Fabrication of a novel polyurethane foam-alginate-zeolite hydrogel and subsequent KSND bacteria encapsulation: evidence of accelerated biofilm colonization and enhanced nitrogen removal efficiency.

Biofilms are used widely to remove nitrogen from wastewater; however, most biofilm carriers (i.e. polyurethane foam, PUF) are hydrophobic organic materials with millimetre-scale apertures, ineffective attachment, and unstable colonization of microorganisms. To address these limitations, hydrophilic sodium alginate (SA) mixed with zeolite powder (Zeo) was cross-linked in PUF to form a micro-scale hydrogel (PAS) with a well-organized and reticular cellular structure. Scanning electron microscopy revealed that immobilized cells were entrapped in the interior of hydrogel filaments and rapidly formed a stable biofilm on the surface. The biofilm generated was 10.3-fold greater than the film developed on PUF. Kinetics and isotherm studies revealed that the as-developed carrier, because of the presence of Zeo, effectively improved the adsorption of NH4+-N by 53%. The PAS carrier achieved total nitrogen removal in excess of 86% for low carbon-to-nitrogen ratio wastewater treated for 30 d, indicating that this novel modification-encapsulation technology has potential for wastewater treatment.

Enhanced stability and nitrogen removal efficiency of Klebsiella sp. entrapped in chitosan beads applied in the domestic sewage system.

Although numerous denitrifying bacteria have been isolated and characterized, their capacity is seriously compromised by traditional inoculant addition and environmental stress in open bioreactors for wastewater treatment. In this study, a biocompatible material, chitosan, was used as a carrier to immobilize a simultaneously heterotrophic nitrifying-aerobic denitrifying bacterium Klebsiella sp., KSND, for continuous nitrogen removal from domestic wastewater in an open purification tank. The results showed that immobilization had no significant effect on cell viability and was beneficial for the reproduction and adhesion of cells. The entrapped KSND exhibited a slightly higher nitrogen removal efficiency of 90.09% than that of free KSND (87.69%). Subsequently, repeated batch cultivation experiments and analysis of the effects of organic contaminants and metal ions were performed using artificial wastewater and domestic wastewater. The findings revealed that the immobilized KSND beads presented desirable biophysical properties with good mechanical stability, cell viability, and enrichment, remarkable stability in organic contaminants and metal ions, and high efficiency nitrogen removal capacity. In conclusion, the developed immobilized denitrifying bacteria system has great potential for continuous wastewater treatment in open bioreactors.