Nutrients Recovery From Post Hydrothermal Liquefaction Wastewater By Microalgae And Metabolic Pathway

Post hydrothermal liquefaction wastewater (PHWW) from algae contains amount of carbon, nitrogen and phosphorus, and various mineral elements, which are the nutrients needed for microalgal growth. Using hydrothermal liquefaction wastewater to cultivate microalgae can realize wastewater resource utilization and reduce the cost of biomass production. There are multiple interesting of economy, environment and energy.This study first analyzed the characteristics of PHWW, investigated the effects of different feedstock for HTL and separation methods for products on the characteristics of PHWW, microalgae biomass production and nutrient recycling. From view of the algal cell activity and the tolerance on high PHWW, we investigated preculture mode and microalgae strains to determine the suitable strain cultured in PHWW. Optimization of the initial concentration of PHWW, initial inoculation size and light-dark cycle, there studied nutrition mode of Chlorella vulgaris in the PHWW to supply some suggestion to improve biomass production and nutrient recycling efficiency.PHWW is a special high concentration organic wastewater. There were amout of carbon, nitrogen and phosphorus, some protein and many minerals, which indicated PHWW has a high resource value. But it needs effective pretreatments for microalgae culture. Carbon was mainly in the form of TOC. TN included ammonia and organic nitrogen.12%～49%o f the organic nitrogen was protein. NH3-N was the main form of nitrogen under hydrothermal liquefaction temperature (260 ℃ and 300 ℃). Under temperature (220 ℃), the nitrogen was mainly in the form of organic nitrogen. Phosphorus presented in the form of PO43--P. COD can be calculated by the equation: COD (mg/L)= 2.8657 x TOC (mg/L)-51615. Nitrogen oxygen-containing organic compounds were the major organic components in PHWW. Solid content was the most severely effect factor on the concentration of TOC, NH3-N, TN and PO43--P, followed by the reaction temperature.Feedstock and separation method for products of hydrothermal liquefaction significantly affected the characateristics of PHWW, thereby affected microalgae biomass productivity and recycling nutrients efficiency. PHWW from high-protein microalgae was relatively higher content in nitrogen and phosphorus. Ether extraction method reduced the TOC concentration and the proportion of nitrogen oxygen-containing organic compouds. The concentration of organic nitrogen and TP concentration was decreased by 7.1% and 52%, respectively. C. vulgaris 1067 resistant the proportion of PHWW (volume ratio) increased from 1.9% to 6.7%, and the highest biomass yield was 1.9 times of that in the PHWW separated by vacuum filtration method. The PHWW of low-protein microalgae had relatively higher concentration of TOC and VFA. Vacuum filtration method was conducive to the microalgae production and nutrients recycling.C.vulgaris 1067, Chlorella regularis var. minima, Chlorella pyrenoidosa, Scenedesmus quadricauda and Microcystis aeruginosa all grew in dilution PHWW with 150～750 mg/L of the initial TN concentration. Microcystis aeruginosa can be used as focusing strain for biomass production with PHWW, followed by C.vulgaris 1067. Domestication with PHWW significantly improved the cell activity of Chlorella regularis var. minima, Chlorella pyrenoidosa, Scenedesmus quadricauda, shortened the lag phase, and improved biomass productivity. Enhancing photosynthesis improved biomass productivity and increase growth rate of C.vulgaris 1067. Enhancing heterotrophic ability shortened growth period. But the biomass accumulation amount and growth rate were both declined. C. vulgaris 1067 achieved the maximum biomass accumulation (0.84 g/L) and productivity (0.065 g/L/d) in 6.7% PHWW medium with the highest nutrients recycling quantity and nutrients conversion to cells. When the initial concentration of TN increased to 750 mg/L, the growth of microalgae was inhibited severely. Initial inoculum size significantly affected the nutrient removal quantity and biomass accumulation. C. vulgaris 1067 with inoculum size of 0.103～0.135 g/L achieved 1.41 g/L of the final amount of bioaccumulation with 58.87% of TOC recovery,57.35% of TN recovery and 60% of the TP recovery. Light-dark cycle affected C. vulgaris 1067 growth and nutrient recycling. All darkness the condition of There was no biomass accumulation but nutrients removal under 24 h dark. Biomass and nutrient removal increased with the increasing of exposure.12:12 was optimized light-dark cycle. C. vulgaris 1067 grew mode in PHWW was mixotrophy with 60% photoautotrophy and 38% chemoheterotrophy. Photoautotrophy was dominant growth mode. Photosynthetic phosphorylation promoted oxidative phosphorylation.