary pretreatment at the start-up-stage of the biological process to separate some POM from the liquid system.The changes in soluble carbohydrates and proteins were monitored to investigate the hydrolysis performance of the sieved POM,with waste activated sludge(WAS)as the control test.The results showed that an average of 35%POM could be entrapped before filtrate mat development.In addition,benefiting from the high polysaccharides concentration,as well as the high availability due to the relatively loose physical structure,a 23%hydrolysis efficiency of POM was obtained,in contrast to that of WAS(3.4%),with a hydrolysis constant of 0.39 h^(−1).The prominent performance was also attributed to the unique microbial communities having been domesticated at a lower temperature,especially the cellulose-degrading bacteria Paraclostridium and psychrophile Psychrobacter,making up 6.94%and 2.56%,respectively.Furthermore,the potential benefits and application of improved POM hydrolysis by start-up stage recovery via mesh sieves combined with anaerobic fermentation were evaluated,including selective POM entrapment,alleviation of blockage and wear,and a reduction in aeration energy.By the proposed strategy,carbon availability for biological nutrient removal(BNR)processes is anticipated to be improved more economically than that can be achieved by primary clarifier elimination.

Photocatalytic reduction of Cr(Ⅵ)by WO_(3)@PVP with elevated conduction band level and improved charge carrier separation property

Photocatalytic reduction of heavy metal ions is a green and promising technology which requires electrons with enough negative energy levels as well as efficient separation property from photo-generated holes of photocatalysts.For WO_(3),the low conduction band edge and the severe photo-generated charge carrier recombination limited its application in photocatalytic reduction of pollutants.In this work,we prepared WO_(3)@PVP with PVP capped WO_(3) by a simple one-step hydrothermal method,which showed an elevated energy band structure and improved charge carrier separation property.XRD,SEM,TEM,XPS,DRS,and the photocurrent density test were carried out to study the properties of the composite.Results demonstrated monoclinic WO_(3) with a size of~100-250 nm capped by PVP was obtained,which possessed fewer lattice defects inside but more defects(W^(5+))on the surface.Moreover,the results of the photocatalytic experiment showed the kinetic constant of Cr(Ⅵ)reduction process on WO_(3)@PVP was 0.532 h^(-1),which was 3.1 times higher than that onWO_(3)(0.174 h^(-1)),demonstratingWO_(3)@PVP with good photocatalytic capability for Cr(Ⅵ)reduction.This can be attributed to the improved charge carrier separation performance,the improved adsorption capacity and the elevated conduction band edge of WO_(3)@PVP.More importantly,the energy band structure of WO_(3)@PVP was proved elevated with a value as high as 1.14 eV than that of WO_(3) nanoparticles,which enables WO_(3)@PVP a promising material in the photocatalytic reduction reaction of heavy metal ions from wastewater.