A belt press is often used to dewater sludge 1 6

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A belt press is often used to dewater sludge.
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1-6 Handbook on Wastewater Management These systems need to be protected from cold weather by a building. Intermittent sand filters are employed in some smaller applications. As wastewater passes through the filter bed, solids are removed. Microorganisms grow in the removed solids layer and provide biological treatment of the wastewater as it flows through the sand bed. The sand will need to be replaced at some point in time. Additionally, these sand filter systems generally perform poorly in the winter. All of the secondary treatment processes produce biosolids. These biosolids are pumped to the solids treatment system for further processing. What comes after Secondary Treatment? In many plants, the next process is called disinfection. Disinfection means the inactivation of disease-causing organisms. It is sometimes confused with sterilization which means the killing of all organisms. In disinfection, the wastewater following secondary treatment is usually treated in one of two ways: (1) chlorination or (2) ultra-violet radiation. Chlorination involves the use of chlorine, either in the form of a gas (less common today), or as a liquid (sodium hypochlorite). The chlorine oxidizes the microorganisms. The effectiveness of this process is monitored by testing the fecal coliform group. This indicator group of microorganisms are easy to grow in a laboratory and are tougher to kill than pathogens. Some chlorination systems also have dechlorination systems to remove any residual chlorine. Ultraviolet (UV) disinfection systems contact the treated secondary wastewater with UV light bulbs that are encased in clear housings. The UV light kills pathogenic organisms by using a germicidal photochemical wavelength. Unlike chlorination, UV leaves no residual in the wastewater with which to be concerned. Plants that use UV must either have dual UV systems or have chlorination as a backup. Additionally, these UV systems are energy consumptive. What is Advanced Treatment? Some treatment plants may be required to remove nutrients (nitrogen and phosphorus) due to the possible negative impacts on the receiving stream (e.g., ammonia toxicity to fish). Advanced treatment processes are used to remove nutrients, additional solids, and/ or biochemical oxygen demand. Advance treatment provides a very high level of treatment that goes beyond secondary treatment. In the case of nitrogen removal, the processes are biological. For phosphorus removal, chemical additives are normally required. Where do all the solids go? Solids that settle out in the primary and secondary clarifiers are referred to as sludge. Sludge from biological treatment processes (e.g., activated sludge) are referred to as biosolids. Sludge is the byproduct of Rotating biologial contactors (Secondary Treatment).
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