Treatment Performance Of Algae Laden Water By Coagulation Enhanced Gravity Driven Ultrafiltration Membrane And Investigation Of Biofilm

Cyanobacteria can produce a series of toxic substances and seriously deteriorate water quality.Eutrophication is the main reason of algae blooming.Consequently,how to remove algae efficiently has become one of the hottest issues in recent years.In the above context,ultrafiltration with good separation efficiency,low energy consumption,and high flux has begun to attract people's attention.Since algae and its metabolites can cause severe membrane fouling,ultrafiltration treatment for algae-containing water has not been widely used.Peter-Varbanets et.al proposed the gravity driven membrane?GDM?system in 2010,which operates as dead end filtration,and keeps the transmembran pressure at 40-100 mbar by gravity.GDM has the advantages of low energy consumption,low operation cost,less membrane fouling,and no need of physical and chemical cleaning.At present,GDM system has been widely used in seawater desalination and other water treatment projects.However,there are few studies on the application of algae removal by GDM system.The article focuses on the algae removal efficiency and membrane fouling characteristics of the GDM system.Different coagulation conditions?pre and in-situ coagulaion?and different kinds of coagulants?positive charge coagulant FeCl₃ and negative charge coagulant hydrated manganese dioxide?on the algae removal efficiency of the GDM system were compared.A variety of water quality testing methods,such as changes in membrane flux,EEM,SEM,FTIR and other membrane fouling characterization methods were analyzed to three different pretreatment on the algae removal efficiency of GDM system.In addition,a comparative analysis of the microbial community structure and diversity in the cake layer of the membrane was analyzed by high-throughput sequencing,which revealed the change of the water quality in the system and membrane fouling mechanism from a microscopic perspective.In this work,it was found that in-situ coagulation of hydrated manganese dioxide can significantly increase floc size,which made the initial settlement of the membrane surface contains more containments than the in-situ coagulation of FeCl₃ through comparative experiments.And it resulted in the most serious membrane fouling and the largest decrease occurred in flux of the four experiments,followed by in-situ coagulation of FeCl₃,while pre-coagulation of FeCl₃ removes most of the algal cells and the extracellular organics,resulting in the lowest membrane fouling.The GDM system can trap algae cells and SMP-like macromolecules and other substances effectively.And it has an excellent removal effect on tryptophan-like and protein-like substances.The removal rate of the substances by in-situ coagulation of FeCl₃ can rise at 90%.And the non-coagulation is 80%,in-situ coagulation of negatively charged coagulant hydrated manganese dioxide is 63%,and the pre-coagulation of FeCl₃ is the lowest,rises at 30%.In situ dosing of FeCl₃ and hydrated manganese dioxide do not destroy algal cells,but can produce stress response to algal cells,which will change the species of algae bacteria.For example,it can make the bacterium which enables the growth and reproduction of the Microcystis aeruginosa such as Rhodobacter genus inhibited or even disappeared.But the Methylophilus genus is newly produced.The newly born genus can contribute to the rapid formation and stable development of the cake layer on the surface of the membrane,making the in situ coagulation of hydrated manganese dioxide's layer become the most porous layer.In addition,the reversible pollution of the membrane is small,so the membrane flux recovery rate is the highest,which is up to 100%.Following by the in situ coagulation of FeCl₃,who's rate is 71.22%.And the pre-coagulation of FeCl₃ is 62.09%.The non-coagulant addition of coagulant is the smallest,whose rate is 48.59%.The microbial community abundance and diversity were highest in the cake layer of the non-coagulantion group,followed by the in-situ coagulation of FeCl₃,and the lowest is the in-situ coagulation of hydrated manganese dioxide.The article focuses on the algae removal efficiency and the membrane fouling characteristics of the coagulation enhanced GDM system.Thus it helps to optimize the GDM system and provides theoretical support for the establishment of algae removal technology by the GDM system.