Improvement of microalgae lipid productivity and quality in an ion-exchange-membrane photobioreactor using real municipal wastewater

To improve the productivity and quality of microalgae-based biodiesel when using municipal wastewater(MW)as nutrients source,an ion-exchange-membrane photobioreactor(IEM-PBR)was used in this study to eliminate the negative effects of pollutants in MW on microalgae Chlorella vulgaris and Scenedesmus obliquus.In the IEM-PBR,the real MW and microalgae cultures were separated in two chambers by the ion-exchange-membranes(IEMs).Nutrients(N,P,etc.)in the MW permeated into microalgae cultures through the IEMs,while pollutants(suspended solids,competitors,etc.)in the MW could hardly permeate into microalgae cultures.As a result,the lipid productivity in the IEM-PBR was improved to 85.7 mg/(L·d)for C.vulgaris and 111.8 mg/(L·d)for S.obliquus,which was slightly higher than that in the traditional photobioreactor(T-PBR)with real MW after centrifugation(82.5 mg/(L·d)for C.vulgaris and 105.8 mg/(L·d)for S.obliquus),but much higher than that in the T-PBR with untreated MW and primary MW(with lipid productivity of 20-30 mg/(L·d)).Besides,the lipid quality obtained in the IEM-PBR had higher proportion of cetane number(ca.60%)and lower linolenic acid content(ca.8%),which showed a superior quality in the IEM-PBR to that in the T-PBR.It demonstrated that the IEM-PBR is an effective approach to improve the productivity and quality of microalgae biodiesel.