double vaults has typically passed a certain storage time and is therefore already more sanitized. however, a secondary form of treatment is optional but recommended for household systems and required for large-scale systems. secondary treatment can be performed at the community or household level and can include thermophilic composting where fecal material is composted at over 50 °c, prolonged storage with the duration of 1.5 to two years, chemical treatment with ammonia from urine to inactivate the pathogens, solar sanitation for further drying or heat treatment to eliminate pathogens. the most difficult pathogens to eliminate from the drying feces in the feces vaults are the helminth eggs which can cause helminth infections. reuse in agriculture or burial main article: reuse of excreta reuse of treated feces in agriculture—like reuse of excreta in agriculture in general—can result in increased crop production through fertilizing effects of nitrogen, phosphorus, potassium and improved soil fertility through organic carbon. if the dried feces are not reused in agriculture they can instead be buried at a minimum depth of 25 cm in which case they normally do not pose a public health risk.: 29 further treatment the required degree of treatment for the collected urine depends entirely on whether this product will be reused in agriculture. if it is not reused, but only infiltrated, then no further treatment is required. urine that leaves the body of a healthy person is close to being sterile and requires much less treatment for pathogen removal than feces or fecal sludge. however, a contamination of urine with fecal pathogens is possible if the uddt is not used correctly, i.e. when some fecal matter finds its way into the urine compartment. also, for a few specific diseases, the relevant pathogens may be found in the urine; for example: leptospira interrogans, salmonella typhi, salmonella paratyphi, schistosoma haematobium, bk virus or simian virus. the ebola virus may also be found in urine from an infected person. the exact survival time of this particular virus in human urine outside of the human body is unclear but probably "up to several days" like with other body fluids at room temperature. for these reasons, urine should always be treated for pathogen removal if it is going to be reused, unless reuse occurs at the same household where the urine was collected and on crops that are only consumed by these household members (in which case an infection among family members is more likely to occur via handshakes and hugs than via urine reuse activities). the simplest and most common method of urine treatment for pathogen removal is via storage in closed vessels. the decomposition of urea that is present in urine into ammonia and hydrocarbonate leads to an increase in ammonia concentration and an increase of ph value to above 9. these two processes lead to pathogen reduction. warm temperatures and low dilution of the urine with water increase pathogen removal.: 34 storage of urine kills bacterial pathogens encountered in urine – including salmonella typhi and paratyphi and mycobacterium tuberculosis – in a relatively short time span: a storage time of five weeks at temperatures below 20 °c or of two weeks at temperatures above 20 °c has been recommended to prevent transmission of mycobacteria when recycling human urine. recommended storage times to kill pathogens in urine vary from one to six months depending on ambient temperatures, the scale of the urine collection system and which crops will be fertilised with the urine. reuse in agriculture or infiltration main article: reuse of excreta reuse of treated urine in agriculture—like reuse of excreta in agriculture in general—can result in increased crop production through fertilizing effects of nitrogen, phosphorus, potassium and improved soil fertility through organic carbon. urine from the uddts can safely be used as nitrogen-rich and phosphorus and potassium containing fertilizer after a recommended storage period for pathogen reduction (see above under "further treatment"). in cases where no reuse is possible or desired, urine is usually infiltrated in the soil unless this practice would cause groundwater pollution. in ethekwini municipality in south africa or in lima, peru, for example, urine from uddts is safely infiltrated into the soil because the groundwater level is very low there and the groundwater is not used for any particular purpose. infiltration can be done by directing the urine to a soak pit or by running a perforated urine pipe from the toilet to an area outside, where the hose is sloping gently downhill (for rural areas). clogging of the pipe's holes can be avoided by ensuring there are no t-junctions, no joints and that a plastic mesh is installed in the urine funnel of the toilet to keep everything other than urine out.very simple home-made design for a uddt with a funnel for urine collection and a bucket for feces collection at a household in addis ababa, ethiopia comparison pit latrines reasons for keeping urine and feces separate in a uddt compared to a pit latrine can be to:: 8 reduce odor (because mixing urine and feces together causes a lot of odor); avoid production of wet, odorous fecal sludge, which has to be removed by someone when the pit latrine is full; allow for the recovery of treated excreta so that it can be used as a fertilizer or soil enhancement. the advantage of uddts compared to pit latrines is the conversion of feces into a dry odorless material and therefore an avoidance of the issues surrounding liquid fecal sludge management (e.g. odor, fly attraction, difficulties in pit emptying). a well-maintained uddt is an odor and insect free toilet which is appreciated by users and allows simple removal and far less offensive and safer handling of the fecal material once the feces vault has filled up. moreover, the risk of water pollution is minimised through the safe containment of feces in above-ground vaults and this allows the toilets to be constructed in locations where pit-based systems are not appropriate. uddts with vaults are also more permanent structures than most pit latrines, the latter of which in rural areas are typically relocated when the pit is full rather than emptying the pit. therefore, pit latrines need more space and people are less willing to invest in a higher quality super-structure as it will have to be dismantled and moved at some point. in the experience of the non-governmental organisation wecf who introduced uddts in eecca countries to people who had pit latrines, it was most successful converting people who were in regions lacking a reliable water supply and wastewater management. since the introduction required behavior change in the recipients, wecf considered awareness raising and training by local partners to be important. sewer- and septic tank-based sanitation the comparison of uddts with sewer-based sanitation systems (sewerage and wastewater treatment plants) is not as straightforward as the comparison with pit latrines as a sewer does not only deal with excreta management like a uddt does, but it also transports greywater, municipal wastewater, stormwater and industrial wastewater. however, the installation of uddts in all households connected to a common sewer would result in vastly reduced volumes of water, nutrients and organic matter that arrive at the associated wastewater treatment plant. sewer-based excreta management is impractical in many regions due to limited water supplies and the high cost of sewer systems and wastewater treatment plants. furthermore, water-based sanitation systems (flush toilets) dilute excreta and create vast wastewater streams, something that uddts do not. similarly, the comparison between uddts and septic tank-based sanitation systems is not as straightforward as the comparison with pit latrines as a septic system also treats greywater. however, the relatively high costs of septic systems, particularly mound-type septic systems can be partially mitigated or, if used in conjunction with an onsite greywater system, eliminated altogether by installing uddts in place of flush toilets. portable uddts offer the potential advantages of greater local control and quick deployment which is particularly useful when there is no capable centralized institutional infrastructure in place or no financial ability to implement larger centralized systems. pharmaceutical residues and other micro-pollutants the separate, waterless collection and treatment of urine and feces in uddts prevents hormones, pharmaceutical residues and other micro-pollutants which are contained in human excreta from entering surface water or groundwater via treated sewage. this is because in conventional sewage treatment plants, these micro-pollutants are only partially removed and the remainder is discharged into surface water, possibly reaching the groundwater. detected concentrations of pharmaceutical residues in groundwater were in the order of 50 ng/l in several locations in germany. moreover, micro-pollutants can also become concentrated in sewage sludge. following treatment, sewage sludge is either landfilled, incinerated, applied on agricultural land or, in some cases, retailed or given away for free to the general public. each of these disposal options comes with myriad potential—and in some cases proven—hazards for human health and environment impacts of these chemicals. by not mixing human excreta with water and the other contaminants that are disposed of in sewers and septic tanks, uddts avoid many of the problems associated with these practices. if the excreta collected from uddts is treated further and buried or used as agricultural or horticultural fertilizer then the pharmaceutical residues in the excreta will be degraded better in terrestrial systems (soil) than in aquatic systems. therefore, uddts (or in fact all urine diversion systems) have an advantage over sewer-based sanitation systems with respect to these problem of micro-pollutants. challenges school uddt in rural areas of western kenya; the steep stairs are not recommended as they are a barrier for people with disabilities operational issues there are several operational problems that can happen with uddts.: 38 the main ones are: urine may accumulate in the urine diversion section of the toilet due to blockages in the urine pipe; odor coming from the feces vault because the contents of the feces vault have become too wet. in this case also flies, other insects or rodents may appear in the feces vault.: 38 if there is insufficient commitment, user preparation, follow-up and support, such operational problems can lead to failure of uddt pilot projects.instructional guide for using a uddt in the kinyarwanda language, rwanda costs uddts are sometimes considered too expensive compared to pit latrines, but this criticism does not include the cost of emptying pits and the potential value of fertilizers that can be recycled via uddts should the users wish to do so (noting that most uddt installations worldwide currently do not reuse excreta in agriculture). rather than looking only at construction costs, long-term operational costs and benefits should also be considered, especially since the regular emptying or re-building of pit latrines may be a significant expense. when a period of for example 10 years is considered, uddts may well be the more economical alternative, since the emptying of feces vaults is simple and safer, thus less expensive, even if users decide to enter into a contract with someone else to do this. compared to flush toilets connected to sewer systems and wastewater treatment plants, uddts are usually less expensive. however, to enable accurate comparisons of costs, this needs to be assessed on a case-by-case basis because the sewer system and treatment plant also transports and treats greywater whereas the uddt does not. this means that the two systems provide a different level of service to the user. an example calculation for such a cost comparison exists for the case of lima, peru. there is even a minimalist uddt model that costs essentially nothing to construct and which only requires salvaging and assembling selected plastic items from the garbage and which can be implemented by the poorest people, disaster victims, and those who want to gain experience with uddts. history the uddts with two dehydration vaults that are known today were originally designed around 1950 in japan and further developed in vietnam in the 1960s as a means of increasing the hygienic safety of excreta reused in agriculture. this means their development was originally closely linked to the ecosan (ecological sanitation) approach to optimizing resource recovery of nutrients and organic matter in agriculture. beginning in the early part of the 2000s, uddts have been seen increasingly as a toilet type that can provide advantages even without any reuse activities attached to it. since the 1990s, modifications of this