The biochemical response of willow plants (Salix viminalis L.) to the use of sewage sludge from various sizes of wastewater treatment plant

Study on the synergistic mechanism of proline in the treatment of high-salt phenolic wastewater by short-time aerobic digestion process

High salt concentrations pose a significant challenge to the efficiency of activated sludge (AS) in phenolic wastewater treatment. As a cellular osmoprotectant, proline (Pro) has the capacity to increase the salt tolerance of microbes in AS, hence improving the efficiency of phenolic wastewater degradation. Nevertheless, the precise mechanism behind this enhancement remains ambiguous. This study utilized short-time aerobic digestion (STAD) to examine the kinetics of phenol degradation (250-750 mg/L) by AS under high-salinity stress (2-8%), with the inclusion of Pro (115-575 mg/L) as an auxiliary agent. The process was optimized via response surface methodology (RSM), and the mitigating effect of Pro on microorganisms in AS subjected to salt stress was evaluated. The results demonstrated that the addition of 468 mg/L Pro substantially improved the ability of AS to withstand high-salinity wastewater with high phenol concentrations, which had a salinity of 5.1% and a phenol concentration of 531 mg/L. The addition led to a mitigation rate of the phenol degradation constant k0 of 38.59 ± 1.54%, resulting in enhanced degradation of chemical oxygen demand (COD), NH4+-N, and NO3--N. In addition, the prolonged presence of Pro increased AS dehydrogenase activity (DHA) by 24.82% after 30 days. Microbial community analysis demonstrated that Pro promoted the proliferation of functional microorganisms such as Proteobacteria, Firmicutes, Acinetobacter, and Comamonas. These bacteria have essential functions in the elimination of phenol and organic matter, as well as the absorption of nitrogen. This study emphasizes the impact of Pro as a compatible solute in the treatment of high-salinity and high-phenol wastewater in the STAD process.

Assessing the quality of sewage sludge: CASE study of the Kumasi wastewater treatment plant

Agricultural application is the primary method of recycling sewage sludge. It is an alternative for recycling this residue, providing nutrients and organic matter to crops and soil. However, sewage treatment and management issues may impact its quality. The main objective of the research was to determine the quality of sewage sludge generated at the Kumasi Wastewater Treatment Plant (KWTP). Understanding the effects of using sludge on soil and plants is critical. To overcome this constraint, the soil microbial biomass was used to quantify the growth of microorganisms. The levels of potentially toxic elements in the sludge using atomic absorption spectrometry (AAS) are based on US EPA part 503 regulations for the disposal and management of biosolids. This study found that trace metal concentrations in the biosolids were lower than the referenced background standards threshold. Although the microbial biomass, nutrients and bacteria levels were within the accepted values for their possible use as soil fertilizer. The ecological risk index (135.10) indicated that the level of arsenic was high in the sludge. The salinity in the sludge was low, with electrical conductivity (EC) being high (60.80-436.00 μS/cm) and pH decreasing with age (6.73-7.69). The sludge produced at KWTP is of good quality and meets international standards with only a high concentration of As. This can be used for soil amendment when As is reduced in the sludge.

Probing the molecular mechanism of interaction between polystyrene nanoplastics and catalase by multispectroscopic techniques

Nanoplastics are emerging pollutants that pose a potential threat to the environment and organisms and are widely distributed in environmental samples and food chains. The accumulation of polystyrene nanoplastics (PS-NPs) in an organism can cause oxidative stress. Currently, toxicity studies of PS-NPs mainly focus on the individual and cellular levels, whereas few studies have been conducted on the molecular mechanisms of the interaction between PS-NPs and catalase (CAT). Based on this, CAT was chosen as the target receptor for molecular toxicity research to reveal the interaction mechanism at the molecular level between PS-NPs and CAT by using various spectroscopic means and enzyme activity detection methods. The results indicated that PS-NPs destroyed the secondary structure of CAT, causing its protein skeleton to loosen and unfold, increasing the content of α-helices, decreasing the content of β-sheets, and exposing the position of the heme group. After exposure to PS-NPs, the internal fluorophore of CAT underwent fluorescence sensitization, resulting in a micelle-like structure, which enhanced the hydrophobicity of aromatic amino acids but did not change their polarity. In addition, the aggregation state of CAT was altered upon binding to PS-NPs, and the volume was further increased. Finally, these structural changes led to a gradual decrease in CAT activity. This study presents a comprehensive assessment of the toxicity of PS-NPs at the molecular level, which can provide more experimental support for the study of the biotoxicological efficacy of PS-NPs.

Halophytes for the sustainable remediation of heavy metal-contaminated sites: Recent developments and future perspectives

Increasing land degradation by high level of metal wastes is of prime concern for the global research communities. In this respect, halophytes having specific features like salt glands, exclusion of excess ions, heavy metals (HMs) compartmentalization, large pool of antioxidants, and associations with metal-tolerant microbes are of great promise in the sustainable clean-up of contaminated sites. However, sustainable clean-up of HMs by a particular halophyte plant species is governed considerably by physico-chemical characteristics of soil and associated microbial communities. The present review has shed light on the superiority of halophytes over non-halophytes, mechanisms of metal-remediation, recent developments and future perspectives pertaining to the utilization of halophytes in management of HM-contaminated sites with the aid of bibliometric analysis. The results revealed that the research field is receiving considerable attention in the last 5-10 years by publishing ∼50-90% documents with an annual growth rate of 15.41% and citations per document of 29.72. Asian (viz., China, India, and Pakistan) and European (viz., Spain, Portugal, Belgium, Argentina) countries have been emerged as the major regions conducting and publishing extensive research on this topic. The investigations conducted both under in vitro and field conditions have reflected the inherent potential of halophyte as sustainable research tool for successfully restoring the HM-contaminated sites. The findings revealed that the microbial association with halophytes under different challenging conditions is a win-win approach for metal remediation. Therefore, exploration of new halophyte species and associated microorganisms (endophytic and rhizospheric) from different geographical locations, and identification of genes conferring tolerance and phytoremediation of metal contaminants would further advance the intervention of halophytes for sustainable ecological restoration.

Sidestream materials show potential as top-dressed soil improvers for peatland forests

The effects of top-dressing of several industrial and farming sidestream materials on the growth of downy birch (Betula pubescens Ehrh.) and Scots pine (Pinus sylvestris L.) seedlings in natural sphagnum peat soil were evaluated. Wood fly ash, industrial filter cake waste, mine tailings sand (quartz feldspar from lithium orebody), and digestate and liquid reject of cow manure from a biogas plant were studied for their physical and chemical properties, as well as for their effects as soil ameliorants on seedling growth during one growing period in a greenhouse. Each material was top-dressed on unfertilised peat in pots in quantities that corresponded to the amounts of ash used in Finnish peatland forest fertilisation (2-6 t ha^-1). During growing, the pH of percolate water from the growing pots was below 4, and in the treatments with filter cake even below 3. However, no clear impairment of seedling growth due to acidity was observed. In all treatments, birch and pine seedlings grew at least as well as in the unfertilised peat (control treatment). Growth was strongest in the peat top-dressed with additives originating from cow manure, in which the high N and P contents promoted growth so much that foliar N was found to be diluted with respect to a high P content in the birch seedlings. No harmful concentrations of heavy metal residues were observed from the materials used. Overall, the results suggest that all the used sidestream materials show potential as soil improvers on forested peatlands.

Antimony speciation, phytochelatin stimulation and toxicity in plants

Antimony (Sb) is a toxic metalloid that has been listed as a priority pollutant. The environmental impacts of Sb have recently attracted attention, but its phytotoxicity and biological transformation remain poorly understood. In this study, Sb speciation and transformation in plant roots was quantified by Sb K-edge X-ray absorption spectroscopy. In addition, the phytotoxicity of antimonate (Sb^V) on six plant species was assessed by measuring plant photosynthesis, growth, and phytochelatin production induced by Sb^V. Linear combination fitting of the Sb K-edge X-ray absorption near-edge structure (XANES) spectra indicated reduction of Sb^V was limited to ∼5-33% of Sb. The data confirmed that Sb-polygalacturonic acid was the predominant chemical form in all plant species (up to 95%), indicating Sb was primarily bound to the cell walls of plant roots. Shell fitting of Sb K-edge X-ray absorption fine-structure (EXAFS) spectra confirmed Sb-O and Sb-C were the dominant scattering paths. The fitting indicated that Sb^V was bound to hydroxyl functional groups of cell walls, via development of a local coordination environment analogous to Sb-polygalacturonic acid. This is the first study to demonstrate the key role of plant cell walls in Sb metabolism.

Evaluation of cytotoxicity and genotoxicity effects of refractory pollutants of untreated and biomethanated distillery effluent using Allium cepa

Environmental pollution caused by the discharge of raw and partly treated distillery effluent has become a serious and threatening problem due to its high pollution load. The aim of the present study was to assess the physicochemical load in alcohol distillery effluent before and after biomethanation treatment and the cyto- and genotoxicity effects of refractory pollutants emanated in raw/untreated and biomethanated distillery effluent on the ultrastructural and biochemical responses of Allium cepa root tip cells. Physicochemical analysis revealed high biochemical oxygen demand (BOD: 47840-36651 mg L^-1), chemical oxygen demand (COD: 93452-84500 mg L^-1) and total dissolved solids (TDS: 64251-74652 mg L^-1) in raw and biomethanated effluent along with metal(loid)s (Fe: 456.152-346.26; Zn: 1.654-1.465; Cu: 0.648-0.562; Ni: 1.012-0.951, and Pb: 0.264 mg L^-1) which were beyond the safe discharge values prescribed by the environmental regulatory agencies. The UV-Visible and Fourier transform infrared spectrophotometry analyses confirmed the high levels of organic, inorganic, and mixed contaminants discharged in raw and biomethanated distillery effluents. Furthermore, GC-MS analysis characterised chemical contaminants, such as hexadecanoic acid, butanedioic acid, bis(trimethylsilyl) ester; hexadecane, 2,6,11,15-tetramethyl, stigmasterol, and β-sitosterol trimethylsilyl ether that have been reported as androgenic-mutagenic, and endocrine disrupting chemicals by the United States Environmental Protection Agency (U.S. EPA). The cytotoxicity measured by A. cepa showed dose depended inhibition root growth inhibition and simultaneous reduction in mitotic index in tested effluents. The chromosomal aberrations studies resulted in laggard chromosomes, sticky chromosomes, vagrant chromosomes, chromosome loss, c-mitosis, chromosome bridge, abnormal metaphase, and disturbed anaphase as found in a dose-dependent manner. Furthermore, dose-dependent enhancement in the levels of malondialdehyde, hydrogen peroxide, and antioxidative enzymes, such as superoxide dismutase, ascorbate peroxidase, and catalase were found to be higher in raw effluents treated root cells compared to biomethanated distillery effluent. Analysis of ultrastructural changes in root tip cells by TEM analysis revealed dramatic changes in the morphology of cell organelles and accumulation of metallic elements in and on the surface tissues. The results concluded that the discharged distillery effluents retained certain toxic pollutants which imposed cytotoxic and genotoxic hazards to A. cepa. Thus, for the sake of environmental protection, the raw as well as the disposed biomethanated effluent must be efficiently treated before its dumping into the terrestrial ecosystem.

Combined effect of tetracycline and copper ion on catalase activity of microorganisms during the biological phosphorus removal

Microbial catalase is a key enzyme that affects the activities of microorganisms, and the catalase activity is affected by pollutants in wastewater. However, the effects of mixed pollutants on catalase activity are rather complex. To reveal the effect of the mixed pollutants on catalase activity of microorganisms, the present study investigated tetracycline and copper ion as pollutants during the biological phosphorus removal. Three concentration ratios of tetracycline and copper ion and 27 different concentration gradients were designed through the direct equipartition ray and the dilution factor method. The effects of mixed pollutants on the catalase activity of microorganisms were analyzed by the nonlinear regression equation and concentration-addition model. The results showed that, with the increase of actuation duration and the pollutant concentration, the inhibitory effects on the catalase activity of microorganisms obviously increased, which indicated that the inhibitory effects are concentration-dependent and time-dependent. The concentration-addition model suggested that when the ratio was 0.297, the combined effect of mixed pollutants on the activity of microbial catalase was mainly antagonism. When the ratio is 0.894, the combined effect was mainly additivity. When the ratio was 2.676, the combined effect transformed from synergism to additivity and antagonism. The study of the combined effects of tetracycline and copper ion on the catalase activity is helpful to further study their ecotoxicological mechanisms in wastewater treatment.

Value-added products from wastewater reduce irrigation needs of Arundo donax energy crop

Irrigation restrictions due to drought periods related to climate change, would affect different crops, especially to non-food crops. In this regard the effect of irrigation reduction should be studied in energy crops in order to obtain a sustainable bioenergy cropping system. Arundo donax, has been considered a crop with high water requirements, it has nevertheless been proven to be drought tolerant. However, there is a lack of knowledge on the effect of reduced irrigation combined with the use of different fertilizers. This work studied the combined effect of value-added products (VAPs) from wastewater (treated sewage sludge) or traditional inorganic fertilizers, and irrigation reduction in Arundo donax crop in a 2-year pot experiment. Plant biometric characteristics, chemical properties and biomass yield were studied as well as the effect of treatment on soil properties. Results showed that under reduced irrigation conditions, biomass production was reduced, especially during the second year. Organic treatments from sewage sludge minimize the effect of irrigation reduction. In these treatments, biomass yield for reduced irrigation was similar to that of the control treatment with irrigation at field capacity. For this reason, it is recommended to use VAPs from wastewater as organic amendments enabling water restriction with lower effect on Arundo production.

Biochar Derived from Domestic Sewage Sludge: Influence of Temperature Pyrolysis on Biochars’ Chemical Properties and Phytotoxicity

The pyrolytic conversion of domestic sewage sludge (SS) into biochar is a promising method to reduce its large volume and recycle its high-value fuel gas as renewable energy and the use of its chemicals as soil fertilizers. Even though the effects of pyrolysis temperature on energy recovery have been extensively studied, little information has been found on nutrient recovery and biochar’s phytotoxicity before its reuse as a soil amendment. This study aims to investigate the ideal pyrolysis temperature that guarantees higher fertility levels as well as meeting quality standards for land disposal. Accordingly, air-dried domestic sewage sludge has been pyrolyzed at 260°C (PSS1), at 420°C (PSS2), and at 610°C (PSS3) with a residence time of 20, 40, and 60 minutes, respectively. The raw sewage sludge and the produced biochars have been analyzed to determine their volatile organic matter (VOM), mineral content (MC), nutrients’ level (total nitrogen TN, available phosphorus P, and potassium K), alkalinity (pH), and salinity (electrical conductivity EC and Na). The toxic effect of biochars derived from SS has been evaluated through the analysis of trace metals (Pb, Cr, Cd, Cu, and Zn) and their toxicity by measuring root elongation inhibition (REI). As expected, pyrolysis temperature has a significant impact on the biochars’ characteristics. This has been justified by higher VOM, TN, and P in the sewage sludge (SS) and the biochar (PSS1) produced at low temperature (260°C). However, higher pH, EC, Na, and K have been found in the biochars (PSS2 and PSS3) produced at higher temperature (420 and 610°C). The effect of pyrolysis temperature on trace metals concentrations has shown different patterns from one element to another, which indicates lower levels in the biochar (PSS2) produced at 420°C. As a result, the lowest REI has been observed in PSS2 compared to that in SS, PSS1, and PSS3, which highlights that 420°C is the ideal pyrolysis temperature for the safe reuse of SS as a soil amendment.

Potential for phytoremediation of nonylphenol from sewage sludge

Nonylphenol (NP) is considered a major contaminant that must be removed to enable safe and environmentally friendly land application of sewage sludge. Phytoremediation is a technology in which plants are used to remove and/or stabilize organic and inorganic contaminants present in the soil, municipal wastewater, and sewage sludge. In this study, a 391-d large pot experiment was conducted to remove NP from sewage sludge by phytoremediation using Zea mays L. 'Yunshi-5', Lolium perenne L., and co-cropping of the two plants. The fate of NP in the soil under the sewage sludge was assessed at the same time. At the end of the experiment, the NP levels in sludge from the various treatments were as follows: control (38.60%) > L. perenne (31.27%) > Z. mays (16.25%) > co-cropping (15.28%). Degradation followed an availability-adjusted first-order kinetics with a decreasing order of half-lives as follows: control (88.2 d) > L. perenne (87.3 d) > co-cropping (66.2 d) > Z. mays (59.1 d). The results indicated that Z. mays and co-cropping could both degrade NP. The concentrations of NP in tissues of different plants differed significantly. The mean bioconcentration factors for Z. mays and L. perenne were 0.16 and 3.69, respectively. Direct removal of NP from sewage sludge by plant uptake was negligible, as was downward movement of NP in the system. Moreover, NP was not detected in soils in any treatments at harvest.

Data-driven prediction and control of wastewater treatment process through the combination of convolutional neural network and recurrent neural network

It is widely believed that effective prediction of wastewater treatment results (WTR) is conducive to precise control of aeration amount in the wastewater treatment process (WTP). Conventional biochemical mechanism-driven approaches are highly dependent on complicated and redundant model parameters, resulting in low efficiency. Besides, sharp increase in business volume of wastewater treatment requires automatic operation technologies for this purpose. Under this background, researchers started to introduce the idea of data mining to model the WTP, in order to automatically predict WTR given inlet conditions and aeration amount. However, existing data-driven approaches for this purpose focus on modelling of the WTP at independent timestamps, neglecting sequential characteristics of timestamps during the long-term treatment process. To tackle the challenge, in this paper, a novel prediction and control framework through combination of convolutional neural network (CNN) and recurrent neural network (RNN) is proposed for prediction of the WTR. Firstly, the CNN model is utilized to automatically extract the local features of each independent timestamp in the WTP and make them encoded. Next, the RNN model is employed to represent global sequential features of the WTP on the basis of local feature encoding. Finally, we conduct a large number of experiments to verify efficiency and stability of the proposed prediction framework.

This work proposes a novel data-driven mechanism for prediction of wastewater treatment results through mixture of two neural network models.

Dissipation of polycyclic aromatic hydrocarbons (PAHs) in soil amended with sewage sludge and sludge compost

In this study, greenhouse experiments were conducted under the condition of different amendment ratios and planting tall fescue (Festuca arundinacea). The amendment ratios of sewage sludge or sludge compost to soil were of 0, 10, 25, and 50% (w/w). The removal rates of PAH, catalase, and dehydrogenase activities of amended soil and accumulation of PAHs by vegetation were detected to investigate the differences of PAH dissipation in sludge-amended and compost-amended soils. The initial PAH concentrations in three amended soils increased with the more addition of sludge or compost. After 126-day experiment, maximum PAH removal rates were observed in sludge-amended and compost-amended soils with PAH concentration of about 200 μg kg^-1. And the removal of PAHs showed better efficiencies in compost soil rather than in sludge soil. The more catalase activity and dehydrogenase activity of soil were obtained, respectively, in sludge soil and compost soil. The results indicated that the mechanism of PAH dissipation in two types of amended soils were different. The abundant amount of microorganism dominated PAH dissipation in sludge soils, and PAHs dissipated mainly caused of intense activity of microorganism in compost soils. In addition, PAH accumulation in tall fescue suggested that the transference approach of PAHs was from soil to the roots, and then accumulated in the shoots of tall fescue. It was prone to store up more PAHs in vegetation in the condition of high molar weight of PAHs, more biomass of vegetation, and heavy PAH concentration in soil.

Evaluation of the environmental and plant growth effectiveness of a new substrate consisting of municipal sludge and fly ash

In order to seek a safe, sustainable, and low-cost method for reuse of municipal sewage sludge, four species of native plants, i.e., Forsythia suspensa, Sophora japonica, Cotinus coggygria, and Ailanthus altissima were planted in flowerpots containing 4 growth substrates consisting of raw sludge and fly ash at volume/volume ratios of 20:80, 40:60, 60:40, and 80:20, respectively. The results showed that the physiochemical characteristics of the sewage sludge and fly ash were complementary. The sludge supplied the nutrients and the fly ash maintained air permeability in the mixed substrate. The mixed substrates containing 40-60% sewage sludge that belonged to sand clay loam were suitable for the seedling growth of the four species. After the end of the growing season, the electrical conductivity, pH, and contents of organic matter, nitrogen, potassium, and heavy metals in the four growth substrates decreased significantly. Moreover, most of the heavy metals were removed from the substrates by seedling root system. A. altissima grew best, and heavy metal enrichments of F. suspense and C. coggygria were stronger than other two species. The results indicate that the new substrates containing 40-60% sludge exhibiting good physiochemical properties, are environmentally friendly, and suitable for landscape planting.

The Influence of Bottom Sediments and Inoculation with Rhizobacterial Inoculants on the Physiological State of Plants Used in Urban Plantings

Bottom sediments accumulate rapidly in urban reservoirs and should be periodically removed. Their high organic matter content makes them valuable fertilizers, but they often contain toxic substances. The present study compares the responses of the dicotyledonous Tagetes patula and monocotyledon Festuca arundinacea to the presence of such sediments in soil and to soil inoculation with two rhizobacterial strains (Massilia niastensis p87 and Streptomyces costaricanus RP92) isolated from contaminated soil. Total soluble protein, total chlorophyll content, as well as chlorophyll a/b ratio, degree of lipid peroxidation (TBARS), α-tocopherol content, total phenolic compounds (TPC) content and anthocyanins content were examined in the leaves of investigated plants. T. patula was more sensitive to the toxic substances in the sediments than F. arundinacea. Rhizobacterial inoculation reduced the toxic effect of the sediment. RP92 has a more favorable effect on the condition of T. patula than p87. F. arundinacea was not adversely affected by the addition of sediments or inoculation with the p87 or RP92 strains. Both tested plant species are suitable for planting on soils enriched with urban sediments, and the addition of bacterial inoculums promote plant growth and reduce the damage caused by the xenobiotics contained in the sediments.

The response of cucumber plants (Cucumis sativus L.) to the application of PCB-contaminated sewage sludge and urban sediment

Background

The increasing production of sewage sludge (SS) engenders the problem of its responsible utilization and disposal. Likewise, urban sediments (SED) are deposited at the bottom of urban reservoirs and sedimentation ponds, and these require periodical dredging and utilization. However, while the SS and SED deposits often contain nutrients such as nitrogen and phosphorus; however, they also contain a variety of hazardous compounds including heavy metals, Persistent Organic Pollutants (POPs) and microbial pollutants. Fortunately, some species of Cucurbitaceae can accumulate high levels of POPs, such as polychlorinated dibenzo-p-dioxins (PCDD), polychlorinated dibenzofurans (PCDF) and polychlorinated biphenyls (PCB), in their tissues.

Methods

SS was collected from the Lodz Municipal Wastewater Treatment Plant and SED from the Sokołówka Sequential Biofiltration System. The SS and SED samples were added to soil in flower pots at three concentrations (1.8 g, 5.4 g and 10.8 g per flower pot), and one pot was left as an unamended control (C). Soil PCB concentrations were determined before cucumber planting, and after five weeks of growth. Also, total soluble protein, total chlorophyll content, chlorophyll a/b ratio and degree of lipid peroxidation (TBARS) were examined in the leaves of the cucumber plants (Cucumis sativus L.) cv. Cezar after five weeks. Antioxidative response was assessed by ascorbate peroxidase (APx) and catalase (CAT) assay.

Results

The initial PCB concentration in soil after application of SS or SED was dependent on the applied dose. After five weeks, PCB concentration fell significantly for all samples and confirmed that the dose of SS/SED had a strong effect. Soil remediation was found to be more effective after SS application. Total soluble protein content in the cucumber leaf tissues was dependent on both the type and the dose of the applied amendments, and increased with greater SS doses in the soil. The total chlorophyll content remained unchanged, and the chlorophyll a/b ratio was slightly elevated only after the application of the highest SS and SED dose. The use of SS and SED did not significantly affect TBARS content. APx activity fell after SS or SED application; however, CAT activity tended to increase, but only in the leaves of plants grown in SS-amended soil.

Discussion

The cultivation of cucumber plants reduces PCB concentration in soil amended with SS or SED; however, this effect is more evident in the case of SS. SS application also induced more intensive changes in the activity of enzymes engaged in antioxidative response and oxidative stress markers in plant tissues than SED. The levels of PCB in the SS may have triggered a more severe imbalance between pro- and antioxidative reactions in plants. Cucumber plants appear to be resistant to the presence of toxic substances in SS and SED, and the addition of SS and SED not only acts as a fertilizer, but also protects against accelerated aging.

Effects of soil amendments on the growth response and phytoextraction capability of a willow variety (S. viminalis × S. schwerinii × S. dasyclados) grown in contaminated soils

This study was conducted to evaluate the effects of lime and bisphosphonates (BPs) such as N10O chelate amendment on the growth, physiological and biochemical parameters, and phytoextraction potential of the willow variety Klara (Salix viminalis × S. schwerinii × S. dasyclados) grown in soils heavily contaminated with copper (Cu), nickel (Ni) and zinc (Zn). The plants were irrigated with tap or processed water (mine wastewater). The results suggest that the combined effects of the contaminated soil and processed water inhibited growth parameters, gas exchange parameters and chlorophyll fluorescence (Fv/Fm) values. In contrast, malondialdehyde (MDA) content, organic acids, total phenolic and total flavonoid contents, and the accumulation of metals/metalloids in the plant tissues were increased compared to the control. When the soil was supplemented with lime and N10O; growth, physiological, biochemical parameters, and resistance capacity were significantly higher compared to unamended soil treatments, especially in the contaminated soil treatments. The combined lime‒ and N10O‒amended soil treatment produced higher growth rates, resistance capacity, photosynthesis rates and phytoextraction efficiency levels relative to either the lime‒amended or the N10O‒amended soil treatments. This study provides practical evidence of the efficient chelate‒assisted phytoextraction capability of Klara and highlights its potential as a viable and inexpensive novel approach for in situ remediation of Cu‒, Ni‒ and Zn‒contaminated soils and mine wastewaters.

Effect of phosphate amendments on improving the fertilizer efficiency and reducing the mobility of heavy metals during sewage sludge composting

Composting has been globally applied as an effective and cost-efficient process to manage and reuse sewage sludge. In the present study, four different phosphates as well as a mixture of ferrous sulfate and monopotassium phosphate were used in sewage sludge composting. The results showed that these phosphate amendments promoted an increase in temperature and the degradation of organic matter as well as reduction on nitrogen loss during 18 days of composting. In addition, ferrous sulfate and phosphate had a synergistic effect on reducing nitrogen loss. The contents of total phosphorus and available phosphorus in the compost with addition of 1% phosphate were 40.9% and 66.1% higher than the compost with control treatment. Using the BCR (Community Bureau of Reference) sequential extraction procedure, the addition of calcium magnesium phosphate significantly reduced the mobility factor of Cd, Zn and Cu by 24.2%, 1.7% and 18.8%, respectively. The mobility factors of Pb were increased in all samples, but the monopotassium phosphate treated sample exhibited the greatest Pb passivation ability with the lowest mobility factor increase (1.8%) among all treatments. The X-ray diffraction patterns of compost samples indicated that the passivation mechanism of Cu and Zn may be the forming CuFeS₂ and ZnCu(P₂O₇) crystals during sewage sludge composting. The germination index showed that the compost of all treatments was safe for agricultural application; the germination index of the calcium magnesium phosphate treatment was 99.9 ± 11.8%, which was the highest among all treatments.

Analysis of the adsorption and retention models for Cd, Cr, Cu, Ni, Pb, and Zn through neural networks: selection of variables and competitive model

In this study, the neural networks are used to predict and explain the behavior of different edaphological variables in the adsorption and retention of heavy metals, both isolated and competing. A comparison with the results obtained using multiple regression, stepwise analysis, and regression trees is performed. In the neural network technique, CEC amorphous and crystallized oxides and kaolinite in the clay fraction are the most selected variables for making the optimal models, while mica and, to a lesser extent, plagioclase, are the next variables selected. Additionally, a competitive model has been considered, using simultaneously different metals. In the competitive model, the model predicts a more intense competence between Pb and Ni for the adsorption process and between Cr and Ni for the retention process.

Phytoremediation of sewage sludge contaminated by trace elements and organic compounds

Phytoremediation is a green technique being increasingly used worldwide for various purposes including the treatment of municipal sewage sludge (MSS). Most plants proposed for this technique have high nutrient demands, and fertilization is often required to maintain soil fertility and nutrient balance while remediating the substrate. In this context, MSS could be a valuable source of nutrients (especially N and P) and water for plant growth. The aim of this study was to determine the capacity willow (Salix matsudana, cv Levante), poplar (Populus deltoides × Populus nigra, cv Orion), eucalyptus (Eucalyptus camaldulensis) and sunflower (Helianthus annuus) to clean MSS, which is slightly contaminated by trace elements (TEs) and organic pollutants, and to assess their physiological response to this medium. In particular, we aimed to evaluate the TE accumulation by different species as well as the decrease of TEs and organic pollutants in the sludge after one cropping cycle and the effect of MSS on plant growth and physiology. Since MSS did not show any detrimental effect on the biomass yield of any of the species tested, it was found to be a suitable growing medium for these species. TE phytoextraction rates depended on the species, with eucalyptus showing the highest accumulation for Cr, whereas sunflower exhibited the best performance for As, Cu and Zn. At the end of the trial, some TEs (i.e. Cr, Pb and Zn), n-alkanes and PCBs showed a significant concentration decrease in the sludge for all tested species. The highest Cr decrease was observed in pots with eucalyptus (57.4%) and sunflower (53.4%), whereas sunflower showed the highest Cu decrease (44.2%), followed by eucalyptus (41.2%), poplar (16.2%) and willow (14%). A significant decrease (41.1%) of Pb in the eucalyptus was observed. Zn showed a high decrease rate with sunflower (59.5%) and poplar (52%) and to a lesser degree with willow (35.3%) and eucalyptus (25.4%). The highest decrease in n-alkanes concentration in the sludge was found in willow (98.3%) and sunflower (97.3%), whereas eucalyptus has the lowest PCBs concentration (91.8%) in the sludge compared to the beginning of the trial. These results suggest new strategies (e.g. crop rotation and intercropping) to be adopted for a better management of this phytotechnology.