Presentation on theme: "Presentation Outline Introduction Properties and Classification of Hazardous Wastes Sources, Types and Quantity of Hazardous Wastes Found in MSW."— Presentation transcript:
Presentation Outline Introduction Properties and Classification of Hazardous Wastes Sources, Types and Quantity of Hazardous Wastes Found in MSW Significance of Hazardous Waste in MSW Physical, Chemical and Biological Transformations of Hazardous Waste Constituents Found in MSW Management of Hazardous Wastes in MSW
Introduction Concerns has grown over the disposal of MSW, which may contain small amount of hazardous waste from households and commercial facilities The fate of hazardous material found in MSW is unknown. When: The products such as compost are produced from MSW MSW are combusted MSW is placed in landfills The long-term effects, if any, on public health and the environment from the presence of these materials also are unknown
Properties and Classification of Hazardous Waste Hazardous waste have been defined as wastes or combinations of waste that pose a potential hazard to humans or other living organisms because: Such wastes are non-degradable or persistent in nature They can be biologically magnified ( occurs as a buildup of chemical contaminants in a food chain accumulating over time) They can be lethal They cause or tend to cause detrimental cumulative effects Safety – related properties Corrosivity Explosivity Flammability Ignitability Reactivity Health – related properties Carcinogenicity Infectivity Irritant ( allergic response) Toxicity Radioactivity Teratogenicity Properties of HZ When dealing with the hazardous waste found in MSW, Municipalities have most commonly used these properties to define a hazardous waste
Properties and Classification of Hazardous Waste Definitions Given by the U.S. Environmental Protection Agency The U.S EPA has published and refined definitions for RCRA hazardous waste Priority pollutants RCRA Hazardous Waste The U.S.EPA has defined RCRA hazardous wastes in three general categories, namely listed wastes, characteristic hazardous wastes and other hazardous wastes Characteristics hazardous waste are established on the basis of their ignitability, corrosivity, reactivity and toxicity. Toxicity is determined by an analysis of constituents derived from an extraction test.
Properties and Classification of Hazardous Waste Categories of RCRA hazardous wastes
Properties and Classification of Hazardous Waste
Definitions Given by the U.S. Environmental Protection Agency Priority Pollutants In 1979, the U.S. EPA was required to prepare a list of toxic pollutants proven to be harmful to human health. Four criteria were used to classify the pollutants 1.Actual or potential damage that a water discharge of these materials may create by virtue of certain toxicological properties. These properties include bioaccumulation, carcinogenicity, mutagenicity or high acute toxicity. 2. Seriousness of discharge of the pollutant by point source 3.The setting of effluent standards for point source discharge 4. Overall environmental effect of the control measures available
Properties and Classification of Hazardous Waste Definitions Given by the U.S. Environmental Protection Agency Other hazardous waste classifications have been proposed by following agencies: International Agency for Research on Cancer National Cancer Institute Environmental Protection Agency – Carcinogen Assessment Group
Sources, Types and Quantity of HW in MSW The sources of hazardous waste found in MSW are : Residential sources Commercial Sources Institutional Construction and demolition Municipal services Treatment plant sites Typical hazardous household products are reported in Table 5-3 The relative distribution of hazardous wastes are presented in table 5-4 There are three types of hazardous wastes generators Small – quantity generator Large – quantity generator Conditionally exempt generator
Sources, Types and Quantity of HW in MSW Small – quantity generator ( in a calendar month) produce between 100 kg – 1000 kg of non-acutely hazardous wastes less than 100 kg of waste resulting from the cleanup of any residue or contaminated soil, water, or other debris involving the cleanup of an acutely hazardous waste less than 1 kg of an acutely hazardous wastes Generators who produce more than the above quantities are considered to be Large – quantity generators Generators who produce less than these quantities are considered conditionally exempt generator conditionally exempt generators are subject to fewest regulatory controls and are permitted to dispose of small amounts of waste in sanitary landfills
Sources, Types and Quantity of HW in MSW Quantity of Hazardous Wastes in MSW It is estimated that the amount of hazardous waste found in MSW (1992) varies from 0.01 to 1 percent by weight, with a typical value of 0.1 percent. These percentages do not account for the HHW that are illegally disposed of onto land and into sewers and storm drains. The reported range is wide because the methods used to identify and classify HW found in MSW are quite variable and the sampling periods not consistent between studies.
Note: In comparing the data reported in tables 5-4 and 5-5, it is clear that the relative distribution of HW will be quite variable depending on the time of the year and the number of HW collection days that have been completed in a given community
Sources, Types and Quantity of HW in MSW Hazardous waste compounds produced by commercial, industrials and agricultural activities that are typically found in MSW
Significance of HW in MSW The small amount of HW found in MSW are of significance because of their occurrence in all solid waste management facilities and their persistence when discharged to the environment The occurrence influences recovery of materials, conversion products (e.g., compost), combustion products, and landfills. Hazardous waste constituents in conversion product will make them unusable. Source separation is being encouraged to eliminate these constituents from solid waste – processing operations Hazardous waste constituents in combustion products are troublesome. They have been found in the gaseous emissions and in the residual materials
Significance of HW in MSW Hazardous waste constituents at landfills are derived from hazardous wastes themselves and/or they may be produced by chemical and biological conversion reactions within the landfill. Long – Term Persistence. Hazardous waste are classified as either non-persistent or persistent. The half – life concept can be used to characterize and compare the relative environmental persistence of various hazardous wastes. t ½ = Ln 2/ Kt
Physical Transformation of HW found in MSW The principal physical transformations that alter the form of the hazardous waste constituents found in MSW are Volatilization Vapor Pressure Volatilization the principal mechanisms leading to the production of the gaseous substances from MSW are volatilization, biodegradation and chemical reaction. Of these, volatilization is thought to be the most important. Hw can occur in the gaseous state as a result of three related processes: volatilization of chemical wastes, Volatilization of liquid chemical wastes Volatilization of chemical waste absorbed on soil or other solid.
Volatilization of chemical process is function of the following exposed surface area time Diffusion coefficient vapor pressure MW Temperature Volatilization of liquid chemical waste in water and leachate is affected by Henry’ s law Temperature liquid turbulence trace constituents concentration in the gas phase wind speed Volatilization of chemical wastes absorbed on soil are affected by: surface area strength of adsorption vapor pressure type of soil or solid pH, Solubility, the amount and type of organics present, size of particle, density of solid waste, reactivity and leaching
Physical Transformation of HW found in MSW Vapor pressure vapor pressure is strongly affected by the temperature The vapor pressure can be used to determine the partial pressure of each component in a mixture of gases. The total pressure of a mixture of non- reacting gases is equal to the sum of the partial pressures of the individual gases (P total = P1 + P2 + P3 + …) The vapor pressure can also be used as a measure of the volatility of the substance Liquids with high vapor pressure will tend to evaporate easily, while liquids with a law vapor pressure will evaporate slowly. Compounds that are considered volatile have vapor pressure greater than 0.1 mm Hg at 20C and/or boiling points less than 100 C. Table 5-8 provides the relationship between Henry’s law constants and the tendency of an organic compound to volatilize.
Physical Transformation of HW found in MSW Distribution of waste between phases the distribution of a substance between two immiscible phases or liquids is defined by the distribution of coefficient knowledge of the amount of a waste in each phase is important in developing waste management plans. The distribution coefficient for two phases is Cx/a/Cx/b = KD Where Cx/a = concentration of solute x in solvent a Cx/b = concentration of solute x in solvent b KD = distribution or partition coefficient
Chemical Transformation The organic hazardous waste constituents in MSW can be transformed by a variety of chemical reactions, some of which are considered briefly below. Chemical Reactions in Combustion Under ideal conditions the combustion process is an effective means of destroying the hazardous organic constituents found in MSW On the other hand, if the combustion process is not ideal, the products of the incomplete combustion can be quite varied and in many cases, toxic. C6H5Cl + O2 …………………… 6CO2 + 2H2O + HCL
Chemical Transformation Chemical Reactions in Landfills the principal classes of chemical reaction that can occur to alter the composition of the hazardous waste compounds found in MSW include 1. Simple substitution 2. Dehydrogeneration (Hydrolysis) 3. Oxidation (Auto – Oxidation) 4. Reduction these reactions occur during landfilling and in completed landfills. In an environment such as landfill where active biological decomposition is occurring, the rates of abiotic reaction may be increased significantly by the activity of biologically produced enzymes.
Biological Transformation Transformations Involving Metals Many of the hazardous inorganic constituents present in MSW ( chromium, lead, mercury) can be converted biologically in a variety of compounds, some of which are extremely toxic. For example, toxic compounds that can be produced under anaerobic conditions such as those in landfills, include methylmercury, dimethylarsinc, etc.. It is interesting to note that as the metallic covers (shells) on households and other batteries decompose with time and mercury is released under anaerobic conditions, the biological transformation of mercury will probably occur for years to come.
Transformations Involving Biodegradable (Non-persistent) Organic Compounds Typically biodegradable chemicals undergo reactions such as simple substitution, Dehydrogenation, oxidation and reduction Transformation Involving Persistent Organic Compounds hazardous organic compounds are biodegradable, but at extremely slow rate. The slowly biodegradable chemicals may undergo one or more of the following biologically mediated reactions Amid and ester hydrolysis Dealkylation Deamination Dehalogenation Double bond reduction Hydroxylation Oxidation Reduction and Ring cleavage
Biological Transformation Many of these reaction lead to the detoxification of the original compound. Unfortunately, many of these reactions also result in the formation of the new toxic compounds, some of which may be more toxic than the original. Combined abiotic and biotic transformaions A number of hazardous waste compounds are transformed by a combination of abiotic/biotic reactions
Management of Hazardous Waste in MSW The most effective way to eliminate the small quantities of hazardous wastes found in MSW is to separate them at the point of generation. The number and types of hazardous components separated will depend on the Storage Collection treatment disposal facility provided by the community Handling and storage of hazardous waste at residential dwellings The only effective way to deal with HHW is to educate citizens about the proper use, storage, and disposal of HHW and to provide them with convenient options for the disposal of these wastes
Management of Hazardous Waste in MSW Household hazardous waste collection programmes Product exchange programme because paint products form a major portion of HHW, paint exchange are being used in a number of communities to reduce the coast of HHW disposal The reuse of latex-based paints has proven to be the most successful Unrecoverable paint must be either combusted in a hazardous waste combustor or disposed of in a hazardous waste landfills Specific collection days one of the most common approaches for HHW management on collection days, community are invited to bring their HHW, at little or no charge for recycling, treatment or disposal Adequate promotion and education are critical 5 – 10 percent of the total HHW is collected through such programmes
Management of Hazardous Waste in MSW Permanent collection sites programmes involving permanent collection facilities allow citizens to drop off wastes at their own convenience For this reason, permanent collection sites have proven to be more effective for collecting HHW than one day collection programme Elimination of hazardous wastes from commercial sources to reduce the toxicity of commingled MSW, most communities have sought to eliminate the discharges of HW from commercial facilities. the key to the elimination of HW from commercial activities is the availability of community or regional facilities for handling and processing hazardosus wastes