Effect Of Zero-valent Iron Research Articles

Degradation of enrofloxacin by Fe0 activated PDS.

In this paper, the effect of zero-valent iron (Fe0) activated persulfate (PDS) on the removal of enrofloxacin (ENR) was investigated, and the effect and mechanism were analyzed by exploring the effects of Fe0 concentration, PDS concentration, pH, and the influence of anion and aqueous matrix on the removal of ENR by the Fe0/PDS system. The results showed that when [ENR] = 20 µmol/L, [Fe0] = 0.15g/L, [PDS] = 0.4 mmol/L, the removal rate of ENR was 85.3% at 90min, the mainradicals were HO•, SO4•- and O2•-. At the same time, the system had a good mineralization effect (TOC removal rate > 40%), in addition, the system did not show obvious toxicity to soil microorganisms after the reaction, furthermore the Fe0/PDS system had a good removal effect on ENR in a wide pH range (4 ≤ pH ≤ 10). There is basically no difference in the removal rate of Fe0/PDS system in ultrapure water and river water.The results of this experiment could provide a reference for the removal of antibiotics based on advanced oxidation techniques based on SO4•-.

Antimony removal using zero-valent iron-manganese bimetallic nanomaterial: Adsorption behavior and mechanism

Although the effectiveness of zero-valent iron (ZVI) and zero-valent manganese (ZVMn) in heavy metal removal is well-established, their combined synergistic potential for antimony (Sb) remediation from wastewater has remained largely unexplored. Addressing this gap, this study introduced a magnetic zero-valent iron-manganese bimetallic material (ZVIM), synthesized via the borohydride reduction method, to investigate its capabilities and underlying mechanisms for Sb reduction and adsorption. The ZVIM, characterized by a high specific surface area of 220 m²/g, exhibited a high adsorption capacity (614.6 mg/g for Sb(III) and 241.7 mg/g for Sb(V)), facilitating over 96.7 % removal for both Sb(III) and Sb(V). The adsorption conformed to the pseudo-second-order kinetic model, and the isotherm data aligned with the Freundlich model, indicative of a heterogeneous adsorption process. The removal of Sb(III) predominantly occurred via surface complexation and electrostatic adsorption to the positively charged ZVIM surface, accompanied by a partial oxidation of Sb(III) to Sb(V). In contrast, the elimination of Sb(V) was primarily facilitated through surface complexation mechanism, encompassing both reduction and electrostatic adsorption. The outcomes of this study shed light on the intricate interactions between Sb species and the ZVIM, revealing the material as a promising candidate for the efficacious removal of Sb from wastewater.

Effect of zero-valent iron (ZVI) on nitrogen and Fe(II) metabolism in anammox-hydroxyapatite (HAP) system under low-temperature stress

Low temperatures could inhibit the activity of anaerobic ammonium oxidizing bacteria (AnAOB). This study investigated the effect of exogenous zero-valent iron (ZVI) on Anammox-hydroxyapatite (HAP) system at 17 ± 1 °C. The results showed that long-term addition of ZVI increased the nitrogen removal efficiency by 8.59 %, and alleviated the inhibition of AnAOB under the condition of low temperature. After addition of ZVI, the activity of AnAOB and the heme c content increased by 58.20 % and 4.83 %, respectively. Moreover, the functional enzyme activities of NIR, HZS, and HZO increased by 94.12 %, 36.36 %, and 16.67 %, respectively. The concentrations of quorum sensing molecules, i.e., C6-HSL and C8-HSL, increased by 191.17 % and 41.54 %, respectively, after ZVI addition. Metagenomic analysis revealed that the addition of 5 g/L ZVI stimulated the relative abundance of Fe(II) metabolism-related genes in AnAOB at 17 ± 1 °C, thereby contributing to the uptake, transport, utilization, and storage of Fe(II). In summary, the addition of ZVI could improve the nitrogen removal performance of the anammox-HAP system at the low temperature.

Effect of zero-valent iron (ZVI) and biogas slurry reflux on methane production by anaerobic digestion of waste activated sludge.

This study aimed to improve anaerobic digestion (AD) efficiency through the addition of zero-valent iron (ZVI) and biogas slurry. This paper demonstrated that methane production was most effectively promoted at a biogas slurry reflux ratio of 60%. The introduction of ZVI into anaerobic systems does not enhance its bioavailability. However, both biogas slurry reflux and the combination of ZVI with biogas slurry reflux increase the relative abundance of microorganisms involved in the direct interspecific electron transfer (DIET) process. Among them, the dominant microorganisms Methanosaeta, Methanobacterium, Methanobrevibacter, and Methanolinea accounted for over 60% of the total methanogenic archaea. The Tax4Fun function prediction results indicate that biogas slurry reflux and the combination of ZVI with biogas slurry reflux can increase the content of key enzymes in the acetotrophic and hydrotrophic methanogenesis pathways, thereby strengthening these pathways. The corrosion of ZVI promotes hydrogen production, and the biogas slurry reflux provided additional alkaline and anaerobic microorganisms for the anaerobic system. Their synergistic effect promoted the growth of hydrotrophic methanogens and improved the activities of various enzymes in the hydrolysis and acidification phases, enhanced the system's buffer capacity, and prevented secondary environmental pollution. PRACTITIONER POINTS: Optimal methane production was achieved at a biogas slurry reflux ratio of 60%. Biogas slurry reflux in anaerobic digestion substantially reduced discharge. ZVI addition in combination with biogas slurry reflux facilitates the DIET process.

Promotion of medium-chain fatty acids and long-chain alcohols production by zero-valent iron: Effect of particle sizes

The effect of zero-valent iron (ZVI) particle size on biological chain elongation (CE) was explored. The addition of ZVI particles with diameters of 50 nm-1000 µm stimulated both medium-chain fatty acids (MCFAs) and long-chain alcohols (LCAs) production, and increased carbon conversion rate of CE process by 2.8–12.2 times. ZVI particle size of 75 µm exhibited the best performance in promoting MCFAs production, achieved the highest MCFAs production of 2164.2 mg/L, which was 11.9 times of control group. ZVI particle size of 1000 µm showed the best performance in stimulating LCAs production, obtained the highest LCAs production of 434.0 mg/L, which was 33.4 times of the control group. Microbial community analysis suggested that different ZVI particle sizes significantly affected genus Clostridium_sensu_stricto_12 and Clostridium_sensu_stricto_7. Functional enzyme analysis revealed that 75 µm ZVI particles induced the strengthened reverse β oxidation pathway, while 1000 µm ZVI particles enhanced the fatty acid biosynthesis pathway.

Enhancing biogas production from cheese whey using Zero-Valent Iron: A comparative analysis of batch and semi-continuous operation modes

Cheese whey (CW) is the primary by-product of dairy industries, and its anaerobic treatment presents several challenges. Among these is the production of high levels of volatile fatty acids (VFAs) due to rapid biodegradation, which leads to a drop in pH and adversely impacts methanogenesis. This study aims to evaluate the impact of Zero-Valent Iron (ZVI) on the anaerobic digestion of CW under both semi-continuous and batch conditions. Since ZVI generates H2 and increases pH under soluble CO2 conditions, the study also focuses on the effects of ZVI on solubilization/hydrolysis, acidification, and microbial response. Three anaerobic bioreactors (R25-PZVI with 25 g/L powder ZVI, R50-SZVI with 50 g/L scrap ZVI, and R-Control without ZVI), at semi-continuous mode, treated cheese whey at varying organic loading rates. After 118 days, R25-PZVI showed the highest CH4 yield and best COD removal, followed by R50-SZVI. Despite NaOH additions, it maintained a lower VFA/ALK ratio than the control. Under semi-continuous mode, CH4 composition in R25-PZVI was 59%, rising to over 95% under batch conditions due to the higher pressure and subsequent solubilization of H2 and CO2. The ZVI mainly impacted methanogenesis and acidogenesis and not solubilization/hydrolysis. 25-PZVI's superior performance was due to its increased H2 generation and alkalinity over 50 g/L SZVI, as was found in the abiotic test. Under semi-continuous conditions, Methanobacterium (a hydrogenotrophic methanogen) and Methanosarcina were the dominant genera in the R25-PZVI reactor. Under batch conditions, Methanothrix displayed a higher abundance, which explained the increased acetic acid utilization.

Effects of zero-valent iron (ZVI) on nitrogen conversion, transformation of sulfamethoxazole (SMX) and abundance of antibiotic resistance genes (ARGs) in aerobic granular sludge process

Even after pre-treatment, livestock and poultry wastewater still contain high concentrations of ammonia and residual antibiotics. These could be removed economically using the aerobic granular sludge (AGS) process with zero-valent iron (ZVI). The interaction of antibiotics and nitrogen in this process needs to be clarified and controlled, however, to achieve good removal performance. Otherwise, antibiotics might generate transformation products (TPs) with higher toxicity and lead to the emergence of antibiotic-resistant bacteria carrying antibiotic resistance genes (ARGs), which could cause persistent toxicity and the risk of disease transmission to the ecological environment. This study investigated the impact of ZVI on AGS for nitrogen and sulfamethoxazole (SMX) removal. The results show that AGS could maintain good ammonia removal performance and that the existence of SMX had a negative impact on ammonia oxidation activities. ZVI contributed to an increase in the abundance of nitrite oxidation bacteria, denitrifying bacteria and the functional genes of nitrogen removal. This led to better total nitrogen removal and a decrease in N2O emission. Accompanied by biological nitrogen transformation, SMX could be transformed into 14 TPs through five pathways. ZVI has the potential to enhance transformation pathways with TPs of lower ecotoxicity, thereby reducing the acute and chronic toxicity of the effluent. Unfortunately, ZVI might enhance the abundance of sul1, sul2, and sul3 in AGS, which increases the risk of sulfonamide antibiotic resistance. In AGS, Opitutaceae, Xanthomonas, Spartobacteria and Mesorhizobium were potential hosts for ARGs. This study provides theoretical references for the interaction of typical antibiotics and nitrogen in the biological treatment process of wastewater and bioremediation of natural water bodies.

Effects of zero-valent iron and magnetite on ethanol and lactic acid production in the anaerobic fermentation of food waste

With the increasing global concern about food waste management, finding efficient ways to convert it into valuable products is crucial. The addition of zero-valent iron and magnetite to enhance ethanol and lactic acid fermentation yields from food waste emerges as a potential solution. This study compared the effects of 50-nm and 500-nm particle sizes of zero-valent iron and magnetite on ethanol and lactic acid fermentation and analyzed the mechanism of action from the perspective of organic matter material transformation and microbiology. The experimental results showed that 500-nm particle size magnetite and zero-valent iron could promote the hydrolysis of polysaccharides and proteins. 500-nm particle size magnetite could increase ethanol production (1.4-fold of the control), while 500-nm particle size zero-valent iron could increase lactic acid production (2.8-fold of the control). Metagenomic analysis showed that 500-nm magnetite increased the abundance of genes for amino acid metabolic functions, while 500-nm zero-valent iron increased the abundance of glycoside hydrolase genes (1.3-fold of the control). It's worth noting that while these findings are promising, they are based on controlled experimental conditions, and real-world applications may vary. his research not only offers a novel approach to augmenting anaerobic fermentation yields but also contributes to sustainable food waste management practices, potentially reducing environmental impacts and creating valuable products.

Pristine/magnesium-loaded biochar and ZVI affect rice grain arsenic speciation and cadmium accumulation through different pathways in an alkaline paddy soil

Cadmium (Cd) and arsenic (As) co-contamination has threatened rice production and food safety. It is challenging to mitigate Cd and As contamination in rice simultaneously due to their opposite geochemical behaviors. Mg-loaded biochar with outstanding adsorption capacity for As and Cd was used for the first time to remediate Cd/As contaminated paddy soils. In addition, the effect of zero-valent iron (ZVI) on grain As speciation accumulation in alkaline paddy soils was first investigated. The effect of rice straw biochar (SC), magnesium-loaded rice straw biochar (Mg/SC), and ZVI on concentrations of Cd and As speciation in soil porewater and their accumulation in rice tissues was investigated in a pot experiment. Addition of SC, Mg/SC and ZVI to soil reduced Cd concentrations in rice grain by 46.1%, 90.3% and 100%, and inorganic As (iAs) by 35.4%, 33.1% and 29.1%, respectively, and reduced Cd concentrations in porewater by 74.3%, 96.5% and 96.2%, respectively. Reductions of 51.6% and 87.7% in porewater iAs concentrations were observed with Mg/SC and ZVI amendments, but not with SC. Dimethylarsinic acid (DMA) concentrations in porewater and grain increased by a factor of 4.9 and 3.3, respectively, with ZVI amendment. The three amendments affected grain concentrations of iAs, DMA and Cd mainly by modulating their translocation within plant and the levels of As(III), silicon, dissolved organic carbon, iron or Cd in porewater. All three amendments (SC, Mg/SC and ZVI) have the potential to simultaneously mitigate Cd and iAs accumulation in rice grain, although the pathways are different.

Deciphering different effects of ZVI and NaOH on metabolic characteristics in the process of methanogenesis recovery from VFA suppression

Dosing zero valent iron (ZVI) or sodium hydroxide (NaOH) is the common method of addressing acidification in anaerobic digestion (AD) systems; however, few studies have discussed and compared their effects on microbial metabolism. In the present study, microbial syntrophy and metabolic pathways under ZVI and NaOH regulation are comparatively analyzed through microbial network analysis and metagenomic/metaproteomic analyses. CH4 yield in the ZVI reactor was 414 mL/gVS, an increase of 23% when compared with that in the reactor with NaOH dosing (336 mL/gVS). The methanogenesis recovery period in the ZVI reactor (37 days) was shorter than that in the NaOH reactor (48 days). Co-occurrence networks indicated that ZVI promoted Methanoculleus and Methanosarcina to establish a complex syntrophic association with SAO bacteria (Syntrophaceticus and Aminobacterium) and syntrophic acetogens (Syntrophomonas), strengthening SAO-hydrogenotrophic methanogenesis (HM) and acetoclastic methanogenesis (AM) pathways simultaneously. Metagenomic analysis showed that the relative abundance of mcrA and fwdB in the ZVI reactor was higher 27% than that in the NaOH reactor. Furthermore, through metaproteomics analysis, much more enzymes related to glucose degradation, bioconversion of butyric acid and pyruvate, conversion of formate and acetate to CO2, and production of CH4 from acetate and CO2 were significantly upregulated under ZVI regulation than under NaOH regulation (fold change relative to control [FC] > 1.5, p < 0.05). The results of the present study enhance our understanding of methanogenic mechanisms under the regulation of ZVI, providing a theoretical basis for its practical application in AD systems experiencing VFA suppression.

Enhanced anaerobic digestion performance of food waste by zero-valent iron and iron oxides nanoparticles: Comparative analyses of microbial community and metabolism

The effects of zero-valent iron (ZVI) and iron oxides nanoparticles on anaerobic digestion (AD) performance of food waste (FW) were comparably clarified in this study. Results indicated that the nanoparticles supplement effectively enhanced the methane yields. As observed, these nanoparticles accelerated organics transformation and alleviated acidification process. Also, the enriched total methanogens and functional bacteria (e.g., Proteiniphilum) were consistent with the promotion of oxidative phosphorylation, citrate cycle, coenzymes biosynthesis and the metabolisms of amino acid, carbohydrate, methane. Additionally, these nanoparticles stimulated electron transfer potential via enriching syntrophic genera (e.g., Geobacter, Syntrophomonas), primary acetate-dependent methanogens (Methanosaeta, Methanosarcina) and related functions (pilus assembly protein, ferredoxins). By comparison, ZVI nanoparticle presented the excellent performance on methanogenesis. This study provides comprehensive understanding of the methanogenesis facilitated by ZVI and iron oxides nanoparticles through the enhancement of key microbes and microbial metabolisms, while ZVI is an excellent option for promoting the methane production.

Effect of zero-valent iron on acidification and methane production using food waste under different food-to-microorganism ratios

During anaerobic fermentation of food waste (FW), acidification destabilizes the fermentation, and affects methane production. This study analyzed the anaerobic fermentation of FW to produce acid and gas under different food-to-microorganism (F/M) ratios after adding zero-valent iron (ZVI) to improve the performance of anaerobic fermentation. Results showed that when the F/M was 2, ZVI had a significant promoting effect on acetic acid, ethanol, and butyric acid production but significantly reduced propionic acid production. Moreover, optimal acid production was observed when 6 g L−1 ZVI powder was added. Furthermore, at ≥6 g L−1 ZVI, the biodegradation rate increased to >70%, and the cumulative methane production of the load increased to >440 mg L−1. Therefore, these results indicate that adding ZVI to FW digestion under different F/M ratios can increase methane production in an anaerobic fermentation system by promoting acetic acid production and reducing propionic acid production.

Effect of zero-valent iron and iron-carbon particles on the denitrification efficiency of anammox process under gradual cooling conditions

Nitrogen pollution in water bodies mainly comes from industrial wastewater discharge, urban sewage discharge, and agricultural pollution. Nitrogen in a nitrate form can adversely affect human health and the environment. In this study, the effects of adding zero-valent iron (ZVI) and iron-carbon (Fe-C) particles on the performance of the anaerobic ammonia oxidation (anammox) process and sludge properties under gradual cooling conditions were investigated. Inoculating a portion of mature anammox granular sludge can speed up the rapid start of anammox. After 90 d of domestication and cultivation, the sludge granulation was achieved, and the influent load was increased. After 30 d of incubation, the total nitrogen (TN) removal efficiency can reach 95.08%. Through batch tests, the short-term effects of adding ZVI and Fe-C particles on anammox sludge were studied. It was found that when 100 mg/L dosage of ZVI was added, the denitrification effect of anammox sludge is the best. When Fe-C particles with Fe/C ratio of 2:1 were added, the anammox sludge had the best denitrification effect. Fe-C particles addition increased the pH of the reaction environment and sludge activity was affected. Continuous flow experiments under gradual cooling conditions showed that the effect of adding Fe-C particles on anammox was better than that of ZVI. After adding ZVI under 15 °C, NH 4 + -N and NO 2 - -N removal efficiency was 78% and 86%. Compared with the low temperature non-dosing ZVI, TN removal load was 1.77 kg/(m 3 ·d), and efficiency was improved by 10.2%. Addition of Fe-C particles promoted the denitrification efficiency, NH 4 + -N and NO 2 - -N removal efficiency was 83.90% and 88.84%. As compared to control the TN removal load was 1.90 kg/(m 3 ·d), and efficiency was improved by 8.4%. The sludge concentration showed a positive correlation with temperature. Results from this study show that simple addition of ZVI and Fe-C particles can stimulate microorganisms to secrete more EPS even under lower temperature. The outcomes of study are significant for wastewater management and pollution control in the waterbodies.

Zero valent iron greatly improves sludge destruction and nitrogen removal in aerobic sludge digestion

Zero-valent iron (ZVI), a low-cost metallic material, has been previously applied in effectively enhancing sewage sludge anaerobic digestion. However, the potential role of ZVI on aerobic digestion of sludge, a completely different sludge treatment method from anaerobic digestion, is still unknown. Herein, the effects of ZVI on the performance of aerobic sludge digestion were systematically studied, focusing on the sludge degradation, nitrogen removal and sludge dewaterability. Results showed ZVI greatly increased the volatile solids (VS) destruction from 27.0 ± 1.3% to 50.0 ± 1.0% and significantly enhanced the TCOD removal from 26.0 ± 1.2% to 47.9 ± 0.9% in aerobic digesters with different ZVI levels (0–20 g/L). The metabolic intermediate transformation steps of solubilization, hydrolysis and catabolism processes in aerobic digestion were all revealed to be enhanced by ZVI. More importantly, the aerobic digesters with higher ZVI levels achieved higher inorganic nitrogen removal, even with higher sludge degradation for ammonium release, due to the occurrence of both chemical and biological denitrification induced by ZVI. Correspondingly, the microbial compositions in the digesters with ZVI shifted towards the direction that was conducive to sludge degradation and nitrogen removal (e.g., aerobic denitrification) compared to control. Further, the dewaterability of the aerobically digested sludge was also improved with ZVI addition, supported by the reducing capillary suction time (CST) and negative surface potential.

Mechanical Properties of Cement Mortars Incorporating Zero-Valent Iron Nanoparticles

AbstractIn this study, the effects of zero-valent iron (ZVI) nanoparticles (NPs) on the mechanical performance of cementitious composites were investigated. For this purpose, the use of a novel nan...

Effect of zero-valent iron and granular activated carbon on nutrient removal and community assembly of photogranules treating low-strength wastewater

Traditional wastewater treatment processes with high energy consumption and greenhouse gas emissions are not suitable for rural areas with low sewage strength and wide distribution. In this study, a microalgae-bacteria synergistic photogranules system was developed under the impetus of green chemical additives to address these challenges. The results showed that zero-valent iron (ZVI) or granular activated carbon (GAC) addition made successful photogranulation treating low-strength wastewater with excellent settleability and stability performance (settling velocity: 14–22 m h−1; integrity coefficient: 0.81–6.62%), while systems without light or additives failed due to the bio-granules disintegration caused by the overgrowth of predators or phototrophic species. A better nutrient removal performance (TN < 15 mg L−1, TP < 0.4 mg L−1) was observed in photogranules systems, and stoichiometric and biological analysis found that the divisions of nitrogen removal by microalgae and bacteria were different for photogranules between GAC and ZVI additions. As a physical enhancer, GAC can be used as the nucleus of photogranules regenerating after granules disintegration rather than affecting the community succession process. However, ZVI addition strengthened the sedimentation ability and stability of photogranules through chemical and biological effects, focusing on enhancing bacterial community diversity, enriching biofilm formation bacteria and inhibiting the overgrowth of filamentous cyanobacteria. Notably, the photogranules process with ZVI addition could be operated under non-aeration conditions without compromising removal efficiency. There existed an ideal distribution of microalgae and bacterial functional species in the photogranules, which seemed to be essential for its self-sustained synergistic symbiosis and stability. Consequently, this work might provide engineering alternatives for realizing carbon neutrality and environmental sustainability of the decentralized wastewater treatment process for low-strength wastewater in rural areas.

Zerovalent Iron Modulates the Influence of Arsenic-Contaminated Soil on Growth, Yield and Grain Quality of Rice

This study aimed to investigate the effects of zerovalent iron (ZVI/Fe0) on growth, yield and grain quality of rice (Oryza sativa L.) cv. BRRI dhan49 in arsenic (As)-contaminated soils. The pot experiment was arranged in a complete randomized design (CRD). The treatments on rice applied were As in soils at As0 (0 mg kg−1), As20 (20 mg kg−1), and As40 (40 mg kg−1) with a combination of ZVI at ZVI0 (0%), ZVI0.5 (0.5%), ZVI1.0 (1.0%), and ZVI1.5 (1.5%) with three replications. Contents of phosphorus (P), potassium (K), manganese (Mn), zinc (Zn), iron (Fe), and As in grains of rice; and Fe and As content in cultivated soils were determined. The application of ZVI had negative or no effect on shoot weight, tiller number, and grain yield. Although application of ZVI had little or no effect on thousand grain weight, P, K, Zn, and Mn of rice grains, Fe content in rice grains was increased by ZVI treatments in a dose-dependent manner. The grain As content was non-significantly reduced by the ZVI application. Soil bacterial population was negatively influenced by the ZVI in a dose-dependent manner which might be linked with As content in the soils. Therefore, a further elaborative study is needed to elucidate the mechanisms of the effects of ZVI and soil As on rice and rhizosphere soil microorganisms.

In-situ methane enrichment of biogas from anaerobic digestion of palm oil mill effluent by addition of zero valent iron (ZVI)

Palm oil mill effluent (POME) is a wastewater effluent that is generated from palm oil milling. Treatment of POME, especially using biological treatment methods, is a challenge as it contains high amounts of organic and sulfur compounds, and it is highly acidic. In this research, the effects of zero-valent iron (ZVI) on the enhancement of methane production from POME via anaerobic digestion were investigated. Furthermore, to identify the reactor operation modes that were suitable for the addition of ZVI, anaerobic digestion of POME was tested in three reaction configurations: batch reactor, fed-batch reactor, and continuous stirred-tank reactor (CSTR). In the batch mode, where acidic POME was fed with 16 g/L of ZVI dose just once, methane production increased by 74%. However, as the oxidation of ZVI under anaerobic conditions led to the production of hydroxyl ions, the pH of the medium continuously increased from approximately 7 to 9, which is not suitable for methanogenesis. In the fed-batch mode that involved intermittent feeding of acidic POME, the pH of the culture media was maintained at 6.8. This is because the extra hydroxyl ions generated from the oxidation reaction of ZVI tended to neutralize the acids in the feeding substrate. In addition, ZVI promoted the production of methane from POME and increased the average methane content in biogas from 62% to 76%. In the CSTR mode, which involved continuous feeding of acidic POME, ZVI increased methane production by 86% (from 1.79 to 3.32 L/day), methane content in biogas from 60 to 75%, and total chemical oxygen demand (tCOD) removal efficiency from 78 to 89 to 88–95%. Thus, the addition of ZVI can be a potential strategy for in-situ methane enrichment of biogas by anaerobic digestion of POME. This is because ZVI acts as a buffer for acid generation and provides extra electrons, ferrous ions, and ferric ions, which promote key microbial activities in the anaerobic digestion process.

Removal of heavy metals in medical waste incineration fly ash by Na2EDTA combined with zero-valent iron and recycle of Na2EDTA: Acolumnar experiment study

ABSTRACT In this study, an effective circulating system was developed to remove heavy metals in medical waste incineration (MWI) fly ash. MWI fly ash (MWIFA)-column experiments were performed to remove Cu, Pb, Zn, Cd, and Ni from MWIFA using EDTA disodium (Na2EDTA). Iron-column experiments were conducted to study the removal effect of zero-valent iron on the five heavy metals from washing wastewater. Toxicity Characteristic Leaching Procedure (TCLP) test method was employed to evaluate heavy metals toxicity of MWIFA residues generated after 0–0.2 mol/L Na2EDTA solution treated. After being washed by 0.2 mol/L Na2EDTA solution, TCLP leaching values of Cu, Pb, Zn, Cd, and Ni were the lowest and satisfied the standard (GB 5085.3–2007), and the leaching values were 58.4 ± 2.0 mg/L, 2.81 ± 0.14 mg/L, 64.3 ± 4.0 mg/L, 0.156 ± 0.005 mg/L, 0.381 ± 0.006 mg/L. Concentrations of Cu, Pb, Zn, Cd, and Ni in iron-column effluent were reduced by 99.7%, 91.6%, 91.6%, 75.4%, and 75.7%, respectively. Na2EDTA was recovered and recycled to the removal of heavy metals from MWIFA. Comparing new Na2EDTA solution with recycled Na2EDTA solution, recycled Na2EDTA and water could be reutilized to dispose MWIFA. The removal efficiencies of Cu, Pb, Zn, Cd, and Ni by recycled 0.2 mol/L Na2EDTA solution were 67.1%, 68.8%, 63.2%, 73.9%, 50.7%, respectively, the removal efficiencies using recovered Na2EDTA decreased by 2.6%, 3.9%, 3.3%, 4.2%, and 1.6%, respectively. Successive batch experiments were also conducted to evaluate industrialization potential and reusable times for recycled Na2EDTA. After four recirculation cycles, extraction efficiencies of Pb and Cd (removal efficiency at different cycles divided by removal efficiency of new Na2EDTA) declined toward 80%. Results from this research indicated that this circulating system possessed industrialization potential. Implications: An effective circulating system was developed to remove heavy metals in MWI fly ash (MWIFA). Integration of Na2EDTA with Fe0 promoted the removal of heavy metals from MWIFA. Na2EDTA, NaCl and water were stepwise extracted from iron-column effluent, respectively. Recovered Na2EDTA can still effectively remove heavy metals from MWIFA. Results from this research indicated that this circulating system possessed industrialization potential.

17 beta-estradiol biodegradation by anaerobic granular sludge: Effect of iron sources

Steroid estrogens, as typical endocrine disrupting chemicals (EDCs), have raised an increasing concern due to their endocrine disrupting effects on aquatic animals and potential hazards on human health. Batch experiments were conducted to study 17 beta-estradiol (E2) removal and Estradiol Equivalent Quantity (EEQ) elimination by anaerobic granular sludge (AnGS) combined with different valence iron sources. Results showed that E2 was effectively biodegraded and transformed into E1 by AnGS. The addition of different valence iron sources all promoted E2 degradation, reduced E2 Equivalent Quotient (EEQ) concentration, and increased methane production in the batch experiments. The enhancement effect of zero-valent iron (ZVI) on E2 removal and EEQ elimination was stronger than that of Fe2+ and Fe3+ in our experiments. The enhancement effect proportion of ZVI corrosion, Fe2+, and Fe3+ in the process of E2 degradation by AnGS combined with ZVI were 42.26%, 40.21% and 17.53%, respectively.