Elephants in Artis Zoo (Amsterdam, the Netherlands) produce high quantities of manure daily, which is currently being discarded as waste. Potentially, elephant manure could be used as a fertiliser and/or soil improver. To explore this, an aerobic incubation experiment was carried out in the laboratory. Results were evaluated by modelling, using default values of dairy cow slurry (DCS) for comparison. It was hypothesised that 1) elephant manure would mineralise slowly and, 2) release relatively small amounts of N compared to dairy cow slurry. The carbon content and C:N-ratio in elephant manure were 419 g kg-1 and 36:1, respectively. The estimated humification coefficient of elephant manure was 0.32, indicating faster mineralisation than of DCS in The Netherlands (0.7). Modelling the results showed that after 10 years of annual additions of 100 kg Norg ha-1, total carbon build-up from elephant manure and DCS was ca. 4800 and 6800 kg ha-1, and total nitrogen mineralisation was 540 and 490 kg N ha-1, respectively. The higher mineralisation rate from elephant manure compared to DCS could be due to occurrence of priming during the incubation experiment and/or different qualities of organic matter fractions. It was concluded from this experiment that elephant manure could be suitable as both a soil improver and fertiliser, and recommendations for follow-up research are given.

Wastewater is an important residual stream in terms of nutrients, in cities especially from household sources. This report explains why improving circularity of sanitation systems is relevant, how it is linked with circular (urban) food production, what circular sanitation systems entail and what opportunities and barriers are present for its realisation. Discussed aspects are related to sustainability, environment, quality, agronomy,legislation, health and safety, technology, economy and awareness and acceptation. The report furthermore provides recommendations to promote the transition from conventional wastewater treatment to circular sanitation and nutrient recovery and reuse in relation to (urban) agriculture. Recommendations for Amsterdam and other cities and stakeholders are: provide clarity in legislation, stimulate and work on quality assurance, tackle legislative barriers, stimulate the demand side for nutrients and biobased fertilisers, make new and renovated buildings circular sanitation proof, assess profitability and sustainability of circular sanitation area-specific, and assign responsibilities in the transition towards circular sanitation.