Process optimization of cultivation of Kirchneriella obesa in cattle farm wastewater

Abstract: Water shortage and pollution are pushing to upgrade the conventional treatment of wastewater in the world. Microalgae-based Wastewater Treatment (WWT) has been widely expected to meet the new demand for the removal of nutrients and pathogens in recent years. However, a pretreatment process is normally required on the microalgae culture in wastewater from a cattle farm, such as settling, centrifugation, aeration, and dilution. It is a high demand for the potential microalgae culture substrates rich in nutrients, such as nitrogen and phosphorus, thereby reducing the cost of the pretreatment process for the better commercialization of the microalgae industry. Particularly, a large amount of breeding wastewater and manure have been rapidly produced in the livestock industry. In this study, the wastewater from a cattle farm was filtered by straw to cultivate the microalgae, in order to timely alleviate the loss of nutrients and environmental pollution. Kirchneriella obesa was selected as the experimental algae species. The mixture of straw-filtered wastewater and BG11 medium was also used as the microalgae culture medium. A systematic investigation was made on the effects of wastewater addition ratio, light intensity, photoperiod, and aeration on the dry weight of microalgae, as well as the ammonium (NH4+-N), Total Phosphorus (TP), and Chemical Oxygen Demand (COD) removal rate. A Central Composite Design (CCD) with a single factor test was carried out to optimize the process parameters during cultivation. The results demonstrated promising potential of WWT in the nutrients removal from cattle farm wastewater. An optimal combination of process parameters for the cultivation was achieved as follows: 26 % of wastewater, light intensity of 9 028 lx, light time of 21.5 h, and the aeration intensity of 2.0 L/min. By the end of the 14-day culture period, the dry weight of Kirchneriella obesa reached 1.141 g/L under optimal conditions, where 99.65%, 99.15%, and 85.83% of NH4+-N, TP, COD were removed, respectively. There were within 2% errors of the predicted and actual values for the response indexes. The dry weight of microalgae and COD removal rate were higher than predicted, indicating the credible optimization for the expected requirements. There was an outstanding interaction of wastewater addition ratio and light time on the dry weight of the algae. A strong correlation was also found between the wastewater addition ratio and aeration amount on the removal rate of NH4+-N, TP, and COD in the culture solution of the algae. But the light intensity and light time had only interacted with the removal rate of TP. This finding can provide a theoretical reference to promote the industrial production of microalgae culture for the wastewater from a cattle farm.