New H.P. Hood Plant Selects Anaerobic/Aerobic Treatment

In March 1999, a request for proposal titled "Proposed ESL Dairy Plant Wastewater Pretreatment System" was issued. Either anaerobic plus aerobic or aerobic only were acceptable options. This turned out to be the H P Hood plant in Winchester, VA, slated for construction in 1999/2000.

After careful review and several waste treatment plant visitations, Hood and Hixson (the consultant) accepted the Paques ADI Inc. proposal that entailed both anaerobic and aerobic processes to pretreat the wastewater from this speciality fluid milk and nondairy products facility. The pretreated effluent will be discharged into a sewer and flow by gravity three miles to the POTW. The POTW effluent discharges into a creek that flows into the Potomac River and on to Chesapeake Bay.

The RFQ specified all the unit operations to be included starting at a raw waste pumping station and ending with treated effluent guaranteed to meet 100/100 mg/l BOD/TSS and 100 mg/l FOG. Scenarios including a high-strength, low-volume waste stream were given in the RFQ. The final decision was to treat the the high strength stream rather than use it as hog feed.

Treating the raw wastewater would be a challenge in view of the incoming pH range of 2-12; temperature, 60-88F; average TSS of 1000 ppm; and peak day fat, oil, and grease (FOG) concentrations approaching 1200 ppm.

The RFQ included a discussion on how nitrogen and phosphorus removal would be done at a future date. The treatment facility must be constructed and ready to treat process wastewater by March 2000.

The wastewater treatment plant will be delivered by Paques ADI Inc. to H P Hood on a design-build basis. ADI Systems Inc. will provide design-build services. The treatment facility comprises a screen, raw waste pumping station, equalization tank, calamity tank, anaerobic digester, and SBR (sequencing batch reactor).

The anaerobic digester is a patentedType S ADI-BVF reactor of one million gallon capacity. The single-tank SBR process has a capacity of two hundred thousand gallons. Initially, the SBR will be run as a simple aeration tank; later on, as the load increases, it will be run in the SBR mode. Oxygen is provided by a jet aeration system. When operating in SBR mode, the waste activated sludge will be returned to the BVF digester for stabilization.

The biogas will be flared, as the quantity is too small for cost-effective utilization. In-plant direct steam injection is provided to heat the high-FOG wastewater under winter conditions.

The pretreatment plant proposed is expected to produce a very high quality effluent when operating under full design load as shown below:

BOD 30 mg/l
SS 30 mg/l
FOG 20 mg/l