The entrapment of mixed microbial cell was accomplished by using a porous material, such as cellulose triacetate, to confine the migration of microorganism. Synthetic glucose, phenol, carbaryl and nitrate wastewater was used as substrate to evaluate this process. Applying entrapped microbial cell techniques for biological water/wastewater treatment was previously investigated mainly by using the pure culture system. For the past six years, the University of Hawaii has investigated this technology for biological wastewater treatment by using a mixed culture approach. It was found that the developed carrier, using cellulose triacetate, is the most suitable for providing the necessary mechanical strength and durability under both the aerobic and anaerobic conditions. It also provides many advantages, such as a short start-up period, high effluent quality in terms of COD, NO3-N concentrations and removal efficiency, low effluent suspended solid concentration, and high SRT with low HRT. The process has potential to replace or upgrade the existing biological processes for water and wastewater treatment. A pre-engineered and packaged plant can be easily developed for a small wastewater treatment system for toxic or hazardous wastewater.