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 University 36 Small Flows Quarterly, Spring 2005, Volume 6, Number 2 Abstract 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, Shigella species, Escherichia coli, 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 100 percent of the influent helminth egg concentrations and satisfy the World Health Organization microbiological guidelines for Category B irrigation with wastewater effluents. Shigella species were not detected, and Escherichia coli and fecal coliform removal were highly variable. The removal of BOD5 and SS was typical for stabilization pond systems, and organically overloaded ponds did not exhibit significant difference from underloaded ones. Sludge analyses showed that all pond sludges are heavily 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 Author’s Note: The perspective presented in this paper is far removed from the technical and regulatory context of wastewater treatment as practiced in the U.S. The paper’s purpose is to present to the readers of the Small Flows Quarterly the problem of excreta-related infections in developing countries and the goal of effective wastewater treatment as a public health imperative using a natural system technology in a way distinct from the U.S. experience. A common scene in Latin America: raw sewage flowing down a street in an urban development near Tegucigalpa, Honduras. Wastewater Treatment Worldwide TABLE 1 Wastewater Treatment Worldwide • There are approximately 4 bil- lion cases of diarrhea each year, causing 2.2 million deaths, mostly among children, from diseases associated with lack of safe drinking water, inadequate sanitation, and poor hygiene. • Intestinal worms (helminths) in- fect at least 10 percent of the population of the developing world (WHO/UNICEF, 2000), and likely infect up to 24 per- cent of the world's population (Chan, 1997). • Protozoan infections probably exhibit a similar prevalence to helminths, and Entamoeba his- tolytica infection is one of the 10 most common infections in the world (Savioli, L. et al., 1992). • Lack of wastewater treatment is a health hazard in all developing countries. With the exception of the U.S., Canada, and some Euro- pean countries, the median per- centage of urban wastewater treat- ed worldwide is very low as seen in Table 1. • The discharge of untreated wastewater is especially a health hazard where receiving waters are used for drinking water sources, bathing, washing, irri- gation, and fisheries. • Conventional wastewater treat- ment methods as practiced in the U.S. and Europe are not afford- able in developing countries (which is the main reason why they don't exist), nor do they nec- essarily provide the requisite de- gree of pathogen removal for the protection of public health, espe- cially parasitic infections. As a result of the above situa- tion, the professional community concerned with sanitation and public health in developing coun- countries in the Western Hemi- sphere with typically high preva- lence rates of excreta-related infections. Wastewater Treatment Issues Outside the U.S. Global Status of Excreta-Related Infections and Wastewater Treatment The provision of drinking water supply, sewerage, and wastewater treatment for communities throughout the world has been a major component of development projects financed over the last 20 years. This effort started with the International Drinking Water Sup- ply and Sanitation Decade move- ment (1981 to 1990), which was spearheaded by the World Bank (Cairncross and Feachem, 1993). During the 1990s, the WHO and the United Nations Children’s Fund (UNICEF) formed the Joint Monitoring Program for Water Supply and Sanitation, whose overall aim was to improve plan- ning and management within countries by support in monitor- ing the water supply and sanita- tion sector (WHO/UNICEF, 2000). The WHO/UNICEF Joint Monitor- ing Program has presented four assessment reports (1991, 1993, 1996, and 2000). The findings of the latest report (WHO/UNICEF, 2000) can be summarized, in part, as follows with additional infor- mation cited from other sources: • Worldwide approximately 1.1 billion people lack access to im- proved water sources. • Approximately 2.4 billion peo- ple have no access to any form of improved sanitation. • Excreted-related infections are a major cause of morbidity and mortality worldwide. Small Flows Quarterly, Spring 2005, Volume 6, Number 2 37 J U R I E D A R T I C L E While there is much interest on natural systems for wastewater treatment (WEF, 2001) or decentral- ized wastewater management sys- tems (Crites and Tchobanoglous, 1998), and while lagoon or waste stabilization pond systems are sub- sumed within these categories, it is clear that in the U.S., pond systems have long fallen out of favor as a treatment 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 recently published revised editions of its constructed wetlands and onsite wastewater design manuals (EPA, 2000 and 2003), it is doubtful that the waste stabilization pond design manual published over 20 years ago (EPA, 1983) will ever be revised. Outside the U.S. it is a quite different story. Waste stabilization pond systems have long been pro- moted in developing countries as the only viable option to help solve the devastating problem of excreta-related disease transmis- sion at an affordable cost (Cairn- cross and Feachem, 1992; CEPIS/ OPS, 2000; Egocheaga and Moscoso, 2004; Feachem, et al., 1983; León and Moscoso, 1996; Mara, 2004; Rolim, 2000; Shuval and Fattal, 2003; and Shuval, et al., 1986). Pond systems in devel- oping countries are typically de- signed for pathogen removal and agricultural reuse using epidemio- logically-based guidelines, such as the World Health Organization’s (WHO) microbiological guidelines for wastewater use in agriculture and aquaculture (WHO, 1989). This approach for wastewater treatment is distinct from that taken historical- ly in the U.S. and Europe and is es- pecially distinct from the current focus of U.S. regulation at the state and federal level. The purpose of this paper is to discuss the issue of wastewater treat- ment from the perspective of devel- oping countries in Latin America and to present a detailed case study, including extensive monitoring re- sults, of stabilization pond use in Honduras—one of the poorest Small Flows Quarterly, Spring 2005, Volume 6, Number 2 38 J U R I E D A R T I C L E tries has long conclud- ed that the principal objective of wastewater treatment in areas where excreta-related infections are endemic should be the removal of pathogens using low- cost appropriate tech- nologies, and that gen- erally the most appropri- ate technology is a waste stabilization pond sys- tem (Cairncross and Feachem, 1992; CEPIS/OPS, 2000; Egocheaga and Moscoso, 2004; Feachem, et al., 1983; León and Moscoso,1996; Mara, 2004; Rolim, 2000; Shuval and Fat- tal, 2003; Shuval, et al., 1986; and WHO/ UNICEF, 2000). The pathogen removal efficiencies of various treatment processes as gen- erally cited in the literature are shown in Table 2. This focus on pathogen removal with stabilization pond systems is distinct from the historical objectives of wastewater treatment in devel- oped countries and is especially far removed from current focus on more stringent effluent regulations with the use of increasingly more costly and complicated technolo- gies in the U.S. Nevertheless, the sheer magnitude of the problem of public health and wastewater treatment in developing countries necessitates a different approach (Figure 1 graphically shows the Removal of Pathogens and Conventional Parameters in Various Treatment Processes TABLE 2 FIGURE 1 Per Capita Gross National Product for the United States, Mexico, and Central America in US Dollars - Year 2000 Gross National Product Per Capita US Dollars gap in per capita gross national product among the U.S. and vari- ous countries of Latin America, which underscores the need for low-cost solutions not used in the U.S.). In fact, the focus on stabi- lization ponds for developing countries is within the same spirit of the interest in natural systems for wastewater treatment in the U.S., with emphasis on natural environmental components to provide 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 this context, it is worthwhile to quote from the classic text, Sanitation and Disease, published over twenty years ago and still relevant today for the problem of wastewater treat- ment in developing countries: “Those whose job is to select and design appropriate systems for the collection and treatment of sewage in developing countries must bear in mind that European and North American practices do not represent the zenith of scien- tific achievement, nor are they the product of a logical and rational design process. Rather, treatment practices in the developed coun- tries are the product of history, a history that started about 100 years ago . . .. Conventional sewage works were originally de- veloped in order to prevent gross organic pollution in European and North American rivers; they were never intended to achieve high removal of excreted pathogens. Their use in tropical countries in which excreted infections are en- demic is only justifiable in special circumstances, for there is an al- ternative treatment process much superior in obtaining low survivals of excreted pathogens—the waste stabilization pond system.” (Feachem, et al., 1983, pp. 63–64) The Situation in Latin America It 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 is further estimated that only 3,100,000 m3/day of this waste- water, or 6 percent of what is gen- erated, receives secondary treat- ment before being discharged into surface waters or reused directly in agriculture or aquaculture (Egocheaga and Moscoso, 2004). Of all the capital cities from Mexi- co City to Buenos Aires, the vast majority do not treat their waste- waters, to say nothing of the thou- sands of smaller cities throughout the region. Surface waters—rivers, streams, lakes and coastal areas— are widely contaminated with raw wastewater discharges throughout Latin America. The problem of wastewater treatment is exacerbated by severe shortages in water quantity for agriculture. Throughout Latin America, there has been an histor- ical tendency to use either raw or diluted wastewaters for irrigation and aquaculture, and it is estimat- ed that at least one million hectares are irrigated with these contaminated sources (Egocheaga and Moscoso, 2004). The effects on public health of excreta-related in- fections have been devastating and have even had deleterious ef- fects on disease morbidity within the U.S. The following examples are typical and illustrate how the magnitude of the problem is not only local, but also affects popula- tions throughout the hemisphere: • The cholera epidemic, which began in Peru in 1991, produced 1,199,804 cases with 11,875 deaths between 1991—1997 in 20 countries including the U.S.; it is estimated that the epidemic cost the country of Peru one billion U.S. dollars in tourism and expor- tation of agricultural products in only 10 weeks (OPS, 1998). The epidemic was caused by the con- sumption of drinking water and food products contaminated with raw sewage. Cholera, which had not been present in the Western Hemisphere for over 100 years, is now endemic in various countries in Latin America. • Five outbreaks of cyclosporiasis from 1995 to 2000 in the U.S. and Canada caused by the emerging protozoan pathogen, Cyclospora cayetanensis, have been linked to raspberries imported from Guatemala (Bern, et al., 1999; Ho et al., 2002). It is as- sumed that the raspberries were irrigated or washed with either raw sewage or sewage-contami- nated water. The principal route of transmission of Cyclospora in- fections in Guatemala is the water-borne route (Bern, et al., 1999). • The largest epidemic of hepati- tis A in the history of the U.S. occurred in 2003, with more than 700 cases in 4 states, all linked to green onions import- ed from two farms in Mexico (Fiore, 2004). It is assumed the onions were contaminated with the virus through irrigation or washing with either raw sewage or sewage-contaminated water (Fiore, 2004). Surface waters obviously play a significant role in the continued transmission of excreta-related in- fections, since they are commonly used for bathing, washing, drink- ing water supply, crop irrigation, and the consumption of fish and shellfish. Professional judgment regarding the principal objective of wastewater treatment in the re- gion dictates the removal of fecal pathogens as the first priority of wastewater treatment. This con- clusion has been reached many times, and most recently by an exhaustive study of wastewater pollution, treatment, and reuse throughout Latin America pub- lished by the Pan American Cen- Small Flows Quarterly, Spring 2005, Volume 6, Number 2 39 J U R I E D A R T I C L E Raw sewage contaminates the streets of Latin America. This photo was taken in the town of Danlí, Honduras. ter for Sanitary Engineer- ing and Environmental Science (Egocheaga and Moscoso, 2004). The study concludes that the proper management of domestic wastewater in Latin America should focus on public health as a first priority, with the removal of pathogens as the principal objective of wastewater treatment. The study also concludes that in order to resolve the problem of agricul- tural demand for water and the sustainability of wastewater treatment in impoverished cities, treatment of wastewater focusing on pathogen re- moval should be inte- grated with the produc- tive reuse of the treated wastewater (Egocheaga and Moscoso, 2004; CEPIS/OPS, 2000). The study concludes that the best available technology for accomplishing this goal is wastewater stabi- lization pond systems, which can most easily meet the WHO guide- lines for wastewater reuse in agri- culture than any other technology. The WHO guidelines are shown in Table 3. Case Study of Honduras Background The provision of water supply and sewerage services for Honduras has been a major component of de- velopment projects financed over the last 15 years. Approximately 81 percent of the estimated total popu- lation of 6.7 million has access to drinking water, and 70 percent has access to sanitation services (OPS, 2002). In spite of these efforts in the public health sector, however, excreta-related infections are still a major cause of morbidity and mor- tality. The cholera epidemic, with over 15,378 cumulative cases dur- ing 1991 to 2000, and the contin- ued high morbidity of intestinal protozoan and helminth infec- tions as shown in Table 4, under- score the persistent public health problems (Girard de Kaminsky, Small Flows Quarterly, Spring 2005, Volume 6, Number 2 40 J U R I E D A R T I C L E age projects within Honduras now require wastewater treatment as a necessary component. It has been generally assumed by the professional community in Honduras that waste stabilization ponds are the treatment option of choice because of their effective- ness in pathogen removal and their 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 Agriculture TABLE 3 1996; OPS, 1998, 2002). Surface waters play a significant role in the continued transmission of excreta-related infections, since the vast majority are polluted with wastewater discharges and are commonly used for bathing, washing crop irrigation, and fish and shellfish harvesting. In an at- tempt to ameliorate the problem, all internationally financed sewer- signed in series (Mara, 2004), which is an added capital and operational expense that should be technically justifiable in poor communities. Because no local data have been available show- ing specific pathogen removal in pond systems, there has been much confusion among profes- sionals and the public in Hon- duras as to what type of design is most appropriate for local conditions. Small Flows Quarterly, Spring 2005, Volume 6, Number 2 41 J U R I E D A R T I C L E Approximately 21 waste stabiliza- tion pond systems have been con- structed in the last 10 years. The ma- jority of the pond systems were funded by USAID-Honduras through its Municipal Development Project. This program, which has as its pri- mary goal the institutionalization of more responsive and effective mu- nicipal government, works with 34 municipalities representing 50 per- cent of the Honduran population. Figure 2 shows a typical design of a pond system, which consists of two facultative ponds in parallel (so one can be taken out of service for desludging), followed by one or two maturation ponds in series. Issues With Effluent Guidelines The environmental protection agency 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 grit chamber for pre-treatment, with a battery of two facultative ponds in parallel followed by two maturation ponds in series. Facultative ponds are designed in parallel so one can be taken out of service for desludging every 5 to 10 years. Faculative Pond Faculative Pond Final Effluent Pretreatment Influent Maturation Ponds in Series with Baffles for Plug Flow TABLE 5 Effluent Standards Promulgated in Honduras Manually cleaned horizontal grit chambers—a technology no longer in use in the U.S.—are used for pretreatment because of high grit loads in sewer systems that can prematurely fill ponds. (León, Nicaragua) dards for municipal wastewater dis- charges that are shown in Table 5. The standards, which are arbitrary, focus on fecal coliforms and do not address specific pathogen removal, which is much more important where excreta-related infections are endemic (Feachem, et al., 1983; Mara, 2004). It is difficult to meet fecal 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 Small Flows Quarterly, Spring 2005, Volume 6, Number 2 42 J U R I E D A R T I C L E Issues With Operation and Maintenance and Sustainability The responsibility for operation and maintenance of pond systems lies with the municipalities. In an attempt to avoid the problem of abandoned 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 for professionals, operators, and the general public. This is a continuing process that requires a long-term commitment. There are many insti- tutional factors that cannot be changed easily, such as the ability and political resolve of the munici- pal governments to charge fees for sewerage and wastewater treatment, and to maintain adequately trained personnel on staff. As an example of the difficulties involved in what would appear to be a simple task, at present, there is not one pond in- stallation in Honduras where an operator measures flow rates at all—let alone on a routine and documented basis. Objectives As a result of the problems men- tioned above, USAID-Honduras de- cided to fund a monitoring study for wastewater stabilization pond in- stallations. The objective of this study was to monitor 10 wastewater stabilization pond systems from dif- ferent climates throughout Hon- duras during the dry season (March, April, May) and wet seaon (Septem- ber, October, November) to develop a local database for improving de- sign parameters and operation and maintenance requirements and to assess the long-term sustainability of systems in the municipalities. It was also planned that this study would help contribute to the development of effluent standards for specific pathogen removal rather than fecal coliform removal, and that con- crete recommendations based on the results could be made for the minimum number of ponds that should be designed in series to re- move specific pathogens, with the goal that the final effluent could be used for agriculture or aquaculture to help foster sustainability. It was hoped that the conclusions would more adequately address the serious public health issues facing financial- ly-strapped municipalities with pop- ulations from 1,000 to over 100,000 persons. Methodology Project Design Ten pond systems were selected at varying locations throughout the country. Eight systems were facultative-maturation pond con- figurations, one an anaerobic-facul- tative pond configuration, and one an anaerobic-facultative-maturation pond configuration. All systems were visited for five consecutive days during the dry and wet sea- sons. Two days were used for the collection of support information, which included age of the system, original design population, physical condition, estimation of accumulat- ed sludge volume using bathymetric methods, level of operation and maintenance, and an evaluation of the long-term sustainability based on municipal support. Each system was then monitored diurnally for three consecutive days. The influent flow rate was con- tinuously monitored using an ISCO area-velocity flow meter, which al- lowed an accurate measurement of peak, minimum and mean flow rates. The influent and effluent of each pond within the system were sampled for helminth eggs, Shigella species, Escherichia coli, 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 pond system, whether anaerobic or fac- ultative, were taken with a dredge and analyzed for helminth egg concentrations and percentage total, fixed, and volatile solids. Rationale for Parameter Selection A major objective of the proj- ect was to monitor pathogens endemic in Honduras using the capabilities of local laboratories, with the idea that routine moni- toring could be continued in the future. Fortunately, one national laboratory within the Secretary of Natural Resources and Environ- ment has the capabilities to ana- lyze water and sludge samples for helminth eggs on a routine basis using a methodology originally developed in Mexico; they can- not, however, distinguish viable from nonviable eggs. Unfortu- nately, the only other analyses in water samples that could be per- formed within the limits of this study on a routine basis by local laboratories were Shigella species (presence-absence test), and the nonpathogenic indicators Es- cherichia coli and fecal coliforms. While it would be highly desir- able to monitor for a protozoan pathogen, there are no laborato- ries in Honduras able to perform the analyses in water samples at this time. The final selected parameters A barefoot boy spearfishing in sewage-contaminated water near Iquitos, Peru. lated hydraulic retention times, mean influent BOD5 concentra- tions, and organic surface loading rates. Basing the measured influ- ent flow rate on the original de- sign populations, the calculated per capita flow rates ranged from 92 to 514 liters per person per day (Lppd), and the majority are much higher than the typical de- sign assumption of 100 to 120 Lppd. The higher flows are likely due to increased connections due to population growth, illegal con- nections from commercial and in- dustrial sources, and inflow and in- filtration into the sewer system. The increase is significant from what was originally assumed in the design and exemplifies the resilien- cy of pond systems for developing countries—mechanical systems such as activated sludge could never handle such an increase over the original design flow. As a result of the higher meas- ured flow rates, the calculated hy- draulic retention times are shorter and the organic surface loading rates higher than anticipated from the original designs. Only two fac- ultative pond systems satisfied the Small Flows Quarterly, Spring 2005, Volume 6, Number 2 43 J U R I E D A R T I C L E Results of Measured Flow Rates, Hydraulic Retention Times, and Loading Parameters for Monitored Pond Systems TABLE 6 for pathogens were, therefore, helminth eggs in water, sludge samples, and Shigella species (pres- ence-absence) in water. Escherichia coli and fecal coliforms were also chosen, despite their limitations for indicating pathogen removal, be- cause they could be easily moni- tored routinely in water samples and used for comparison with other studies in the literature. It was also hoped that Escherichia coli would be more representa- tive of bacterial removal than fecal coliforms. The conventional parameters of SS, BOD5, pH, temperature and dissolved oxygen were selected to assess system performance in terms of organic loadings. Sludge samples at the entrance to each primary pond system, whether anaerobic or facultative, were taken with a dredge and analyzed for helminth egg concentrations and percentage total, fixed, and volatile solids. The objective of sludge sampling was to estimate degradation and accumulation rates, the extent of grit entering the system, and the public health risks of sludge handling due to helminth egg concentrations. Sampling and Analytical Methods With the exception of the helminth analyses, all samples were analyzed according to Standard Methods (APHA, 1995). The samples for helminth eggs, SS, and BOD5 were 24-hour flow-weighted com- posites, while those for Shigella species, Escherichia coli and fecal col- iforms were grab samples taken at different times throughout a 24- hour period. The sludge samples were taken daily with the dredge (approximately 1.0 L) over the three-day period at the entrance to each pond where sludge depth was estimated to be greatest; this method is limited and was meant only to give a rough idea of sludge characteristics since sludge cores give a much more accurate account of deposition and decomposition processes and helminth survival rates (Nelson, et al., 2004). Results Flow rates, Hydraulic Retention Times, and Organic Loading Rates Table 6 presents the results of pond flow rate monitoring, calcu- WHO guideline of an eight- to 10-day minimum deten- tion time for helminth egg removal; nevertheless, as will be discussed below, all of the systems met the WHO guidelines for 100 percent helminth egg re- moval. The mean influent BOD5 was found to vary greatly among systems, ranging from 71 to 437 mg/L. As a result of higher than expected flow rates and influent BOD5 values, the organic surface loading rates of the majority of fac- ultative ponds exceeded the estimated maximum load- ings for the latitudes and climates of Honduras, which is estimated to be be- tween 280 to 350 kg BOD5/ha/day as shown in Figure 3. In spite of this, the overall BOD5 re- moval was about what would be expected for normally loaded sta- bilization pond systems as dis- cussed below. Once again this shows the resiliency of pond sys- tems to handle widely varying load- ing rates and still maintain ade- quate treatment levels. Table 6 also shows that those ponds that were designed as anaerobic ponds (Danlí and Tela) were operating below the range of optimum volumetric loading rates for anaerobic ponds of 100 to 300 g BOD5/m3/day, and that one overloaded facultative pond (Catacamas East), was approaching the volumetric loading of an anaer- obic pond. Nevertheless, none of these ponds exhibited odor prob- lems, and their performance was similar to the other, lesser loaded ponds, again demonstrating the re- siliency and wide margin of safety typical of pond systems. Helminth Egg Removal Table 7 shows the results of helminth egg monitoring. The arithmetic mean concentration of helminth eggs in raw wastewater ranged from 9 to 744 eggs/L. The helminths found in raw waste- water and sludges were, in order of abundance, Ascaris lumbricoides, Trichuris trichiura, and Anquilos- tomas (hookworm), and reflect the prevalence of helminth in- Small Flows Quarterly, Spring 2005, Volume 6, Number 2 44 J U R I E D A R T I C L E Helminth Egg Removal Wastewater Stabilization Pond Systems in Honduras TABLE 7 and Villanueva), all of the faculta- tive ponds removed 100 percent of the influent helminth eggs. The ponds at Danlí and Vil- lanueva were anaerobic and likely fections found in the general population. (Examples of eggs found in raw wastewater are shown in Plate 1.) With the excep- tion of three ponds (Danlí, Pajuiles, Organic Surface Loading Rate Versus Influent BOD5 for Various Hydraulic Retention Times (HRT) FIGURE 3 Points represent systems monitored. did not achieve 100 percent removal as a re- sult of insufficient hy- draulic detention time or resuspension with rising gases from anaer- obic digestion. The car- ryover of helminth eggs in the facultative pond at Pajuiles could have been due to the burrow- ing activity of turtles or crocodiles observed in the pond. Table 7 also shows the results for helminth egg concentrations in facultative or anaerobic pond sludges. The con- centrations ranged greatly among systems, from a mean of one egg per gram dry sludge at Tela to 4,473 eggs per gram dry sludge at Pa- juiles. Although no dif- ferentiation was made between viable and nonviable eggs, the re- sults in Table 7 leave no doubt that pond sludges pose a serious health risk with helm- inth eggs and need to be properly managed during pond desludging operations and ultimate disposal. Shigella Species The presence of Shigel- la species was not detect- ed throughout the study. One of the problems with measuring bacterial pathogens is that they are likely pres- ent in wastewater only during an outbreak or epidemic episode; after the episode passes they are only present in asym- ptomatic carriers in very small concentrations that are difficult to detect in wastewater. Fecal Coliforms and Escherichia coli The results of fecal coliform and Escherichia coli log10 removal are shown in Table 8 and Small Flows Quarterly, Spring 2005, Volume 6, Number 2 45 J U R I E D A R T I C L E At least four maturation pond systems have crocodiles, which feed on turtles and birds. Frogs are also abundant in several maturation pond systems. (Santa Cruz 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 throughout Honduras, which illustrates the widespread problem of infections. Because there is no immunity to parasitic infections, as long as the environment is contaminated transmission will continue to occur. Eggs are approximately 50 µm in diameter, a size that can easily be removed by sedimentation in facultative ponds. Photos courtesy of Dr. Gilberto Padilla Small Flows Quarterly, Spring 2005, Volume 6, Number 2 46 J U R I E D A R T I C L E Figures 4 to 7. For facultative ponds it appears that it may be possible to achieve a 2.0 log10 removal of both fecal co- liforms and E. coli if the hydraulic detention time is greater than 10 days. The maturation pond results (Figures 6 and 7) are much more inconsistent and do not show a correlation between hydraulic detention time and bacteria re- moval. These results exemplify the difficulty in using fecal col- iforms or Escherichia coli as indi- cators of bacterial pathogens for wastewater as has been reported in the literature (Feachem, et al., 1983; and Mara, 2004.) Conventional Wastewater Constituents The conventional wastewater constituent analyses of BOD5 and SS (Table 8) show that each pond system is functioning as would be expected in terms of performance and removal efficiencies, in spite of being loaded above their origi- nal designs. Dissolved oxygen analyses and visual inspection showed that four as-designed facul- tative ponds (Catacamas East, Mo- rocelí and Villanueva) were not facultative and were functioning as anaerobic ponds. In spite of being anaerobic, however, the ponds per- formed well in terms of removal of BOD5, SS, fecal coliforms, Escherichia coli and helminth eggs, and they did not have any serious odor problems. Solids Analyses in Facultative Sludges Desludging of ponds has been found to be a significant expense for poor municipalities if it is not planned for and budgeted years in advance (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 Table 9 show that the per- cent total solids ranged from 11.6 to 15.5 percent, volatile solids from 23.9 to 31.4 percent, and fixed solids from 68.0 to 76.1 per- cent. The high percentage of fixed solids is a result of the effect of in- organic solids entering the ponds from lack of grit chambers. The volume of sludge in each facultative pond was measured by Summary of Monitoring Results for E. coli, Fecal Coliforms, BOD5, and SS for all Systems Monitored, Wet and Dry Seasons TABLE 8 solids analyses by assuming that pond sludge without grit should have a volatile solids content of approximately 50 percent after di- gestion (Metcalf and Eddy, 2003). The results in Table 9 show that sludge accumulation rates per 1,000m3 of wastewater treated are taking soundings on a grid from a launch. Sludge accumulation rates were then calculated by using the measured flow rates and the num- ber of years the pond system had been in operation. Grit accumula- tion rates were then estimated from the results of the sludge Removal of Escherichia coli in Facultative Ponds in Honduras FIGURE 5 Fecal Coliform Removal in Faculative Ponds in Honduras FIGURE 4 47 J U R I E D A R T I C L E Removal of Escherichia coli in Maturation Ponds in Honduras FIGURE 7 Small Flows Quarterly, Spring 2005, Volume 6, Number 2 Summary of Results for Primary Pond Sludges TABLE 9 Fecal Coliform Removal in Maturation Ponds in Honduras FIGURE 6 Summary of Physical Condition, Operation and Maintenance, and Sustainability Issues in Monitored Systems TABLE 10 an order of magnitude lower than accumulation rates from conven- tional processes (Metcalf and Eddy, 2003), which is another ad- vantage of stabilization ponds since sludge handling is kept to a minimum. If facultative ponds are not 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 of total sludge accumulation as shown in Table 9. While this does not appear to be significant, dur- ing storm events, significant quantities of grit can enter pri- mary ponds and cause blockages at inlets, and even prematurely fill a pond (Oakley, et al., 2000). For this reason it is recommended that grit chambers be installed in all systems. Physical Condition, Monitoring, Operation and Maintenance, and Sustainability Issues Table 10 presents a summary of the physical conditions, moni- toring, operation and mainte- nance, and sustainability issues encountered in the systems as- sessed in this study. Most installa- tions are physically well main- tained, but many are hydraulically and organically overloaded without accurate flow measuring devices and grit chambers. At least three installations are in urgent need of desludging. Monitoring in all installations is nonexistent, and nowhere are flow rates measured or samples taken for laboratory analysis. The few installations where attempts were made to measure sludge ac- Discussion and Conclusions In a country such as Honduras, where wastewater treatment es- sentially does not exist, the only realistic option that has a possibil- ity of success in helping solve seri- ous public health problems is the introduction 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 needs and conditions. The results of this project have enabled the following observations and conclusions to be drawn. Effluent Standards and Wastewater Reuse Parasitic infections, such as helminth infections, are the major public health problem related to excreta-related infections as indi- cated in the ubiquitous presence of 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 routinely monitored in local laboratories, it makes more sense to initially orient treatment objectives and effluent standards on helminth egg removal rather than on an arbitrary level of fecal coliform concentration that has no demonstrated relation to problem pathogens, and which is difficult to achieve without design- ing numerous ponds in series. Using this conceptual framework, waste- water treatment in municipalities using two ponds in series can easily meet WHO´s Category B require- ments for restricted irrigation, trans- forming what was once a serious public health problem into a poten- tial resource for agriculture. This, in poor municipalities, is much more preferable than proposing more la- goons in series at a greater cost, or more complex technologies using disinfection, which are beyond the technical and financial capabilities of the municipalities. As far as concern for bacterial pathogens, the literature shows that Small Flows Quarterly, Spring 2005, Volume 6, Number 2 48 J U R I E D A R T I C L E cumulation had sludge depths approaching the water surface at the inlets! Adequate operator training 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 installations have rudimentary technical sup- port to train and pay an operator to physically maintain the system, and the public generally accepts pond systems as a public health benefit. None of the municipali- ties, however, adequately plan for system expansion, nor measure in- creased loads (nor how to manage them) as growing populations continuously connect to the sewer systems. As primary ponds reach levels where desludging is impera- tive, there is a real possibility that an installation could be aban- doned because of operation and maintenance costs, which, unfor- tunately, is a common problem throughout Latin America. In the barrio of Belem in Iquitos, Perú, hundreds of persons live in houses over the river in which raw sewage is discharged from the city of Iquitos. In addition, each house has its own latrine above the water. In this photo a woman washes dishes next to the latrine on the left. they typically exist in concentra- tions 3 or 4 orders of magnitude lower than fecal coliforms (Feachem, et al., 1983). Studies performed in Latin America have shown that a 3-cycle log10 removal of fecal coliforms removes essential- ly all of the bacterial pathogens of concern (León and Moscoso, 1996; Mara and Cairncross, 1989). As an example, Figure 8 shows the results of removal of Vibrio cholerae 01 as com- pared to fecal col- iforms in the waste stabilization pond system of San Juan in Lima, Perú at the height of the cholera epidemic in 1991 (León and Moscoso, 1996). The highest con- centration of Vib- rio cholerae 01 measured in raw sewage was only 2,700 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 Small Flows Quarterly, Spring 2005, Volume 6, Number 2 49 J U R I E D A R T I C L E as compared to 5.2 E+08 MPN/100mL for fecal coliforms. The first facultative pond essentially removed the vast majority of Vibrio cholerae 01, and no significant concen- trations remained in the effluents of the first or second maturation ponds. Until further studies can show more de- tailed survival of various bacterial pathogens in pond systems, in would seem that two ponds in series that remove at least 3, log10 cycles of fecal coliforms should remove the vast majority of bacterial pathogens. Pathogenic proto- zoa pose another concern, but at present they cannot be analyzed for in wastewater treatment systems on a routine basis. Vari- ous studies have suggested, howev- er, that they are effectively removed in stabilization pond systems (Scott, 2003). System Design for Pathogen Removal The results of this study suggest the following recommendations for systems design: • All systems should be designed using flows measured in the field instead of assuming per capita flow rates. Because there is no historical record of flows and their increase with time, much caution needs to be used in the design and useful life of systems. • Horizontal grit chambers should be designed for all systems to ensure that primary ponds do not prematurely fill with grit. • It is best to avoid anaerobic ponds since their increased load- ings require desludging more fre- quently (at least every three years), which is an added expense and risk for the municipality. • Two facultative pond systems in parallel with at least a 10-day detention time followed by one maturation pond with at least a 5-day detention should remove 100 percent of helminth eggs, satisfy WHO's Category B for re- stricted irrigation, and reason- ably ensure removal of bacterial and protozoan pathogens. This design also allows for the maxi- mum interval of desludging and hence the minimum need for sludge handling. • All designs should incorporate agricultural (or aquaculture) reuse as an integral part of the system using the WHO guide- lines. This, hopefully, would help municipalities look at wastewater treatment in a more positive light than they have in the past and foster sustainability. A well-designed and maintained facultative pond. (Masaya, Nicaragua) Sustainability Sustainability is by far the most important issue for wastewater treatment in Honduras. It makes little sense to argue over techno- logical details and removal effi- ciencies if the municipalities themselves do not have the in- frastructure and the financial ca- pabilities to adequately operate, plan for expansion, and desludge their systems. Latin America has historically had serious problems making drinking water systems sustainable, and the median ratio of urban drinking water tariff to unit cost of production is less than one for the Region (WHO/UNICEF, 2000). If there is difficulty in mak- ing drinking water systems sustain- able, it is obvious that wastewater treatment will be even more formi- dable a task. It is for this reason that waste stabilization pond systems in- tegrated with agricultural or aqua- culture reuse offer the best promise to help address some of this hemi- sphere’s most serious public health problems. Acknowledgements This project was funded by USAID-Honduras and administered by the U.S. Army Corps of Engi- neers. Pond monitoring was con- ducted by ECOMAC, Tegucigalpa, Honduras. The author thanks Mauricio Cruz of USAID-Honduras and Luis Eveline and Victor Ponce Small Flows Quarterly, Spring 2005, Volume 6, Number 2 50 J U R I E D A R T I C L E A girl collects polluted water for domestic water supply-a serious problem throughout Latin America. (Flores, Guatemala) A well-designed pond system for a community of approximately 10,000 persons in the valley of Amarateca, Honduras.