Ecological Engineering 37 (2011) 948–954
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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
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Performance of integrated houhold constructed wetland for domestic wastewater treatment in rural areas
Shubiao Wu a ,David Austin b ,Lin Liu a ,Renjie Dong c ,∗
a
洛杉矶教师罢工
Key Laboratory of Agricultural Engineering in Structure and Environment of Ministry of Agricultural,College of Water Conrvancy &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 revid form 24January 2011Accepted 15February 2011Available online 2 April 2011Keywords:
Constructed wetland Rural areas
Houhold 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 purification systems is bad on the key issues of affordability and appropriateness in Chine rural areas.This paper describes an integrated houhold constructed wetland (IHCW)system planted with willow (Salix babylonica )to treat houhold 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 t of specifications.The IHCW has achieved high overall removal efficiencies 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 significant 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 u in developing countries.
© 2011 Elvier B.V. All rights rerved.
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1.Introduction
Domestic wastewater treatment in rural areas is esntial to prevent pollution of aquatic environments,which has been of increasing concern for both rearchers and government officials (Ichinari et al.,2008).The 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 rvices 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 Chine 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.
秋冬服装搭配Houholds in rural areas that do not have public wers must depend on on-site treatment systems to manage their wastewater.Many on-site wastewater treatment technologies,such as ptic
∗Corresponding author.
E-mail address: (R.Dong).
tanks,drain-field 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 the requirements.High total suspended solids (TSS),biochemical oxygen demand (BOD),total fecal coliforms,total nitrogen (TN),and total phosphorus (TP)make ptic tank effluent unsuitable discharge to water bodies (Carroll et al.,2006).Traditional leach-field 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 tables.Lagoons tend to be unpleasant from an aes-thetic perspective and becau
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 efficiency,as well as low cost and simple operation (Brix and Arias,2005;Siracusa and La Rosa,2006),but can be limited by asonal 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/$–e front matter © 2011 Elvier B.V. All rights rerved.doi:10.leng.2011.02.002
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Fig.1.Schematic diagram of the integrated houhold constructed wetland system (the doted red line shows the waterflow path).(For interpretation of the references to color in thisfigure 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 esntial to conduct rearch into an alternative disposal system bad 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 Houhold Constructed Wetland,IHCW)for rural houhold wastewater treatment.The system consists of a two-stage dimentation tank and a vertical-flow,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 t
o run normally in freezing temperatures.This concept appears to offer advantages for houhold wastewater treatment in develop-ing countries,where really low-cost,convenient construction and operational simplicity are esntial.statement是什么意思
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-flow model to avoid damage from low temperatures in winter (Fig.1).The system consisted of a two-stage dimentation tank and a verticalflow constructed wetland bed ction.The frame structure was precast with magnesia cement andfiber 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 di-mentation tank consists of two gments with equal empty-bed volume for each gment of0.5m3.The empty volume of the wet-land bed ction 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 andfish scales from the kitchen)fromflow-ing into the tank.Wastewaterflows into thefirst gment from the inlet basin and then into the cond gment via afloating valve installed in thefirst gment to allow intermittent system feeding.In order to maintain normal operation during the winter period,0.4m of sawdust insult
开阔眼界英文
s the bed.Wastewaterflows from the dimentation 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 effluentflows into the bottom gravel layer and then through the dewatered alum sludge placed in the outlet,andfinallyflows 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 modified 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 coefficient of3.8.Seventyfive 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 verticalflow wetland bed ction.The willow was lected as the wetland plant for veral reasons.In China people would prefer a tree in their backyard rather than wetland plants. The experience of some constructed wetla
nd systems with willows in Demark has successfully provided a showca of good perfor-mance in nutrients and heavy metals removal(Haslgren,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 eded in November2007. Sampling evens occurred from March2008to February2009.Dur-ing the experiment operation,houhold wastewater influent was comprid of kitchen and laundry effluents.The hydraulic loading rate was about0.12m d−1.Water samples of approximately200ml were collected from the influent,dimentation tank(cond g-ment),and effluent(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(al 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 analy
zed 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 nsor(Pt1000,Yonghua, China)installed in the middle depth of the bed(Fig.1).
风格英文Face-to-face questionnaires were conducted among158home-respondents to evaluate farmers’willingness to pay for treatment and the potential application of the integrated houhold con-structed wetland in rural villages.
3.Results
The wastewater ud for experiment was generated in a single houhold,excluding toilet wastewater.Average concentrations
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Fig.2.Concentrations of influent,dimentation tank and effluent in integrated houhold 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
万圣节英语怎么说Construction cost of one integrated houhold 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 influent were 302.4mg/l,128.6mg/l,30.7mg/l and 5.0mg/l,respectively,and the aver-age concentrations in effluent were all continuously reduced to 11.8mg/l,3.8mg/l,3.5mg/l and 0.6mg/l,respectively (Fig.2).
Average removal efficiencies 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 decrea of average removal efficiency for BOD 5,TSS,and NH 4-N duri
ng winter (1.3%,1.1%and 5.4%,respectively);while an increa 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 decread to −8◦C during winter (Fig.4).
The total construction cost of the integrated houhold con-structed wetland system was 259US dollars,including precast frame structure,gravel and sand,and installation (Table 1).Of the houholders polled on cost issues,23%respondents were reluctant to pay any money for wastewater treatment facilities construction,
32%took a “wait and e”position,and 45%were willing to pay (Fig.5a).The percentage of houholder’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).The attitudes may be cloly 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 tho obrved with constr
ucted wetlands (Haberl et al.,1995;Lakatos et al.,1997).Pretreatment in the dimentation tank also plays an important role by removing 32%of BOD 5and 46%of TSS (Fig.6).This treatment performance was similar to that obrved for primary ttling (Metcalf and Eddy,2003).
Anaerobic degradation in the dimentation tank may have also played an important role in treatment.Domestic wastewater from a single rural family traditionally comes from kitchen and laun-dry effluent.It is highly biodegradable (Elmitwalli and Otterpohl,2007).The dimentation tank had dissolved oxygen (DO)concen-trations <0.8mg/l,which was esntially an anaerobic condition with little temperature variation.Sedimentation tank removal of NH 4-N and TP was just 15%and 17%.As expected,nitrification was limited by low dissolved oxygen concentration in the dimenta-tion tank (Beccari et al.,1992;Paredes et al.,2007).The rate of TP removal was consistent with a dimentation process (Metcalf and Eddy,2003).The dimentation tank clearly fulfils primary treatment buffering of BOD 5and TSS to the treatment system by moderating high influent concentrations (Fig.7).The clear bene-fit of the dimentation tank ction lies not only in concentration reduction of BOD 5and TSS,but also to avoid or relieve clogging
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Fig.3.Pollutants removal efficiencies in integrated houhold constructed wetland system ((a)bioche
mical oxygen demand (BOD),(b)total suspended solids (TSS),(c)ammonia-nitrogen (NH 3-N),and (d)total phosphorus
gendarme
(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 efficiency 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 ttlement,plants uptake,and bacteria adsorption and substrate affinity (Greenway and Woolley,1999;Vymazal,2007;Kadlec and Wallace,2008),but compared to adsorption to substrate other mechanisms of phos-phorus removal are not significant 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 ud (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 dispod as landfill.At prent,there is
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Fig.5.Willingness to pay (a)and payment level (b)for the houholders to treat their domestic wastewater in rural areas.(158respondents were
investigated.)
Fig.6.Average contribution to pollutants removal by dimentation 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 cas for wet-lands constructed with alum sludge in China.Therefore,this study investigated u of dewatered alum sludge as a substrate in the treatment system to remove phosphorus.The average concentra-tion of TP in influent 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 effluent 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 influence 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 nitrifica-tion.Although aerobic biofilm systems can maintain nitrification below 6◦C (Choi et al.,2008),nitrification has commonly been obrved to drop off rapidly below 6◦C (Werker et al.,20
02;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 nitrification.The insulation layer allows effluent temperature to remain above 6◦C in winter.The obrvation that the average removal effi-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,Mæhlum 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 asons.Expen and energy
