Basic wastewater management

Basic Methods of Waste Management written by: Learn some of the main methods used in managing waste products today. The process includes collection, transportation, sorting, recycling, clearance, and disposal of waste materials. Waste management includes radioactive substances and other materials that are in a solid, liquid, or gaseous state, and their management techniques also differ from each other.

Basic wastewater management

Sludge treatment and disposal The residue that accumulates in sewage treatment plants is called sludge or biosolids. Sewage sludge is the solid, semisolid, or slurry residual material that is produced as a by-product of wastewater treatment processes.

This residue is commonly classified as primary and secondary sludge. Primary sludge is generated from chemical precipitationsedimentation, and other primary processes, whereas secondary sludge is the activated waste biomass resulting from biological treatments. Some sewage plants also receive septage or septic tank solids from household on-site wastewater treatment systems.

Quite often the sludges are combined together for further treatment and disposal. Sewage sludge treatment using thermal hydrolysis and anaerobic digestionMixed sludge received from secondary wastewater treatment is passed through a dissolved-air flotation tank, where solids rise to the surface and are skimmed off.

The thickened sludge is pulped with steam, then passed to thermal hydrolysis, where large molecules such as proteins and lipids are broken down under heat and pressure.

The hydrolyzed sludge is passed through a flash tank, where a sudden drop in pressure causes cells to burst, and then to anaerobic digestion, where bacteria convert dissolved organic matter to biogas which can be used to fuel the treatment process. Digested sludge is passed through a dewatering step; the dried solids are disposed of, and the water is sent back to secondary treatment.

Treatment and disposal of sewage sludge are major factors in the design and operation of all wastewater treatment plants. Two basic goals of treating sludge before final disposal are to reduce its volume and to stabilize the organic materials.

Stabilized sludge does not have an offensive odour and can be handled without causing a nuisance or health hazard. Smaller sludge volume reduces the costs of pumping and storage. Treatment methods Treatment of sewage sludge may include a combination of thickeningdigestion, and dewatering processes.

Thickening Thickening is usually the first step in sludge treatment because it is impractical to handle thin sludge, a slurry of solids suspended in water. Thickening is usually accomplished in a tank called a gravity thickener. A thickener can reduce the total volume of sludge to less than half the original volume.

An alternative to gravity thickening is dissolved-air flotation. In this method, air bubbles carry the solids to the surface, where a layer of thickened sludge forms. Digestion Sludge digestion is a biological process in which organic solids are decomposed into stable substances.

Digestion reduces the total mass of solids, destroys pathogens, and makes it easier to dewater or dry the sludge. Digested sludge is inoffensive, having the appearance and characteristics of a rich potting soil. Most large sewage treatment plants use a two-stage digestion system in which organics are metabolized by bacteria anaerobically in the absence of oxygen.

In the first stage, the sludge, thickened to a dry solids DS content of about 5 percent, is heated and mixed in a closed tank for several days.

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Acid-forming bacteria hydrolyze large molecules such as proteins and lipids, breaking them into smaller water-soluble molecules, and then ferment those smaller molecules into various fatty acids.

The sludge then flows into a second tank, where the dissolved matter is converted by other bacteria into biogasa mixture of carbon dioxide and methane. Methane is combustible and is used as a fuel to heat the first digestion tank as well as to generate electricity for the plant.

Anaerobic digestion is very sensitive to temperatureacidity, and other factors. It requires careful monitoring and control.

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In some cases, the sludge is inoculated with extra hydrolytic enzymes at the beginning of the first digestion stage in order to supplement the action of the bacteria.

It has been found that this enzymatic treatment can destroy more unwanted pathogens in the sludge and also can result in the generation of more biogas in the second stage of digestion.

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Another enhancement of the traditional two-stage anaerobic digestion process is thermal hydrolysisor the breaking down of the large molecules by heat. This is done in a separate step before digestion. In a typical case, the process begins with a sludge that has been dewatered to a DS content of some 15 percent.

Basic wastewater management

The hydrolyzed sludge is cooled, diluted slightly with water, and then sent directly to the second stage of anaerobic digestion. Sludge digestion may also take place aerobically—that is, in the presence of oxygen.- Bio-medical waste, - Agricultural waste, - Animal waste, - Mineral waste, - Nuclear Waste.

4. Various ways of waste classification - According to the form - Basis of moisture content - Basis of their property - According to their effect on environment. 5. The importance of waste management and the health hazard associated with improper waste management. Explanation: The seven factors are ground conditions, ground water level, location and type of water source, topography, quantity and quality of wastewater produced, climatic, socio-cultural factors.

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Basic wastewater management

However, it is not required for the Basic Operations Course. It is the course text for the Grade 3 “Supervision and Technical Operations Course” and the Grade 4 “Management. MUB does much more than provide water and treat sewage.

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B.F. Environmental Consultants Inc. has been involved with the siting and design of water, wastewater, and stormwater management systems for over 20 years. Waste management is the control of materials that have become redundant and therefore need to be discarded. The process includes collection, transportation, sorting, recycling, clearance, and disposal of .

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