In-situ remediation of eutrophic Wolong Lake sediments using novel PVA-SA-Biochar and PVA-SA-zeolite embedded immobilized indigenous microorganisms: A pilot study

Abstract

Sediment restoration has become a key link in river and lake pollution control. This present study carried out the investigation on the selection of dominant microbial bacteria, selection and optimization of microbial immobilized carrier materials, and the effect of embedded immobilized microbial in-situ remediation of bottom sediment based on the actual restoration pilot project of eutrophic Wolong Lake. The composite of denitrifying and photosynthetic bacteria at a ratio 1:2 showed the best performance in the COD, TN, and TP removal of 74.86%, 65.2%, and 67.5%, respectively. Denitrifying bacteria to photosynthetic bacteria optimal composite bacterial solution with Polyvinyl alcohol-sodium alginate (PVA-SA), PVA-SA-zeolite and PVA-SA-biochar carriers were selected, and the effects of different carriers were analyzed and compared in terms of multiple characteristics. PVA-SA-biochar carriers showed the best ammonia-nitrogen transfer performance, mass transfer coefficient 0. 681×10-9 m2/s, specific surface area 76.3 m2MB/g and performed best in terms of mechanical strength and chemical stability. The effects of biochar, PVA and SA contents on COD removal (Y) were analyzed using the 3D-Response surface methodology. Biodegradation capacity (G-value) increased from 0.68×10-3kg/(kg·h) at the beginning of the test to 2.32×10-3 kg/ (kg·h) after 80 days of the remediation test with a growth rate of 258.82%. The water quality index has been greatly improved indicating that the restoration effect was good. Alpha diversity analysis showed that the Shannon and Simpson indexes increased and decreased respectively. The relative abundance of Bacteroidota, Proteobacteria, Planctomycetota and Chloroflexi, closely related to the processes of denitrification, decarbonization and phosphorus removal increased while Chloroflexi decreased compared with before restoration. The embedded immobilized microbial technology strengthened the remediation effect of the bottom mud (sediment) and its overlying water.