The implementation of stricter wastewater standards is resulting in configuration changes in wastewater treatment. As facilities upgrade from carbonaceous removal to nitrification, total nitrogen and phosphorous reduction, the type of sludge produced is altering significantly.
Typically, stricter wastewater regulations for nutrient recovery require increasing aeration requirements and result in production of growing quantities of secondary and chemical sludge, often at the expense of primary sludge. It is well understood that secondary sludge is harder to treat than its primary equivalent; therefore increasing levels of this type of sludge will have detrimental impacts downstream. As legislation tightens further, extended aeration times are required during processing to remove more nutrients. Work has shown that extended aeration further exacerbates the treatability of secondary sludge downstream.
This paper explains how changes in wastewater treatment caused as a result of tightening legislation fundamentally alter the nature of the sludge produced and how these changes impact downstream processing, especially with respect to sludge production and type; sludge energy content; performance of downstream anaerobic digestion and dewatering; potential for thermal energy recovery and impact on carbon footprint.
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