The Impact Of Carbon Sources On The Characteristics Of Extracellular Polymeric Substances In A Self-floccutating Microalga Neocystis Mucosa SX

Microalgae have the characteristics of fast growth,high photosynthetic efficiency and strong adaptability.They can absorb and remove pollutants from wastewater to improve water quality.However,the effective separation of microalgal cells from wastewater is inevitable for microalgae-based wastewater treatment process.At present,the high energy consumption of microalgae-water separation has become one of the important bottlenecks for the large-scale application of microalgae-based wastewater treatment process.Compared with other methods,flocculation is a promising method due to low cost and simple operation.Extracellular polymeric substances(EPS)are considered to be the important factors affecting the flocculation of microalgae.However,there are few reports on EPS,and no universal method has been reported for EPS extraction from microalgae.In addition,there are abundant carbon sources in real wastewater.The response of EPS in microalgae to varied carbon sources has still remained unclear.Based on above reasons,a self-flocculating microalga was used as the experimental species in this study to explore the optimal method of extracting EPS from microalga and the impact of carbon sources on the physicochemical properties of EPS.The main research results were as follows:(1)A self-flocculating microalga was isolated from local soil samples in Shanxi Province.After being cultured in BG-11 medium,it was identified by molecular methods.According to the phylogenetic analysis,it was reasonable to identify the microalga as Neocystis mucosa SX.(2)The EPS of N.mucosa SX was extracted by five methods: cation exchange resin(CER),EDTA,heating,acidic treatment and alkaline treatment.The results indicated that both CER and heating treatment extracted more EPS with rich chemical groups than other three methods.Moreover,it was favorable for EPS extraction by prolonging treatment time for CER method and raising temperature for heating treatment.Nevertheless,long treatment time for CER method and high temperature for heating treatment resulted in severe cell lysis,which could not represent the real contents of EPS in microalgae.Therefore,it is not suitable to EPS extraction.Based on both EPS extraction efficiency and cell viability,we believe that the CER extraction for 6 h could be applied for the subsequent research.(3)The impact of carbon sources on the physicochemical characteristics of EPS in a microalga N.mucosa SX was studied.In this study,N.mucosa SX was cultured in synthetic wastewater with glucose,sodium acetate,sucrose and starch as carbon sources.The results showed that starch as carbon source promoted the production of EPS via the cell lysis and the stress induced by available carbon starvation.Compared to notable change on EPS content,the chemical structure and the monomer composition of extracellular polysaccharides did not significantly respond to different carbon sources.However,the proportion of functional groups and monomers had a notable response to different carbon sources.EPS in the microalga cultivated with starch had a higher proportion of hydrophobic groups C-(C/H)(26.81%)and a lower proportion of hydrophilic groups C-OH(54.82%),compared to the microalga cultivated with the other three carbon sources.The proportion of functional groups and monomers had a notable response to carbon sources.The change of EPS characteristics may affect the flocculation efficiency of microalgae.