Performance evaluation of reverse logistics enterprise – an agent-based simulation approach

Reverse logistics (RL) has been applied in many industries and sectors since its conception. Unlike forward logistics, retracing consumer goods from the point of consumption to the point of inception is not a well-studied process. It involves many uncertainties such as time, quality and quantity of returns. The returned products can be remanufactured, have parts harvested, or be disposed safely. It is important to implement these activities in a cost-effective manner. The aim of this research is to measure the performance of the RL enterprise with the help of an agent-based simulation model. The major entities in the RL network are considered as Agents that can act independently. There are several different agents: collector agent, sorting-cum-reuse agent, remanufacturing agent, recycler agent, supplier agent and distributor agent. The individual performances of the agents are measured and recommendations are given to improve their performance, leading to the enhancement of the total performance of the RL enterprise. The approach is applied to a case study involving cell phone remanufacturing.     

Pyrolysis of waste animal fats in a fixed-bed reactor: Production and characterization of bio-oil and bio-char

Several animal (lamb, poultry and swine) fatty wastes were pyrolyzed under nitrogen, in a laboratory scale fixed-bed reactor and the main products (liquid bio-oil, solid bio-char and syngas) were obtained. The purpose of this study is to produce and characterize bio-oil and bio-char obtained from pyrolysis of animal fatty wastes. The maximum production of bio-oil was achieved at a pyrolysis temperature of 500 °C and a heating rate of 5 °C/min. The chemical (GC–MS analyses) and spectroscopic analyses (FTIR analyses) of bio-oil showed that it is a complex mixture consisting of different classes of organic compounds, i.e., hydrocarbons (alkanes, alkenes, cyclic compounds…etc.), carboxylic acids, aldehydes, ketones, esters,…etc. According to fuel properties, produced bio-oils showed good properties, suitable for its use as an engine fuel or as a potential source for synthetic fuels and chemical feedstock. Obtained bio-chars had low carbon content and high ash content which make them unattractive for as renewable source energy.     

Co-treatment of fruit and vegetable waste in sludge digesters. An analysis of the relationship among bio-methane generation,process stability and digestate phytotoxicity

The co-digestion of a variable amount of fruit and vegetable waste in a waste mixed sludge digester was investigated using a pilot scale apparatus. The organic loading rate (OLR) was increased from 1.46 kg VS/m³ day to 2.8 kg VS/m³ day. The hydraulic retention time was reduced from 14 days to about 10 days. Specific bio-methane production increased from about 90 NL/kg VS to the maximum value of about 430 NL/kg VS when OLR was increased from 1.46 kg VS/m³ day to 2.1 kg VS/m³ day. A higher OLR caused an excessive reduction in the hydraulic retention time, enhancing microorganism wash out. Process stability evaluated by the total volatile fatty acids concentration (mg/l) to the alkalinity buffer capacity (eq. mg/l CaCO₃) ratio (i.e. FOS/TAC) criterion was <0.1 indicating high stability for OLR <2.46 kg VS/m³ day. For higher OLR, FOS/TAC increased rapidly. Residual phytotoxicty of the digestate evaluated by the germination index (GI) (%) was quite constant for OLR < 2.46 kg VS/m³ day, which is lower than the 60% limit, indicating an acceptable toxicity level for crops. For OLR > 2.46 kg VS/m³ day, GI decreased rapidly. This corresponding trend between FOS/TAC and GI was further investigated by the definition of the GI ratio (GIR) parameter. Comparison between GIR and FOS/TAC suggests that GI could be a suitable criterion for evaluating process stability.     

1株异养硝化-好氧反硝化细菌DK1的分离鉴定及其脱氮特性

从某反应器活性污泥中分离筛选出1株假单胞菌属(Pseudomonas sp.)细菌,命名为DK1,并对该菌进行脱氮特性研究.在以葡萄糖为碳源,C/N量比为5时,分别以NaNO_3和NaNO_2为氮源,二者的好氧反硝化速率为4.09 mg·(L·h)-1和4.43mg·(L·h)~(-1).以二者同时为氮源脱氮率为100%;此外,菌株DK1具有异养硝化性能,NH_4~+-N平均去除速率为2.32mg·(L·h)-1.缺氧时以NO_2~--N为氮源菌株DK1可将一系列梯度浓度NO_2~--N(约100~300 mg·L-1)在36 h内降为0.当NO_3~--N和NO_2~--N同时存在时,菌株DK1会优先利用NO_3~--N进行反硝化.同时该菌株还具有同步硝化反硝化(SND)性能,可同时去除NH_4~+-N、NO_2~--N或NH_4~+-N、NO_3~--N,30 h内脱氮率分别达95.06%和94.69%.相同时间内在NH_4~+-N、NO_2~--N和NO_3~--N三者均存在时,脱氮效果最佳,达100%.菌株DK1的高效SND及反硝化性能表明其在处理含氮废水方面有一定的潜力和应用价值.     

流态对生物添加强化硝化效果的影响

在15℃、相同氮负荷和添加强度条件下运行SBR和CSTR以对比分析两种典型流态(推流式和完全混合式)对硝化菌添加强化硝化效果的影响.结果表明,添加期间,SBR中氨氧化速率(AUR)和亚硝酸盐氧化速率(NUR)分别为添加前的2.34和2.39倍,停止添加后又分别降为添加前的2.01和1.78倍;添加期间CSTR中AUR和NUR分别为添加前的2.63和2.44倍,停止添加后又分别降为添加前的1.48和1.31倍.荧光原位杂交结果显示,添加期间,SBR中氨氧化菌(AOB)和亚硝酸盐氧化菌(NOB)的个数百分比分别为添加前的2.67和2.71倍,添加停止后,又分别降至原来的2.14和1.95倍;CSTR中AOB和NOB分别为添加前的2.91和1.77倍,但在添加停止后CSTR中AOB和NOB分别降至添加前的1.25和1.50倍.因此,硝化菌添加期间,两种流态的添加效果接近,但是在添加停止后,由于流态对硝化菌中K-决策者(Nitrosospira、Nitrospira)和r-决策者(Nitrosomonas europaea、Nitrobacter)的选择作用,添加的硝化菌在完全混合式条件下比推流式条件下更容易被系统淘汰.     

不同运行模式下改良型CAST工艺处理生活污水的除磷性能

实验采用改良型CAST工艺,以生活污水为研究对象,考察了C/P、回流比及温度等不同运行模式对系统除磷性能的影响.结果表明,常温条件下进水C/P由50升至100,系统除磷率均值从15%迅速升至95.6%,除磷性能显著提高;继而降低C/P至75,除磷性能因进水碳源不足再度下降,除磷率均值为51.4%,且长期投加易降解碳源引发系统污泥膨胀并导致污泥大量流失.C/P较低情况下,回流比由25%降低至12.5%,除磷性能提高2.3倍,继续降低回流比至0,除磷性能反而下降;温度实验研究则表明,低温系统(14℃±1℃),除磷率稳定维持在90%以上,而高温短程硝化系统(27℃±1℃)除磷率仅为14.1%,可见低温更有利于系统磷的去除.吸磷小试发现,常温系统污泥以O_2、NO_3~-和NO_2~-为电子受体均能进行吸磷,而低温系统污泥能以O_2、NO_3~-为电子受体进行吸磷,高温系统污泥则仅能以O_2为电子受体进行少量吸磷.此外,实验还发现,系统短期闲置导致的污泥"饥饿"有利于系统除磷率的提高.     

基于生态分区的我国湖泊营养盐控制目标研究

为更好地控制我国湖泊的富营养化水平,在五大湖泊生态分区的基础上,对不同生态分区的100个湖泊总氮(TN)、总磷(TP)、TN/TP与叶绿素a(Chl-a)的关系进行了分析,进而提出了不同生态分区的湖泊营养盐控制目标.结果表明,五大湖泊生态分区中,东北湖区富营养化水平最低,华北湖区富营养化水平最高,近几年五大湖区湖泊富营养水平呈上升趋势.从TN、TP对五大生态分区湖泊Chl-a浓度的影响看,TP是东北和华北湖区湖泊藻类生长的限制性营养盐,而TN和TP同时是中东部、云贵和蒙新湖区湖泊藻类生长的限制性营养盐.从TN/TP判断,在TN/TP<10的湖泊中,除华北湖区外的其他4个湖区湖泊Chl-a均受TN显著影响;TP仅对东北、蒙新湖区湖泊的Chl-a有显著影响.在TN/TP>17的湖泊中,除蒙新湖区外的其他4个湖区湖泊Chl-a均受TP显著影响,而在中东部、云贵和蒙新湖区,TN对Chl-a也有显著影响.在10相似文献   

缙云山土地利用方式对土壤轻组及颗粒态有机碳氮的影响

选取缙云山阳坡同一海拔处亚热带常绿阔叶林(以下简称林地)、果园、坡耕地和撂荒地这4种不同土地利用类型,在0~60 cm深度内每隔10 cm采集一个土样,测定土壤轻组有机碳氮(LFOC、LFON)和颗粒态有机碳氮(POC、PON)含量,并计算其分配比例和碳氮比.结果表明,在0~60 cm土壤深度范围内,林地转变为坡耕地后,LFOC及LFON含量分别降低了71.42%和38.46%(P0.05),转变为果园后变化不明显,坡耕地撂荒后其含量分别升高了3.77倍和1.38倍(P0.05);林地转变为坡耕地或果园后,POC及PON含量均无明显变化,而坡耕地撂荒后其含量分别增加了4.12和1.25倍(P0.05).林地转变为坡耕地后土壤LFOC及LFON分配比例显著降低,转变为果园后则明显升高,而POC及PON分配比例变化均不明显;坡耕地撂荒后,LFOC、LFON、POC、PON分配比例均显著增加.土壤SOC/TN为撂荒地(12.93)林地(8.53)果园(7.52)坡耕地(4.40),LFOC/LFON为撂荒地(16.32)林地(14.29)果园(11.32)坡耕地(7.60),POC/PON为撂荒地(23.41)坡耕地(13.85)林地(10.30)果园(9.64).以上研究结果表明林地开垦为果园或坡耕地后容易导致土壤轻组有机碳氮的损失,而坡耕地撂荒则有利于土壤活性有机碳氮的积累;林地转变为坡耕地减弱了土壤有机碳氮的活性,而林地转变为果园以及坡耕地撂荒均使土壤有机碳氮活性增强;林地转变为坡耕地和果园加剧了土壤有机质的矿化,相对而言,坡耕地撂荒后有利于土壤有机质的固定.     

不同部位玉米秸秆对两种质地黑土CO2排放和微生物量的影响

秸秆还田后作物残体的分解是农田生态系统碳循环及养分周转平衡的一个至关重要环节.为了探索秸秆化学性质和土壤质地对黑土区土壤CO2排放和微生物量的影响,本文通过室内恒温培养实验研究了添加不同植株部位玉米秸秆(根、茎下部、茎顶部、叶)进入黑土区两种质地土壤(砂壤土和黏壤土)后的CO2排放、微生物量,并分析了它们与秸秆C/N、木质素含量的关系.结果表明,添加不同部位秸秆一致增加土壤CO2排放量,激发效应值介于216.53~335.17μmol·g-1,黏壤土大于砂壤土.激发效应值与木质素/N之间的线性回归关系明显好于激发效应与木质素含量、C/N、含氮量之间的线性关系.添加秸秆增加MBC和MBN含量,降低MBC/MBN,微生物群落氮固持的速率高于碳固持.添加秸秆后,砂壤土微生物量增加的幅度大于黏壤土,总溶解性氮含量小于黏壤土.结果说明,秸秆的木质素和氮含量均会对它的分解和CO2排放产生影响,木质素/N比木质素含量、C/N等更好地说明秸秆分解和CO2排放的差异;与黏壤土相比,在砂壤土中实施秸秆还田可以取得更好的土壤碳固存、微生物量和氮素保持效果.     

微生物燃料电池改性阳极处理PTA废水

探讨了不同改性阳极对微生物燃料电池(microbial fuel cell,MFC)产电性能及其对MFC处理难降解废水能力的影响.以单室空气阴极为基础,利用0.1 g电气石、质量分数75%二氧化锰/埃洛石纳米管(manganese bioxide/halloysite nanotube,MnO_2/HNT)和多壁碳纳米管-羧基(multi-walled carbon nanotube-carboxyl,MWCNT-COOH)对MFC阳极进行修饰.结果表明,不同改性阳极的MFC对含精对苯二甲酸(purified terephthalic acid,PTA)废水的去除率均高于70%,且化学需氧量(chemical oxygen demand,COD)去除率在79%以上.相较于其他几种改性阳极,以MWCNT-COOH改性材料作阳极的MFC产生的最大输出电压最高,获得的最大功率密度最高,分别为529 mV和252.73 mW·m~(-2).