1、BIOLOGICAL BIOFILM PROCESSES By,Dr. Alaadin A. Bukhari Centre for Environment and Water Research Institute KFUPM,PRESENTATION LAYOUT,Introduction Biofilm Physical and Chemical Properties Kinetics of Biofilm Systems Biological Biofilm Systems Trickling Filter Fludized Bed Packed Bed,INTRODUCTION,Used
2、 for removal of organic pollutants from wastewaters Biological treatment is popular due to: low cost effective in removal of a wide range of organic contaminants effective in removal of colloidal organics can remove toxic non-organic pollutants such as heavy metals,Principles of Biological Processes
3、,Aerobic: Organic matter + O2 CO2 + H2O + cell + energyAnaerobic:N1POrganic matter intr. + CO2 + H2O + cell + energyN1Pintermediates + CH4 + CO2 + energy,Process Limitations in Treating Hazardous Wastewater,Acclimation period is usually required Sensitivity of the microorganisms to shock loading Pro
4、cesses may produce by-products that are more toxic than the initial substance Certain industrial wastewater required pretreatment Temperature should not exceed 110F (43 C),BIOFILMS,Definition:“A gelatinous layer consisting of cells immobilized in an organic polymer matrix of microbial origin”,Physic
5、al Characteristics,Thickness ranges from few microns to over 1000 microns Surface is irregular “rough” Specially heterogeneous Consists of two compartments: Base film Surface film,Chemical Properties,The Extra-Cellular Polymers (EPS) give the biofilm its chemical properties EPS compounds are dominat
6、ed by hydroxyl and carboxylic groups ( OH-, COO- ) The biofilm has a net anionic charge which influence transport of contaminants,Kinetics of Biofilm Systems,Physical mass transport:The rate of mass transport of substrate from the bulk liquid across a unit area of the stagnant liquid layer to the bi
7、ofilm surface is called the flux.Ns = KL (Sb - Ss) where:Ns = flux in units of mass per unit area per unit timeKL = mass transfer coefficient, length per timeSb = substrate concentration in the bulk liquidSs = substrate concentration at the biofilm surface,Several correlations have been suggested de
8、scribing the mass transfer coefficient such as:KL = 1.3 Sc-1/2 Re-1/2 orK = 0.817 Sc-2/3 Re-1/2where: = viscosity of fluidSc = Schmidt number ( /Pd)Re = Reynolds number,Reaction at the Surface of the biofilm,The rate of consumption of substrate at the surface of the biofilm is given by Monod kinetic
9、s:qm Ss-rs = - (Ks + Ss)where: -rs = reaction rate, mass per unit time per unit area qm = maximum specific substrate removal rate, mass perunit time per unit area Ks = saturation constant, mass per unit volume Ss = substrate concentration at the biofilm surface,Mass Transfer Within the Biofilm,Subst
10、rate transport within the biofilm occurs through the process of diffusion which is characterized by Ficks law as the following:Ns = -D (ds/dx) where:D = diffusion coefficient, area per unit timeds/dx = concentration gradientDiffusion within the film:Ns = -De (ds/dx),Biological Biofilm Systems,Types
11、of biofilm systems Fixed-medium systems Trickling filters Packed bed reactors Moving-medium systems Rotating biological contactors Fluidized bed reactors,Trickling Filters,Trickling filters consists of three major components; filter media, distribution system, and underdrain system.Filter Media The
12、filter media provide the surface and voids Should have the following characteristics: Provide large surface area Allows liquid to flow in a thin sheet Has sufficient void spaces Biologically inert Chemically stable Mechanically stable,Typical Media Used,Stone media usually crushed granite or lime st
13、one size ranges between 2-4 inches surface area ranges from 50-98 m2/m3 with around 50% voids Plastic media Provides large surface area Provides large void spaces Dumped plastic media, surface area ranges from 98-340 m2/m3 with void ratios of 95% Modular plastic media, surface area ranges from 81-19
14、5 m2/m3,Distribution system Provides uniform hydraulic loading on the filter surface Rotational speed is usually 1 rev/10 minUnderdrain system Supports the media Collects the effluent Permits circulation of air through the bed Made of vitrified clay (for stone media) or simple metal gratings (for pl
15、astic media)Configuration Trickling filters can be employed as a single unit, units in series, or units in parallel,Filter design parameters Hydraulic Loading Flow per unit area (m3/day.m2) Upper and lower limits should be considered Lower limit to wet all of the media (for plastic media limit is hi
16、gher than stone media) higher limit to prevent flooding of filter bed,Organic loading Is the mass application rate of organic matter per unit volume of reactor (lb BOD/day-1000ft3) Higher organic loading leads to excessive growth of microorganisms Recirculation is used to increase the hydraulic load
17、ing while keeping organic loading constant,Advantages: Ideal for remote sites or small communities due to their simplicity and ease of operation Can handle shock loading due to the large mass of microorganisms present in the filter and the nature of the biofilm Produce dense sludge that can be easil
18、y removed by settling,Disadvantages: There is no control on the effluent quality in response to change in flow rate, organic concentration, and temperature Breeding of flies and other insects in the summer months creates a nuisance condition in the vicinity,Fluidized Bed Systems,Description: Fluidiz
19、ed bed systems are a combination of attached-growth and suspended-growth systems Bed media consists of small particles usually sand or granular activated carbon. Also, glass particles and fabricated media can be used The bed packing material is kept in a suspension by an upward flow of influent wast
20、ewater The effluent is discharged into a settling tank to separate biomass escaping in the effluent,Principles of the Process: Liquid is passed upwards through a bed of solid particles As the liquid velocity is increased, the bed expands The particles separate and become free to more relative to eac
21、h other The liquid velocity required to achieve this effect depends on the relative densities of the liquid and the particles, as well as the size and shape of the particles,Advantages: Eliminate problems of clogging A very large surface area is available for the growth of microorganisms Small compa
22、ct systems Because the microorganisms are attached to the solid particles, wash-out of microorganisms are eliminated Eliminate the need to recycle microorganisms back to the reactor as the case of activated sludge systems Eliminates flow short-circuiting Efficient mass transport,Disadvantages: Requi
23、res high degree of control Large accumulations of biological film on the surface of the particles can lead to aggregation of particles which would adversely affect system performance,Packed-bed Systems,Submerged upflow reactor packed with synthetic media Operated under anaerobic conditions Recycle i
24、s desirable to dilute influentMedia used: Sand particles Plastic media Aluminum oxide particles,Advantages: Cell yield is low No oxygen is required Production of energy source (CH4) Low nutrient requirementsDisadvantages: Low growth rates Sensitivity to pH changes Susceptibility to toxicity and inhibition,Summary Application of the process has great potential Robust process in comparison with other biological processes Room for research is open,Thank You,
