Refrigeration waste heat utilization for drying applications: a review

ABSTRACT

Cold chain industry has a vast potential for waste heat recovery. It is a matter of importance for energy efficiency point of view, as global energy demand is increasing day by day. Ample amount of low-grade energy is either unutilized or underutilized. The heat rejected by a Heat pump or refrigeration system emerged as a promising solution for dehydration by utilizing low-grade waste heat despite higher investment. As compared to solar drying technology, heat pump drying evolved as a reliable method regarding better process control, energy efficiency, and quality of the product to be dried. Energy utilized through the refrigeration system’s waste/exhaust heat recovery in combination with or without renewable energy source enhances the overall efficiency of the system and also reduces the cost. This useful review investigated and compared the research findings of waste heat utilization through heat pump and from condenser of refrigeration system on laboratory, pilot as well as industrial scale for drying of various fruits, vegetables, and agro products. Various drying parameters like drying rate, moisture content, Specific Moisture Extraction Rate (SMER), Coefficient of Performance (COP), Exergy efficiency, and temperature as well as humidity conditions inside the drying chamber were also reviewed to promote the technological advancement of energy utilization by commercial cold storage waste heat recovery.     

Genotypic variations in the accumulation of Cd exhibited by di erent vegetables

It is an important approach to use the Cd-contaminated soils properly by growing low accumulator or excluder plants for Cd to produce safe foods. To find the suitable vegetable species for growing in Cd-contaminated soils, in the present study the variations in the Cd accumulation for twenty eight vegetable species and several cultivars of five common vegetables (cowpea, kidney pea, bitter gourd, cucumber and squash) were investigated in two soil Cd levels (1 and 2 mg/kg Cd). Experimental results showed that highly significant di erences in Cd concentration were evident among 28 vegetables. For example, spinach Cd concentrations were 110-fold and 175-fold higher than that of sweet pea under the 1 and 2 mg/kg Cd exposures, respectively. For Cd accumulation, the order of vegetable species was: leafy vegetables > solanaceous vegetables > kale vegetables > root vegetables > allimus > melon vegetables > legumes. Distinctive di erences were also identified when comparing di erent cultivars of the five common vegetables with an average range of 0.003–0.094 mg/kg Cd. Our results indicated that a large genotypic variation existed among vegetable species or cultivars when subjected to Cd exposure. Therefore, it is important and feasible to elect/breed vegetable species/cultivars with low accumulation of Cd, especially in mildly Cd-contaminated soils.     

Polybrominated diphenyl ethers in food and associated human daily intake assessment considering bioaccessibility measured by simulated gastrointestinal digestion

The concentrations of PBDEs in 299 vegetable and animal-based food samples of 31 species, collected in Shanghai, China, and the bioaccessibility of PBDEs in part of the samples were determined. The PBDE concentrations ranged from 0 to 1245.4 pg g⁻¹ with animal-based food containing more PBDEs than vegetables. The bioaccessibility of PBDEs, determined by a method simulating human gastrointestinal digestion process, were from 2.6% to 39.9% in vegetables, and from 5.2% to 105.3% in animal-based food. For animal-based food, good correlations were observed between the bioaccessibility of PBDEs and the fat content, thus the fat content in animal-based food was able to be used to estimate the bioaccessibility of PBDEs. The total daily intake of PBDEs via ingestion of vegetables and animal-based food for an average Shanghai resident was estimated as 13 235.7 and 13 668.0 pg d⁻¹, respectively, but the amounts available for human absorption were reduced to 2674.4 and 4316.6 pg d⁻¹ after the PBDE bioaccessibility was considered. Finally, the contributions of different food groups to the total daily intake of PBDEs were evaluated. The results revealed that, when not considering the bioaccessibility of PBDEs, vegetables were the leading contributor (49.2%), followed by fish (34.0%). However, the sequence was reversed after the PBDE bioaccessibility was taken into account. The results indicated that human exposure to PBDEs via food ingestion might have been significantly overestimated and the exposure assessment could be misleading if the bioaccessibility of PBDEs was not considered.     

北京市菜地土壤和蔬菜铬含量及其健康风险评估

对北京市97种蔬菜的345个蔬菜样品和54个菜地土壤中的铬含量进行了研究.结果表明,北京市菜地土壤中铬含量的含量范围、算术均值、中值、几何均值分别为25.4～86.3、44.5、42.2、43.4 mg·kg-1,均低于<土壤环境质量标准>中的蔬菜地土壤质量标准,但显著高于北京市土壤铬背景值.蔬菜铬的含量范围、算术均值和几何均值分别为0.4～1034、64.6、22.7μg·kg-1.叶菜类和根茎类蔬菜的铬平均含量显著高于特菜类,其它类型的蔬菜铬含量差异不显著.北京市本地产蔬菜和裸露地蔬菜的铬含量均分别显著高于市售外地产蔬菜和设施栽培蔬菜.甘蓝的铬富集系数较高,小白菜、云架豆和冬瓜次之,而西红柿、黄瓜、大葱、叶甜菜、萝卜、大白菜、茄子和辣椒和部分特菜等铬富集系数最低.北京市居民从蔬菜中摄入铬的量为每人50.5μg·d-1,目前已存在一定的潜在健康风险.     

Comparison of concentrations of mercury in ambient air to its accumulation by leafy vegetables: An important step in terrestrial food chain analysis

A biomonitoring network with leafy vegetables was established near a chlor-alkali plant in order to compare the accumulation of mercury to the atmospheric total gaseous mercury (TGM) concentration. Based on data obtained in the reference area the ‘normal’ mercury concentration in vegetables is between 0.6 and 5.4 μg kg⁻¹ FW. The effect detection limits (EDLs) are between 1.2 and 11.0 μg kg⁻¹ FW and the biological detection limits (BDLs), the lowest [TGM] that can be detected significantly, are between 3 and 4 ng m⁻³. The accumulation rate is lowest for lettuce and high for curly kale that proved to be an excellent accumulator and as such it is very useful for biomonitoring purposes. A comparison made in the 1980s between biomonitoring results with grass and the mercury concentration in leafy vegetables from private gardens nearby proved to be valid when applied to the current biomonitoring results with vegetables.     

专用叶面营养对叶菜的增产效果及其机理研究

采用大田试验研究专用叶面营养液对主要叶菜的增产效果;并以芥菜为供试叶菜系统研究了专用叶面营养液对叶菜的增产机理。结果表明;专用叶面营养液可明显促进芥菜对Ｎ、Ｐ、Ｋ养分的吸收,提高叶片硝酸还原酶活性、叶绿素含量及光合速率,增加产量和改善品质。专用叶面营养液分别优于这种营养液中的营养物质和生长调节剂。芥菜喷施专用叶面营养液,与对照相比,叶绿素含量、光合速率、硝酸还原酶活性分别增加２０．２％、３６％、１．２０１μｇ／（ｇ·ｈ）;平均增产２４．６％;Ｖｃ、可溶性糖分别增加８７ｍｇ／ｋｇ和１．７ｇ／ｋｇ。     

养殖场周边土壤-蔬菜系统磺胺类药物残留及风险评价

采集了新乡市周边不同种类、规模的养殖场施用粪便的土壤以及蔬菜样品,并采用高效液相-荧光分析法测定了样品中磺胺嘧啶、磺胺间甲氧嘧啶和磺胺甲恶唑这3种主要磺胺类药物的残留情况.结果表明,3种磺胺类药物在土壤和蔬菜中的总含量范围分别为7.60~176.26μg·kg~(-1)和ND~32.70μg·kg~(-1),平均含量分别为70.73μg·kg~(-1)和7.08μg·kg-1.土壤中药物平均残留量均低于兽药国际协调委员会规定的生态毒害效应触发值(100μg·kg~(-1)).不同种类蔬菜中药物的残留量不同,青菜、油麦菜、白菜和大葱这4种蔬菜中3种磺胺类药物的平均残留量最高.所有蔬菜样品中3种药物的残留水平未超过磺胺类药物的日允许摄入量,但仍不能忽略人类长期食用所导致人体抗药细菌或基因的形成.     

长期施用粪肥蔬菜基地蔬菜中典型抗生素的污染特征

利用高效液相色谱-串联质谱(HPLC-MS/MS)技术,分析了珠三角地区某长期施用粪肥蔬菜基地蔬菜中16种典型抗生素的含量,并初步评价其健康风险.结果表明,绝大部分抗生素不同程度被检出,检出率为11%～100%,大多数含量<5μg·kg-1(干重),最高为23.88μg·kg-1,平均为0.91μg·kg-1,以恩诺沙星、环丙沙星、磺胺二甲基嘧啶和磺胺嘧啶为主.各蔬菜样品中至少检出1种抗生素,最多达10种.蔬菜不同器官中喹诺酮类抗生素含量为地下部>地上部.人体通过食用研究区蔬菜摄入抗生素的量低于日允许摄入量(ADI),表明其健康风险较小,但多种抗生素的联合毒性及其耐药性问题不容忽视.     

不同种类蔬菜重金属富集特征及健康风险

蔬菜中重金属累积引发的健康风险逐渐被重视.通过文献查阅与实地样品采集,搭建了我国蔬菜-土壤系统重金属元素含量数据库,系统地分析了我国蔬菜可食部位中7项重金属含量特征和不同种类蔬菜对重金属的生物累积能力.此外,采用蒙特卡罗模拟评估了通过摄入4种类型蔬菜导致的非致癌健康风险.蔬菜可食部位ω(Cd)、ω(As)、ω(Pb)、ω(Cr)、ω(Hg)、ω(Cu)和ω(Zn)的平均值分别为0.093、 0.024、 0.137、 0.118、 0.007、 0.622和3.272 mg·kg^-1,其中5种有害元素的超标率为：Pb(18.5%)>Cd(12.9%)>Hg(11.5%)>Cr(4.03%)>As(0.21%).叶菜类蔬菜表现出较高的Cd富集能力,根茎类蔬菜表现出较高的Pb富集能力,其富集系数的平均值分别为0.264和0.262,而豆类蔬菜和茄果类蔬菜表现出较低的重金属富集能力.健康风险结果表明,蔬菜摄入的单项元素非致癌风险在可接受范围,其中儿童的健康风险高于成人.单项元素非致癌风险HQ平均值表现为：Pb>Hg>Cd>As&...     

蔬菜镉(Cd)富集因子变化特征及其影响因素

本研究以湖南省攸县为例,测定重金属镉(Cd)在585个灌溉水样品和625对土壤蔬菜样品中的含量水平,结合农业与气象调查数据,应用典型相关分析及路径分析模型研究各环境因子对于Cd在土壤-蔬菜系统累积水平的影响.结果表明研究区灌溉水、土壤、蔬菜中Cd含量差异较大.蔬菜Cd富集因子(PUF)服从自然对数分布,有10%的概率大于1.土壤pH和土壤有机质对PUF有着显著的直接效应,土壤阳离子交换量,灌溉水pH,降雨量和氮肥施肥量通过与pH及土壤有机质的相关关系间接影响PUF变化.研究区土壤pH和土壤有机质含量较低,对于Cd在土壤-蔬菜系统中的累积风险应给予一定关注.