The AGF process uses existing anaerobic reactors to improve the digestion process. Anaerobic bacteria are conserved by concentrating the bacteria and returning them to the digester. The digester's bacterial and solids concentration are maintained at a higher level.

Solids retention times (SRT's) can be three to four times the hydraulic retention time (HRT). The percentage of solids converted to gas is significantly improved. More methane gas is produced.

Waste Solids

Solids are periodically wasted from the thickened return solids stream. Since the waste solids are highly concentrated, only a small volume must be wasted. The waste solids flow is approximately 1/4th to 1/5th of the influent flow to the digester.

The concentrated waste solids are also charge neutralized. The time and polymer required to further dewater the waste solids are substantially reduced. Belt press dewatering is commonly reduced to 1/4th the conventional time required.

Gas Flotation Separation

The AGF process uses "Anoxic Gas Flotation" to accomplish solids separation. Flotation is a natural non-disruptive anoxic process which does not adversely affect bacterial viability. Flotation is more effective than settling without the adverse effects of more intense separation techniques. Gas flotation can also improve gas quality by significantly reducing the H2S and CO2 concentration of the product gas.

Use of CO2 flotation creates carbonates which provide many benefits including the prevention of struvite formation and scaling.

Flotation separation can also remove hydrophobic proteins, enzymes, and organic acids resulting in a relatively clear effluent.

During flotation, both charge induced particle attachment and surface tension effects accomplish solids separation. Consequently, less polymer and energy are required for flotation separation.

Effluent Quality

Seventy five to eighty percent of the of the raw sludge flow to the digester is discharged from the AGF unit as a relatively clear effluent. Typically the effluent contains less than 1000 mg/L of total solids.

The inhibitory end-products of digestion such as ammonia and sulfide are removed with the effluent. Removal of the inhibitory end-products enhances the anaerobic digestion process. Ammonia and soluble phosphate can be recovered as a valuable product.