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Vurdering af muligheder og begrænsninger for recirkulering af næringsstoffer fra by til land

Summary and conclusions

An increasing demand in the Danish society for recycling wastes and save resources for waste disposal has lead to an increased interest in alternative ways to handle waste. This is reflected by peoples increased interest in collecting urine from separation toilets to be used as fertilisers for crops and in fields.

This investigation was initiated to assess the microbiological quality of stored urine collected from separation toilets. The investigation included four projects selected from the Environmental Protection Agency´s (EPA) action plan to promote ecological developments of cities and treatment of sewage under the Theme 3 "Assessment of the potential and limitations for re-cycling of nutrients from urban to rural areas". The four projects (Hyldespjældet, Møns Museumsgård, Hjortshøj og Kolonihaveforeningen) represents different solutions in different urban housing communities with different users.

The investigation does not include studies of pathogen survival on soil and crops neither does it include a risk assessment of the re-cycling of human urine. A risk assessment of re-cycling humane urine will be reported in a separate report from a project financed by the EPA. The present report is part of the project entitled "Assessment of the potential and limitations for re-cycling of nutrients from urban to rural areas" under Theme 3, which is reported in a separate report to EPA..

Monthly samples were collected from the urine separation tanks from the four projects during periods of 4 to 6 months with the aim to determine the microbiological quality of stored urine. Samples were analysed for a number of bacterial indicators: total bacterial counts at 37° C, faecal entercocci and E. coli, and several bacterial and parasitological pathogens: Salmonella, Campylobacter, Cryptosporidium parvum, Giardia duodenalis and other pathogenic intestinal parasites. The pH and temperature of stored urine were measured and the urine was visually inspected. Because of findings of the parasite Cryptosporidium parvum in the urine tanks, the studies of this parasite were expanded to include the viability and infectivity of the parasite eggs.

The four different urban housing communities are described with focus on the type of housing and the users anticipated to use the toilets (children/adults).

Additional experimental studies were carried out to determine the survival of several important bacterial pathogens in stored urine. The bacterial pathogens studied included: Salmonella typhimurium, Salmonella enteritidis, Campylobacter jejuni, Vibrio cholerae O1, Vibrio parahæmolyticus, E. coli O157:H7, Shigella flexneri and Shigella dysenteriae. The survival studies were done at 7° C og 20° C.

The results of the analyses of urine samples from the storage tanks showed that the number of enterococci and E. coli were reduced to below the detection limit (< 10 per ml) in the tanks at the four projects after 3 to 4 months storage. Some variation was observed between the projects.

Total bacterial counts at 37^oC decreased for Hyldespjældet and Møns Museumsgård after 2 months storage. However, the total bacterial counts were fairly constant in the subsequent 3 to 4 months storage period (100-1000 bacteria per ml). A small increase in bacterial counts, which was seen during the Spring period, may have been caused by bacterial growth in the tanks. The total bacterial counts at 37^oC for Hjortshøj showed only limited variation (10⁴ per ml) during the four months of analysis. This could be caused by contamination with soil bacteria through a hole in the lit of the storage tank. Except for one tank, the total bacterial counts were reduced in Kolonihaveforeningen to below the detection limit of 100 bacteria per ml after 1 to 4 months of storage. Seven urine storage units showed numbers of total bacterial counts at 37^oC below the detection limit after 2 months of storage.

The bacterial pathogens, Salmonella og Campylobacter, were not detected in any urine samples. The parasitological pathogens, Cryptosporidium parvum og Giardia were found in repeated samples from the storage tanks in Hyldespjældet, Møns Museumsgård and Hjortshøj. Samples from Hyldespjældets and Hjortshøjs contained 1 to 3 parasite eggs (oocysts) per ml urine in 5 of 9 samples. No other parasitological pathogens were detected. Additional studies of C. parvum showed that some of the eggs were viable and infective. The relative number of viable eggs did not appear to be reduced during the study period. However, the actual numbers of parasite eggs could not be determined as the quantification was associated with great uncertainties. The viability and infectivity of Giardia were not investigated. Only few infective C. parvum eggs are needed to cause infection in humans (low infectious dose).

Results from the experimental studies showed that the numbers of all bacterial pathogens were reduced to below the detection limits of 10 bacteria per ml during a 20 days period. The numbers of V. parahæmolyticus and V. cholerae were reduced much faster than the other pathogens. Salmonella, Shigella and Campylobacter could not be detected 2 to 3 days after inoculation of the urine and E. coli O157:H7 showed the longest survival between 16 and 20 days.

The results from our investigations show that following a storage period of 4 months the number of bacterial pathogens and indicator bacteria in humane urine can be expected to be reduced to < 100 per ml urine. In Sweden, a 6 months storage period at 20° C is recommended if the urine is to be used on all crop types without restrictions. Shorter periods of storage, for example 1 month at 4° C, are suggested if the urine is to be used on fodder crops; on crops to be processed (eg. dried or heat-treated) before human consumption; and if relative small volumes of urine are used, eg. as fertilisers in gardens of the urine producers (Jönsson et al., 2000). Thus, the Danish and Swedish investigations show that 4 months storage of separated urine results in a marked and significant bacterial reduction. The re-cycling of urine as fertiliser seem therefore associated with only very little if any risks for bacterial-related gastro-intestinal infections for humans and animals when handling urine and consuming crops fertilised with urine. The shown reductions in bacterial numbers assumes that new urine or other material containing bacteria are not introduced to the tanks after initiation of storage. A possible re-growth of total bacterial counts at 37^oC and enterococci in urine during storage should be further studied.

The results of the occurrence and survival of parasites, including Cryptosporidium parvum og Giardia duodenalis, and the knowledge about the survival of viruses in urine are insufficient, but indicate that viable and infective parasites, and viruses, may be found in urine after 6 months storage. Further investigations are needed to assess the occurrence and survival of parasite eggs and viruses in stored urine before any guidelines may be prepared about the survival of these micro-organisms. A separate report on survival of viruses in stored human urine will be published financed by the EPA.