Implementation of a Membrane Biological Reactor at Schofield Barracks

Trey Maddox, Engineer Intern, and Karl Santa, Mechanical Engineer, Utilities Division, Directorate of Public Works, USAG-HI, Schofield Barracks, Hawaii

The island of Oahu has a population approaching one million people. The primary source of drinking water for the population is groundwater. The groundwater on Oahu is a natural freshwater resource but this resource is limited. Planners have projected that by the year 2020 groundwater sources on Oahu will be fully developed. Our island water supply is a precious resource that needs special attention and protection. To extend the life of this precious resource, we need new creative and innovative ideas for water conservation.

The large presence of the U.S. Army on Oahu makes them a major player in the role of conserving our water resources. One method the Army is using to achieve sustainability is upgrading the Wastewater Treatment Plant (WWTP) at Schofield Barracks to increase the versatility of the reuse of the wastewater. Successful design and implementation of the new technological upgrades at the WWTP resulted in the improved quality of the treated water from R2 quality to R1 quality. While the R2 quality was constrained to agricultural use, the R1 quality water can be used for irrigation of golf courses and other large grassy areas in the vicinity. The increased use of the wastewater alleviates the demand on the groundwater sources.

  Installation of MBR

The rapid population growth experienced at Schofield Barracks not only requires increased conservation but increased capacity of the WWTP. The challenge the Army was faced with was limited space and a limited budget to implement new technological upgrades of the WWTP. Due to the Army's goals and constraints, a Membrane Biological Reactor system (MBR) was chosen as the ideal solution.

The operation of the MBR technology involves the use of hollow strands of porous plastic fiber with billions of microscopic pores on the surface. The pores form a physical barrier to impurities while allowing pure water molecules to pass through and be collected inside the hollow fiber. Implementation of an MBR would meet stringent reuse water quality standards while increasing capacity, achieve a cost-effective and reliable solution, maximize reuse of the existing infrastructure, and minimize the plant footprint. The new plant design will increase the flow capacity from 2.3 million gallons per day (MGD) to 4.2 MGD. The increased capacity is essential for the rapid population growth experienced at Schofield Barracks. The new MBR system is ideal for the new stringent discharge and reuse limits, tight budgets, and limited space the Army is faced with at Schofield Barracks.

Construction of the MBR began in March 2006 and was completed in November 2006. In the MBR system, the fibers are submerged in an aerated biological reactor. Before the wastewater reaches the MBR it first goes through a fine screen that removes larger particles that could damage the fibers. Following the anoxic zone, the wastewater enters an aeration zone where the bacteria consume the organic compounds before the wastewater reaches the membrane. After passing through the membrane the water has been stripped of contaminants such as bacteria and viruses, suspended solids, parasites, and some organic macro molecules. This puts the MBR in the ultrafiltration range. Once the water goes through the membrane it is sent through UV disinfection which is the final stage of the process before the water is considered R1 quality.

The membrane bioreactor has several distinct advantages over the previous existing conventional activated sludge system. The benefits of the implementation of the MBR resulted in the following improvements:

  • Higher quality effluent (R1) with numerous possible applications for reuse
  • Higher capacity without increasing the plant footprint
  • Elimination of secondary clarifiers
  • Increased automation
  • Modular expandability
  • Built-in redundancy
  • Higher mixed liquor concentrations (8-10,000 mg/L compared to 1200 mg/L)

Due to the limited space and the limited supply of groundwater in Hawaii, the membrane bioreactor was an ideal solution for the Schofield Barracks wastewater treatment plant. The MBR is also in line with the Army's emphasis on sustainability.

On June 5, 2007, Aqua Engineers and the U.S. Army as a partnership were awarded a 2007 Global Ecomagination Leadership Award. This was awarded by General Electric as a result of the successful design and implementation of the new technological upgrades at the Wastewater Treatment Plant at Schofield Barracks.

Trey Maddox can be reached at (808) 656-1410 ext. 1104 or trey.maddox@us.army.mil; Karl Santa can be reached at (808) 656-2682 ext. 1226 or karl.santa@us.army.mil. Aqua Engineers, a firm specializing in water and wastewater projects in Hawaii, can be reached at ae@aquaengineers.com.