Nutrients removal from the secondary effluents of municipal domestic wastewater by Oscillatoria tenuis and subsequent co-digestion with pig manure

Batch experiments were carried out to investigate the performance of Oscillatoria tenuis to remove nitrogen, phosphorus and chemical oxygen demand (COD) from secondary effluents of municipal domestic wastewater. Meanwhile the potential of biogas production by collected O. tenuis co-digested with pig manure was also investigated. O. tenuis had a biomass productivity of 150 mg L-1 d(-1), a removal rate of (96.1%), total phosphorus (82.9%) and COD (92.6%) within 7 d at an aeration rate of 1.0 L/min. The biochemical methane potential (BMP) test for O. tenuis fermented with pig manure was evaluated at three different ratios. The cumulative methane yield was 183 mL CH4/gVS(add) at a mixing ratio (MR) of 3.0, 191 mL CH4/gVS(add) at a MR of 2.0 and 84 mL CH4/gVS(add) at a MR of 1.0. The maximum methane yield appeared at the ratio of 2.0. Meanwhile, acid-, alkali- and thermal-pretreatments were applied to raw microalgae biomass to promote biogas production. The highest methane productivity (256 mL CH4/gVS(add)) was achieved by the thermal-pretreatment at 120 degrees C, which was about 1.5 times higher than the non-pretreatment group (191 mL CH4/g VSadd).