ERT 417Waste Treatment In Bioprocess Industry Semester 1 2011/2012 Huzairy Hassan School of Bioprocess Engineering UniMAP
“Evaluate the biological treatment methods for waste treatment in industries. Calculate and design the basic structure of waste Treatment Unit operations”. Biological treatment / Unit operation
Biological Processes for wastewater treatment Activated sludge process Aerated lagoons
INTRODUCTION Objectives of Biological Treatment: a) Transform (i.e., oxidize) dissolved and particulate biodegradable constituent s by microorganisms into acceptable end products, b) Capture and incorporate suspended and non-settleable colloidal solids into a biological floc or biofilm, c) Transform and remove nutrients, such as nitrogen and phosphorus.. why??? d) In some cases, remove specific trace organic constituents and compounds.
Trickling filters Rotating biological contractors
Aerobic biological oxidation of organic matters Nutrients for microbes to Converts organic matters to CO2 and H2O Biomass produced vi = stoichiometric coefficient
Composition & Classification of Microorganisms ** Revise the cell components, compositions, structure, DNA, RNA, microbial Growth & metabolism, C & N sources …
Aerobic, heterotrophic Aerobic, autotrophic Anaerobic, heterotrophic
Bacterial reproduction: In 30 min of generation time (time required bacteria to divide into 2 organisms) 1 bacterium would yield ~ 17 x 106 bacteria in 12 h and the mass ~ 8.4 µg Biomass yield Y = g (biomass produced) / g (substrate consumed)
Microbial Growth Kinetics Growth kinetics govern the substrate oxidation and biomass production TSS conc. in biological reactor • Organic compounds mostly defined as biodegradable COD (bCOD) or ultimate carbonaceous BOD (UBOD). bCOD and UBOD comprise of soluble (dissolved), colloidal and particulate biodegradable components. • Biomass solids in bioreactor = TSS & VSS • The mixture of solids resulting from combining recycled sludge with influent wastewater in bioreactor = mixed liquor suspended solids (MLSS) and mixed liquor volatile suspended solids (MLVSS)
Rate of utilization of soluble substrates (-ve : substrate decreases with time) rsu = rate substrate conc. change due to utilization, g/m3.d k = max specific substrate utilization rate, g substrate/ g microbe . D Ks= substrate conc. at one-half max substrate utilization rate g/m3
2) Rate of Biomass Growth with soluble substrate 3) Rate of oxygen uptake
Example 7-5 Determine Biomass and Solids Yields For an industrial wastewater activated sludge process, the amount of bsCOD in the influent wastewater is 300 g/m3 and the influent nbVSS concentration is 50 g/m3 . The influent flowrate is 1000 m3 /d, the biomass concentration is 2000 g/m3, the reactor bsCOD concentration is 15 g/m3 , and the reactor volume is 105 m3. If the cell debris fraction fd is 0.10, determine: • The net biomass yield • The observed solids yield • And the biomass fraction in the MLVSS
Solution: ? ?
Aerobic Biological Oxidation Wide range of microorganisms used: Ex: Aerobic heterotrophic bacteria able to produce extracellular biopolymers that result in the formation of biological flocs, then separated by gravity settling. • Protozoa: consume free bacteria and colloidal particulates – aid effluent clarification.
Stoichiometry: Electron acceptor Electron donor
Biological Nitrification Nitrification: 2-step biological processes; • Ammonia (NH4-N) is oxidized to nitrite (NO2-N) • Nitrite is oxidized to nitrate (NO3-N) Why?? • Ammonia – associate DO conc. & fish toxicity • Need for nitrogen removal: – control eutrophication & water-reuse application
Stoichiometry: Nitroso-bacteria (Nitrosococcus, Nitrosospira, etc): 2NH4+ + 3O2 2NO2- + 4H+ + 2H2O (Nitrobacter, Nitrococcus, Nitrospina, etc):
Anaerobic Fermentation & Oxidation Three basic steps in anaerobic oxidation of wastes: • Hydrolysis: particulate material is converted to soluble compounds that can then be hydrolyzed further to simple monomers that are used by bacteria that perform fermentation. 2) Fermentation (or acidogenesis): Amino acids, sugars, and some fatty acids are degraded further. The principle products are acetate, H2, CO2, and propionate and butyrate. Acetate, H2, CO2 precursors of methane formation (Methanogenesis)
3) Methanogenesis: Carried out by 2 groups of microorganisms (or Methanogens): a) Aceticlastic methanogens – split acetate into methane and CO2 CH3COOH CH4 + CO2 b) Hydrogen-utilizing methanogens - use H2 as electron donor and CO2 as the electron acceptor to produce methane
Nuisance organisms in anaerobic fermentation - When the wastewater contains significant concentrations of sulfate - Sulfate-reducing bacteria can reduce sulfate to sulfide (toxic to methanogenic bacteria) - Then, how to solve?? How??
Environmental factors: • Anaerobic processes are sensitive to pH & inhibitory substances (ex: NH3, H2S, etc.) • pH near neutral preferred ; • pH below 6.8 methanogenic activity is inhibited • Due to about 30-35 % CO2 (high) produced in anaerobic process, high alkalinity is needed to neutralize pH • Range of alkalinity, i.e., 3000-5000 mg/L as CaCO3 is often found. In industrial wastewater applications which mainly contain carbohydrates, it is necessary to add alkalinity for pH control.