<Photo: the toilet purifying system of the NIOO presented at the Poep = Goud (Poo = gold) Festival stand>
The researchers worked with a concentrated stream of toilet water, which contains a lot of nitrogen and phosphorus. This waste is separately collected in the NIOO building and goes into a fermenter, where biogas is produced. They have now shown that with the wastewater that is treated in this way – the effluent – you can cultivate algae. ‘We have a proof of principle that you can cultivate algae on concentrated toilet water’, Packo Lamers of Bioprocess Technology says, who is working together with Tania Fernandes of NIOO. They published their research last month in the magazine Environmental Science & Technology.
The researchers worked with the algae Chlorella sorokiniana, a green algae that according to Lamers ‘grows fast on almost anything’. Previously it was already shown that algae grows on urine. The challenge was that toilet water has relative high amounts of nitrogen relative to phosphorus. ‘At a given moment the algae has removed all the phosphor out of the wastewater, but the nitrogen is still present. The algae does absorb the remainder of the nitrogen, but slowly. This needs to be optimized.’ A point of worry was therefore also the high ammonium concentration in the wastewater after the treatment in the Biodigester. But it was found that the ammonium concentration was not toxic for the algae.
Because the wastewater is really concentrated, you need a lot of algae for the purification, says Lamers. ‘For 1 gram of nitrogen in the wastewater you need 10 grams of algae per litre of water.’ The normal wastewater, that also includes shower and washing machine water, is too diluted to allow algae to grow on it, Lamers states. ‘These are mega water flows, which requires larger and thus more expensive culture systems to be able to purify using algae. Also, the harvesting of the algae would be less efficient.’
With this process, you kill two birds with one stone, because you can use the algae (with the nitrogen and phosphorus) as fertilizer. Lamers: ‘Perhaps it is also possible to use part of the algae biomass as raw material for bioplastics and biofuel.’