Ecological Engineering 37 (2011) 948–954
Contents lists available at ScienceDirect
Ecological
Engineering
j o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /e c o l e n
g
Performance of integrated household constructed wetland for domestic wastewater treatment in rural areas
Shubiao Wu a ,David Austin b ,Lin Liu a ,Renjie Dong c ,?
a
Key Laboratory of Agricultural Engineering in Structure and Environment of Ministry of Agricultural,College of Water Conservancy &Civil Engineering,China Agricultural University,100083Beijing,PR China b
CH2M HILL,Mendota Heights,MN,USA c
College of Engineering,China Agricultural University,100083Beijing,PR China
a r t i c l e i n f o Article history:
Received 1May 2010
Received in revised form 24January 2011Accepted 15February 2011Available online 2 April 2011Keywords:
Constructed wetland Rural areas
Household wastewater treatment
a b s t r a c t
As environmental legislation has become stricter in recent years,the issue of wastewater treatment in rural areas has become an increasing concern.Choice of the most suitable on-site puri?cation systems is based on the key issues of affordability and appropriateness in Chinese rural areas.This paper describes an integrated household constructed wetland (IHCW)system planted with willow (Salix babylonica )to treat household domestic wastewater in rural villages in northern China.The precast frame structure of IHCW is strong and waterproof.It can be mass-produced and installed per a standard set of speci?cations.The IHCW has achieved high overall removal ef?ciencies for BOD 5,TSS,NH 4-N,and TP:96.0%,97.0%,88.4%and 87.8%,respectively.A 0.4m biomass layer cover on the system provided signi?cant system thermal insulation,maintaining high treatment performance in freezing winter conditions.The system is cost effective and does not need any operational energy inputs,demonstrating its feasibility for single-family use in developing countries.
? 2011 Elsevier B.V. All rights reserved.
1.Introduction
Domestic wastewater treatment in rural areas is essential to prevent pollution of aquatic environments,which has been of increasing concern for both researchers and government of?cials (Ichinari et al.,2008).These concerns are a prelude to toughing environmental legislation.
Estimates from the World Health Organization (WHO)and the Water Supply and Sanitation Collaborative Council indicate that <18%of rural populations have access to sanitation services in developing countries (Massoud et al.,2009).In fact,the amount of domestic wastewater treated in China is just 11%for county towns and <1%for rural villages (Pan et al.,2007).To address this situ-ation,in 2005,the Chinese government put forward the strategic plan “New Socialist Countryside Building”.Methods of improving the living environment and dealing with domestic wastewater in rural areas have been an urgent concern of the China State Council and State Environment Protection Administration.
Households in rural areas that do not have public sewers must depend on on-site treatment systems to manage their wastewater.Many on-site wastewater treatment technologies,such as septic
?Corresponding author.
E-mail address:wsb4660017@https://www.doczj.com/doc/de6348731.html, (R.Dong).
tanks,drain-?eld systems,lagoons,aerobic biological treatment units,membrane bioreactors (MBRs)and constructed wetlands are available (Nakajima et al.,1999;Abegglen et al.,2008).A “Most Appropriate Technology”is the one that is economically afford-able,environmentally sustainable,and socially acceptable.On-site treatment systems often do not meet these requirements.High total suspended solids (TSS),biochemical oxygen demand (BOD),total fecal coliforms,total nitrogen (TN),and total phosphorus (TP)make septic tank ef?uent unsuitable discharge to water bodies (Carroll et al.,2006).Traditional leach-?eld systems are prone to failure in areas with impermeable,heavy clay soils,and also pro-vide inadequate treatment in areas with highly permeable soils and high water https://www.doczj.com/doc/de6348731.html,goons tend to be unpleasant from an aes-thetic perspective and because of odor production (Burkhard et al.,2000;García et al.,2001).Aerobic biological treatment unit and membrane bioreactors (MBRs)effectively remove pollutants,but have high capital,operations and maintenance costs that are not affordable in developing countries (Nakajima et al.,1999;Daude and Stephenson,2004;Ichinari et al.,2008;Ren et al.,2010).Con-structed wetlands have high pollutant removal ef?ciency,as well as low cost and simple operation (Brix and Arias,2005;Siracusa and La Rosa,2006),but can be limited by seasonal changes in treatment capacity and large area requirements (Brix,1994).It is apparent that a successful and sustainable system entails a wide range of criteria including environmental,technical and social cul-
0925-8574/$–see front matter ? 2011 Elsevier B.V. All rights reserved.doi:10.1016/j.ecoleng.2011.02.002
S.Wu et al./Ecological Engineering37 (2011) 948–954
949
Fig.1.Schematic diagram of the integrated household constructed wetland system (the doted red line shows the water?ow path).(For interpretation of the references to color in this?gure legend,the reader is referred to the web version of the article.)
tural factors.That is the underlying reason some currently available practices adopted from other countries can be incompatible with local requirements,limitations,and conditions(Massoud et al., 2009;Ren et al.,2010).It is therefore essential to conduct research into an alternative disposal system based on local requirements and conditions for the treatment of wastewater from a typical single family in rural China.
This paper describes a new on-site wastewater treatment sys-tem(Integrated Household Constructed Wetland,IHCW)for rural household wastewater treatment.The system consists of a two-stage sedimentation tank and a vertical-?ow,constructed wetland bed.The precast structure is strong and waterproof.Modular con-struction allows for installation with unskilled labor.It is expected that the system may overcome the local limitations of soil con-ditions and unskilled construction.Additionally,the insulating biomass layer at the wetland bed surface allows the system to run normally in freezing temperatures.This concept appears to offer advantages for household wastewater treatment in develop-ing countries,where really low-cost,convenient construction and operational simplicity are essential.
2.Materials and methods
The experiment took place in the backyard of a rural family in Chang Ping,Beijing,China.It was an insulated,at-grade,vertical-?ow model to avoid damage from low temperatures in winter (Fig.1).The system consisted of a two-stage sedimentation tank and a vertical?ow constructed wetland bed section.The frame structure was precast with magnesia cement and?ber glass fabric which is strong and waterproof.In plan view the structure is ellipti-cal with the bottom smaller than the top to facilitate transportation. It can be directly installed after excavation.The two-stage sedi-mentation tank consists of two segments with equal empty-bed volume for each segment of0.5m3.The empty volume of the wet-land bed section is1.2m3(area×depth:1.2m2×1.0m).A steel sieve was installed in the inlet basin to prevent large solids(such as vegetable leaves and?sh scales from the kitchen)from?ow-ing into the tank.Wastewater?ows into the?rst segment from the inlet basin and then into the second segment via a?oating valve installed in the?rst segment to allow intermittent system feeding.In order to maintain normal operation during the winter period,0.4m of sawdust insults the bed.Wastewater?ows from the sedimentation tank downwards through a60mm diameter perfo-rated plastic pipe with5mm holes located at the top of the sand layer and then trickles through the wetland bed.The ef?uent?ows into the bottom gravel layer and then through the dewatered alum sludge placed in the outlet,and?nally?ows into the ground.The dewatered alum sludge is a byproduct from drinking water treat-ment plants and has been reported to enhance P removal due to its high content of amorphous aluminum(Babatunde and Zhao,2007, 2009;Razali et al.,2007).
The bed media from the bottom to the top are washed gravel, pea gravel and sand which was modi?ed according to the stan-dard design criteria(Brix and Arias,2005):a15cm layer of washed gravel with particle size of10–30mm,15cm of washed pea gravel with particle size of5–12mm,and90cm of washed sand.The effective size of the washed sand is0.45–1mm with a uniformity coef?cient of3.8.Seventy?ve kilograms of washed dewatered alum sludge derived from drinking water treatment plant with particle size of0.5–1mm was put in the outlet of the system.The medium surrounding the distribution pipe network was10cm of gravel with particle size of10–30mm.
A willow(Salix babylonica)with a trunk diameter of40mm was planted in the vertical?ow wetland bed section.The willow was selected as the wetland plant for several reasons.In China people would prefer a tree in their backyard rather than wetland plants. The experience of some constructed wetland systems with willows in Demark has successfully provided a showcase of good perfor-mance in nutrients and heavy metals removal(Hasselgren,1998; Sander and Ericsson,1998),probably due to the well-developed root system willows produced.Willows are also cold hardy in the harsh climatic conditions of northern China.
The system was planted and then seeded in November2007. Sampling evens occurred from March2008to February2009.Dur-ing the experiment operation,household wastewater in?uent was comprised of kitchen and laundry ef?uents.The hydraulic loading rate was about0.12m d?1.Water samples of approximately200ml were collected from the in?uent,sedimentation tank(second seg-ment),and ef?uent(Fig.1)at7–10days intervals to evaluate the treatment performances.Wastewater parameters of biochemical oxygen demand(BOD5,5210B.5-day BOD test),total suspended solids(TSS,2540D.total suspended solids dried at103–105?C), ammonia-nitrogen(NH4-N,4500G.automated phenate method), and total phosphorus(TP,4500F.automated ascorbic acid reduc-tion method)were measured on the same day of collection in the Key Laboratory of Agricultural Engineering in Structure and Envi-ronment of China Ministry of Agriculture according to the Standard Methods(AWWA,1999).The pH and DO were measured in situ for each sample using a portable meter(Orion-5-Star,510M-62).For each of the parameters,samples were collected and analyzed in triplicate.Mean and standard deviation values were reported.The daily air temperature of meteorological data in terms of maximum and minimum was provided by the Beijing Meteorological Bureau, Beijing,China.The temperature of the vertical constructed wetland bed was determined by a temperature sensor(Pt1000,Yonghua, China)installed in the middle depth of the bed(Fig.1).
Face-to-face questionnaires were conducted among158home-respondents to evaluate farmers’willingness to pay for treatment and the potential application of the integrated household con-structed wetland in rural villages.
3.Results
The wastewater used for experiment was generated in a single household,excluding toilet wastewater.Average concentrations
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Fig.2.Concentrations of in?uent,sedimentation tank and ef?uent in integrated household constructed wetland system ((a)biochemical oxygen demand (BOD),(b)total suspended solids (TSS),(c)ammonia-nitrogen (NH 3-N),and (d)total phosphorus (TP)).
Table 1
Construction cost of one integrated household constructed wetland system.Items
Cost (US dollars)Precast frame structure 147Gravel and sand 36Installation
30Pipes and joints 22Excavation 22Willow 2Sum
259
of BOD 5,TSS,NH 4-N and TP in the in?uent were 302.4mg/l,128.6mg/l,30.7mg/l and 5.0mg/l,respectively,and the aver-age concentrations in ef?uent were all continuously reduced to 11.8mg/l,3.8mg/l,3.5mg/l and 0.6mg/l,respectively (Fig.2).
Average removal ef?ciencies of BOD 5,TSS,NH 4-N and TP out-side of winter were 96.3%,97.3%,90.0%,and 87.6%,respectively and 95.0%,96.2%,84.6%,88.2%in winter period (Fig.3).There was negligible decrease of average removal ef?ciency for BOD 5,TSS,and NH 4-N during winter (1.3%,1.1%and 5.4%,respectively);while an increase of 0.6%was achieved for TP removal in winter period.The insulting sawdust layer is most probably responsible for the minimal change between winter treatment performance and the rest of the year (Wallace et al.,2001).The sawdust insulating layer kept the wetland bed temperature constantly above 6?C even as the minimum air temperature decreased to ?8?C during winter (Fig.4).
The total construction cost of the integrated household con-structed wetland system was 259US dollars,including precast frame structure,gravel and sand,and installation (Table 1).Of the householders polled on cost issues,23%respondents were reluctant to pay any money for wastewater treatment facilities construction,
32%took a “wait and see”position,and 45%were willing to pay (Fig.5a).The percentage of householder’s willingness to pay ranges from 3to 6dollars per year was 54.1%,but just 6.4%were willing to pay more than 12dollars per year (Fig.5b).These attitudes may be closely related to local economic conditions,especially the farmer’s income level.Clearly,the cost of wastewater treatment technology must be extremely low before rural villages will adopt it.4.Discussion
High removal rates of BOD 5and TSS in the study system were similar to those observed with constructed wetlands (Haberl et al.,1995;Lakatos et al.,1997).Pretreatment in the sedimentation tank also plays an important role by removing 32%of BOD 5and 46%of TSS (Fig.6).This treatment performance was similar to that observed for primary settling (Metcalf and Eddy,2003).
Anaerobic degradation in the sedimentation tank may have also played an important role in treatment.Domestic wastewater from a single rural family traditionally comes from kitchen and laun-dry ef?uent.It is highly biodegradable (Elmitwalli and Otterpohl,2007).The sedimentation tank had dissolved oxygen (DO)concen-trations <0.8mg/l,which was essentially an anaerobic condition with little temperature variation.Sedimentation tank removal of NH 4-N and TP was just 15%and 17%.As expected,nitri?cation was limited by low dissolved oxygen concentration in the sedimenta-tion tank (Beccari et al.,1992;Paredes et al.,2007).The rate of TP removal was consistent with a sedimentation process (Metcalf and Eddy,2003).The sedimentation tank clearly ful?ls primary treatment buffering of BOD 5and TSS to the treatment system by moderating high in?uent concentrations (Fig.7).The clear bene-?t of the sedimentation tank section lies not only in concentration reduction of BOD 5and TSS,but also to avoid or relieve clogging
S.Wu et al./Ecological Engineering 37 (2011) 948–954
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Fig.3.Pollutants removal ef?ciencies in integrated household constructed wetland system ((a)biochemical oxygen demand (BOD),(b)total suspended solids (TSS),(c)ammonia-nitrogen (NH 3-N),and (d)total phosphorus
(TP)).
Fig.4.Meteorological air temperature and wetland bed temperature change with experiment operation.
of the constructed wetland bed by excessive particulate or organic loading (Austin et al.,2007;álvarez et al.,2008;Barros et al.,2008;Chen et al.,2008).
Phosphorus removal in this system exhibited 87.6%overall removal ef?ciency outside of the winter period and 88.2%in the winter period (Fig.3).This removal rate is far higher than what can be achieved in conventional constructed wetlands (Vymazal,2007;Yates and Prasher,2009).Phosphorus removal in constructed wetlands is an integrated process including settlement,plants uptake,and bacteria adsorption and substrate af?nity (Greenway and Woolley,1999;Vymazal,2007;Kadlec and Wallace,2008),but compared to adsorption to substrate other mechanisms of phos-phorus removal are not signi?cant in wetland systems (Brix,1997;Vymazal,2007).Therefore,this study did not detect phospho-rus uptake by willows.Since traditional wetland systems employ gravel and/or sand as the substrate,P removal is often poor due to their limited P adsorption capacity.Removal of P in all types of constructed wetlands is low unless special substrates with high sorption capacity are used (Vymazal,2007).
Some studies have demonstrated that dewatered alum sludge has the potential to enhance P removal due to its high content of amorphous aluminum (Babatunde and Zhao,2007,2009;Razali et al.,2007).It is a byproduct from drinking water treatment plants and commonly be disposed as land?ll.At present,there is
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Fig.5.Willingness to pay (a)and payment level (b)for the householders to treat their domestic wastewater in rural areas.(158respondents were
investigated.)
Fig.6.Average contribution to pollutants removal by sedimentation tank and constructed wetland bed ((a)biochemical oxygen demand (BOD),(b)total suspended solids (TSS),(c)ammonia-nitrogen (NH 3-N),and (d)total phosphorus (TP)).
no report of published studies and demonstrated cases for wet-lands constructed with alum sludge in China.Therefore,this study investigated use of dewatered alum sludge as a substrate in the treatment system to remove phosphorus.The average concentra-tion of TP in in?uent and the volume of domestic wastewater produced from a single rural family per day is assumed to be 5.0mg/l and 120l/d.The TP concentration in ef?uent is required to be <1.0mg/l according to China regulation.This standard requires 480mg phosphorus removal per day.The longevity of the 75kg alum sludge in this system could be at least 10years,which was calculated in batch tests as 31.9mg P/g by alum sludge (Babatunde et al.,2009).
Seasonal in?uence on constructed wetland performance can be particularly important in cold climates.Microbial activity is linked to temperature,with bacterial growth and metabolic rates reduced with decreasing temperature (Faulwetter et al.,2009).Low wastewater temperature is a special concern for nitri?ca-tion.Although aerobic bio?lm systems can maintain nitri?cation below 6?C (Choi et al.,2008),nitri?cation has commonly been observed to drop off rapidly below 6?C (Werker et al.,2002;Xie et al.,2003).In northern China,the lowest winter temperature often drops to ?8?C.An insulating layer,such as a surface layer of sawdust,is important to prevent freezing of the wetland bed and also to ensure cold temperatures do not inhibit nitri?cation.The insulation layer allows ef?uent temperature to remain above 6?C in winter.The observation that the average removal ef?-ciency in winter was not much less than the rest of the year may be attributed higher wastewater temperatures maintained by the insulating layer.The low temperature performance of this technol-ogy is therefore robust.
For cold-climate constructed wetland design,M?hlum et al.(1995)advocated a system consisting of an aerobic pretreatment step followed by constructed wetland units that perform nearly the same during winter and summer seasons.Expense and energy
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Table 2
Summary of hypothetical EPA rural community wastewater treatment technologies costs (1995US dollars,adapted from USEPA,1997)and the integrated household constructed wetland system costs.Technology
Total capital cost Annual operation and maintenance cost Total annual cost Centralized system
2,321,840–3,750,53029,740–40,260216,850–342,500Alternative small-diameter gravity sewers 598,100729055,500Collection and small on-site systems
510,00013,40054,500Integrated household constructed wetland system
34,965
700
3518
Assumptions :All technology options presented are assumed to have a 30-year life span.All of the options considered are capable of achieving the secondary treatment level.The rural community consists of 450people in 135
homes.
Fig.7.Sedimentation tank and ef?uent concentrations change with different in?uent loading concentrations ((a)biochemical oxygen demand (BOD),(b)total suspended solids (TSS),(c)ammonia-nitrogen (NH 3-N),and (d)total phosphorus (TP)).
requirements of this system,however,are not appropriate for Chi-nese rural householders with limited income.Phosphorus removal for the study technology was similar that achieved by M?hlum et al.(1995)using a ?lter medium with high phosphorus adsorp-tion.
Cost estimates on a national and/or international basis for wastewater treatment systems are dif?cult to develop,primarily due to varying conditions of each community such as popula-tion density,land costs,and local performance requirements.The USEPA developed cost estimates of centralized and decentralized approaches to wastewater management for a hypothetical 135-home rural community (USEPA,1997).The study revealed that decentralized systems such as onsite systems are generally more cost effective for managing wastewater in rural areas than conven-tional centralized wastewater treatment system.The integrated household constructed wetland system is even more cost effective (Table 2).Despite the fact that the IHCWs system is more suitable,there is still a $20.4(US)gap for a Chinese rural household to con-struct a integrated household constructed wetland system between the average annual payment levels of $5.66(calculated from Fig.5)and $26.1total annual cost (calculated from Table 2).The local gov-ernment would need to ?ll the gap.Choosing a “Most Appropriate
Technology”is not an easy task,but is necessary to avoid failure.The two key issues in managing a treatment technology are afford-ability and appropriateness (Grau,1996).Affordability relates to the economic conditions of the https://www.doczj.com/doc/de6348731.html,ernment support is important in developing countries to realize implementation of sanitary infrastructure,even when decentralized.Appropriate-ness relates to environmental and social conditions,which requires appreciation of local cultures,active participation,and correct maintenance training of local people.
5.Conclusion
1.Without public sewers and limited economic conditions,the integrated household constructed wetland system planted with willow effectively treated household domestic wastewater.The high overall removal ef?ciencies for BOD 5,TSS,NH 4-N,and TP were achieved for 96.0%,97.0%,88.4%and 87.8%,respectively.
2.The 0.4m insulating biomass layer maintained bed temperature above 6?C in the face of freezing temperatures common in north-ern China winters.There was no signi?cant loss of treatment during the winter as a result.
954S.Wu et al./Ecological Engineering37 (2011) 948–954
3.Dewatered alum sludge obtained from a drinking water plant
and incorporated into the wetland bed proved to effectively remove phosphorus.If widely used,this method would have the additional bene?t of reducing alum loading of land?lls.
4.The frame precast structure(magnesia cement and?ber glass
fabric)is strong and waterproof.It could be industrially produced and installed to standard speci?cations during con-struction.
5.The system is much more cost effective than others reported in
the peer-review literature,but there is still an affordability prob-lem.Support from the government will be needed to implement this infrastructure.
Acknowledgment
The authors are pleased to acknowledge the?nancial support provided by Agricultural Scienti?c and Technical Achievements Transform Project(Project No.21318008).
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H o u s e h o l d R e g i s t e r Under Supervision of the Ministry of Public Security of for Attention I. Residence Booklet has legal effect to prove a citizen’s identity status and mutual relations among family members, and is the main basis for residence registration authority to investigate and confirm his/her registered permanent residence. In so doing, the household owner or members of this household shall, of his/her own free will, show the booklet. II. The household owner shall well keep the booklet, and is prohibited to modify, transfer or lend it. If loss arises, such shall be immediately reported to the residence registration authority. III. The registration right of the booklet belongs to residence registration authority, and any other organization or individual shall not make any record on it. IV. If the members are increased or decreased, or registration items change in this household, registration shall be declared to residence registration authority by holding the booklet. V. When the whole household moves out of residence jurisdictional area, the residence booklet shall be returned to residence registration authority for cancellation. Basic Information of Household Register of Residence Change
表示日常生活用品 tea table 茶几 coffee table 咖啡台 smoking set 烟具 ashtray 烟灰缸 thermos bottle/vacuum bottle 热水瓶 door knob 门把手 safety door hook 安全门钩 corridor 走廊 elevator 升降电梯 escalator 滚梯 rocking chair 摇椅 hanging seat 吊椅 swivel armchair 旋转扶椅 footstool 凳子 chaise longue 躺椅 folding chair 折叠椅 wardrobe 衣柜 cloth rail 挂衣服的栏杆 hook 钩子 wall shelf 装在墙上放东西的架子 bracket 墙上突出之托架 magazine file 装杂志等的架子 shoe cabinet/storage 鞋柜 wall cabinet 壁橱 hook rack 挂钩架 TV bench 电视柜 bookcase 书架 braked castor 装在家具脚上方便推行的轮子（如：storage unit on castors） 10-drawer chest 十个抽屉的储存柜bathroom 浴室，厕所 flushing system 冲水系统 flush toilet 抽水马桶 flush pipe 冲水管 foul drainage system 排污水系统 drainage 排水道 ventilation shaft/pipe 通风管道 toilet seat 马桶坐圈 toilet lid 马桶盖 squatting pot 蹲式马桶 urinal 小便池
Household goods 家庭用品 cleaning product 洗涤用品 Domestic article 家庭用品 冰箱refrigerator 电饭锅automatic rice cooker 蒸锅steamer 烤箱oven 烧烤架grill 烤面包机toaster 打蛋器egg beater 刨冰机ice crusher 食品加工机food processor 洗衣袋laundry bag 洗衣桶pail 烫衣板ironing board 蒸汽电熨斗steam and dry iron 电熨斗electric iron 烘干机laundry drier 旋转式脱水机spin-drier 洗衣机washing machine 暖气片radiator 电扇electric fan 落地电扇stand fan 摇头电扇oscillating fan 床头灯bed light/bed lamp 日光灯fluorescent lamp 吊灯ceiling lamp/pendant lamp 台灯desk/table lamp 壁灯wall light 落地灯floor lamp 枝状吊灯chandelier 水表water gauge 插头plug 插座outlet/receptacle 木工carpenter 电工electrician 杂务工utility man 管道工plumber 油漆工painter 纸巾paper towel 围裙apron 餐具tableware 盘子plate 碟子dish 碗bowl 碗橱cupboard 餐桌dining table 食品柜larder 可以折叠边缘的桌子drop-leaf table 案板chopping board 装餐具的容器cutlery tray 晾干餐具的容器（类似铁丝筐）dish drainer 桌布table cloth 浆糊paste 胶水glue 胶条adhesive tape 包装纸packing paper 绳子string 吸尘器管子的托架vacuum hose holder 浇水壶，喷壶watering can 毛毯blanket 垫子cushion carpet 地毯（一般指大的整块的，铺房间的那种） rug 地毯（一般指小块的，放在沙发等边上的那种） 床架bed frame/bed base 床头板headboard 沙发床sofa bed 折叠床folding guest bed 架在空中的床（下面可放沙发、桌子等）loftbed frame 上下铺的床bunkbed frame 板条床slatted bed base 弹簧床sprung base 床上用品bedding 被子quilt 毛巾被cotton terry blanket 羽绒被feather quilt 棉被cotton quilt
Household wealth 家庭财富 The balance-sheet boom 资产负债表的繁荣 Household wealth, and debt, is forecast to swell in 2015 预计2015年家庭财富和债务将膨胀 Jan 3rd 2015 | From the print edition WITH the excesses of Christmas nearly over, Britons are planning their budgets for the new year. Their decisions will be crucial for the economy. After paying down debts to repair their balance-sheets in the years after the financial crisis, consumers are spending again. Yet wealth, like wages, remains lower than in 2007. A recovery in riches is an essential component of official forecasts for further growth. 随着圣诞节购物狂潮接近尾声，英国人开始进行新一年的规划预算。他们的决定对经济状况至关重要。金融危机之后几年，在偿还完资产负债表的债务后，消费者们又开始消费了。然而家庭财富和工资一样，仍然低于2007年。财富复苏是官方预测未来发展的一个必要因素。 When the financial crisis hit, wealth immediately suffered (unlike real wages, which hardly budged in 2008 but have fallen every year since). Household net worth—ie, assets minus debts—plummeted by 12% in 2008, driven by a 13% fall in housing wealth, which makes up just under half of all household assets. The hole is not yet filled: adjusting for inflation, housing wealth—￡168,000 ($261,000) per household—remains 13% below its pre-crisis peak. Financial wealth, which includes investments in stocks and shares, has fared slightly better, but is still down 4% on 2007. 当金融危机袭来时，财富首当其冲遭受损害（不像实际的工资，2008年勉强回升但从那以后逐年下降）。家庭净值，也就是资产减去债务，在2008年骤然下降了12%，这是受了约占家庭资产一半的房屋财富下降13%的影响。这个窟窿至今还没有被填上：通货膨胀调整、家庭财富(每户168，000英镑（261，000）美元)保持在比危机前峰值低13%的水平。包括股票投资在内的金融财富稍有起色，但仍比2007年低7%。 As a result, households reduced their debts from 2008. Savings jumped from around 7% of income pre-crisis to 11% by 2010. By 2013 the average household had ￡62,000 worth of debt, down 16% in real terms on 2007. Largely as a result of this frugality, household net worth, which averaged ￡320,000 in 2013, has recovered about half its losses from the crisis (see first chart).
Men and women employed in full-time jobs have to share evenly household chores and caring for children at home. Do you agree or disagree? Give reasons for your answer and include any relevant examples from your knowledge or experience. In modern society, male and female both have full-time jobs and whether they should share the household and care for children at home has been a debatable issue. In terms of the question whether it should be recommended, I will discuss such one in the following essay. To start with, sharing equally household and looking after children at home will ease the burden for women who employed in full-time jobs. Generally speaking, a woman who has a full-time job will clean room and cook for whole family after getting off work, while her husband is reading newspaper. But, once they share household and care for children, the women will not do anything just relax at home in a certain day when men should keep house clean and care for children in turns. In addition, ladies employed full- time job will have more time. When male is cleaning home and looking after children, female no longer need to get home as quick as possible, since their husbands will prepare dinner for family. Ladies have spare time to chat with friends and have dinner with colleagues. Finally, gentlemen with full-time jobs will benefit from doing household and caring for kids. Obviously, without help with female, men could not find their shirts easily. They also eat fast food rather than delicious food from their wives. However, by dong household for a period time they can manage family lightly like find clothes and make meals. Meanwhile, men may promote emotion with children via caring for them. In this time, husbands can play games with children to keep a close relationship. To sump, based on the above discussion, I am agreeing the idea of men and women should share equally household and caring for children. Band 5.5 I’d like to say that you have done a very good job in organizing
3.2 正交变换 为了给出求解最小二乘问题的更实用的算法，这一节我们来介绍两个最基本的初等正交变换，它们是数值线性代数中许多算法的基础。 3.2.1 Householder变换 使用Gauss变换将一个矩阵约化为上三角形式是基于一个简单的事实：对于任一个给定的向量，可构造一个初等下三角阵，使，这里是的第一列，. 这一节我们来讨论如何求一个初等正交矩阵，使其具有矩阵的 功能。这样，对一个矩阵的上三角化任务，便可以由一系列的初等正交变换来完成。 定义3.2.1设满足，定义为 ， (3.2.1)则称为Householder变换。 Householder变换也叫做初等反射矩阵或镜像变换，它是著名的数值分析专家Householder在1958年为讨论矩阵特征值问题而提出来的。下面的定理给出了Householder变换的一些简单而又十分重要的性质。 定理3.2.1设是由(3.2.1)定义的Householder变换，那么满足： 对称性：； 正交性：； 对合性：； 反射性：对任意的，如下图所示，是关于的垂直超平面的镜像反射。
证明（1）显然。（2）和（3）可由（1）导出。事实上，我们有 (4)设，则可表示为 其中利用和可得 这就说明了为关于的镜像反射。 Householder变换除了具有定理3.2.1所述的良好性质外，它的主要用途在于，它能如Gauss变换一样，可能通过适当选取单位向量，把一个给定向量的若干个指定的分量变为零。 引理1 设为两个不相等的向量，且，则存在一个Householder变换满足
证明令，构造Householder变换阵 由于，因此 ， 从而 引理证毕定理3.2.2 设，则可构造单位向量，使由(3.2.1)定义的Householder变换满足 ， 其中 证明由于 故欲使，则应为
Household Register Under Supervision of the Ministry of Public Security of for Attention I. Residence Booklet has legal effect to prove a citizen’s identity status and mutual relations among family members, and is the main basis for residence registration authority to investigate and confirm his/her registered permanent residence. In so doing, the household owner or members of this household shall, of his/her own free will, show the booklet. II. The household owner shall well keep the booklet, and is prohibited to modify, transfer or lend it. If loss arises, such shall be immediately reported to the residence registration authority. III. The registration right of the booklet belongs to residence registration authority, and any other organization or individual shall not make any record on it. IV. If the members are increased or decreased, or registration items change in this household, registration shall be declared to residence registration authority by holding the booklet. V. When the whole household moves out of residence jurisdictional area, the residence booklet shall be returned to residence registration authority for cancellation. Basic Information of Household
CISPR14 Electromagnetic compatibility- requirements for household appliances,electric tools and similar apparatus
Overview CISPR14Introduction Main Tests involved Test System
Introduction CISPR14-1 Emission Latest edition:5.0released2005 Applies to the conduction and radiation of radio-frequency(RF) disturbances from appliances whose main functions are performed by motors and switching or regulatory devices,unless the RF energy is intentionally generated or intended for illumination Covers such equipment as household electrical appliances, electric tools,regulating controls employing semiconductor devices, motor-driven electro-medical apparatus,electric toys,automatic dispensing machines and cinema or slide projectors. Frequency range covered are from9KHz to400GHz
Module one Unit 3 Household appliances 目标导学 知识详解 【课文情景描述】 汉语描述 家用电器 英语描述 Household appliances 【课文内容全译】 教材原文 Do you know how to use it, Li Hui? -- Sure. It’s a piece of cake. What’s the use of this button? It’s for playing videos, VCDs or DVDs. What’s that button for? That’s for selecting channels larger than 10. How’s it different from an ordinary TV? This picture and sound are far better on digital TV set than on an ordinary one.
Would you like to watch anything? Yes, I’d love to. What a big TV it is! How nice it is! 汉语翻译 李辉，你知道怎么使用它吗？ 当然，小菜一碟。 这个按钮有什么用？ 这个用来放收音机、VCD和DVD。 这个按钮用来干什么？ 那是用来选择大于10 的频道。 这个和普通电视机有什么区别？ 数码电视机的图像和声音远比普通电视机的好。 你喜欢用这个看什么吗？ 是的，我喜欢。 这个电视好大啊！ 这个真好！ 【课文词汇全解】 1. household a. 家庭的；家用的 household expenses 家用开支 household chores 家里的杂活 household appliances 家用电器household n. 家庭，一家人，家务 例句： He loved being part of a huge household. 他喜欢成为大家庭的一员。 2. digital a. 数字的，数码的 digital TV 数码电视机 digital camera 数码照相机 digital recording 数字录音 例句： Most of the computers we are using are digital computers. 我们正在使用的计算机大多数是数字计算机。 3. machine n. 机器；机械（装置） washing machine 洗衣机 sewing machine 缝纫机 slot machine（投币）自动售货机 例句： My mother-in-law has a sewing machine. 我婆婆有一台缝纫机。 4. cleaner n. 清洁器；清洁工人 do a clean job 干得很出色 make a clean sweep of 彻底改变 clean v. 清洁，打扫
雅思写作生活类话题范文：Household goods Question In many countries, more and more people buy a wide range of household goods like television microwave oven and rice cooker. Do you think this is a positive or negative development? Sample answer With the proliferation of high-tech products in every walk of life, an overwhelming majority of families have possessed more than one piece of electrical device. Whether it does more good than harm to the society is what this essay focuses on. Admittedly, a growing proportion of families nowadays have been accustomed to living with these amazingly versatile appliances. On one hand, thanks to the sophisticated design, doing domestic chores ceases to be a bother. For instance, a vacuum cleaner can help make even the carpeted floor dustless and a micro-wave oven make cooking a manageable and enjoyable process. Desirably, the present device can be so service-oriented that a rice cooker can automatically start to work as long as its owner presses a button on a remote control or set the schedule in advance. Thus the time and energy saved allows people to work and rest better. On the other hand, some appliances such as television set and stereo system benefit the families in quite a different way. It has been a routine for many families to gather around a TV after dinner watching their favored programs, which can be entertaining and informative in most occasions and educational in some. Nevertheless, it can be a potential threat to the health of family members as well as the environment as a whole. Firstly, the convenience brought about by the appliances also deprives them of the possibilities to consume a regular amount of calories at home, which, in a long run, is likely to undermine their health since many of them have sat through a day in the workplace. Another detrimental effect is the notorious radiation and it has been reported that when some electrical device are placed in a limited close space, the radiation they give off is not added but multiplied and this can trigger cancer, hurt one' s eyesight and particularly damage the pregnant. Pitifully, a large proportion of the electricity is not made good use of since the poor design and some people just use them lavishly.