The pollution of microcystins (MC) following the breaking out of cyanobacterial bloom has raised more and more concerns; the removal of MC in water body has been a focus of attention. In natural environment, biofilms formed in the surface of submerged mineral particles, the transport and persistence of pollutant in aquatic system can be influenced by their adsorption onto biofilms and the remobilization of biofilms. In this research, a kind of self-designed simple biofilm collection device was uesd to culture and collect the biofilm in different depths (20 cm and 100 cm water depth) of the Donghu Lake of Wuhan City, and the characteristics of their growth and activity were studied. It aimed to understand further the biochemical characteriatics of biofilms; In the addition, the adsorption of MC on the biofilms in different water depths, and the biodegradation of MC with the biofilms cultured in different water depths for same times as well as in same water depths for different times were investigated. The purpose was to reveal the environmental behaviors of MC, hoping to support theoretical accordings and technique instruction for controlling the MC pollution in aquatic environment with the biology method.
The main results were summarized as follows:
1. The growth of biofilms in natural water was influenced by such factors as photic condition, water temperature, pH, dissolved oxygen (DO) and nutrient level, meteorological and hydrological conditions also influenced it. The growth of biofilms formed in Lake Donghu in autumn went through four periods like “the latent adaptation period-the increasing period-the detachment period-the renewing period”, the extraeclluar polysaccharides, COD and dehydrogenase of biofilm were positive correlated with the biofilm biomass, and the growth rate of biofilms developed in the water depth of 20 cm was faster than that in the water depth of 100 cm, furthermore, the biomass of biofilm developed in the water depth of 20 cm was larger and its activity was higher than that in the water depth of 100 cm.
2. The biofilms cultured in Lake Donghu for 15d could adsorb MC-RR, the adsorption balance time was about 6-8h, and the maximum adsorption amount was 6.94% of the initial MC-RR amount. The adsorption amount of MC-RR gradually increased with the balance concentrate of MC-RR increasing, and moreover, the adsorption behavior of MC-RR onto biofilms could be well described by the Langmuir adsorption isotherm(R＞0.99). The pH and the ionic strength could affect the adsorption of MC-RR, and the lower pH or increasing ionic strength could enhance the biofilms adsorption of MC-RR.
3. The biodegradation of MC by biofilms cultured in Lake Donghu under oxygen-containing conditions experienced the lag period of 2-3d. During the biodegradation, the pH of solution rise steadily, and the degradation rate with the biofilms cultured in water depth of 20 cm was faster than that in the water depth of 100 cm, and the degradation rate improved as the number of the slides adhering biofilms increased. Also, the degradation of MC was closely relative to the biofilms culture time. The biodegradation process could be described as the equation: y=A/[1+Bexp(-Ct)], the degradation rate increased as the temperature became high or microbial biomass were large.