sludge.pdf

Sludge Treatment and Disposal Introduction Sludge management is complex and costly process…20-60% of the total operation cost of wastewater treatment Sludge: solid by-products from wastewater treatment plant Biological treatment: organic matter converte...

Sludge Treatment and Disposal Introduction Sludge management is complex and costly process…20-60% of the total operation cost of wastewater treatment Sludge: solid by-products from wastewater treatment plant Biological treatment: organic matter converted into microbial biomass = bio-solid Primary sludge: consists of suspended solids Secondary sludge: consists of biological solids (biomass) 11/06/2024 1  Sludge treatment Objective is to concentrate impurities into solids and then removal of solids from bulk liquid Concentration of solids = sludge = contain objectionable materials need to be dispose off properly Major contaminants in sludge a. Metals b. Organics c. Pathogenic microorganisms 11/06/2024 2  1. Sludge Thickening A. Vacuum filtration….. most widely used method in the treatment of sludge B. Centrifugation…. uses the action of centrifugal force to promote accelerated settling of particles in a solid- liquid mixture C. Gravity thickening…similar to suspended growth system, deeper tanks are used to provide more thickening capacity D. Dissolved air flotation….water is aerated at high pressure, this water is released near the bottom of tank of sludge Air is released in the form of bubble that float the solids to the surface. Sludge is skimmed off at the top of the tank. Liquid is removed from the bottom. 11/06/2024 3  How gravity thickening works Gravity thickening increases the solids concentration by allowing the particles to settle to the base of a vessel, producing a concentrated (thickened) solids stream at the vessel base and a supernatant (diluted) stream at the surface. Sedimentation, or settling, is the simplest of the thickening processes. A gravity sludge thickener has the same design features as a primary sedimentation tank used for wastewater treatment, and most often has cylindrical geometry. 11/06/2024 4  HOW DOES DISSOLVED AIR FLOTATION WORK Wastewater is pumped into a flotation tank or basin and hit with dissolved air causing microscopic bubbles adhere to suspended solids causing them lift to the surface of the water where it may then be removed by a skimming device and drained toward a sludge discharge tank. 11/06/2024 5  2. Sludge Stabilization Sludge is rich in pathogenic microorganisms. Easily putrescible (Liable to decay). Rapidly develop unpleasant smell. Become rotten. Stabilization is used to stabilize the biodegradable fraction of organic matter in sludge. It stop natural fermentation of sludge (chemical changes through enzymes). This reduce the risk of putrefaction and also diminish the concentration of pathogenic microorganisms. 11/06/2024 6  Stabilization can be divided into A. Biological stabilization: specific bacteria promote the stabilization of biodegradable fraction of organic matter B. Chemical stabilization: Chemical oxidation of organic matter accomplished sludge stabilization… by lime, pH is raised above 12. High pH and high temperature reduce pathogens C. Physical stabilization: Heat stabilize the organic fraction of sludge 11/06/2024 7  A. Biological Stabilization a. Anaerobic digestion b. Aerobic digestion c. Composting 11/06/2024 8  a. Anaerobic digestion Most common process use for primary sludge Primary sludge contains organics that induce rapid growth of biomass in aerobic conditions. Anaerobic digestion treated sludge by producing liquids and gases and minimum biomass. Variety of organics ….. Variety of microorganisms involved Organic……alcohol/acid/CO2/H2…… methane 11/06/2024 9  b. Aerobic digestion Organisms metabolize their own protoplasm. Mineralized sludge is produced at the end which contains mostly non-biodegradable cell fragments. Energy consumption is more than anaerobic digestion. 11/06/2024 10 c. Composting Composting can be defined as the aerobic thermophilic (optimal growth temperatures between 50 and 55 °C) decomposition of organic wastes. Composting is an process of mixing sewage sludge with agricultural byproduct sources of carbon such as straw or wood chips. In the presence of oxygen, bacteria digesting both the sewage sludge and the plant material generate heat to kill disease-causing microorganisms and parasite Its most valuable features are moisture retaining and humus forming properties. Compost benefits the soil by providing useful nutrients and minerals. It has been commonly applied to parks and gardens because it increases the soil water absorbing capacity and improves the soil structure. The most important criteria for successful composting are: (1) Complete mixing of organic solids (2) Uniform particle size (3) Adequate aeration (4) Proper moisture content (5) Proper temperature and pH (6) Proper carbon-nitrogen ratio in the raw solids 11/06/2024 11  3. Conditioning of Sludge This pre-treatment is referred to as conditioning, which takes the form of either: a) Chemical conditioning, by dosing with inorganic coagulants (such as iron or aluminium) and/or organic flocculants (or polymers), or. b) Thermal conditioning by heating the sludge under controlled conditions. 11/06/2024 12  Chemical Conditioning 11/06/2024 13  4. Sludge Drying / Dewatering Reduction of the sludge weight by sludge drying …… by evaporating the bound water in the sludge. Sludge drying is based on contact, convection or radiation procedures. a. During the contact drying, the warmth is supplied by the contact between the damp product and a heated wall. b. Convection drying is by treating the sludge with hot-air. Air is heated to a high temperature with a burner or steam heat exchanger and brought in contact with the sludge in a drum or belt dryer. c. The radiation drying is that the warmth is supplied through radiation to the sludge…….solar radiation or infrared heating elements. 11/06/2024 14  Dewatering can be done naturally (dry beds by filtration and evaporation) 11/06/2024 15  Sludge De-watering process 11/06/2024 16  Sludge drying: low temperature Dryness of dried sludge : 80 to 90% Very low temperature technology : 40°C-60°C No smells No contaminated air Very high quality of condensate Allowing heat recovery, possibility to use recycled energy 11/06/2024 17  Hot air drying: Indirectly heating the insulated hot air chamber with steam or gas. Heat is transferred through the walls of the process chamber and into the material in process 11/06/2024 18  Solar drying 11/06/2024 19  5. Reduction of sludge Sludge incineration is achieved by the organic compounds' oxidation at elevated temperatures (waste incinerators are operated at 980/C to 1200/C). In this process, the biosolids' burning can be achieved through supplying excess quantity of air to the combustion chamber toward the production of carbon dioxide and water, having only the by-product of ash inert material. 11/06/2024 20