The AGF pasteurization process takes advantage of the enhanced digestion capabilities of the AGF process. Typically the AGF process increases the capacity of a single digester by three to four times it's conventional capacity. Additional digesters are then available to redigest pasteurized solids. An AGF separator occupies less that 1/4 the space of a single digester, uses less energy than that required to mix a single digester, and will cost less than 1/3rd the cost of a single digester.

The AGF process makes additional digesters available for the re-digestion of pasteurized solids with pathogen free bacteria. The low volume of waste solids from the AGF process can be economically pasteurized in small pasteurization tanks with detention times of 0.5 to 1.0 hours. The pasteurization tanks typically have a volume of 100 gallons per 1.0 mgd of treatment plant capacity.

Pasteurization Operation

Small quantities of thickened waste solids are withdrawn from the float, or thickened return flow at one hour (±) intervals throughout the day. The float solids are generally 5.5% to 6% total solids. The thickened solids are diluted to a digester concentration of 2.75% to 3.5% with steam to reach the 70°C pasteurization temperature. The pasteurized solids are then re-digested in a secondary digester. Re-digestion of the pasteurized solids increases the total volatile solids reduction by an additional 5% to 10%. A total process volatile solids reduction of 70% to 80% is expected. The remaining 20 to 30% are Class A biosolids. However, since they have little or no odor and do not possess vector attraction characteristics, we give these solids a mark of A+.

Heat & Energy Requirements

The secondary digester obtains sufficient heat from the pasteurized influent. No additional digester heating is required.

The AGF pasteurization process is more economical than other thermophilic or pasteurization processes since only a small fraction of the total flow is heated to higher temperatures. Each of the AGF digesters are operated at mesophilic temperatures. The AGF pasteurization process does not require any more additional heat than that required by two conventionally insulated mesophilic digesters, unlike thermophilic processes. The excess gas produced can be used for energy production.

Implementation

The existing digesters, heat, and mixing systems are used. The process can be implemented by simply adding an AGF unit, pasteurization tank, and steam injector. The AGF can be installed in an existing tank. The process can be installed in 3 to 6 months.