Research:

• Microbial mobilization and biotransformation of arsenic in municipal landfills.
  
  
• Agricultural chemicals as a major non-point source of arsenic: microbial transformation of organic arsenicals.
  
  
• Application of sulfate-reducing bacteria for the biomineralization of heavy metals.
  
  
• Biological removal of Cu in wastewaters from semiconductor manufacturing: part of this work is supported by the NSF/SRC sponsored (Engineering Research Center for Environmentally Benign Semiconductor Manufacturing).
  
  
• Hydrogen sulfide as the main electron donor for denitrification of petroleum refinery effluents: A novel approach for simultaneous removal of S, N and C.
  
  
• Currently, Dr. Sierra is developing the web site for knowledge transfer - Anaerobic granular sludge bed reactors for sustainable development.