Sanitization of biosolids from chemically enhanced primary treatment plant: composting or alkali stabilization?

Abstract

This study was aimed at evaluating two pathogen reduction alternatives: composting and alkali stabilization of biosolids at the Cañaveralejo Wastewater Treatment Plant (PTAR-C), based in Cali, Colombia. Composting was used (biosolids; Filter press mud; biosolids (B) + filter press mud (C) + pruning trees (P); biosolids (B) + Organic waste from open market (ROPM) + pruning trees (P)) for a 61-days period. Alkali treatment was carried out for 13 days. Slaked lime and coal ash were applied to the biosolids and final products of composting. 8, 15 and 30 % (weight/weight) were the concentrations used for hydrated lime and ash. For both treatments pH, humidity, temperature, Chemical Oxygen Demand (COD), Total Kjeldahl Nitrogen (TKN), Ammonium Nitrogen (N-NH), helminth eggs, and Faecal Coliforms (FC) were monitored. The 4results showed that the better compost was (B+C+P) removed pathogens, but compost remained as a class B category, with 3-1geometric mean for FC of 4x10UFC g, indicating that the process cannot achieve a class Acategory. Alkali stabilization showed that coal ash produced similar microbiological FC quality of composting for all concentrations, revealing that it is a weak technology from a cost-effective point of view. Slacked lime with 30 and 15% (weight/weight) concentrations -1achieved FC zero (0) UFC g, meeting the Environmental Protection Agency EPAstandard for a class A. This situation can be associated with raising the pH. For 8% (weight/weight) concentration microbiological quality was lower than the former and did not achieve a class A.