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Health risk with ecosan technologies
Today, 1.1 billion people (15% of the population of the world) practice open defecation, which is well known to cause a large percentage of all deaths, particularly of infants. Compared to this baseline, almost any sanitation intervention  gives a measurable health improvement. The most frequent form of sanitation in use in communities around the world is the single pit latrine, often without a proper cover or protection. There are known problems with these systems - particularly regarding the release of microbial pathogens into groundwater and the lack of effective pathogen sanitation.
Ecological sanitation (Ecosan) aims to set up appropriate technological systems that work on a small scale, are effective at treating feces and are affordable and manageable by local communities with limited technical knowledge. The question is the level of risk associated with different interventions and whether any of them can objectively be considered to be 'safe'.
Corrales et al. studied the effectiveness of a local type of D-VIP (called a Abonera Seca Familiar - which does not separate urine and feces), a solar latrine and a pit latrine on measured intestinal parasites in rural El Salvador. LASF users were found to have a higher prevailence of two indicator pathogens (Ascaris and Trichuris spp) than users of solar or pit latrines. They concluded that the latrines did not meet the conditions for complete destruction of the pathogens and may even encourage persistence of the pathogens in some circumstances. Viable Ascaris and Trichuris ova were detected in LASF samples that had been stored for up to 2 years. The emptying of these latrines was therefore considered a significant health risk.
Bhagwan et al suggested that too often VIPs are built without considering how quickly they will be filled or what to do when they are filled. As as result, filled latrines are left without attention, leaving users without a form of safe sanitation and may have implications as to the safety of the intervention.
Sherpa et al considered double ventilated improved pits (which they described as ecosan toilets) in Nepal, which were designed to be used by 5-6 people for 6 months, then stored for another 6 months (whilst the alternative vault was being used). Several of the measured pathogens were not seen to reduce during the whole period of measurement, indicating that the conditions were not sufficient to kill off virulent spores and other resistant life stages. Concluded that 6 months was far too short, and that likely more than 1 year storage would be needed give a sufficient pathogen die-off to meet the WHO standards.
In an interesting study, Jensen et al attempted to replicate conditions in a non urine-diversion D-VIP system by comparing Ascaris destruction in heaps prepared from fresh local latrines. The study was conducted on open heaps because it was concluded that adequate mixing was not possible in the pits. They determined that 99% destruction was observed within all the studied heaps, with the initial pH making little difference to the survival of the pathogen. However, they also determined that the temperatures within the heap were highly variable and concluded that the results suggested 99% reduction was likely within 3 months, the standard storage time in Vietnam. Importantly, they also concluded that the mixing in the heaps may well be better than that in a D-VIP and that the majority of local people had single VIP latrines anyway.
Nwaneri et al  made some important points about the microbiological processes going on in VIP latrines. Most NGOs and academics seem to regard the process as essentially aerobic, some operators regard it as anaerobic. As this paper points out, it is possible for the latrine to operate both aerobically and anaerobically at the same time, which has important implications as to the sanitisation of (largely anaerobic) pathogens in the feces.
There is generally a confusion of terms between some forms of pit latrines (particularly VIP latrines) and composting toilets. However, pit latrines can generally be understood to be more permeable to the soil, so that leachate flows can escape, whereas urine diversion vaults are thought to be more impermeable. Although they are a very common intervention, pit latrines should not be considered to be effective systems of feces sanitation and so excavation of them may be difficult and risky.
Mehl studied single pit urine diversion (which she described as composting) latrines in Panama for her MSc thesis. These were pits which were used for 6 months, during which ash or sawdust had been added, after which they were covered for another 6 months and left 'to compost' and another pit was dug elsewhere. There is no information to suggest that the latrine was ventilated. Many pathogens were discovered in the sludge after the storage time and it was found that the pits remained at near ambient temperatures. It was therefore suggested that they never reached the temperatures necessary for pathogen destruction. An assessment of the C/N ratio suggests that it was close to that found in raw sludge and therefore that composting had not been occuring in the pits.
Tønner-Klank et al considered the pathogen kill in composting toilets. The abstract of their work reads:
“Compost toilet systems were assessed for their ability to reduce microbial indicators and pathogens. Indicator bacteria showed large variations with no clear trend of lower bacterial numbers after longer storage. In controlled composting experiments, thermophilic conditions were only reached when amendments were added (grass and a sugar solution). Even then it was impossible to ensure a homogenous temperature in the composting fecal material and therefore difficult to achieve a uniform reduction and killing of indicator organisms.”
Endale et al considered the primary pathogen removal efficiency of ecosan (presumably pit latrine) systems. The abstract of their work reads:
“An experimental study was conducted to assess the pathogen removal efficiency of primary treatment of ecological sanitation (eco-san) system. Ash, lime and soil were used as covering and treatment materials of faeces in the system. A significant rise in pH was observed when the faeces were treated with lime and ash, with a pH value of 11.3 and 9, respectively. Lime treatment was effective in complete destruction of faecal coliforms within 24 h while ash treatment took 30 days of storage to give the same result. On the other hand, no immediate destruction of Ascaris ova was observed during primary treatment of eco-san faeces. Dehydration and storage were other parameters which were considered in the experiment. Faecal coliforms tolerated a moisture content of 3% in untreated faeces while a large number of Ascaris lumbricoides eggs were inactivated by the same level of desiccation, even in the absence of alkaline treatment. The study showed a strong direct relationship between moisture content and viability of Ascaris egg (r = 0.806, p = 0.01) and a negative correlation between viability of eggs and storage time (r = −0.895, p = 0.01). Generally, the treatment methods used in this experiment showed a substantial potential of faeces sanitization, with removals ranging from 54 to 100% after a minimum of 40 days storage.”
Hoko et al  considered urine diversion single pit latrines in Zimbabwe where material was left 6-8 months before application to land. They found that it was overwhelmingly women who were responsible for cleaning the toilet whereas responsibility for spreading the feces was much more evenly split between men and women. Most users interviewed considered the UDDT to be more sanitary than the pit latrines, but that might have been because they were newer whereas the need to spread sludge from the UDDT led to the perception of that aspect being more risky.
Jimenez et al  considered the pathogen levels in crops which had been spread with sludge from ecosan toilets from Kwazulu Natal in South Africa and found unacceptably high levels on spinach and carrot crops, suggesting that the material should only be spread on crops which are not eaten uncooked and/or not in contact with the soil.
Hawksworth considered the safety of urine diversion D-UDDT in eThekwini Municipality, Durban, South Africa. There the latrines had been installed by the municipality as purely a collection system, so they were periodically emptied mechanically. Pathogen presence was measured in latrines in two communities. 89.5% of the sampled latrines were found to contain one or more protozoan or helminth parasites, although it is not clear how long the material had been stored in individual latrines. In another experiment, he also discovered indicator pathogens in latrines that had been standing beyond the recommended storage time of 1 year indicating that it was not yet safe to handle.
McKinley et al  showed that there may be some significant effects of urine on Ascaris in sludge, which means that the time required to attain safe levels in a urine diversion system is longer than in systems where urine and feces are not separated.
Austin  considered the effect of ventilation shafts on pathogen breakdown in urine diversion latrines, and concluded that and outdoor heap was more effective than either type of pit latrines (possibly due to the extra effect of UV radiation on the sludge) but that the ventilation had no effect on the aeration or heat of the material in the latrine. Therefore concluded that the vent only had an effect on flies and odours in the superstructure. The pathogens were destroyed beyond the legal limits for sludge application in South Africa within 6-9 months, concluding that at least a year is necessary for storage in pit latrines.
A paper by the same author has an abstract that reads:
The most advantageous approach to pathogen destruction in a urine-diversion toilet vault is to maximize the effects of various environmental factors (i.e., pH, temperature, moisture content, type of bulking agent, and storage time). To quantify these effects, a field experiment was set up, consisting of 6 urine-diversion toilet vaults, each with a different combination of feces and bulking agent (soil, ash, wood shavings, sodium hydroxide, or straw) and ventilation (ventpipe/no ventpipe). The pH of the mixes varied from 6.37 to 10.09. Temperature probes, which were connected to a data logger, were inserted to the heaps, and the logger monitored over a period of nearly 10 months. Mean heap temperatures ranged from 16.8°C in winter to 27.6°C in summer. In addition, samples were taken at intervals from the various heaps in the vaults and also from an open heap exposed to the elements. The samples were subjected to microbiological testing to quantify the pathogen dieoff over time. In the vaults, there was a 3log 10 (99.9%) reduction of total coliform between 130 and 250 days, fecal coliform between 100 and 250 days, and fecal streptococci from 125 days and longer. In the open heap, these times varied, from 115 days for both total and fecal coliform, to 140 days for fecal streptococci. Viable Ascaris ova were reduced to zero between 44 and 174 days in the vaults and by 44 days in the open heap. The results of this research showed that ventilation of the vault by means of a ventpipe does not result in any meaningful difference in the vault temperature or the rate of pathogen dieoff. While the type of bulking agent used does not significantly affect the temperature of the heap, it does have an effect on the rate of pathogen dieoff. The ordinary soil mix was seen to give the best results, and this was ascribed to the effect of competing microorganisms in the soil itself. It is concluded that, for safety, vaults of urine-diversion toilets should be sized for a storage period of 9 to 12 months from the last use.
There have been many claims about the effectiveness of forms of composting toilet which has led to them being a preferred WASH intervention in many situations. Some claim that pathogens can be eradicated from these types of low tech composting units within a few months. There have been worries about this kind of talk for some time, though.
The widely quoted "Guidelines on Safe Use of Urine and Faeces in Ecological Sanitation Systems" from 2004 said
Many toilets are called “composting toilets” without actually achieving a well-functioning process; it is rather storage and anaerobic putrification, desiccation or alkalization that occurs. Unless good maintenance can be ensured, mainly obtained in large and well-insulated composting units that receive faecal and food wastes from a large number of persons, it is questionable if one could rely on domestic-scale “composting” units as an efficient process for pathogen reduction. Composting is therefore not considered as a first-hand choice for primary treatment but rather as an option for secondary treatment of faeces at a municipal scale or level.
More recent work, some of which has been shown here, indicates that Schönning and Stenström were right - composting toilets are highly variable in their effectiveness based on a range of factors which are not properly understood. Part of the problem lies in the variability of the construction and operation of the toilets and the confusing mix of terms. But the performance cannot simply be put down to these factors.
It is not really even possible to make recommendations about the storage times needed to ensure the efficient breakdown of pathogens from composting toilets, as seen above, advice ranges from a few months to several years.
The best advice appears to be to assume that nothing has happened in the composting toilet with the pathogens, and that it has not been at all sanitised so handling the material may be high risk. One should therefore handle it with extreme care, preferably not touching the compost with bare hands, and immediately dispose of the compost away from the home and water courses. Ideally further treatment of the sludge would occur. In a situation where microbial analysis and hospital treatment is not available, the best advice may be some kind of larger composting site where the feces can be mixed well with other carbon rich materials. Even if there has been some pathogen destruction from the toilet system, this is still good advice as it offers another barrier to infection.
Singha et al  considered pathogen reduction in 10-15kg batches of feces treated with worms and concluded that there was evidence of substantial improvement in total coliforms and E.coli indicator species within 12 weeks.
Hill and Baldwin considered vermiculture as an alternative to "latrine style microbial composting toilets' and concluded that they are more effective at pathogen destruction than composting toilets and carried less risk to users.
Bowan et al  considered the effect on the pathogen Ascaris by Vermicomposting worms. Here is the abstract to their work:
Vermicomposting is a novel means of reducing organic wastes using a living system composed of earthworms and biosolids. The end product is a highly processed material more favored by the general public. Vermicomposting must take place at temperatures below 35°C in order to maintain worm viability and be successful. This has the disadvantage that it does not reach the 55°C temperatures required by law for pathogen inactivation in composting systems. Pathogen reduction in the composting process is in a large part time and temperature dependent, so it is difficult to understand how vermicomposting can produce a pathogen free product. Although it seems likely that the earthworms may inactivate various bacterial and viral pathogens, there is some concern based on prior literature that they may not successfully inactivate the eggs of helminths that find their way into the biosolids of municipal treatment plants. Thus, this work looked at the ability of Eisenia foetida worms to kill Ascaris eggs in potting soil. Over a six-month period, there was no significant (α=0.05, p=0.563) decrease in the mean number of eggs recovered from soil containing worms sampled at 1, 5, 11, 13, 14, 18, 28, and 183 days after egg addition. In terms of viability, at 1 week after the eggs and worms were placed together, there was no significant reduction (α=0.05, p value=0.272) in the mean egg viability with or without worms being present (91.8% vs. 93%, respectively). After a period of 6 months in the presence of E. foetida earthworms, the mean viability of the eggs recovered was 77.2%. In this study, E. foetida earthworms did not achieve a one-log reduction in A. suum numbers or viability.
Rodríguez-Canché et al considered the effect of vermiculture on septic tank waste:
This study evaluated the potential of earthworms (Eisenia fetida) to remove pathogens from the sludge from septic tanks. Three earthworm population densities, equivalent to 1, 2, and 2.5 kg m-2, were tested for pathogen removal from sludge. The experimental phase lasted 60 days, starting from the initial earthworm inoculation. After 60 days, it was found that earthworms reduced concentrations of fecal coliforms, Salmonella spp., and helminth ova to permissible levels (<1000 MPN/g, <3 MPN/g, and <1 viable ova/g on a dry weight basis, respectively) in accordance with Official Mexican Standard of environmental protection (NOM-004-SEMARNAT-2002) (SEMARNAT, 2002). Thus, sludge treatment with earthworms generated Class A biosolids, useful for forest, agricultural, and soil improvement.
In the book Vermiculture Technology: Earthworms, Organic Wastes, and Environmental Management, Edwards and Subler  review the literature showing the pathogen reduction impacts of vermiculture and indicate that much lower temperatures are required for vermiculture than those required in standard aerobic composting to achieve pathogen destruction, otherwise the worms die. However, tests have indicated that even with low temperatures, pathogen reduction can be achieved to meet the standards set by the USDA.
At first glance, it appears that many of the same risk factors should be taken into account with vermiculture as with composting toilets - in perfect conditions, the technology has the potential to reduce pathogens to safe levels but in suboptimal conditions there may be less pathogen destruction than might be expected.
However, it does appear that there are several factors that make vermiculture significantly safer than composting toilets. First, it is known that vermiculture requires lower temperatures of operation than is needed to kill pathogens in aerobic composting. Which suggests that this might be more viable in non-perfect conditions where it is hard to get composting up to acceptable and more uniform conditions. Second, we have several examples of vermiculture units around the world which meet local pathogen standards of safety - including Mexico and the USA.
On the other hand, there appear to be far fewer available studies on vermiculture and there is disagreement between them about the effectiveness of the worms on pathogens in the compost. Also the operation is likely to be more complex than a simple urine diversion Ventilated Improved Pit toilet, where the feces is collected, stored for 6 months and spread. Worms need to be cultivated and managed - and the site probably needs to be larger than an individual pit latrine to be effective.
In terms of risk, it appears that there is likely to be similar risks associated with emptying the urine diversion toilets and additional risk to those working a larger composting site. Care may need to be taken to site the treatment unit so that it cannot contaminate watercourses, and there may be cultural problems with managing this kind of facility. However the risks of the finished vermiculture sludge appear to be lower than those associated with stored latrine sludge, and the pathogen reduction takes less time.
Peepoo bags are a system of sanitation developed by a Swedish academic team and promoted by a Swedish private company. The concept is that mixed urine and feces is deposited into a bag, which is sealed and eventually collected, stored and added to sand to make a marketable soil amendment. Therefore it might generally be said to be an Ecosan intervention. Their website states:
Peepoo works as a micro-treatment plant sanitising human excreta shortly after defecation. Inside Peepoo there are five grams of urea. When the urea in Peepoo comes into contact with faeces or urine, a breakdown into ammonia and carbonate takes place, driven by enzymes that naturally occur in faeces. As the urea is broken down, the pH-value of the material increases and sanitisation begins. Within 2-3 weeks all disease-producing pathogens found in human faeces are inactivated, provided the temperature at some time during the day reaches 20°C.
This is based on the idea that there is improved pathogen destruction of feces when extra urea is added to it, so that simple storage at 20°C 'breaks down all pathogens'.
This claim is based on science conducted at the Swedish University of Agricultural Science.
Nordin's doctoral thesis  (which is linked from the peepoo website) is the basis of this. In it, laboratory analyses were conducted to establish the effectiveness of added urea on the breakdown of pathogens in feces. Table 9 on page 75 gives the pathogen destruction results at a range of temperatures and treatments. At 24°C, the urea treatment gives safe levels (according to the text) within <1 week for Salmonella and E.coli , 2.5 months for Enterococcus and 2.5 months for Ascaris spp. The text on page 76 suggests that this may not be sufficient breakdown of Ascaris. This work does not then seem to support the claim that all pathogens are destroyed within 2-3 weeks nor that a single daily maximum of 20°C is required (the incubations appeared to be constant temperatures). Otherwork by the same group  suggests that inactivation of Ascaris was not achieved by the concentrations of urea used or took at least 6 months. And other work by the same team looked at the breakdown of Salmonella, Enterococcus and indicator viruses. Whilst Salmonella was destroyed to low levels within days, Enterococcus required 3 months and the viral indicator 8 months in the highest urea treatment at 24°C.
In a different study group, McKinley et al  studied the effects of urine (which contains urea, which is converted to ammonia) and ash on Ascaris survivial survival in feces. Their results suggest a minimum of 8 weeks are needed at 18°C.
Fidjeland considered a microbial risk assessment of a field trial in Uganda of urea treated feces for his Masters thesis. In considering storage for 2 months, the Quantitative Microbial Risk Assessment used a standard model to assess the likelihood of infection transfer in food and to farmers handling the sludge. Assuming a standard safe risk limits for Ascaris, it was found that only a 4% urea treatment was safe for farmers without protective clothing, which suggests that additional urea needs to be added to that in the peepoo bags during the 2 month storage period. The model also suggested that higher levels of urea were necessary to give low risks on edible foods. This leads to the conclusion that there may be a pathway for transmission from the farmer into the home. However, questions were also asked regarding the reliability of the Ascaris model.
The system is supposed to be one to replace Open defecation and the flying toilet phenomena, particularly in urban or disaster situations. And providing that the bag stays sealed once it has been used, it is possible to understand how this is an improvement. The risk to users should be quite low and the risk to those who collect and handle the bags should also be low. The system is supposed to collect, and then further treat the bags following the minimum storage time. The problems is that in areas where the bags have been extensively trialled, there does not appear to have been adequate post treatment. Given that there doesn't appear to be research showing adequate pathogen destruction from laboratory studies, never mind imperfect conditions in the field, this can be considered a fairly high risk activity.
Terra Preta Sanitation
Terra Preta Sanitation is a sanitation system developed and researched at the Hamburg University of Technology and is essentially a multi-modal system involving a dry toilet where charcoal is added, a storage phase involving lactofermentation and a vermiculture digestion phase. The idea is to produce compost which is similar to Terra Preta soils, which are black, humus rich soils in Brazil which are thought to be a relic of an ancient sanitation system.
Factura et al tested the system in laboratory analysis at the Hamburg University of Technology involving collection of material for two weeks with additions of charcoal after each use, followed by four weeks of lactofermentation in an airtight bucket followed by vermiculture using earthworms. Treatment with earthworms showed a significant improvement in the numbers of test pathogens found after 60 days, suggesting that it met the USDA Class B biosolid standard.
Itchon et al  conducted a field trial in the Phillippines and showed that bacterial and Ascaris pathogens were reduced below measurable limits.
Clearly there is a knowledge deficit on this technology as there is little published research on the topic. However, a multi-modal system seems to provide some additional barriers and give greater credibility to the system. Whilst at any given step in the process, the sludge may still not be sufficiently sanitised, additional steps may well mean that the chances of pathogen survival are reduced. In terms of risk, there may be significant risks for those collecting the feces, however there is some evidence that the lacto-fermentation has some effect leading to reduced risk at the vermiculture stage.
In a recent discussion, Gina Itchon and Ralph Otterpohl, authors of the papers mentioned above posted comments about the safety and sanitation of TPS and other ecosan systems.
I remain very hesitant about re-using human feces for agricultural use because in my country Ascaris infestation is a public health problem with infection rates going up to 80% of the population in certain places.
And Ralf goes further, stating that he does not think any material from toilets should be spread on food crops for 10 years. Including material from his own TPS system.
Arborloos are a simple form of ecosan, practiced where there is a lot of land available. In brief, shallow pits are dug on which the toilet superstructure is placed. When it is nearly full, the superstructure is moved elsewhere and a layer of soil is added and a tree is planted.
In terms of risk, this appears to offer a low risk to workers as the sludge is not directly handled. However, it is possible that the pathogens are not being composted in the latrines, so the soil beneath the old pits may still have significant levels of pathogens and may not have the benefits of being exposed to UV light as with other forms of ecosan. Recent studies have indicated that pathogens are often found in soil long after the last application of the pathogens.
So whilst there may be limited risk to groundwater of a well situated arborloo, the risk of pathogens in the buried feces may be high for many years. According to Morgan vegetables are routinely grown in former Arborloo pits, often with good yield responses. Care should be taken to avoid infection transfer, for example by ingesting soil attached to the crop.
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