Environmental Energy & Engineering - Technologies

High Rate Anaerobic Digestion

High Rate Anaerobic Digestion

High rate anaerobic digestion retains anaerobic bacteria through a variety of means. The process decouples the hydraulic retention time (HRT) from the solids retention time (SRT). The high rate anaerobic "contact process", utilizing gravity sedimentation, has been used for over a hundred years. However gravity sedimentation produces a low concentration bacterial recycle stream. The process can be significantly improved (SRT / HRT ratio) by producing a concentrated recycle stream without adversely affecting the anaerobic bacterial consortia.

E3 developed the AGF process that utilizes biogas for the flotation, concentration, and recycle of a concentrated bacterial biomass stream. Consequently, SRT / HRT ratios greater than three are achieved. An SRT / HRT ratio of three means that the digester size can be reduced to one third of the conventional size while achieving the same percentage solids conversion to gas.

In the AGF process the waste solids contain substantially all of the fine particulate matter and phosphorus and a majority of the nitrogen and potassium. A liquid effluent containing the ammonia nitrogen and soluble potassium is relatively clear and suitable for reuse.