Intensifying Activated Sludge Using Media-Supported Biofilms

Processes combining flocculent suspended growth and media-supported biofilms (hybrid processes) have existed for decades. Interest and practical use of such processes has increased significantly in recent years, however, due to advances in understanding the interactions and synergies between suspended growth and biofilms, along with the availability of newer biofilm media. A key reason for increased use of hybrid processes is that they offer significant opportunities to intensify treatment by allowing effective treatment of organic, nitrogen, and phosphorus loads in bioreactors that are much smaller than those required for processes using only suspended growth.

This manuscript provides an overview of developed and emerging hybrid processes. The factors controlling the design (and resulting size) of suspended growth processes are reviewed, along with options currently available to intensify them, such as replacing the secondary clarifier with membranes (membrane bioreactors, MBR), sludge granulation, and hybrid processes. Hybrid processes using fixed media, moving media (moving bed bioreactor, MBBR, media) and membrane aeration biofilm reactor (MABR) media are described, along with the mechanisms that allow for much smaller bioreactors (intensification). Of these options, MABR not only offers process intensification, but also significant energy savings because of significantly increased oxygen transfer efficiency. The variety of current design procedures used to design hybrid processes are then reviewed, along with some representative case histories.

The following chapter provided increasing detail on hybrid processes. A novel approach for designing them is presented, along with the use of biological process simulation software to design hybrid systems and characterize their performance characteristics. Approaches to model oxygen transfer in MABR-based hybrid processes are addressed in connection with the discussion of process simulation. The unique characteristics of MABR-based hybrid systems under dynamic loadings are addressed.

This manuscript should be of interest to wastewater treatment process designers, along with those seeking more compact and energy-efficient wastewater treatment options. The advantages of MBBR-based hybrid processes are now well-established in practice, leading to their increased use. MABR-based hybrid processes are much newer and offer further systematic process and energy advantages. The evolution of hybrid technologies also demonstrates the potential for continued improvement of biological wastewater treatment.

FEATURES

• Reviews current approaches for intensifying biological wastewater treatment processes and their mechanistic basis.
• Reviews hybrid suspended growth/biofilm-based wastewater treatment processes, including the newly developed membrane aerated biofilm (MABR)-based processes.
• Presents a novel method for characterizing the performance and process intensification advantages of hybrid processes.
• Provides guidance for simulating the performance of hybrid processes, including oxygen transfer in MABR hybrid processes.
• Describes and characterizes the unique dynamic performance characteristics of MABR-based hybrid processes.