Disposal of sludge

As far back as the 19fi0s, sludge disposal was already regulated by a number of constraints. This prompted the construction of many on-site incineration units in refineries. 

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In all types of biological processes, excess sludge is produced which must be disposed of. The treatment and disposal of sludge are major problems which can be costly to deal with. Anaerobic processes have the advantage here, since they produce considerably less sludge than aerobic processes (on the order of 5 percent of aerobic processes for the same throughput). 

As already noted, all the sludge produced at a treatment plant (whether it be sewage or industrial in origin) must be disposed of ultimately. Treatment processes such as have been described may reduce its volume or so change its character as to facilitate its disposal, but still leave a residue which in most cases must be removed from the plant site. Like the liquid effluent from the treatment plant, there are two broad methods for the disposal of sludge ... 

Landfill and surface impoundment disposal are most often used for wastewater treatment sludge, but a significant number of mills dispose of sludge through land application, conversion to sludge-derived products (e.g., compost and animal bedding), or combustion for energy recovery.25... 

The new Polish Waste Act (issued May 2001) strictly regulates sludge application. The disposal of sludge to the land used for vegetable cultivation as well as to pastures and meadows is prohibited, what minimizes the possibility for persistent chemicals to enter the food chain. 

One of the major environmental problems facing the pulp and paper industry is the disposal of sludges. These arise from the settlement of... 

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. 

Second, the most important potential sources of nuisance in the disposal of sludges to land are the transfer of liquid sludge to a tanker, and the act of spreading itself. This is especially so with anaerobically digested sludges. 

It is clear then, that the concept of Odom Potential of a sludge or slurry can be a useful tool not only to the odour specialist but also to the operators of sewage treatment works and agricultural slurry handling facilities in minimising the nuisance from the disposal of sludges. 

In many cases, anaerobic filter treatment was found to successfully treat pharmaceutical industry wastewater. This can be an excellent alternative for conventional aerobic treatment, which is energy intensive and requires the disposal of sludge. The anaerobic filter, on the other hand, can produce energy in the form of biogas and does not require... 

An important technology for removal of S02 is Flue Gas Desulfurization (FGD), carried out in units known as scrubbers. Most scrubbers contact the flue gas with a slurry of lime or limestone to capture the sulfur oxides and produce a sludge containing calcium sulfite and calcium sulfate. However, disposal of sludge is another environmental problem, and some scrubbers include oxidation to convert all the calcium sulfite to sulfate (gypsum), which can be used for wallboard manufacture. Fluidized-bed combustion units add a sulfur... 

The disposal of sludge will probably remain a battling issue for the next decade. Over the ages it has been the orphan of the wastewater industry—overshadowed by the efficient management of the liquids. 

Moses, C. T. Young, K. W. Stern, G. Farrell, J. B. Co-Disposal of Sludge and Refuse in a PUROX Converter ACS Symposium on Solid Wastes and Residues at the 175th Meeting of ACS, Anaheim, California, March 1978. 

FIGURE 5.1 I Multiple hearth combustion unit with emission controls, for the disposal of sludges and combustible solid wastes. Rakes around air preheat tube at center of multiple hearth unit rotate slowly around tube to move initial sludges or solids across each tray and down, eventually to exit as ash from the base of the unit. (Adapted from Sebastian and Cardinal [74]. Excerpted by special permission from Chemical Engineering [Oct. 1998]. Copyright 1968, by McGraw-Hill, Inc., New York, NY 10020.)... 

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