S.H.W.-L15-17: Hazardous Waste Treatment

Oxidation and Reduction

Applied for the treatment and removal of a variety of inorganic and organic wastes. The net result of these reactions is the conversion of the waste to a non-hazardous form or to a form that can be isolated physically.

Chemical Precipitation

Applied in hazardous waste treatment primarily for the removal of heavy metal ions from water > the most widely used means of precipitation metal ions is by the formation of hydroxides.

Liquid-Liquid Extraction

the separation of constituents from a liquid solution by contact with another immiscible liquid in which the constituents are more soluble

Liquid-Solid Extraction (leaching)

the separation of the constituents from solids by contact with a liquid in which the constituents dissolve

Extraction

an important type of phase transfer (liquid-liquid, liquid-solid extraction)

Co-composting-solid phase

Mixing of hazardous waste with biodegradable solids to act as bulking agent and thermal source. Usually need two different materials as good bulking agent and good thermal source. Process takes place in windrow, static piles or in vessels. Used for solids contaminated with coal tar or for TNT-contaminted sediments and soils.

Encapsulation

Enclose waste within casing or layer or inert substance

On-site v. off-site treatment

-For hazardous waste, most processes suitable for on-site treatment -For wastewater, central treatment-but requires pre-segragation of toxic effluents

Collection and Transport: Hazardous Waste

-Important role in terms of disposal cycle and in control -Most incidents of improper disposal of hazardous waste have occurred during transport >>results from disposal contracts between waste generator and hauler

Leaching properties of waste or residue

-Influence of pH and other chemical variables on leaching -pH value: major chemical variable controling the leaching of minor and major elements from waste or residue -Cationic and anionic constituents are bound to these solid residues by adsorption/desorption on mineral surface with a pH-dependent charge. -The general leaching behaviour can be further modified by the effect of other chemical parameters (redox potential, complexation of inorganic components).

Biological treatment of hazardous waste: characteristics

-Optimize a natural process -Is suitable for low concentration organic wastes (sludge) -Require good control of process conditions -Is relatively low cost, effective, and tolerant to changes in waste -Is most widely used for wastewater treatment -May be on-site or off-site -New applications being developed

Characteristics of Biological Treatment of Organic Wastes

-Optimize a natural process -Use ubiquitous microorganism (bacteria, fungi) -Require control of temperature and nutrient balance -May be aerobic or anaerobic

Aims of Hierarchy of preferred waste management options:

-To limit the quantity of HW requiring final disposal -To move waste management options up the hierarchy -To treat wastes as close as possible to the point of generation (e.g., on-site treatment by simple physical processes)

Minimize and Avoid: HW Hierarchy

-Top of waste hierarchy -Reduce pressure on treatment and disposal facilities -Reduce costs -Safe resources

Key considerations for biological treatment

-Waste reduction and avoidance by generators should always be a priority -Role of on-site vs off-site technologies -Need to consider residues from treatment processes and their disposal -Transitional technologies may be used until final igh-quality installations are available

Soil heaping-solid phase

-combine land treatment and windrow composting -effective for treating large volumes of contaminated soil and other wastes with low concentration of organics -valuable where available land area is restricted

In-situ bio-remidiation

-enable treatment without excavation and removal of contaminated material -an aerobic process -enhance natural biodegradation -influenced by hydrogeological factors -can reduce contamination to acceptable levels in a relatively short time (1-2 years)

Co-combustion in cement kilns

-existing lime or cement kilns can be adapted to burn hazardous wastes -suitable for interim and long term use -avoid need for new facility -save on due costs in cement making

Land treatment-solid phase

-involve applying wastes uniformly to prepare land at controlled rates -aimed at degradation of organic constituents -remove other waste constituents e.g., suspended solids, heavy metals -purely a treatment process-land NOT suitable for cultivation

Physical Precipitation

-physical changes in the solution, a process in which a solid forms -solute in solution

Photolytic reactions

-protons or electromagnetic radiation (consisting of short wavelength visible light or ultra-violet radiation) are absorbed by a molecule, causing a chemical reaction to occur. Photolysis: Applied to destroy a number of kinds of hazardous wastes > useful in breaking chemical bonds in refractory organic compounds -The addition of chemical oxidant (e.g., potassium peroxodisulfate K2S2O8) enhances destruction of oxidizing active photolytic products.

When should encapsulation be utilized?

-recommended for inorganic hazardous wastes -as a pretreatment step prior to landfill disposal

Chemical extraction and leaching

-removal of hazardous constituents by reaction with extractants in solution -ion exchange: removing cations or anions from solution onto solid resin -ion taken up by an ion exchange resin may be removed by treating the resin with concentrated solutions of acid or salt -use of ion exchange in hazardous waste treatment for removal of low level of heavy metal ions from wastewater.

Technology selection and criteria:

1) At on-site level, to deal with a particular waste stream 2) At national level, to decide what off-site facilities are needed to deal with residues from individual premises 3) Always need to know quantities and types of wastes 4) There will always be a need for landfill

Technology criteria for on-site treatment of wastes

1) Can it deal with amount and type of waste? 2) Will it enable compliance with regulations? 3) What are the likely costs? 4) What are the implications for operation? 5) Are there any workplace, environmental or social concerns? 6) What residues will be generated that have to be removed off-site?

What are the management strategies for the identification of hazardous wastes?

1) Identity hazardous wastes and track quantities 2) Regulate the hazardous waste from the time it is first generated through the transport to final treatment or disposal.

Example of an application of thermal treatment:

A rotary kiln incinerator which is one of the method widely used for hazardous waste

Principles of HW treatment:

After avoidance, minimization and recycling, the next stage in the waste hierarchy is treatment. The principles of treatment are as follows: 1) Volume reduction 2) Destruction 3) Containment

Advantages of biological waste treatment

In the right conditions - i.e., temperature, humidity, and pH - biological treatment is effective and tolerant to changes in waste composition-these may results in a short period of inactivity but do not halt the process.

Factors influencing biological process conditions:

Biological treatment processes require a control of: -Temperature -pH -Moisture -level or aeration -inhibitors such as metals -nutrients

Electrolysis-overview

Break down chemical compounds with electrical charge

A generator is considering less expensive options for incineration regarding the management of the chlorobenzene. Options available under the RCRA generator standards are: a) Disposal in an approved hazardous-waste landfill b) On-site treatment to volatilize the chlorobenzene c) Recycling the solution directly into the process from which it was generated d) Both (b) and (c)

C) Recycling the solution directly into the process from which it was generated

Destruction:

Convert hazardous to non-hazardous substances (e.g., by chemical, biological, or thermal processes)

Hierarchy of preferred was management options: Desirability ->

Dump < Dispose (controlled) < Treat and Process < Recover materials (recycle and reuse) < Minimize < Avoid

How is identifying hazardous wastes and tracking quantities effective?

Effective identification and labelling by the generators are essential for control.

Electrolysis

Electrochemical reduction + oxidation species in a solution by means of electricity applied to electrode from an external source . Once species in a solution (usually metal ion) is reduced by electrons at the cathode and another gives up electrons to the anode, where it is oxidized.

Emerging Application for biological treatment

For many waste types, biological treatment is still in early stage of development New applications are being tested and developed e.g. -For treating additional hazardous waste streams -For integrating biological processes with physical-chemical treatment

Containment:

Isolate hazardous materials (e.g., by solidification or stabilization)

When is land treatment suitable?

Land treatment is suitable for: only sludge and waste oils, organics sludge and liquids, widely used in the US by petroleum industry, also possible to treat wastes from wood treatment, e.g., preservatives such as creosote, pentachlorophenol.

Molecular Separation

Often based upon membrane processes in which dissolved contaminants or solvent are forced through a membrane > pressure-driven process

What happens after metals are recovered?

Recovered metals are usually recycled to the process that produces the waste

Volume Reduction:

Reduce the volume of waste with no hazardous components (by filtration and absorption as an example)

Separation

Separating components of a mixture that are as ready in two different phases. -Many wastes are composed of aqueous/organic mixtures in colloidal sized emulsion. -Once emulsion is broken, centrifugation can be used to separate the phases (e.g., filtration or centrifugation, decantation/sedimentation, floatation)

Why is the regulation of hazardous waste, from the time it is first generated through the transport to final treatment or disposal, necessary?

Some hazardous wastes require special control from the time of generation through their transportation, temporary storage, treatment and disposal.

Factors influencing biological treatment:

Suitability of the waste: -composition -physical form -pH Biological treatment is only suitable for organic wastes with relatively low toxicity It is not 100% efficient in destroying organic material

Thermal Treatment of waste by incineration:

allow energy recovery, materials recycling

Treatment Option 2:

Thermal(the destruction of wastes by oxidation), stabilization and solidification, combined treatment methods -All treatments are aimed at modifying physical and chemical properties of the hazardous component -Most treatments leaves residues for disposal

Adsorption

Transfer of a substance from a solution to a solid phase. Activated carbon adsorption: to remove a variety of contaminants from liquid and gaseous streams.

Stabilization

Treat waste to minimize migration

Thermal Treatment of waste by gasification:

allow recovery of useful materials

Solidification

Use cement-based process

Chemical Treatment: examples

acid/base neutralization, chemical precipitation, chemical flocculation, oxidation/reduction, chemical extracting and leaching, ion exchange

Biodegradation of organic into simple inorganic species with suitable microbes: by

activated sludge treatment, rotating biological contractor, aerated lagoons and stabilization ponds, anaerobic digestion, land application

Neutralization-overview

adjust pH to neutral

A manufacturer generates a liquid waste that contains 4% by weight of chlorobenzene as its principal organic hazardous component (POHC). The specific gravity of the waste is 1.1. During the incineration process, 4,200 gal of waste is burned in a batch burn. Ata combustion efficiency of 99.99%, the maximum allowable release of chlorobenzene (kg) in the batch is: a) 0.0375 b) 0.070 c) 0.15 d) 0.30 Note: 1 kg = 2.2 lb, 1 gal = 8.34 lb Chlorobenzene (C6H5Cl) Specific gravity is broadly defined as the ratio of the density (mass of a unit volume of a substance to the density if a standard reference substance)

b) 0.070

High-molecular-weight and strongly hydrophobic organic compounds are common soil contaminant due to petroleum crude oil spills. These compounds are most often partitioned to soils containing: a) silicate clay b) humid matter c) sand d) gravel

b) humid matter

Land application

biodegrade organic matter through action with soil microbes

Activated Sludge Treatment

biodegrade organic species with bioactive sludge in aqueous phase

Rotating Biological contactor

break down aqueous organic species in contact with bacterial rich filter

Hydrolysis

break down constituents by adding water

Aerated lagoons and stabilization ponds

break down organic wastes in shallow pools with oxygen

Thermal source (co-composting)

by biological decomposition

Benzene is biodegrading in petroleum-contaminated soil at the rate of 0.2%/day, corrected for chemical dispersion. First-order chemical kinetics is the only treatment technology. If the original concentration averages 17 mg/kg for the benzene, the time (years) required to achieve a soil benzene concentration of 5mg/kg is most nearly: a) 0.5 b) 1.12 c) 1.67 d) 2.33

c) 1.67 years

What are the most common metals recovered from electrolysis?

cadium, copper, gold, silver, lead, zinc

Hazardous waste origin and effect:

causes: occurrence of dangerous chemicals and their mixtures effects: hazardous wastes may pose a substantial present or potential hazard to human health or the environment when improperly treated, stored or disposed of, or otherwise mismanaged treatment: waste requires special approaches with higher and both health and environmental risk

Chemical Treatment: Overview

chemical reduction and oxidation, neutralization, precipitation, dechlorination, hydrolysis, electrolysis

In a RCRA Subtitle C hazardous waste landfill, the low-permeability soil should have an in-place conductivity (cm/s) less than: a) 1x10^-4 b) 1x10^-5 c) 1x10^-6 d) 1x10^-7

d) 1x10^-7

What are the basic elements of the quantitative risk assessment process? a) Hazard identification, exposure assessment, ecological assessment, toxicity assessment b) Hazard identification, ecological assessment, regulatory review, risk characterization c) Dose-response assessment, site survey, population characterization, risk characterization d) Hazard identification, exposure assessment, toxicity assessment, risk characterization

d) Hazard identification, exposure assessment, toxicity assessment, risk characterization

Anaerobic digestion

degrade organic waste in the absence of oxygen

Good bulking agent (co-composting)

dry molasses are poor bulking agent

Molecular Separation: Electrodialysis

electric potential driven process, removes ionic comments from water -it produces moderate quality water produce (i.e. several hundred mg/L salt)

Chemical Adsorption

electronic interaction between specific surface sites and solute molecules

Co-composting process can take place in windows, turned to

ensure adequate aeration

Co-composting process can take place in static piles, where air is

forces or sucked through material

Co-composting process can take place in vessels, which offers

greater process control/VOC contaminant

Thermal Treatment of waste: by (3)

incineration, pyrolysis, gasification

Biological treatment for hazardous waste, used for:

low contaminant-concentration organic wastes, e.g., sludge

In hazardous waste application, electrolysis is most widely used in the recovery of ______, mostly from electroplating media from wastewater and rinsing water from the electronics industry and from metal finishing operations.

metal

Physicochemical Treatment

physical and chemical treatment processes are often used in combination to maximize treatment benefits ex: solvent extracting, flocculation and coagulation, membrane separation, ion exchange, leaching, etc.

Treatment Option 1:

physical, chemical, physical and chemical, biological -All treatments are aimed at modifying physical and chemical properties of the hazardous component -Most treatments leaves residues for disposal

When is neutralization often required?

prior to the application of other waste treatment processes -in a biochemical treatment, microorganisms usually require a pH range of 6 to 9

Neutralization

process used to eliminate waste acids and bases -Strongly acid or basic solutions are corrosive to pipes, containers, and mixing apparatuses -Lime is a widely used base for treating acidic wastes -Sulphuric acid is relatively inexpensive for treating alkaline metals -For some applications, acetic acid is preferable since its a weak acid, natural product, and biodegradable

Recycle and Reuse of Hazardous Wastes

recycle: materials may first require cleaning/separation reuse: no treatment except for any necessary cleansing

Dechlorination

remove chlorine from organic materials

Sieving and Screening

remove coarse metal

Manual Separation

remove selected wastes by visual inspection

Decanting, Centrifuging

remove water content

Precipitation

separate hazardous constituents from solution

Methods of physical treatment include:

separation, extraction, physical precipitation, adsorption, molecular separation

Sedimentation

settle solids separate liquid

How are industrial hazardous waste problems solved?

since they are transportable, and pose hazard either in short or long term basis, classification is advised. -. Industrial hazardous waste generators -. Non-industrial hazardous waste generators. Standard Industrial Classification (SIC) codes: Used to identify groups of hazardous waste generators.

Disposal Options for HW:

soil biodegradation, underground injection, deep mines -Landfill and disposal may include: Co-disposal Disposal in engineered hazardous waste sites or cells within sites

Thermal Treatment of waste by pyrolysis:

thermal decomposition of materials at elevated temperatures in an inert atmosphere

Why are industrial hazardous waste problems a unique issue?

they are transportable, and pose hazard either in short or long term basis

Bulking agent

to create void spaces for passage of air

Chemical reduction and oxidation-overview

use oxidizing and reducing agents to transform constituents

Slurry-phase treatment

used for solid waste, sludge, or contaminated soil Needs mixing to: -homogenize slurry -breakdown solid poarticles -oxygenate -increase contact with microorganisms

Physical Adsorption

van der Waals forces, weak interactions

Good thermal source (co-composting)

wood chips are poor thermal source

Advantages of slurry-phase treatment

▪ Degrades waste at a faster rate, needs less land, than solid-phase treatment ▪ Potential for use with additional waste streams e.g. Wastes from wood preserving, petroleum refinery wastes