ERT 319 Industrial Waste Treatment HANNA ILYANI ZULHAIMI hanna@unimap.edu.my

Biological Treatment: Processes of Industrial Wastes

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 excess nutrients, such as nitrogen and phosphorus. (why?) d) In some cases, remove specific trace organic constituents and compounds.

For industrial wastewater perspective: To remove or reduce the concentration of organic and inorganic compounds.  because some of the constituents and compounds are toxic to microorganism, pretreatment may be required before discharging to municipal collection. Pretreatement here is meant by chemical treatment. Biological treatment cannot oxidize all compound since it deals with living things (microorganism).

Aerated lagoons (suspended growth) Biological Processes for wastewater treatment Activated sludge process (suspended growth) Aerated lagoons (suspended growth)

Trickling filters (attached growth) Rotating biological contractors RBC (attached growth)

Trickling filter

vi = stoichiometric coefficient Aerobic biological oxidation of organic matters Nutrients for microbes to Converts organic matters to CO2 and H2O Biomass produced This the general equation for aerobic biological exodation. As u can see, in order for microbes to convert organic material (substrates), it needs nutrients to tranforms it to new cell (biomass). Organic material = substrate = benda yang nak urai = food Biomass = microbes (active, decay), inert particulate vi = stoichiometric coefficient

Composition & Classification of Microorganisms ** Revise the cell components, compositions, structure, DNA, RNA, microbial Growth & metabolism, C & N sources … Refer Chapter 7, page 555-563

COMMON TERMINOLOGY IN BIOLOGICAL TREATMENT PROCESS

Bacteria metabolism Aerobic, autotrophic Aerobic, heterotrophic Heterotrophic= use organic compound to form new cell and CO2 and H20 Autotrophic = use carbon to produce new cells and no2 or no3 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) VSS- common method to measure biomass growth

Quiz 1 Explain the term below: Aerobic Anaerobic Heterotrophic Autotrophic Phototroph Chemotroph

Microbial Growth Kinetics (Empirical study) 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) Solid = biomass, non-biodegradable volatile suspended solid (nbVSS) and inert inorganic total suspended solid (iTSS)

Rate of Utilization of Soluble Substrates (-ve : substrate decreases with time) r, su = 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 X= biomass concentration, S= limiting substrate concentration g/m3

2) Rate of Biomass Growth with soluble substrate Specific biomass growth rate, μ= rg/ 3) Rate of oxygen uptake

4) Effects of temperature

5) Total volatile suspended solids & Active biomass

Example 7-5 Determine Biomass and Solids Yields An aerobic complete mixed treatment process is used to treat an industrial wastewater. 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/day, the aerobic tank biomass concentration is 2000 g/m3, the reactor bsCOD concentration is 2.4 g/m3 and the reactor volume is 335 m3. if the cell debris fraction, fd is 0.1, Determine (use the kinetic coefficient given in table 7-8) the net biomass yield the observed solids yield the biomass fraction in the MLVSS

Aerobic Biological Oxidation There are wide range of microorganisms used: Aerobic heterotrophic bacteria: 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 2-step biological processes; Ammonia (NH4-N) is oxidized to nitrite (NO2-N) Nitrite is oxidized to nitrate (NO3-N) Why?? Ammonia & nitrite – associate DO concentration & fish toxicity Need for nitrogen removal: control eutrophication & water-reuse application Total conc. of organic and ammonia nitrogen in municipal wastewater: 25-45 mg/L

Stoichiometry: Nitroso-bacteria (Nitrosococcus, Nitrosospira, etc): Two step oxidation of ammonia to nitrate Nitroso-bacteria (Nitrosococcus, Nitrosospira, etc): 2NH4+ + 3O2 2NO2- + 4H+ + 2H2O Nitro-bacteria (Nitrobacter, Nitrococcus, Nitrospina, etc) Nitrate: Safer form to aquatic lives

Biological Denitrification The biological reduction of nitrate to (nitrite) then to nitric oxide, nitrous oxide, and nitrogen gas. Biological nitrogen removal is used in wastewater treatment : where there are concerns for eutrophication, and where groundwater must be protected against elevated NO3-N concentration. 2 modes of nitrate removal: Assimilating nitrate reduction (ANR) Dissimilating nitrate reduction (DNR)

ANR involves the reduction of nitrate to ammonia for use in cell synthesis (Fig 7-20) Assimilation occurs when NH4-N is not available and is independent of DO concentration. DNR is coupled to the respiratory electron transport chain, and nitrate or nitrite is used as an electron acceptor for the oxidation of a variety of organic or inorganic electron donors (Fig 7-20). Microorganism for denitrification: both heterotrophic and autotrophic ( most are facultative aerobic organisms with the ability to use oxygen as well as nitrate or nitrite). - Example: Achromobacter, Acinetobacter, Bacillus, Chromobacterium, Pseudomonas, Rhizobium, etc.

Biological Denitrification

Nitrogen cycle

Types of Denitrification Process Substrate driven Endogenous driven

Substrate driven In the first flow, nitrate produced in the aeration tank is recycled back to the anoxic tank (anaerobic). Because the organic substrate in the influent wastewater provides the e- donor for oxidation-reduction reactions using nitrate, the process is termed substrate denitrification. Or because the anoxic process precedes the aeration tank, the process is known as a preanoxic denitrification.

Endogenous driven In the second process, denitrification occurs after nitrification and the e- donor source is from endogenous decay. BOD removal has occurred first, and is not available to drive the nitrate reduction reaction, and called postanoxic denitrification. It has much slower rate of reaction than preanoxic denitrification. Often, an exogenous carbon source such as methanol or acetate is added to postanoxic processes to provide sufficient BOD for nitrate reduction and to increase rate of denitrification.

Anaerobic Fermentation & Oxidation Used primarily for treatment of waste sludge and high-strength organic wastes. As a pretreatment step due to low quality effluent. Advantages: Lower biomass yield Energy (methane) can be recovered from biological conversion of organic substrate Cost-effective; savings in energy, nutrient addition and reactor volume.

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)

b) Hydrogen-utilizing methanogens 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

How?? 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??

pH near neutral are preferred ; Environmental factors: Anaerobic processes are sensitive to pH & inhibitory substances (ex: NH3, H2S, etc.) pH near neutral are 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.

Types of Biological Process for Wastewater Treatment Suspended Growth Process Attached Growth Process (Biofilm)

SUSPENDED GROWTH BIOLOGICAL TREATMENT PROCESS

Suspended Growth Processes (SGP) Microbes are maintained in liquid suspension by mixing methods Most common SGP: Activated-sludge process (ASP) ASP uses activated mass of microbes capable of stabilizing a waste under aerobic conditions. mix wastewater with microbial suspension at certain contact time mechanically. MLSS & MLVSS biomass measurement = a complete mixed system (influent + sludge) MLSS flows to clarifier (where microbial suspension is settled and thickened) “Activated sludge” Activated sludge is returned to aeration tank to continue biodegradation of organic material

Activated Sludge Process 1 Reactor- microbes are kept in suspension and aerated 2 Liquid-solids separation (ex: clarifier) 3 Recycle system – returning solids from clarifier to reactor

Plug-flow Activated Sludge Process

Complete mix Activated Sludge Process

Selection & Design of Physical Facilities for Activated Sludge Process Aeration Systems Aeration Tanks Solids Separation Solid Separation Facilities

Selection & Design for Activated Sludge Processes Aeration System Aeration system must be adequate to: Satisfy the bCOD of the wastes Satisfy the endogenous respiration by the biomass Satisfy the O2 demand for nitrification Provide adequate mixing Maintain minimum dissolved O2 conc. throughout the tank  If the O2 transfer efficiency of aeration system is known, we can design/estimate the actual air requirements for diffused air aeration or installed power of mechanical surface aerators.

Aeration system (Air Bubble)

Aeration-achieved via diffused air (diffuser) or surface aerator. Aeration equipment must be designed with enough flexibility to: Meet minimum dan max O2 demand Prevent excessive aeration and save energy

Aeration Tanks and Appurtenances (support facilities) Usually constructed of reinforced concrete and left open to atmosphere Capacity if aerated with diffused air: capacity range of 0.22 to 0.44 m3 /s  at least 2 tanks needed capacity range of 0.44 to 2.2 m3 /s  at least 4 tanks needed capacity range over 2.2 m3 /s  at least 6 tanks or more Depth of wastewater in the tanks: between 4.5 and 7.5 m Freeboard: 0.3 – 0.6 m above waterline Width-to-depth ratio of the tanks (spiral-flow mixing): 1:1, 2.2:1 or 1.5:1 (most common) Tank with diffusers on both sides, greater width are permissible. Triangular baffles or fillet may be placed longitudinally in the channel to eliminate dead spot

2. FLOW DISTRIBUTION For multiple units of primary sedimentation tanks & aeration tanks Methods of splitting or controlling the flow rate, for ex: splitter boxes equipped with weirs or control valves or aeration tanks influent control gates. Hydraulic balancing of flow by equalizing the head loss from the primary sedimentation basins to the individual aeration tank.

3. Froth control systems Foaming: when the aerated wastewater which contains soap, detergents & other surfactants Foaming action produces froth that contains sludge solids, grease, and wastewater bacteria. Wind may lift & blow the froth  contaminate when it touches, slippery, and difficult to remove once it has dried. solutions: remove froth by spraying clear water or screened effluent through nozzles. adding antifoaming chemical additives in spray water.

4. Nocardia Foam Control Nocardia foam is a thick layer of brown biological foams that forms on the top of aeration tanks and clarifiers. Nocardia organisms grows and tend to trap air bubbles  float to the surface and accumulate as scum (dirty foam) Controlled by: Spraying chlorine solution directly into foam layer. in some cases, spray nozzles installed within a hood located across the width of plug flow aeration tanks. may not be effective, because it can cause floc breakup & inhibit BOD removal and nitrification. Addition of cationic polymer.

Solids Separation Facilities To provide well-clarified effluent and concentrated solid. Sludge collector Activated sludge settling tank types: circular or rectangular. Circular tank: Diameter : 2 – 60 m (or 10 -40 m). tank radius: not more than 5X side water depth.

Solid Separator (Clarifier)

Sludge collectors (rectangular): Rectangular tank Max length:<10 x depth, commonly 90 m. Width=6 m, use multiple sludge collection if 6m <width <24m. Sludge collectors (rectangular): Chain and flight

Other type of settling tank : stacked clarifiers b) Traveling bridge Other type of settling tank : stacked clarifiers tube and plate settlers intrachannel clarifiers

Suspended Growth Aerated Lagoons Suspended growth aerated lagoons are relatively shallow earthen basins varying in depth from 2 – 5 m, provided with mechanical aerators on floats or fixed platforms. Mechanical aerators: to provide oxygen for biological treatment of wastewater , to keep the biological solids in suspension. Suspended growth aerated lagoons are operated on a flow-through basis or with solid recycle. Types of suspended growth aerated lagoon: Facultative partially mixed. Aerobic flow through with partial mixing. Aerobic with solids recycle and nominal complete mixing.

Process Design Considerations for flow-through lagoons: BOD Removal (the basis of design is SRT and HRT) BOD conc: S/S0=1/1+kt Effluent characteristics TSS and BOD conc. Temperature effects Oxygen requirement Energy requirement for mixing

Example 7-6 Design of a Complete-Mix Suspended Growth Process Design a flow-through aerated lagoon to treat a wastewater flow of 3800 m3/d, including the number of surface aerators and their kilowatt rating. The treated liquid is to be held in a settling basin (lagoon) with a 2-d detention time before being discharged. Assume that the following conditions and requirements apply: Influent TSS = 200 g/m3 (influent TSS are not degraded biologically) Influent sBOD = 200 g/m3 Effluent sBOD = 30 g/m3 Effluent suspended solids after settling = 20 g/m3 Kinetic coefficients: Y = 0.65 g/g, Ks = 100 g/m3, k = 6.0 g/g.d, kd = 0.07 g/g.d for T = 20 to 25 ⁰C Total solids produced are equal to computed volatile suspended solids divided by 0.85 First-order observed soluble BOD removal-rate constant k20 = 2.5 d-1 at 20 ⁰C.

8. Summer air temperature = 30 ⁰C 9 8. Summer air temperature = 30 ⁰C 9. Winter air temperature during coldest month = 6 ⁰C 10. Wastewater temperature during winter = 16 ⁰C 11. Wastewater temperature during summer = 22 ⁰C 12. Temperature coefficient, θ = 1.06 13. Aeration constants: α = 0.85, β = 1.0 14. Aerator oxygen transfer rate = 1.8 kg O2/kWh 15. Elevation = 500 m 16. Oxygen concentration to be maintained in liquid = 1.5 g/m3 17. Lagoon depth = 3.3 m 18. Design SRT = 5d 19. Power required for mixing = 8 kW/103/m3

ATTACHED GROWTH BIOLOGICAL TREATMENT PROCESS

Attached Growth Processes Microorganisms are attached to an inert packing material. The organic material and nutrients are removed from wastewater flowing past the attached growth (or Biofilm). Example of packing material : rock, gravel, slag, sand, redwood, plastics, etc. The packing can be submerged completely in liquid or not submerged, with air or gas space above biofilm liquid layer.

Attached growth biological treatment process Most common: Trickling filter – wastewater is distributed over the top area of a vessel containing non-submerged packing material Attached growth biological treatment process

Trickling Filter

Process flow in Trickling Filter The wastewater is applied over the bed of supporting media (rocks, stones, ceramic pieces, slag, etc) by rotating arms. The effluent is collected in the secondary clarifier, to separate washed out biomass solids before final disposal. As the wastewater trickles through the filter media, growth of microorganism takes place on the surface of packing material known as bio-film or slime layer. When the wastewater passes over this film, contact between substrates or food (waste) and microorganism is established, thus, the waste is decomposed aerobically by the attached biomass. (Facultative bacteria attach in trickling filters, decompose the organic material in the wastewater along with aerobic and anaerobic bacteria). Then, a stage comes when anaerobic conditions are developed nearer to the media surface and the microorganisms cannot remain attached or fixed to the media. the slime layer then eventually peels off (or washed out) and removed from the filter along with (next) flow. the washed out of slime layer is called sloughing.

Typical trickling filter process flow diagram Single stage

Two stage

Design Criteria of Trickling Filter Dosing rate Loading criteria

Design Criteria of Trickling Filter Dosing rate Dosing rate in trickling filter is the depth of liquid discharged on top of packing for each pass of the distributor. For higher distributor rotational speeds, the dosing rate is lower. With 2 or 4 arms, TF is dosed for every 10 – 60s. Investigations show that reducing distributor speed results in better filter performance improve BOD removal reduce Psychoda & Anisopus fly population biofilm thickness, and odors.

Higher Dosing Rate Larger water volume applied / revolution Greater agitation – causes more solids to flush out Greater wetting efficiency Wash away fly eggs Thinner biofilm – increase surface area & more aerobic biofilm

Loading criteria Quantifying biomass / biological & hydrodynamic properties in Trickling filter are not possible. Why ?? Attached growth is not uniformly distributed in TF. The biofilm thickness can vary. Biofilm solids concentration may range from 40 to 100 g/L. The liquid does not uniformly flow over the entire packing surface area. Hence, use broader parameters such as: volumetric organic loading, unit area loadings, and hydraulic application rates  used as design / operating parameters to relate treatment efficiency

ROTATING BIOLOGICAL CONTACTORS (RBC) RBC consists of series of closely spaced circular disks (polystyrene or polyvinyl chloride) submerged (typically 40%) in wastewater and rotated through it. The disks are attached to a horizontal shaft.  The assembly of shaft, disks and rotating equipments is called one module. Normally in industrial waste treatment, more than 3 modules arranged in series or parallel.

Removal Mechanism of RBC As the shaft rotates, the surfaces of rotating disks alternately come in contact with the microorganisms and organic content of wastewater and atmosphere. During the rotation, the microbes get attached to the disks, and O2 from atmosphere is transferred to the wastewater to maintain aerobic condition. The microbes attached to the disks surface grow in the form of biological film and consume organic content in the wastes. After some times, as the bio-films thickens, an anaerobic condition develops nearer to the disks surface , then the slime layer gets washed out (sloughing) by incoming waste water flow. the sloughed bio-films is ultimately removed in the secondary clarifier before final disposal of treated effluent. ………>> Similar mechanism to Trickling filter <<…………

Schematic Diagram of RBC Mechanism

Process Design Consideration for RBC Staging of RBC unit- why? Loading criteria Assume first stage 12-20g sBOD/m2d Total BOD loading 24-30g BOD/m2d Effluent characteristics - Refer Table 9-8 Secondary clarifier design Similar with those used in trickling filter

Example 9-7 Design of staged RBC for BOD Removal Given the following design conditions, develop a process design for a staged RBC system Parameter Unit Primary Effluent Target Effluent Flowrate BOD sBOD TSS m3/d g/m3 4000 140 90 70 20 10

Solution: Page 938 Follow step in page 937 Determine influent and effluent sBOD conc. and WW flowrate Determine RBC disk area for the first stage based on max SBOD of 12-15 g sBOD/m3d Determine number of RBC shaft using standard disk density 9300 m2/shaft Select number of trains, flow,number of stages,disk area/shaft Based on assumption in Step 4, calculate the sBOD in each stage. If the effluent sBOD is met, calculate the organic and hydraulic loading.

THANK YOU!