Coupled Technology Of Microalgae Culture And Anaerobic Digestion By Chlorella Vulgaris

Carbon dioxide?CO₂?is a major contributor of greenhouse gas on the impact of the global climate change.Micralgae culture in closed photobioreactors could be used for CO₂ biofixation.Microalgae could be converted to biogas by anaerobic digestion?AD?.CO₂ in the biogas and the liquid digestate from the AD of microalgae could be reused for microalgae culture.In this research,the growth of Chlorella vulgaris by autotrophic culture,mixotrophic culture and heterotrophic were studied.The effects of hydrothermal pretreatment on the AD and solid-liquid separation of microalgae biomass was investigated.All of above provided a theoretical basis for the c oupled technology of microalgae culture and anaerobic digestion by Chlorella vulgaris.The inorganic carbon,light energy and nitrogen were the main factors which affected the growth of Chlorella vulgaris by autotrophic culture.When the CO₂ concentration in the gas is less than 10%,the lack of inorganic carbon was the limiting factor which affected the growth of Chlorella vulgaris.Under low light intensity?36.0?mol/?m²·s??condition,the high concentration of inorganic carbon inhibited the growth of Chlorella vulgaris when the CO₂concentration in the gas was higher than 10%.Under the high light intensity?119.3?mol/?m²·s??condition,the nitrogen was the limiting factor effect the growth of Chlorella vulgaris when the CO₂ concentration in the gas was higher than 10%.pH of the culture was too low when the CO₂ concentration in the gas was 100%,this affected the growth of microalgae.In order to reducing the cost of microalgal biomass production,pH control was necessary for microalgal biomass yieid optimization.There was a compensating effect between light intersity and CO₂ concentration.While increasing the concentration of CO₂ and the light intensity at the same time,the growth inhibition of Chlorella vulgaris by high concentration of CO₂ could be avoided.Under mixotrophic culture of Chlorella vulgaris by simulated liquid digestion,the maximum biomass yeild rate of Chlorella vulgaris was2771 mg/?L·d?.Under mixotrophic culture by acetate,the maximum biomass yeild rate of Chlorella vulgaris was 1528 mg/?L·d?.Under heterotrophic culture condition,the biomass yeild and maximum biomass yeild rate of Chlorella vulgaris were 10.4 g/L and 2709 mg/?L·d?by fed-batch culture.The biomass yeild of Chlorella vulgaris by heterotrophic culture was higher than that by mixotrophic culture,and the maximum biomass yeild rate of Chlorella vulgaris between heterotrophic culture and mixotrophic culture were not significantly different.After the hydrothremal pretreatment of Chlorella vulgaris,the contribution of biogas yeild by the orgnic matter in liquid phase increased from 17.5%to41.9%compare to the control,while the contribution of biogas yeild by the orgnic matter in solid phase decreased from 4.0%to 0.2%.The behavior of transformation of particulate organic matter to soluble organic matter increased the methane yeild and maximum methane yield rate of Chlorella vulgaris after hydrothremal pretreatment.The volume of algae cake was significantly decreased after the hydrothremal pretreatment.After the hydrothremal pretreatment at 180?,the volume of algae cake gave a maximum reduction of volume above 75%.