Reading the actual paper now. Important bits: The composition of excreted normal human urine, is:4 urea 6–18 g day−1, uric acid 1.8 g day−1, creatinine 0.5–0.8

Reading the actual paper now. Important bits: The composition of excreted normal human urine, is:4 urea 6–18 g day−1, uric acid 1.8 g day−1, creatinine 0.5–0.8 g day−1, amino acids 0.12 g day−1 and peptides 0.5 g day−1. Variable amounts of lactic acid, citric acid, bilirubin and porphyrins, ketone bodies (aceto-acetic acid; β-hydroxybutyrate; acetone), and small amounts of hexose (glucose) and pentose (arabinose) sugars may also be present in normal urine. When considering the bio-available organic content of excreted urine, compounds such as urea and uric acid are not included, since they cannot be utilised as carbon-energy (C/E) sources by the microbial community inside an MFC. In total, the dry weight content of metabolisable organic substrates, within excreted urine, was estimated to be 0.78 g/human/day.4 Due to the insignificant amount of lipid in urine, this has also been ignored. Therefore, the mean calorific value of 1 g of carbohydrates, peptides, proteins or amino-acids (as metabolisable substrates within urine) has been estimated to be 2.08 kcal Which, if I'm reading it correctly, means you can extract 1.62 kCal of energy per day from your urine (assuming 100% efficiency). This is not a lot. Even if you collected all the urine from a city of one million people, it would be roughly 80 kilowatts.