Effect of ferrous iron loading on dewaterability, heavy metal removal and bacterial community of digested sludge by Acidithiobacillus ferrooxidans

Application of sponge iron-carbon to enrich anaerobic ammonia-oxidizing bacteria from sludge mixture and coupled denitrification for degradation of industrial wastewater

For the treatment of industrial wastewater, coupled iron‑carbon micro-electrolysis (ICME) with anaerobic ammonia oxidation (anammox) and denitrification was optimized under the following conditions: Fe/C = 2, C/N ≤ 2, and the temperature was 30 °C. The coupled ICME enriched ammonia-oxidizing bacteria (AnAOB) and denitrifying bacteria (DB) in the mixed sludge on the 76th day of the present experiment. Stable operation was achieved on the 78th day. The COD and TN removal rates during the operation were 86.20 % and 87.12 %, respectively, while the control group (without iron and carbon) had removal rates of 74.30 % and 60.31 % which were 11.9 % and 26.81 % higher, respectively. Notably, the abundance of AnAOB in the system increased from 0.44 % to 1.43 % during the operation from day 76 to day 100. High-throughput sequencing demonstrated that Candidatus_Kuenenia was a key anaerobic ammonia-oxidizing bacterium. Based on the experimental results, the ICME process could rapidly enrich anaerobic ammonia-oxidizing bacteria to change the microbial community structure of the sludge under the water quality conditions of industrial wastewater and increasing the tolerance of certain DB and Candidatus_Kuenenia to water quality. By combining with iron‑carbon, the rapid modification of mixed sludge was achieved, and the iron‑carbon micro-electrolysis coupled denitrification anaerobic ammonia oxidation process was established, which provides a certain reference value for treating industrial wastewater.

Biogenic iron mineral formation and the fate of arsenic driven by its coupling with ferrous iron in acid mine drainage environment

Acid mine drainage (AMD) containing arsenic produced during coal mining is a global environmental problem. However, the coupled driving process of the key element Fe and the associated element As in the AMD environment has received little attention. Therefore, in this study, we investigated the A. ferrooxidans-mediated ferrous iron-arsenic interaction in a simulated AMD system. We reveal that in As-rich AMD the co-existing element As can regulate the metabolic activity of A. ferrooxidans to accelerate the oxidation of Fe2 + and the subsequent formation of Fe3+ minerals, thereby altering the pH and ORP of the system. XRD, SEM, and XPS analyses showed that the synthesized Fe mineral mainly consisted of As-containing schwertmannite (Sch). As in an AMD system could be efficiently removed (98.7 % after 72 h) through the formation of Fe minerals, thereby reducing its own environmental risk. SO42- plays an important role in As precipitation on the surface and in crystal tunnels of Sch. As-containing Sch is not only beneficial for the precipitation of As, but also for long-term reduction in As toxicity in AMD systems. Our results provide new insight for evaluating the fates of Fe and As, and the environmental and ecological risks of As in AMD produced from natural coal mines.

Unveiling the Bioleaching Versatility of Acidithiobacillus ferrooxidans

Acidithiobacillus ferrooxidans is a Gram-negative bacterium that thrives in extreme acidic conditions. It has emerged as a key player in biomining and bioleaching technologies thanks to its unique ability to mobilize a wide spectrum of elements, such as Li, P, V, Cr, Fe, Ni, Cu, Zn, Ga, As, Mo, W, Pb, U, and its role in ferrous iron oxidation and reduction. A. ferrooxidans catalyzes the extraction of elements by generating iron (III) ions in oxic conditions, which are able to react with metal sulfides. This review explores the bacterium's versatility in metal and elemental mobilization, with a focus on the mechanisms involved, encompassing its role in the recovery of industrially relevant elements from ores. The application of biomining technologies leveraging the bacterium's natural capabilities not only enhances element recovery efficiency, but also reduces reliance on conventional energy-intensive methods, aligning with the global trend towards more sustainable mining practices. However, its use in biometallurgical applications poses environmental issues through its effect on the pH levels in bioleaching systems, which produce acid mine drainage in rivers and lakes adjacent to mines. This dual effect underscores its potential to shape the future of responsible mining practices, including potentially in space, and highlights the importance of monitoring acidic releases in the environment.

Enhancement of Mn2+, Fe2+ and NH4+-N removal by biochar synergistic strains combined with activated sludge in real wastewater treatment

Acinetobacter sp. AL-6 combining with biochar was adapted in activated sludge (AS & co-system) to decontaminate Mn2+, Fe2+ and NH4+-N, and treat activated sludge (AS) for its activity and settling performance improvement. Specifically, the co-system promoted the growth of bacteria in the activated sludge, thus increasing its ability to nitrify and adsorb Mn2+ and Fe2+, resulting in the removal of high concentrations of NH4+-N, Mn2+, Fe2+ and COD in the reactor by 100%, 100%, 100%, and 96.8%, respectively. And the pH of wastewater was increased from 4 to 8.5 by co-system also facilitated the precipitation of Mn2+ and Fe2+. The MLVSS/MLSS ratio increased from 0.64 to 0.95 and SVI30 decreased from 92.54 to 1.54 after the addition of co-system, which indicated that biochar helped to improve the activity and settling performance of activated sludge and prevented it from being damaged by the compound Mn2+ and Fe2+. In addition, biochar promoted the increase of the tyrosine-like protein substance and humic acid-like organic matter in the sludge EPS, thus enhanced the ability of sludge to adsorb Mn2+ and Fe2+. Concretely, compared with AS group, the proteins content and polysaccharides content of the AS & co-system group were increased by 13.14 times and 6.30 times respectively. Further, microbial diversity analysis showed that more resistant bacteria and dominant bacteria Acinetobacter sp. AL-6 in sludge enhanced the nitrification and adsorption of manganese and iron under the promotion of biochar. Pre-eminently, the more effective AS & co-system were applied to the removal of actual electrolytic manganese slag leachate taken from the contaminated site, and the removal of NH4+-N, Mn2+, Fe2+ and COD remained high at 100%, 100%, 71.82% and 94.72%, respectively, revealing advanced value for high engineering applications of AS & co-system.

Enhancing sludge dewaterability in sequential bioleaching: Degradation of dissolved organic matter (DOM) by filamentous fungus Mucor sp. ZG-3 and the influence of energy source

This study aimed to enhance sludge dewatering through sequential bioleaching, employing the filamentous fungus Mucor sp. ZG-3 and the iron-oxidizing bacterium Acidithiobacillus ferrooxidans LX5. The mechanism by which Mucor sp. ZG-3 alleviates sludge dissolved organic matter (DOM) inhibition of A. ferrooxidans LX5 was investigated, and the optimal addition of energy source for enhanced sludge dewaterability during sequential bioleaching was determined. Sludge dissolved organic carbon (DOC) decreased to 272 mg/L with a 65.2% reduction by Mucor sp. ZG-3 in 3 days, and the degraded fraction of sludge DOM was mainly low-molecular-weight DOM (L-DOM) which inhibited the oxidization of Fe2+ by A. ferrooxidans LX5. By degrading significant inhibitory low-molecular-weight organic acids, Mucor sp. ZG-3 alleviated DOM inhibition of A. ferrooxidans LX5. In the sequential bioleaching process, the optimal concentration of FeSO4·7H2O for A. ferrooxidans LX5 was 4 g/L, resulting in the minimum specific resistance to filtration (SRF) of 2.60×1011 m/kg, 40.0% lower than that in the conventional bioleaching process with 10 g/L energy source. Moreover, the sequential bioleaching process increased the sludge zeta potential (from -31.8 to -9.47 mV) and median particle size (d50) of the sludge particle (from 17.90 to 27.44 μm), contributing to enhanced sludge dewaterability. Inoculation of Mucor sp. ZG-3 during the bioleaching process reduced the demand for energy sources by A. ferrooxidans LX5 while improving sludge dewaterability performance.

Enhancement of sludge dewaterability by repeated inoculation of acidified sludge: Extracellular polymeric substances molecular structure and microbial community succession

Improving the dewatering performance of sewage sludge is of great scientific and engineering significance in the context of accelerated urbanization and increasingly strict environmental regulations. Acidified sludge (AS) can improve sludge dewatering performance, but the dewatering effect of repeated inoculation is unclear. The effects of long-term repeated inoculation of AS on the sludge dewaterability were investigated. The molecular structure and microbial community succession of extracellular polymeric substances (EPS) are emphasized. The results revealed that increasing the inoculation ratio of AS reduced the pH, absolute value of sludge zeta potential, and sludge particle size, and the decreasing trend was more evident with prolonging treatment time. Under the conditions of 30% and 50% AS inoculation, the dewatering performance of the sludge was significantly improved (p < 0.05). Compared with the raw sludge, the specific resistance of filtration (SRF) and capillary suction time of 30% inoculation were reduced by 64.3% and 50.1% after 30 cycles, respectively. Excluding loosely bound (LB)-EPS, soluble (S)-EPS and tightly bound (TB)-EPS exhibited a visible decrease, the protein in TB-EPS was significantly related to sludge dewaterability (p < 0.05). The fluorescent components of aromatic protein and fulvic acid-like substances in TB-EPS were significantly associated with SRF, with a correlation coefficient 0.99 (p < 0.05). Both the increase in the percentages of random coil and decrease in α-helix in TB-EPS contributed to improving dewaterability. Increasing Firmicutes and decreasing Chloroflexi levels improved the sludge dewatering capacity. Repeated inoculation did not disrupt the dewatering effect of AS rather increased the feasibility of the engineering application of AS. Considering the dewatering performance and cost synthetically, 30% AS inoculated ratio is feasible for practical applications.

Effect of Anthropogenic Disturbances on the Microbial Relationship during Bioremediation of Heavy Metal-Contaminated Sediment

Soil, sediment, and waters contaminated with heavy metals pose a serious threat to ecosystem function and human health, and microorganisms are an effective way to address this problem. In this work, sediments containing heavy metals (Cu, Pb, Zn, Mn, Cd, As) were treated differently (sterilized and unsterilized) and bio-enhanced leaching experiments were carried out with the addition of exogenous iron-oxidizing bacteria A. ferrooxidans and sulfur-oxidizing bacteria A. thiooxidans. The leaching of As, Cd, Cu, and Zn was higher in the unsterilized sediment at the beginning 10 days, while heavy metals leached more optimally in the later sterilized sediment. The leaching of Cd from sterilized sediments was favored by A. ferrooxidans compared to A. thiooxidans. Meanwhile, the microbial community structure was analyzed using 16S rRNA gene sequencing, which revealed that 53.4% of the bacteria were Proteobacteria, 26.22% were Bacteroidetes, 5.04% were Firmicutes, 4.67% were Chlamydomonas, and 4.08% were Acidobacteria. DCA analysis indicated that microorganisms abundance (diversity and Chao values) increased with time. Furthermore, network analysis showed that complex networks of interactions existed in the sediments. After adapting to the acidic environmental conditions, the growth of some locally dominant bacteria increased the microbial interactions, allowing more bacteria to participate in the network, making their connections stronger. This evidence points to a disruption in the microbial community structure and its diversity following artificial disturbance, which then develops again over time. These results could contribute to the understanding of the evolution of microbial communities in the ecosystem during the remediation of anthropogenically disturbed heavy metals.

Triple action of FeCl3-assisted hydrothermal treatment of digested sludge for deep dewatering

In this study, a FeCl₃-assisted hydrothermal treatment (HTT) process under mild conditions (90 °C-130 °C) was developed for deep dewatering of anaerobically digested sludge. HTT of sludge at 90 °C-130 °C with 4%-6% Fe³⁺ ions loading based on total sludge solids followed by mechanical dewatering reduced sludge water content from 82% to 38%-53% and sludge weight by 62%-72%. The treatment increased the flowability of sludge through reduction of apparent viscosity and disintegration of colloidal forces between sludge particles. This study unveiled that FeCl₃-assisted HTT process had three mechanisms for improving sludge dewaterability and flowability. The treatment hydrolysed sludge flocs in the presence of Lewis acid FeCl₃ and high temperature (90-130 °C). Fe³⁺ ions also improved dewaterability through the formation of double electric layers and neutralisation of surface negative charges, leading to flocculation of sludge flocs. More importantly, the hydrolysed sludge components produced during HTT process acted as reducing agents and led to in-situ generation of iron oxyhydroxide nanoparticles through reduction-oxidation reactions, further enhancing flocculation/co-precipitation of sludge flocs. The treatment reduced EPS content and changed conformational structures of EPS proteins by breaking down hydrogen bond-maintaining α-helix which led to a loose EPS protein structure and enhanced hydrophobicity and flocculability. Furthermore, the FeCl₃-assisted treatment promoted immobilisation of the majority of heavy metals in the sludge matrix through co-precipitation/complexation reactions with iron species and organic/inorganic matters. This indicates that the FeCl₃-assisted treatment reduced direct toxicity/bioavailability of the majority of heavy metals and the treated sludge may be suitable for land application. Overall, this study provides new insights into mechanism of FeCl₃-assisted HTT process for dewaterability of anaerobically digested sludge and immobilisation of heavy metals.

Effects of hydrochar derived from hydrothermal treatment of sludge and lignocellulose mixtures on soil properties, nitrogen transformation, and greenhouse gases emissions

In this study, hydrochar samples derived from hydrothermal treatment (HTT) of sludge and sludge-biomass mixtures were applied to a sandy soil and their effects on soil properties, soil nutrients, greenhouse gas (GHG) emissions, and soluble heavy metals were investigated. The application of untreated sludge and hydrochar derived from HTT of sludge at 180 °C led to the highest soluble nitrate, CO₂ and N₂O emissions, followed by the application of hydrochar samples derived from HTT of sludge-biomass mixtures at 180 °C. Although the application of hydrochar samples derived from HTT of sludge alone and sludge-biomass mixtures at 240 °C in sandy soil led to the lowest emissions of CO₂ and N₂O, it resulted in lower levels of soil electrical conductivity (EC), cation exchange capacity (CEC) and soluble phosphorus. The application of hydrochar samples derived from HTT at 240 °C led to the production of CH₄ and lower nitrate-N contents than hydrochar samples derived from HTT at 180 °C. These results indicated that the soils containing hydrochar samples from HTT at 240 °C were anaerobic, which might inhibit the growth of plants. The application of hydrochar samples derived from HTT of sludge-biomass at 180 °C led to significantly improved contents of soil soluble phosphorus (2.56 and 2.84 g kg^-1 soil) and soil nitrate-N (160.2 and 263.2 mg kg^-1 soil) at the end of 60 days of incubation. However, these contents were lower than the contents of soluble phosphorus (3.71 and 4.45 g kg^-1 soil) and nitrate-N (528.3 and 583.2 mg kg^-1 soil) with the application of untreated sludge and sludge derived from HTT of sludge alone at 180 °C. Although more studies are needed to understand the mechanisms and effects on different soils, this study provides useful insights into the application of hydrochar derived from sludge-biomass mixture in soil.

Acidithiobacillus sp. applied to sewage sludge bioleaching: perspectives for process optimization through the establishment of optimal operational parameters

Using Acidithiobacillus sp. during bioleaching assays is a well-known biological approach to solubilizing metals within sewage sludge. However, sludge dewatering has also been reported as a secondary treatment benefit. Based on a literature review, the present work provides perspectives regarding the enhancement of bioleaching outcomes on a laboratory scale by establishing optimal operational parameters. Data from different studies suggest that greater bioleaching efficiency may be achieved using a 10% (v/v) mixed inoculum of Acidithiobacillus thiooxidans and Acidithiobacillus ferrooxidans in a ratio of 4:1, supplemented with ferrous sulfate (FeSO4) and elemental sulfur (S0), and an initial system pH near 6.0. However, operational parameters must be established according to the type of sludge being treated due to differences in their compositions. Bioleaching duration is also an aspect that must be considered since treatments conducted for longer than 48 h increased the concentration of Extracellular Polymeric Substances (EPS), a characteristic associated with reducing dewaterability performance.

Effects of lignocellulosic biomass type on nutrient recovery and heavy metal removal from digested sludge by hydrothermal treatment

Sludge is a nutrient-rich organic waste generated from wastewater treatment plants. However, the application of sludge as a nutrient source is limited by its high contents of water and pollutants. In this study, the effects of biomass type on nutrient recovery and heavy metal removal from digested sludge by hydrothermal treatment (HTT) were investigated. Blending biomass with digested sludge for HTT at 180-240 °C increased the recovery of nitrogen in the treated solids. At the HTT temperature of 240 °C, HTT with hardwood sawdust led to the highest nitrogen recovery of 70.6%, compared to the lowest nitrogen recovery of 36.5% without biomass. Blending biomass slightly decreased the recovery of phosphorus compared to those without biomass. Nevertheless, the lowest phosphorus recovery of 91.3% with the use of hardwood sawdust at the HTT temperature of 240 °C was only ∼7.0% less than that without biomass. Blending biomass reduced the contents of macro-metals such as Ca, Fe, Mg and Al in treated solids but the metal contents varied with different biomasses. Regarding the heavy metals, the use of rice husk did not decrease the contents of Ni and Co while blending bagasse did not decrease the content of Cr at HTT temperatures of 210 °C and 240 °C compared to the use of other biomasses. The different effects of biomass type on nutrient recovery and heavy metals were likely related to the types and abundances of organic acids such as acetic acid, oxygen-containing functional groups such as C-OH and COOH, oxide minerals such as silica from biomasses and the overall effects of these factors. This study provides very useful information in selection of lignocellulosic biomass for HTT of sludge for nutrient recovery and heavy metal removal.

Industrial sludge valorization and decontamination via lipid extraction and heavy metals removal using low-cost protic ionic liquid

Sludge is a heterogenous organic-rich matter that comprise of highly valuable biopolymers along with various contaminants including heavy metals. Sludge valorization as a renewable resource and inexpensive feedstock is key for sludge realization in circular economy context. This study presents the use of low-cost protic ionic liquid (PIL) as an integrated process medium to decontaminate heavy metal contaminated industrial sludge while selectively extract the lipid content. The treatment process focused on the use of 1-methylimidazole chloride for its higher heavy metal extraction performance compared to other screened ionic liquids (ILs). The treatment was also able to selectively extract lipids from industrial sludge, leaving a protein/carbohydrate rich solid product. Process temperature was shown to have a key impact on the biopolymers' fractionation. Operating at temperatures above 120 °C resulted in higher recovery of proteins in the lipid-rich fraction, compromising the quality of the lipid stream. Variation of the PIL acid/base (a/b) ratio also had a significant impact on the deconstruction of the sludge biopolymers, with a/b ratio of 1 resulting in highest recovery of all biopolymers. Optimal water concentration as co-solvent was found at 30 wt%, with lipid recovery reaching 60% and heavy metals extraction ranging between 29 and 89%.