By John D. Dyson
Full-scale AquaPrime unit at RRWRD, Rockford, Ill.
Primary filtration and primary effluent cloth media filtration are both emerging technologies in wastewater treatment. The goal of these technologies is to reduce the organic loading to the secondary treatment process, which saves energy and can increase capacity. This is achieved by diverting biological oxygen demand (BOD5) and volatile suspended solids (VSS) from raw wastewater prior to main biological treatment and the anaerobic digestion process, reducing activated sludge loading and increasing gas production in the digestion process. In primary filtration, the cloth media filter replaces the primary clarifier; in primary effluent filtration, the cloth media filter follows the primary clarifier and precedes the secondary process.
An additional application may consist of filtration of gravity thickener overflow (GTO) and centrate sidestreams as a pretreatment step to remove solids and debris. This has the potential to decrease operation and maintenance costs by reducing the BOD5 and total suspended solids (TSS)/VSS load. Capturing solids and diverting TSS/VSS and BOD5 from the proposed sidestream biological treatment to the anaerobic digesters has the same potential to reduce aeration demand and operational costs.
Background
In 2013, the California Energy Commission (CEC) and Kennedy Jenks Consultants funded a primary effluent filtration study. A cloth media filter from Aqua-Aerobic Systems Inc. was among the five technologies selected to participate. Its performance exceeded expectations: the unit ran the entire two years with 99 percent uptime and no cloth wear. The TSS was reduced by 50 to 60 percent to the aeration basin. By the end of the study, the Aqua MiniDisk® cloth media filter was one of only two technologies remaining.
Based on the success of the CEC study, independent testing of primary filtration was conducted at the Rock River Water Reclamation District (RRWRD) in Rockford, Ill. This testing was conducted over six months using water pumped from before the primary clarifier. The performance of the primary clarifier was compared to the performance of the cloth media filter. OptiFiber PA2-13® cloth filtration media and OptiFiber PES-14® cloth filtration media were tested utilizing the AquaPrime configuration with much success. Several pilot units were subsequently developed.
Although most of the piloting has been done on municipal wastewater, the system’s three zones of settling enable it to filter high-solids waste streams including fats, oils and grease (FOG) typical in food processing plants, as well as heavier settled solids that may be in other industrial waste streams.
Primary filtration and wet weather pilot system.
Cloth Media Filtration Unit Design
Cloth media filtration has been used in tertiary applications for over 20 years. Its proven performance and operational advantages model a viable solution for primary filtration or wet weather treatment applications.
The outside-in flow path in cloth media filters, specifically the AquaPrime filter, allows for three zones of solids removal, discussed below. These three zones become even more critical in wet weather applications due to the high solids environment in primary filtration and wet weather treatment applications.
Floatable Zone: The top, or floatable, zone is where floatable scum is allowed to collect on the water surface. As the water level increases, the scum is removed by flowing over the scum removal weir, where it’s then directed to the plant’s waste handling facilities. The floatable scum is removed typically one to three times per day by opening a floatable valve.
Filtration Zone: The middle, or filtration, zone is where the majority of solids are removed through filtration. Here, solids deposit on the outside of the cloth media, forming a mat as filtrate flows through the media. Once a predetermined liquid level or time is met, the backwash shoe contacts the media directly and solids are removed by vacuum pressure using the backwash pump. During backwash, fibers fluidize to provide an efficient release of stored solids deep within the fiber.
Solids Zone: The bottom, or solids, zone is where heavier solids collected on the bottom of the tank are removed on an intermittent basis from the hopper using collection laterals and the backwash pump.
Pilot Testing
A pilot trailer and three stand-alone units have been specifically designed for primary filtration and wet weather filtration applications. The unit is currently traveling around the United States and is collecting data at various plants. These primary filtration studies show excellent removal efficiencies in both TSS and BOD across all pilot testing sites: 75-85 percent removal of TSS and 45-60 percent removal of BOD, a 20-30 percent increase over conventional primary sedimentation.
Energy Reduction
Cloth media filtration produces significant energy and capital cost savings as a result of carbon diversion. The high organic energy content of the VSS removed in cloth media filtration means more biogas energy production in the anaerobic digestion process. Further, due to reduced organic loading, the process reduces electrical energy required for aeration in secondary treatment.
Other benefits include the possibility of expanding plant capacity by reducing the organic loading upstream of the secondary process. It is also compact, requiring 10-20 percent of the footprint of a conventional sedimentation solution.
Conclusion
AquaPrime cloth media filtration is a viable technology for treating many different primary and primary effluent applications, both municipal and industrial. The technology provides a high-quality effluent, easy operation, and major operating savings in reduced energy consumption in the treatment facility. IWW
About the Author: John D. Dyson is a product channel manager for Aqua-Aerobic Systems Inc.
References
Caliskaner, Onder; Tchobanoglous, George; Young, Ryan; and Laybourne, Sarah. “Demonstration of Primary Effluent Filtration for Carbon Diversion to Save Energy and Increase Plant Capacity,” Proceedings, WEFTEC 2014, New Orleans, LA, 2014.
