TWO-PHASE ANAEROBIC DIGESTION: AN UPDATE ON THE AG PROCESSES

This paper deals with two-phase acid/gas anaerobic digestion (sometimes called DuPage two-phase digestion). Plant scale experience has shown this process to have several advantages over similar sized single-phase mesophilic digesters. The advantages include greater operational stability, better control of foaming, higher volatile solids (VS) destruction, higher gas production, good dewatering characteristics and capability of meeting coliform and vector attraction reduction requirements for Class A biosolids. These advantages are achieved with smaller tanks so they are more economical to build and operate. This paper describes the process variations, each of the known existing or proposed full-scale plants and discusses the experiences with the acid/gas process.