Bioremediation of oligotrophic waters by iron-humus-containing bio-immobilized materials: Performance and possible mechanisms

The combined pollution and oligotrophic characteristics of surface water led to poor self-purification capacity of water bodies. In this study, humic acid (HA) and fulvic acid (FA) were used to promote the denitrification process of strain Zoogloea sp. ZP7. Subsequently, iron and different humus (HA and FA) composites were encapsulated by polyvinyl alcohol (PVA) and sodium alginate (SA) to prepare two biological immobilization (BI) carriers Fe-HA@PVA/SA (FHB) and Fe-FA@PVA/SA (FFB), which immobilized strain ZP7. The BI materials were added to the water remediation system model and operated for three stages (synthetic wastewater, actual polluted surface water, sediment-contaminated surface water) for 48 days. The results showed that FHB (FFB) could remove up to 89.7 % (88.6 %), 90.5 % (89.5 %), 82.2 % (81.5 %), and 90.4 % (80.8 %) of total nitrogen, nitrate, COD_Mn, and phosphate from the actual polluted surface water within 16 days of stage II. In addition, the incorporation of FHB and FFB was effective in controlling the release of organic matter and heavy metals from the sediments. Microbial community analysis showed that Zoogloea became the dominant species in actual water bodies. KEGG database analysis illustrated that the expression of genes related to denitrification and iron redox cycle was enhanced. This work provides a novel approach into the in-situ bioremediation of actual nutrient-poor water bodies.