Physico chemical processing of hazardous waste WASTE MANAGEMENT

Physico chemical processing of (hazardous*) waste WASTE MANAGEMENT AND TECHNOLOGY Mecislav Kuras Institute of Chemical Technology in Prague * Besides hazardous waste, we recognize also non-hazardous waste and inert waste (see presentation on Waste Landfill“). Nonhazardous and inert wastes are typically not subjected to physico-chemical treatment.

hazardous waste origin and effect Waste is classified as hazardous if: - it is listed in the Hazardous Waste List; - it is mixed with or contaminated by any of the components listed in the Hazardous Waste List; - it should display one or more of the hazardous properties. Cause of hazard – occurence of dangerous chemicals and their mixtures. Most dangerous – hazardous waste from industry, especially from chemical industry and other industries dealing with chemical processes (metallurgy, pharmacy, petrochemistry, glass, machinery, etc. ) containing mixtures of chemicals often of unknown composition and origin. Treatment of them requires special approaches with higher cost and health and environmental risk. Effects: Hazardous waste is a waste which may pose a substantial present or potential hazard to human health or the environment when impropoperly treated, stored or disposed of, or otherwise mismanaged.

hazardous waste – EU definition Council Directive 91/689/EEC of 12 December 1991 on hazardous waste: For the purpose of this Directive 'hazardous waste` means: - wastes featuring on a list to be drawn up in accordance with the procedure laid down in Article 18 of Directive 75/442/EEC on the basis of Annexes I and II to this Directive, not later than six months before the date of implementation of this Directive. These wastes must have one or more of the properties listed in Annex III. The list shall take into account the origin and composition of the waste and, where necessary, limit values of concentration. This list shall be periodically reviewed and if necessary by the same procedure, - any other waste which is considered by a Member State to display any of the properties listed in Annex III. Such cases shall be notified to the Commission and reviewed in accordance with the procedure laid down in Article 18 of Directive 75/442/EEC with a view to adaptation of the list. Properties of wastes which render them hazardous* explosive, oxidizing, highly flamable, irritant, harmful, toxic, carcinogenic, corrosive, infectious, teratogenic, mutagenic, substances and preparations which release toxic or very toxic gases in contact with water, air or an acid, substances and preparations capable by any means, after disposal, of yielding another substance, e. g. a leachate, which possesses any of the characteristics listed above, ecotoxic *see appendix at the end of presentation

hazardous waste - production The total amount of waste produced in the European Union is currently about 1 800 000 tonnes per year. Approximately 90 000 tonnes of this waste is hazardous. Czech Republic in 2010*: total (tons) category of waste hazar dous (tons) other (tons) production of waste 24 123 560 1 370 679 22 752 881 manufacturing industry (including chemical industry) 4 202 463 550 376 3 652 088 waste and water management 2 507 187 550 690 1 956 497 municipal waste 3 334 5 028 3 329 * Statistical Yearbook of the Czech Republic

hazardous wastes - significant part of industrial wastes, especially wastes of chemical character The approach used to develop systems to treat and dispose of industrial wastes is distinctly different from the approach used for municipal wastes. There is a lot of similarity in the characteristics of wastes from one municipality, or one region, to another. Best approach to designing a treatment system for municipal wastes is to analyze the performance characteristcs of many existing municipal systems and deduce an optimal set of design parameters for the system under consideration. In the case of industrial wastes, however, few industrial plants have a high degree of similarity between products produced and waste generated. Therefore, emphasis is placed on analysis of the wastes under consideration, rather than on what is taking place at other industrial locations.

character of industrial wastes Wastes from industries are customarily produced as: - liquid wastes (process wastes, which go to an on-site or off-site waster treatment systems), - solid wastes (including hazardous wastes, which include some liquids) - air pollutants These wastes are managed and regulated differently depending on the characteristics of the wastes and process producing them. The three phases of wastes are closely interrelated, both as they are generated and managed by individual industrial facilities. Industrial wastes that are discharged to neither air nor water are classified as solid, industrial or hazardous wastes.

Interrelation of industrial wastes categories - examples Solid wastes disposed of in the ground can influence the quality of groundwater and surface waters by way of leachate entering groundwater and traveling with it through the ground, then entering a surface water body with groundwater recharge. Volatile organics in that recharge water can contaminate the air. Air pollutants can fall out to become surface water or groundwater pollutants, and water pollutants can infiltrate the ground or volatilize into the air. Additionally, waste treatment proces can transfer substances from one of the three waste categories to one or both of the others. Waste treatment or disposal systems themselves can directly impact the quality of the air, water or ground.

Methods for treating industrial liquid wastes three categories Chemical methods - changing the chemical structure involve exchanging or sharing electrons between atoms. Physical methods - without necessarily changing the chemical structure of substances. Biological methods - involve living organisms like bacteria or other microorganisms using organic or, in some instances, inorganic substances for food. In so doing , the chemical and physical characteristcs of the organic and/or inorganic substances are changed. In being so used, complex organic molecules are systematically broken down, than reassembled as new cell protoplasm.

Treatment of air discharges from industry The discharge, or release, of substances to the air, no matter how slight, is regarded as air pollution. Discharge can be direct, by means of a stack, vent, hood, or the like, or indirect, by way of leaks from a building´s windows, doors, or other openings(fugitive emissions). Fugitive emission must be considered to evaluate a facility total emissions. Methods used for controlling particulate emissions: - gravity and inertial separators, including so-called cyclones are dry, „nomoving parts“ devices. They take advantage of the relatively high specific gravity of certain types of particulate matter, incl. fly ash, dust, cement particles, and organic solids, - electrostatic precipitators which take advantage of the electrostatic charge on the surface of particles - fabric filters, which make use of physical blocking and adsorption, - wet scubers, which make use of a liqiud to entrap particulate, thus removing them from a gas stream.

Solid waste treatment and disposal If a manufacturing process generates „scrap“ that cannot be reused, it may be treated as solid waste. When a final residue is produced that cannot be further treated or disposed of economically on-site, it must be shipped offsite for disposal. Disposal of final treatment residues and plant wastes in general depends on the source and chemical characteristic of the waste material itself. Thus, the first step is to determine into which category the waste belongs: - hazardous waste, having one of the hazarous properties determined by law, - nonhazardous solid waste. There a lot of industrial wastes that must be classified as hazardous wastes. Hazardous wastes are typically the most toxic, expensive and regulated type of industrial waste. Industrial nonhazardous waste do not meet the definition of hazardous waste, but they are excluded from most municipal landfills because of their physical and chemical characteristics.

Physico-chemical treatments of hazardous waste „Physico-chemical treatment“ is defined in the EU legislation (Directive 2008/98/EC, which repealed Directive 2006/12/EC) as a waste disposal operation: „D 9 Physico-chemical treatment not specified elsewhere in this Annex which results in final compounds or mixtures which are discarded by means of any of the operations numbered D 1 to D 12 (e. g. evaporation, drying, calcination, etc. )“ Physical and chemical treatments are strongly interrelated. For example a precipitate of a hazardous waste compound formed by a chemical reaction is separated from the reaction mixture by physical means such as sedimentation and filtration. In order to characterize wastes for physical treatment, it is necessary to know their chemical properties – p. H of wastewater or the chemical properties of solids that may be dangerously reactive when produced by the drying of sludges.

Physico-chemical waste treatment Physico-chemical treatment is applied mostly for industrial waste of chemical character. One of the first steps to consider in waste treatment is separation, which can save tremendous amount of effort and expense by resagregating wastes in forms that can be treated most economically or which may be not even hazardous. Separation may be as simple as draining an aqueous layer from organic one in two-phase waste. Methods of physical treatment Physical treatment of wastes depends upon the physical properties of the material treated, as state of matter, solubility in water and organic solvents, density, volatility, boiling point and melting point. It consists especially of: phase separation, sedimentation, filtration, membrane separation (reverse osmosis, nanofiltration, ultrafiltration), sorption by activated carbon or resin, distillation and stripping, drying and evaporation, extraction

Treatment options Physical, chemical and biochemical treatment option from these three areas are strongly interrelated. For example, a precipitate of a hazardous waste compound formed by chemical reaction is separated from the reaction mixture by physical means, such as sedimentation or filtration. Before considering physical treatment and their treatment options it is useful to have an overview of the various kinds of treatment to which hazardous substances may be subjected, including their advantages and disadvantages. Safety dictates that the first thing to do with hazardous waste is to consider any acute hazards that it may pose and take appropriate preventive actions. Important examples are cyanides and sulfides, which can react with acids or hydrolyze to give toxic HCN or H 2 S respectively. Reactive wastes must be treated with the appropriate reagents to reduce their hazards. One of the first step to consider in waste treatment is separation. Separation frequently results in resource recovery that yields materials of economic value. For example separation of hazardous substances sorbed to spent activated carbon can give an carbon product that can be reactivated and used again.

Methods of physical treatment Separation of components of a mixture that are already in two different phases. Sedimentation and decantation are easily accomplished with simple equipment. In many cases the separation must be aided by mechanical means, particularly filtration or centrifugation. Flotation is used to bring suspended organic matter or finely divided particles to the surface of a suspension. Many wastes are composed of aqueous / organic mixtures in colloidal sized emulsion. An important and often difficult waste treatment step consists of separation of these components, a process called emulsion breaking. Acids (including waste acids), other chemical reagents and heat may all be employed for this purpose. Once an emulsion is broken, centrifugation can be used to separate the phases.

Waste forming aqueous / organic mixtures Mixture of undesirable substances or „pollutants“ in water. Lot of wastes (especially industrial) are in a form of solution or emulsion. Solution – one or more substances (solutes) dissolved in another medium (solvent). When dissolved, the solutes become distributed uniformly throughout the solvent volume. Substances that ionize into cations and anions (e. g. sodium chloride) are soluble in polar solvents such as water (hydrophilic substances). Substances that do not ionize (oils) are poorly soluble in polar solvents but highly in non-polar solvents (hydrophobic substances). Emulsions – hydrophobic substances can be induced to go into a state that is equivalent in many way to a water solution by emulsification. Emulsion is equivalent to solution in that it consists of a stable mixture that will not separate under quiescent conditions. As a mixture flows from one place to another , it does not change in character. Two ways to accomplish emulsification: - with emulsifying agent (detergent) - to mix hydrophobic substance with water together vigorously Emulsion decomposition (water and oil phases) – heating or aditives.

Stable mixture – pollutants will not settle out of water under gravity (sedimentation). To treat water – another processes than simple sedimentation. Effective treatment process – need to recognise forces responsible for the mixture stability. Five general types of mixtures: 1. true solution – stability arises from hydrogen bonding between water molecules and electrical charge of each ion 2. emulsion – caused by emulsifiyng agent (detergent) – link of small droplets of liquid substance to water – one agent portion dissolved in water another dissolved in droplets of pollutant 3. emulsion in which stability of droplet pollutant mixture in water arises from repulsion caused by like electric charges in the droplet surface 4. colloidal suspension – small particles of nonsoluble solid are held away from each others by repulsive forces of like electric charge on surface of each solid particle 5. Solution in which ions that would normally not be soluble in water under prevailing conditions are held in solution by so called chelating agents.

Phase transfer or phase transition An important type of phase transfer is extraction, including liquid and liquid-solid extraction. Transfer of substance from a solution to a solid phase is called sorption. An important example is sorption on activated carbon. Physical precipitation – process in which a solid forms from a solute in solution as result of physical changes in the solution (cooling the solution, evaporation of solvents, alteration of solvent composition). (Compare to chemical precipitation in which a chemical reaction in solution produces an insoluble material).

Activated-carbon adsorption can be used to remove of wide variety of contaminants from liquid and gaseous streams (most frequently used for organic compounds). The process is relative nonspecific, and thus, is widely used as a broad spectrum treatment operation when the chemical composition of a stream is not fully understood. Common treatment application include groundwater treatment, chemical-spill response, industrial wastewater treatment, air-pollution control system. Physical adsorption results from the action of van der Waals forces, relatively week interactions produced by the motion of electrons in their orbitals. Chemical adsorption or chemisorption , involves electronic interactions between specific surface sites and solute molecules, resulting in the formation of a bond that can have all of the characteristics of a „true chemical bond. “ Electrostatic adsorption based on the forces between ions and charged functional groups and is synonymous with the term ion-exchange. The adsorption process is reversible - possibility to remove the adsorbed contaminants after the adsorption capacity of the carbon has been exhausted. Both result from electrostatic interaction.

Solvent extraction is referred to two different types of processes: Liquid-liquid extraction is 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) is the separation of the constituents from solids by contact with a liquid in which the constituents dissolve. In hazardous wastes treatment the term „solvent extraction“ is usually reserved to liquid-liquid extraction, especially extraction of organic compounds from aqueous solution into immiscible solvents. Solvent extraction is physical separation process, used for transfer of constituents from one liquid solution (or solid matrix) to another. The constituents are unchanged chemically. Application - for separation of a valuable constituent from impurities present in the original solution or concentration of a constituent for ease of subsequent recovery or treatment.

Molecular separation is often based upon membrane processes in which dissolved contaminants or solvent are forced through a membrane. The most widely used membrane process is reverse osmosis in which water from wastewater is forced through a membrane that is selective to water yielding purified water product and leaving behind a concentrated liquor containing impurities. Other membrane processes include ultrafiltration and electrodialysis in which ions in a solution subjected to electrolysis migrate selectively through alternate membranes that allow for the passage of cations and anions.

Membrane separation processes play an increasing role in the reduction or recycling of hazardous wastes. This processes separate the contaminant (solute) from a liquid phase (solvent, typically water). Main functions: volume reduction, recovery or purification of the liqiud phase, concentration or recovery of the contaminant or solute. Pressure driven processes: Reverse osmosis - water separation from a feed stream containing inorganic ions. The purity of recovered water is relatively high - water is suitable for recycling. Nanofiltration separates ions or organic components from water by limiting the size of membrane pores through which a contaminant can pass. Typically used for removing contaminants with molecular weight 100 -500 from water. Ultrafiltration - separates organic compounds from water according to the size (molecular weight) of the organic molecules. Membranes are manufactured with the capability to remove contaminants with the molecular weigh between 100 - 1, 000. Microfiltration - separates with a micrometre sized membrane (0. 1 to 10 m) Electric potential driven processes Electrodialysis - removes ionic components from water. It produces moderate quality product water (i. e. several hundred mg/L salts ).

Fundementals of membrane separation

Reverse osmosis treatment of landfill leachate

Pressure driven membrane separation processes http: //www. eco-web. com/edi/090714. html

Membrane separation – reverse osmosis When semipermeable membrane separates two solutions of different dissolved - solid concentration, pure water flows through the membrane into the concentrated solution (resulting in osmotic pressure), while ions (i. g. dissolved salts) are retained behind the membrane. This process is known as osmosis. During reverse osmosis, pressure is applied to the more concentration solution to reverse the normal osmotic flow, and pure water is forced through the semipermeable membrane into tle less concentrated solution. The purified stream that passes through the membrane is called permeate, the concentrated stream retained by the membrane is known as concentrate. Advantages of reverse osmosis: - both the recovered solvent and the concentrates solute can be recycled to a manufacturing process, - the separation process does not require an energy-intensive phase change such as is required for destillation or evaporation - capital costs are also relatively low.

Membrane separation – ultrafiltration, nanofiltration, electrodialysis Ultrafiltration (UF) and nanofiltration (NF) utilise pressure and a semipermeable membrane to separate nonionic material from a solvent (such as water). These membrane - separation techniques are particularly effective for the removal of suspended solids, oil and grease, large organic molecules, and complexed heavy metals from wastewater stream. In UF and NF systems, the membrane retains material based solely on size, shape and molecule flexibility. The membrane acts as a sieve to retain dissolved and suspended materials that are physically too large to pass throug its pores. The major difference between UF and NF is the molecular weight of separated species. Both methods utilise identical operating principles. Electrodialysis relies on ion-exchange membrane in a direct-curent electrical field to separate inorganic ionic species from solution. Like reverse osmosis membranes, electrodialysis membrane are sensitive to fouling that limit wastetreatment application of this technology. The metal-finishing and electroplating industry is the greatest potential market for these systems.

Methods of chemical treatment The applicability of chemical treatment to waste depends upon the chemical properties such acid-base, oxidation-reduction, precipitation, reactivity, flammability, corrosivity and compatibility with other wastes. An attractive feature of chemical treatment is the opportunity to treat wastes with other wastes, e. g. mutual neutralisation of waste acids with waste bases. It consists especially of: - acid/base neutralisation - chemical precipitation - chemical flocculation - oxidation/reduction - chemical extraction and leaching - ion exchange

Acid/base neutralisation Neutralisation is a process used to eliminate waste acids and bases as shown by the following reaction: H+ + OH- → H 2 O Although simple in principle, neutralisation can present some problems in practice, such as evolution of volatile contaminants or mobilisation of soluble substances. The heat generation from the above reaction when the waste envolved are relatively concentrated can result in dangerous hot solution and even spattering. Strongly acidic or basic solutions are corrosive to pipes, containers and mixing apparatus. Lime (Ca(OH)2) is a widely used base for treating acidic wastes. Sulphuric acid (H 2 SO 4) is a relatively inexpensive acid for treating alkaline wastes. However, addition of too much sulphuric acid can produce highly acidic products. For some applications, acetic acid (CH 3 COOH), is preferable. It is a weak acid and also naturalproduct and biodegradable. Neutralistion, or p. H adjustment, is often required prior to the application of other waste treatment processes (biochemical treatment – microorganisms usually require a p. H range of 6 to 9.

Oxidation/reduction Oxidation and reduction can be used 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 nonhazardous form or to a form that can be isolated physically. Ozon, O 3, is a strong oxidant that can be generated on-site by an electrical discharge through dry air or oxygen: 3 O 2 → 2 O 3 electrical discharge Oxidation of organics (CH 2 O) + (O) → CO 2 + H 2 O organic matter Oxidation of inorganics Cyanide: 2 CN- + 5 OCl- + H 2 O → N 2 + 2 HCO 3 - + 5 Cl. Iron (II): 4 Fe 2+ + O 2 + 10 H 2 O → 4 Fe(OH)3 + 8 H+ Reduction of inorganics Chromate 2 Cr. O 42 - + 3 SO 2 + 4 H+ → Cr 2(SO 4)3 + 2 H 2 O Permanganate Mn. O 4 - + 3 Fe 2+ + 7 H 2 O → Mn. O 2(s) + 3 Fe(OH)3 (s) + 5 H+

Chemical precipitation Precipitation is used in hazardous waste treatment primarily for the removal of heavy metal ions from water as shown for the chemical precipitatiopn of cadmium: Cd 2+ (aq) + HS- → Cd. S (s) + H+ (aq) The most widely used means of precipitation metal ions is by the formation of hydroxides such as chromium (III) hydroxide: Cr 3+ + 3 OH- → Cr(OH)3 The source of hydroxide ions, OH-, is a base (alkali), such as lime (Ca(OH)2, sodium hydroxide (Na. OH), or sodium carbonate (Na 2 CO 3). Sulfide precipitation is very effective means of treatment, because the solubility of some heavy metal sulfides is extremely low. Sources of sulfide ions include sodium sulfide, Na 2 S, sodium hydrosulfide (Na. HS), hydrogen sulfide (H 2 S), and iron (II) sulfide. Some metals can be precipitated from solution in the elemental metal form by the action of a reducing agent (e. g. sodium borohydride, Na. BH 4). Metal ions can be converted to the elemental form and removed from solution by reaction with more active metal by a process called cementation – the reduction of toxic cadmium with relatively harmless zinc: Cd 2+ + Zn → Cd + Zn 2+

Electrolysis consists of the electrochemical reduction and oxidation of chemical species in solution by means of electricity applied to electrode from an external source. One species in solution (usually a metal ion) is reduced by electrons at the cathode and another gives up electrons to the anode and is oxidised there. Cathode (-) Cu 2+ + 2 e- → Cu Anode (+) H 2 O → ½ O 2 + 2 e- + 2 H+ In hazardous waste application electrolysis is most widely used in recovery of metals, mostly from electroplating media, from wastewater and rinsewater from the electronics industries and from metal finishing operations. The metals that are most commonly recovered by electrolysis are cadmium, copper, gold, lead, silver and zinc. Recovered metals are usually recycled to the process that produces the waste.

Chemical extraction and leaching Chemical extraction or leaching in hazardous waste treatment is the removal of a hazardous constituents by reaction with extractants in solution. Acidic solutions dissolve poorly soluble heavy metal salts by reaction of the salt anions with H+. Pb. CO 3 + H+ → Pb 2+ + HCO 3 Ion exchange is a means of removing cations or anions from solution onto a solid resin. Ions taken up by an ion exchange resin may be removed by treating the resin with concentrated solutions of acid, base or salt (Na. Cl). The net result is to concentrate the ions originally removed from dilute solution in water into a much more concentrated solution. The greatest use of ion exchange in hazardous waste treatment is for removal of low level of heavy metal ions from wastewater. Ion exchange is employed in the metal plating industry to purify rinsewater and spent plating bath solution.

Leaching properties of waste or residue Influence of p. H and other chemical variables on leaching. p. H value – major chemical variable controling the leaching of minor and major elements from waste or residue. p. H value influenced the solubility of important minerals (oxides, hydroxides, carbonates). Cationic and anionic constituents are bound to these solid residues by adsorption/desorption on mineral surface with a p. H-dependent charge. Leaching of cationic constituents increases towards low p. H, anionic constituents towards high p. H. Calcium – typical cation leaching behaviour (concentration increase towards low p. H). Molybdenum is present as the oxyanion molybdate (Mo. O 42 -) – leaching concentration increasing towards high p. H. Amphoteric behaviour of e. g. Pb and Zn that can be present both in cationic and anionic form, show substantial and increasing leachability both at low (cationic form) and high (anionic form) p. H value. The general leaching behaviour can be further modified by the effect of other chemical parameters (redox potential, complexation of inorganic components).

Photolytic reactions or the process of photolysis are those in which protons or electromagnetic radiation consisting of shortlwavelenght visible light or ultraviolet radiation are absorbed by a molecule, causing a chemical reaction to occur. Photolysis can be used to destroy a number of kinds of hazardous wastes. In such applications it is most useful in breaking chemical bonds in refractory organic compounds. Photolysis can be used to destroy several kinds of hazardous waste substance, such as dioxins, herbicides (atrazin), 2, 4, 6 -trinitrotoluene (TNT) and polychlorinated biphenyls (PCB). The addition of chemical oxidant such as potassium peroxodisulfate K 2 S 2 O 8, enhances destruction of oxidising active photolytic products.

(Appendix) PROPERTIES OF WASTES WHICH RENDER THEM HAZARDOUS Explosive: substances and preparations which may explode under the effect of flame or which are more sensitive to shocks or friction than dinitrobenzene. Oxidizing: substances and preparations which exhibit highly exothermic reactions when in contact with other substances, particularly flammable substances. Flammable: liquid substances and preparations having a flash point equal to or greater than 21°C and less than or equal to 55°C. Highly flammable: liquid substances and preparations having a flash point below 21°C (including extremely flammable liquids), or substances and preparations which may become hot and finally catch fire in contact with air at ambient temperature without any application of energy, or solid substances and preparations which may readily catch fire after brief contact with a source of ignition and which continue to burn or to be consumed after removal of the source of ignition, or gaseous substances and preparations which are flammable in air at normal pressure, or -substances and preparations which, in contact with water or damp air, evolve highly flammable gases in dangerous quantities. Irritable: non-corrosive substances and preparations which, through immediate, prolonged or repeated contact with the skin or mucous membrane, can cause inflammation. Harmful: substances and preparations which, if they are inhaled or ingested or if they penetrate the skin, may involve limited health risks.

Toxic: substances and preparations (including very toxic substances and preparations) which, if they are inhaled or ingested or if they penetrate the skin, may involve serious, acute or chronic health risks and even death. Carcinogenic: substances and preparations which, if they are inhaled or ingested or if they penetrate the skin, may induce cancer or increase its incidence. Corrosive: substances and preparations which may destroy living tissue on contacts. Infectious: substances containing viable micro-organisms or their toxins which are known or reliably believed to cause disease in man or other living organisms. Teratogenic: substances and preparations which, if they are inhaled or ingested or if they penetrate the skin, may induce non-hereditary congenital malformations or increase their incidence. Mutagenic: substances and preparations which, if they are inhaled or ingested or if they penetrate the skin, may induce hereditary genetic defects or increase their incidence. Substances and preparations which release toxic or very toxic gases in contact with water, air or an acid. Substances and preparations capable by any means, after disposal, of yielding another substance, e. g. a leachate, which possesses any of the characteristics listed above. Ecotoxic: substances and preparations which present or may present immediate or delayed risks for one or more sectors of the environment

Questions related to the presentation - Which type of waste is mainly processed by physico – chemical techniques? - Principal physical processes for waste treatment. - Principles of membrane separation. - Principal chemical processes for waste treatment. - Interrelationship between physical and chemical processing of waste.