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Sewage sludge processing is a key issue in water resource recovery facilities due to the inefficacy of conventional treatments to produce high quality biosolids to be safely used in agriculture. Under this framework, the performances of several enhanced stabilization processes, namely ultrasound-pretreated Mesophilic Anaerobic Digestion (US+MAD), thermophilic anaerobic digestion (TAD), thermal-pretreated TAD (TH+TAD) and ultrasound-pretreated inverse Temperature Phased Anaerobic Digestion (US+iTPAD) have been investigated. Such enhanced processes resulted in higher biogas yields and higher destruction of pathogens with respect to conventional MAD process, thus suggesting their feasibility in full-scale implementation perspectives. A procedure for technical-economic comparison of new sludge processing lines against conventional ones (benchmarking) was developed, based on the definition of technical issues (e.g. reliability, complexity, etc.) which are rated for each situation. Moreover, capital and operating costs were estimated. The enhanced processes analyzed in this work showed some potentially critical items, mainly related to energy balance and reagent consumption. Water Environ. Res., 88, 468 (2016). [ABSTRACT FROM AUTHOR]

In this work we have performed a feasibility study of two upgrading alternatives for sewage sludge stabilization aimed to the reduction of the produced sludge and to the improvement of its qualitative characteristics with respect to its final destination: agricultural use or incineration. The first upgrading (1) proposes the separated thickening: primary sludge is thickened by gravity while dynamic thickening is applied to secondary sludge. The second upgrading (2) introduces a post-aerobic digestion stage (after the anaerobic one), in addition to separate thickening. Technical-economic and environmental assessments have been performed in comparison to a conventional wastewater treatment plant, which operates with gravity thickening and anaerobic digestion of mixed sludge. In the post-aerobic stage, operated with intermittent aeration, additional volatile solids removal of 45% and nitrification and denitrification efficiencies of 97% and 70%, respectively, were achieved. Both upgrading alternatives gained a positive technical evaluation with the only exceptions of the item “ Thermal energy consumption ” in upgrading 1 for agricultural reuse, and, to a minor extent, the “ Energy available for external recovery ” for incineration in both upgrading options. Cost analysis showed that the two upgrading alternatives are generally cheaper than the conventional plant, even if the results are dependent on local conditions, which have to be considered. Results of the environmental assessment showed that the upgrades with incineration perform better than the reference for all impact categories except freshwater eutrophication, with upgrading 2 as the best option. For the agricultural use, different results were obtained for the different impact categories with critical aspects mainly related to phosphorus and ammonia emissions for upgrading 1. [ABSTRACT FROM AUTHOR]