University of California Water Resources Center

For biological treatment of drinking water, several crucial issues need to be addressed: firstly, microorganisms used in the treatment must be confined and free from leaking into the bulk water; secondly, certain nutrients, particularly, organic carbon source must be provided for optimal microbial growth; finally, the end products of biological conversions must be non-toxic to humans and animals. These objectives are difficult to attain in a typical water treatment plant, as a result, most water treatment technologies employed in America have not been out of scope of physical-chemical treatment. In this study, however, application of artificially-immobilized microorganisms in alginate gel beads to drinking water treatment has proved to be a viable technology in solving these problems associated with the removal of high concentrations of soluble pollutants, such as nitrate in raw water sources. Naturally-derived alginate beads were used as support materials for immobilized microorganisms from activated sludge. Calcium tartrate was co-immobilized into the gel structure and it functions both as an organic carbon source and as a stabilizing agent for the gel structure. Several batches of denitrification experiments were carried out to test the feasibility ofthis immobilization technology. The results of these experiments show that the nitrate removal rate is very high. There was very low concentrations of residual nitrite in the treated water. The alginate beads containing microorganisms survived the harsh hydrodynamic environment with high biomass retention both in treatment experiments and the stability testing experiment. The alginate beads are also recyclable and are very easy to use in immobilization procedures.