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Physico-chemical treatment of Hazardous waste

Physico-chemical treatment

• a range of cool processing techniques• aim to reduce the hazardous potential of wastes• may also offer re-use or recycling opportunities• often used in combination to optimise hazardous wastes

treatment

Chemical processes use chemical reactions to transform hazardous wastes into less hazardous substances

Physical processes enable different waste components to be separated or isolated, for

re-use or appropriate treatment or disposal

Physico-chemical treatments

On-site vs off-site in central treatment facility

•Some physical processes on-site eg sedimentation •Treatment may be integrated into manufacturing process

On-site treatment reduces: • volumes needing transport• transport costs

Physico-chemical treatment

• Off-site treatment allows for dedicated waste handling and treatment systems

• Should provide:•Waste receiving station•Storage facilities for wastes awaiting treatment•Treatment areas for number and variety of processes used •Storage and disposal facilities for treatment residues eg reaction products, filter cake and wastewater•Storage for treated wastes to be incinerated, where appropriate •Laboratory services•Trained personnel

Treatment residues

All physico-chemical treatment processes generate residues which may:

•be hazardous wastes themselves

•be more concentrated than original waste

•be suitable for recycling

•require further treatment

•need to be landfilled

Sludge from physico-chemical treatment after pressing

Source: Safe hazardous waste management systems 2002 ISWA

Physical processes

• Many different physical treatment processes• Most are simple and low-cost • Choice depends on physical form of waste and its

characteristics

Options include:·Separation·Sedimentation·Flotation·Drying·Evaporation·Sludge dewatering ·Filtration

Source: Safe hazardous waste management systems 2002 ISWA

Filter press

Separation

Examples of separation techniques:

• Sieving and screening - for dry materials of different particle size

• Distillation - to separate liquids • Use of washing medium - to extract

contaminants from soils or soluble components from solid wastes

Adsorption

Adsorbents Application

Activated carbon Solvent recoveryElimination of odoursGases purification

Alumina Drying of gases andliquids

Bauxite Treatment of petroleumfractionsDrying of gases andliquids

Molecular sieves Selective removalof contaminantsfrom hydrocarbons

Silica gel Drying and purifying gases

Sedimentation•Used to separate particles held in suspension in a liquid which is principally aqueous

•Uses gravity•May require mechanical or manual stirring•Suitable for a wide range of hazardous wastes

• metals in waste water• neutralised acids and alkalis containing suspended

metal hydroxides• metals that have been precipitated

•Sludges may need further screening, drying or dewatering

•Separated liquid may need further treatment

Sedimentation - example

Source: Davd S Newby 1991

Flotation

•Relies on the natural behaviour of particles less dense than water

• Is suitable for a range of waste types eg oil/water separation

•Efficiency can be improved by blowing air through the liquid

size of air bubbles should be varied according to waste type

Drying and evaporation

May be needed after sedimentation

Options include: • Sludge drying beds • Centrifugal separation • Filtering and pressing

Drying and evaporation - example

Belt filter - a continuous filtering process widely used for

dewatering sludgesam management, Wiley

Chemical processes•change chemical properties of waste •use a chemical to treat a chemical •need details of waste composition and reactivity •need qualified staff to:

•assess waste composition•monitor chemical reaction •check reaction results

Options include:·Reduction and oxidation·Neutralisation·Precipitation

Reduction and oxidation

Some common oxidising and reducing reagents

Oxidising reagents

•Sodium or calcium hypochlorite

•Hydrogen peroxide

•Chlorine

•Potassium permanganate

•UV

•Ozone

Reducing reagents

•Ferrous sulphate

•Sodium sulphite

•Sulphuric acid

•Iron

•Aluminium

•Zinc

•Sodium borohydride

Oxidation in practice

• Needs expert design, careful operation to be safe

• Is cost effective

•Enables avoidance of harmful side reactions

Commonly used for cyanides

Easiest oxidising reagents:

sodium or calcium hypochlorite

Reduction in practice

Commonly used for chromates and chromic acids from chromium plating and tanning industries

Cr VI reduced to Cr III then removed by precipitation

Common reducing reagents:• ferrous sulphate • sodium sulphite/sulphuric acid

Chemical Oxidation and reduction: (I) Oxidation reduction methods provide another important chemical treatment

alternative for hazardous wastes. One important chemical redox treatment involves the oxidation of cyanide wastes from metal finishing industry, using chlorine in alkali solution. In this reaction CN- is first converted to a less toxic cyanate. Further chlorination oxidises the cyanate to simple carbondioxide and nitrogen gas.

important redox treatment process is the reduction of hexavalent chromium Cr(VI) to trivalent chromium Cr(III) in large electroplating operations. Sulphur dioxide is used as the reducing agent and the reactions are as follows.

A large variety of oxidisable contaminants in waste water and sludges are oxidised by ozone which can be generated on site by an electrical discharge through dry air or oxygen.

Ozonolysis: Ozone is a very powerful oxidising agent. Although this process has not been demonstrated in any full-scale facility, its application to TCDD and PCBs is quite promising. With respect to TCDD it was demonstrated that if the dioxins were suspended as an aerosol combined with CCl4, 97% degradation of TCDD was possible. Ozone in conjunction with UV radiation has been shown effective for the destruction of polychlorinated phenols and pesticides. In both the cases the key requirements were to concentrate the TCDD in a medium where they were susceptible to attack and provide a free radical for reaction with dioxin molecule.

Neutralisation

• A batch process• Used for wide variety of acidic and alkaline wastes• Acid wastes are neutralised by alkalis, and vice versa• Used to treat liquid wastes, sludges and gases • Reactions must be laboratory tested to control pH,

identify complementary reagents • Neutralised liquid usually sent for sedimentation

Precipitation

• Causes soluble substances to become less soluble/insoluble

• Often used in combination with other treatment processes eg reduction, neutralisation

• Effective treatment for wastewater containing toxic metals which arise in metal-plating and finishing industry, and mining

• Calcium hydroxide (lime) most widely used reagent

Chemical precipitation:

This technique can be applied to almost any liquid waste stream containing a precipitable hazardous constituent. By properly adjusting pH, the solubility of toxic metals can be decreased, leading to the formation of a precipitate that can be removed by settling and filtration. Quite often lime [Ca(OH)2] or caustic soda is used for precipitation of the metal ions as metal hydroxides. For example the following reaction suggests the use of lime to precipitate the metal as hydroxide.

Chemical ppt methodChromium is precipitated as hydroxide.

Sodium carbonate also has been used to precipitate metals as hydroxides (Fe(OH)3•XH2O), carbonates (CdCO3), basic carbonate salts (2PbCO3•Pb(OH)2). Carbonate ion hydrolyses in water to give hydroxide ion

Chemical ppt methodsEven lower concentrations of metals in the effluent can be removed by precipitating them as sulphides. Ferrous sulphide can be used as a safe source of sulphide ion to produce sulphide precipitates with other metals that are less soluble than ferrous sulphide. Reducing agents such as sodium borohydride can be used to precipitate the metal ions from solution in the elemental form.

Chemical MethodsNeutralisationWaste acid with an alkali e.g. sulfuric acid with sodium carbonate:H2SO4 + CO3 2- → SO4 2- + CO2 + H2O OxidationUsing common oxidising substances such as hydrogen peroxide or calcium hypochlorite e.g.cyanide waste with calcium hypochlorite:CN- + OCl- → OCN- + Cl- OCN- + H3O+ → CO2 + NH3

ReductionUsed to convert inorganic substances to a less mobile and toxic form e.g. reducing Cr(VI) toCr(III) by the use of ferrous sulphate:14H+ + Cr2O7 2- + 6Fe2+ → 6Fe3+ + 2Cr3+ + 7H2OHydrolysisDecomposition of hazardous organic substances e.g. decomposing certain organophosphoruspesticides with sodium hydroxide.PrecipitationParticularly useful for converting hazardous heavy metals to a less mobile, insoluble formprior to disposal to a landfill e.g. precipitation of cadmium as its hydroxide by the use ofsodium hydroxide:Cd2+(aq) + 2OH- → Cd(OH)2(s)

Hydrolysis: Hydrolysis treatment can be given to those hazardous waste constituents which are very reactive with water. Examples of those substances are halides, carbide, hydride, alkoxide, and active metal.

Ion exchange: Ion exchange is judged to have some potential for the application of interest in situations where it is necessary to remove dissolved inorganic species. However other competing processes - precipitation, flocculation and sedimentation - are broadly applicable to mixed waste streams containing suspended solids and a spectrum of organic and inorganic species. These competing processes also usually are more economical. The use of ion exchange is therefore limited to situations where polishing step was required to remove an inorganic constituent that could not be reduced to satisfactory levels by preceding treatment processes. One example for this is the use of anion exchanges for the removal of anionic nickel cyanide complex and chromate ions from waste solutions.

Ion -exchange resins have also been used in the removal of radionuclides from radioactive wastes

Wet air oxidation: It is the aqueous phase oxidation of dissolved or suspended organic substances at elevated temperatures (150-325oC) and pressures (2000 kPa to 20,000 kPa) water. Which makes up the bulk of the aqueous phase, serves to catalyse the oxidation reactions so they proceed at relatively low temperature, and at the same time serves to moderate the oxidation rates removing excess heat by evaporation. It also acts as excellent heat transfer medium, which enables the wet air oxidation process to be thermally self-sustaining with relatively low organic feed concentrations. The high pressures allow high concentration of oxygen to be dissolved in water and the high temperature assist the reaction to occur. In wet air oxidation, the waste is pumped into the system with high-pressure pump and mixed with air from an air compressor. The waste is passed through a heat exchanger and then to a reactor where atmospheric oxygen reacts with the organic matter waste, sometimes in the presence of catalysts. The oxidation is accomplished by a temperature increase. The gas and liquid phases are separated. System pressure is controlled to maintain the reaction temperature. The process can be used for the removal of cyanide from electroplating waste solutions.

Other chemical processesPractical options can include:

•Hydrolysis eg for some pesticides

•Electrolysis eg for silver recovery from

photographic wastewaters

•Dechlorination eg for solvents

•Chlorolysis eg for residues from chlorinated

hydrocarbon manufacture

Hazardous waste compatibility

Combined physical & chemical processes

Two common examples:·Solvent extraction·Coagulation and flocculation

Coagulation and flocculation

Physico-chemical treatment

Source: David S Newby

Thermal treatment

Thermal treatment = destruction of hazardous waste by thermal decomposition

Thermal treatment methods include: • incineration - complete combustion using excess oxygen• gasification - incomplete combustion in the partial absence

of oxygen• pyrolysis - thermal decomposition in the total absence of

oxygen

Application of thermal treatment

Suitable for organic wastes Thermal treatment processes:

• require high capital investment • are highly regulated• need skilled personnel• require high operating and safety standards• have medium to high operating costs

Good practice in hazardous waste combustion

3 Ts:

• Time

• Temperature

• Turbulence

Flue gas cleaning systems

Examples of Calorific Value

Mixed waste from plant cleaning operations 10,000 - 30,000 kj/kg

Wastewater 5,000 kj/kg

(0 - 10,000kj/kg depending on organic content)

Industrial sludge 1,000 - 10,000 kj/kg

Paints and varnishes >20,000 kj/kg

Chlorinated hydrocarbons 5,000 - 20,000 kj/kg

For comparison, MSW = ~10,000kj/kg

Source: Indaver

CombustionRequires:

• addition of excess air • mechanical mixing of waste • even distribution and aeration of waste

Behaviour of waste during combustion varies according to its heat value and its formSome low CV wastes burn easily = strawSome low CV wastes are difficult to burn = wet sludgesSome high CV wastes burn easily = tank bottoms Some high CV wastes are difficult to burn = contaminated soils, certain plastics

Certain wastes change their physical characteristics during combustion

Combustion techniquesBed plate furnaces: use gravity to mix waste - used for homogeneous and wet wastes such as sludge cake

Fluidised bed furnaces: waste is introduced into a bed of sand which is kept in suspension - used for wastes of similar size and density

Incineration grates: wastes fed onto the grate are turned or moved to ensure aeration of the waste mass via holes in the grate - used for solid wastes eg municipal wastes, not liquids or sludges

Rotary kilns: wastes are placed in slowly rotating furnace - suitable for solids, sludges and liquids

Operation of the furnace

• good understanding of waste characteristics

• technical skills• control of waste feed • mixing of wastes • temperature to be kept at required level

despite variations in waste• excess air• flue gas control• regular maintenance

Must be consistentNeeds:

Source: David C Wilson

Energy recovery

Waste combustion produces heat but combustion of low CV wastes may not be self-supporting

Energy recovery is via production of steam to generate electricity

• Only steam production: 80% efficiency is typical• Steam can be used for in-house demands• Steam can be delivered to adjacent users eg other industrial plants• Electricity can be generated: 25% efficiency typical

Opportunities to sell heat are improved where facilities are in industrial areas

Sale of surplus energy improves plant economics

Waste-to-energy Incinerator

By-products of incinerationMay be:

• solid • liquid• gaseous

Comprise:• recovered materials such as metals, HCl• flue gases• slag and ash• products of the flue gas treatment, also called air

pollution control (APC) residues • wastewater

Flue gasesQuantity and type of pollutants in emissions depend on:

• pollutants in waste• technology • efficiency of operation

Average 6 - 7 Nm3 of flue gas per kg waste

Specific collection/treatment for:Dust - staged filters

Chlorine - neutralised by scrubbing with lime

Sulphur - washing stage

Dioxins - combustion control, activated carbon

Source: David C Wilson

Dioxins

• Family of around 200 chlorinated organic compounds, a few of which are highly toxic

• Widespread in the environment

• Present in waste going to incineration

• Can be re-formed in cooling stages post-combustion

• 3Ts help destroy dioxins in waste, reduce reformation

• Use of activated carbon to filter from flue gases

• Emissions limits extremely low

Example of flue gas cleaning technology

Source: Indaver

Fuel blending

Reception/storage of waste in drums

and bulk

Shredding and separation of solids

and liquids

Treatment of solids

Storage ‘Hot-Mix’

Treatment of liquids

Washing and recovery of

metal

Reception of liquid waste in

bulkTankfarm

Buildings and civil constructions

Control and safety systems

NORCEM

Main process

Export

Sale

Source: Ian Miller

Examples of technology 1Rotary kiln incinerator

Source: Guyer, Howard H Industrial processes and waste stream management, Wiley

Examples of technology 2 Fluidised bed combustion

Circulating fluidised bed Bubbling fluidised bed

Source: Guyer, Howard H Industrial processes and waste stream management, Wiley

The waste will be put into the incinerator batch by batch, fuel is DO. In the primary incinerator, fuel is pumped into the incinerator through the fire nozzles to burn the waste and always maintain the temperature in the incinerator at a temperature (550 - 6500c).

The gas produced after burning from the primary incinerator is directed through to the secondary incinerator to burn the remaining elements in the exhaust gas at higher temperatures (about 1000 - 1.2000C. Similar to the primary incinerator, DO fuel is injected into the secondary to maintain the temperature inside. Gas formed from waste incinerators will be directed through the heat exchanger to reduce the temperature below 3000C to avoid the formation of toxic Dioxin / Furan.

After cooling down process, gas is led through the absorbent device that has gasket ceramic rings inside. By contact process between gas phase and liquid phase (NaOH), components of acid gases such as HCl, HF, COX, SOx, NOx, dust ... are removed from exhaust gases prior to discharge into the environment through 20m high of chimney. The absorption solution is circulated and NaOH is added frequently to ensure appropriated concentration for treating process.

Periodically, the solution will be discharged into the wastewater treatment system and replace it by new solution. Heat generated from the treating process is utilized for drying the wastes and sludge to limit emissions of heat into the environment and save fuel for treating process.Residue ash generated from burning will be conducted to solidify before moving to the landfill.

PyrolysisPyrolysis = thermal decomposition process which takes place in the total absence of oxygen

Products of pyrolysis: • combustible gases• mixed liquid residue

Advantages: • low operating temperature • no need for excess air so less flue gas• by-products are combustible

Gasification

Gasification = incomplete combustion in the partial absence of oxygen

Enables efficient destruction of hazardous waste at lower temperatures than incineration

Thermal destruction is ensured by a combination of high-temperature oxidation followed by high temperature reduction

Products:• useful gases eg hydrogen, carbon monoxide• solid char

Plasma Arc

A thermal process developed for commercial application in some coutries like autralia uses the very high temperatures, in excess of 10,000K, which can be attained in arcs formed across high voltage electrodes. This is particularly useful for the destruction of difficult hazardous liquids and gases such as some of the halogenated organics. This process is particularly applicable for the destruction of waste halons and CFCs.

Plasma Furnace Incineration, or "thermal treatment", is the high temperature reduction of wastes via combustion. Incineration can attain a 75-95% reduction in waste mass, and can destroy hazardous pollutants with efficiencies as high as 99.99%! A wide variety of thermal treatments exist. One system that is gaining popularity is the plasma furnace. These are used to treat hazardous wastes. They operate at incredibly high temperatures (8,000-10,000 degrees Celsius) using gaseous Argon. At these temperatures you atomize everything! Gaseous Argon is injected into the incinerator and then spun by a radio frequency coil until it reaches operating temperatures. A spray of hazardous waste is then injected via a nebulizer tube, and the combustion reaction is allowed to occur. Some drawbacks are that they can only handle small amounts of waste at any one time, and they are time consuming (in terms of operation and maintenance) and expensive. Plasma technology is extremely effective if used correctly.

100 kW steam plasma process for treatment of PCBs (polychlorinated biphenyls) waste( Liquid)

100 kW steam plasma process for treatment of PCBs (polychlorinated biphenyls) wasteActual reactor

Photolysis: In photolysis, chemical bonds are broken under the influence of light. In primary photochemical process, the target species is converted to an electronically excited state, usually a diradical, which is sufficiently energetic to undergo chemical reaction. The fate of the excited molecule and therefore the effectiveness of a photolysis treatment process, depends on its chemical structure and on the medium in which it is carried out. For the photolysis process to be effective in the treatment of hazardous wastes stream, the radiation source must be sufficiently energetic, must be absorbed by the target species and the final photochemical products must be less toxic. To date much of the research work on the treatment of highly toxic wastes has centered on two types of constituents: polychlorinated biphenyls (PCBs) and chlorinated dibenzo-p-dioxins(CDDs) eg: tetrachloro dibenzo-p-dioxin (TCDD). The three requirements of photolysis of TCDD are 1) Dissolution in a light transmitting film 2) presence of organic hydrogen odour and 3) ultraviolet light. In such photolysis reactions initially a reactive intermediate such as HO• is formed which participitate in chain reactions that lead to the destruction of the compound.

Biological treatment of hazardous wastes: Biological processes are in general, the most cost effective techniques for treating aqueous waste streams containing organic constituents. The physical and chemical properties of the compound influence its biodegradability. With appropriate organisms and under right conditions, even phenol which is considered to be biocidal can be degraded. The microorganism must be allowed to acclimate to the waste to be treated prior to routine operation of the process. Even some compounds which were considered as biorefractory may be degraded by microorganisms adapted to their biodegradation.

Some pestcid is degraded by properly acclimated pseudomonas. The relatively highly chlorinated PCBs are degraded by anaerobic bacteria under less anaerobic condition. These products can be further decomposed. To increase the biodegradability of the hazardous wastes, the pH of the medium should be adjusted to an optimum value of 6-9 and the oxygen level should be high. Concentrations of soluble inorganics in the hazardous wastes should be kept low so that enzymatic activity is not inhibited. Trace concentrations of inorganics may be partially removed from the liquid waste stream during the biological treatment, because of adsorption onto the microbial cell coating. 22 ……………22(CHO)COHO→+

In aerobic waste treatment, hazardous wastes such as chemical processes wastes and land fill leachates can be degraded by aerobic microorganisms such as bacteria and fungi in the presence of oxygen. In anaerobic waste treatment, microorganisms degrade different organic wastes in the absence of oxygen. During the process H2S is generated which precipitates toxic heavy metal ions as their sulphides. The overall degradation of the hypothetical organic compound (CH2O) can be written as follows.

Land treatment Land treatment of hazardous wastes involves controlled application of the waste onto the soil surface. The objectives of land treatment are the biological and chemical degradation of organic waste constituents and the immobilisation of inorganic waste constituents. Land treatment differs from land fills in that with land treatment, the assimilative capacity of the soil is used to detoxify, immobilise, and degrade all or a portion of the applied waste. Land fills are containments that store hazardous wastes and control the migration of wastes or by-products from the land fill sites. Liners are not required with land treatment. Hazardous wastes should not be placed in a land treatment site unless the waste can be made less hazardous or nonhazardous by the reactions occuring in the soil. Hazardous-waste land treatment is the controlled application of hazardous waste on the aerobic soil horizon, accompanied by continued monitoring and management in order to alter the physical, chemical and biological characteristics of the waste and to render the waste less hazardous. .

Land treatment of wastes is accomplished by mixing the wastes with soil under appropriate conditions. Important microorganisms like bacteria, including those from the genera, agrobacterium, anthrobacteri, bacillus, flavobacterium, pseudomonas are involved in biodegradation. In addition actinomycites and fungi are all involved in the biodegradation of wastes. Bacterial cultures may develop through acclimation over long periods of time and which are able to degrade these normally recalcitrant compounds. Land treatment is applicable to petroleum refining wastes, biodegradable organic chemical wastes including organochlorine compounds. However it is not suited to the treatment of waste containing acids, bases, toxic inorganic compounds, salts, heavy metals and excessively soluble volatile and flammable organic compounds

Surface impoundments: A surface impoundment is a man-made excavation, diked area, or natural topographic depression designed to hold an accumulation of liquid wastes. The construction is similar to that described for land fills in that bottom walls should be impermeable to liquids and provision must be made for leachate collection. Proper geological siting and construction with floors and walls composed of low-permeability soil and clay are important in preventing the pollution, since the chemical and mechanical challenges to the liner materials in surface impounds are severe.

Underground injection: Underground injection or deep-well disposal consists of injecting the hazardous liquid wastes under pressure to the underground strata isolated by impermeable rock strata from the acquifiers. The following factors must be taken into consideration before discharge of hazardous wastes into the deep wells. Since the wastes are injected into a region of elevated temperature and pressure, some chemical reactions may occur involving the waste constituents and the mineral strata. Corrosion may be severe. Problems such as clogging may occur if the liquid wastes contains oils, soils, and dissolved gases. The main concern with underground injection is the potential for contaminating underground drinking water supplies, if the disposal well is not properly cased or if it is damaged.

Treating by solidifying method    Before the solidifying process, materials should be crushed to appropriate size, and then put into the mixer machine for each batch. The addition agents such as cement, sand and polymer are added to carry out the dry mixing, and then continue to add water to do the wet mixing process. The mixing process helps for the components to be mixed and form the homogeneous mixture. After required mixing time, the mixture is added to the cube mold. After 28 days maintaining solid cube, solidifying process occurs and isolates completely contaminated components.

The solid cube will be tested the compressive capacity, the possibility of leak, and stored carefully in warehouse before transporting to the landfill.

Treating Fluorescent Lamp

Final disposal

Management and disposalThe major issues of concern for hazardous wastes inIndia are import, illegal dumping sites and in-complete data ongeneration and disposal of hazardous wastes in the country.Industrial incinerators in use are generally not efficient and aremerely a combustion chamber and source of emission of dioxinsand furans. Environmentally sound management of hazardouswastes would require Common Hazardous Waste ManagementFacility (CHWMF) for industrial clusters spread all over thecountry, as it is not possible to have hazardous wastemanagement facility for each unit, particularly in the case ofsmall and medium scale units.

Land fills: In order to protect public health and environment the design of hazardous waste land fills should be adequate. The figure below shows the three levels of safeguard that has been incorporated into the system.

To promote movement of waste to pumps for extraction to the surface and subsequent treatment, a leachate collection system has been designed by contours. To channel the leachate to a pumping station below the land fill, plastic pipes are used, the collected leachates are brought to surface using pumps and they are given waste specific treatment which includes (1) passing the leachate Indian Institute of Technology Madrasthrough a column consisting of sorbent material such as carbon or flyash. (2) theleachate is also subjected to suitable physical-chemical units such as chemicaladdition, flocculation, sedimentation, pressure filtration, pH adjustment, andreverse osmosis to remove the dissolved waste. To provide a back up leachatecollection system, a secondary system of another barrier is contoured. Thesecondary collection system in the event of failure of primary system conveys theleachate to pumping station, which in turn relays the waste water to the surfacefor treatment.The third safeguard system consists of a series of discharge wells up-gradientand down-gradient to monitor ground water quality area and to control leachateplumes if primary and secondary systems fail. Upgradient wells gives thebackground levels of selected chemicals in the ground water, which can becompared with the concentrations of these chemicals in the discharge from thatof the down-gradient wells. Thus this system provides an alarm mechanism if theprimary and secondary systems fails.Land fills are allowed with sufficient vent points so that if methane isgenerated, it may be burned off continuously.

The design for bottom liners of the landfill disposal units included a pressure relief system; a 3-ft-thick secondary clay liner, a 60-mil HDPE secondary geomembrane layer; a geosynthetic drainage layer and leak detection system; a 3-ft-thick primary clay liner; and a geosynthetic/gravel primary leachate collection system. Golder has conducted numerous drilling programs at the facility, including one to obtain subsurface soil information in support of design of a new, double-lined hazardous waste landfill cell and surrounding slurry trench cutoff wall.

Sanitary Landfill

Hazardous Waste Landfill

Major point included geotechnical evaluation and foundation design for the facility constructed over a closed landfill cell, as well as design of the lining, leachate collection, and piping systems. Additional engineering services: •Testing geosynthetic material friction angles in the lab to determine factor of safety against sliding failures •Performlaboratory tests of geotextile to confirm applicability as a filter to very fine natural soils •Perform laboratory tests of in-plane transmissivity of various combinations of geotextiles & geonets for leachate collection •Perform the destructive seam strength testing & prepared detailed "as-built" drawings & testing documentation •Perform construction quality assurance monitoring & testing for landfill disposal cells, final cover systems, and stormwater drainage systems

Sanitary Landfills: Trade-offs

Fig. 16-12, p. 391

Clay and plastic liningto prevent leaks; pipescollect leachate frombottom of landfill

GroundwaterLeachatemonitoringwell

Groundwatermonitoringwell

Leachate pumpedup to storage tankfor safe disposal

Leachatestoragetank

Leachatetreatment system

Pipes collect explosivemethane for use as fuelto generate electricity

Electricitygeneratorbuilding

When landfill is full,layers of soil and clayseal in trash

Methane storageand compressorbuilding

Methane gasrecovery well

Compactedsolid waste

Leachatepipes

Probes todetectmethaneleaks

Topsoil

Garbage

ClaySand

Garbage

Subsoil

Synthetic liner

SandClay

Sand

Deep-well Disposal

Surface Impoundments: Trade-offs

Topic as per syllabus

• Hazardous waste disposal site clean up, site safety and sampling plans, remediation and feasibility study, solidification of radioactive waste disposal.

Hazardous Waste Land Disposal Units (LDUs)

• Landfill• Surface impoundment• Waste pile• Land treatment unit• Injection well• Salt dome formation• Salt bed formation• Underground mine• Underground cave

• Specific regulations have been developed for four types of land disposal units under Subtitle C of RCRA (40 CFR Parts 264/265). These units include:

• Hazardous waste disposal site clean up

Landfills are excavated or engineered sites where non-liquid hazardous waste is deposited for final disposal and covered. These units are selected and designed to minimize the chance of release of hazardous waste into the environment. Design standards for hazardous waste landfills require a double liner; double leachate collection and removal systems (LCRS); leak detection system; run on, runoff, and wind dispersal controls; construction quality assurance (CQA) program. Liquid wastes may not be placed in a hazardous waste landfill. Operators must also comply with inspection, monitoring, and release response requirements. Since landfills are permanent disposal sites and are closed with waste in place, closure and post-closure care requirements include installing and maintaining a final cover, continuing operation of the LCRS until leachate is no longer detected, maintaining and monitoring the leak detection system, maintaining ground water monitoring, preventing storm water run on and runoff, and installing and protecting surveyed benchmarks.

Surface Impoundments are natural topographic depressions, man-made excavations, or diked areas formed primarily of earthen materials used for temporary storage or treatment of liquid hazardous waste. Examples include holding, storage, settling, aeration pits, ponds, and lagoons. Hazardous waste surface impoundments are required to be constructed with a double liner system, a leachate collection and removal systems (LCRS), and a leak detection system. To ensure proper installation and construction, regulations require the unit to have and follow a construction construction quality assurance (CQA) program. The regulations also outline monitoring, inspection, response action, and closure requirements.Waste Piles are non-containerized piles of solid, non-liquid hazardous waste that are used for temporary storage or treatment. In addition to the standard double liner and leachate collection and removal systems (LCRS), waste piles are required to have a second LCRS above the top liner. Waste piles must also have run on and runoff controls, be managed to prevent wind dispersal of waste, and are subject to inspection, monitoring, and release response requirements. When closing a waste pile, all waste residue and contaminated soils and equipment must be removed or decontaminated.

Land Treatment Units use naturally occurring soil microbes and sunlight to treat hazardous waste. This is accomplished by applying the hazardous waste directly on the soil surface or incorporating it into the upper layers of the soil in order to degrade, transform, or immobilize the hazardous constituents. Land treatment units rely upon the physical, chemical, and biological processes occurring in the topsoil layers to contain the waste. Because of this, the units are not required to have liner systems or an leachate collection and removal systems (LCRS). Before hazardous waste can be placed in a land treatment unit, operators must complete a treatment demonstration to demonstrate the unit's effectiveness and ability to treat the hazardous waste. Once operational, operators must monitor the unit (unsaturated zone monitoring) to ensure that all hazardous constituents are being treated adequately. Unit closure consists primarily of placing a vegetative cover over the unit and certifying that hazardous constituent levels in the treatment zone do not exceed background levelsSalt Dome Formations, Salt Bed Formations, Underground Mines, and Underground Caves are geologic repositories. Because these units vary greatly, they are subject to environmental performance standards, not prescribed technology-based standards (e.g., liners, leachate collection systems, leak detection systems). The standards require that these miscellaneous units must be located, designed, constructed, operated, maintained, and closed in a manner that ensures the protection of human health and the environment.