Biomass Characteristics Of Chlorella Vulgaris And Fe/P Cycle Mechanism In Fe-P-rich Coprecipitation Water

Chlorella Vulgaris（C.vulgaris）is an effective biological treatment method for eutrophic water.However,in a large number of endogenous P-polluted waters,P pollution will continue or even aggravate.In order to explore the relationship and process of C.vulgaris and endogenous P re-release,and to achieve macroscopic control of algal biomass by rationally regulating water conditions.In this paper,C.vulgaris is selected as the experimental object,and Fe-P-rich co-precipitation water was used as the application environment.Around the research system of C.vulgaris,Fe-P co-precipitation and overlaying water,column experiment,comprehensive batch experiment,orthogonal experiment and co-culture methods are used.The effects of different water conditions such as flow rate,disturbance rate,solid-liquid ratio and particle size on the growth of C.vulgaris and the biochemical interaction between C.vulgaris and Fe-P co-precipitation were studied.The optimization of different water conditions and the Fe/P release process under the activity of C.vulgaris are discussed.The main conclusions are as follows:（1）The effects of flow velocity and particle size on C.vulgaris migration in Fe-P-rich coprecipitate water were investigated.A flow rate of 100 ml/h or less could significantly enhance the retention of C.vulgaris migration behavior.The retention factor R_f tends to the maximum(R_f50<R_f150<R_f100)when the flow rate is 100 ml/h.The inhibition of C.vulgaris migration by Fe-P coprecipitation was enhanced at a moderately flow rate,and C.vulgaris may be forcibly desorbed once the flow rate was exceeded.In addition,when the sediment particle size was more than 100 M,the flow rate had a weak effect on C.vulgaris biomass accumulation in Fe-P coprecipitation,and the Fe-P coprecipitation would have biomass accumulation to the maximum extent.Therefore,the effect of C.vulgaris migration process on biomass should be comprehensively considered in the analysis of specific waters.（2）The effects of disturbance rate,solid-liquid ratio and particle size on the growth of C.vulgaris were evaluated by biomass,specific growth rate and p H.For biomass,the disturbance intensity of water body was V_{150 r/min}>V_{100 r/min}>V_{50 r/min},the particle size of Fe-P coprecipitation was S_30-40M>S_10-20M>S_5-7M,and the solid-liquid ratio was R_{25 g/L}>R_{125 g/L}>R_{250 g/L}.In addition,the three factors have different effects on the p H and specific growth rate of C.vulgaris,respectively.Therefore,it is feasible to achieve macro-regulation of C.vulgaris growth in the watershed by adjusting water disturbance rate,coprecipitation particle size and solid-liquid ratio.（3）The single-factor effects of three physical factors such as water disturbance rate,solid-liquid ratio and the particle size of Fe-P co-precipitation on the growth of C.vulgaris were evaluated.Three physical factors have relatively significant effects on the biomass,solution p H and specific growth rate of C.vulgaris.The significance of the impact on biomass at the0.05 level is the disturbance rate>particle size>solid-liquid ratio.At the 0.05 level,the significance of the impact on the p H of the solution is the disturbance rate>solid-liquid ratio>particle size.The significance of the impact on the specific growth rate at the 0.05 level is the disturbance rate>particle size>solid-liquid ratio.（4）Through the response surface method BBD design,the interaction of the three physical properties of water disturbance rate,solid-liquid ratio and Fe-P co-precipitation particle size on the growth of C.vulgaris was analyzed.Biomass,p H and specific growth rate were optimized for uphill climbing.First,the disturbance rate and solid-liquid ratio,disturbance rate and particle size both have a strong interaction on the biomass of C.vulgaris.When the biomass optimization reaches 7.6×10⁶ cell/m L,the optimal levels of the three physical factors are the disturbance rate of 145 r/min,the solid-to-liquid ratio of 53 g/L（0.053 g/m L）,and the particle size of 7 M.At the same time,the specific growth rate and p H value of the solution under this condition will reach 0.3 d^-1 and 8.96,respectively.Second,the solid-liquid ratio and the particle size of the Fe-P co-precipitation have a strong interaction on the p H value of the solution.When the lowest p H value is optimized to 8.82,the best levels of the three physical factors are the disturbance rate of 150 r/min and 25 g/L（0.025 g/m L）solid-liquid ratio and 7M particle size,respectively.Third,the disturbance rate and the solid-liquid ratio have a strong interaction effect on the specific growth rate of C.vulgaris.When the specific growth rate of C.vulgaris is optimized to 0.32,the three-factor combination levels are 50 r/min disturbance rate,25 g/L solid-liquid ratio and 30-40 M particle size,respectively.Considering the effects of three physical factors on C.vulgaris growth,and maintaining appropriate p H and high specific growth rate,the optimal levels of the three factors were disturbance rate of 50 r/min,solid-liquid ratio of 25 g/L and particle size of 30-40 M,respectively.The biomass of C.vulgaris increased 1.5 times within 7 days,and the maximum biomass of C.vulgaris reached8.9×10⁶ cell/m L.（5）The biochemical process of C.vulgaris and Fe-P coprecipitation was investigated,and the effectiveness of C.vulgaris in Fe-P co-precipitation waters was evaluated.During the co-cultivation of C.vulgaris and Fe-P co-precipitate,the interaction process mainly consists of three phases,including Fe/P re-release in the first phase,adsorption in the second phase and self-development of C.vulgaris in the third phase.These three stages are cycled periodically.The growth of C.vulgaris is closely related to the content of Fe-P coprecipitation in the water body.Among them,0.02-2 mg/200m L,that is,the amount of Fe-P coprecipitation of 0.1-10mg/L is more conducive to the growth of C.vulgaris.When the p H is 7,C.vulgaris can promote the dissolution and release of Fe-P.At a concentration of 5.6×10⁵-8×10⁵ cell/m L,the release amount（ΔQ）of Fe-P in 200 m L water can reach 0.275-2.25 mg/L.At the same time,due to the flocculation behavior of Fe³⁺in the release phase will inhibit the growth of C.vulgaris,specific growth rate is 0.3-0.4 d^-1,and the removal rate of phosphorus is less than30%.During the Fe-P coprecipitation release phase,the specific growth rate of C.vulgaris was 0.3-0.4 d^-1,and 0.02-2 mg/200m L Fe-P reached the highest 0.53 d^-1 in the solution.A small amount（0.02-2 mg）of Fe-P co-precipitation has the most significant effect on the growth of C.vulgaris.The flocculation in the third phase is mainly affected by self-flocculation.In the short term,the growth of C.vulgaris is inhibited under the condition of high Fe-P content,and at the same time,P pollution continues to increase.From a long-term perspective,the dissolution and release of Fe-P co-precipitates by C.vulgaris has biological cyclical significance in the water-sediment system.In Fe-P-rich coprecipitation water,the maximum removal rate of phosphorus by C.vulgaris is 30%.In P-polluted waters,one of the main endogenous phosphorus storage methods,the Fe/P cyclic release of Fe-P co-precipitation under the activity of C.vulgaris,also depends on the environmental conditions of the basin water.In the long term,the biotransformation of phosphate plays a key role in the ecological balance of the water-sediment system.