In essence, wastewater treatment involves a major operation of separation, which concentrates and converts suspended and soluble nutrients into set-tleable form that can be separated from the bulk of the liquid. The settleable byproducts of wastewater treatment from preliminary treatment, primary treatment, and secondary treatment processes and/or advanced treatment processes are called sludge. The higher degree of treatment of food and agricultural wastewater, the more sludge is created in the processes involved, which has to be appropriately handled unless the sludge is used for land applications or polishing lagoons. The complexity of sludge, due mainly to the characteristics of raw wastewater and treatment processes involved, often means that sludge management is a costly operation in wastewater treatment. The proper utilization and disposal of sludge is one of the most critical issues facing wastewater treatment plants today. Nearly all wastewater treatment plants face the problem of storing and disposing sludges. Landfill costs are skyrocketing; incineration permits are expensive and difficult to obtain; and land application is limited by availability of permitted land.
Additionally, the amount of sludge produced in wastewater treatment is large, though 97% of it is primarily water trapped in the solids; addition of chemicals in physicochemical treatment processes of wastewater treatment increases the amount of sludge produced in the treatment plant. Given the difficulty associated with direct disposal of this enormous watery lump of waste materials to either landfill or waterways, it is not surprising that the main task of sludge treatment is to reduce the quantity of sludge through removal of water. Sludge also needs to be "stabilized" by converting organic solids into harmless inert forms so that the treated sludge can be handled or used as soil conditioners without causing a nuisance or health hazards. Several basic operations of sludge treatment are commonly used in municipal and industrial wastewater treatment: thickening, stabilization, conditioning, dewatering, reduction, and disposal.
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Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.