MAINTAINING CLASS B BIOSOLIDS POST-DEWATERING THROUGH LOWLEVEL LIME DOSING

Biosolids production at the Charlotte-Mecklenburg Utilities McAlpine Creek Wastewater Management Facility currently averages 40 dry tons per day. The preferred beneficial reuse option for biosolids is land application. However, due to offensive odors and fecal coliform regrowth/ reactivation issues associated with post-digestion biosolids handling, the final product is rendered unsuitable for land application. Following a baseline development, a series of benchscale tests were performed to investigate the efficacy of chemical addition (ferric chloride, sodium hypochlorite and liquid lime) to slow down or to prevent fecal re-population, and at the same time decrease odor emissions from the final dewatered product. The bench tests and fullscale trials revealed that liquid lime had strong potential to effectively control fecal re-growth/reactivation. Following the initial tests, a comprehensive full-scale testing with liquid lime alone and a combination of ferric chloride and liquid lime were performed. The liquid lime doses applied varied from 3 % to 9 % by wt, while the ferric chloride dosage was kept at 2 % by wt. The major objective was to provide lime dosing high enough to attain satisfactory fecal regrowth/ re-activation control, but also low enough to yield biosolid pH values below 11 to minimize generation of offensive odors. All the doses applied provided successful and sustained fecal coliform re-growth/reactivation control over a 30 day storage period. Full-scale land application trials with odor characterization using odor panel and compound-specific results of the applied biosolids revealed that McAlpine Creek biosolids should not pose any greater risk of generating odor complaints than other biosolids currently being land applied.