Summary and conclusions, Miljøstyrelsen

More Knowledge about the Use of Diverting Toilet System Technologies

Summary and conclusions

The basis for the project was the growing interest in the technology of diverting toilet systems and their components for separate collection of urine and faeces. The function of the system components must, however – be reliable, allowing collection of the residuals in concentrations suitable for treatment in biogas plants and wet composting plants as well as for use as fertilizer in agricultural production.

The introduction reflects on the historical development, moving away from the use of diverted human residuals as being merely a routine approach to a removal paradigm rather than a reflected development regarding recirculation of nutrients and organic material to agriculture. There is need for qualitative modernisation within wastewater handling. New technologies as well as new concepts are needed to design the desired human fertilizer products. Moreover, there must be a readiness in the functional systems of the society and of institutions to eventually redesign structural conditions like regulatory and economic management directions for this process.

The second chapter presents four selected investigation areas. First, investigations and considerations regarding the establishment of source diverting vacuum toilets in a residential area in Hanover, Germany, with 32 source collecting vacuum toilets. The second reviews and analyses a number of investigations regarding diverting faeces and paper using source collecting or source diverting flushing toilets. The third area focuses on the functioning and running of waterless urinals as a possible collecting method for concentrated urine. The fourth considers the risks of blockages in the urine collection system of source diverting double flushing toilets and the possibilities of avoiding or solving these problems.

In chapter three source diverting vacuum toilets are presented. In relation to the test of an "Ecovac 2" toilet mounted on a central plant with 32 source collecting "Evac" vacuum toilets, this type of toilet is presented and experiences from operation of the toilets are given. The investigation is among others carried out in a co-operation with Stadtwerke Hanover. The investigation points out that source diverting vacuum toilets should present useful potentials for a more concentrated collection of faeces in blocks of flats than can be achieved with the source collecting vacuum toilet technology.

The water requirements for flushing the source collecting vacuum toilets in 32 flats with a level of 8.2 litres(person-day)(1998), 8.0 litres/p/d(1999) and 9.2 litres/p/d have resulted in water savings of 80% compared to the former use of toilets with a daily amount of water flush of approximately 40 litres/p/d. The concentration of dry matter from the source collecting toilets is estimated at 1% DM. By means of source diverting toilets the DM-percentage should be able to reach a level of 1.75 – 3.5%.

The electricity consumption of 0.006 kWh/(person/day)(2000) as well as the level of noise (sound levels of 35 – 52 dBa in the living rooms, 43 – 53 dBa in the kitchens and 52 – 60 dBa in the entrances) can be reduced by using diverting toilet technology.

The diverting vacuum toilet has aroused great interest in Germany and is as a part of "Öko-Technik-Park Hannover", continuously used for demonstration etc. during EXPO-2000 in Hanover. Extensive written information material has been worked out, which also informs about the toilet. Some development of the toilet is, however, required, among others of the vacuum valves of the faeces outlet. These valves must be tested for a long period under practical real-life conditions. Another possibility is to take advantage of the existing use of the source diverting vacuum toilets establishing a small vacuum system in each flat. This would have a very positive influence on the operation stability and the consequences of blockages. The individual systems would be able to transport residuals including grinded food residuals from the individual households in separate pipe transporting systems with separate vacuum motors and sluice valves to one or more common collection tanks.

Source collecting as well as source diverting vacuum systems allow collection of 100% of human residuals. Source diversion gives, however, a much higher DM-percentage and a possibility of separate collection and differentiated use of human fertilizer products.

Chapter four deals with the "Aquatron" separators. Four investigations on the use of "Aquatron" separators to separate faecal material and paper from the flush water using source-collecting or diverting toilets are presented and discussed.

The efficiency of the separation depends on a number of factors, such as the speed of the water reaching the separator, the size of particles at the arrival, the amount of paper in the water, the amount of flush water and so on. The size of particles is determined not only by the consistency of the excreted faeces but also depends on the transporting pipes, their length, vertical falls, changes of directions etc. Highest concentration of dry matter, organic matter and nutrients could be achieved by using source-diverting toilets in single houses with short pipe lengths and modest vertical fall.

A laboratory test at SPI in Borås, Sweden, resulted in 1% and 2.4% of water through the particle outlet at three litre clean water flush and one and six metre 110 mm diameter with 5% fall. Flushing of seven grams of paper gave 100% of paper and approx. 12% of flush water through the particle outlet. By flush of rod shaped particles 2 – 5 mm diameter or split peas 6 – 7 mm, 7.4% of the 2 – 5 mm particles together with 2.6% of the flush water and 98.3 of the 6 – 7 mm particles and 2.3% flush water through the particle outlet at one metre pipe length (99.8% particles and 2.5% water at six metre pipe).

During measurements on an installation in a summer cottage, with a collecting toilet flushing three litres, collection was recorded of 43.2% of DM, 57.7% of VS (organic matter), 11.8% of N, 29% of P and 17.5% of K and a DM-percentage of 2.6 and a VS-percentage of 2.24 in the collected material from the particle outlet. Estimates of the potential concentration in collected material from the particle outlet by faecal flush of 4.0 – 8.8% DM and 2.7 – 5.8% VS show that great potentials should be achieved in the use of diverting toilets.

Measurements of collected material from 22 source diverting toilets and two parallel separators in a social building complex with four stores and a basement showed 38% of DM, 51% of VS , 55% of N as well as of P and 43% of K through the particle outlet. However, the DM-percentage was only 0.22 and the VS-percentage only 0.16. Even if the concentrations of DM, VS and nutrients were low because of a combination of big vertical falls, long pipes, large and frequent flushes, systematic flushing of urine, drying paper etc., the collection percentages for nutrients were much higher than in the summer cottage installation due to source diversion. It is unsatisfactory that about 13% of the flush water leaves through the particle outlet and that the main part of the dry matter including the paper disappears through the outlet for water. The amount of water through the particle outlet can be reduced by reducing the water flush from six or nine litres to four litres, by reducing the frequency of flushing and by refraining from flushing out paper used for urine only and using a sanitary bin instead.

Further, it seems necessary to reject long vertical falls of up to four floors, as these may split faeces as well as paper into pieces. Until those problems are solved it is advised not to install separators in large multi-storey buildings.

At a laboratory test of separation of particular material by flushing collected faecal material, 90 grams wet weight/portion, with 4 litres of water through pipes of 110 mm diameter with one meter vertical fall and further two meter transport with 5% fall, results were completely different from the results of the multi-storey building. At the laboratory test the separation was very efficient. Approximately 80% of DM as well as VS were collected from the particle outlet together with approximately 70% of N, P as well as K. The DM-percentage was 10, and only 2.6% of the flush water went to the particle outlet. By flushing six litres the DM-percentage fell to 7.7. The flushed faecal material only contained small amounts of paper. Bigger amounts of paper could, based on tests at SPI in Borås, have resulted in more water to the particle outlet. Even if 12% of the flush water joined the paper by flushing the faeces together with 7 grams of paper, the DM-percentage by four litre flushes is estimated to be 6.5 – 7.

A system consisting of diverting double-flushing toilets in combination with "Aquatron" separators has a potential for collection of 80% of the substances in urine and 70% of the substances in faeces. Usage in multi-storey buildings, however, requires a disciplined flushing regime as well as special pipe installations or many separate systems without big vertical slopes. In the future it may also be possible to collect coarse grinded food residuals in concentrated form by use of a separator.

It is concluded that it is possible to collect a product with a rich concentration of organic material and nutrients. This especially applies to the use of diverting toilets in single households with a faecal flush of three to six litres and without flush of paper used by urination only. If paper used by urination only is frequently flushed out, the situation will change quickly. If the aim is a concentrated collection in a closed container, frequent six to nine litre flushes of paper especially in multi-storey buildings with pipes for many toilets would create problems. Further tests and investigations of how to solve the above mentioned problems should be made before installing separators in multi-storey buildings.

Chapter five presents different waterless urinals based on different principles. The principles are described, and experiences from using the urinals are reported. The experiences are good. Waterless urinals should in the future be a decisive component for a cost efficient collection of concentrated urine.

Waterless urinals have a collection percentage of 100 and secures a maximum concentration of substances. It would be of interest to investigate whether normal vegetable oils as rape oil could be used as a sealing liquid, and whether fresh urine in a liquid lock in combination with natural perfumes would cause odour problems. There is also a need to investigate aspects of transport in pipes of concentrated urine.

Chapter six focuses on blockages in the urine system of diverting toilets. The results of analysis and collections of experience are presented. Blockages have occurred in almost all of the investigated toilets. Possibilities of avoiding and solving problems are discussed, among others by means of electromagnetic water treatment. It is concluded that all of the investigated blockages could be remedied with a mechanical cleaning wire or by using NAOH. An interesting development in efforts to reduce the formation of hard crystals as well as secure better collection of concentrated urine would be an outlet valve that prevents the flush water for urine to enter the urine pipe. Magnetic water treatment could possibly be used in connection with irrigation of urine in drip irrigation systems to prevent blockages related to the use of hard water. It is essential to investigate these possibilities.

Diverting toilets, vacuum technology, separators and waterless urinals should all be important factors in elements for a sustainable society with collection and recirculation of nutrients and organic matter in urine and faeces to agriculture. Waterless urinals seem to be the technical system component that is most easy to establish and run in order to collect big amounts of concentrated urine. Whether it should be recommended to establish diverting vacuum toilets or diverting double flushing toilets in combination with a separator, depends highly on the concrete location and on the users.