Harnessing native bacterial consortium to boost duckweed biomass and chromium removal from batik industry effluents

Batik industry is one of the largest contributors to chromium hexavalent (Cr(VI)) pollution due to the dying and pigmenting process. Remediation agents such as duckweed and bacteria have been commonly used to treat wastewater (WW)-containing Cr(VI). This study utilized native bacterial consortium from the batik WW environment to enhance duckweed growth and Cr(VI) removal. Among the formulated consortia, consortium G4 showed the highest growth promotion on duckweed in WW by 1.3 to 2-fold, while other consortia showed a contrasting result. Additionally, duckweed chromium uptake in WW reached 74 % after 12 days when applied with G4. Consortium G4 features two plant growth-promoting bacteria, Enterobacter mori TALD 1.2 and Enterobacter cloacae TALA 5, along with two chromium-reducing bacteria, Lysinibacillus fusiformis TALA 1.1 and Bacillus thuringiensis TA1. Several combinations of the G4 members were also tested for chromium reduction activity in an NB medium containing 100 mg L^-1 Cr(VI). The original G4 combination showed the fastest Cr(VI) removal, achieving an 81.93 % Cr(VI) reduction within 48 h and a 99 % reduction within 105 h. Interestingly, combining only the chromium-reducing bacteria TALA 1.1 and TA 1 significantly reduced chromium reduction activity and bacterial growth, possibly due to carbon source competition. Thus, the complete members of consortium G4 enhance cross-feeding, with each species playing a vital role in improving interspecies interactions and aiding in chromium reduction. This study underscores the importance of designing a specific and compatible consortium to collaborate with duckweed, offering insights into environmental management practices for other contaminated sites.