In this case study, a nutrient budget was made to estimate import and export flows of
phosphorus (P) on the ecotourism resort of Chumbe Island, Zanzibar. The P content in
imported foods and goods was calculated using supply lists containing information on
quantities of items bought and standard food composition data. Foods and goods not
included in the standard data were subsampled for P analysis.
Total P import to Chumbe Island was 41.0 kg/year. More P was imported with foods to the guest kitchen than to the staff kitchen (13.2 and 9.1 kg P/year, respectively) although the guest kitchen served fewer meals (9333 and 14113 meals, respectively). This is explained by the more P-rich foods served in the guest kitchen. When charcoal and firewood were included, the staff and guest kitchens imported equal amounts of P since the staff kitchen used both firewood and charcoal while the guest kitchen only used
charcoal as a complement to gas.
Ash and biodegradable waste such as fruit peel were composted on-site and used to
facilitate the degradation process in composting toilets. Biodegradable waste from both
kitchens contributed 4.8 kg P/year to the compost heap, while the ash from kitchen stoves
contributed an estimated max. 17.4 kg P/year. Despite uncertainties regarding P amounts
in the kitchen waste, estimations showed that P was lost from the compost heap during all
stages of decomposition. Animals and birds scattering the compost during feeding and
leaching during the rainy season are possible reasons for these losses.
In the guest kitchen greywater system, sludge and grease were removed before the
greywater was discharged into a small mangrove swamp, while staff kitchen greywater
was poured untreated into a mud-hole in rocky ground. The guest kitchen contributed
slightly more to P discharge (0.3 kg P/year) than the staff kitchen (0.2 kg P/year). The
sludge (discharged at unspecified locations on Chumbe) contained another 0.1 kg P/year.
The grease (added to compost) contained no P.
Food scraps from both kitchens containing 2.4 kg P/year and composted toilet waste
containing 21.6 kg P/year were re-exported to Zanzibar, i.e. approx. half the P imported
was exported. The other half of imported P was lost from compost, greywater outlets, as
sludge or dissipated through fly ash dispersal.
To avoid P accumulation on ...
