1.3. Experiment design
Subsequently, the medium was replaced with fresh modified BG11 medium which contained four different P concentrations, which were K2HPO4·3H2O at 0.01, 0.1, 0.6 and 3 mg/L. The potassium ion concentration in the four media was adjusted to be consistent with BG11 medium by adding 0.1 mol/L KCl solution. Simultaneously, the flow rate was reduced to 25 L/hr. Other conditions were the same as mentioned above, and the experiment then began. The effects of phosphorus on biofilm structure and function were monitored throughout the biofilm colonization process. Samplings were conducted every 3–4 days. To prevent phosphorus depletion and to maintain the imposed nutrient conditions, the medium of each treatment was refreshed after every sampling. The experiments were conducted for 28 days in total.