Preliminary Study On The Cultivation Of Chlorella Sorokiniana Using Silk Industry Wastewaters

As a main primary producer on the earth,microalgae have a lot of advantages relative to other plants,such as high photosynthetic efficiency,fast regeneration speed,and strong environmental adaptability.Cells of microalgae are rich in carbohydrates,proteins,lipids and other value-added components and can be used as an additive of high quality feed in animal husbandry.Thus,microalgae could be considered as a renewable bioresource with wide application.However,the requirements of water and nutrients are high during microalgae cultivation at large-scale,which have been recognized as the main restrictive factors for the large-scale cultivation.Previous studies documented that cultivating algae in wastewater was an economic and environmental way to reduce the cost of microalgae cultivation,which could recycle nutrients from wastewater,save freshwater and reduce the cost of wastewater treatment.In this study,the feasibility of microalgae cultivation using wastewaters(cooking wastewater,reeling wastewater and frigon wastewater)taken from 3 different sections in a silk production factory was investigated.Firstly,4 diffenents algal strains,including Chlorella sorokiniana(FACHB-275),Chlorella pyrenoidosa,Chlorella vulgaris(UTEX-2714)and Scenemus obliquus(FACHB-417),were used to screen the optimal strain with strong adaptability according to their growth characteristcs.Then,wastewaters(cooking wastewater,reeling wastewater and frigon wastewater)taken from 3 different sections in a silk production factory were used to cultivate microalgae to determine the optimal wastewater for algal cultivation by comparing the growth characteristics of microalgae,monitoring the nutrient removal in wastewater,and analyzing the chemical compositions of algal biomass.Finally,the wastewater was divided into two parts:sterilization and non-sterilization,to investigate the effects of bacteria on the growth of microalgae,nutrient removal and algae biochemical components.The main results were as follows:(1)Chlorella sorokiniana(FACHB-275)showed the best growth characteristics among the 4 algal strains.At the end of cultivation,the biomass of Chlorella sorokiniana reached1.16 g/L,the chlorophyll content was 15.8 mg/L,and the F_v/F_m was stable at 0.71.(2)The physicochemical properties of cooking wastewater,reeling wastewater and frigon wastewater were different,among which frigon wastewater was not suitable for algae cultivation directly because of its high turbidity and salinity.The reeling wastewater was not sufficient to support the algal growth with a final biomass of 0.20 g/L because it had low nutrient concentrations,which would be consumed very quickly.Nutirents in cooking wastewater were suitable for the growth of chlorella with a final biomass of 0.49 g/L.(3)Mixed wastewaters had positive synergetic effects on algae growth.The final biomass of C.sorokiniana in mixed wastewater was 0.37~0.56 g/L.When the frigon wastewater was mixed with the other two wastewater in the proportion of 1:3 and 1:7,the removal efficiency of TP could be significantly improved,reaching more than 90%.The COD removal efficiency was also improved by mixing wastewater,which was in the range of 89.3~92.9%.(4)Initial inoculation density and autoclaved of wastewater would affect the growth of C.sorokiniana.When the initial inoculation density was less than 0.04 g/L,bacteria in the cooking wastewater would affect the algal physiological states and cause the decrease of algal biomass.When the inoculation density was 0.08 g/L,the biomass was basically the same when the alga grew in the autoclaved wastewater or not.When the inoculation density was 0.16 g/L,the presence of bacteria could promote the algal growth.The data indicated that the inhibition effects of bacteria on the algal growth would be eliminated with the increase of initial dry cell density.(5)Initial inoculation density of C.sorokiniana and autoclaved of wastewater would affect the removal of nutrients in wastewater.This alga could quickly remove nutrients from the cocoon wastewater,especially at the high initial inoculation density.The bacteria in the cocoon wastewater would help to remove nutrients,especially at the initial stage of algae cultivation.(6)The algal chemical compositions were affected by initial inoculation density and bacteria.Increasing inoculation density and bacterial presence were beneficial to oil accumulation,when the inoculation density was 0.16 g/L and bacteria existed,the highest oil content was 31.5%;inoculation density had little effect on protein accumulation,and aseptic culture could increase protein accumulation by about 5%;moreover,in the presence of bacteria,increasing inoculation density would cause a decrease in carbohydrate content(the maximum decline was 5.9%)relative to the absence of bacteria.