| Microalgae-based municipal wastewater treatment process not only effectively removes nutrients from wastewater but also accumulates biomass for the production of biodiesel and other high value-added products.Nevertheless,the high cost for harvesting microalgae biomass becomes one of the bottlenecks for the development of above process.Although it is effective to harvest microalgae via inorganic flocculants,heavy metal ions can affect cell activity of microalgae.In this study,an oil-rich microalga was used to treat municipal wastewater.Moreover,the effect of ferric chloride on flocculation characteristics,physiological activity,total lipid content and wastewater treatment performance of the microalga was studied,which aims to provide some technical support for mineral flocculant harvesting microalgae biomass.The main findings are as follows:（1）After wastewater treatment,P.kessleri TY was flocculated with different dosages of ferric chloride,and the flocculation characteristics,physiological activity and total lipid content of P.kessleri TY were determined.When the dosage of ferric chloride was 100 mg/L and sedimentation time was 5 min,the flocculation efficiency of P.kessleri TY suspension reached 96.7%.At the same time,P.kessleri TY cell showed the highest PDHA activity,indicating good cell vitality.Further increasing FeCl3 dosage or prolonging sedimentation time not only did not significantly improve the flocculation efficiency,but also led to an increase in numbers of dead cells.According to SOD and CAT activity of microalgal cells,it was speculated that excessive reactive oxygen species（ROS）were produced in cells of P.kessleri TY flocculated with high dosage of ferric chloride,which caused oxidative stress reaction.Excessive accumulation of ROS resulted in cell death once increased antioxidant enzyme activity was insufficient to remove ROS induced by high dosage of ferric chloride.These results indicated that high dosage of ferric chloride（more than 100 mg/L）did not significantly improved the flocculation efficiency of the microalga.Moreover,the physiological activity of P.kessleri TY decreased with increasing ferric chloride concentration or prolonging flocculation time.It was also found that the lipid content of P.kessleri TY did not be affected by flocculation with ferric chloride.（2）Flocculated cells of P.kessleri TY were used as inoculated biomass for municipal wastewater treatment.It was showed that the performance on the growth and pollutants removal of P.kessleri TY flocculated with different dosages of ferric chloride was basically consistent with the microalga harvested with natural sedimentation..The chlorophyll content of P.kessleri TY was low as cells flocculated with high dosage of ferric chloride was used to wastewater treatment.Meanwhile,values of chlorophyll fluorescence parameters increased.It was also found that the number of dead cells increased with the increasing of dosage of ferric chloride.High concentration of ferric chloride destroyed the chloroplast of some cells,which resulted in lowe chlorophyll content.These results indicated that P.kessleri TY harvested with ferric chloride could be used as inoculated biomass for municipal wastewater treatment,and the wastewater treatment performance is basically same as that of P.kessleri TY harvested with natural sedimentation.Based on above results,it was suggested that 100 mg/L of ferric chloride was used to harvest cells of P.kessleri TY.Besides,harvested cells could be subsequently used as inoculated biomass for municipal wastewater treatment. |
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