Water and Wastewater Industry (CPT150X) PDF

Chemical Process Technology CPT150X Water & Wastewater Industry  OBJECTIVES Identify the national standards and legislation for potable water and wastewater. Investigate the chemical and physical operations of: - typical potable water; and - industrial was...

Chemical Process Technology CPT150X Water & Wastewater Industry  OBJECTIVES Identify the national standards and legislation for potable water and wastewater. Investigate the chemical and physical operations of: - typical potable water; and - industrial wastewater treatment processes.  GLOSSARY Effluent: When the water flows out of the plant into a body of water after it has been processed.1 Influent: the untreated or contaminated water flowing into the WWTP ready for processing.1 NWA: National Water Act Potable water: aka Drinking water 2 SANS: South African National Standards WWTP: Wastewater Treatment Plant WWTW: Wastewater Treatment Works DWEA: Department of Water and Environmental Affairs  WATER AND WASTEWATER INDUSTRY Legislation: The Bill of rights contained in the Constitution of the Republic of SA gives everyone the right to access sufficient water, as well as to an environment (Section 24) not harmful to their health and well-being. Which South African legislation regulates water resources? The National Water Act No 36 of 1998 ”ensures that South Africa's water resources are protected, used, developed, conserved, managed and controlled in a sustainable and equitable manner, for the benefit of all people”.3 “The National Water Act aims to protect, use, develop, conserve, manage and control water  WATER AND WASTEWATER INDUSTRY (cont.) South African National Water Act waste discharge standard guidelines shows the indicators for wastewater quality management, highlighting the limit values for discharging wastewater into a receiving water body.5  WATER AND WASTEWATER INDUSTRY (cont.) The Water Services Act, 1997 (Act 108 of 1997), prescribes the legislative duty of municipalities as water-service authorities to provide water supply and sanitation according to national standards and norms.3 The Water Services Act provides a legal context for the regulation of the water services sector and provides for certain general powers of the Minister and for the monitoring of water services and intervention by the Minister or by the relevant Province. 3 Primary objective of the Act? To ensure that everybody has access to the basic water supply and sanitation services necessary for  WATER AND WASTEWATER INDUSTRY (cont.) National standards in South Africa: The South African National Standard (SANS) 241 is a drinking/potable water specification that states the minimum requirements for potable water to be considered safe for human consumption.6 Consists of the following parts, under the general title Drinking water: Part 1: Microbiological, physical, aesthetic and chemical determinands. Part 2: Application of SANS 241-1. Industrial wastewater discharge standards City of Cape Town: Wastewater and industrial effluent by-law of 2006 (South Africa (Western Cape), 2006), was updated in 2013 to ensure consistency with national legislation; and to  WATER AND WASTEWATER INDUSTRY (cont.) Main water uses are: Domestic Recreational Industrial Agricultural Natural environment Wastewater emanate from four primary sources: 1. Municipal sewage 2. Industrial wastewater 3. Agricultural runoff 4. Storm water and Urban runoff  WATER AND WASTEWATER INDUSTRY (cont.) Most common functions of water in industry Steam generation and/or heating Cooling Constituent of the product, product dilution or product conditioning Reagent make-up Product or surface washing Transport of materials or wastes  WATER AND WASTEWATER INDUSTRY (cont.) Wastewater composition refers to the actual amounts of physical, chemical and biological constituents present in wastewater. The most commonly considered water quality constituents in raw water supplied are: Water quality parameters pH Electrical conductivity (EC) Chloride Total hardness Iron (Fe) Chemical oxygen demand (COD) Manganese (Mn) Alkalinity Sulphate  WATER AND WASTEWATER INDUSTRY (cont.) Treatment objectives are concerned with: The removal of suspended and floatable material The treatment of biodegradable organics The elimination of pathogenic organisms Conventional treatment processes consist of 4 stages: 1. Preliminary treatment 2. Primary treatment 3. Secondary treatment 4. Tertiary and/or advanced treatment YouTube link: https://www.youtube.com/watch?v=FvPakzqM3h8  1. PRELIMINARY TREATMENT Preliminary treatment protects the operation of the wastewater treatment plant. How? By removing any constituents (e.g. large solids and grit) which can clog or damage pumps, or interfere with subsequent treatment processes. How? Using different types of screens and a grit chamber.  2. PRIMARY TREATMENT In primary treatment, physical and/or chemical operations are used to remove the floating and settleable solids found in wastewater. For example: sedimentation and flotation Sedimentation8: particles in suspension in water are allowed to settle out of suspension under the influence of gravity. The particles that settle out become sediment, and are known as sludge. Flotation9: dissolved air flotation (DAF) is an alternative clarification process. In DAF systems pressurised air is pumped into the wastewater forming small bubbles which adhere to the suspended matter causing them to float to the surface of the water where they are removed by a Sedimentation  Flotation DAF systems are designed to remove total suspended solids (TSS), biochemical oxygen demand (BOD), and oils and greases (O&G) from a wastewater stream.10  3. SECONDARY TREATMENT In secondary treatment, biological and/or chemical processes are used to remove most of the organic matter. Most of the suspended and dissolved organic matter are oxidised by biological oxidation using aerobic microorganisms. Aerobic treatment occurs in the presence of air and utilises aerobic microorganisms (called aerobes), which use molecular/free oxygen to Aerobes convert the organic impurities into carbon dioxide, water and biomass.  4. TERTIARY TREATMENT In tertiary and/or advanced treatment, additional processes are used to remove residual constituents, such as nitrogen and phosphorous, not removed after secondary treatment. For example: Filtration, ion exchange, reverse osmosis, adsorption, membranes, and disinfection.  4. TERTIARY TREATMENT (cont.) Membrane filtration11: used for inorganic effluent treatment since it can remove suspended solids, organic components, as well as inorganic pollutants such as heavy metals. - For heavy metal removal, several forms of membrane filtration, such as ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO) / distillation, can be used depending on the particle size of the pollutant. Filtration  Filtration Saline water can be treated to yield fresh water via reverse osmosis (aka distillation). The method requires more energy than water treatment of local surface waters and is used in coastal areas or where water such as groundwater has high salinity.12 Filtration Flow diagram for a pressure driven membrane process  Filtration Pressure driven component separation through the different membranes  4. TERTIARY TREATMENT (cont.) Ion exchange11: is a reversible ion exchange process in which an insoluble substance (i.e. resin) takes ions from an electrolytic solution and releases additional ions of the same charge in a chemically comparable amount without changing the resin's structure. Adsorption11: is a mass transfer process in which a substance is transported from the liquid phase to the surface of a solid/liquid (i.e. adsorbent) and becomes physically and chemically bonded (i.e. adsorbate). - Activated carbon (AC) or biological-activated carbon (BAC) are effective adsorbents for a wide variety of contaminants. The removal of color,  4. TERTIARY TREATMENT (cont.) Disinfection involves removing or inactivating pathogenic or any other living microorganisms (i.e. bacteria, viruses and other pathogens) to ensure the treated water can be reused. The main disinfection processes are: 1. Chlorination 2. Ozonation 3. Ultraviolet light 4. Electro-disinfection  WASTEWATER TREATMENT TECHNOLOGIES13 1. Chemical treatment 2. Physical treatment 3. Biological treatment 4. Physico-chemical treatment A combination selected from the above processes (depending on the season and contaminants and chemicals present in the raw water) is used for both municipal drinking water treatment and industrial wastewater treatment.  1. CHEMICAL TREATMENT14 Utilises the addition of chemicals to make water suitable for re-use or discharge. For example: chemical precipitation, chemical disinfection, advanced oxidation process (AOP), ion exchange, and chemical neutralisation.  1. CHEMICAL TREATMENT (cont.) Chemical precipitation11: used to reduce heavy metal concentrations in wastewater. - The dissolved metal ions are transformed to an insoluble phase by a chemical interaction with a precipitant agent such as lime. AOPs11 are used in the treatment of hazardous wastewater due to its high oxidation potential and degradation performance. - Oxidants like Fenton’s reagent, ozone or hydrogen peroxide are added to the wastewater to degrade harmful substances for discharge.  2. PHYSICAL TREATMENT15 The separation of solids from wastewater through: - Sedimentation via gravity settling. - Filtration involves the use of membranes or mechanical filters (e.g. sand filters) to achieve solid-liquid separation. - Membrane filtration16 (e.g. microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), reverse osmosis (RO), forward osmosis (FO) and electrodialysis). - Dissolved air flotation (DAF).  2. PHYSICAL TREATMENT (cont.) Electro Dialysis (ED)17 is a membrane process, during which ions are transported through semi permeable membrane, under the influence of an electric potential/current. The membranes are cation- or anion-selective, allowing either positive ions or negative ions to flow through. - Cation-selective membranes are polyelectrolytes with negatively charged matter, which rejects negatively charged ions and allows positively charged ions to flow through. By placing multiple membranes in a row, which alternately allow positively or negatively charged ions to flow through, ions can be Electrodialysis  3. BIOLOGICAL TREATMENT18 Treats wastewater containing biodegradable elements. Consists of adding an optimal amount of microorganisms to eliminate dissolved and suspended organic chemical components through biodegradation through two biological processes: biological oxidation and biosynthesis. - Biosynthesis19: is a multi-step, enzyme- catalysed process where substrates are converted into more complex products in living organisms. Is a sustainable practice that has been successful for over a century.  4. PHYSICO-CHEMICAL TREATMENT Focuses on the separation of colloidal particles through the addition of chemicals called coagulants and flocculants.20 - Coagulation for flocculation: the addition of coagulants destabilizes colloidal suspensions by neutralising their charges, resulting in the aggregation of smaller particles during the coagulation process. - Coagulant aids (aka polyelectrolytes) are used to increase coagulation of suspended solids for more robust floc formation and improved removal. - Chemical flocculants are used to generate a floc in the water that traps suspended solids.21  WASTEWATER TREATMENT TECHNOLOGIES (cont.) Constituent Unit processes Coagulation/ flocculation, Turbidity and particles sedimentation, granular filtration Major dissolved inorganics Softening, aeration, membranes Minor dissolved inorganics Membranes Sedimentation, filtration, Pathogens disinfection Major dissolved organics Membranes, adsorption  WATER AND WASTEWATER INDUSTRY (cont.) Selection of a treatment process or a combination of processes depends on: Water / wastewater characteristics Required water / effluent quality Deterioration of supplied water quality and/or future upgrading of effluent quality standards Cost and availability of land (e.g. large scale biological processes versus more compact physio- chemical processes)  WATER AND WASTEWATER INDUSTRY (cont.) Blue drop and Green drop - The Blue Drop and Green Drop Certification Programmes are forms of Incentive-based Regulation (IBR) pioneered by the South African Water Sector since 2008.23 - Is a method of awarding Water Services Authorities with Blue and/or Green Drop status if they are compliant with drinking water and wastewater legislative and other best practice requirements are implemented.  WATER AND WASTEWATER INDUSTRY23 (cont.) The Blue Drop Certification (BDC) programme is the regulation tool introduced by the Department of Water and Environmental Affairs (DWEA) with the aim of restoring the trust of the general public in the quality of tap water, by certifying the water quality of a municipality. Green Drop Certification is awarded to wastewater systems that obtain scores of above 90% when compared against the criteria set for wastewater management, while a system that achieved less than 31% is regarded as a dysfunctional system which would require appropriate interventions.