Enhanced lipid production by Chlorella pyrenoidosa through magnetic field pretreatment of wastewater and treatment of microalgae-wastewater culture solution: Magnetic field treatment modes and conditions

[Display omitted] •The wastewater pretreatment by magnetic field is beneficial for microalgae growth.•Bottom-MF pretreatment mode shows a better effect on algae culture than bypass-MF.•The concentrations of COD and NH4-N in wastewater are reduced by MF pretreatment.•The MF treatment on microalgae culture solution is favored for lipid production.•Bypass-MF treatment time of microalgae is not very important for lipid production. The cultivation of microalgae in municipal wastewater not only purifies the wastewater but also transforms nutrients into biomass that contains high-value lipids. In this study, conventional static bottom-magnetic field (bottom-MF) equipment and cost-effective bypass-magnetic field (bypass-MF) equipment were designed and independently coupled with a microalgae-wastewater system in different positions to evaluate the effect of magnetic field (MF) on microalgae biomass production and lipid accumulation. When the MF equipment was applied in the wastewater pretreatment unit, the bottom-MF pretreatment mode exhibited a more beneficial effect on subsequent biomass and lipid accumulation. However, when the MF equipment was applied in the microalgae-wastewater culture unit, there was no significant difference between the bottom-MF and bypass-MF modes. The results of the orthogonal experiment suggested the optimum conditions for lipid production were wastewater pretreatment by bottom-MF at 5000 Gs for 1 h, followed by microalgae-wastewater culture treatment by bypass-MF at 5000 Gs for 3 h.