Cyanobacterial bloom mitigation using proteins with high isoelectric point and chitosan-modified soil

Abstract

A new environmental friendly method was developed for cyanobacterial bloom mitigation using local lake shore soil modified by protein with high isoelectric point (pI) and chitosan jointly. Results suggested that 5 mg L−1 lysozyme- (pI ≈11) and 100 mg L−1 bromelain (pI ≈9.5)-modified 10 mg L−1 soil can both reduce the surface charge of Microcystis aeruginosa, the dominant species forming cyanobacterial blooms, from −26 to −10 mV and remove 73 and 60 % of algal cells in 30 min, respectively. The limited improvement of removal efficiency was due to the small flocs (<60 μm) formed by charge neutralization, which need more than 90 min to settle in static condition. However, when the small flocs were linked and bridged by the other modifier, chitosan with long polymer chain, large flocs of about 800 and 300 μm were formed and more than 80 % of algal cells were removed in 5 and 30 min by lysozyme-chitosan-modified soil and bromelain-chitosan-modified soil, respectively. The lower removal ability of bromelain-modified soil was due to the lower charge density leading to less powerful in destabilization of algal cells. Depending on the bicomponent modification mechanism including charge neutralization of proteins with high pI and netting and bridging function of chitosan with long polymer chain, it is possible to flocculate cyanobacterial blooms in natural waters effectively using locally available materials.