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.
A phase-feeding strategy of nutrients based on requirements of Chlorella vulgaris in different physiological phases was examined to maximize the biomass and lipid productivity.This strategy includes reduction of duration in adaption phase(stage-I),enhancement of biomass in growth phase(stage-II)and improvement of lipid productivity in stationary phase(stage-III).The duration of microalgae in adaption phase was reduced from 52 h to 34 h at nitrogen and phosphorus feeding rates of 5.11 mg/(L·d)and 0.54 mg/(L·d),whereas the maximum biomass concentration during growth phase was improved to(4.03±0.25)g/L at nitrogen and phosphorus feeding rates of 20.04 mg/(L·d)and 4.21 mg/(L·d).In stationary and decline phases,a maximum lipid productivity of 132.30 mg/(L·d)was achieved when nutrients supply was stopped at 128 h,which was 28.86 mg/(L·d)higher than that when nutrients supply was stopped at 104 h.This multi-phase cultivation could be a promising strategy for simultaneous enhancement of microalgae biomass and lipid productivity.
