The physical plants for freezing systems, reed systems, and vermistabilization systems are similar in appearance and function. In all cases, a bed is required to contain the sand or other support medium, the bed must be underdrained, and a method for uniform distribution of sludge is essential. Vermistabilization beds must be covered and probably heated during the winter months in most of the United States. The other two concepts require neither heat nor covers. Table 9.11 summarizes the criteria and the performance expectations for these three concepts. The annual loading rate for the vermistabilization process is much less than for the other concepts discussed in this section; however, vermistabilization may still be cost effective in small to moderate-sized operations, as thickening, digestion, conditioning, and dewatering can all be eliminated from the basic process design. Freezing sludge does not provide any further stabilization. Digestion or other stabilization of wastewater sludges is strongly recommended prior to application on freezing or reed beds to avoid odor problems.
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