| The post-treatment and recovery of nutrients in the anaerobic-digested effluents from poultry wastes is becoming a major concern due to the environmental issues. Microalgae have been widely applied in wastewater recovery and CO2assimilation with producing high value-added products. Coupling microalgae cultivation with wastewater treatment may provide an economically and environmental friendly way for the removal of pollutants and biomass production. The anaerobic-digested effluents from poultry wastes are usually opaque and biorefractory, which is unfavourable for microalgae growth. Therefore, a proper pretreatment is needed for improving the effluent conditions to satisfy the algal cultivation. The objectives of this work were to determine the species of microalgae cultivated in special conditions (poultry waste anaerobic digested effluents or high CO2levels) and optimize the biomass production of C. pyrenoidosa Y3cultured in poultry waste anaerobic digested effluents (PWADE) using a response surface methodology (RSM). The most critical supplemental nutrients added to the PWADE for algae growth were determined by the Plackett-Burman design (PBD). A central composite design (CCD) was used to optimize the screened components to maximize the biomass yield and chlorophyll-a content of C. pyrenoidosa Y3. The nutrients removal efficiency in the PWADE by the pre-treatment of chitosan flocculation was investigated and the characteristics of flocculation of chitosan were determined. The potential of pretreated effluents for cultivating Chlorella pyrenoidosa was also evaluated. According to the results from the experiments, the following conclusion can be drawn:Chlorella pyrenoidosa Y3was most suitable for treating PWADE,2%(v/v) PWADE was the optimum medium substrate. Spirulina platensis was most suitable for high level CO2fixation. The maximum biomass yield1.184g/L of and chlorophyll-a content of20.275mg/L were obtained from Spirulinaplatensis cultured at a light cycle of L:D of15:9and CO2concentration of10%(v/v). The CO2fixation capacity was1.134g/L and the protein content of the Spirulina platensis reached to42%(w/w).Based on the single factor design, PBD and CCD, the maximumbiomass yield of0.819g/L was obtained from C. pyrenoidosa Y3cultivated in the2%(v/v) PWADE substrate with addition of4.81g/L NaHCO3and92.9mg/L MgSO4ยท7H2O after20d of the cultivation. The chlorophyll-a content of algae reached to27.51mg/L, andabout100.0%NH4-N and59.5%total phosphorus were removed from the PWADE with the optimized medium condition.The pre-treatment of PWADE with chitosan flocculationat an optimum initial pH value of8.5and dissolved in HC1solution was suitable for the subsequent microalgae cultivation. The COD, turbidity and color in5%(v/v) PWADE were reduced by83.5%,100%and93.1%with chitosan dosage of600mg/L, respectively. At a chitosan dosage of1650mg/L, the COD, turbidity and color in10%(v/v) PWADE were reduced by82.2%,99.3%and91.6%, respectively. The chitosan flocculation process involves bindinginsoluble particles and/or dissolved organic matter into large agglomerates and the sweep-out mechanism to remove the pollutant in PWADE.The maximum biomass production of0.739g/L and chlorophyll-a content of21.03mg/L were obtained from C. pyrenoidosaYZ cultured for20days in the5%(v/v) PWADE flocculated by chitosan (150mg/L) dissolved in HC1, which was1.7times for biomass and1.2times for chlorophyll-a higher than that of algae cultured in the non-flocculated5%(v/v) PWADE medium. The biomass production and chlorophyll-a content were0.719g/L and13.71mg/L for C. pyrenoidosaY3cultured for20days in the10%(v/v) PWADE flocculated with chitosan of1650mg/L dissolved in HC1, respectively. The algae could not survive in the10%(v/v) PWADE without pre-treatment. |
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