The present study investigated the interaction between starch and lipid accumulation in a green microalgae enrichment culture. The objective was to optimize the lipid content by manipulation of the medium in regular batch culture. Two medium designs were evaluated: First a high ortho-P concentration with vitamin supplementary (Pi-vitamins supplemented medium), second normal growth medium (control). Both media contained a low amount of nitrogen which was consumed during batch growth in three days. The batch experiments continued for another 4 days with the absence of soluble nitrogen in the medium. When the mixed microalgal culture was incubated in the Pi-vitamin supplemented medium, the lipid, and starch content of the culture increased within the first 3 days to 102.0 ± 5.2 mg/L (12.7 ± 0.6% of DW) and 31.7 ± 1.6 mg/L (4.0 ± 0.2% of DW), respectively. On the last day of the experiment, the lipid, and starch content in Pi-vitamin medium increased to 663.1 ± 32.5 mg/L (33.4 ± 1.6% of DW) and 127.5 ± 5.2 mg/L (6.4 ± 0.3% of DW). However, the lipid and starch content in the control process, reached to 334.7 ± 16.4 mg/L (20.1 ± 1.0% of DW) and 94.3 ± 4.6 mg/L (5.7 ± 0.3% of DW), respectively. The high Pi-vitamin medium induced storing lipid formation clearly while the starch formation was not affected. The lipid contents reported here are among the high reported in the literature, note that already under full growth conditions significant lipid levels occurred in the algal enrichment culture. The high lipid productivity of the reported mixed microalgae culture provides an efficient route for efficient algal biodiesel production.

The disruption of nutrient cycles caused by human activities such as agriculture and burning fossil fuels is impacting ecosystem services on global and local scales. The increasing concentration of carbon dioxide in the atmosphere contributes to rising global temperatures and ocean acidification, whereas the accumulation of nutrients in water systems is leading to degradation of water quality and biodiversity. City populations play a major role in carbon dioxide and nutrient emissions as ‘end consumers’ of resources. The current challenge towards more resource-efficient cities is to transform urban metabolism from linear to cyclical. Discharged nutrients and carbon dioxide can be used as input for algae, which fixate carbon very efficiently into energetic storage compounds as starch or lipids. However, cities often lack the space to implement large-scale algae production. This article evaluates the potential of reusing nutrients and carbon dioxide to produce algae, food and biofuel on water nearby coastal and delta cities. First, nutrients and carbon dioxide discharge is estimated and two scenarios are developed. From the cities nutrient production, the potential algal yield is evaluated and translated into feed, food and oil yields. Two delta cities are chosen as case studiesRotterdam and Metro Manila. The conclusion of this article is that Floating Production can help cities increasing their resilience in the field of food and energy. Floating Production can also contribute to a solution for global land shortage. The combination of food and energy production with floating urban development provides a climate-proof urban expansion in delta and coastal areas.