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The Need for Wastewater

Treatment in Latin America:A Case Study of the Use of Wastewater

Stabilization Ponds in Honduras

CONTRIBUTING WRITER WITH PHOTOS BY

Stewart M. Oakley, Ph.D.,Department of Civil Engineering, California State UniversityA b s t r a c t

This paper discusses the issue of wastewater treatment in developing

countries, especially in Latin America, and presents a detailed case study of

the use of stabilization pond systems in Honduras. Ten pond systems in

Honduras were monitored during dry and wet seasons to develop a database

for performance, improving designs, and developing more appropriate

effluent standards based on local conditions. The pond systems were

monitored for flow rates, helminth eggs, S h i g e l l a species, E s c h e r i c h i a c o l i ,fecal coliforms, and conventional parameters, including BOD5 and

suspended solids (SS). Pond sludges were also monitored for helminth eggs,

and percent total solids, volatile solids, and fixed solids. Results show that

the majority of ponds have higher flow rates (with lower hydraulic

retention times) and much higher organic loading rates than those assumed

by designers. Nevertheless, all of the systems monitored removed 100percent of the influent helminth egg concentrations and satisfy the World

Health Organization microbiological guidelines for Category B irrigation

with wastewater effluents. S h i g e l l a species were not detected, andE s c h e r i c h i a c o l i and fecal coliform removal were highly variable. Theremoval of BOD5 and SS was typical for stabilization pond systems, andorganically overloaded ponds did not exhibit significant difference fromunderloaded ones. Sludge analyses showed that all pond sludges areheavily contaminated with helminth eggs and that several ponds are in

need of desludging. Planning for system expansion, and adequately

financing operation and maintenance, including pond desludging, are

major issues within municipalities for long-term sustainability. The

study concludes that at this time treatment objectives in municipalities

should focus on helminth removal, with the objective of using pond

effluents for agricultural and aquaculture reuse to enhance long-term

sustainability of pond systems

Authors Note: The perspective presented in this paper is far removed fromthe technical and regulatory context of wastewater treatment as practiced in

the U.S. The papers purpose is to present to the readers of the Small FlowsQuarterly the problem of excreta-related infections in developing countries

and the goal of effective wastewater treatment as a public health imperativeusing a natural system technology in a way distinct from the U.S. experience.

A common scene in Latin America: rawsewage flowing down a street in an urbandevelopment near Tegucigalpa, Honduras.


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Wastewater Treatment WorldwideTABLE 1 Wastewater Treatment Worldwide

There are approximately 4 bil-lion cases of diarrhea each year,causing 2.2 million deaths,mostly among children, fromdiseases associated with lack ofsafe drinking water, inadequatesanitation, and poor hygiene.

Intestinal worms (helminths) in-fect at least 10 percent of thepopulation of the developingworld (WHO/UNICEF, 2000),and likely infect up to 24 per-cent of the world's population(Chan, 1997).

Protozoan infections probablyexhibit a similar prevalence tohelminths, and E n t a m o e b a h i s -t o l y t i c a infection is one of the 10most common infections in theworld (Savioli, L. et al . , 1992).

Lack of wastewater treatment is ahealth hazard in all developingcountries. With the exception ofthe U.S., Canada, and some Euro-pean countries, the median per-centage of urban wastewater treat-ed worldwide is very low as seenin T a b l e 1 . The discharge of untreatedwastewater is especially a healthhazard where receiving watersare used for drinking watersources, bathing, washing, irri-gation, and fisheries.

Conventional wastewater treat-ment methods as practiced in theU.S. and Europe are not afford-able in developing countries(which is the main reason whythey don't exist), nor do they nec-essarily provide the requisite de-gree of pathogen removal for theprotection of public health, espe-cially parasitic infections.

As a result of the above situa-tion, the professional communityconcerned with sanitation and

public health in developing coun-

countries in the Western Hemi-sphere with typically high preva-lence rates of excreta-relatedinfections.W a s t e w a t e r T r e a t m e n tI s s u e s O u t s i d e t h e U . S .G l o b a l S t a t u s o f E x c r e t a - R e l a t e dI n f e c t i o n s a n d W a s t e w a t e rT r e a t m e n tThe provision of drinking watersupply, sewerage, and wastewatertreatment for communitiesthroughout the world has been amajor component of developmentprojects financed over the last 20years. This effort started with theInternational Drinking Water Sup-ply and Sanitation Decade move-ment (1981 to 1990), which wasspearheaded by the World Bank(Cairncross and Feachem, 1993).

During the 1990s, the WHO andthe United Nations ChildrensFund (UNICEF) formed the JointMonitoring Program for WaterSupply and Sanitation, whoseoverall aim was to improve plan-ning and management withincountries by support in monitor-ing the water supply and sanita-tion sector (WHO/UNICEF, 2000).The WHO/UNICEF Joint Monitor-ing Program has presented fourassessment reports (1991, 1993,1996, and 2000). The findings ofthe latest report (WHO/UNICEF,2000) can be summarized, in part,as follows with additional infor-mation cited from other sources:

Worldwide approximately 1.1billion people lack access to im-proved water sources.

Approximately 2.4 billion peo-ple have no access to any formof improved sanitation.

Excreted-related infections are amajor cause of morbidity and

mortality worldwide.

While there is much intereston natural systems for wastewatertreatment (WEF, 2001) or decentral-ized wastewater management sys-tems (Crites and Tchobanoglous,1998), and while lagoon or wastestabilization pond systems are sub-sumed within these categories, it isclear that in the U.S., pond systemshave long fallen out of favor as atreatment option for municipalities.This is principally a result of increas-ingly stringent discharge require-ments (Metcalf and Eddy, 2003). Al-though the U.S. Environmental Pro-tection Agency (EPA) has recentlypublished revised editions of itsconstructed wetlands and onsitewastewater design manuals (EPA,2000 and 2003), it is doubtful thatthe waste stabilization pond designmanual published over 20 years ago

(EPA, 1983) will ever be revised.Outside the U.S. it is a quite

different story. Waste stabilizationpond systems have long been pro-moted in developing countries asthe only viable option to helpsolve the devastating problem ofexcreta-related disease transmis-sion at an affordable cost (Cairn-cross and Feachem, 1992; CEPIS/OPS, 2000; Egocheaga andMoscoso, 2004; Feachem, et al.,1983; Len and Moscoso, 1996;

Mara, 2004; Rolim, 2000; Shuvaland Fattal, 2003; and Shuval, etal. , 1986). Pond systems in devel-oping countries are typically de-signed for pathogen removal andagricultural reuse using epidemio-logically-based guidelines, such asthe World Health Organizations(WHO) microbiological guidelinesfor wastewater use in agricultureand aquaculture (WHO, 1989). Thisapproach for wastewater treatmentis distinct from that taken historical-

ly in the U.S. and Europe and is es-pecially distinct from the currentfocus of U.S. regulation at the stateand federal level.

The purpose of this paper is todiscuss the issue of wastewater treat-ment from the perspective of devel-oping countries in Latin Americaand to present a detailed case study,including extensive monitoring re-sults, of stabilization pond use inHondurasone of the poorest


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tries has long conclud-ed that the principalobjective of wastewatertreatment in areaswhere excreta-relatedinfections are endemicshould be the removalof pathogens using low-cost appropriate tech-nologies, and that gen-

erally the most appropri-ate technology is a wastestabilization pond sys-tem (Cairncross andFeachem, 1992;CEPIS/OPS, 2000;Egocheaga andMoscoso, 2004;Feachem, et al., 1983;Len and Moscoso,1996;Mara, 2004; Rolim,2000; Shuval and Fat-tal, 2003; Shuval, et al.,

1986; and WHO/UNICEF, 2000). Thepathogen removal efficiencies ofvarious treatment processes as gen-erally cited in the literature areshown in T a b l e 2 .This focus on pathogen removalwith stabilization pond systems isdistinct from the historical objectivesof wastewater treatment in devel-oped countries and is especially farremoved from current focus onmore stringent effluent regulations

with the use of increasingly morecostly and complicated technolo-gies in the U.S. Nevertheless, thesheer magnitude of the problem ofpublic health and wastewatertreatment in developing countriesnecessitates a different approach(Figure 1 graphically shows the

Removal of Pathogens and Conventional Parameters in Various Treatment ProcessesTABLE 2

FIGURE 1 Per Capita Gross National Product for the United States, Mexico, and Central America in US Dollars - Year 2000

GrossNationalProductPerCapitaUSDollars

gap in per capita gross nationalproduct among the U.S. and vari-ous countries of Latin America,which underscores the need forlow-cost solutions not used in theU.S.). In fact, the focus on stabi-lization ponds for developingcountries is within the same spiritof the interest in natural systemsfor wastewater treatment in theU.S., with emphasis on naturalenvironmental components toprovide the desired treatment,and the benefits of fewer opera-tional personnel, less energy con-sumption, and less sludge produc-tion than conventional mechani-cal systems (WEF, 2001). In thiscontext, it is worthwhile to quotefrom the classic text, Sanitation andDisease, published over twenty

years ago and still relevant todayfor the problem of wastewater treat-ment in developing countries:

T h o s e w h o s e j o b i s t o s e l e c t a n dd e s i g n a p p r o p r i a t e s y s t e m s f o r t h e c o l l e c t i o n a n d t r e a t m e n t o fs e w a g e i n d e v e l o p i n g c o u n t r i e sm u s t b e a r i n m i n d t h a t E u r o p e a na n d N o r t h A m e r i c a n p r a c t i c e s d on o t r e p r e s e n t t h e z e n i t h o f s c i e n -t i f i c a c h i e v e m e n t , n o r a r e t h e y t h ep r o d u c t o f a l o g i c a l a n d r a t i o n a ld e s i g n p r o c e s s . R a t h e r , t r e a t m e n tp r a c t i c e s i n t h e d e v e l o p e d c o u n -t r i e s a r e t h e p r o d u c t o f h i s t o r y , ah i s t o r y t h a t s t a r t e d a b o u t 1 0 0y e a r s a g o . . . . C o n v e n t i o n a ls e w a g e w o r k s w e r e o r i g i n a l l y d e -v e l o p e d i n o r d e r t o p r e v e n t g r o s so r g a n i c p o l l u t i o n i n E u r o p e a n a n dN o r t h A m e r i c a n r i v e r s ; t h e y w e r e


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n e v e r i n t e n d e d t o a c h i e v e h i g h r e m o v a l o f e x c r e t e d p a t h o g e n s .T h e i r u s e i n t r o p i c a l c o u n t r i e s i nw h i c h e x c r e t e d i n f e c t i o n s a r e e n -d e m i c i s o n l y j u s t i f i a b l e i n s p e c i a lc i r c u m s t a n c e s , f o r t h e r e i s a n a l -t e r n a t i v e t r e a t m e n t p r o c e s s m u c hs u p e r i o r i n o b t a i n i n g l o w s u r v i v a l so f e x c r e t e d p a t h o g e n s t h e w a s t es t a b i l i z a t i o n p o n d s y s t e m . (Feachem, et al., 1983, pp. 6364)T h e S i t u a t i o n i n L a t i nA m e r i c aIt is estimated that the urban

population of Latin America, with

approximately 340,000,000 per-sons connected to sewers, gener-ates 52,000,000 m3/day of waste-water (Egocheaga and Moscoso,2004; WHO/UNICEF, 2000). It isfurther estimated that only3,100,000 m3/day of this waste-water, or 6 percent of what is gen-erated, receives secondary treat-ment before being discharged intosurface waters or reused directly inagriculture or aquaculture(Egocheaga and Moscoso, 2004).

Of all the capital cities from Mexi-co City to Buenos Aires, the vastmajority do not treat their waste-waters, to say nothing of the thou-sands of smaller cities throughoutthe region. Surface watersrivers,streams, lakes and coastal areasare widely contaminated with rawwastewater discharges throughoutLatin America.

The problem of wastewatertreatment is exacerbated by severeshortages in water quantity for

agriculture. Throughout LatinAmerica, there has been an histor-

ical tendency to use either raw ordiluted wastewaters for irrigationand aquaculture, and it is estimat-ed that at least one millionhectares are irrigated with thesecontaminated sources (Egocheagaand Moscoso, 2004). The effects onpublic health of excreta-related in-fections have been devastatingand have even had deleterious ef-fects on disease morbidity withinthe U.S. The following examplesare typical and illustrate how the

magnitude of the problem is notonly local, but also affects popula-tions throughout the hemisphere:

The cholera epidemic, whichbegan in Peru in 1991, produced1,199,804 cases with 11,875deaths between 19911997 in 20countries including the U.S.; it isestimated that the epidemic costthe country of Peru one billionU.S. dollars in tourism and expor-tation of agricultural products inonly 10 weeks (OPS, 1998). Theepidemic was caused by the con-

sumption of drinking water andfood products contaminated withraw sewage. Cholera, which hadnot been present in the WesternHemisphere for over 100 years, isnow endemic in various countriesin Latin America.

Five outbreaks of cyclosporiasisfrom 1995 to 2000 in the U.S.and Canada caused by theemerging protozoan pathogen,C y c l o s p o r a c a y e t a n e n s i s , have beenlinked to raspberries imported

from Guatemala (Bern, et al . ,1999; Ho et al., 2002). It is as-

sumed that the raspberries wereirrigated or washed with eitherraw sewage or sewage-contami-nated water. The principal routeof transmission of C y c l o s p o r a in-fections in Guatemala is thewater-borne route (Bern, et al.,1999).

The largest epidemic of hepati-tis A in the history of the U.S.occurred in 2003, with morethan 700 cases in 4 states, alllinked to green onions import-

ed from two farms in Mexico(Fiore, 2004). It is assumed theonions were contaminated withthe virus through irrigation orwashing with either raw sewageor sewage-contaminated water(Fiore, 2004).

Surface waters obviously play asignificant role in the continuedtransmission of excreta-related in-fections, since they are commonlyused for bathing, washing, drink-ing water supply, crop irrigation,and the consumption of fish andshellfish. Professional judgmentregarding the principal objectiveof wastewater treatment in the re-gion dictates the removal of fecalpathogens as the first priority ofwastewater treatment. This con-clusion has been reached manytimes, and most recently by anexhaustive study of wastewaterpollution, treatment, and reusethroughout Latin America pub-lished by the Pan American Cen-

Raw sewage contaminates the streets of Latin America.This photo was taken in the town of Danl, Honduras.


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ter for Sanitary Engineer-ing and EnvironmentalScience (Egocheaga andMoscoso, 2004). Thestudy concludes that theproper management ofdomestic wastewater inLatin America shouldfocus on public health asa first priority, with the

removal of pathogens asthe principal objective ofwastewater treatment.The study also concludesthat in order to resolvethe problem of agricul-tural demand for waterand the sustainability ofwastewater treatment inimpoverished cities,treatment of wastewaterfocusing on pathogen re-moval should be inte-

grated with the produc-tive reuse of the treatedwastewater (Egocheagaand Moscoso, 2004;CEPIS/OPS, 2000). Thestudy concludes that thebest available technologyfor accomplishing thisgoal is wastewater stabi-lization pond systems,which can most easilymeet the WHO guide-lines for wastewater reuse in agri-

culture than any other technology.The WHO guidelines are shown inT a b l e 3 .C a s e S t u d y o f H o n d u r a sB a c k g r o u n dThe provision of water supplyand sewerage services for Hondurashas been a major component of de-velopment projects financed overthe last 15 years. Approximately 81percent of the estimated total popu-lation of 6.7 million has access todrinking water, and 70 percent has

access to sanitation services (OPS,2002). In spite of these efforts inthe public health sector, however,excreta-related infections are still amajor cause of morbidity and mor-tality. The cholera epidemic, withover 15,378 cumulative cases dur-ing 1991 to 2000, and the contin-ued high morbidity of intestinalprotozoan and helminth infec-tions as shown in T a b l e 4 , under-score the persistent public healthproblems (Girard de Kaminsky,

age projects within Hondurasnow require wastewater treatment

as a necessary component.It has been generally assumed

by the professional community inHonduras that waste stabilizationponds are the treatment option ofchoice because of their effective-ness in pathogen removal andtheir low operation and mainte-nance costs (Oakley, et al., 2000).

TABLE 4 Prevalence of Excreta-Related Parasites in Honduras

World Health Organization Recommended Microbiological Guidelines for Wastewater Use in AgriTABLE 3

1996; OPS, 1998, 2002). Surfacewaters play a significant role inthe continued transmission ofexcreta-related infections, sincethe vast majority are pollutedwith wastewater discharges andare commonly used for bathing,washing crop irrigation, and fishand shellfish harvesting. In an at-tempt to ameliorate the problem,all internationally financed sewer-


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signed in series (Mara, 2004),which is an added capital andoperational expense that shouldbe technically justifiable in poorcommunities. Because no localdata have been available show-ing specific pathogen removal inpond systems, there has beenmuch confusion among profes-sionals and the public in Hon-duras as to what type of designis most appropriate for localconditions.

Approximately 21 waste stabiliza-tion pond systems have been con-structed in the last 10 years. The ma-jority of the pond systems werefunded by USAID-Honduras throughits Municipal Development Project.This program, which has as its pri-mary goal the institutionalization ofmore responsive and effective mu-nicipal government, works with 34municipalities representing 50 per-cent of the Honduran population.F i g u r e 2 shows a typical design of apond system, which consists of twofacultative ponds in parallel (soone can be taken out of service fordesludging), followed by one ortwo maturation ponds in series.I s s u e s W i t h E f f l u e n t G u i d e l i n e s

The environmental protectionagency for the government of Hon-duras has promulgated effluent stan-

FIGURE 2 Typical Pond System Design

A typical pond system design, with a bar screen and horizontal gritchamber for pre-treatment, with a battery of two facultative ponds inparallel followed by two maturation ponds in series. Facultative pondsare designed in parallel so one can be taken out of service fordesludging every 5 to 10 years.

Faculative

Pond

Faculative

Pond

Final

Effluent

Pretreatment

Influent

Maturation Ponds in Series

with Baffles for Plug Flow

TABLE 5Effluent Standards Promulgated in Honduras

Manually cleaned horizontal grit chambersa technology no longer inuse in the U.S.are used for pretreatment because of high grit loadsin sewer systems that can prematurely fill ponds. (Len, Nicaragua)

dards for municipal wastewater dis-charges that are shown in T a b l e 5 .The standards, which are arbitrary,focus on fecal coliforms and do notaddress specific pathogen removal,which is much more importantwhere excreta-related infections areendemic (Feachem, et al., 1983;Mara, 2004). It is difficult to meetfecal coliform standards more strin-gent than 10,000/100mL with stabi-lization ponds (Oakley, et al., 2000)unless four or five ponds are de-

Maximum Permissible

Concentration


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I s s u e s W i t h O p e r a t i o n a n dM a i n t e n a n c e a n d S u s t a i n a b i l i t yThe responsibility for operationand maintenance of pond systemslies with the municipalities. In anattempt to avoid the problem ofabandoned systems that has fre-quently occurred in other countries,USAID-Honduras has sponsored nu-merous workshops on waste stabi-

lization pond design, monitoring,and operation and maintenance forprofessionals, operators, and thegeneral public. This is a continuingprocess that requires a long-termcommitment. There are many insti-tutional factors that cannot bechanged easily, such as the abilityand political resolve of the munici-pal governments to charge fees forsewerage and wastewater treatment,and to maintain adequately trainedpersonnel on staff. As an example of

the difficulties involved in whatwould appear to be a simple task, atpresent, there is not one pond in-stallation in Honduras where anoperator measures flow rates atalllet alone on a routine anddocumented basis.O b j e c t i v e sAs a result of the problems men-tioned above, USAID-Honduras de-cided to fund a monitoring studyfor wastewater stabilization pond in-stallations. The objective of this

study was to monitor 10 wastewaterstabilization pond systems from dif-ferent climates throughout Hon-duras during the dry season (March,April, May) and wet seaon (Septem-ber, October, November) to developa local database for improving de-sign parameters and operation andmaintenance requirements and toassess the long-term sustainability ofsystems in the municipalities. It wasalso planned that this study wouldhelp contribute to the development

of effluent standards for specificpathogen removal rather than fecalcoliform removal, and that con-crete recommendations based onthe results could be made for theminimum number of ponds thatshould be designed in series to re-move specific pathogens, with thegoal that the final effluent could beused for agriculture or aquacultureto help foster sustainability. It washoped that the conclusions wouldmore adequately address the serious

public health issues facing financial-ly-strapped municipalities with pop-

ulations from 1,000 to over 100,000persons.M e t h o d o l o g yP r o j e c t D e s i g nTen pond systems were selectedat varying locations throughoutthe country. Eight systems werefacultative-maturation pond con-figurations, one an anaerobic-facul-tative pond configuration, and onean anaerobic-facultative-maturationpond configuration. All systemswere visited for five consecutive

days during the dry and wet sea-sons. Two days were used for thecollection of support information,which included age of the system,original design population, physicalcondition, estimation of accumulat-ed sludge volume using bathymetricmethods, level of operation andmaintenance, and an evaluation ofthe long-term sustainability basedon municipal support. Each systemwas then monitored diurnally forthree consecutive days.

The influent flow rate was con-tinuously monitored using an ISCOarea-velocity flow meter, which al-lowed an accurate measurement ofpeak, minimum and mean flowrates. The influent and effluent ofeach pond within the system weresampled for helminth eggs, S h i g e l l aspecies, E s c h e r i c h i a c o l i , fecal col-iforms, suspended solids (SS), five-day biochemical oxygen demand(BOD5), pH, and temperature; dis-solved oxygen was also measured

at various points within faculta-tive ponds. Sludge samples at the

entrance to each primary pondsystem, whether anaerobic or fac-ultative, were taken with a dredgeand analyzed for helminth eggconcentrations and percentagetotal, fixed, and volatile solids.R a t i o n a l e f o r P a r a m e t e rS e l e c t i o n

A major objective of the proj-ect was to monitor pathogensendemic in Honduras using thecapabilities of local laboratories,with the idea that routine moni-

toring could be continued in thefuture. Fortunately, one nationallaboratory within the Secretary ofNatural Resources and Environ-ment has the capabilities to ana-lyze water and sludge samples forhelminth eggs on a routine basisusing a methodology originallydeveloped in Mexico; they can-not, however, distinguish viablefrom nonviable eggs. Unfortu-nately, the only other analyses inwater samples that could be per-formed within the limits of thisstudy on a routine basis by locallaboratories were S h i g e l l a species(presence-absence test), and thenonpathogenic indicators E s -c h e r i c h i a c o l i and fecal coliforms.While it would be highly desir-able to monitor for a protozoanpathogen, there are no laborato-ries in Honduras able to performthe analyses in water samples atthis time.

The final selected parameters

A barefoot boy spearfishing in sewage-contaminated water near Iquitos, Peru.


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lated hydraulic retention times,mean influent BOD5 concentra-tions, and organic surface loadingrates. Basing the measured influ-ent flow rate on the original de-sign populations, the calculatedper capita flow rates ranged from92 to 514 liters per person per day(Lppd), and the majority aremuch higher than the typical de-

sign assumption of 100 to 120Lppd. The higher flows are likelydue to increased connections dueto population growth, illegal con-nections from commercial and in-dustrial sources, and inflow and in-filtration into the sewer system.The increase is significant fromwhat was originally assumed in thedesign and exemplifies the resilien-cy of pond systems for developingcountriesmechanical systemssuch as activated sludge could

never handle such an increase overthe original design flow.

As a result of the higher meas-ured flow rates, the calculated hy-draulic retention times are shorterand the organic surface loadingrates higher than anticipated fromthe original designs. Only two fac-ultative pond systems satisfied the

Results of Measured Flow Rates, Hydraulic Retention Times, and Loading Parameters for Monitored Pond SystemsTABLE 6

for pathogens were, therefore,helminth eggs in water, sludgesamples, and S h i g e l l a species (pres-ence-absence) in water. E s c h e r i c h i ac o l i and fecal coliforms were alsochosen, despite their limitations forindicating pathogen removal, be-cause they could be easily moni-tored routinely in water samplesand used for comparison withother studies in the literature. Itwas also hoped that E s c h e r i c h i ac o l i would be more representa-tive of bacterial removal thanfecal coliforms.The conventional parametersof SS, BOD5, pH, temperature anddissolved oxygen were selected toassess system performance interms of organic loadings. Sludgesamples at the entrance to eachprimary pond system, whetheranaerobic or facultative, were

taken with a dredge and analyzedfor helminth egg concentrationsand percentage total, fixed, andvolatile solids. The objective ofsludge sampling was to estimatedegradation and accumulationrates, the extent of grit enteringthe system, and the public healthrisks of sludge handling due to

helminth egg concentrations.S a m p l i n g a n d A n a l y t i c a lM e t h o d sWith the exception of thehelminth analyses, all samples wereanalyzed according to S t a n d a r dM e t h o d s (APHA, 1995). The samplesfor helminth eggs, SS, and BOD5were 24-hour flow-weighted com-

posites, while those for S h i g e l l aspecies, E s c h e r i c h i a c o l i and fecal col-iforms were grab samples taken atdifferent times throughout a 24-hour period. The sludge sampleswere taken daily with the dredge(approximately 1.0 L) over thethree-day period at the entrance toeach pond where sludge depth wasestimated to be greatest; thismethod is limited and was meantonly to give a rough idea of sludgecharacteristics since sludge coresgive a much more accurate accountof deposition and decompositionprocesses and helminth survivalrates (Nelson, et al., 2004).R e s u l t sF l o w r a t e s , H y d r a u l i c R e t e n t i o nT i m e s , a n d O r g a n i c L o a d i n g R a t e sT a b l e 6 presents the results ofpond flow rate monitoring, calcu-


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WHO guideline of an eight-to 10-day minimum deten-tion time for helminth eggremoval; nevertheless, aswill be discussed below, allof the systems met theWHO guidelines for 100percent helminth egg re-moval.

The mean influent

BOD5 was found to varygreatly among systems,ranging from 71 to 437mg/L. As a result of higherthan expected flow ratesand influent BOD5 values,the organic surface loadingrates of the majority of fac-ultative ponds exceeded theestimated maximum load-ings for the latitudes andclimates of Honduras,which is estimated to be be-

tween 280 to 350 kgBOD5/ha/day as shown in F i g u r e 3 .In spite of this, the overall BOD5 re-moval was about what would beexpected for normally loaded sta-bilization pond systems as dis-cussed below. Once again thisshows the resiliency of pond sys-tems to handle widely varying load-ing rates and still maintain ade-quate treatment levels.T a b l e 6 also shows that thoseponds that were designed as

anaerobic ponds (Danl and Tela)were operating below the rangeof optimum volumetric loadingrates for anaerobic ponds of 100to 300 g BOD5/m3/day, and thatone overloaded facultative pond(Catacamas East), was approachingthe volumetric loading of an anaer-obic pond. Nevertheless, none ofthese ponds exhibited odor prob-lems, and their performance wassimilar to the other, lesser loadedponds, again demonstrating the re-siliency and wide margin of safety

typical of pond systems.H e l m i n t h E g g R e m o v a lT a b l e 7 shows the results ofhelminth egg monitoring. Thearithmetic mean concentration ofhelminth eggs in raw wastewaterranged from 9 to 744 eggs/L. Thehelminths found in raw waste-water and sludges were, in orderof abundance, A s c a r i s l u m b r i c o i d e s ,T r i c h u r i s t r i c h i u r a , and Anquilos-tomas (hookworm), and reflectthe prevalence of helminth in-

Helminth Egg Removal Wastewater Stabilization Pond Systems in HondurasTABLE 7

and Villanueva), all of the faculta-tive ponds removed 100 percent ofthe influent helminth eggs.

The ponds at Danl and Vil-

lanueva were anaerobic and likely

fections found in the generalpopulation. (Examples of eggsfound in raw wastewater areshown in P l a t e 1 .) With the excep-tion of three ponds (Danl, Pajuiles,

Organic Surface Loading Rate Versus Influent BOD5 for Various Hydraulic Retention Times (HRTFIGURE 3

Points represent systems monitored.


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did not achieve 100percent removal as a re-sult of insufficient hy-draulic detention timeor resuspension withrising gases from anaer-obic digestion. The car-ryover of helminth eggsin the facultative pondat Pajuiles could havebeen due to the burrow-ing activity of turtles orcrocodiles observed inthe pond.T a b l e 7 also showsthe results for helminthegg concentrations infacultative or anaerobicpond sludges. The con-centrations rangedgreatly among systems,from a mean of one eggper gram dry sludge at

Tela to 4,473 eggs pergram dry sludge at Pa-juiles. Although no dif-ferentiation was madebetween viable andnonviable eggs, the re-sults in T a b l e 7 leaveno doubt that pondsludges pose a serioushealth risk with helm-inth eggs and need tobe properly managedduring pond desludging

operations and ultimatedisposal.S h i g e l l a S p e c i e sThe presence of S h i g e l -l a species was not detect-ed throughout the study.One of the problemswith measuringbacterial pathogens isthat they are likely pres-ent in wastewater onlyduring an outbreak orepidemic episode; after

the episode passes theyare only present in asym-ptomatic carriers in verysmall concentrations thatare difficult to detect inwastewater.F e c a l C o l i f o r m sa n d E s c h e r i c h i ac o l iThe results of fecalcoliform and Escherichiacoli log10 removal areshown in Table 8 and

At least four maturation pondsystems have crocodiles, whichfeed on turtles and birds. Frogsare also abundant in severalmaturation pond systems. (SantaCruz de Yojoa, Honduras.)

a)Ascaris lumbricoides (fertile) b)Ascaris lumbricoides (fertile and unfertile)

c) Trichuris trichiura d) Anquilostomas

PLATE 1: Examples of helminth eggs found in all of the raw wastewaters sampled throughoutHonduras, which illustrates the widespread problem of infections. Because there is no immunityto parasitic infections, as long as the environment is contaminated transmission will continue tooccur. Eggs are approximately 50 m in diameter, a size that can easily be removed by sedimentationin facultative ponds.

Photos courtesy of Dr. Gilberto Padilla


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Figures 4 to 7. For facultativeponds it appears that it may bepossible to achieve a2.0 log10 removal of both fecal co-liforms and E. coli if the hydraulicdetention time is greater than 10days. The maturation pond results(Figures 6 and 7) are much moreinconsistent and do not show acorrelation between hydraulicdetention time and bacteria re-moval. These results exemplifythe difficulty in using fecal col-iforms orEscherichia coli as indi-cators of bacterial pathogens forwastewater as has been reportedin the literature (Feachem, et al.,1983; and Mara, 2004.)C o n v e n t i o n a l W a s t e w a t e rC o n s t i t u e n t s

The conventional wastewaterconstituent analyses of BOD5 and

SS (T a b l e 8

) show that each pondsystem is functioning as would beexpected in terms of performanceand removal efficiencies, in spiteof being loaded above their origi-nal designs. Dissolved oxygenanalyses and visual inspectionshowed that four as-designed facul-tative ponds (Catacamas East, Mo-rocel and Villanueva) were notfacultative and were functioning asanaerobic ponds. In spite of beinganaerobic, however, the ponds per-formed well in terms of removal ofBOD5, SS, fecal coliforms, E s c h e r i c h i ac o l i and helminth eggs, and they didnot have any serious odor problems.S o l i d s A n a l y s e s i n F a c u l t a t i v eS l u d g e sDesludging of ponds has beenfound to be a significant expensefor poor municipalities if it is notplanned for and budgeted years inadvance (Oakley, et al., 2000).Pond sludge analyses were there-fore performed to develop parame-

ters on sludge accumulation rates,including grit loads. The faculta-tive pond sludge analyses summa-rized in T a b l e 9 show that the per-cent total solids ranged from 11.6to 15.5 percent, volatile solidsfrom 23.9 to 31.4 percent, andfixed solids from 68.0 to 76.1 per-cent. The high percentage of fixedsolids is a result of the effect of in-organic solids entering the pondsfrom lack of grit chambers.

The volume of sludge in eachfacultative pond was measured by

Summary of Monitoring Results forE. coli, Fecal Coliforms, BOD5, and SSfor all Systems Monitored, Wet and Dry Seasons

TABLE 8

solids analyses by assuming thatpond sludge without grit shouldhave a volatile solids content ofapproximately 50 percent after di-gestion (Metcalf and Eddy, 2003).

The results in T a b l e 9 showthat sludge accumulation rates per1,000m3 of wastewater treated are

taking soundings on a grid from alaunch. Sludge accumulation rateswere then calculated by using themeasured flow rates and the num-ber of years the pond system hadbeen in operation. Grit accumula-tion rates were then estimatedfrom the results of the sludge

Removal ofEscherichia coliin Facultative Ponds in HondurasFIGURE 5

Fecal Coliform Removal in Faculative Ponds in HondurasFIGURE 4


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Removal ofEscherichia coliin Maturation Ponds in HondurasFIGURE 7

Summary of Results for Primary Pond SludgesTABLE 9

Fecal Coliform Removal in Maturation Ponds in HondurasFIGURE 6

Summary of Physical Condition, Operation and Maintenance, and Sustainability Issues in Monitored SystemsTABLE 10

an order of magnitude lower thanaccumulation rates from conven-tional processes (Metcalf andEddy, 2003), which is another ad-vantage of stabilization pondssince sludge handling is kept to aminimum. If facultative ponds arenot overloaded, a pond with a 10-day detention time can most like-ly operate up to 10 years or more

without the need for desludging.Grit accumulation is estimated

to be approximately 5 percent oftotal sludge accumulation asshown in T a b l e 9 . While this doesnot appear to be significant, dur-ing storm events, significantquantities of grit can enter pri-mary ponds and cause blockagesat inlets, and even prematurelyfill a pond (Oakley, et al., 2000).For this reason it is recommendedthat grit chambers be installed in

all systems.P h y s i c a l C o n d i t i o n ,M o n i t o r i n g , O p e r a t i o n a n dM a i n t e n a n c e , a n dS u s t a i n a b i l i t y I s s u e sT a b l e 1 0 presents a summaryof the physical conditions, moni-toring, operation and mainte-nance, and sustainability issuesencountered in the systems as-sessed in this study. Most installa-tions are physically well main-tained, but many are hydraulically

and organically overloaded withoutaccurate flow measuring devicesand grit chambers. At least threeinstallations are in urgent needof desludging.

Monitoring in all installationsis nonexistent, and nowhere areflow rates measured or samplestaken for laboratory analysis. Thefew installations where attemptswere made to measure sludge ac-


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D i s c u s s i o n a n d C o n c l u s i o n sIn a country such as Honduras,

where wastewater treatment es-sentially does not exist, the onlyrealistic option that has a possibil-ity of success in helping solve seri-ous public health problems is theintroduction of wastewater stabiliza-tion pond systems. Even these sim-ple resilient pond systems, however,will fail if their design, implementa-tion, operation and maintenance,planning, and municipal commit-ment are not suited to local needsand conditions. The results of thisproject have enabled the followingobservations and conclusions to bedrawn.E f f l u e n t S t a n d a r d s a n dW a s t e w a t e r R e u s eParasitic infections, such ashelminth infections, are the majorpublic health problem related toexcreta-related infections as indi-cated in the ubiquitous presenceof helminth eggs in raw waste-waters throughout the country.Since the project results dramati-

cally showed that every pond sys-

tem removed 100 percent of influ-ent helminth eggs, and since

helminth eggs can be routinelymonitored in local laboratories, itmakes more sense to initially orienttreatment objectives and effluentstandards on helminth egg removalrather than on an arbitrary level offecal coliform concentration thathas no demonstrated relation toproblem pathogens, and which isdifficult to achieve without design-ing numerous ponds in series. Usingthis conceptual framework, waste-water treatment in municipalitiesusing two ponds in series can easily

meet WHOs Category B require-ments for restricted irrigation, trans-forming what was once a seriouspublic health problem into a poten-tial resource for agriculture. This, inpoor municipalities, is much morepreferable than proposing more la-goons in series at a greater cost, ormore complex technologies usingdisinfection, which are beyond thetechnical and financial capabilitiesof the municipalities.

As far as concern for bacterial

pathogens, the literature shows that

cumulation had sludge depthsapproaching the water surface at

the inlets! Adequate operatortraining is a key issue to help re-solve these problems.

The wherewithal of the munic-ipality to properly manage the in-stallation and plan for the future,though, is the key to sustainabili-ty. The majority of installationshave rudimentary technical sup-port to train and pay an operatorto physically maintain the system,and the public generally acceptspond systems as a public healthbenefit. None of the municipali-

ties, however, adequately plan forsystem expansion, nor measure in-creased loads (nor how to managethem) as growing populationscontinuously connect to the sewersystems. As primary ponds reachlevels where desludging is impera-tive, there is a real possibility thatan installation could be aban-doned because of operation andmaintenance costs, which, unfor-tunately, is a common problemthroughout Latin America.

In the barrio of Belemin Iquitos, Per, hundredsof persons live in houses

over the river in whichraw sewage is dischargedfrom the city of Iquitos.In addition, each househas its own latrine abovethe water. In this photo awoman washes dishes nextto the latrine on the left.


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they typically exist in concentra-tions 3 or 4 orders of magnitude

lower than fecal coliforms(Feachem, et al., 1983). Studiesperformed in Latin America haveshown that a 3-cycle log10 removalof fecal coliforms removes essential-ly all of the bacterial pathogens ofconcern (Len and Moscoso, 1996;Mara and Cairncross, 1989). As anexample, F i g u r e 8shows the results ofremoval ofV i b r i oc h o l e r a e 01 as com-pared to fecal col-iforms in the waste

stabilization pondsystem of San Juanin Lima, Per atthe height of thecholera epidemicin 1991 (Len andMoscoso, 1996).The highest con-centration of V i b -r i o c h o l e r a e 01measured in rawsewage was only2,700 MPN/100mL

Removal of Fecal Coliforms and Vibrio cholerae 01 in San Juan Pond System, Lima, Peru, in 1991. Source:Leon and Moscoso, 1996.

FIGURE 8

as compared to 5.2E+08 MPN/100mLfor fecal coliforms.The first facultativepond essentiallyremoved the vastmajority of V i b r i oc h o l e r a e 01, and nosignificant concen-trations remained

in the effluents ofthe first or secondmaturation ponds.Until further studiescan show more de-tailed survival ofvarious bacterialpathogens in pondsystems, in wouldseem that two pondsin series that removeat least 3, log10 cyclesof fecal coliforms

should remove thevast majority ofbacterial pathogens.

Pathogenic proto-zoa pose anotherconcern, but atpresent they cannotbe analyzed for inwastewater treatmentsystems ona routine basis. Vari-

ous studies have suggested, howev-er, that they are effectively removed

in stabilization pond systems (Scott,2003).S y s t e m D e s i g n f o r P a t h o g e nR e m o v a lThe results of this study suggestthe following recommendations forsystems design:

All systems should be designedusing flows measured in thefield instead of assuming percapita flow rates. Because thereis no historical record of flowsand their increase with time,much caution needs to be usedin the design and useful life ofsystems.

Horizontal grit chambers should

be designed for all systems toensure that primary ponds donot prematurely fill with grit.

It is best to avoid anaerobicponds since their increased load-ings require desludging more fre-quently (at least every threeyears), which is an added expenseand risk for the municipality.

Two facultative pond systems inparallel with at least a 10-daydetention time followed by onematuration pond with at least a

5-day detention should remove100 percent of helminth eggs,satisfy WHO's Category B for re-stricted irrigation, and reason-ably ensure removal of bacterialand protozoan pathogens. Thisdesign also allows for the maxi-mum interval of desludging andhence the minimum need forsludge handling.

All designs should incorporateagricultural (or aquaculture)reuse as an integral part of the

system using the WHO guide-lines. This, hopefully, wouldhelp municipalities look atwastewater treatment in amore positive light than theyhave in the past and fostersustainability.

A well-designed and maintained facultative pond. (Masaya, Nicaragua)


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S u s t a i n a b i l i t y Sustainability is by far the mostimportant issue for wastewatertreatment in Honduras. It makeslittle sense to argue over techno-logical details and removal effi-ciencies if the municipalitiesthemselves do not have the in-frastructure and the financial ca-pabilities to adequately operate,plan for expansion, and desludgetheir systems. Latin America hashistorically had serious problemsmaking drinking water systemssustainable, and the median ratioof urban drinking water tariff tounit cost of production is less thanone for the Region (WHO/UNICEF,2000). If there is difficulty in mak-ing drinking water systems sustain-able, it is obvious that wastewatertreatment will be even more formi-dable a task. It is for this reason thatwaste stabilization pond systems in-tegrated with agricultural or aqua-

culture reuse offer the best promiseto help address some of this hemi-spheres most serious public healthproblems.A c k n o w l e d g e m e n t sThis project was funded byUSAID-Honduras and administeredby the U.S. Army Corps of Engi-neers. Pond monitoring was con-ducted by ECOMAC, Tegucigalpa,Honduras. The author thanksMauricio Cruz of USAID-Hondurasand Luis Eveline and Victor Ponce

A girl collects pollutedwater for domesticwater supply-a serious

problem throughoutLatin America. (Flores,Guatemala)

A well-designed pond system for a communityof approximately 10,000 persons in the valleyof Amarateca, Honduras.


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four primary waste stabilizationponds in central Mexico. W a t e rR e s e a r c h . vol. 38. pp. 111127.Oakley, S. M. 1998. M a n u a l d ed i s e o , o p e r a c i n y m a n t e n i m i e n t op a r a l a g u n a s d e e s t a b i l i z a c i n e nc e n t r o a m r i c a . AIDIS/AGISA,ERIS/USAC, INFOM, UNICEF,OPS/OMS, and CARE.Guatemala.

Oakley, S. M., A. Pocasangre, C.Flores, J. Monge, and M.Estrada. 2000. Wastewaterstabilization pond use inCentral America: Theexperiences of El Salvador,Guatemala, Honduras andNicaragua. W a t e r S c i e n c e a n dT e c h n o l o g y . vol. 42. pp. 5158.Organizacin Panamericana deSalud (OPS). 1998. L a s a l u d e nl a s A m r i c a s . vol. I.Washington,D.C., 1998.

. 2002. L a s a l u d e n l a sA m r i c a s . vol. I. Washington,D.C.

Rolim, S. 2000. S i s t e m a s d e l a g u n a sd e e s t a b i l i z a c i n . Bogot,Colombia: , McGraw-Hill.

Savioli, L., et al. 1992. Intestinalparasitic infections: a solublepublic health problem,T r a n s a c t i o n s o f t h e R o y a l S o c i e t yo f T r o p i c a l M e d i c i n e a n d H y g i e n e86. pp. 353354.Shuval, H. and B. Fattal. 2003.Control of pathogenicmicroorganisms in wastewaterrecycling and reuse inagriculture. H a n d b o o k o f w a t e ra n d w a s t e w a t e r m i c r o b i o l o g y . D.Mara and N. Horan eds.London: Academic Press. # pp.241262.

Shuval, H., A. Adin, B. Fattal, E.Rawitz, and P. Yekutiel. 1986.

Stewart Oakley, Ph.D.,

is professor of environmental engineering in

the department of civil engineering at Califor-

nia State University, Chico. He has worked ex-

tensively in the last 20 years in Latin America

in the areas of low-cost wastewater treatment

and solid waste management. He is currently

finishing a wastewater stabilization pond de-

sign manual and a sanitary landfill design and

operation manual for the government of Honduras and

the U.S. Agency for International Development. For more

information about this article, please contact Dr. Oakley at

[email protected].

CONTRIBUTING WRITER

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