ETE student Rosanne Wielemaker was awarded the 13th Rachel Carson Environmental Thesis Prize, last November 2015 for her M.Sc. thesis ‘Harvest to harvest’. This prize is awarded annually by VVM, a network organization of environmental professionals. Only outstanding theses on environmental and sustainability research may compete. In her thesis, Wielemaker aims to close nutrient cycles in urban agriculture by using nutrients recovered from household waste via ‘new sanitation’ systems. The jury evaluated her thesis as ‘very good’. They particularly appreciated the originality and integral approach, and its valuable contribution to urban agriculture.
Closing nutrient cycles
Cities import high quantities of water, energy, and food, while producing waste flows containing disposed and excreted nutrients. These nutrients are mostly not recovered for reuse. However, according to Wielemaker, more and more cities produce food within their city boundaries. ‘These urban agriculture systems offer the possibilities to utilize recovered nutrients from the city’s sanitation and kitchen waste, thereby closing nutrient cycles’, she states. ‘But for effective resource management and an efficient reuse of recovered nutrients, such as nitrogen (N) and phosphorous (P), supply and demand should be matched.’
Balance nutrient flows
Nutrient demand from urban agriculture remains unquantified and unmanaged. Similarly, nutrient supply from sanitation systems is also largely unknown. Therefore, Wielemaker calculated both nutrient supply from waste and demand from urban agriculture systems to balance nutrient flows for a virtual situation in the city of Rotterdam. Her results showed that nutrient demand from Rotterdam’s urban agriculture was relatively high. ‘Current use of P exceeds the actual need by a factor three to seven’, Wielemaker explains. ‘So the demand for this nutrient can be reduced dramatically.’ The results further showed that for 1 ha of urban agriculture, household wastewater and kitchen waste collected from 25-45 individuals could supply 100 % of P and about 50% of N by recovering nutrients.
Wielemaker’s study shows that recovering nutrients from urban waste can match nutrient demand by urban agriculture in Rotterdam to a large extent, increasing self-sufficiency of the city, while closing nutrient cycles.