Cultivation of Scenedesmus acuminatus in open ponds and simultaneous nutrient removal from source separated urine
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Increasing human population calls for food security and providing enough food is coupled with frequent use of chemical fertilizers in agriculture. Phosphorus and nitrogen are one of the most essential nutrients for living organisms and the main components of chemical fertilizers. Currently, the only way to obtain phosphorus, is mining it from finite phosphate rock. However, majority of the phosphorus is after one-time use of fertilizer irreversibly wasted and drained into the natural water bodies causing uncontrollable microalgal bloom. In detail, urine is a source that concentrates high amount of phosphorus and nitrogen. Using source separated urine as a natural fertilizer for microalgal cultivation represents attractive and promising method to recover phosphorus and nitrogen. This study is the first pilot study reported in the literature that tests source separated urine as a growth medium for microalgal cultivation in open ponds with potential to recover the nutrients. Scenedesmus acuminatus was cultivated for 94 days in two different set ups: a) batch set up with 400 l working volume and 20x diluted urine; and b) semi-continuous set up with 2000 l working volume and 20x or 15x diluted urine. Results showed that S. acuminatus can achieve high yields when cultivated in 20x (2.3 g of VSS/ l of pond volume). Moreover, results showed that semi-continuous cultivation of microalgae grown on 15x and 20x diluted urine is sustainable and feasible (maximum microalgal yield was 0.45 g of VSS/ l of pond volume). The analysis of nutrient concentration showed that phosphorus and nitrogen were removed from 20x and 15x diluted urine, but further measurements are needed to exactly determine how much of phosphorus and nitrogen were recovered by S. acuminatus.