RESUMEN
Biosolids are the solid by-product of wastewater treatment and contain high-organic matter and nutrient content, which can be utilized in food production and gardening. In 2014, this study's target nutrient recovery facility (NRF) in the Mid-Atlantic region of the U.S. adopted thermal hydrolysis pretreatment (THP) and anaerobic digestion (AD) to upgrade biosolids from Class B (lime-stabilized) to Class A. The pathogen, nutrients, and metals contents were compared with that of Class B biosolids from the same facility throughout a one-year period. Following optimization and equilibrium, stable biosolids were produced that satisfied all Environmental Protection Agency (EPA) Class A biosolids standards. Class A biosolids produced had fecal coliform density consistently below the 1000 MPN/g d.w. limit set by the EPA, at 35.85⯱â¯81.10 MPN/g d.w. (nâ¯=â¯301). Metal concentrations were greater in Class A than Class B biosolids as a result of biosolids mass reduction, but these levels were substantially lower than regulatory limits. Metal concentrations were (in mg/kg d.w.): Asâ¯=â¯6.43⯱â¯0.400 (nâ¯=â¯141), Cdâ¯=â¯3.39⯱â¯0.117 (nâ¯=â¯147), Crâ¯=â¯88.4⯱â¯2.00 (nâ¯=â¯148), Cuâ¯=â¯401⯱â¯9.81 (nâ¯=â¯148), Pbâ¯=â¯68.1⯱â¯2.19 (nâ¯=â¯148), Hgâ¯=â¯1.21⯱â¯0.116 (nâ¯=â¯148), Moâ¯=â¯14.9⯱â¯0.321 (nâ¯=â¯148), Niâ¯=â¯23.8⯱â¯0.911 (nâ¯=â¯146), Seâ¯=â¯10.0⯱â¯0.573 (nâ¯=â¯140), Znâ¯=â¯778⯱â¯14.9 (nâ¯=â¯148), Kâ¯=â¯850⯱â¯21.7 (nâ¯=â¯134). In addition, Class A biosolids were rich in total nitrogen (N) and higher in total phosphorus (TP), but low in potassium (K) content. Concentration of K was 850⯱â¯21.7â¯mg/kg d.w. (nâ¯=â¯134), TKN was 52,000⯱â¯13,300â¯mg/kg d.w. (nâ¯=â¯43), TP was 34,500⯱â¯6130â¯mg/kg d.w. (nâ¯=â¯42), and ammonia-N was 7860⯱â¯1350â¯mg/kg d.w. (nâ¯=â¯43).