###### Abstract  
Adding organic compounds to wastewater can improve the carbon/nitrogen ratio and benefit microalgae growth. We studied microalgal growth, nutrient removal and lipid accumulation of _Chlorella pyrenoidosa_ cultured in a mixture of swine wastewater (SW) and furfural wastewater (FW). The mix ratio of SW:DFW (diluted furfural wastewater) had a significant effect on microalgae growth. As the mix ratio of SW:DFW decreased from 1:0.5 to 1:19, the maximum microalgal biomass increased, while the specific growth rate initially increased and then decreased. The efficiency of nutrient removal also depended on the mix ratio of wastewater. The highest chemical oxygen demand (COD) removal efficiency (57.30%) occurred at the mix ratio of SW:DFW = 1:3. The highest removal efficiencies of total phosphorous (TP) reached 61.93% when the mix ratio of SW:DFW was 1:9. Wastewater at the mix ratio of SW:DFW = 1:19 had a maximum lipid productivity of 49.48 mg L\({}^{-1}\) d\({}^{-1}\), which was 4.9 times higher than that at a mix ratio of SW:DFW = 1:0.5. These results showed that _C. pyrenoidosa_ can be used to remove nutrients from mixed wastewater sources and simultaneously produce algal lipids. Chlorella pyrenoidosa; swine wastewater; furfural wastewater; nutrient removal; lipid production; mixotrophic growth +
Footnote †: journal: Applied sciences  
have been used to culture microalgae and these have resulted in high removal efficiencies of contaminants [2]. Many microalgae strains are able to acclimatize to wastewater environments and can tolerate high levels of harmful pollutants [10; 11]. For microalgae grown in wastewater, the mixotrophic growth mode is involved since most wastewater has organic matter [12; 13]. However, several common types of wastewater, such as swine, municipal and domestic wastewater, have high nitrogen concentration, thus leading to the low C/N ratio (carbon to nitrogen source ratio) which is not beneficial to the mixotrophic growth of microalgal cells [13]. Therefore, the addition of an exogenous organic carbon source to wastewater has been proposed to enhance the mixotrophic growth of microalgae. This can increase the growth rate of microalgae compared to photoautotrophic cultivation [7]. In addition, microalgae mixotrophically grown in wastewater with addition of organic matter had a greatly increased nutrient removal rate and efficiency [14]. [PERSON] et al. [15] showed that the addition of sodium acetate significantly stimulated algal growth and also increased lipid productivity when _Scenedesmus obliquus_ was cultured in municipal wastewater. Several kinds of organic compounds are potential carbon sources for algal mixotrophic culture in wastewater. These include glucose, glycerol and sodium acetate [2; 13]. However, the addition of these compounds increases the treatment cost and is not cost-efficient and sustainable [16]. The use of an organic carbon source from wastewater has been considered as an option. [PERSON] et al. [13] reported that enhancements of lipid productivity and nutrient removal were achieved by adding acidified starch wastewater to the mixotrophic culture of _Chorella pyrenoidosis_. There are several other types of wastewater that contain organic acids. Furfural wastewater (FW) is a highly acidic wastewater generated by depolymerizing lignocellulosic crop stalks with sulfuric acid at high temperature [17]. Large amounts (4-6 million tons annually) of furfural wastewater are produced in China [17], and this furfural wastewater typically requires costly treatment. Wastewater treatment using microalgae integrated with biodiesel production is an environmentally friendly and cost effective way to achieve resource recovery and recycling [4; 5; 18; 19]. Oleaginous microalgae cultured in wastewater can purify wastewater and also reduce the cost of microalgal lipid production [20]. Many studies have evaluated microalgae-based wastewater treatment integrated with algal lipid production.