# Effects of Caprolactam Wastewater on Algal Growth and Nutrients Removal by _Arthrospira platensis_
## 2 Materials and Methods
### Effects of Heat-Treated WCP on the Growth of A. platensis  
The heat-treated WCP was prepared by boiling mixed WCP at 100 \({}^{\circ}\)C for 30 min. During the boiling process, the air was aerated into the WCP, and deionized water was added to compensate for the evaporated water. The boiled WCP was then cooled to room temperature and deionized water was added to return the initial volume of the WCP.  
The heat-treated WCP was diluted to different concentrations (12.5%, 25.0%, and 50.0%), and then nutrients were added to the medium according to the method described in Section 2.3. The medium without WCP was used as the control. All the culture media of the treatment and control had consistent concentrations of each nutrient, including N and P sources.  
The treatment and control were cultivated as described in Section 2.3, and the biomass DW was measured at the end of the culture period. Three parallel cultures were grown for each treatment and control group.  
Effects of WCP Supply Modes on the Growth, Photosynthetic Pigments, and Biochemical Components of A. platensis  
To minimize the negative impact of WCP on the growth of _A. platensis_, different WCP supply modes were tested. For fed-batch mode 1, 3.13% (\(v/v\)) mixed WCP was added daily 16 times, and the accumulated WCP concentration reached 50.0%. For fed-batch mode 2, 12.5% (\(v/v\)) mixed WCP was added every 4 days for 4 times, and the accumulated WCP concentration reached 50.0%. For comparison, WCP was added at the beginning to reach a concentration of 50% in batch mode, and no WCP was added for the control. The culture conditions were maintained as described in Section 2.3, but the incubation period was 16 d. During the 16 d of cultivation, the biomass of each treatment and control was harvested four times on days 4, 8, 12, and 16. The biomass DW was measured before and after harvest to calculate the net increase in biomass. After harvest, the biomass DW was maintained at a minimum of 0.3 g/L. The harvested biomass was freeze-dried, and the contents of chlorophyll a (Chl-a), carotenoid (Car), and PC, as well as biochemical components (proteins, carbohydrates, and total lipids) were determined.  
Addition of 50% mixed WCP at the beginning made a NaNO\({}_{3}\) concentration of 3.30 g/L and a KH\({}_{2}\)PO\({}_{4}\) 0.13 g/L for batch mode. To ensure consistent initial concentrations of N and P sources in the culture media of the treatment and control, 3.30 g/L of NaNO\({}_{3}\) and 0.13 g/L of KH\({}_{2}\)PO\({}_{4}\) were added to the culture medium of the control, 3.10 g/L of NaNO\({}_{3}\) and 0.12 g/L of KH\({}_{2}\)PO\({}_{4}\) were added to the culture medium of fed-batch mode 1, and 2.48 g/L of NaNO\({}_{3}\) and 0.10 g/L of KH\({}_{2}\)PO\({}_{4}\) were added to the culture medium of fed-batch mode 2. To maintain consistent total concentrations of N and P sources in the culture media of the treatment and control, after the first, second, and third harvest, 0.83 g/L of NaNO\({}_{3}\) and 0.03 g/L of KH\({}_{2}\)PO\({}_{4}\) were added to each culture medium. The formulations of the culture media and the concentrations of each nutrient after harvest are shown inSupplementary Tables S2 and S3. Three parallel cultures were grown for each treatment and control group.