Hazardous Waste Treatment: Processes & Options PDF

Treatment process screening Recycling, treatment and disposal options  There are many different types of hazardous waste. It is not possible to find a suitable treatment/disposal process for all hazardous waste. There are also many processes for recovery, recycling, reuse, trea...

Treatment process screening Recycling, treatment and disposal options  There are many different types of hazardous waste. It is not possible to find a suitable treatment/disposal process for all hazardous waste. There are also many processes for recovery, recycling, reuse, treatment, and disposal. The choice of the most appropriate solution depends on many factors. Regulations, Costs, Social safety standards, Applicability of process technology. Effective hazardous waste management requires an integrated approach. Screening appropriate technologies Address options at the top of the hierarchy Consider treatment principles Evaluate treatment and disposal options Select technology - on-site or off-site - according to waste type and circumstances Consider simple options Try to avoid obsolete technologies Carry out technology assessment  In general, there will be a number of options available for the management of hazardous waste and the choice of method may be guided by strategic considerations. Strategic assessment of waste management options has been carried out by many organizations responsible for environmental policy, and the result is invariably a table of strategic priorities, producing a hierarchy of preference to aid selection. In its simplest form, this hierarchy is as follows Waste prevention/minimization Recovery Disposal The concept of waste prevention and minimization incorporates a number of measures that can lead to a positive change in waste generation. Where waste prevention is not possible, reuse, recycling and recovery are in many cases a preferable alternative to final disposal. Hazardous waste recovery, treatment, and disposal facilities Hazardous waste recovery/recycling refers to the effective use or reuse of a waste as a substitute for a commercial product or use of a waste as an ingredient or feedstock in an industrial process. It also refers to the recovery of useful constituent fractions within a waste material or the removal of contaminants from a waste to enable it to be reused. Use and reuse of hazardous waste Return of a Waste to the Original Process Substitution for Raw Material in Another Process Recovery of hazardous waste Processing Hazardous Waste for Product Recovery Processing Hazardous Waste As a By-Product Hazardous Waste Treatment Various technical options and alternative methods can be used for treatment. The result must focus on making the waste harmless or less hazardous, reducing its volume and texture, separating it for reuse and isolating it for final disposal. Treatment of hazardous waste aims to change the physical and/or chemical properties of the waste in order to reduce risks. The aim of treatment Volume reduction - reducing the volume of the hazardous parts of the waste by concentrating the hazardous components, perhaps by filtration or absorption. Destruction - the conversion of hazardous substances into non- hazardous substances by chemical, biological or thermal processes. For example, incineration destroys organic waste by burning it at high temperatures. Containment - Containing the waste to prevent its pollutants from escaping into the environment. This may be done by solidification or stabilization.  There are several treatment options that can be used separately or in combination. Treatment methods include: Physical methods: drying, screening, grinding, evaporation, sedimentation, filtration, fixation, etc. Chemical methods: Oxidation, reduction, neutralization, hydrolysis, etc. Physical and chemical methods Biological methods: composting, aerobic and anaerobic decomposition, activated sludge, enzyme treatment, etc. Thermal methods: incineration, boiling, autoclaving, UV treatment, microwave processing, etc. Stabilization and solidification Combined treatment methods  Physical treatment processes typically involve the separation of solids from solids, solids from liquids and liquids from liquids. In rare cases, separation of gases from solids or liquids may be required. Typically, physical treatment is the least expensive and least complex treatment process. Chemical treatment processes rely on chemical reactions either to precipitate hazardous constituents, which can then be separated from the bulk of the waste by physical processes, or to destroy or reduce the hazardous constituents. Physical and chemical treatment processes are often used in combination. Biological treatment processes use living organisms to either consume the contaminants in a waste and break them down into a non-hazardous form, or to absorb and concentrate the hazardous constituents. In either case, the organisms can then be separated from the bulk of the waste by physical means if necessary. Biological treatment is widely used for contaminated soil, wastewater and landfill leachate.  Thermal treatment processes involve the destruction of waste by oxidation. It is used for both liquid and solid wastes. Thermal treatment is widely used for organic waste, pharmaceutical waste and pesticides. Immobilization processes convert the waste into an insoluble, rock-hard material. They are generally used as a pre-treatment prior to landfill. The conversion is achieved by mixing the waste with various reactants to produce the cement-like product. This method is widely used for the disposal of hazardous waste sludges and soils containing heavy metals. Combined treatment processes are often required. In many cases, a chemical process carried out on a waste requires a subsequent physical process to achieve separation of the products of the chemical process. In turn, the solids may need to be subjected to further physical treatment, such as filtration, to further concentrate the solids. Disposal options Landfill and land disposal: Co-disposal Disposal in engineered hazardous waste sites or cells within sites Other options: Soil biodegradation Underground injection Deep mines  Properly designed, constructed and managed landfills can be used to dispose of hazardous waste. Disposal takes place in lined, discrete cells that are capped and isolated from each other and the environment. Uncontrolled disposal of hazardous waste on land is not acceptable. Some liquid or sludge wastes are biodegraded in soils. Controls are required if the sludge is contaminated with heavy metals. Deep well injection is sometimes used for pumpable wastes, such as brine solutions from oil production, which are injected into wells. Highly toxic residues, after appropriate stabilization, are sometimes placed in deep mines in disused salt mines under carefully controlled conditions. These options are becoming less acceptable and neither is likely to be widely appropriate and should not be considered by developing countries when choosing appropriate technologies. Selection of appropriate treatment options At local (on-site) level, to deal with a specific waste stream At national level, to decide what off-site facilities are needed to deal with residues from individual sites The first step is to identify and quantify the main types of hazardous waste. There will always be a need for landfill Questions to consider when selecting on-site treatment methods Can it handle the amount and type of waste? Will it enable compliance? What are the likely costs? What is the impact on operations? Are there any workplace, environmental or social concerns? What residues will be generated that will need to be removed off- site? Selection of appropriate technologies to implement the national strategy The type and quantity of waste The desired characteristics of the treatment outputs The role of a central landfill for stabilized waste from individual producers Technical suitability of treatment alternatives Economic and financial considerations Occupational, environmental and social considerations Technology assessment How to evaluate overall aspects of a technology choice? Environmental Technology Assessment (EnTA) can examine the wider impacts of a technology option. The process is similar to LCA, but applied to technologies rather than products. Environmental Impact Assessment evaluates the location and social impacts of a technology or development project. Risk Assessment examines the hazards and risk reduction measures of a technology or process. Key points to consider before making a decision on treatment or disposal Waste reduction and prevention by producers should always be a priority Role of on-site vs. off-site technologies Residues from treatment processes and their disposal must be considered Transitional technologies can be used until definitive high quality facilities are available Key questions for technology selection Who can carry out a technology assessment? Which wastes are not acceptable? Transport - how will the waste be received? How will the received waste be monitored? Who will design the facility? Who will train the operators? What features address specific national issues? How simple/sophisticated is the operation of the facility? How will the performance of the facility be monitored? What other environmental impacts are possible? What occupational hazards are likely? What is the permitting process? Is an EIA required? Non-technical factors in waste technology selection Adequacy of the national waste management system National policy, legislation and international standards Compliance with regulations Permitting situation Physical infrastructure Human resources and skills Costs and resources Socio-political conditions Geographical and geological conditions Opportunities for cooperation with other countries Technical factors in waste technology selection Waste characteristics Scale of technology application Maturity of the technology Robustness of the technology Field of application of the technology Characteristics of the treated product Anticipation of future needs Complexity and maintainability of the equipment Volume reduction Secondary waste and compatibility with existing processes Research and development status Security and nuclear safety The selection of hazardous waste control processes should be based on three different criteria: Waste type Treatment options Technical suitability Waste type The physical form of the waste (liquid, emulsion, slurry, sludge, powder, bulk) affects the choice of control technology. Chemical composition, physical properties, hazardous waste constituents in the waste material, volume/mass ratio and source variability are also important factors in process selection. Water solubility is a physical parameter of particular importance. Liquids that are soluble in water are called "aqueous liquids". Liquids that are not soluble in water are called "non-aqueous phase liquids" (NAPLs) and these substances are difficult to control in the event of leakage to the subsurface and groundwater. Different techniques are used for liquids denser than water (DNAPLs) and liquids lighter than water (LNAPLs). Treatment Options The choice of control technology should take into account the availability of treatment options, current and future needs of the case, treatment objectives, regulatory requirements for the area and the efficiency and reliability of the techniques for different cases. Technical Suitability The use of separate or combined technologies, the need for pre- treatment, the sensitivity of the technology to change and its potential for modification are considerations in technology selection. Waste management flow diagram for a fully integrated hazardous waste management facility  A lifecycle approach to hazardous waste is taken, starting with waste generation and including risk assessment, application of control technologies, disposal and post-disposal care. Successful hazardous waste management depends on the application of this integrated approach.