Study On Condition Optimization Of Cultivating Chlorella Vulgaris Using Municipal Wastewater And Additional Carbon Source

Microalgae can be used to manufacture high value-added products,such as biofuels,health products and cosmetics due to the advantages of high photosynthetic rate,strong environmental adaptability and high content of lipid.The main reason of high cost on large-scale microalgae cultivation is the demand for water resources and large nutrients?N and P?.Cultivating algae in wastewater is a way to removal nutrients from wastewater,save freshwater,fix CO₂ and combine other environmental technology such as recycle of crude glycerol,which could achieve a win-win goal of economic,environmental,energy.In this study,Chlorella Vulgaris?UTEX2714?was cultured in real wastewater with low-cost carbon source and municipal wastewater was purifying during cultivation process of Chlorella Vulgaris.At first,Chlorella Vulgaris was cultured in raw,primary effluent and centrate,that were collected from three different locations of a wastewater treatment plant,with autoclaved or not.The biomass and nutrients removal were compared to choose the wastewater that is more suitable for Chlorella Vulgaris growth.In order to evaluate effect of different carbon sources and concentration on algae growth,two different carbon source?CO₂and crude glycerol?were added to the wastewater.The contribution of nutrients removal by microalgae and bacteria in centrate was compared after adding 2 g/L crude glycerol.Finally,in order to assess the more suitable HRT and get higher biomass and nutrients removal rate,Chlorella Vulgaris was semi-continuous cultivated in MPBR with crude glycerol addition,filtering by membrane module and aeration.The main research results are as follows:?1?Chlorella Vulgaris?UTEX2714?could be cultured in raw,primary effluent and centrate.The difference of biomass production and nutrients removal was not obvious with autoclaved wastewater or not.Centrate was more suitable for Chlorella Vulgaris growth and higher biomass?1.17 g/L?and biomass yield?135.71 mg/L/d?were obtained in centrate.The removal efficiencies of TP were above 94.00%;TN,NH₄⁺-N were above 76.00%in all three wastewaters.The removal of TN,NH₄⁺-N were 30.00 mg/L and 28.60 mg/L in centrate,respectively.The removal efficiencies of TN,NH₄⁺-N,TP,COD in centrate were 85.28%,90.35%,99.09%and 61.98%,respectively.?2?The biomass was 1.57 g/L with 5%CO₂ addition in centrate,which was the highest biomass in all groups and was 1.60 times that of control group.The carbon element content in algae cells were above 52.00%in CO₂ group,which was higher than control?40.11%?;Carbohydrate and lipid were increased significantly with CO₂ addition.?3?The removal rates of ammonia nitrogen and total nitrogen were 95.12%and 95.47%with 5%CO₂ addition in centrate,which was significantly higher than control?74.36%and60.29%?.The removal rate of total phosphorus in CO₂ group was lower than that in control due to the system was acidic after adding CO₂.The CO₂ was the main carbon source for Chlorella Vulgaris growth in CO₂ groups,which resulted removal rate of COD was slightly lower than control group.?4?1 g/L and 2 g/L crude glycerol addition could promote growth of Chlorella Vulgaris,and 4,6 g/L crude glycerol were not good for Chlorella Vulgaris growth and nutrients removal.The highest biomass in different crude glycerol groups was 1.45 g/L and the content of protein and lipid increased with 2 g/L crude glycerol addition.The C,H element content in algae cells increased significantly after adding 2 g/L crude glycerol.The removal rates of ammonia nitrogen and total nitrogen reached 99.32%and 97.52%in 2 g/L crude glycerol group.It was easy to make pH of system below to 7.00 during decomposition and utilization of crude glycerol.Precipitation of phosphorus was reduced due to low pH and that resulted the removal rate of TP in crude glycerol groups were slightly lower than control group.The removal of COD was enhanced with addition of crude glycerol,the removal of COD was405.0 mg/L after adding 2 g/L crude glycerol and it was 3.80 times of control.?5?The removal rates of ammonia nitrogen and total phosphorus in bacteria algae group,algae group,bacteria group were 99.32%,91.75%,44.41%and 43.48%,45.98%,14.97%,respectively.The removal of COD in centrate were 405.00,388.00,619.00 mg/L,respectively.The results showed algae greatly contributed to nitrogen and phosphorus removal,and bacteria greatly contributed to COD removal.?6?The shortest HRT was 5 d in MPBR semi-continuous cultivation process of Chlorella Vulgaris.The algae should be harvested during biomass range was 1.99-2.21 g/L which was1.5 times of batch group.The biomass was increased by optimizing cultivation of Chlorella Vulgaris that were crude glycerol addition,filtration of membrane modules and aeration.The removal efficiencies range of ammonia nitrogen,total nitrogen,total phosphorus and COD were 96.26%-99.20%,92.44%-94.04%,53.63%-58.58%,59.44-65.57%when HRT was 5d.