LiSSARYJNTER.MATICNAL REFERENCE CENTREFCR COMMUNITY WATER SUPPLY ANDSANITATION (IRC)

351.285 RE

REUSE OF WASTEWATER AT THE SAN JUAN DE MIR;STABILIZATION PONDS: PUBLIC HEALTH, ENVIRONlViiMMAND SOCIOECONOMIC IMPLICATIONS1

Carl R. Bartone2

Sewage wastewater reuse, common in many arid and semiaridparts of the American, offers potential economic benefits but posessignificant health risks. This article reviews extensive field studiesdesigned to determine how well waste stabilisation ponds ('perillingunder the desert conditions of coastal Peru can reduce the associatedhealth hazards.

Introduction

The large-scale reuse of untreated domesticsewage for irrigation is commonplace in manyarid and semiarid zones of Latin America, as aresult of increasing population pressures, watershortages, and protein shortfalls. Twenty percent of the land is arid or semiarid. having only5% of the water resources of the Region; butthis land supports 60% of the population (367m i l l i o n people in 1983—/). Hence, rivers t h a tadequately served the inhabi tants ' water supply ,waste disposal, and irrigation requirements inearl ier t imes cannot meet these needs today. Thissuggests the su i t ab i l i t y of some form of landdisposal and the increased importance of reuse.

However, this practice may pose some healthrisk for farm workers and for the general popu-lation consuming agricultural produce from sew-

1 age reuse sites. High rates of enteritis, otherdiarrhcal diseases, typhoid, and hepatitis occurin the populations that generate the sewage, andthe environmental survival of the pathogenic or-

'Reprintcd, with minor changes, from the lexl by theauthor in American Water Works Association ResearchFoundation. Proceedings of the Water Reuse SymposiumIII. August 26-31. IV84. "Future of Water Reuse." Denver.Colorado. 1985. This article wi l l also be published inSpanish in the Boletln de la Oficina Sanitaria Puna-mericana.

^Coordinator of Research and Technology Development,Pan American Center for Sanitary Engineering and Environ-mental Sciences (CEP1S), Casilla 4337. Lima 100. Peru.

ganisms associated with these diseases is favoredby (he prevai l ing tropical conditions. It is there-fore essential tha t any sewage reuse project haveat least the min ima l effect ive sanitary controlmeasures needed to mi t iga te potential publichealth risks.

Some examples of reuse in Lat in America arcas follows:

• In Chile the "Zanjon dc la Aguada" irriga-t ion canal receives 80% of Santiago's domesticand indust r ia l sewage and is used together w i t hthe polluted waters of the lower Maipo R ive r toirrigate some 16.(XX) hectares of land near theci ty . Of t h i s , an area of 6,200 hectares irrigatedwith six cubic meters per second of raw sewagesupplies the city wi th hor t icu l tura l productsThere are problems with Salmonella. E. coli,Sltigella. Hepatitis A. Entamoeba histolytica.Giardia lamblia. and other pathogens. Salmo-nella antibodies have been detected in 57%of the population and typhoid antibodies in30% (2).

• Irrigation District No. 3 near Mexico Citycomprises 41,500 hectares irrigated with raw ormixed sewage. Other irrigation districts near thecity also use raw sewage. Tests to detect fecalcoliforms in the irrigation water have indicatedan average concentration of 10 MPN/lOOml/1

It has been shown that edible crops for raw con-

r\MPN Most probable numbcj 35 /, ~\ ^ (_J Q 3

V. e>\ Jifla\U»ti^pw\Zflt\ou;tooL\^l

148 PAHO BULLETIN • vol. 19. no. 2. 1985

sumption from these reuse sites were contami-nated with fecal coliforms on the order of 3,000MPN E. a;///lOg (3).

• Along the Peruvian desert coast 33 reuseprojects have been identified (Table I ) , manyusing waste s tabi l iza t ion pond eff luents . How-ever, there are some uncontrolled reuse sites inand around Lima (hat irrigate a to ta l of 2.800hectares wi th two cubic meters per second ofraw domestic and industr ia l sewage. Peruvian

authorities are currently planning the reuse ofI wo and a half cubic meters per second of treatedsewage to irrigate 4,000 hectares of desert landto the south of Lima (4).

These and other experiences throughout theThird World clearly show that reuse is a rea l i tyand tha t economic demand often creates spon-taneous indiscr imina te reuse. The responsiblepublic health author i t ies must an t i c ipa te these

Table I. Sewage reuse sites in I'tru.

Lixallon

1 ) Ayacucho2) Tacna3) Piura4) lea5) Nazca6) Huarul7) Puerile Piedra8) Monsefu9) Vim

10) Chocopc1 1) Moqucgua12) Lunn13) Olinos14) San Pedro dc Lajas15) Chiquian16) Buenos Aires17) Arequipa18) Ventanilla19) Cafielc20) Sullana21) Paita22) Cajamarca23) Chincha24) Chepen25) Huanta26) Juliaca27) Lambaycque28) Parcona29) Lima:

a) San Juanb) San Juanc) Villa el Salvadord) Callao, Collector No. 6e) San Mart (ndePorrcs,

Collector Comas0 San Miguel, Collector

Palomino

Row(liters persecond)

601501 10270

2050371556

30-----

1.160-----------

200160

1.0001,000

940

10

Ars;:(hectare^)

k —

200-

300-------------

195---------

75

1,600220-

1,000

1.750

40

Treatment provided

Imhoff tanks + facultative pondsAerated ponds + facultative pondsPondsFacullalive pondsFacultative pondsFacultative pondsAerated ponds"PondsFacultative pondsAerated pondsFacullalive pondsImhol f tankImhoff tankImhoff tankImhoff lankFacultative pondsPercolating filtersFacultative pondsRaw for vegetablesFacultative pondsFacullalive pondsFacultative pondsFacullalive pondsFacullalive pondsPercolating filtersFacultative pondsFacullalive pondsFacullalive ponds

Raw for silvicultureFacultative pondsRaw for vegetablesRaw for vegetables*

Raw for vegetables*

Raw for vegetables

Sources: F. Yinez el »l. <•>> and I. M. Zapaler (1-1).'Receives industrial wastes.

Bartone • STABILIZATION PONDS AND WASTEWATER REUSE 149

economic pressures and plan for and implementadequate sanitary control measures. In addi-tion to the risk of microbial contamination bybacteria, viruses, and parasites, there are po-tent ial problems of chemical contamination ofedible crops, livestock, dairy products, and fishthrough the bioaccumulation of trace metals andtoxic organic substances. Clearly, then, there isa pressing need for field research aimed at eval-uat ing sanitary control strategies relating toreuse.

Since 1977 the Pan American Center forSanitary Engineering ynd Environmental Sci-ences (CEPIS). in cooperation w i t h Peruvianhealth authorit ies, has undertaken extensive fieldand laboratory studies of the q u a l i t y of thetreated eff luents and pathogen survival charac-teristics. The aim of th is research has been toevaluate the health risks of reuse and to dem-onstrate the effectiveness of waste s tabi l iza t ionponds as sanitary control fac i l i t i es employedprior to reuse.

The San Juan Reuse Project

The San Juan de Miraflores sewage reuseproject, which is located on the southern edgeof Lima, began in 1961 with the constructionof 21 experimental waste s tabi l iza t ion ponds oc-cupying 20 hectares of desert land. The pondsentered into operation in 1964, and the treatedeff luents have since been used for agr icul ture ,s i lv i cu l tu re , and park i rr igat ion. Aquaculture ex-periments have also been carried out in ad-vanced-level polishing ponds. These uses aresummarized in Table 2.

Table 2. Reuse at the San Juan experimental site.

SILVICIJLTURK

Creation of grcenbcltsIrrigation of recreational parksRecovery of sanitary landfi l l site

AGRICULTURE

Irrigation of horticultural produce (squatters)• vegetables, fruit treesIrrigation of forage crops (squat'crs)• alfalfaIrrigation of animal feed crops grown for zoological

park• papaya, banana, cornIrrigation used for commercial flower-raising• roses

AQUACULTURE:

Pish/prawn• Tilapia• giant malaysian shrimpAquatic plants for poultry feed• duckweed

Site Description

The San Juan s tabi l izat ion ponds were origi-n a l l y designed as two-cell f acu l t a t ive ponds w i t haverage depths of 1.3 to 1.5 meters. The 21ponds are arranged in two batteries—an upperbattery of 10 ponds and a lower bat tery of I Iponds. They are bu i l t over porous, a l l u v i a l ,sandy subsoils. Average r a i n f a l l in the area isless than 15 mm per year. Average da i ly temper-atures range from I5"C in the win ter months to23"C in the summer months.

The San Juan complex receives sewage fromthree lower-class Lima neighborhoods—SanJuan de Miraflores. Pamplona Baja. and Ciudaddc Dios—with a sewered population of some108.500 (59%) out of a total population of about193.000. The average sewage flow is 360 litersper second. The treated effluents are used toirrigate some 280 hectares of forests and parksand 220 hectares of farmland, wi th another1,300 hectares being planned forgreenbelts withlow irrigation requirements (see Table 2). Mostof the farmland on the perimeter of the experi-mental site itself has been occupied and operatedsince 1964 by squatter families.

The Research Program

Since these experimental ponds began operat-ing in 1964, they have provided valuable designinformation to Peruvian engineers—as may beseen by the number of pond installations thathave subsequently been bui l t and utilized forreuse (see Table 1). Since 1977 CEPIS and a

150 PAHO BULLETIN • vol. 19, no. 2. 1985

number of other international agencies and Peru-vian research institutions have cooperated in de-veloping a comprehensive reuse research pro-gram at San Juan, with the aim of evaluatingthe experiences there and further extending thoseexperiences to other parts of Peru and theAmericas.

The research program includes three projectsthat have already been concluded, three that arcunderway, and three that have been proposedand are currently under negotiation with differ-ent fund ing agencies. Each of these projects hasfocused on a particular aspect of treatment andreuse. They are as follows:

Concluded projects:1977-1979—an engineering evaluation of pond per-

formance and design criteria.1980-1982—an evaluation of the sanitary risks of

treated eff luent reuse for agriculture, cmphasi/-ing bacicriologic concerns.

1983-1984—an cvalualion of aquaculture usingtreated pond effluents .

Projects underway:

1984-19X6—an evaluat ion of potential groundwatercontaminat ion due to in f i l t r a t ion from ponds and.irrigation sites.

1984-1985—a study of the sanitary aspects of duck-weed production in t reatment ponds and use ofsuch duckweed as poultry feed.

1984-1985—a feasibil i ty study of the San Bartoloreuse scheme to irrigate 4,000 hectares of desertland using two and a half cubic meters per secondof Lima sewage.

Proposed projects:1985-1986—an epidemiologic and socioeconomic

evaluation of sewage reuse.1985-1986—an evaluation of the toxicologic risks

of sewage reuse.1985-1986—-an evaluation of the virologic risks of

sewage reuse.

The remainder of this article wil l concentrate onthe description and findings of the concludedresearch efforts, for which CEPIS was primarilyresponsible. However, some preliminary discus-sion of the other ongoing and proposed projectswil l also be presented.

Phase I: Engineering Appraisal

The first phase of the San Juan research pro-gram began in 1977 wi th an engineering ap-praisal of the waste stabilization ponds. Themain purpose of the study was to evaluate aseries of s tabi l izat ion ponds working under avariety of loading conditions in a tropical env i -ronment, in order to develop local design cri-teria. The s tudy was performed by CEPIS wi ihthe f inancial support of the In te rna t iona l De-velopment Research Center ( IDRC) of Canada,and with the participation of the National Agrar-ian Univers i ty ( U N A ) of Peru.

Eight ponds were chosen for inclus ion in thestudy. Since they had been in operation for over10 years already, the ponds were drained anddried and the sludge was removed. This providedan opportunity to observe sludge characteristicsand bu i ldup , inc lud ing the influence of in le tstructure design. New in le t and outlet structureswere bui l t that incorporated rectangular or i r i an-gular weirs for (low measurement, along wi tha Parshall ( v e n t u r i ) f lume to measure to ta l rawsewage flow and d iv id ing chambers to controlinflows to the ponds. The ponds were sequenccdas shown in Figure I . in four two-cell series ofprimary and secondary lagoons. As ihc pondswere ref i l led , in f i l t r a t ion data were collected andall the hydrau l i c structures were cal ibrated. Thedividing chambers were set to achieve averageloading rates of 400, 600, 800, and 1.000 kgper hectare-day to primary ponds P I , P2, P3.and P4, respectively (see Figure I ) .

The data collection program lasted for sixmonths. Field measurements included continu-ous hydraulic recording of the raw sewage flowand daily observation of inlet and outlet flows;monthly infiltration studies; daily temperaturemeasurements of raw sewage and of all pondeffluents; and daily Secchi depth (water trans-parency) measurements in all ponds. Dailymeteorologic information was obtained—in-cluding wind speed and direction, ambient tem-perature, evaporation, soiar radiation, and hoursof sunshine. Qualitative observations of pondappearance, color, odor, scum, and floating mat-ter were also recorded daily. Two series of con-

Bartone • STABILIZATION PONDS AND WASTEWATER REUSE 1 5 1

t inuous twenty-four-hour tests were performedin the secondary ponds to obtain vertical profilesof diunial dissolved oxygen and temperaturealong with a l k a l i n i t y and pH data.

The sampling and analysis program was per-formed in CEP1S' laboratory according to stan-dard methods with detailed laboratory manualsprepared for chemical and microbiologic proce-dures (5. 6). Hourly samples of raw sewagewere taken by means of a low-cost automaticsampler developed at CEPIS. Weekly grab sam-ples were obtained from all ponds near the outletstructures. Laboratory determinations includedtotal and dissolved five-day biological oxygendemand (BOD5) and chemical oxygen demand(COR); suspended solids and residue (total, vol-a t i le , and fixed); a l k a l i n i t y ; calcium; hardness;pH; potassium; sodium; conductivity; chlorides;sulfates; ammonia nitrogen; organic nitrogen;n i t r i t e and n i t ra te nitrogen; and total phosphateand orthophosphate. Microbiologic determina-tions included idenlification and counting ofalgae; identif icat ion and counting of pathogenic

protozoa and helminths; enumeration of totaland fecal coliforms by most probable number(MPN) techniques; and the isolation of Sal-monella with complete biochemical and serotypeidentification (the latter performed at the Peru-vian National Reference Laboratory for En-terobacteria).

The detailed analysis and interpretation ofthese data have been reported elsewhere byYdnez et al. and Ydnez (4. 7. 8). Only the majorfindings are highlighted in this paper.

Biological Oxygen Demand (BODj)Loads and Removal

During the study period, BODS loads on theprimary ponds ranged from 200 to 1.200 kg perhectare-day. It was found that the overall aver-age removal efficiencies for the primary andsecondary ponds were 80.6% and 76.5%, re-spectively (4). These efficiencies were re la t ive ly

Figure I. Arrangement of the San Juan stabilization ponds during Phase I, theengineering evaluation phase. The loading rates for the four two-pond series were

400, 600, HOO, and 1,000 kilograms BOD* per hectare-day (kg/ha-d).

SEWAGE

pi = FLOW MEASUREMENT FLUMEdc = DIVIDING CHAMBER

7

? dc

1 —————————

1

dcr— i

J L

400

i p 4

1 2ha

S1 i

1 4 ha

!

P2 i

1.1 ha

Jdc

————— P ————————600

I

1

T S 2

1 5 ha

P3 i

9 ha

J800 1000 KG/HA-D

P4 "

7 ha

' ' S3 v S4

1.3 ha I3na

152 I'AHO BULLETIN vol. 19. no. 2. 1985

constant over the f u l l range of applied loads.This was corroborated by comparison with re-search results reported for other tropical coun-tries (4). Yanez (8) concludes that significantlyhigher aerial loading rates can be used for designpurposes in tropical climates than those conven-t iona l ly adopted in temperate /.ones.

An analysis of the correlation between aerialBODS loads versus the ratio of inf luent toeff luent ammonia nitrogen showed that at 20"Cthe ammonia fraction remained less than one forloading rates up to 357.4 kg BOD^ per hectare-day. Since in a biological reactor ammonia ni-trogen usua l ly increases only through anaerobicprocesses, the indicated load represents theupper l imi t between facultative ponds and pre-dominant ly anaerobic ponds. Adjusting for thewater temperature, Yanez (8) recommends theuse of the following design equation for faculta-t ive ponds:

La = 357.4 x 1.085 (T-20)

series. For complete removal of protozoa, atleast two ponds in series were needed with atotal min imum detention time of 36 days. Yanezet al. (4) attributed the appearance of parasitesin secondary effluents to resuspension due totemperature inversions, and suggested that re-moval could be improved using baffled pondeff luent weirs for the retention of floatablcs orscum. Further research was recommended.

Fecal Colifonn Removal

In all but the most highly loaded (P4-S4)series, there was an apparent reduction of twolog cycles in E. co!i. from !08 M P N / I O O m l inraw sewage to 10 MPN/IOOml in secondaryeffluents. However, the data were loo scatteredto permit defini te conclusions, and so furtherresearch was recommended on coliform survivalcharacteristics (4).

where La is the maximum applied BOD^ loadin kg per hectare-day and T is the water temper-ature in "C. Higher loadings (and thus smallerareas) are obtained using this relationship intropical climates as compared wi th conventionaldesign relationships based on ambient air tem-peratures, since in tropical climates water tem-perature remains higher than the average air tem-perature.

Parasite Removal

Although the primary ponds removed thegreat majority of intestinal parasites, it wasfound that under coastal Peruvian conditionsprimary ponds are not enough for complete re-moval of pathogenic protozoa and helminths. Itwas shown that helminths were completely re-moved by two ponds in series with a totalminimum retention time of 5.5 days. However,a few protozoan organisms were found in sec-ondary pond effluents of the more highly loaded

Salmonella Survival

Regarding Salmonella survival , the informa-t ion collected included the . isolation of nineserotypes and positive isolation in 20 out of 20tests of pond eff luents . Contrary to expectations,two stabil ization ponds in series w i t h a totaldetention time of 36 days were not enough tocompletely destroy Salmonella species. Addi-t ional ly , the serotypes isolated (pr incipal lyParatyphi B, Derby, and Newport) were preva-lent in the area of Lima and were found to havedeveloped resistance to antibiotics. This couldpose a problem, since it implies that pathogenicSalmonella serotypes have acquired genetic R-factor resistance and may be more d i f f i cu l t todestroy in the water environment. Also, thereis a possibility that this resistance can be trans-ferred from Salmonella to other pathogenic bac-teria in ponds via R-factorplasmids. This, alongwith the increased reuse of domestic sewage inthe urban fringe areas of Lima, could representa public health problem of increasing magnitude.More detailed studies were recommended, in-

Barione STABILIZATION PONDS AND WASTEWATER REUSE 153

e luding enumeration of Salmonella, in order tof u l l y evaluate the Salmonella destruction poten-t ia l of stabilization ponds (4).

Phase II: Pathogen Survival Studies

The main purpose of the second phase of re-search at San Juan was to investigate the reduc-tion of pathogenic organisms achieved througha series of waste stabilization ponds, wi th theobjective of developing practical information forthe design of ponds under tropical conditionsand for the large-scale agricultural reuse oftreated ef f luents . The project was conceived andexecuted at the request of the Peruvian Minis t ryof Health, and was financed by that Minis tryand the Inter-American Development Bank(1ADB).

For th is s tudy the ponds were resequenced,as shown in Figure 2. so that they formed two

three-cell series ( P I - S I - T I and P3-S3-T3) anda four-cell series (P2-S2-T2-C2). This config-uration allowed for pathogen survival studieswith longer hydraulic detention times. Also, inaccordance with the recommendations emergingfrom the previous phase, all pond e f f luen t weirswere baffled to reduce the potential for parasitetransport via floating matter. Additional Howmeasurement (Palmer-Bowlus type) flumeswere incorporated. In pond S2, three baffleswere installed to convert the pond from a mixedreactor to a plug-How reactor. When the mod-ified ponds were completely f i l led , all hydraul icmeasurement flumes and weirs were cal ibrated.Aerial BOD loading rates were maintained be-tween 250 and 350 kg per hectare-day dur ingth i s phase.

Because the true hydraul ic detention times ofthe ponds appeared in phase I to be considerablyshorter than the theoretical detention times, thecomplete m i x i n g assumption required checking.An intensive program of hourly temperature pro-

Figure 2. Arrangement of the San Juan stabilization ponds during Phase II, the sanitary evaluation(pathogen survival ) phase.

S E W A G E

pl dc pf dc

pl = FLOW MEASUREMENT FLUMEdc - DIVIDING CHAMBERi r r = IRRIGATION WATER

250-350 K G / H A - D

P1

1 2 ha

\ i}S^

1 4 har><nl>vj

tP2

1 1 ha

T1

1 5 ha

IS2.

T2

1irr

19 ha

r

C213 ha 13 ha

Iirr irr

154 • PAHO BULLETIN vol. 19. no. 2. 1985

file measurements was undertaken to charac-terize the stratification characteristics of theponds. Also, 16 dye tracer studies were carriedout to determine the hydraulic characteristics ofall the ponds, particularly their dispersion con-stants.

To determine bacteria dieoff rates, three typesof tests were conducted. These were done(1 ) in full-scale stagnant ponds with no influentor effluent; (2) in plastic bags immersed in pondsand filled with 100 liters of pond water; and(3) in pond S2, which was of the plug-flow type.In i t i a l ly , parallel tests were conducted in thestagnant ponds and plastic bags. However, be-cause the sampling procedure for stagnant pondswas too cumbersome and the dieoff results forboth tests gave exactly the same results, the firsttype of test was abandoned in favor of the sec-ond. A total of 31 dieoff tests were performed,12 in the primary ponds, 13 in the secondaryponds, five in the tertiary ponds, and one in thequaternary pond.

Other field measurements made were s imi larto those made in phase 1, with additional cont inu-ous hydraulic recorders being instal led at thenew flume locations.

The sampling and analysis program was con-siderably reduced so as to concentrate primarilyon total and soluble BOD (one, three, five, andseven day), COD, ammonia nitrogen, and totaland suspended solids. Microbiologic determina-tions included the identification and relativecounting of parasites, total and fecal coliformenumeration using MPN procedures, and 5a/-monella enumeration using MPN techniques to-gether with biochemical and serotype identifica-tion methods (6). Data were collected biweeklyover a period covering 17 months.

Detailed data analysis and assessment reportshave already been presented. A description ofpond temperature dynamics has been providedby Burgers (9). Lloyd (10) has analyzed thebacteria dieoff data. And an overall report oftracer studies, dispersion and stratificationcharacteristics, BOD removal performance, andpathogen survival has been provided by Ydnez(7). The main points of their findings are sum-marized here..

Temperature and Thermal Stratification

The following relat ionship was developed forPeruvian coastal conditions from water and am-bient air temperature records (9):

T = 8.49 + 0.82Ta [2]Tm = 4.64 -f 0.91Ta |3]

where T and Tm are the average and m a x i m u mwater temperatures and Ta is the average airtemperature, in "C. Equation [2] is of great im-portance locally, as it allows the use of equation[ 1 ] for design purposes. Equation [3) applies tostratified conditions. Daytime thermal s t ra t i f ica-tion occurred when solar radiation exceeded 160calories per square centimeter per day and therewere at least six hours of direct sunshine. Forstrat if icat ion events, the thermocline set up be-tween 30 and 60 cm.

Hydraulic Performance

Tracer studies verified a high degree of short-circui t ing in the ponds during s t ra t i f ica t ion ,which facil i tated the rapid transport of viablepathogens through them. The tracer studies alsoprovided data for the calculat ion of the true de-tention periods and of the dispersion factors ofthe ponds. On the basis of these results, Yanez(7) recommended the design of rectangularponds with a dispersion factor of 0.6 and withmaximum distance between the inlet and outlet.

Fecal Coliform Removal>

The reduction of E. coli in three-cell pondsystems with a ten-day true hydraulic detentiontime was found to be 99.98% and 99.96% insummer and winter, respectively (10). Based on31 mortality rate tests in primary through quater-nary ponds, the average dieoff rate for E. coltwas found to be 0.84 per day (7). More rapiddieoff was achieved in the secondary and tertiary

Bartone STABILIZATION PONDS AND WASTEWATER REUSE 155

ponds, as compared to the primary ponds, prob-ably due to the higher pH and oxygen levels,scarcer nutrients, and greater likelihood ofpredator and antagonistic organisms being pre-sent. For design purposes under coastal Peruvianconditions, the following equation is proposed:

Kb = 0.84 x 1.07(T-20)

where Kb is the net bacterial mortality (per day)and T is the water temperature in "C (7).

Compared wi th other treatment processes,s tab i l i za t ion ponds in series are much more ef-ficient at removing fecal colifonns. By addingadditional pond cells or increasing polishingpond volumes to obtain detention periods on theorder of 20 days, i t should be feasible to obtainE. coli levels below 1,000 MPN/lOOml.

Salmonella Survival

With respect to Salmonella, reductions of99.8% were obtained in three-cell systems. Rawsewage concentrations of 2,400 MPN/lOOmlwere reduced to 4.5 MPN/lOOml in tertiaryeffluents (10). In a series of comparative mortal-ity tests. Salmonella dieoff rates were found tobe very s imi lar to rates for E. coli (7). Thissuggests that E. coli is an appropriate indicatororganism for Salmonella in waste stabilizationpond systems. Increasing the detention time to20 days, which would bring E. coli counts downto' acceptable levels, would also further reduceSalmonella.

Parasite Removal

During this phase, with the use of baffledeffluent weirs in the primary ponds, no path-ogenic protozoa or helminths tDxild be detectedin secondary pond effluents. For complete re-moval, it appears that pond systems which pro-duce four log reductions in E. coli through atwenty-day retention period will certainly re-

move parasitic ova as well. Therefore, althoughthe mechanisms of removal are completely dif -ferent, fecal coliform indicators may be usedwith confidence to assess the health risks fromparasites, and monitoring of the latter may bedispensed with (10).

Phase III: Aquaculture Appraisal

As part of a larger project to evaluate theproduction of fish (Tilapio nilotica) and prawns(Macrobrachium rosenbergii) in the San Juanpolishing ponds receiving treated eff luents .CEPIS carried out a water-quality monitoringprogram. The overall project objectives were:( I ) to determine the efficiency of the experimen-tal wastewater-aquaculture system for con-t r o l l i ng environmenta l conditions in (he ponds,in order to foster good fish growth: (2) to dem-onstrate the economic v iab i l i ty of the sewage-aquaculture system; and (3) (o evaluate any pub-lic health problems that might be associated wRfchuman consumption of the fish and prawns. Fishstocking, survival, and production studies werecarried out by the National Agrarian Universi ty(UNA) . Fish microbiology and parasitologywork was done by the I n s t i t u t e for H i g h - A l t i t u d eVeterinary Research ( IVITA) . The project wasfunded by the United Nations DevelopmentProgram (UNDP), the World Bank, and theGerman Agency for Technical Cooperation(GTZ).

Because of somewhat stringent water-qualityrequirements, fish experiments were plannedonly for advanced polishing ponds receiving atleast treated effluents from secondary ponds.Therefore, the ponds were resequenced as shownin Figure 3 to create a four-cell series and afive-cell series. The quaternary ponds (Cl andC2) and the quintenary pond (Q2) were designedas shallow ( I m ) batch ponds that received onlysufficient makeup water to compensate for infil-tration and evaporation losses. All other pondswere continuous-flow ponds. Aerial BOD5loading rates were set between 250 and 350 kgper hectare-day. Fish were stocked at different

156 PAHO BULLETIN • vol. 19. no. 2. 1985

Figure 3. Arrangement of the San Juan stabilization ponds during Phase III, the aquacultureappraisal phase.

SEWAGE pi = FLOW MEASUREMENT FLUME

7P.V dc pfi — i rs»«'i

dcr— i

Pfi -iLLJ ix"sj 1 1 1 v *^i

250-350 TKG/HA-D T

P1

1 2 h a

i

1

'51

4 ha 1><J

T1

P2

1 1 ha

<

1 5 ha

>

|

Cl-^~

c,2

9 ha\

O

i 3 ha

"

\

OC = UIVIUINU l/MAMtttn

irr = IRRIGATION WATER

po ' coi O i O \311

1 t7ha ! I 8ha —— J

x O O OT2 C2 Q2

I 3 ha 5 ha 6 ha

t

intervals in ponds T l , C l . T2, C2. and Q2.while prawns were only experimented with inponds C2 and Q2.

The water-quality monitoring program lasted12 months. Routine twice-daily sampling wasestablished for the fish ponds (at 10 a.m. and2:30 p.m.) for temperature and dissolved oxygenat 20, 40, and 60 cm, and for pH and total am-monia. This also permitted the routine calcula-tion of the un-ionized ammonia fraction, whichis toxic to fish. In addition, temperature anddissolved oxygen profiles were recorded everytwo hours for periods of three to five days inthe fish ponds on a rotational basis, along withdiucnal pH measurements. The remainder of thefield observation program was similar to thatemployed in the previous phases.

Laboratory measurements included analysisof weekly raw sewage samples and samples fromall the fish ponds for BOD5, COD, ammonianitrogen, organic nitrogen, orthophosphatephosphorus, detergents, and alkalinity. In addi-tion, total and fecal coliform, parasite, and pri-mary productivity determinations were made

monthly. During the last months of the program,standard plate count and Salmonella determina-tions were done in pond water and sedimentsamples, and fecal coliforms and parasites wereanalyzed in sediments.

The aquaculture experimental program hasonly recently been concluded, and much of thedata is st i l l to be worked up. Therefore, onlythe preliminary findings of the water-qualitymonitoring program wil l be discussed here.

Environmental Conditions in theFish Ponds

Fish survival and growth can be adverselyaffected by sustained low dissolved oxygen con-centrations or high levels of un-ionized ammoniaor detergents. Monitoring and control of thesevariables is essential for successful fishcultureproduction. The data summarized in Tables 3aand 3b (7 /> show that on the average acceptablevalues were attained at San Juan in the batch-op-erated polishing ponds (Cl , C2, and Q2). Only

Bartone e STABILIZATION PONDS AND WASTEWATER REUSE 157

marginal water qual i ty was obtained in the ter-tiary treatment ponds. In the case of dissolvedoxygen and un-ionized ammonia, conditionswere controlled in large part by the photo-synthet ic cycle.

Dissolved oxygen concentrations in the after-noon usual ly reached supersaturated levels due

to the high algal biomass present in the advancedstabilization ponds. At n igh t , the dissolved oxy-gen often dropped to very low levels becauseof biomass respiialion. but early morning recov-ery was rapid. At the loading rates used, lowlevels of dissolved oxygen should not be a prob-lem for fish. The prawns, however, may have

Table 3a. Environmental condition* In the San Juan stabilization pond* used for aquacullurr apal.The figures shown are averages obtained via daily .sample* taken from May 1983 through April 19X4.

Time

Morning

Aftcrmxin

Water samplefrom desig-nated pond

(see Figure 3)

TlClT2C2Q2

TlClT2C202

Dissolved oxygen (mg/1 ) atindicated depth:

20cm

2.74.64.25.34.2

7.61 1 .515 413.412. X

40cm

2.03.62.64.33.0

5.89.3

12.411 .09.6

nOcm

1.63 .1I . X3.72.3

4.07.05.57.35.X

Temperature ("C) itindicated derxh:

1-0cm

22.523.624.323.423.8

24. 1,25.627.325.226.0

40cm

22.523 624.323.42.3.8

23.925.527.124 925.7

f)0cm

22.523.624.223.323.7

23.625.125.524.525.0

pH(uni t s )

7.88.2X . I8.68.5

8.18.7X 59.09 0

Totalammonia

I m p / l )

1 1 . 32.5X.51.91.4

1 1 . 32.4X . II X1 .4

Un-ioni/rdammonia

(m*/ 1)

0.60.3

' 0.70.30.2

1.0O.X1.30.60.5

Table 3b. Envlronmer'n? renditions in the San Juan stabilization ponds used for aquacullure appraisal.The figures shown are «"rrages obtained via weekly samples Uken from May 1983 through April 1984.

Raw sewage or watersample fiom designated

pond (see Figure 3)

Sewage

PISITlCl

P2S2T2C202

Concentration (mg/l) of:

BOD5

155.7

12.611.720.916.5

10.610.418.77.86.8

Ammonianitrogen

31.4

23.516.610.72.6

19.816.88.82.51.6

Organicnitrogen

18.1

12.1

12.09.8

10.7

14.49.89.0

10.510.8

Nitratenitrogen

0.25

----

0.050.080.320.510.15

MBASdclergcnl.s

1.38

1.621.461.120.94

1.551.781.130.850.98

AlkaJinily

270.5

215.5196.9189.8141.0

241.4185.6135.9116.6121.2

158 PAHO BULLETIN vol. 19. no. 2. 1985

been stressed by persistently low benthic dis-solved oxygen concentrations.

It is recommended that total ammonia nitro-gen levels be maintained below 2 mg per literto avoid fish toxicity effects. In the case of SanJuan, this was not possible in the tertiary ponds,where the average concentrations ranged fromeight to 12 mg per liter. At these levels, theUNA investigators reported apparent stressingand stunted fish growth relative to that found inthe advanced polishing ponds (J. Moscoso andH. Nava, personal communication). The levelsin the latter ponds were maintained at satisfac-tory concentrations by their batch-flow style ofoperation, which significantly reduced the am-monia loadings to the ponds. Short-term toxicityproblems may arise in ponds on sunny days whenphotosynthetic activity of algae often drives thewater pH above 10. Under these conditions, al-most all of the ammonia is in the un-ionizcdform.

Hard detergents are used in Peru, but thelevels in raw sewage are not high. In all of thefish ponds, detergent concentrations werearound 1 mg per liter of melhylblue activatedsubstance (MBAS).

In summary, it was found that su i tab le en-

vironmental conditions for fish production couldbe maintained in advanced polishing pondsunder Peruvian conditions.

Fecal Coliform Removal

Considering that E. coli was shown to be agood indicator organism for Salmonella andparasites, monitoring was continued during theth i rd phase. The results are shown in Figures 4and 5 (II). The tendencies observed in previousphases were confirmed, in that E. coli concen-trations were reduced to I .(XX) MPN/IOOmlthrough four ponds, and down to 100 MPN/lOOrn! through five ponds. Again , no parasitessurvived the secondary ponds. Thus, wastestabilization ponds with adequate retentionperiods can produce irrigation water meetingcommon guidelines for unrestricted use (12).

No other conventional sewage treatment pro-cess, except perhaps for disinfect ion, can matchthe a b i l i t y of s tabi l izat ion ponds to removepathogens. Ponds thus offer a good appropriatetechnology option for tropical Third Worldcountries. In combination wi th reuse, they canconsti tute an effective sanitary control measure.

Figure 4. Total coliform and fecal coliform counts(obtained using MPN techniques) in raw sewage

and in water samples from ponds PI, SI,Tl, and Cl (see Figure 3).

Figure 5. Total coliform and fecal coliform counts(obtained using MPN techniques) in raw sewage

and in water samples from ponds P2, S2,T2, C2, and Q2 (see Figure 3).

ii8 'f

lOCO

XrfO

AM.M

a -

** u

«

.u

>«

>

.

*

^

/

•/

\

I D '-^

L\\

\\\\

\\\\

\\\\

\\\\

x

—

K\\

\\\\

\\\\

\\\\

\\Y

I

K\\

\\\\

\\\\

\\\\

\]

r;

/

Serin

•'•

•

T;

X

/X

XV

//

g:;;:7"

|X

^

j !™~

•|« » S 1i" ll

C 0

S«tit» ? PonOl

Bartone STABILIZATION PONDS AND WASTEWATER REUSE 159

Epidemiologic and SocioeconomicFactors

A number of preliminary studies have beenconducted to identify the key epidemiologic andsocioeconomic variables that should requirefurther investigation at San Juan. The followingis a brief description of the most important fac-tors involved:

A socioeconomic survey was carried out onthe population in direct contact with the SanJuan experimental project by Matos Mar (13).This included, first, the site-worker populationconsisting of eight government workers and theirfamilies. The workers were responsible for theoperation and maintenance of the site and of theponds themselves, and for s i lvicul ture activities(principally growing eucalyptus forests and rec-reational parks) and experimental farming (rais-ing animal food crops for the zoological park).Then there were 16 farm families that had settledon the perimeters of the site itself, occupying36.5 hectares, and that irrigated with treatedeffluents. These families, known locally as theprecarios, were squatters who invaded the siteduring the 1960s and managed to remain despitea constant threat of eviction. The site authoritiesexercised l i t t le or no control over their use ofthe water, nor over their cult ivation or marketingof food or animal forage crops. Immediatelyadjacent to the experimental site, two othergroups (totaling 51 families) settled more re-cently on 171 hectares of desert land. Both ofthese groups take water from raw sewage canalsthat are meant to irrigale nearby greenbelt areas.In all, it has been estimated that 388 people aredirectly involved in sewage reuse activities.

These three local populations use the San Juaneffluents, raw or treated, principally for agricul-ture. Most obtain water for drinking and domes-tic use from vendors who bring it in tankertrucks. Local water application rates for farmirrigation in the desert climate reach about oneliter per second per hectare; the water is appliedby flood irrigation every five to seven days.Crops are grown year-around. Typical total pro-ductivity is in excess of 500 tons per year for

the 16 squatter families at San Juan. The cropsgrown include alfalfa and other forage products,fruit from trees, and horticultural produce (corn,potatoes, onions, tomatoes, squash, beans, cel-ery, and lettuce). Al l of the farm families, with-out exception, raise farm animals such as pigs,cows, goats, chickens, and ducks.

Food crops are consumed directly, sold toneighboring populations, or sold in truckloadsby the growers to intermediaries who in turnmarket them in the nearby slum communities—including the principal markets of San Juan deMirafiores and Vi l l a Maria del Triunfo (13, 14).

Epidemiologic data were collected by Campos(15) from the populations in the districts produc-ing the sewage and from those consuming theproduce from the reuse site. These data showthat the most prevalent infectious diseases in thearea are acute diarrheal diseases (principalagents are rotaviruses, enterotoxigenic and en-teropathogenic E. coli. Campylobacter. Sal-monella, and Shigella); typhoid and paratyphoidfever; viral hepatitis; poliomyelitis; and diseasesinvolving intestinal parasites such as Entamoebahistotytica and Giardia lamhtia. The mortalityand morbidity associated with these diseases inLima are high. For example, in 1978 acutediarrheal diseases caused 10.3 in fan t deaths perihousand l ive births and were ihe leading causeof death among children less than five years ofage in Peru (16). Mortality from typhoid andparatyphoid fever in Peru in 1980 was 1.74deaths per thousand among the total population,the highest in Latin America. 1980 morbidityand mortality data on selected (often waterbome)enteric diseases in Lima are shown in Table 4.

Data collected by Lucas (17) on intestinal para-sites near San Juan indicate that the rate of infec-tion by Ascaris lumbricoides was 31.1% amonga group of 61 subjects from families l iving andworking at the San Juan pond site, while therate in a group of 139 students from a localschool one kilometer from the site was only5.8%. Although the experimental design of thestudy does not permit hypothesis testing, theseresults indicate that a detailed study should beconducted of A. lumbricoides transmissionaround the reuse site.

160 PAHO BULLETIN • vol. 19. no. 2. 1985

Table 4. 1980 Illnesses and deaths from selected enteric diseases in Lima among the generalpopulation and among those less than five years old. (The total Lima population was

approximately 4,447,000 and the population under five was approximately 513,BOO In 1980.)

Reported deaths among:

Diseased)

Acute diarrhea! diseasesTyphoid feverHepatitisPoliomyelitis

The wholepopulation

1.686154

5015

The population0-5 years old

1 .355399

12

Reported case* among:

The wholepopulation

35.8528.1422.574

121

The population()-5 years old

26.4311.0971.156

1 1 7

Suurcr: M. Campos 1/4)

This example and the above dala indicate aneed to be especially cautious, so as to keep thereuse process from creating an addi t iona l l i n kin the chain of transmission of enteric diseases.An epidcmiologic evaluat ion of the role of reusein the transmission of the predominant patho-gens, and the establishment of an adequatelysupervised sanitary code are therefore essentialconditions for continued and expanded reuse on(he Peruvian desert coast.

The economic benefits for developing coun-tries resulting from safe, controlled reuse proj-ects are many: the recovery of arid lands foragr icu l ture ; the creation of employment and set-t lement opportunities; increases in food produc-tion that can help resolve protein deficits andimprove nutr i t ion; the potential for increasedrecreational opportunities and amenities throughthe creation of parks and greenbelts; and thedevelopment of a viable alternative to otherforms of sewage disposal and their correspond-ing pollution and public health problems. TheSan Juan example shows that Lima can considerreuse as a technically and economically feasiblealternative to its current practice of ocean dis-posal. In the near future. Lima will have to makecostly decisions about expanding its sewerageinfrastructure. Lima can spend tens of mil l ionsof dollars building ocean outfalls to protect itsrecreational beaches and fishing areas, or it caninvest those same resources in a large-scale reusescheme that can produce the above benefits.

And. indeed, the very potent ia l of benefi tssuggests that reuse may generate addi t ional re-sources that can help finance (he required t reat-ment ponds.

The public health "risks" of reuse must beviewed in the same l i gh t . Only 43% of the urbanpopulation in Latin America is connected tosewer systems, and of the wastewaters collected,over 90% are discharged direct ly w i t h o u l t reat -ment of any kind (18). In the s lum communi t i esthat everywhere surround the urban centers, ih i ssituation is especially pronounced, and so ex-creta disposal is a pr ior i ty san i t a t ion and h e a l t hproblem. Localized solut ions t h a i involve low-cost sewer systems, waste s t ab i l i za t ion ponds.and reuse may provide better sani tat ion for mi l -lions of urban poor. Also, the fact that indis-criminate reuse takes place anyway out of eco-nomic necessity, as illustrated at the beginningof this paper, highlights the need for well-or-ganized reuse projects with adequate sanitarycontrols. That is. greater public health risk maylie in not considering reuse and fa i l ing to planfor it in tel l igent ly .

Future Research Requirements

Thus far. the San Juan research program hasshown that under tropical conditions wastestabilization ponds in series can provide an effi-cient and effective means of treating domestic

Bartone STABILIZATION PONDS AND WASTEWATER REUSE 161

sewage and removing pathogenic bacteria andparasites. The effluents meet common guide-lines for unrestricted irrigation. Also, the pondscan be designed and operated so as to maintainenvironmental conditions suitable for fish pro-duction. Suitable design criteria have been pre-sented.

Since groundwater constitutes a major sourceof domestic water supply for Lima and the entirePeruvian coastal area, potential groundwatercontaminat ion problems due to inf i l t ra t ion fromtreatment ponds and reuse sites must be eval-uated. Such research is currently being per-formed by the local water supply authorities wi ththe support of the British Geological Survey.The British Overseas Development Agency, andCEPIS.

In order to extract the maximum benefit fromsewage reuse, additional resource recovery andrecycling opportunities must be identified andevaluated. A project recently started involvesthe production of duckweed (Lemmiceac) in theponds and its use as a poultry feed. An evaluationof the sanitary implications is included. Thisresearch is being done by investigators fromU N A , the Nutri t ion Research Ins t i tu te in Lima,and Johns Hopkins Universi ty, with fundingfrom the United States Agency for Internat ionalDevelopment.

Many important public health questions re-main. As already mentioned, more needs to beknown about the epidemiology of sewage reuse.Since classic epidemiologic techniques wouldbe diff icul t to apply, because of the small samplesize and expense, a more straightforward studyhas been proposed (19) to evaluate the healthand nutritional status and socioeconomic stand-ing of the reuse workers and their families. Oneaim is to identify the many direct and indirecthealth benefits from reuse.

Although much is now known about the be-havior of pathogenic bacteria and parasites inthe ponds, no work has been carried out onviruses. Even in the developed countries, thisis a research area that has been greatly neglecteduntil recently. With the emergence of new tech-niques for more easily identifying and enumerat-ing pathogenic viruses associated with sewage,

the author believes that these methods must betransferred to the developing countries asquickly as possible, and that field research mustbe initiated. A project to evaluate the virologicimplications of reuse at San Juan has been sub-mitted for funding.

Finally, there is a need to take a closer lookat the question of the bioaccumulation of toxicsubstances in the treatment and reuse ecosystem.This has not been considered a serious problemat the San Juan complex, since the sewage ismainly of domestic origin. However, the large-scale reuse of Lima wastewatcrs wi th a strongindustr ial component is another matter . A pro-posal has also been put forth to conduct a screen-ing study of the most sensitive biological com-ponents of the reuse ecosystem for evidence oftrace metals and organic toxic substances thatare known to be used in the area.

Technology Transfer

The long-term goal of CEPIS is to apply theinformation obtained through these research ef-forts for the development and transfer of appro-priate technology that w i l l benefit the countriesof the Region. To accomplish t h i s , the Centerseeks to f u l l y integrate research wi th t r a i n i n gand information exchange act ivi t ies , and to es-tablish working l inks between inst i tutes in othercountries conducting similar studies.

In the area of training, over the past four yearsCEPIS has presented an annua l internat ionalpostgraduate short course on waste stabilizationpond design and operation for Latin Americansanitary engineers. An extensive amount of di-dactic material has been produced and distrib-uted as part of the course. Also, environmentalengineers, scientists, and technicians from theRegion have had the opportunity for in-servicetraining on research methods as part of the SanJuan program. In all, 44 professionals and stu-dents have received such training in CEPIS forperiods ranging from a few weeks to 16 months.Six graduate theses have resulted from studentparticipation in the project in coordination with

• national universities.

162 PAHO BULLETIN e vol. 19, no. 2. 1985

On the technical information side, in additionto the production of research reports, articles,theses, and didactic materials, several importantmanuals have been published in Spanish. Theseinclude a manual on experimental methods forevaluating stabilization ponds (20); a mono-graph of the design of waste stabilization pondsunder tropical conditions (8); a manual on chem-ical procedures for the analysis of water andwastewater (5); and a manual on microbiologicprocedures for the analysis of water and waste-water (6). To facil i tate the exchange of informa-t ion , CEPIS also coordinates the Pan AmericanNetwork for Information and Documentation onWater and Sanitation (REPID1SCA). The net-work collects, analyzes, and reports on nat ionall i tera ture in Spanish and Portuguese that deals

with appropriate technology; and CEPIS pub-lishes a quarterly abstract journal of the regionaldocument data base and makes document copyservices available to other investigators (21).

There is a growing interest w i t h i n the Regionin expanding research on low-cost treatment op-tions and sewage reuse. In response to t h i s ,CEPIS/PAHO plans for the coming year to b u i l dup a research network wi th the aim of s t i m u l a t i n gsuch investigations in national i n s t i t u t i ons acrossthe Region and encouraging the exchange ofresults and findings between research engineersand scientists. The participation of leading in-st i tutions in developed countries w i l l also besought when appropriate, so as to encourage thetransfer of information about (he i r experiencesin th is field.

ACKNOWLEDGMENTS

The author grateful ly acknowledges the support of the many in s t i t u t i onsthat have participated in and funded the San Juan research program, as men-tioned in the body of t h i s article. Special recognition is due Dr. Fabidn Ya-nez, who init iated the research program at San Juan and directed the first twophases. The dedication and hard work of the entire CEPIS research team isalso greatly appreciated. The opinions expressed are solely those of the author ,however, and are not necessarily (hose of CEPIS or PAHO.

SUMMARY

The reuse of sewage wastewater for irrigation iscommonplace in many arid and scmiarid zones ofLatin America. The practice involves significanthealth problems, however, and so it is essential thatany reuse project employ at least the minimal effectivesanitary control measures needed to mitigate potentialpublic health risks. To help assess the ability of wastestabilization ponds to provide such control underdesert conditions prevailing along the Peruvian coast,the Pan American Center for Sanitary Engineeringand Environmental Sciences has been conducting ex-tensive field and laboratory studies at waste stabiliza-tion ponds of the San Juan de Miraflores sewage reuseproject on the southern outskirts of Lima. This articleprovides a descriptive overview of those studies.

The first phase of the work, begun in 1977, eval-uated the effects obtained with four sets of two pondsin series receiving average organic waste loads of400, 600. 800, and 1,000 kilograms of BOD perhectare-day. Among other things, the results indicatedthat while BOD removals were consistently high, notall pathogenic protozoa were removed by two pondsin series with a minimum detention time of 5.5 days,that 36 days of detention time were not enough todestroy all Salmonella species, and that certain Sal-monella serotypes isolated demonstrated resistance toantibiotics.

The second phase of the work, using two sets ofthree ponds in series and one set of four ponds inseries, focused primarily on pathogen survival. Over-

Bartone • STABILIZATION PONDS AND WASTEWATER REUSE 163

al l , the data tended to confirm that stabilization pondsin series remove fecal coliforms more efficiently thanmost other treatment processes. They also indicatedthat detention periods on the order of 20 days shouldmake it feasible to obtain E. coli levels below 1.000MPN per 100 ml. In addition, the results suggestedthat pond systems which produce a ten-thousand-foldreduction in fecal coliforms will remove virtually allpathogenic protozoa and he lmin th eggs as well. Intropical climates maximum detention time can beachieved by appropriate design of rectangular ponds.

The third phase of the study, which used one setof four ponds in series and one set of five, dealt withproduction of fish (Tilapia niloiica) and prawns (Ma-crohrachium rosenhergii) in ponds beyond (he sec-ondary maturation ponds. Preliminary results of thiswork have indicated that adequate environmental con-

ditions for raising fish could be maintained in ad-vanced "polishing" ponds such as these, but prawnproduction could be affected by low dissolved oxygenand high ammonia conditions.

At the same time, epidemiologic data from Limaindicate that acute diarrhea! diseases and parasiteinfections are prevalent in the population of the studyarea. This situation indicates a need for special cau-tion—so as to keep the sewage reuse process fromcreating an additional avenue for transmission of en-teric diseases. However, the potential economic ben-efits of reuse are considerable; and the fact that indis-criminate reuse takes place anyway in many placessuggests that the greatest public health risk may beincurred by not considering reuse and fa i l ing to planfor it i n t e l l i gen t l y .

REFKRENCKS

(1) Economic Commission for La t in America.Management and Environment in Latin Amer-

ica . I n : Water Development Supply and Management.(Volume 12). Pergamon Press, Oxford. 1979.

(2) Court Moock, L., H. Bac/,a-Sommers, and R.Gome/. Dia/. Intensif icat ion of water use from theMaipo River , Chile. In: United Nations. EconomicCommission for Lat in America. Water Managementand Knvironmeni in Latin America. Pergamon Press,Oxford. 1979, pp. 259-272.

(3) Direccion General de Usos de Agua. Reusodel agua en la ag r i cu l tu ra . Secretaria dc1 RecursosHidraul icos , Mexico Ci ty , 1974.

(4) Yane/., F.. R. Rojas, M. L. Castro, and C.Mayo. Evaluation of the San Juan StabilisationPonds: Final Research Report of the First Phase. PanAmerican Center for Sanitary Engineering and En-vironmental Sciences, Lima, 1980.

(5) Esparza, M. L. Procedimienlos simplificadosde analisis qui'micos de aguas residuales. TechnicalDocument Scries. No. 10. Centro Panamericano deIngenien'a Sanitaria y Ciencias del Ambiente. Lima,1983.

(6) Mayo, C. Procedimientos simplificados deandlisis microbio!6gicos de aguas residuales. Techni-cal Document Series, No. 12. Centro Panamericanode Ingenien'a Sanitaria y Ciencias del Ambiente.Lima. 1984.

(7) Yanez, F. Indicator and Pathogen OrganismsDie-away in Ponds under Tropical Conditions. Paperpresented at the 56th Annual Conference of the WaterPollution Control Federation, Atlanta. 2-6 October1983.

(8) Ydnez. F. Avances en el tratamiento de aguasresiduales por lagunas de estabilizaci6n. Technical

Document Series, No. 7. Centro Panamericano deIngenien'a Sani tar ia y Ciencias del Ambiente . Lima,1982.

(9) Burgers, L. Temperature behavior in s tab i l iza-tion ponds under tropical conditions. Pan AmericanCenter for Sanitary Engineering and EnvironmentalSciences. Lima, 1982.

(10) Lloyd. B. J. Lagoon Treatment of Sewageand the Health Risks Associated w i t h the Surv iva l ofEnteric Pathogens, wi th Particular At ten t ion to Coas-tal Peru. Unive r s i ty of Surrey. United Kingdom.1982.

I l l ) Bartone, C. R . . M. L. Espar/a, C. Mayo.O. Rojas, and T. V i tko . Moni tor ing and Maintenanceof Treated Water Qual i ty in the San Juan LagoonsSupporting Aquaculture: Final Report of Phases MI.Pan American Center for Sanitary Engineering andEnvironmental Sciences, Lima. 1984.

(12) World Health Organization. Reuse of Ef-fluents: Methods of Wastewater Treatment and HealthStandards. WHO Technical Report Series. No. 517.Geneva, 1973.

(J3) Matos Mar, J. Informe sobre la situaci6nsocio-econdmica de las familias que utilizan las aguasde las iagunas de San Juan de Miraflores. Institutode Estudios Peruanos, Lima. 1984.

(14) Zapater, J. M. Reuso de aguas residualespara riego en la zona de Lima Melropolitana. Univer-sidad Nacional Agraria, La Molina, 1983.

(15) Campos, M. Cuadro epidemiol6gico de lasenfermedades infecciosas relacionadas a la disposi-ci6n de excretas en Lima Metropolitans. Instituto deMedicina Tropical "Alexander von Humbolt," Lima,1984.

(16) Pan American Health Organization. Health

164 PAHO BULLETIN • vol. 19, no. 2. 1985

Conditions in the America*. 1977-1980. PAHO Sci-entific Publication No. 427. Washington, D.C.,1982.

(17) Lucas, C. Prevalencia de parasites humanosenteYicos en la zona de San Juan. Thesis. Universidadde Lima. 1980.

(18) Bartone, C. R.. and H. J. Salas. Developingalternative approaches to urban wastewater disposalin Latin America and the Caribbean. Bull Of SanitPanam 18(4):323-336, 1984.

(19) Bartone. C. R., B. Cvjetanovic, and T.Schorr. A Protocol for the Epidemiological andSocioeconomic Investigations of Health Impacts from

ihe Use of Treated Effluents for Irrigation in San Juande Miraflores. Pan American Center for Sanitary En-gineering and Environmental Sciences, Lima, 1984.

(20) Yinez, F. Manual de metodos experimen-tales: Evaluaci6n de lagunas de estabilizacicm. Tech-nical Series. No. 24. Pan American Health Organiza-tion/Pan American Center for Sanitary Engineeringand Environmental Sciences. Lima, 1982.

(21) Bartone, C. R. Planning regional document-delivery services for the Water Decade: The LatinAmerican and Caribbean Region. UNESCO Journalof Information Sciences 4(4):253-262. 1982.

ROTARY INTERNATIONAL PROMOTES IMMUNIZATION ACTIVITIES

The Rotary Foundation, an international nonprofit corporation, has provided overa mi l l ion dollars in grant funds since 1979 to support Lat in American Health M i n i s t r i e s 'expanded programs on immuniza t ion , in coordination wi th PAHO and other agencies.

In 1982, the Board of Directors of Rotary Internat ional (a worldwide associationof Rotary clubs) set a goal to collaborate in the immunizat ion.of all the .world's chi ldrenagainst polio by 2005, the hundredth anniversary of Rotary, and since then workdirected toward this goal has been carried out in 19 Lat in American. Afr ican . As i an ,and Western Pacific countries. Rotary Internat ional has. to dale, awarded a tota l ofUS$7.6 mi l l ion in grants for tha t purpose.

Providing expert advice for polio i m m u n i z a t i o n is but one e lement of Rotary's Polio2005 campaign. The organization has also pledged to raise U S S I 2 0 m i l l i o n to fundexperts, vaccines, and equipment .

Up to now. Rotary In ternat ional has supported the following countries in c;irryiiii!out EPI work, in coordination with PAHO:

Country

BelizeBoliviaCosta RicaEl SalvadorGuatemala

Rotary grant(US$)

5 1 .200104,00050.000

247.000374.000

Country

HaitiHondurasPanamaSt. Lucia

Rotary (iranl(USS)

196.000207.000537.00066.000

Persons and institutions interested in this work may obtain further information bywriting to The Rotary Foundation, 3-H, 1600 Ridge Ave., Evanston, Illinois 60201,U.S.A.

Source: Pan American Health Organization, EPI Newsletter 7(2):2-3. 1985.