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Agricultural wastes are inexpensive materials for soil remediation. However, the direct water extracts from these wastes showed low efficiency for Pb removal, thus limiting their application. In this study, citrus pericarp (CP) and pineapple peel (PP), as the common agricultural wastes, were inoculated with lactic acid bacteria to produce fermentation liquors (FCP and FPP) for improving Pb removal efficiency. Results showed that the Pb removal rates by FCP and FPP reached 37.3 and 43.6%, and increased by almost 50.0% than those by CP and PP. The ecological risk of Pb reduced by 83.0-88.2% after five times continuous washing with FCP and FPP, and the Pb concentrations conformed to soil remediation standard of China. Moreover, soil organic carbon 1.5 times increased in the washed soils, while total potassium improved by 40.7-68.0%. The mechanisms of Pb removal by these wastes involved in adsorption-desorption of Pb

Utilization of allelochemicals to inhibit overgrowth of toxic cyanobacteria is considered to be an environmentally friendly approach. However, the regulatory role of the signaling molecule nitric oxide (NO) on cyanobacteria under allelopathic stress remains unanswered. Here we demonstrate that the effect of NO on the cyanobacterium Microcystis aeruginosa depends on allelopathic stress of pyrogallic acid (PA). The experimental results revealed that general stimulation of M. aeruginosa by PA occurred within the concentration range 0.4-0.8 mg/L. In parallel with increasing concentration of PA (1.6-16.0 mg/L), the growth of M. aeruginosa was observed to decrease. The effect of NO on M. aeruginosa was evaluated by addition of the NO scavenger hemoglobin. In the stimulation stage, intracellular NO was seen to decreased to modulate the level of reactive oxygen species (ROS) and to maintain redox homeostasis of the cells. In the inhibition stage, the physiological characteristics of M. aeruginosa were changed significantly. Additionally, the accumulation of S-nitrosothiol by M. aeruginosa indicated that the high concentrations of PA induced nitric oxidative stress in M. aeruginosa. This study provides a new thought to understand the role of NO in controlling harmful algal blooms through the allelopathic effect of aquatic macrophytes.

The application of modified clay is an effective and common method to control harmful algal blooms (HABs), but the impact on benthic organisms caused by the settlement of clay–algae flocs (CAFs) should also be considered. In this study, a simulation experiment was carried out to investigate the responses of antioxidant enzyme activities and the accumulation dynamics of microcystins (MCs) in Corbicula fluminea to CAFs after migrating HABs to the sediment surface via chitosan-modified clay. We collected sediments, C. fluminea, algal cells, and lake water from Sancha Lake in Sichuan in June 2020. We simulated four treatments in the experiment—a control treatment, a modified clay treatment, an algal cells treatment to simulate the natural deposition of algae, and a modified clay with algal cells treatment. Then, each treatment was quickly stirred for 3 min (100 r min−1), and then slowly stirred for 20 min (30 r min−1). Water and sediments samples were taken at 3, 7, and 15 days to determine the chlorophyll-a and MCs, and C. fluminea samples were collected to analyze the MC content and antioxidant enzyme activity and malondialdehyde content. One-way ANOVA was used to identify the differences between each treatment. Results showed that the enzyme activities of catalase, glutathione reductase, glutathione peroxidase and superoxide, and superoxide dismutase in the controlling HABs treatment were significantly lower at the end of the experiment compared with the control and the other two treatments—namely, clay only, and algal cells only—while the malondialdehyde content was significantly higher than in the other three treatments, indicating that deposition of CAFs resulted in oxidative damage in C. fluminea. Moreover, a significant increase in MCs in sediments and C. fluminea was also found after deposition of CAFs at 7 and 15 days, which represents a disadvantage of applying modified clay to control HABs. This study shows that the application of chitosan-modified clay to control HABs can result in the reduction of antioxidant enzyme activities in C. fluminea, ultimately leading to their death with a mortality rate significantly higher compared with the control. Moreover, an accumulation trend of MCs in C. fluminea was also found in the HABs control treatment.

Cd is a heavy metal that contaminates soils. These kinds of heavy metals pose a serious threat to food security, ecosystems, and human health. To improve the phytoremediation efficiency of moderately Cd-contaminated cropland soils and achieve simultaneous production and remediation, intercropping ryegrass (Lolium perenne L.) with hollyhock (Althaea rosea) was investigated using pot experiments, and Bacillus thuringiensis (B. thuringiensis) inoculation was used as a booster to strengthen the absorption and accumulation of Cd in plants. The results showed that intercropping (Int treatment) decreased the Cd concentration in plants compared to hollyhock and ryegrass monocropping. However, the Cd accumulation in ryegrass and hollyhock was promoted by B. thuringiensis addition to intercropping (Int-B treatment), as the biomass of ryegrass and hollyhock was 2.33 and 1.13 times that of the Int treatment, respectively. Compared with the Int treatment, the total Cd concentration in soils of the Int-B treatment decreased by 8.1%, while diethylenetriaminepentaacetic acid solution extracted Cd (DTPA-Cd) increased by 18.2%, indicating that B. thuringiensis increases the available Cd concentration in soils to promote Cd adsorption by hollyhock enrichment plants. High-throughput sequencing results further revealed that the dominant microflora in the soils of the Int and Int-B treatments were consistent with the control, although their abundance and diversity decreased slightly. Overall, intercropping with B. thuringiensis addition effectively increased the hollyhock remediation efficiency in moderately Cd-contaminated soils, and the concentration of Cd in forage crops of ryegrass was lower than the limit value of "Hygienic standards for feeds' (GB 13078-2017) in China.

Microplastics (MPs) have attracted widespread attention as an organic class of pollutants as well as pollutant carriers in recipient aquatic ecosystems. In this study, tetracycline (TC) adsorption by polystyrene (PS), with multiple aging-based temporal changes in the adsorption mechanism, was observed. The results revealed that the pseudo-second-order model accurately predicted the TC adsorption kinetics for different types of PS. In addition, the isothermal adsorption processes fit the Freundlich model; however, their interactions were drastically weakened at lower temperatures or increasing salinities. Corresponding to the electrostatic interactions, adsorption TC was largely pH-dependent, with the maximum adsorbed TC content on the PS surface at a pH of 5 in an aqueous environment. More importantly, mechanistic studies have revealed that, compared to virgin PS, TC complexes with aged PS are principally controlled by hydrogen bonding and ionic interactions, followed by π-π, polar-polar, and van der Waals interactions. These findings will aid in understanding the insights of TC and aged PS interactions and the underlying interactive molecular forces, which will be advantageous for comprehending the real case scenario of inter-pollutant interactions and related environmental pollution.

The direct discharge of urine into water bodies leads to environmental pollution, and an increase in the water treatment cost, whereas recycling of the nutrients in urine is of significant economic value. A single-compartment reactor was investigated for the recycling of phosphate and simultaneous removal of nitrogen from urine wastewater by electrochemical magnesium induction, and electrochemical oxidation for the removal of residual nitrogen from the supernatant. The results demonstrated that phosphate recovery capacity was greater than 11 mg P cm−2 h−1 at a current density of 15 m A cm−2 and anodizing time of 20 min; the removal rates of ammonium and total nitrogen in the synchronous electrochemical oxidation were 80% and 75%, respectively, at a current density of 45 m A cm−2 and anodizing time of 60 min. The anodizing time and initial pH were determined to be critical control factors in the electrochemical struvite induction and nitrogen electrochemical oxidation. The on-site electrochemical nitrogen oxidation could rapidly utilize the alkaline supernatant following phosphate recovery. Thus, the integration of the single-compartment reactor, electrochemical magnesium dosage, and simultaneous nitrogen electrochemical oxidation demonstrates potential for application to decentralized reactors to treat source-separated urine.

The iron (Fe) cycle in the rice-soil system affects arsenic (As) uptake by rice. The effect of Fe on As uptake can be influenced by the addition of biochar, but has not been thoroughly investigated. In this study, the effects of maize straw-derived biochar (MB) on Fe and As translocation were determined by analysing the Fe and As concentrations in pore water, dithionite-citrate-bicarbonate (DCB) extracts, and rice plants. As-contaminated soils were supplemented with 0 or 1% biochar and 0 or 90 mg kg−1 P, and rice plants were grown for 70 d. Results indicated that biochar addition increased the concentrations of Fe and As in pore water, while P did not affect them. Additionally, biochar promoted the accumulation of Fe and As in roots. However, the rice biomass increased by 28% upon biochar addition, indicating that the rice plants became more tolerant to As toxicity with biochar. Specifically, biochar increased the root triphenyl tetrazolium chloride (TTC) reductive intensity, reduced the root H2O2 concentration, and promoted iron plaque (IP) formation. Moreover, the positive correlation between IP/DCB-extractable As and crystalline Fe on the rice root surface indicated that crystalline Fe appeared to be the determinant species of IP and played a central role in As segregation. In addition, biochar increased both crystalline Fe formation on the root surface and the Fe content in the cell wall, which enhanced As sequestration. Overall, rice could effectively tolerate As stress under biochar treatment since As could be retained on the root surface and root cell wall with MB.

Large amounts of microplastics can accumulate in wastewater treatment plants (WWTPs), and sludge disposal is suspected to be a major source of microplastics pollution in the environment. It is therefore important to investigate the distribution of microplastics in the sludge of each processing unit of WWTPs. However, little information is available on this topic in China. Accordingly, in this study, the abundance and characteristics of microplastics in the sludge of two WWTPs in Chengdu were investigated. The abundance of microplastics in the sludge samples ranged from 44.4 n·kg−1 to 750.0 n·kg−1. Microplastics were mainly divided into particles (32.16%), debris (28.14%) and fibers (17.08%) according to their shape, and the colors of the microplastics were mainly green (35.19%) and translucent (18.06%). The particle sizes were mainly larger than 1 mm in dimension. Polyethylene, polypropylene and polystyrene were the prevalent types of microplastics analyzed. Our results provide basic information for better understanding the characteristics of microplastics in sludge and for improving sludge treatment.

Water composite pollution is still a great challenge in the field of water treatment. Especially for microplastic (MP), as an emerging pollutant, its wide distribution in water and persistent eco-environmental influence have received great concerns in recent years. Nevertheless, the removal characteristics and mechanism of conventional coagulation on MP composite pollution is quite insufficient. In this study, the coagulation removal performance and mechanisms of MP (polyethylene, PE) and norfloxacin (NOR) was investigated by polyaluminium chloride (PAC) and anionic polyacrylamide (APAM). Compared with single system, the removal efficiency of PE was significantly improved (99.0%) under plateau stage in composite system, while the removal efficiency of NOR was slightly decreased to around 42% regardless of the addition of APAM. The scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), zeta potential and One-way analysis of variance (ANOVA) of experimental data were used to explore the coagulation mechanisms. The results demonstrated that the removal of individual PE and NOR was mainly controlled by charge neutralization and sweep flocculation by PAC and APAM, and adsorption by formation of Al-NOR complex, respectively. Importantly, in composite system, the removal of PE was enhanced not only by the stronger charge neutralization but also the adsorption via the formation of PE-NOR-Al complex. Furthermore, the removal efficiency of PE and NOR in neutral and weak alkaline conditions was higher than that in weak acidic or strong alkaline conditions. The presence of metal ions and humic acid had obvious inhibition and promoting effects on the removal efficiency of PE and NOR. This study can provide a new perspective on fundamental understanding in characteristics and mechanisms of MP composite pollutants removed by coagulation.

Controlling the release of phosphorus (P) in sediments is important to prevent eutrophication and harmful algal blooms in water bodies. Here we explored the effect of mobile aerators on the control of P release from sediments in a eutrophic pond. The dissolved oxygen in the water body recovered significantly after six months of aeration, becoming 4.2–5.8 times higher than in the control. The pH and Eh values at the sediment–water interface considerably increased, while the concentration of soluble reactive phosphorus (SRP) in pore water significantly decreased, resulting in the alteration of SRP fluxes from 1.69 mg/m2 d to −53.49 mg/m2 d. Moreover, the inert P in sediments increased by 5.2% of the total P at the end of the study compared with the initial state, and the calcium-bound phosphorus (HCl–P) increased by 96.6%. However, although aeration reduced the concentration of SRP in the water column, the total P concentration was 2.45 times higher than that of the control, and the content of redox-sensitive P (BD-P) in the sediment also increased by 200%. Overall, although mobile aeration can maintain the microenvironment of the sediment interface and increase the inert P content in the sediment to reduce the P flux, it cannot reduce the risk of release of mobile P.

Soil washing with environmentally friendly eluents is a rapid remediation technique for farmland polluted by heavy metals. In this study, polyepoxysuccinic acid (PESA), ethylenediamine tetra (methylene phosphonic acid) sodium (EDTMPS), and phosphonyl carboxylic acid copolymer (POCA) were applied to remedy paddy and arid soils polluted by Pb and Cd. At the same time, ethylenediaminetetraacetic acid (EDTA) was used as a control eluent. PESA showed comparable removal of soil Pb and Cd (over 80.0%) with EDTA, and EDTMPS and POCA removed two heavy metals by 35.2-50.3%. For labile fractions, PESA significantly removed Pb by 93.5-96.7% and Cd by 84.9-90.3% in two soils. EDTMPS and POCA removed Pb by 75.5-85.8% in two soils, while they only removed Cd by 11.7-42.2% in paddy soil, and 76.3-81.7% in arid soil. The risks of total heavy metal concentrations were reduced from the high risk to low risk in paddy soil, and to considerable risk in arid soil, while only dropped to considerable or even had no change by EDTMPS and POCA leaching. The risks of the two soils reduced from high to low or considerable level after PESA washing based on labile fraction change, and to considerable or high level after EDTMPS and POCA leaching, respectively. Therefore, PESA is an ecological benefit eluent for remediating the farmland polluted by heavy metals, and the risk assessment based on labile fraction more easily identifies the dynamic change of heavy metal during the washing process.

As a multifunctional material, biochar is considered a potential adsorbent for removing heavy metals from wastewater. Most biochars with high adsorption capacities have been modified, but this modification is uneconomical, and modifying biochar may cause secondary pollution. Thus, it is necessary to develop an efficient biochar without modification. In this study, spent P. ostreatus substrate and spent shiitake substrate were used as the raw materials to prepare biochar. Then, the physicochemical properties of the biochars and their removal efficiencies for Pb(II) were investigated. The results showed that the physicochemical properties (e.g., large BET surface area, small pore structure and abundant functional groups) contributed to the large adsorption capacity for Pb(II); the maximum adsorption capacities were 326 mg g−1 (spent P. ostreatus substrate-derived biochar) and 398 mg g−1 (spent shiitake substrate-derived biochar), which are 1.6–10 times larger than those of other modified biochars. The Pb(II) adsorption data could be well described by the pseudo-second-order kinetic model and the Langmuir model. This study provides a new method to comprehensively utilize spent mushroom substrates for the sustainable development of the edible mushroom industry.

A novel electrocatalytic anode (ECA)/α-MnO2/peroxymonosulfate (PMS) synergistic system was developed and evaluated for the removal of combined tetracycline (TC) and hexavalent chromium (Cr(VI)) pollution from waste waters. The factors affecting the efficiency of the removal of the combined pollutants, such as the synthesis time of the electrode, the amounts of raw materials, the PMS dose, the voltage, the initial pH and the coexisting ions were investigated. The breakdown products of PMS in the ECA/α-MnO2/PMS system improved the conductivity of the solution and the electrical current promoted the conversion of the valence state of Mn ions, resulting in a synergistic effect between the ECA and PMS activation processes, which improved the efficiency of removal of TC. The cathode chamber was fully utilized to simultaneously reduce Cr(VI). Synergistic effects occur in the ECA/α-MnO2/PMS system in appropriate ranges of the voltage or PMS dose, although the efficiency of the removal of TC depends mainly on the electrical current in the system. Both hydroxyl (•OH) and sulfate (SO4•−) radicals played important parts in the degradation of TC. The main degradation products of TC were identified and degradation pathways proposed. The synergistic effects between the ECA process and a Fenton-like process was studied, providing a new approach for the study of electro-Fenton technology and the removal of combinations of TC and Cr(VI) from waste waters.

Heavy metals (e.g., arsenic (As)) and tetracycline (TC) usually coexist in wastewater from livestock farm, whereas the co-adsorption behaviours and mechanisms of As(V) and TC were not well-known. This study investigated the adsorption and co-adsorption of As(V) and TC by a novel yttrium-immobilized-graphene oxide-alginate hydrogel (Y-GO-SA) to explore the adsorption behaviours and mechanisms. The adsorption of As(V) and TC was pH-dependent. The maximum adsorption capacities under the studied concentrations were 273.39 mg/g for As(V), and 477.9 mg/g for TC, respectively, which are much higher than many other reported adsorbents. Furthermore, As(V) adsorption was due to ion exchange between hydroxyl groups and H2AsO42− groups and H-bonds formed with O-containing groups on Y-GO-SA, and the adsorption of TC by Y-GO-SA was mainly ascribed to electrostatic interaction, H-bonds, π − π EDA interaction, n-π EDA interaction, and cation-bonding bridge effects. The co-adsorption of As(V) and TC in binary system indicated that the presence of TC obviously suppressed the adsorption of As(V) due to the competition for active sites, whereas the effect of presence of As(V) on adsorption of TC can be negligible due to the balance contributions from its contrary effects, i.e. enhancement (anion-π interaction) and reduction (competition for Y ions) in TC adsorption. Finally, the hydrogels performed well in the treatment of livestock farm waste water. It can be anticipated that the prepared 3D hydrogel can be used as a powerful adsorbent in the practical application of waste water treatment, owing to its easy separation, high adsorption and good reusability.

Colored photonic TiO2 photoelectrodes have been prepared by a simple anodizing-annealing method. Traditionally, the photoelectrocatalytic (PEC) properties of the film are obtained by measuring the actual decomposition of organic pollutants under ultraviolet or visible light, which may take tens of minutes or even hours. Here, through the combined analysis of the apparent features and PEC properties, we found that the structure would affect the color and optical performance, and the films with different colors showed different PEC performance. Interestingly, after repeated verifications, we got a rule that the PEC performance of the TiO2 films decreased in the order with typical color of yellow, blue-green, dark yellow, blue, yellow-grey, and purple. Therefore, we provide a new idea for the visualization screening of PEC performance for the film photoelectrodes, that is, color can be used as a quick selection indicator for TiO2 films.

Nanocomposite adsorptive membranes with nanosorbents incorporated have become a promising material for the treatment of heavy metal-containing water, but their practical applications have been limited by the aggregation of nanosorbents in the membrane matrix. In this study, a homogenous in-situ generated ferrihydrite nanoparticles (NPs)/polyethersulfone (PES) adsorptive membrane was prepared for the removal of lead from water for the first time. The XRD, TEM and XPS results showed that ferrihydrite particles with the size smaller than 10 nm were successfully introduced into the composite membrane. The SEM-EDS result indicated a homogenous distribution of the in-situ generated ferrihydrite NPs in PES membrane. With more generated NPs, the membrane structure varied from a larger finger-like macro-void structure (i.e. M3, M6) to a suppressed finger-liker macro-void structure, due to the contributions of viscosity hindrance and thermodynamic enhancement to the demixing rate. Besides, the surface hydrophilicity and water flux increased gradually. The membrane M9 was stable for treating lead-contaminated water at pH above 3.0, with the optimal adsorption pH at 5.5. Furthermore, the M9 displayed the highest adsorption capacity of Pb2+ of 64.77 mg/g, high selectivity toward Pb2+, and excellent reusability without significant loss of adsorption of Pb2+. In filtration process, the M9 can effectively remove Pb2+ mainly by adsorption via cation exchange between Pb2+ and H+ in the presence of ferrihydrite NPs in membrane. More importantly, the presence of humic acid can significantly enhance Pb2+ removal by M9 via adsorption and size exclusion mechanisms (caused by either chelation with HA or barrier effect caused by HA filter cake). Therefore, the present nanocomposite adsorptive membrane can be used as a promising material for treatment of heavy metal-containing water.

Iron (Fe) dissimilatory reduction might impact chromium (Cr) mobility in the rice rhizosphere, but it is poorly understood. We assessed rhizosphere microbes' role in Cr immobilization and bioavailability by conducting the pot experiment to test different biochar sources (PMB - pig manure and PSB - pine sawdust) and phosphorus (P) levels impact on Cr mobility. Results showed that PMB application increased root biomass (23-65 %) and decreased root Cr concentration (46-74 %) regardless P treatment. However, P addition reduced root and shoot biomass in control and PMB treatments by 33-43 % and 25-26 %. Therefore, low P input is recommended in Cr-contaminated soil. Moreover, Geobacter was the key microbial groups which may be involved in promoting Cr release by increasing Fe dissolution. Finally, Geobacter and Fe dissimilatory reduction play a central role in Cr translocation and they should be considered in strategies to reduce rice Cr uptake by biochar application.

In order to seek a possible path for utilization bottom ash, the solid waste from biomass incineration for power generation, its basic characteristics were investigated, and removing methylene blue (MB) from aqueous solution was attempted as well. Results indicated bottom ash dominantly contained Si and Ca-related minerals with >35 mineral elements, meanwhile, it was typically characterized by alkalinity (pH of 9.5) and low specific surface area (14.5m2/g). As the only bottom ash was employed for removing MB, removal efficiency was lower than 44%, however, it was greatly improved to 100% as hydrogen peroxide was supplemented (final concentration of 4.0%). Based on the elucidated mechanisms, Fenton-like reaction was triggered by bottom ash, which was dominantly responsible for removing MB, rather than the adsorption by bottom ash. Besides, increasing reaction temperature and duration dramatically promoted MB removal by bottom ash with the aid of hydrogen peroxide (HBA). A great promotion on MB removal from 92.3mg/g to 143.9mg/g was achieved as pH was adjusted from 2.0 to 5.0, indicating MB removal was pH-dependent. The maximum removal of 260.9mg/g was achieved by HBA at a relatively high initial MB concentration of 2000.0mg/L, suggesting a great potential in treating dye wastewater by functionalizing bottom ash with the aid of hydrogen peroxide. Moreover, the released heavy metals and derived by-products from MB removal were acceptable in consideration of their potential environmental risks. Thus, the current work offers a new path to valorize the solid waste in biomass electricity generation plant.