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CHAPTER 2 INDUSTRIAL WASTE
ENVIRONMENTAL HEALTH ENGINEERING ECH 4102 by: Dr. N Abdullah
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LEARNING OBJECTIVES Identify different sources and the major types industrial toxic & hazardous waste Distinguish treatment technologies for different type of industrial waste Describe Hazardous waste management and control
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Waste
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The Universe of Waste Sources & composition of solid wastes
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What is industrial waste?
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TYPES OF INDUSTRIAL WASTE
Toxic substances are primarily associated with industrial wastes Range of toxic substances present in industrial wastes is too broad to catalogue
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Source of Industrial Waste
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Hazardous waste sources
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INDUSTRY HAZARDOUS WASTE
Valley of Drums Q: How to classify and assess the hazard?
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HAZARDOUS WASTE Classification
Definition: Listed in EPA regulations Ignitable, corrosive, reactive, or toxic Declared by the generator
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HAZARDOUS WASTE CHARACTERISTIC
Ignitable waste (EPA HW No. D001) Liquids: flash point < 60°C Solids: cause fire under standard temp. & pressure Corrosive waste (EPA HW No. D002) Liquids: pH < 2 or > 12.5; corrode steel at > 0.25 in/yr rate Reactive waste (EPA HW No. D003) Unstable, react violently w/ air or water For potentially explosive mixtures w/ water Emit toxic fumes Toxicity Leach toxic constituents for solid wastes Toxicity Characteristic Leaching Procedure (TCLP) Crush to < 9.5 mm particle size Agitate in a weak acetic acid in liquid: solid = 20:1 by weight 18 hrs after, filter through 0.6~0.8 µm glass fiber filter Analyze sample for constituents
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HAZARDOUS WASTE ASSESSMENT CRITERIA
Bioconcentration Ability of material to be retained in animal tissue Many pesticides will reside in fatty tissue of animals Most concern – aquatic animals (seals & penguins) & birds ( pelicans, eagles, falcons, condors) that feed on fish LD50 amount of chemical that is needed to kill half of a group of test specimens e.g mice Animals in a toxicity study are fed progressively higher doses of chemical until half of them die, & this dose is known as median lethal dose (50%) The lower amount of toxin used to kill 50% of specimens, higher toxic value of chemical & will not break down quickly; as smaller creatures are eaten by larger ones, concentration in fatty tissue of larger organisms can reach toxic levels for them
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HAZARDOUS WASTE LC50 Phytotoxicity
Concentration at which some chemical is toxic used where the amount ingested cannot be measured, such as in aquatic environment or in evaluating quality of air Specimens such as goldfish, are placed in a series of aquariums, & increasingly higher concentrations of toxin are administered Fraction of fish dying within a given time is recorded Phytotoxicity Chemical is considered toxic if it exhibits toxicity to plants All herbicides are toxic materials & when they must be disposed of, they must be treated as hazardous waste ROUGH GUIDELINE : A WASTE IS CONSIDERED TOXIC IF IT IS FOUND TO HAVE LD50 OF < 50 mg/kg body weight OR IF THE LC50 < 2mg/kg
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Toxicity assessment CDI = chronic daily intake (mg/kg body weight. day) C = chemical concentration (mg/L) CR = contact rate (L/day) EDF = exposure duration (yr) & frequency (day/yr) BW = body weight (kg) AT = average time (d)
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CDI equation for different exposure pathway
INGESTION IN DRINKING WATER INGESTION WHILE SWIMMING INGESTION OF CONTAMINATED FOOD INHALE AIRBORN AD= ABSORBED DOSE ABS = ABSORPTION FACTO R FOR SOIL CONTAMINANT AF= SOIL TO SKIN ADHERE FACTOR AT= AVERAGE TIME BW= BODY WEIGHT CA=CONTAMINANT CONCENTRATION CDI=CHRONIC DAILY INTAKE CF= CONVERSION FACTOR (FOR SOIL & WATER) CR= CONTACT RATE CS= CHEMICAL CONCENTRATION IN SOIL CW=CHEMICAL CONCENTRATION IN WATER ED= EXPOSURE DURATION EF=EXPOSURE FREQUENCY ET=EXPOSURE TIME FI=FRACTION INGESTED IR=INGESTION RATE PC=CHEMICAL-SPECIFIC DERMAL PERMEABILITY CONSTANT SA=SKIN SURFACE AREA AVAILABLE FOR CONTACT INGESTION OF CONTAMINATED SOIL DERMAL CONTACT WITH SOIL DERMAL CONTACT WITH WATER
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Types of Industrial Waste
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TOXIC WASTE SOURCES TOXIN SOURCES
ACIDS – mainly inorganic but some organic causing; pH < 6 ACID MANUFACTURE, BATTERY MANUFACTURE, CHEMICAL INDUSTRY, STEEL INDUSTRY ALKALIS – causing pH > 9 BREWERY WASTES, FOOD INDUSTRY, CHEMICAL INDUSTRY, TEXTILE MANUFACTURE ANTIBIOTICS PHARMACEUTICAL INDUSTRY AMMONIACAL NITROGEN COKE PRODUCTION, FERTILIZER MANUFACTURE, RUBBER INDUSTRY CHROMIUM – mainly hexavalent but also less toxic trivalent form METAL PROCESSING, TANNERIES CYANIDE COKE PRODUCTION, METAL PLATING DETERGENTS – mainly anionic but some cationic DETERGENT MANUFACTURE, TEXTILE MANUFACTURE, LAUNDRIES, FOOD INDUSTRY HERBICIDES & PESTICIDES – mostly chlorinated hydrocarbons CHEMICAL INDUSTRY METALS – mainly Cu, Cd, Co, Pb, Ni, & Zn METAL PROCESSING & PLATING, CHEMICAL INDUSTRY PHENOLS COKE PRODUCTION, OIL, REFINING, WOOD PRESERVING SOLVENTS – mostly benzene, acetone, carbon tetrachloride & alcohols CHEMICAL INDUSTRY, PHARMACEUTICALS
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EXAMPLES OF HAZARDOUS WASTE GENERATED BY INDUSTRIES
WASTE GENERATOR WASTE TYPES Chemical Manufacturers Acids and Bases, Spent Solvents, Reactive Waste, Wastewater Containing Organic Constituents Printing Industry Heavy Metal Solutions, Waste Inks Solvents, Ink Sludges Containing Heavy Metals Petroleum Refining Industry Wastewater Containing Benzene & other Hydrocarbons Sludge from Refining Process Leather Products Manufacturing Toluene and Benzene Paper Industry Paint Waste Containing Heavy Metals, Ignitable Solvents Construction Industry Ignitable Paint Waste, Spent Solvents, Strong Acids and Bases Metal Manufacturing Sludges containing Heavy Metals, Cyanide waste, paint waste
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INDUSTRY HAZARDOUS WASTE
From 1956 until 1972, the 17-acre site was operated as a hazardous waste disposal facility. Over 34 million gallons of industrial waste, primarily from metal finishing, electroplating, and pesticide production were deposited in evaporation ponds.
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METAL PROCESSING WASTES
Metal Finishing: involves stripping, removal of undesirable oxides, cleaning and plating. The most ubiquitous contaminants are chromium, zinc, copper, nickel, tin and cyanides. Alkaline cleaners, grease and oils are universally present. Two major sources of waste: Concentrated solutions Rinse waters Sources of wastes –numerous & extremely variable in quantity & quality Metals forms: large particles of pure metal in suspension metallic ions & complexes in solution
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METAL PROCESSING WASTES
Wastes can be classified as follows: MINING – ore production & washing (also contains inert SS) ORE PROCESSING – smelting, refining, quenching, gas, scrubbing (also contains sulfides, ammonia & organics) MACHINING – metal particles usually mixed with lubricants DEGREASING – metals mostly in solution with cyanides, alkalis & solvents PICKLING – acids with metals & metallic oxides in solution DIPPING – alkalis with sodium carbonate, dichromate, plus metals
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METAL PROCESSING WASTES
POLISHING – particles of metals & abrasives together ELECTROCHEMICAL OR CHEMICAL BRIGHTENING & SMOOTHING – acids, mainly sulfuric, phosphoric, chromic & nitric with metals in solution CLEANING – hot alkalis with detergents, cyanides & dilute acids plus metals in solution PLATING – acids, cyanides, chromium salts, pyrophosphates, sulfamates & fluoroborates plus metals in solution ANODIZING – chromium, cobalt, nickel & manganese in solution
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Characteristics of Metal-Plating Wastes
Most stripping baths - acidic contain H2SO4, HNO3 and HCl Alkaline baths - sodium sulfide cyanide and hydroxide are also used. [chemicals] are usually less than 10%, 100,000 mg/l. Common plating baths are as follows: Bath formula Metallic + cyanide (ppm) Rinse Conc, ppm 0.5gph drag-out 2.5gph drag-out Nickel, 40oz/gal nickel sulfate 8oz/gal nickel chloride 6oz/gal boric acid 82,000 Ni 171 Ni 855 Ni Chromium, 53 oz/gal chromic acid .53 oz/gal sulfuric acid 207,000 Cr 431 Cr 2155 Cr Cadmium 3.5 oz/gal cadmium oxide 14.5 oz/gal sodium cyanide 23,000 Cd 57,700 CN 48 Cd 120 CN 240 Cd 600 CN
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Metal Processing Waste
method of treatment – depends on form of metal, Conc., pH, other constituents, & desired effluent standard Treatment are : Modifications in design and/or operation- to minimize or eliminate the waste. installation a P-Chemical treatment plant Modifications include: - eliminating breakable containers - drip pans, rinses - reducing spillage - fog rinses - reclaiming metals Fog rinses- spray nozzo
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LAUNDRY WASTES 4 gallons of waste per pound of clothes.
Waste originates from dye, grease, starch, scouring, dirt Most installations contain machines and use gal. of water per washing cycle. 22 gal. are cold and 8 hot resulting in an average discharge water at 100F. 50,000 gal/wk installation can be expected. 100 lbs of detergent are used per week Analysis Commercial Domestic pH 10.3 8.1 Alkalinity, ppm 511 678 TDS, ppm 2114 3314 BOD5,ppm 1860 3813 Grease, ppm 554 1406 Treatment of Laundry Wastes Acidification with H2SO4, CO2 or SO2 followed by coagulation with alum or ferric sulfate. After chemical coagulation, trickling filtration and activated sludge processes are effective.
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CANNED FOOD WASTE Require great deal of water as wash water from cleaning vegetable, sorting, peeling and coring, spillage from filling and sealing machines, wash water from cleaning floors, tables, belts. Product Volume, per case, gal BOD5 ppm SS Asparagus 70 110 30 Carrots 23 1830 Spinach 3 6300 630 Apricots 57-80 260 Tomatoes, whole 3-15
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MEDICAL WASTE : New York and New Jersey beach closures due to washed-up medical wastes November 1988 – Medical Waste Tracking Act (MWTA) added medical waste to RCRA Types of medical waste: Cultures and stocks Pathological wastes Human blood and blood products Used sharps Animal waste Isolation waste Unused sharps
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MEDICAL WASTE Method of Disposal:
Favored treatment option is incineration Required for “Red Bag” (or Yellow bag in some countries )(potentially infectious) waste Used for most waste for extra safety and “aesthetics” (incinerated waste is not recognizable as medical waste)
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RADIOACTIVE WASTE High-level waste : spent nuclear fuel
Transuranic waste – defense-related waste Uranium mill tailings Low-level waste Natural occurring radioactive materials (NORM) accelerator-produced radioactive waste Mixed waste – radioactive and hazardous
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Livestock & Animal Waste
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EXAMPLE: Hog industry
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TOXICITY FROM THE COLLECTION SYSTEM
Uncontrolled discharge – lead to poisonous gases Health of sewer workers – damage Levels of HCN & H2S of 0.03% in atmosphere are toxic H2S –problem of anesthesia – difficult detection Some organic solvents may cause similar difficulties
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TOXICITY FROM THE COLLECTION SYSTEM
High cost of constructing a waste collection system 70% of the total cost for treatment & disposal Strict control on discharge of toxic substances eg. HCN, H2S Some organic solvents may cause similar difficulties Tend to be immiscible with water, volatile & intoxicating Also may form explosive mixtures
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TYPICAL CONSENT CONDITIONS FOR DISCHARGE TO SEWERS
PARAMETER CONSENT CONDITION MAXIMUM TEMPERATURE 40-50OC pH 6-10 SUBSTANCES PRODUCING INFLAMMABLE VAPOURS NIL CYANIDE CONCENTRATION 5-10 mg/L SULFIDE CONCENTRATION 1 mg/L SOLUBLE SULFATES 1250 mg/L SYNTHETIC DETERGENTS 30 mg/L FREE CHLORINE 100 mg/L MERCURY 0.1 mg/L CADMIUM 2 mg/L CHROMIUM 5 mg/L LEAD ZINC 10 mg/L COPPER ZINC EQUIVALENT (Zn + Cd + 2Cu + 8Ni) 35 mg/L TOTAL NON-FERROUS METAL TOTAL SOLUBLE NON-FERROUS METAL
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Industrial Waste Treatment
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SUMMARY OF ALTERNATIVE TREATMENT TECHNOLOGIES (1992)
Other innovative (<1%) Soil aeration, in situ flaming & chemical neutralization (2%) Solvent extraction (<1%) Thermal desorption (5%) Dechlorination (<1%) Off-site incineration (15%) Soil vapor extraction (18%) On-site incineration (11%) In situ flushing (3%) In situ bioremediation (4%) Ex situ bioremediation (6%) Soil washing (3%) Solidification/stabilization (28%) In situ vitrification (<1%)
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Number of applications
Application of Innovative Treatment Technologies 100 90 VOCs 80 SVOCs 70 60 Metals Number of applications 50 40 30 20 10 Soil vapor Thermal Bioreme- diation In situ flushing Solvent Soil washing extraction desorption extraction
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PRE-TREATMENT Pretreatment is on-site, advantages:
recovering specific substances in an uncontaminated condition avoidance of contamination of a much larger wastewater stream In some cases, dilution of the wastes by admixture with sewage reduces the toxic inhibition many industrial wastes are deficient in some nutrient (N or P) problem in treatment due to inhibition of bacterial growth, so easier & cheaper to develop the necessary bacterial flora in an on-site treatment plant
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PRE-TREATMENT Key factors in deciding for or against pre-treatment:
Availability of space Availability of expertise Sludge and/or odor production may create a nuisance Possibility for the introduction of clean technologies 1- the site may be too restricted or land may be too valuable to be used for a treatment plant 2 the company may not wish to get involved in effluent treatment 3
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PHYSICAL METHODS PROCESS AIM EXAMPLES SCREENING
REMOVAL OF COARSE SOLIDS Vegetable canneries, paper mills CENTRIFUGING CONCENTRATION OF SOLIDS Sludge dewatering in chemical industry FILTRATION CONCENTRATION OF FINE SOLIDS Final polishing & sludge dewatering in chemical & metal processing SEDIMENTATION REMOVAL OF SETTEABLE SOLIDS Separation of inorganic solids in ore extraction, coal & clay production FLOTATION REMOVAL OF LOW SPECIFIC GRAVITY SOLIDS & LIQUIDS Separation of oil, grease & solids in chemical & food industry FREEZING CONCENTRATION OF LIQUIDS & SLUDGES Recovery of pickle liquor & non-ferrous metals SOLVENT EXTRACTION RECOVERY OF VALUABLE MATERIALS Coal carbonizing, plastics manufacture ION EXCHANGE SEPARATION & CONCENTRATION Metal processing REVERSE OSMOSIS SEPARATION OF DISSOLVED SOLIDS Desalination of process & wash water ADSORPTION CONCENTRATION & REMOVAL Pesticide manufacture, dyestuffs removal
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PHYSICAL PRE-TREATMENT METHODS
Devices to improve effluent quality eg. screening, filtration, coarse or fine, to reduce solids, grease trap, grit arrestors, sedimentation etc. The effluent from high-rate filters often has a BOD & COD similar to settled sewage & is suitable either for discharge to a sewer or for further biological treatment on site COD – CHEMICAL OXYGEN DEMAD – WHICH ALWAYS EXCEEDS BOD, IS THE OXYGEN CONSUMED BY A SAMPLE WHEN TREATED WITH ACIDIC DICHROMATE SOLUTION. IT RESULTS FROM OXIDATION OF BOTH ORGANIC & INORGANIC CONSTITUTENTS.
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CHEMICAL METHODS may be used in addition to biological treatment
Aims- to convert waste into a settleable form For oxidizing particular compounds (eg. Cyanide) since it is expensive & liable to lead to the production of undesirable chlorinated organics For pH correction & improving solid removal
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COMMON PRE-TREATMENT METHODS
COMMON CHEMICALS USED: CHEMICAL PURPOSE CALCIUM HYDROXIDE pH adjustment, precipitation of metals & assisting sedimentation SODIUM HYDROXIDE Used mainly for pH adjustment in place of lime SODIUM CARBONATE pH adjustment & precipitation of metals with soluble hydroxide CARBON DIOXIDE pH adjustment ALUMINIUM SULFATE Solids separation FERROUS SULFATE CHLORINE Oxidation ANIONIC POLYELECTROLYTES Enhance coagulation & flocculation
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PRIMARY SEDIMENTATION TREATMENT
Wastewater treatment : preliminary, primary & secondary (+tertiary if necessary) Preliminary – usually screening & grit removal; - have little effect on toxic materials - (But Effect primary sedimentation to toxic wastes –important) - Toxic materials in suspension (e.g., Particulate metals) – effectively removed Good flocculant - has great capacity for adsorption & removes majority of dissolved metals, pesticides & other toxic organics Effect toxic material to primary sedimentation – insignificant due to purely physical process of sedimentation & flocculation Beneficial since it renders less inhibitory waste material into biological treatment But, selectively concentrates toxins in sludge & may give problem in digestion & in sludge disposal
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PRIMARY SEDIMENTATION TREATMENT
Chemicals addition – enhance the effectiveness of primary sedimentation; also, assist the precipitation process ADVANTAGES: enables industry to avoid secondary biological treatment Enables waste to be discharged to a sewer, estuary or sea DISADVANTAGES: can be expensive, often requires pH correction, & may produce large quantities of sludge with a disposal problem
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PRIMARY SEDIMENTATION TREATMENT
Chemically enhanced sedimentation main aim: increase removal of solids But since many toxins (metals & chlorinated organics) adsorb strongly, their removal also increase to levels similar to combined primary & secondary treatment
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PRIMARY & SECONDARY TREATMENT
TYPICAL FOR ENHANCEMENT: LIME METAL CONC. IN WASTEWATER (mg/L) % REMOVAL BY SEDIMENTATION % REMOVAL (WITH LIME) BY SEDIMENTATION IRON 6.3 48 80 COPPER 0.6 28 60 CHROMIUM 0.34 40 58 LEAD 0.12 33 55 MERCURY 0.028 15 50 NICKEL 0.08 ZINC 0.7 38 70
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PROCESSING WASTES -Precipitation by pH Adjustment-
Technique most commonly employed to precipitate metal Optimum pH – varies depend on metal Typical value – 8.0 – 9.0 Zinc – avoid high pH to prevent formation of zincates Other constituents of waste (e.g., Ammonia) – can affect solubility of metal hydroxide; thus, impossible to predict accurately level of residual metal in treated effluent
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PROCESSING WASTES -Precipitation by Reducing Agent-
not all hydroxide precipitation – satisfied with pH adjustment Example : Cr6+ present in wastes from metal plating Must reduce to Cr3+ form before treatment with lime or caustic soda Reducing agents – sodium bisulfate, sulfur dioxide & ferrous sulfate Reduction process – carried out under acid conditions & subsequent addition of alkali precipitates trivalent chromium hydroxide
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PROCESSING WASTES -Precipitation by Integrated treatment-
Particular type of precipitation system used in metal plating industry Principal feature – rinsing stage immediately after metal plating stage – chemical rinse which precipitates metal from liquid around the article being plated Further water rinse is required to wash off treatment chemical
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PROCESSING WASTES -Precipitation by Integrated treatment-
Advantages : Water can practically reused Metals are not precipitated in a mixture – can be recovered However, sometimes difficult to adapt system to existing plating lines – require extra tank in line
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PROCESSING WASTES -Settlement for Solid Liquid separation-
Once metals precipitated from solution – liquid & solid phases must be separated 2 Methods of settlement: Small installation circulate or rectangular tank installation effluent flow <25 m3/day convenient to carry on batch basis settlement can take place in same tanks as that used for reaction (e.g., SBR)
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PROCESSING WASTES -Settlement for Solid Liquid separation-
Larger installation –continuous flow system Size of tanks – depend on maximum effluent flow rate & configuration adopted for tank Common type – vertical upward flow pattern having a central feed well, peripheral collection launder, & sludge cone at the bottom Clarification – enhanced by flocculating agents\ Size & mode of operation of precipitation system – affects quality of effluent - But, typical figures for well-designed, efficiently operated, settlement system for metal hydroxide precipitates – range 10 – 30 mg/l ss
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PROCESSING WASTES -Flotation for Solid Liquid separation-
alternative to settlement Process - consists in the carrying of metal hydroxides & other particles in suspension to surface of liquid in flotation vessel by increasing particles buoyancy using bubbles which adhere to the particles Scum containing gas – bubbles Separated solids – skimmed off
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PROCESSING WASTES -Flotation for Solid Liquid separation-
Variations in process – in method of producing carrier gas bubbles May be done by : Injecting a super-saturated solution of air in water under pressure into tank (dissolved air flotation) or By injecting air through diffuser (dispersed air flotation) or By electrolysis of water to yield fine bubbles of H2 & O2 (electrolytic flotation) gas bubbles produced – extremely small ( m)
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PROCESSING WASTES -Filtration for Solid Liquid separation-
Use of direct filtration – for phase separation Seldom appropriate – filter media tends to blind (e.g. clog) rapidly – due to gelatinous nature of metal hydroxide precipitates Where more granular precipitate is obtained – direct filtration satisfied & high quality effluent can be obtained
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OTHER SEPARATION TECHNIQUES
Ion Exchange Evaporation Molecular filtration Solvent Extraction Electrodialysis Flash mixing Flocculation Sedimentation Filtration Carbon treated water GAC adsorbers Sump Sludge Raw
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ION EXCHANGE SEPARATION
to remove dissolved ionic species from contaminated aqueous streams Treatment for both anionic & cationic contaminants Ion exchangers – insoluble high-molecular weight polyelectrolytes that have fixed ionic groups attached to a solid matrix Types of ion exchangers: Natural Synthetics- widely used due to greater stability, higher exchange capacity & greater homogeneity Resins used: polymeric materials that have chemically treated to render them insoluble, & to exhibit ion exchange capacity
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ION EXCHANGE SEPARATION
Often in form of spherical resin beads; membranes also available Most common synthetic ion-exchange materials: copolymers of styrene divinylbenzene (dvb) Treated water Influent Carbon out Carbon in Parallel operation Series Moving (pulsed) bed High contaminant removal Long column runs Small systems Moderate removals Large systems
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EVAPORATION To concentration of aqueous solution
use only where effluent contains high concentration of valuable material One application – on concentration of static rinses (drag out) from electroplating operations, especially chromium plating Method: rinse liquor is evaporated to metal concentration which makes concentrate suitable for direct reuse in plating bath
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MOLECULAR FILTRATION 2 categories: ultrafiltration (UF)
reverse osmosis (RO) Differentiating characteristic – molecular weight cutoff of membrane & corresponding pressure differentials required to achieve a given membrane flux
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with trans-membranes up to 500 psi Significant economic implication
MOLECULAR FILTRATION Differences RO UF 1. Molecular cutoff limit Da Da RO membranes will retain most organic materials as well as many of inorganic solutes 2. Pressure differential with trans-membranes up to 500 psi as high as 50 psi Significant economic implication
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MOLECULAR FILTRATION Often when RO is used, upstream UF is provided as pre-treatment Main operational problem – chemical & biological fouling of membrane (particularly with RO – membrane deterioration) RO process – used on effluents from electroplating in electronic components industry Continuous development of process & improved mechanical strength of membranes – increase range of applications
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SOLVENT EXTRACTION In general, solvents used are too expensive to be used just once, & contaminants are highly concentrated in the extract Thus, spent solvent from liquid-liquid extraction operations needs further treatment – to reclaim solvent for reuse & to reduce further volume containing contaminants Some solvent re-purification sequences include the use of distillation or adsorption
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ELECTRODIALYSIS Can remove dissolved inorganics (mineral content of wastewater) When inorganic salt dissolved in water solution, it ionizes to produce positive charge cations & negative charge anions When electrical potential passed through solution, cations migrate to negative electrode & anions to positive electrode Commercial semi-permeable membranes – allow passage of ions of only one charge: Cation-exchange membranes – permeable only to positive ions Anion-exchange membranes – permeable only to negative ions
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Different Types of Innovative Remediation Technologies
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BIOLOGICAL METHODS For organic waste Most popular
Either aerobic or anaerobic Anaerobic - popular for treating high strength industrial wastes
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BIOLOGICAL TREATMENT Further treatment : biological
Key to successful – adaptation of microbes to the presence of toxin Bacteria & protozoa – can acclimatize & great adaptability in degrading new synthetic organic & toxic compounds
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BIOLOGICAL TREATMENT BIOLOGICAL PROCESSES FOR TREATING TOXIC WASTEWATERS PROCESSES REACTOR TYPE ADVANTAGES & DISADVANTAGES AEROBIC DISPERSED GROWTH Tend to be completely mixed, therefore dilutes toxin but affects whole biomass. Liable to cause settling problems as well as interfere with oxidation FIXED FILM Tend to be plug flow so no dilution unless recirculation is used. Biomass more robust for shock loads but metazoa more sensitive ANAEROBIC Tend to be completely mixed and suffer from washout of methanogens. The latter are also more sensitive than acidogens to toxic effects and have a low growth rate Tend to be plug flow but level of attachment not as good as aerobic filters. Need recirculation to dilute toxins
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TOXIC LEVELS IN AEROBIC BIOLOGICAL TREATMENT
TOXIN SIGNIFICANT LEVEL HYDROGEN IONS pH < 6 or > 9 PHENOLS 50 – 100 mg/L AMMONICAL-N 500 – 1000 mg/L ZINC 10 – 50 mg/L CHROMIUM 5 – 20 mg/L LEAD 5 – 30 mg/L ALKYL BENZENE SULFONATES 3 – 20 mg/L SULFIDES 5 – 50 mg/L
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TOXIC EFFECTS IN ANAEROBIC TREATMENT INHIBITORY CONCENTRATION (mg/L)
BIOLOGICAL TREATMENT TOXIC EFFECTS IN ANAEROBIC TREATMENT TOXIN INHIBITORY CONCENTRATION (mg/L) IN SEWAGE IN SLUDGE CHROMIUM - 2 CADMIUM COPPER 1.5 IRON 10 LEAD 100 NICKEL 80 ZINC 50 DETERGENT 2% OF SS BENZENE 50 – 200 CARBON TETRACHLORIDE CHLOROFORM 0.1 DICHLOROPHEN 1 γ-BHC 48 TOLUENE
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Industrial Waste Disposal
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DISPOSAL OF TOXIC WASTES
Proper disposal to prevent any short or long term hazard to man & environment Some require treatment prior to disposal (e.g., hazardous) Methods: Incineration To land To Sea Solidification (radioactive waste)
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Incinerator
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-Incineration- Reduces waste to solid residues, gases, and water vapor
Process reduces waste volume by 80–90% Solid residues need further disposal (landfilling) Emissions have to be closely monitored and controlled Economic considerations Incineration costs about $125,000 per ton (cost is affected by plant capacity) Typical plant capacity is about 1,000 tons per day frequently used for decomposition of organic toxins Examples of successful use of incineration Treatment of toxic sulfide liquor from Kraft process for making paper pulp Treatment of steel pickle liquor Advantage - regenerate useful compounds
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DISPOSAL OF TOXIC WASTES -Incineration-
Disadvantages: Require ‘care’ when deal with halogenated materials – irritant corrosive gases may produce Also a danger to treatment plant – become too complex Serious problem on toxic wastewater – metallic wastes & radioactive wastes due to characteristics of: Contain hazardous elements that cannot be broken down Appear to be less toxic substances that can replace them
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DISPOSAL OF TOXIC WASTES -To Land-
Where wastewaters contain human toxins – require great care to avoid contaminate groundwater For less hazardous wastes – lagoon; may have connection with watercourse but also permits infiltration (+ some evaporation & possibly some degradation) Long term – swelling & blinding of soil may reduce infiltration capacity More hazardous – land disposal policy : segregation followed by long term containment of hazardous material in impervious disposal sites
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TREATMENT OF HAZARDOUS WASTES
Secure landfill – instead of one impervious liner, require multiple liners & must be stabilized or in containers Similar to sanitary landfill – leachate is collected & a cap is placed on landfill once completed Require continued care; EPA require 30 years monitoring
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DISPOSAL OF TOXIC WASTES -To Sea-
unlimited capacity for dilution & infinite retention time Capable of diluting acute toxins below toxic threshold but problems may arise with substances that accumulate due to geochemical or biochemical mechanisms Further complication – international aspect; may transport around the world
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DISPOSAL OF TOXIC WASTES -To Sea-
Common practice: Discharge by pipeline to inshore waters Dispersion in buoyant jet can give adequate initial dilution But, inshore areas sensitive to pollution; being used as shellfisheries & recreational zones
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DISPOSAL OF TOXIC WASTES -To Sea-
Deep sea disposal Several international agreements - volume of hazardous disposal has declined & nature of waste has changed Organohalogens, carcinogenic substances, Hg & Cd compounds, & plastics – banned Less hazardous material – still takes place but in packaged form & only in deep sea
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DISPOSAL OF TOXIC WASTES -Solidification-
make some hazardous wastes suitable for disposal (e.g., oily wastes, sludges contaminated with pcbs & fly ash contaminated with heavy metals) reduce mobility of hazardous constituents by binding them into solid matrix (low permeability – leach resistance)
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DISPOSAL OF TOXIC WASTES -Solidification-
Binding mechanisms – depend on agent employed (typical: cement based, possolanic or silicate based, thermoplastic based or organic polymer based Cheaper agents widely used – cement, asphalt & pozzolanic-based Promising result in short term tests Longer term – less certain except for vitrification Technique – only financially possible for nuclear waste Disadvantages are cost and irreversible
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Industrial waste Management
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HAZARDOUS WASTE MANAGEMENT
7% Air quality 7% Solid waste 50% Hazardous waste 36% Water quality (wastewater/water supply) 1998 Share of Environmental Consulting
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Industrial Waste Management Hierarchy
Waste minimization Waste audit Waste reduction Waste Exchange Recycling Waste audit (after step 4.) Source reduction Waste exchange Recycling Treatment
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1. Waste minimization 1st strategy is to perform waste audit
Waste audit steps: Identify waste stream Identify sources Establish priority of waste streams for minimization Implement Track Evaluate progress
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1. WASTE MINIMISATION Strategies to minimize as far as possible the types, quantities & concentration of any toxic wastes discharged through good housekeeping: extending the life of process solutions by filtration, topping up, adsorption Altering the production process to use less toxic compounds, e.g. Substituting copper pyrophosphate for copper cyanide in electroplating solutions Dry cleaning prior to wash-down, which remove a large proportion of the pollutant in solid form
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1. WASTE MINIMISATION Attempt to minimize (cont.):
Evaporation of strong organic liquors, which can often produce a burnable product Minimizing & segregating any flows which contain toxic material. separate wastes for safety reasons, e.g. Cyanides or sulfides & acid wastes, trichloroethylene (TCE) & alkaline wastes to segregate for treatment reasons, but segregation can be very expensive
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Options of Industrial waste Management
Arid region = very dry land, use for disposal of nuclear waste Salt formation = waste contain 99% NaCL, for safe disposal (deep repository of waste) Surface impoundment = disposed of waste in indented soil area such as pit, lagoon, pond Landfill = buried the waste underground Underground injection =
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