| Microalgae is a kind of microalgae with short growth cycle.It has the characteristics of high photosynthetic efficiency,strong environmental adaptability and high cell lipid content,making it the most potential renewable energy at present.At present,the research on microalgae at home and abroad mainly focuses on the single factor to explore the flocculation effect and flocculation efficiency.However,there are few studies on the multi-factor interaction of flocculation effect,the detection of ion residual concentration in flocculation supernatant and the utilization of residual supernatant after microalgae flocculation,which hinder the development of microalgae industry.In view of this situation,this paper studied the flocculation harvesting of Chlorella and the anaerobic fermentation characteristics of the supernatant after harvesting.The effects of flocculant type,concentration,oscillation frequency and standing time on the flocculation harvesting of Chlorella cultured to the middle and late stages were studied.The influence of each factor on the flocculation efficiency of Chlorella was studied by single factor.On the basis of single factor study,the quadratic orthogonal rotation center combination optimization experiment was carried out for the three factors of flocculant concentration,oscillation frequency and standing time.The influence of each factor and its interaction on the flocculation efficiency of Chlorella and the concentration of ferric and aluminum ions in the supernatant after flocculation was studied.Subsequently,the supernatant after microalgae flocculation was used for anaerobic fermentation to study the influence of ferric sulfate and aluminum sulfate in the supernatant after flocculation on the anaerobic fermentation process.(1)In this paper,the effects of different flocculants(ferric sulfate,aluminum sulfate)on the efficiency of Chlorella flocculation and the residual concentration of ferric and aluminum ions under different concentrations,oscillation frequency and standing time were systematically studied.The results of quadratic orthogonal rotation center combination optimization test showed that there were interactions among flocculant concentration,oscillation frequency and standing time.Among them,the interaction between flocculant concentration and oscillation frequency was strong,and the oscillation frequency had a great influence on Chlorella flocculation test and ion residual concentration.When aluminum sulfate concentration is 0.56g/L,oscillation frequency is 138 rpm,standing time is 30 min,the flocculation efficiency of Chlorella is 94.28%.When the concentration of ferric sulfate is 0.51g/L,oscillation frequency is 76 rpm,standing time is 5min,the flocculation efficiency of Chlorella is 92.24%.Aluminum sulfate concentration is 0.53g/L,oscillation frequency is 148 rpm,standing time is 17 min,aluminum ion residual concentration is 0.25mg/L.Ferric sulfate concentration is 0.56g/L,oscillation frequency is 146 rpm,standing time is 20 min,ferric ion residual concentration is 0.007mg/L.(2)In this paper,the effects of supernatant,aluminum sulfate and ferric sulfate on the daily methane production,cumulative methane production and volatile fatty acid content of anaerobic fermentation with time were systematically studied,and the effects of ferric ions and aluminum ions on the gas production characteristics of anaerobic fermentation under different concentrations were clarified.The results showed that ferric sulfate and aluminum sulfate had a promoting effect on methane production in anaerobic fermentation process,and excessive concentration would have an inhibitory effect.0.5g/L ferric sulfate had the best effect on methane production,and the cumulative methane production was 21275.68 mL,which was 46.32% higher than that of the control group.The maximum cumulative gas production was 29550.39 mL,which was 23.83%higher than that of the control group.The inhibition effect of 0.8g/L ferric sulfate was the strongest.The cumulative methane production was 13185.61 mL,which was 9.31% lower than that of the control group.The maximum cumulative gas production was 21253.6mL,which was 10.94%lower than that of the control group.The methane production of 0.05g/L aluminum sulfate group was the best.The cumulative methane production was 18873.67 mL,which was 32.83% higher than that of the control group.The maximum cumulative gas production was 30650 mL,which was29.46% higher than that of the control group.0.3g/L aluminum sulfate had the strongest inhibitory effect.The cumulative methane production was 13127.55 mL,which was 7.61% lower than that of the control group.The cumulative gas production was 18336 mL,which was 22.55% lower than that of the control group. |
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