2. Intraparticle transport of reactants into the catalyst particle (if it is porous 3. Adsorption of reactants at interior sites of the catalyst particle 4. Chemical reaction of adsorbed reactants to adsorbed products(surface reaction 5. Desorption of adsorbed products 6. Transport of products from the interior sites to the outer surface of the catal yst particle
2. Intraparticle transport of reactants into the catalyst particle (if it is porous) 3. Adsorption of reactants at interior sites of the catalyst particle 4. Chemical reaction of adsorbed reactants to adsorbed products (surface reaction) 5. Desorption of adsorbed products 6. Transport of products from the interior sites to the outer surface of the catalyst particle
Rate Expressions Used in Environmental modeling Tab. 4-2 Constituent transformation and removal processes(i.e,, fate processes) in the environment Process Comments Constituents ffected Adsorption/ Many chemical constituents tend Metal trace desorption to attach or sorb onto solids. The organics, NH4+, implication for wastewater PO43- is that a substantial fraction of some toxic chemicals is associated with the suspended solids in the effluent. Adsorption combined with solids settling results in the removal from the water column of constituents that might not otherwise decay
Rate Expressions Used in Environmental Modeling Tab. 4-2 Constituent transformation and removal processes(i.e., fate processes) in the environment Process Comments Constituents affected Adsorption/ desorption Many chemical constituents tend to attach or sorb onto solids. The implication for wastewater discharges is that a substantial fraction of some toxic chemicals is associated with the suspended solids in the effluent. Adsorption combined with solids settling results in the removal from the water column of constituents that might not otherwise decay Metal, trace organics, NH4 + , PO4 3-
Algal synthesis The synthesis of algal cell tissue using the NH4, NO3, PO4 pH, nutrients found in wastewater Bacterial Bacterial conversion(both ae robic and BODs, nitrification conversion anaerobic) is the most important process denitrification, in the tra nsformation of constituents sulfate reduction re leased to the environme nt. The anaerobic exertion of BOD and NOD is the most fermentation In common example of bacte rial conve rsion bottom se dime nts) encounte red waterquality conversion management. The de pletion of oxygen in priority organIc the aero bic conversion of organic wastes pollutants, etc is also known as deoxygenation. Solids discharged with treated wastewater are partly organic. Upon settling to the bottom, they decompose bacterially either anaero bically or aero bically depending on local conditio ns. The bacterial tra nsformation of toxic organic compounds is also of great significance
Algal synthesis The synthesis of algal cell tissue using the nutrients found in wastewater NH4 + ,NO3 - ,PO4 3- ,pH, etc Bacterial conversion Bacterial conversion (both aerobic and anaerobic) is the most important process in the transformation of constituents released to the environment. The exertion of BOD and NOD is the most common example of bacterial conversion encountered in waterquality management. The depletion of oxygen in the aerobic conversion of organic wastes is also known as deoxygenation. Solids discharged with treated wastewater are partly organic. Upon settling to the bottom, they decompose bacterially either anaerobically or aerobically, depending on local conditions. The bacterial transformation of toxic organic compounds is also of great significance. BOD5 ,nitrification, denitrification, sulfate reduction, anaerobic fermentation (in bottom sediments), conversion of priority organic pollutants,etc
Chemical Important che mical reactions that occur Chemical reactions in the environment include hydrolysis, disinfection, hotochemical, and oxidation-reduction decomposition reactions. Hydrolysis reactions occur organic compounds between contaminants and water specific ion exchange, element substitution Filtration Removal of suspended and colloidal TS colloidal solids by straining(mechanical and particles chance contact) sedime ntation interception, impaction, and adsorption. Flocculation Flocculation is the term used to desc ribe Colloidal and small the aggregation of smaller particles into particles larger particles that can be re moved by sedimentation nd filtration Flocculation brought a bout by Brownian motion. diffe rential velocit gradients, and diffe rential settling in hich large particles overtake smaller particles and form larger particles
Chemical reactions Important chemical reactions that occur in the environment include hydrolysis, photochemical, and oxidation-reduction reactions. Hydrolysis reactions occur between contaminants and water. Chemical disinfection, decomposition of organic compounds, specific ion exchange, element substitution. Filtration Removal of suspended and colloidal solids by straining (mechanical and chance contact), sedimentation, interception, impaction, and adsorption. TSS, colloidal particles Flocculation Flocculation is the term used to describe the aggregation of smaller particles into larger particles that can be removed by sedimentation and filtration. Flocculation is brought about by Brownian motion, differential velocity gradients, and differential settling in which large particles overtake smaller particles and form larger particles. Colloidal and small particles
Gas The process whereby a gas is ta ken up by a 0,, CO, CH, NH3, H, S absorption/desor liquid is known as a bsorption For exa mple, pti when the dissolved oxygen concentration in a body of water with a free surface is be low the saturation concentration in the water a net transfer of oxygen occurs from the atmosphere to the water. The rate of transfer(mass per unit time per unit surface area) is pro po rtio nal to the amo unt by which the dissolved oxygen is be low saturation. The addition of oxygen to water is also known as reae ration. Desorptio n occurs when the concentration of the gas in the liquid exceeds the saturation value, and the re is a tra nsfer from the liquid to the atmosphere
Gas absorption/desor ption The process whereby a gas is taken up by a liquid is known as absorption. For example, when the dissolved oxygen concentration in a body of water with a free surface is below the saturation concentration in the water, a net transfer of oxygen occurs from the atmosphere to the water. The rate of transfer (mass per unit time per unit surface area) is proportional to the amount by which the dissolved oxygen is below saturation. The addition of oxygen to water is also known as reaeration. Desorption occurs when the concentration of the gas in the liquid exceeds the saturation value, and there is a transfer from the liquid to the atmosphere. O2 ,CO2 ,CH4 ,NH3 ,H2S