Abstract:[Objective] To optimize the embedding-based immobilization conditions of Aspergillus niger, preliminarily study the degradation mechanism of deltamethrin (DM) and its intermediate product 3-phenoxybenzoic acid (3-PBA) by immobilized A. niger, and further evaluate the performance of immobilized A. niger applied to agricultural cultivation. [Methods] With biochar-doped sodium alginate as an immobilized carrier, we employed single factor test and response surface methodology to optimize the immobilization conditions of A. niger. The content of DM and 3-PBA was determined by high performance liquid chromatography. [Results] Sodium alginate concentration, biochar concentration, and inoculum size were significant factors affecting DM removal rate, with the optimal values of 25.27, 1.28, and 125.28 g/L, respectively, for A. niger immobilization. After the application of immobilized A. niger, the half-life of DM in soil was shortened from 7.6 d to 5.2 d. Moreover, A. niger had a degradation effect on 3-PBA, which reached the lowest concentration of 1.45 mg/kg at the time point of 21 h. Impressively, the restoration with A. niger immobilization significantly improved the germination rate of tomato seeds, and recovered 6 growth indicators such as plant height and root length to varying degrees compared with the DM alone group. After 28 days of remediation by immobilized A. niger, both root enzyme activity and microbial number in the contaminated soil were improved to different degrees. [Conclusion] After optimization of the immobilization scheme of A. niger, the removal rate of DM in soil was significantly improved. The immobilization of A. niger can not only accelerate the degradation of DM and simultaneously degrade 3-PBA, but also enhance the tolerance of tomato to DM in the contaminated soil.
