biofilmreactors

A biofilm reactor is a type of reactor in which microorganisms form a biofilm on a surface and treat substrates in a continuous flow. Unlike suspended-growth systems, where cells float freely in the liquid, biofilms provide a structured community attached to carriers or tank walls. This configuration can enhance biomass retention and enable high treatment efficiencies at relatively low energy input.

Common configurations include fixed-bed biofilm reactors, where wastewater flows over stationary packing; moving-bed biofilm reactors (MBBR) that use suspended carriers to increase surface area; fluidized-bed biofilm reactors where carriers are kept in suspension; and rotating biological contactors, which present discs with attached biofilm that rotate to provide aeration.

Biofilms are held together by extracellular polymeric substances and exhibit gradients of nutrients and oxygen. Mass-transfer limitations govern performance; substrate diffuses into the biofilm while enzymes act within. Operational parameters include hydraulic retention time, loading rates, temperature, pH, and dissolved oxygen. Start-up may require an acclimation period to establish stable biofilms, and biofilms can be thinned or scraped to control thickness.

Applications include municipal and industrial wastewater treatment, groundwater remediation, bioremediation of pollutants, membrane biofilm reactors for compact treatment, and certain bioprocessing operations where high cell density is advantageous.

Advantages include high biomass retention, robustness to shock loads, and efficient treatment of low-solubility substrates; potential energy savings. Limitations involve biofilm aging and clogging, carrier washout, slower start-up, and more complex maintenance. Design must consider carrier material, surface area, and mass-transfer enhancements.

Performance is typically evaluated by removal efficiency, chemical oxygen demand (COD) or biological oxygen demand (BOD) removal, nitrogen removal, biofilm thickness, and hydraulic performance. Developments include novel carriers and hybrid configurations that combine biofilm with suspended-growth processes.