Advanced Absorption-microalgae Hybrid CO₂ Capture Process Based On Wastewater Recycling

With the burning of fossil fuels,the emission of greenhouse gases,especially CO₂,is gradually increasing,causing increasingly serious environmental problems such as iceberg melting and sea level rise.More researches focus on CO₂ capture,among which chemical absorption method is the most widely used technology at present.However,it has some problems such as high energy consumption.Microalgae immobilization of CO₂ have caused attention in recent years and microalgae photosynthesis to fix CO₂ and produce biomass is considered to be a kind of environmentally friendly technology.But the key problem of biological method is the low CO₂ solubility in the reactor,and insufficient gas-liquid contact is also easy to cause CO₂ escape,resulting in a decline of microalgae carbon fixation rate.In this paper,an absorption-microalgae hybrid CO₂ capture technology based on wastewater recycling was proposed.Abundant microalgae biomass was obtained while CO₂ was efficiently captured,and efficient purification of wastewater was also realized.In this paper,two strains of Chlorella L166 and L38 were selected as the objects and cultured in soybean wastewater with different dilution ratios to determine the appropriate wastewater proportion.The experiment showed that when the wastewater of soybean was diluted to 5 times and 10 times,the highest purification effect of wastewater and the best growth condition of Chlorella can be obtained.After determining the proportion of wastewater,NH₄HCO₃ was selected as the major chemical absorption liquid in system.The experiment explored L166 and L38 biomass production under different feeding modes of soybean wastewater（direct feeding and batch feeding mode）.It was found that batch feeding mode can promote the continued growth of the Chlorella in the late period of cultivation and the highest chlorophyll concentration of L166 and L38 were 31.7 mg/L and 34.2 mg/L,respectively.Under the condition of NH₄HCO₃ with 5-time diluted soybean wastewater,COD removal rate was 50.0%～65.0%,and NH₄⁺-N removal rate was70.0%～80.0%,and TP removal rate was 95.0%～100.0%.The mode of batch feeding could reduce the NH₃ escape rate in the system to 15.8%,and the carbon utilization rate of Chlorella was up to over 60.0%.At the same time,the economic benefits of soybean wastewater in the system compared with the traditional BG-11 medium were also evaluated.Through further optimization of feeding mode,it is found that the feeding mode of more supply in the early stage and less in the late stage was beneficial to the removal of COD（66.3%） to a certain extent compared with the average feeding mode.Meanwhile,the effect of NH₄HCO₃ and KHCO₃ solution used in hybrid system on the wastewater purification and biomass production were also compared.At the same time,the growth of Chlorella L38 in pH-controlled system was found to be better than that of the unregulated system.Adjusting pH was not only an effective way to reduce ammonia toxicity and promote microalgae growth,but also had a certain potential for wastewater treatment（the highest COD removal rate was 77.6%）.