Co-immobilization of <i>Pseudomonas stutzeri</i> YHA-13 and <i>Alcaligenes</i> sp. ZGED-12 with polyvinyl alcohol–alginate for removal of nitrogen and phosphorus from synthetic wastewater

<div><p>Nitrogen (N) and phosphorus (P) are the two main factors causing water eutrophication. Immobilized micro-organisms have been widely studied in N and P removal. However, the effects of various immobilizing conditions on the removal efficiency of N and P using immobilized micro-organism beads (IMOBs) remain unclear. Polyvinyl alcohol (PVA) and alginate, as the two frequently immobilizing-used matrixes, were used for co-immobilizing <i>Pseudomonas stutzeri</i> YHA-13 and <i>Alcaligenes</i> sp. ZGED-12. PVA, alginate and CaCl ₂ contents, immobilization time and different wet biomass ratios of <i>P. stutzeri</i> to <i>Alcaligenes</i> sp. were conducted to elucidate their roles in and influences on the removal efficiency of N and P from synthetic wastewater. The application potential of IMOBs was estimated as well. Results showed that IMOBs prepared by cross-link of 4% PVA and 2–3% alginate with 5% CaCl ₂ and saturated boric acid solution for 10–15 min are the best ones in removal of N and P. Though IMOBs containing <i>P. stutzeri</i> and/or <i>Alcaligenes</i> sp. were capable of removal of the two nutrients, the highest removal efficiency was observed when the wet biomass ratio of <i>P. stutzeri</i> to <i>Alcaligenes</i> sp. was adjusted to 2:2. In addition, the IMOBs were of good ability to remove chemical oxygen demand (COD), NO ₃⁻, NO ₂⁻, NH ₄⁺− <i>N</i>, total nitrogen (TN) and total phosphorus (TP) from artificial wastewater. Of which, micro-organisms immobilized in matrixes were mainly responsible for NO ₃⁻ and TP removal. Therefore, <i>P. stutzeri</i> YHA-13 and <i>Alcaligenes</i> sp. ZGED-12 are reliable bioresources to remove N and P from wastewater.</p>