to adhere to minimum design and installation standards existed in a project called the "erdos eco-town project" in erdos located in the inner mongolia autonomous region of china. the project was implemented during 2003–2009. this urban installation for 3000 residents in multi-storey buildings utilized uddts that shared ventilation and urine collection pipework and made use of chutes that extended down into basements for the collection of feces. the uddt system was accompanied by greywater treatment facilities, solid waste composting and the reuse of these materials as a fertilizer in agriculture. however, due to several problems related to improper design and installation, the lack of a cohesive plan to address these deficiencies and the resulting resident objections, the uddts were replaced by conventional flush toilets in 2009. the main reasons for why these uddts were replaced with flush toilets were odor problems in the apartments as well as problems with the plumbing pipework for the urine pipes and the ventilation system. another factor was that "water shortage (which had been a driver for dry toilets) was no longer regarded as a problem since a pipeline was built to the yellow river and deeper fossil water resources were extracted". types single vault uddts with a single vault have interchangeable containers to collect the fecal material. depending on the size of the vault, two or more containers can be stored inside. containers should be limited to a maximum volume of approximately 50 litres, so that they still can be manually moved when they fill up. once a container is full, it can be left for further dehydration or removed for further treatment. removal of the container requires care due to fresh, potentially pathogen-loaded feces being on top of the pile in the container. because of the limited ventilation within a plastic bucket, such single-vault uddts may not reduce the pathogen load as effectively as double-vault uddts. therefore, a post-treatment of the fecal material is usually required. this can be achieved through further dehydration, composting processes or heat treatments. on the other hand, if the container is made from a material that has a high permeability with air, such as woven sacks or baskets, then the drying performance in single vault uddts may be similar to that of double vault uddts. double vault double-vault uddts are alternatively called twin-vault, two-vault or two-chambered uddts. in double-vault uddts, the fecal material dehydrates in situ. the two above-ground vaults are used alternately. while one vault is filling up, the other (full) one stores the fecal material under dry conditions for at least six months.: 4 during this resting period, no fresh feces are allowed to enter the full vault. in order to switch from one vault to the other, the user interface can either be switched or both vaults can be equipped with fixed seats and a cover sufficient to prevent access to the full vault. when the second vault becomes full and at least six months have passed, the first vault is emptied with a shovel and then the user interface is moved over accordingly. the vaults are commonly sized so that one vault fills up in six to twelve months.: 4 other (portable, mobile) example of a portable (mobile) uddt constructed out of molded plastic at a household in vermont, u.s. further information: portable toilet other types of uddts exist which are essentially variations of the single-vault type, but which are more self-contained, sometimes referred to as portable, mobile or stand-alone units and identifiable by their one-piece molded plastic shells or, in the case of diy versions, simple plywood box construction. most users of self-contained uddts rely upon a post-treatment process to ensure pathogen reduction. this post-treatment may consist of long-term storage or addition to an existing or purpose-built compost pile or some combination thereof. a post-treatment step is unnecessary in the case of very modest seasonal use. mobile uddts are typically either fabricated of new materials in a factory or workshop using a mix of proprietary and off-the-shelf parts—and then sold to the public either directly or via distributors or retail outlets; or fabricated at home out of wood, using new and re-purposed parts and materials. they are typically compact and lightweight, allowing one person to easily lift, transport, and maneuver them into place. likewise, installation is a relatively simple process given that everything needed for the proper functioning of the toilet, except a source of electrical power for those models that include a fan and some allowance for exterior ventilation, is contained within the molded or wooden carcass. one advantage of this type of uddt is that they are portable, making them an interesting option for remote or temporary installations and for installations aboard moving vehicles or non-stationary residences such as boats, recreational-vehicles (i.e. caravan, camper van, motor home) and tiny-houses. features common to this type of uddt include: a smooth, easy-to-clean exterior surface a molded seat with a cover (both or either sometimes fitted with a rubber or neoprene gasket to further assist in isolating the toilet's inner workings) a molded urine diversion bowl (or bucket and funnel assembly) to facilitate the separate collection and storage in separate containers of urine and feces (the containers consisting of either a proprietary design or, in the case of diy versions, readily-available or re-purposed buckets, bottles or jugs) some allowance for either passive or active mechanical ventilation either consisting of a screened or filtered air inlet and a screened or filtered exhaust outlet (the latter consisting of a standard fitting to allow hook-up to a length of piping or tubing that is connected to the outdoors). features unique to some designs include: cleats for fastening the toilet to the floor (particularly useful when the toilet is installed in a moving vehicle or non-stationary residence) spill-proof urine storage to aid in leak-prevention during stormy weather or when otherwise underway (as in a moving boat or rv) built-in agitator for mixing and aerating the contents of the feces container (which greatly aids in drying and odor prevention) automatically or manually deployed pivoting or hinged trap door for covering the feces container when not in use. health aspects during normal use, a uddt is just as hygienic and safe to use as any other type of toilet. however, health aspects need to be considered during removal and emptying of the urine and feces containers of a uddt. these health risks during emptying of the feces vault or container are significantly lower when compared to emptying the pit of pit latrines or the buckets of some types of dry toilets without urine diversion. however, the health risks are somewhat higher when compared to a flush toilet where the user does not have to carry out any emptying or maintenance tasks at the household level unless the flush toilet plugs, back-flows or otherwise experiences operating problems. compared to a flush toilet being flushed without closing its lid, a uddt would have a lower risk of clostridium difficile spreading via aerosolization, as it does not involve turbulent water. regarding the health risks associated with reuse activities, the world health organization's guidelines' from 2006 titled "guidelines for the safe use of wastewater, excreta and greywater in agriculture" explain the management of health risks associated with the use of excreta in agriculture. the key concept in these guidelines is the multiple barrier approach which can also be applied to reuse activities in connection with uddts.dried fecal matter from uddts after external composting, now ready for reuse (addis ababa, ethiopia) usage wiping materials for wiping of the anal area after defecation—or for wiping after urination—uddt users can avail themselves of the same materials that are utilized while using other types of toilets. suitable biodegradable materials available in the surroundings can also be used, such as toilet paper, leaves, corn cobs or sticks. these materials are deposited along with feces in the feces portion of the toilet so that everything can eventually decompose together. for example, in ecuador the soft, perfumed leaves of piper auritum, piperaceae and melastomataceae are being used. users have also used stones, although this makes the vault fill up very fast and is therefore not practical for uddts. for portable uddts in particular, used toilet paper can alternatively be placed in a separate waste bin (for subsequent incineration, composting or disposal), as the addition of soiled toilet paper into the relatively small feces container could otherwise lead to it being filled rather quickly with mainly just toilet paper. anal cleansing with water further information: anal cleansing uddts can accommodate users who prefer anal cleansing with water rather than with toilet paper by utilising either a three-hole urine diversion squatting pan or an area and drain next to the urine diversion pedestal where washing can take place—away from the urine and feces holes. this is essential so as not to contaminate the urine and to keep the feces as dry as possible. due to the fecal content of anal cleansing water, it should be considered as blackwater and treated or disposed of accordingly. anal cleansing water can be drained into a soak pit, planted mulch bed or an infiltration trench. the anal cleansing water should be discharged into coarse material below the ground, but well above the water table to avoid groundwater pollution. some uddt designs are arranged such that the users do their anal cleansing with water above the urine compartment. this may be done for simplicity reasons, i.e. in order to avoid the need for a third hole and drain pipe for the anal cleansing water. this mixture of urine and anal cleansing water requires further treatment to remove pathogens before it can be safely utilized in agriculture. water for anal cleansing can be supplied via a hose or spigot fed by a pressurized water delivery system or a gravity fed system supplied by a rainwater tank located overhead or from a water bottle or jug that the user carries into the toilet cubicle. cover materials for most uddt types, users are encouraged to add a handful or scoopful of dry cover material directly after each defecation event. this cover material is added to promote dry conditions in the feces vault (by absorbing moisture), to control odor, to prevent infestation by flies and to create a visual barrier for the next user. it is also important to ensure that enough air can flow through the pile of drying feces. for this reason bulky or fibrous material that is dry and that decomposes slowly is recommended. a range of cover materials and combinations of these materials can be used, depending on what is readily available: sawdust, rice hulls (suitable in areas where rice is grown), soil, wood ash (might not be available in sufficient volumes). lime can also be used but is often more expensive than other options. lime and wood ash both have the advantage of raising the ph value of the feces pile, thus adding to the pathogen killing abilities. it can be beneficial to select the cover material carefully in order to not only cover the feces but also to inoculate them with beneficial soil microbes. in that case, finished compost could be used as cover material. no cover materials added in some circumstances and for reasons of simplicity, it can be sufficient to not use cover materials at all or to use toilet paper itself as cover material. one example is the case where the uddt has a mechanized ventilation system and a view guard, like the uddt manufactured by separett. also in the case of public toilets, it can be easier to let the caretaker perform the task of adding cover material, rather than the user. resulting products further treatment the required degree of treatment for the collected dried feces depends entirely on whether this product will be reused in agriculture. if it is not reused, but only buried, then no further treatment is required. the dried feces are in almost all cases not entirely sanitized when removed from a vault of the uddt, so careful handling is obligatory. in scenarios wherein excreta is to be reused in agriculture, a secondary treatment of fecal matter and storage of urine is advisable to ensure adequate sanitization. fecal material from single vault uddts must always be post-treated, even if just via prolonged storage. fecal material from