Growth of the microalga Botryococcus braunii in secondarily treated sewage

Urban wastewater from secondary treatment is rich in compounds of nitrogen, phosphorus, and other nutrients. The elimination of such compounds, in the few cases in which it is carried out, is achieved through tertiary treatment. The development of an alternative study is proposed on a tertiary treatment using the microalga Botryococcus braunii (A race). Experiments were carried out in batch photobioreactors at laboratory scale. The operating conditions were: pre-culture during 1 week, pH of culture medium under 8.0, temperature maintained constantly at 25EC, air-supply volume between 0.5 and 1.5 v/v/min, 12 h light/12 h darkness cycles and mechanical stirring at 60 rpm only during the culture stage. The results show the possibility of using secondarily treated sewage from domestic wastewater as a medium to grow B. braunii and for removal of nitrogen and phosphorus by algal consumption. In this way, notable amounts of lipids and biomass yields were determined, using only wastewater as the culture medium and a relatively low supply of carbon dioxide.