Sewage disposal, cost

Service facilities, cost of 175-176 Service life definition of 270 values of 271-276 Sewage disposal, cost of 811-812 Shearing for equipment fabrication, 447... 

Noncombustible or toxic liquid wastes that do not lend themselves to disposal by any of the means just outlined are the most difficult to dispose of safely. These kinds of wastes provide the strongest incentive for a producer to develop a use of the waste stream to minimize ultimate disposal costs. Thus, acidic pickling plant wastes, which contain iron plus unused sulfuric or hydrochloric acids may be used to precipitate phosphate from secondary sewage effluent (e.g., Eq. 5.25). Or they may be blended with aqueous alkaline wastes containing phenolate and unexpended sodium hydroxide to neutralize the pH extremes of both streams. 

This is an option that is not open to the farmer or the sewage works operator. The cost and practicability of enclosing the processes used in sewage treatment varies considerably, but in the disposal of sludge or animal slurries to land there is never a realistic option that the dispersion of odours once transferred to the gas phase might be effectively controlled. 

Another material treated with microwave pyrolysis has been sewage sludge. Disposal of this material, which is a by-product in wastewater treatment processes, is a considerable problem and currently accounts for up to 60% of the operational cost of wastewater treatment plants. Microwave pyrolysis of sludge provides a rapid and efficient process with reduced process time and energy requirements compared with conventional pyrolysis [54]. 

The advantages of fluidized bed incinerators include simple compact design, low cost, high combustion efficiency, low gas temperatures, and large surface area for reaction. The disadvantages are the ash removal and carbon that build up in the bed. They are mainly used in petroleum and paper industries, wood chips, and sewage sludge disposal. 

The large volume of sludge produced during sewage treatment and its high water, low solids content pose a substantial secondary environmental problem, its ultimate disposal. Frequently, the costs of sludge treatment and ultimate disposal or destruction equal all the other costs of sewage treatment [56]. 

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