Comparison of Class A Systems Small Digester Facilities

摘要

In recent years there has been much more interest in 2-stage digestion systems, especially thosethat produce Class A Biosolids. Their popularity is in part due to their ability to treat moresludge than conventional digestion systems while achieving a Class A product. Another reasonfor their popularity is due to the variations in 2-stage digestion processes available.This paper will review three treatment facilities, each with a wastewater treatment capacity ofless than 15 MGD; that utilize variations of the 2-stage digestion process. The 2-stage processfor each plant includes a thermophilic first stage process followed by mesophilic anaerobicdigestion to produce Class A Biosolids. The three facilities are:1.Franklin Township, PA2.Lakeland, FL3.London, OHEach of these facilities underwent a plant upgrade that included an upgrade of the digestionfacility. Each had a goal to achieve Class A Biosolids while utilizing a land application program.Adding digester capacity was also important to the overall upgrade at each plant.In considering their options, each plant determined the most cost effective method for achievingClass A Biosolids was to install a first stage thermophilic process. However, each used adifferent approach to the overall 2-stage process. The systems chosen include pasteurization, 2-stage thermo-meso anaerobic digestion and 2-stage anoxic thermophilic-mesophilic anaerobicdigestion. Each process provides Class A pathogen reduction in the first stage and relies on amesophilic anaerobic digestion in the second stage for volatile solids reduction.Information contained within this paper will focus on the facility design for each plant and theoperating data.