Epsilon Archive for Student Projects

Abstract

It is important that the current urine separating systems are evaluated to allow improvements to be made and consequently increase their future propagation. In order to increase the knowledge about urine separating systems this study was made. It included, among other things, measurements of amounts of urine as well as of the composition of urine collected at Nytorgsgatan 4 in the city of Hallsberg. The study was increased after an inquiry that also included the district of Understenshöjden in the city of Stockholm. In the inquiry, the users were asked questions about odour, cleaning of toilets and occurrence of blockages in the urine water locks etc. It was shown that within two years from the installation of the toilets precipitation had accumulated that could block the flow completely. The last study in shis is on methods to clear the blockages.

The collected urine solution from Nytorgsgatan contained 2.8 g of nitrogen, 0.22 g of phosphorus and 0.68 g of potassium per litre. These amounts correspond to 3.4 g of nitrogen, 0.27 g of phosphorus and 0.82 g of potassium per person per day and corresponded to 46, 40 and 49% respectively of the expected amounts, calculated from the average excretion per person with the urine as given by the Swedish Environmental Protection Agency. The amounts were adjusted after the time the average person at Nytorgsgatan spent at home per day. The concentrations of heavy metals in the urine were low. When using urine as a fertiliser, the amounts of heavy metals to arable land were much below the permitted ones when using sewage sludge as a pertiliser, except for copper where the amounts were slightly under the permitted level.

The enquiry concentrated on the disadvantages with urine separating toilets, to find problems which could be solved. Odour, bad flushing and blockages in the water locks were three causes of dissatisfaction with urine separating toilets. Most of the problems with odour could have been avoided by careful installation of the toilet and better sealing of the joints. The persons in the enquiry found that the cleaning of the toilt Dubbletten was more difficult than that of conventional toilet, due to odour, precipitation and bad flushing of the urine bowl. The wnquiry showed that all inhabitants who had lived in the area for more than six months had had some kind of blockage in the urine water lock. All 98 of the examined water locks had reduced flow. In 77 of these the blockages were caused by hair and other such foreign bodies. Such blockages were easy to remedy. The other 21 blockages were dut to hard precipitation, which blocked up to 75% of the cross-section area.

Hard precipitation, containing large proportions of metal phosphates, can be very hard to remove. It is always possible to remove them with mechanical aids, such as a cleaning wire but it can be very time consuming. Another problem with mechanical cleaning is that it can wear out the water locks. Chemical cleaning methods have been tested for that reason. The most efficient chemicals were sodium hydroxide, hydrochlorid acid and an industrial cleaning agent containing phosphoric acid. Sodium hydroxide was the most efficient of the studied chemicals. It reduced the precipitation by 80 to 100%, but it also rewuired large amounts of water afterwards to rinse out loose and softened precipitation. The other two chemicals reduces less of the precipitation but they also attacked the oxide that had been formed in the water locks and left a smooth copper surface. Those chemicals did not need any particular rinsing afterwards. The use of socium hydroxide can increase the urine solution's pH in the collection tank while acids can reduce the pH level. A high pH is preferable because of higher reduction in micro-organisms.