Kinetics simulation of Cu and Cd removal and the microbial community adaptation in a periphytic biofilm reactor

The effect of polyvinyl chloride (PVC) color on biofilm development and biofilm-heavy metal chemodynamics in the aquatic environment

Plastic surfaces are colonized by microorganisms and biofilms are formed in the natural aquatic environment. As the biofilm develops, it changes the density and buoyancy of the plastic-biofilm complex, results in plastic sinking, and increases the heavy metals accumulated by biofilm's mobility and availability in aquatic ecosystems. In this experiment, biofilms were cultured on five colors of polyvinyl chloride (PVC; transparent, green, blue, red, black) in an aquatic environment to investigate the effects of plastic color on biofilm formation and development (Phase 1) and to study the effects of being sunk below the photic zone on biofilm (Phase 2). The PVC color significantly affected the biofilm formation rate but had no impact on the final biofilm biomass. After sinking the biofilm-PVC below the photic zone in Phase 2, the layer of diatoms on the biofilm surface began to disintegrate, and the biomass and Chlorophyll-a (Chla) content of the biofilm decreased, except on the red PVC. Below the photic zone, the microbial community of the biofilm changed from primarily autotrophic microbes to mostly heterotrophic microbes. Microbial diversity increased and extracellular polymeric substances (EPS) content decreased. The primary factor leading to microbial diversity and community structure changes was water depth rather than PVC color. The changes induced in the biofilm led to an increase in the concentration of all heavy metals in the biofilm, related to the increase in microbial diversity. This study provides new insights into the biofilm formation process and the effects on a biofilm when it sinks below the photic zone.

Recent innovations and challenges in the eradication of emerging contaminants from aquatic systems

Presence of emerging pollutants (EPs), aka Micropollutants (MPs) in the freshwater environments is a severe threat to the environment and human beings. They include pharmaceuticals, insecticides, industrial chemicals, natural hormones, and personal care items and the pollutants are mostly present in wastewater generated from urbanization and increased industrial growth. Even concentrations as low as ngL^-1 or mgL^-1 have proven ecologically lethal to aquatic biota. For several years, the biodegradation of various Micropollutants (MPs) in aquatic ecosystems has been a significant area of research worldwide, with many chemical compounds being discovered in various water bodies. As aquatic biota spends most of their formative phases in polluted water, the impacts on aquatic biota are obvious, indicating that the environmental danger is substantial. In contrast, the impact of these contaminants on aquatic creatures and freshwater consumption is more subtle and manifests directly when disrupting the endocrine system. Research and development activities are expected to enable the development of ecologically sustainable, cost-effective, and efficient treatments for practical systems in the near future. Therefore, this review aims to understand recent emerging pollutants discovered and the available treatment technologies and suggest an innovative and cost-effective method to treat these EPs, which is sustainable and follows the circular bioeconomy.

Magnetic reed biochar materials as adsorbents for aqueous copper and phenol removal

Organics and heavy metals are common pollutants in many wastewaters and water bodies. Adsorption processes by magnetic materials can rapidly remove these pollutants from water and effectively recycle adsorbent. In this study, magnetic analyzer, X-ray diffraction, Flourier transform infrared spectroscopy, and granulometry were used to characterize the synthesized magnetic reed biochar materials (ZnFe₂O₄/biochar). Influences of adsorption time, pH, temperature, initial solution concentration, and adsorption equilibrium concentration on adsorption performances were investigated for Cu²⁺ and phenol adsorption by ZnFe₂O₄/biochar. Adsorption kinetic and isotherm models were used to describe the adsorption processes. Adsorption of phenol and Cu²⁺ by ZnFe₂O₄/biochar reached saturation within 45 min and increased slightly with the increase of temperature from 15 to 45 °C. Adsorption of Cu²⁺ increased with the increase of pH, while the adsorption of phenol peaked at pH = 6. The adsorption processes fit the pseudo-second order kinetics model, and both conformed to the Langmuir model. The fitting results show that the maximum single-component adsorption capacity of phenol and Cu²⁺ by ZnFe₂O₄/biochar is 63.29 and 12.20 mg/g, and the maximum bi-component adsorption capacity reaches 40.16 and 9.48 mg/g, respectively. All the findings demonstrate that ZnFe₂O₄/biochar has good adsorption performance for phenol and Cu²⁺.

A kinetic study on the nitrification process in the upflow submerged biofilter reactor

In extent of this study, ammonium removal from wastewater through biological nitrification process was performed in upflow biofilm reactors. The effects of hydraulic retention time (HRT) and nitrogen loading rate (NLR) on the nitrification process were investigated. For the nitrification process, the optimum HRT and NLR were determined to be 80 hr and 0.044 kg/m³.day, respectively. It is observed that the efficiency increased from 53% to 96% along with the increase in HRT from 22 hr to 80 hr and the decrease in NLR from 0.165 kg/m³.day to 0.044 kg/m³.day.The substrate consumption kinetics were studied in the attached growth reactor, and the Monod kinetic model, first-order kinetic model, modified Stover-Kincannon and Grau second-order kinetic models were examined. For the substrate consumption kinetic study, experimental studies were performed at 125, 150, 175, 200, 225 mg NH₄-N/L substrate concentrations and 62 hr at HRT during the nitrification process. As a result of the considering kinetic studies, it was determined that the kinetic study was suitable for the modified Stover-Kincannon kinetic model that had the highest coefficient of regression by 0.997 and when the effluent NH₄-N concentrations and NH₄-N removal efficiencies calculated using kinetic models were examined, it was observed that the results closest to the experimental results (4.5, 10.1, 19.7, 26.2 and 42.3 mg NH₄-N/L) were obtained through the modified Stover-Kincannon model (4.16, 10.71, 18.92, 28.12 and 39.51 mg NH₄-N/L).

A novel biotechnology based on periphytic biofilms with N-acyl-homoserine-lactones stimulation and lanthanum loading for phosphorus recovery

This study presents an approach for developing periphytic biofilm with N-acyl-homoserine-lactones (AHLs) stimulation and lanthanum (La, a rare earth element) loading, to achieve highly efficient and stable phosphorus (P) recovery from wastewater. AHLs stimulated biofilm growth and formation, also improved stable P entrapment by enhancing extracellular polymeric substance (EPS) production and optimizing P-entrapment bacterial communities. Periphytic biofilms loading La is based on ligand exchanges, and La loading achieved initial rapid P entrapment by surface adsorption. The combination of AHLs stimulation and La loading achieved 99.0% P entrapment. Interestingly, the enhanced EPS production stimulated by AHLs protected biofilms against La. Moreover, a method for P and La separately recovery from biofilms was developed, achieving 89-96% of P and 88-93% of La recovery. This study offers a promising biotechnology to reuse La from La-rich wastewater and recover P by biofilm doped with La, which results in a win-win situation for resource sustainability.

Microbial Cd(II) and Cr(VI) resistance mechanisms and application in bioremediation

The heavy metals cadmium (Cd) and chromium (Cr) are extensively used in industry and result in water and soil contamination. The highly toxic Cd(II) and Cr(VI) are the most common soluble forms of Cd and Cr, respectively. They enter the human body through the food chain and drinking water and then cause serious illnesses. Microorganisms can adsorb metals or transform Cd(II) and Cr(VI) into insoluble or less bioavailable forms, and such strategies are applicable in Cd and Cr bioremediation. This review focuses on the highlighting of novel achievements on microbial Cd(II) and Cr(VI) resistance mechanisms and their bioremediation applications. In addition, the knowledge gaps and research perspectives are also discussed in order to build a bridge between the theoretical breakthrough and the resolution of Cd(II) and Cr(VI) contamination problems.

The legacy of trace metal deposition from historical anthropogenic river management: A regional driver of offshore sedimentary microbial diversity

River management, both modern and historical, have dramatically modified offshore environments. While numerous studies have described the modern impacts, very few have evaluated the legacies remaining from hundreds of years ago. Herein, we show trace metal enrichment in the surface sediment of the abandoned Yellow River Delta, hypothesized to be associated with ancient river management. Essentially, anthropogenic modification caused the river to shift, creating a 12.4×10³ km² area with elevated trace metals; characterized by clear metal deposition gradients. Geographical factors related to the ancient river mouth had the most significant influences on Zn (explained by distance to the river mouth, DTM) and Cd (DTM and sediment salinity), while the sediment absorptive capacity was associated with the reallocation of Cu (clay, silt, and iron), Ni (clay and iron), and Pb (silt and iron). Trace metal legacies showed stronger influences on prokaryotic diversity than on micro-eukaryotic diversity, with the former best described by changes in rare, rather than dominant families and classes, and explainable by an "overlapping micro-niche" model. The ancient river's legacies provide evidence of longer-term human disturbance over hundreds of years; as its impacts on associated benthic microbiomes have led to lessons for modern-day waterway management of benthic ecosystems.

Effects of biochar and crop straws on the bioavailability of cadmium in contaminated soil

Numerous studies have been investigated the potential of biochar (BC) derived from various materials and crop straw (CS) to decrease the bioavailability of heavy metals in soil contaminated with cadmium (Cd), and thereby reduce their potential risk to human health and the ecological environment. However, little attention has been given to the comparison of heavy metal remediation efficiency using BC and CS such as peanut vine (PV) and rice straw (RS), especially in soil contaminated with Cd. Here, we explore if Cd bioavailability is affected in contaminated soil by BC and CS. Peanuts were grown in plastic pots, which contained BC or CS at 5% (dry weight, w/w) in controlled environment mesocosms. The bioavailability of Cd in contaminated soil was measured by Cd concentration in the plant and the concentrations of various forms of Cd in the soil. At the same plant age, growth with BC (compared with PV and RS) led to 13.56% and 8.28% lower rates of Cd content in the aboveground parts, 40.65% and 35.67% lower rates of Cd content in the seeds, yet 9.08% and 7.09% lower rates of Cd content in the roots, yet 35.80% and 28.48% lower rates of exchangeable Cd content in the soil. Moreover, BC amendment enhanced the biomass of peanut and physiological quality. Thus, BC had a greater impact on immobilizing Cd in the soil. The results imply that BC was more significantly (P < 0.05) remarkable in decreasing the Cd bioavailability and improving the biomass of peanut. BC has greater potential for enhancing soil quality and promoting peanut growth. In conclusion, this research demonstrates an understanding of employing BC as a promising inexpensive and eco-friendly amendment to remediate soil contaminated with Cd.

Paddy periphyton reduced cadmium accumulation in rice (Oryza sativa) by removing and immobilizing cadmium from the water-soil interface

Periphyton plays a significant role in heavy metal transfer in wetlands, but its contribution to cadmium (Cd) bioavailability in paddy fields remains largely unexplored. The main aim of this study was to investigate the effect of periphyton on Cd behavior in paddy fields. Periphyton significantly decreased Cd concentrations in paddy waters. Non-invasive micro-test technology analyses indicated that periphyton can absorb Cd from water with a maximum Cd²⁺ influx rate of 394 pmol cm^-2 s^-1 and periphyton intrusion significantly increased soil Cd concentrations. However, soil Cd bioavailability declined significantly due to soil pH increase and soil redox potential (Eh) decrease induced by periphyton. With periphyton, more Cd was adsorbed and immobilized on organic matter, carbonates, and iron and manganese oxides in soil. Consequently, Cd content in rice decreased significantly. These findings give insights into Cd biogeochemistry in paddy fields with periphyton, and may provide a novel strategy for reducing Cd accumulation in rice.

Physiological responses and accumulation ability of Microcystis aeruginosa to zinc and cadmium: Implications for bioremediation of heavy metal pollution

Algae has potential to remediate heavy metals. However, the physiological responses of live algae to heavy metals are not well studied. In this study, the physiological responses of Microcystis aeruginosa to zinc (Zn) and cadmium (Cd) ions and its ability to accumulate ions were investigated. Low concentrations (<0.1 mg/l) of Zn and Cd had little influence on algal growth and physiological processes, whereas concentrations above 0.1 mg/l increased the esterase activity (from 42.5% to 621.9%), superoxide dismutase activity (from 12.8% to 45.4%), and malondialdehyde content (from 18.2% to 103.9%), and dramatically inhibited the cell division (from 12.6% to 70.0%) and photosynthetic performance (from 7.1% to 53.1%) of M. aeruginosa. The accumulation of Zn or Cd ions by M. aeruginosa increased exponentially with the initial concentration of metallic ions. Collectively, these findings reveal that M. aeruginosa has considerable potential in the remediation of freshwater lakes with heavy metal contamination during cyanobacterial blooms, where metallic ions are lower than 0.1 mg/l.

Enhanced Adsorptive Bioremediation of Heavy Metals (Cd2+, Cr6+, Pb2+) by Methane-Oxidizing Epipelon

Cadmium (Cd), chromium (Cr) and lead (Pb) are heavy metals that have been classified as priority pollutants in aqueous environment while methane-oxidizing bacteria as a biofilter arguably consume up to 90% of the produced methane in the same aqueous environment before it escapes into the atmosphere. However, the underlying kinetics and active methane oxidizers are poorly understood for the hotspot of epipelon that provides a unique micro-ecosystem containing diversified guild of microorganisms including methane oxidizers for potential bioremediation of heavy metals. In the present study, the Pb²⁺, Cd²⁺and Cr⁶⁺ bioremediation potential of epipelon biofilm was assessed under both high (120,000 ppm) and near-atmospheric (6 ppm) methane concentrations. Epipelon biofilm demonstrated a high methane oxidation activity following microcosm incubation amended with a high concentration of methane, accompanied by the complete removal of 50 mg L⁻¹ Pb²⁺ and 50 mg L⁻¹ Cd²⁺ (14 days) and partial (20%) removal of 50 mg L⁻¹ Cr⁶⁺ after 20 days. High methane dose stimulated a faster (144 h earlier) heavy metal removal rate compared to near-atmospheric methane concentrations. DNA-based stable isotope probing (DNA-SIP) following ¹³CH₄ microcosm incubation revealed the growth and activity of different phylotypes of methanotrophs during the methane oxidation and heavy metal removal process. High throughput sequencing of ¹³C-labelled particulate methane monooxygenase gene pmoA and 16S rRNA genes revealed that the prevalent active methane oxidizers were type I affiliated methanotrophs, i.e., Methylobacter. Type II methanotrophs including Methylosinus and Methylocystis were also labeled only under high methane concentrations. These results suggest that epipelon biofilm can serve as an important micro-environment to alleviate both methane emission and the heavy metal contamination in aqueous ecosystems with constant high methane fluxes.

Microbial aging of hydrochar as a way to increase cadmium ion adsorption capacity: Process and mechanism

Microbially-aged hydrochar were prepared to investigate how aging affected their ability to remove Cd²⁺ from aqueous solutions. Based on aging time in an anaerobic fermenter, four samples were produced: HC, M20-HC, M40-HC, and M60-HC. Results indicated increases in specific surface area, pH, and negative charge on hydrochar surface with aging process. Also, there were a decrease in O/C and an increase in surface functional groups, such as -COOH. The adsorption experiments confirmed the positive correlation between aging time and adsorption performance. The 60-day-aged M60-HC treatment displayed the maximum adsorption capacity, which was 3.8 times higher than that of HC. The Langmuir and pseudo-second-order kinetic equations fitted well with isothermal and kinetic data, respectively. Thermodynamic study indicated that Cd²⁺ adsorption is dominated by chemisorption. This study showed that microbial aging process is an effective and promising measure to improve hydrochar adsorption capacity for Cd²⁺.

Responses of Periphyton Microbial Growth, Activity, and Pollutant Removal Efficiency to Cu Exposure

Periphyton is an effective matrix for the removal of pollutants in wastewater and has been considered a promising method of bioremediation. However, it still needs to be verified whether periphyton can maintain microbial activity and pollutant removal efficiency when dealing with the influence with complex components, and the underlying mechanisms of periphyton need to be revealed further. Herein, this study investigated the microbial growth, activity and functional responses of periphyton after removal of Cu from wastewater. Results showed that the cultivated periphyton was dominated by filamentous algae, and high Cu removal efficiencies by periphyton were obtained after 108 h treatments. Although 2 mg/L Cu²⁺ changed the microalgal growth (decreasing the contents of total chlorophyll-a (Chla), the carbon source utilization and microbial metabolic activity in periphyton were not significantly affected and even increased by 2 mg/L Cu²⁺. Moreover, chemical oxygen demand (COD) removal rates were sustained after 0.5 and 2 mg/L Cu²⁺ treatments. Our work showed that periphyton had strong tolerance and resistance on Cu stress and is environmentally friendly in dealing with wastewater containing heavy metals, as the microbial functions in pollutant removal could be maintained.