Rapid Harvesting the Microalgae Nannochloropsis oculata with Polyamide from Isolated Bacillus subtilis DYU2

Polyamide produced from Bacillus subtilis DYU2 was found to have excellent flocculating ability. With the addition of 200 mg/L of polyamide and 50 mg/L of polyaluminum chloride (PAC), the optimum temperature for flocculation performance of polyamide was 30℃, giving the highest flocculating activity and rate of 100.0 and 98.0% within 10 minutes, respectively. Analysis with Fourier transform infrared spectrophotometry (FT-IR), nuclear magnetic resonance spectrometry (NMR) and amino acid identification shows that the polyamide biopolymer mainly possesses the structure of poly-glutamic acid (PGA). The average molecular weight of PGA was about (3.12–3.30) × 10^6 Da as determined by gel permeation chromatography. The major components of PGA were total sugars, uronic acids, proteins and polyamides (homopolymer of glutamic acid), accounting for a weight ratio of approximate 15.0, 2.5, 4.5 and 49.0% (w/w), respectively. Moreover, mechanisms describing the flocculation process with PGA were proposed based on the experimental observations.