Treatment Performance And Mechanism Of Algae Laden Water By Gravity Driven Membrane

Harmful blue algae blooms occurring in freshwater has always been a spotlight in environmental science.Producing odorous substance,toxins and competing with nutrients,blue algae can change the sensory properties and deteriorate the water quality.Effective removal of algae has always been an important subject in water research.Membrane technology is remarkable in algae removal.Especially,with high flux and low cost,ultrafiltration has become the first choice in membrane water treatment.But,as a result of membrane fouling,ultrafiltration has not been widely used in algae laden water treatment.Gravity driven membrane(GDM)was proposed by Peter-Vabanets in 2010 which is driven by gravity pressure of 40-100 mbar.Not any electricity with less membrane fouling,GDM system can save a lot of operating cost of water treatment plant.Nowadays,GDM system is widely used in seawater and wastewater treatment.However,the applications of GDM in algae laden water are rarely reported.The objective of this paper is to study performance and fouling mechanism of GDM system which was used to treat algae laden water.The influence of coagulation to water quality and the system was studied.In order to study the effect to membrane processing caused by different substances,blue algae cells,large particles and natural organic matters(NOM)was considered.GDM can remove large particles(algae cells etc.)and soluble microbial products(SMP)effectively,but the results of small molecules removal like humic acid(HA)was not very well.The effects of coagulation to flux was not constant.For pure algae,coagulation can raise the stable flux;for actual algae laden water,coagulation can remove large particles but leave the small molecules like HA which is a major pollutants to membrane.For the sake of studying the membrane fouling characteristics of GDM,the GDM system was compared with a vacuum suction filtration system which is often used by membrane filtration plant.GDM had an extremely thin fouling layer that contained SMP and HA.By contrast,suction filtration caused the compacted pollutants to block membrane pores which can reduce the effective filtration area.What is more,suction power can tear pores up which is badly affects membrane's working life.According to XDLVO theory and Hermia's model,membrane fouling theory of different kinds of algae laden water was analyzed.During the initial filtration period(about 100-200 h),all kinds of pollutants participated in pore blocking.As the filtration process goes,the cake layer formed gradually and flux tended to be stable.Large particles are important component of cake layer which can speed the cake formation up and build a loosely porous cake layer.Coagulation to pure algae brought lots of hydrophilic hydroxyl.The hydrophilic function of hydroxyl reduced the contact interaction energy of pollutants and membrane surface which can relieve membrane fouling.However,for actual algae laden water,coagulation made the particles in supernatant get larger which enhanced the contact interaction energy of pollutants and membrane.Focusing on membrane filtration performance of algae laden water and fouling mechanism,this research can provide theoretical insights for further application.