Remediation of Lead Contamination by Aspergillus niger and Phosphate Rocks under Different Nitrogen Sources

Abstract

Co-application of Aspergillus niger (A. niger) and phosphate rocks (PR) has been practiced by environmentalists for lead (Pb) remediation. The secretion of organic acid by A. niger usually dominates the dissolution of PR and Pb immobilization. In this study, two types of PR (fluorapatite (FAp) and phosphogypsum (PG)) were investigated in Pb remediation by A. niger under three different forms of nitrogen (ammonium, nitrate, and urea). Our results reveal that the formation of pyromorphite and lead oxalate contributed to Pb removal by the combination of A. niger with FAp and PG. PG showed a significant capability for Pb remediation compared with FAP, over 94% of Pb vs. 50%. Compared with nitrate and urea, ammonium significantly decreased Pb cation concentrations from 1500 mg/L to 0.4 mg/L. Due to ammonium containing sulfate, the lead sulfate formed also contributed to Pb removal. However, nitrate stimulated A. niger to secrete more oxalic acid (~1400 mg/L) than ammonium and urea (~200 mg/L), which can form insoluble lead oxalate. These insoluble minerals can reduce the availability of removed Pb. Despite the efficacy of both ammonium and nitrate for Pb remediation, our findings suggest that nitrate is the primary candidate in this regard due to high oxalic acid secretion.

Isolation and screening of phosphorus solubilizing bacteria from saline alkali soil and their potential for Pb pollution remediation

“…Studies have shown that environmental stress significantly inhibits the rate of tricarboxylic acid cycle in microorganisms, thereby reducing the secretion of succinate (an intermediate of the tricarboxylic acid cycle) ( Guarnieri et al, 2017 ; Teng et al, 2019 ). In addition, some studies have shown that oxalic acid secreted by Aspergillus niger can form PbC 2 O 4 precipitation with Pb 2+ ( Ceci et al, 2015 ; Feng et al, 2022 ). Therefore, the reduction of oxalic acid in solution may also be transferred to the precipitate in the form of Pb oxalate.…”

“…Phosphorus solubilizing microorganisms (PSM), as a type of environmental functional microorganism, can enhance phosphorus utilization by plants via releasing organic acids, enzymes and other biological secretions to dissolve insoluble phosphorus sources in the environment ( Rodriguez et al, 2006 ; Shao et al, 2021 ; Zhu et al, 2022 ). In addition, with the further study of PSM, it has been proved that they can be used in the remediation of HMs in soil ( Park et al, 2011 ; Teng et al, 2019 ; Feng et al, 2022 ; Lai et al, 2022 ). The greatest advantage of PSM in HMs remediation is their ability to release phosphate ions that combine with HMs ions to form more stable metal-phosphate compounds ( Chen et al, 2020 ; Lai et al, 2022 ).…”

Lead remediation is promoted by phosphate-solubilizing fungi and apatite via the enhanced production of organic acid

“…In addition, the released P can be also isolated by PSF and not easily absorbed by plants, promoting the Pb remediation process ( Menezes-Blackburb et al, 2016 ). However, the secretion of oxalic acid by PSF is usually influenced by different factors, such as pH, nutrients, phosphate types, and Pb concentration ( Tian et al, 2019 ; Feng et al, 2022 ). Therefore, the appropriate technology and conditions are needed in Pb remediation by PSF and phosphate.…”

“…Nitrogen is a key factor affecting the metabolism of A. niger and the dissolution of phosphate rock ( Paulo et al, 1988 ; Tian et al, 2018 ). Compare with ammonium and urea, nitrate can significantly increase the secretion of oxalate by A. niger and reduce the Pb concentration in Pb remediation with Ca-P ( Feng et al, 2022 ). For nitrogen, nitrate is the suitable resource in Pb remediation by PSF and phosphate.…”

“…The decomposition of inputted urea can produce carbon dioxide and form carbonates, which inhibits the growth of A. niger and the secretion of organic acids ( Cinthya et al, 2006 ; Su et al, 2021 ). Ammonium and nitrates are more efficient in Pb remediation by A. niger and phosphate ( Feng et al, 2022 ). In addition, calcium can stimulate A. niger to secrete more organic acids, hence the calcium-based nitrogen fertilizer is more suitable for Pb remediation by PSF and phosphate ( Tian et al, 2021a ).…”