Class B biosolids production from wastewater sludge with high pathogenic content generated in an advanced primary treatment

Alkaline post-stabilization of wastewater sludge with high pathogenic content (up to 10(10) NMP/g TS of Salmonella sp. and up to 89.8 helminth eggs/g TS) was studied to evaluate the feasibility of producing Class B biosolids. The sludge was produced in pilot systems using different advanced primary treatment processes treating wastewater generated in Mexico City. Samples were dewatered to different dryness ranging from 11.5 to 29.0% TS and stabilized using quicklime in doses ranging from 15 to 40% (w/w). The levels of pathogens round in dewatered sludge were up to 8 log and 1.95 lag higher than those found in primary sludge generated in the United States for Salmonella sp, and helminth eggs respectively. Distribution of genera of helminths indicated that more than 90% of the eggs found were Ascaris, while the rest were Hymenolepis, Trichuris, Toxocara and Taenia. Minimum and maximum removals ranged between 3.6 to 9.5 log for fecal coliforms; 3.7 to 7.9 log for Salmonella sp.; and 0.1 to 1.3 log for helminths. The recommended quicklime dose was determined for different solids contents in order to achieve the pH-time criteria and the levels of microorganisms required by the US EPA. Metal concentrations were below the maximum levels established for land application of biosolids.