Phytoremediation of sewage sludge contaminated by trace elements and organic compounds

Optimizing nutrients from fly ash-amended soil through microbial-assisted phytoremediation using response surface methodology

Nutrients are vital ingredients to boost plant health. The availability of nutrients is limited in fly ash (FA) waste to properly implement phytoremediation. The research explored the integration of microbes and treated wastewater irrigation in phytoremediation to provide the necessary nutrients for plant growth in fly ash-amended soils. The Box-Behnken method was used to design the experimental layout for the pot study. Response surface methodology (RSM) was applied as the optimization approach to model predictions for nutrient accumulation. The implemented pot study attained the highest morphological indicators with a plastochron index of 33.40, an absolute growth rate of 2.63 cm/day, and a leaf area of 2681.68 cm2 and attained maximum biomass of 24.91 g for the treatments that included a mid-range of the variables. The combination of FA 14.98%, microbial dose 4.07 mL, and treated wastewater as the irrigation source was found to be the optimized combination for nitrogen and phosphorus accumulation of 212.4 and 8.867 mg/L.

Source and migration patterns of heavy metals and human health risk assessment of heavy metals in soil-corn straw-flue gas system

The process of rapid urbanization in Northeast China has resulted in severe heavy metal pollution in the environment. In this study, we investigated the characteristics of heavy metal pollution in soil-corn straw and its combustion flue gas system, and the health risks of heavy metal pollution. The results showed that Cu and Zn in soil were more easily absorbed by corn straw roots. Heavy metals in soil, corn straw and flue gas from corn straw burning all pose some health risk to humans, and are more harmful to children than adults. The concentrations of heavy metals in both soil and flue gas from corn straw burning have reached extremely high ecological risk. The main sources of heavy metal elements in soils are, in order, industrial production, agricultural production activities and metallurgical production. This study highlights the key issues of heavy metal contamination in soil-corn straw and its combustion flue gas system, provides an auxiliary guide for the next step in analyzing the transfer mechanisms, and suggests a rational approach to mitigate heavy metal contamination.

Global Situation of Bioremediation of Leachate-Contaminated Soils by Treatment with Microorganisms: A Systematic Review

This systematic review presents the current state of research in the last five years on contaminants in soils, especially in leachates from solid waste landfills, with emphasis on biological remediation. In this work, the pollutants that can be treated by microorganisms and the results obtained worldwide were studied. All the data obtained were compiled, integrated, and analyzed by soil type, pollutant type, bacterial type, and the countries where these studies were carried out. This review provides reliable data on the contamination of soils worldwide, especially soils contaminated by leachate from municipal landfills. The extent of contamination, treatment objectives, site characteristics, cost, type of microorganisms to be used, and time must be considered when selecting a viable remediation strategy. The results of this study can help develop innovative and applicable methods for evaluating the overall contamination of soil with different contaminants and soil types. These findings can help develop innovative, applicable, and economically feasible methods for the sustainable management of contaminated soils, whether from landfill leachate or other soil types, to reduce or eliminate risk to the environment and human health, and to achieve greater greenery and functionality on the planet.

The Physiological Response of Different Brook Willow (Salix acmophylla Boiss.) Ecotypes to Salinity

Few phytoremediation studies have been conducted under semi-arid conditions where plants are subjected to drought and/or salinity stress. Although the genus Salix is frequently used in phytoremediation, information regarding its tolerance of drought and salinity is limited. In the present study, Salix acmophylla Boiss. cuttings from three sites (Adom, Darom and Mea She'arim) were tested for tolerance to salinity stress by growing them hydroponically under either control or increasing NaCl concentrations corresponding to electrical conductivities of 3 and 6 dS m^-1 in a 42-day greenhouse trial. Gas exchange parameters, chlorophyll fluorescence and concentration, and water-use efficiency were measured weekly and biomass was collected at the end of the trial. Root, leaf and stem productivity was significantly reduced in the Adom ecotype, suggesting that Darom and Mea She'arim are the more salt-tolerant of the three ecotypes. Net assimilation and stomatal conductance rates in salt-treated Adom were significantly reduced by the last week of the trial, coinciding with reduced intrinsic water use efficiency and chlorophyll a content and greater stomatal aperture. In contrast, early reductions in stomatal conductance and stomatal aperture in Darom and Mea She'arim stabilized, together with pigment concentrations, especially carotenoids. These results suggest that Darom and Mea She'arim are more tolerant to salt than Adom, and provide further phenotypic support to the recently published data demonstrating their genetic similarities and their usefulness in phytoremediation under saline conditions.

Isolation and characterization of a highly effective bacterium Bacillus cereus b-525k for hexavalent chromium detoxification

The chromate resistant Gram-positive Bacillus cereus strain b-525k was isolated from tannery effluents, demonstrating optimal propagation at 37 °C and pH 8. The minimum inhibitory concentration (MIC) test showed that B. cereus b-525k can tolerate up to 32 mM Cr⁶⁺, and also exhibit the ability to resist other toxic metal ions including Pb²⁺ (23 mM), As³⁺ (21 mM), Zn²⁺ (17 mM), Cd²⁺ (5 mM), Cu²⁺ (2 mM), and Ni²⁺ (3 mM) with the resistance order as Cr ⁶⁺ > Pb²⁺ > As³⁺ >Zn²⁺ >Cd²⁺ >Ni²⁺ >Cu²⁺. B. cereus b-525k showed maximum biosorption efficiency (q) of 51 mM Cr⁶⁺/g after 6 days. Chromate stress elicited pronounced production of antioxidant enzymes such as catalase (CAT) 191%, glutathione transferase (GST) 192%, superoxide dismutase (SOD) 161%, peroxidase (POX) 199%, and ascorbate peroxidase (APOX) (154%). Within B. cereus b-525k, the influence of Cr⁶⁺ stress (2 mM) did stimulate rise in levels of GSH (907%) and non-protein thiols (541%) was measured as compared to the control (without any Cr⁶⁺ stress) which markedly nullifies Cr⁶⁺ generated oxidative stress. The pilot scale experiments utilizing original tannery effluent showed that B. cereus b-525k could remove 99% Cr⁶⁺ in 6 days, thus, it could be a potential candidate to reclaim the chromate contaminated sites.

Sewage Sludge as N-Fertilizers for Crop Production Enabling the Circular Bioeconomy in Agriculture: A Challenge for the New EU Regulation 1009/2019

The fertilizer framework in the European Union has recently been reviewed by EU Regulation 1009/2019 that excluded sewage sludge from the list of the possible constituents of organic fertilizers relying on their origin, not on their quality. This paper aimed to carry out a complete characterization of sewage sludge obtained from a pharmaceutical manufacturing process (PDSS) to demonstrate that sewage sludge obtained from a standardized and controlled manufacturing process can be safely recycled as organic fertilizer. The agronomic and environmental characteristics of the PDSS product were analyzed and compared to other organic fertilizers. Its fertilizing potential was also evaluated through plant growth trials. PDSS was characterized by a high concentration of total N (6.6% w/w), which was all present in organic form. PDSS also showed a low concentration of heavy metals, an absence of pathogens and low concentrations of organic contaminants. Plant growth trials showed that the PDSS was able to improve lettuce and carrot growth (+25 and +46% of dry weight compared to the unfertilized control), as well as their physiological status. Considering all the results, the exclusion of sewage sludge relying only on its origin and not on its quality appears to conflict with the principles of the circular bioeconomy.

Utilization of sludge derived from landfill leachate treatment as a source of nutrients for the growth of Nicotiana alata L

The sludges derived from the leachate treatment (LS) represent an important environmental and operational problem in the landfill management. On the other hand, they can be utilized as an alternative source of nutrients and organic matter. The main objective of this work was to evaluate the reuse of the LS of a sanitary landfill in Santa Fe city - Argentina, as an organic amendment for the development of Nicotiana alata L. plants. Different doses of LS were applied to a soil mixture for potted seedling growth. The response surface methodology was applied, using a one-factor design. Once the phenological stage of flowering began, the plants were harvested. Physiological and biochemical determinations were made in order to evaluate the effects of the different amendments. Application of LS notably improved growth parameters such as stem height, leaf area and dry matter. Additionally, the content of proteins and photosynthetic pigments was enhanced. Through the multiple regression statistical analyses, the relationship between the response variables and the sludge content was established. The multivariate optimization analysis yielded 53% as the optimal sludge content. Our results indicate that this sludge, in appropriate doses, can be used as an organic amendment for the revegetation of sanitary landfills.

Simultaneous heavy metal removal and sludge deep dewatering with Fe(II) assisted electrooxidation technology

A hybrid sludge conditioning strategy with electrooxidation and Fe(II) addition was used for heavy metal removal from sewage sludge and industrial sludge, with simultaneous sludge dewatering and stabilization. With the addition of 82 mg/g DS Fe(II) and treatment time of 4.5 h, heavy metal removals of 72.95% and 78.49% for Cu, 66.29% and 84.26% for Zn, and 36.52% and 36.99% for Pb were achieved from sewage sludge and industrial sludge samples respectively. The system pH decreased to 2.33 and 2.98 and the oxidation-reduction potential (ORP) values increased to 435.90 mV and 480.60 mV in sewage sludge and industrial sludge samples, respectively, which was conducive to the desorption and dissolution of heavy metals from sludge structures and the degradation of the organic compounds that complexed with heavy metals. In addition, the hybrid conditioning process demonstrated excellent dewatering performance due to the efficient electrochemical disintegration of sludge flocs together with the coagulation of sludge particles by Fe(III) generated via electrooxidation. The strong acidic and oxidative environment produced by the enhanced electrooxidation process was also responsible for pathogen inactivation.

Compost-mediated arsenic phytoremediation, health risk assessment and economic feasibility using Zea mays L. in contrasting textured soils

Maize (Zea mays L.) is considered as a potential energy-yielding crop which may respond to compost application for arsenic (As) phytoremediation depending on soil type and compost application levels in soil. Here, we explored compost-mediated As phytoremediation potential of maize in the two different textured soils (sandy loam soil and clay loam soil) at varying As (0-120 mg kg^-1) and compost (0-2.5%) levels under glasshouse conditions. Results revealed that in the absence of compost maize plants grown at different soil As levels (0-120 mg kg^-1) accumulated 1.20-1.71 times more As from sandy loam soil than that of clay loam soil. The compost addition in soil at all levels, with 120 mg kg^-1As enhanced As accumulation in maize plants in the clay loam soil by 13%, while it reduced As phyto-uptake by 27% in sandy loam soil. This may be due to an increase in phosphate-extractable (bioavailable) soil As content from 2.7 to 3.8 mg kg^-1 in clay loam soil. The estimated daily intake (EDI) of As (0.03-0.15 μg g^-1 of body weight day^-1) was above the US EPA's standard value. Arsenic phytoremediation potential of the maize plants was found to be economical for sandy loam soil with 1% compost level and for clay loam soil at 2.5% compost level, suggesting soil type specific dose dependence of compost for As phytoremediation programs. Novelty statement: To our knowledge, the role of compost in economic feasibility of energy crops at contaminated soils in general, and in the growing of maize at As-contaminated soil in particular, has not been addressed, so far. Moreover, it is the first time to evaluate environmental and health risk of compost-mediated As phytoremediation in different soil types.This study provided new insights of economic evaluation and risk assessment in the phytoremediation and mechanisms of compost in biomass production of energy crop at different As concentration. These aspects in phytoremediation studies are imperative to understand for developing safe, cost-effective and soil specific remediation strategies.

Effect of Biowastes on Soil Remediation, Plant Productivity and Soil Organic Carbon Sequestration: A Review

High anthropogenic activities are constantly causing increased soil degradation and thus soil health and safety are becoming an important issue. The soil quality is deteriorating at an alarming rate in the neighborhood of smelters as a result of heavy metal deposition. Organic biowastes, also produced through anthropogenic activities, provide some solutions for remediation and management of degraded soils through their use as a substrate. Biowastes, due to their high content of organic compounds, have the potential to improve soil quality, plant productivity, and microbial activity contributing to higher humus production. Biowaste use also leads to the immobilization and stabilization of heavy metals, carbon sequestration, and release of macro and micronutrients. Increased carbon sequestration through biowaste use helps us in mitigating climate change and global warming. Soil amendment by biowaste increases soil activity and plant productivity caused by stimulation in shoot and root length, biomass production, grain yield, chlorophyll content, and decrease in oxidative stress. However, biowaste application to soils is a debatable issue due to their possible negative effect of high heavy metal concentration and risks of their accumulation in soils. Therefore, regulations for the use of biowastes as fertilizer or soil amendment must be improved and strictly employed to avoid environmental risks and the entry of potentially toxic elements into the food chain. In this review, we summarize the current knowledge on the effects of biowastes on soil remediation, plant productivity, and soil organic carbon sequestration.

Effects of sewage sludge supplementation on heavy metal accumulation and the expression of ABC transporters in Sinapis alba L. during assisted phytoremediation of contaminated sites

ATP binding cassette (ABC) transporters, types C, G, and B were monitored via qPCR in order to investigate the influence of heavy metal (HM) contamination of post-industrial and post-agricultural soils and the effects of its supplementation with sewage sludge, on Sinapis alba plants. Five house-keeping genes were selected and validated to ensure the best reference points. The relative expression of ABC types C and G genes was profoundly affected by experimental conditions and included their upregulation after plants exposure to heavy metals and downregulation after supplementation with sewage sludge. However, ABC type C was more responsive then type G. The experimental conditions altered the expression of ABC type C gene faster than ABC type G and thus, the expression of ABC type C can therefore potentially be used as a bioindicator during assisted phytoremediation of degraded sites. In clean soil, supplementation with sewage sludge with a slight content of heavy metals still caused an upregulation in the expression of ABC types C and G, which showed that proper toxicity assessments are necessary to ensure safe application of sewage sludge into soils. Results showed that the analysed genes take a significant part in plants metal detoxification and that their expression is regulated at transcriptional level after exposure to soil contaminated with heavy metals by both, industrial activities and by sewage sludge supplementation. Thus, their expression can potentially be used as an early-warning biomarker when soil supplementation with sewage sludge is incorporated into the soil-management process.

Hemp-Based Phytoaccumulation of Heavy Metals from Municipal Sewage Sludge and Phosphogypsum Under Field Conditions

The aim of this study was to evaluate the ability of three hemp cultivars to accumulate heavy metals under sewage sludge (SS) and phosphogypsum (PG) application. The field study was carried out from 2014 to 2016 on Luvisol (loamy sand) in Poland. The experiment scheme included five treatments—T0: the control without fertilization, T1: 170 kg N (nitrogen) ha−1 from sewage sludge, T2: 170 kg N ha−1 from sewage sludge and 100 kg ha−1 of phosphogypsum, T3: 170 kg N ha−1 from sewage sludge and 500 kg ha−1 of phosphogypsum, and T4: 170 kg N ha−1 from sewage sludge and 1000 kg ha−1 of phosphogypsum. It was found that the application of municipal sewage sludge enriched the soil with the bioavailable forms of heavy metals to the greatest extent and contributed to the highest increase in their contents in vegetative and generative organs of hemp plants. These parameters showed a phosphogypsum dose-dependent decline, which could hinder the phytoextraction process. The greatest extractions of heavy metal(loid)s (HMs) from the soil treated with SS and PG were achieved by the Tygra variety, which had the highest bioconcentration factor (BCF) and biomass yield.

Modeling and optimizing the removal of cadmium by Sinapis alba L. from contaminated soil via Response Surface Methodology and Artificial Neural Networks during assisted phytoremediation with sewage sludge

The study was aimed to model and optimize the removal of cadmium from contaminated post-industrial soil via Sinapis alba L. by comparing two modeling approaches: Response Surface Methodology (RSM) and Artificial Neural Networks (ANN). The experimental design was done using the Box-Behnken Design method. In the RSM model, the quadratic model was shown to predict the closest results in comparison to our experimental data. For ANN approach, a two-layer Feed-Forward Back-Propagation Neural Network model was designed. The results showed that sewage sludge supplementation increased the efficiency of the Sinapis alba plant in removing Cd from the soil. After 28 days of exposure, the removal rate varied from 10.96% without any supplementation to 65.9% after supplementation with the highest possible (law allowed) dose of sewage sludge. The comparison proved that the prediction capability of the ANN model was much higher than that of the RSM model (adjusted R-square: 0.98, standard error of the Cd prediction removal: 0.85 ± 0.02). Thus, the ANN model could be used for the prediction of heavy metal removal during assisted phytoremediation with sewage sludge. Moreover, such approach could also be used to determinate the dose of sewage sludge that will ensure highest process efficiency.

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.

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.

Absorption, accumulation and distribution of metals and nutrient elements in poplars planted in land amended with composted sewage sludge: A field trial

Interest in the application of sewage sludge as amendments to grow trees has continued to increase, especially for fast-growing trees such as poplars. In this study, two-year field trial was conducted to determine the effects of compost sewage sludge (CSS) soil application on the distributions of metal and nutrient elements in poplars (Populus × euramericana 'Guariento') and poplar growth. Soil was amended with one of four CSS treatments in both study years: control (2012, 2013: 0 t/ha), SS1 (2012: 7.5 t/ha, 2013: 15 t/ha), SS2 (2012: 15 t/ha, 2013: 30 t/ha), and SS3 (2012: 30 t/ha, 2013: 45 t/ha). During the two-year field trial period, CSS treatments significantly affected leaf K, Mg, Ni, Cr, and Pb contents and root P contents. The element contents in different plant parts responded differently to the different CSS application rates; microelement contents in roots and trace element contents in leaves were significantly affected by the high sludge treatment. The CSS application significantly influenced Ca, Na, Cu, Ni, and Pb accumulation in aerial parts of poplar and the distributions of N, S, Ni, Mg, and P between roots and leaves or stems, and significantly increased the diameter at breast height (DBH) of poplars by 2.4-18.6%. The CSS application of 15 t/ha per year resulted in the largest average increase in DBH of 11.1%; therefore, it could be considered as the most suitable application rate. In summary, CSS application can improve nutrition uptake in various parts of poplars and promote the growth of poplar. Poplar forest amendment is a good CSS disposal strategy.

Catharanthus roseus potential for phyto-stabilizing metals in sewage sludge

This work evaluated the potential of Catharanthus roseus in phytoremediation of As, Ba, Cd, Cu, Cr, Ni, Pb, Se and Zn in sewage sludge-based substrates. C. roseus was cultivated for 108 days in a treatment containing sewage sludge:vermiculite (70:30%) and in the control with 100% commercial substrate. The plants cultivated in sludge showed approximately four times greater height, number of leaves and stem diameter, as well as 89% higher fresh mass than those of the control. The highest concentrations of the metals were obtained in the roots of plants grown in the sludge, and ranged from 2.04 (Cd) to 1121 mg kg^-1 (Zn). Cu, Cd and Zn had a higher bioconcentration factor than 1 in both treatments. On the other hand, the translocation factor value in the control was greater than 1 for Ba, Cd, Cu, Ni, Se and Zn. The results showed that C. roseus was efficient in the phytoremediation of the evaluated metals, in which the translocation process was progressive in the treatment that presented higher metal content.

Effects and mechanisms of phytoalexins on the removal of polycyclic aromatic hydrocarbons (PAHs) by an endophytic bacterium isolated from ryegrass

Plant-endophyte synergism has been demonstrated to play a key role in the phytoremediation of contaminated water and soil. Phytoalexins, a type of chemical component in the plant apoplast, can be produced by plants in response to stimulation by endophytes. Phytoalexins may have distinct effects on the nutritional and metabolic functions of endophytes; however, direct evidence is not available to prove the effect of phytoalexins on the hydrophobic organic contaminants (HOC)-degradation activity of endophytes. In this paper, three different types of phytoalexins, coumarin, resveratrol and rutin, were selected to study their effect on the removal of polycyclic aromatic hydrocarbons (PAHs) by an endophytic bacterium Methylobacterium extorquens C1. The effects of the three phytoalexins on bacterial sorption and intracellular enzymatic activities were tested to further analyze the mechanism by which the phytoalexins affect the PAH degradation performance of M. extorquens C1. The results showed that the removal rate of PAHs by M. extorquens C1 increased in the presence of low levels of the three phytoalexins. The most effective concentrations of coumarin, resveratrol and rutin were 0.20, 0.15, and 0.25 mg/L, respectively, and the removal rate of PAHs was increased by approximately 18.3-35.0%. At the optimal concentrations, the three phytoalexins significantly promoted the sorption of PAHs by M. extorquens C1, and also enhanced the activities of catechol dioxygenases and dehydrogenase of M. extorquens C1. The positive effect of phytoalexins on both bacterial sorption and intracellular enzymatic activities promotes the overall removal of PAHs from endophytes. These results may deepen our understanding of plant-microbe cooperative mechanisms in the degradation of organic pollutants and provide a new approach for chemically enhanced bioremediation in the future.

Capability of the Invasive Tree Prosopis glandulosa Torr. to Remediate Soil Treated with Sewage Sludge

Sewage sludge improves agricultural soil and plant growth, but there are hazards associated with its use, including high metal(loid) contents. An experimental study was conducted under greenhouse conditions to examine the effects of sewage sludge on growth of the invasive tree Prosopis glandulosa, as well as to determine its phytoremediation capacity. Plants were established and grown for seven months along a gradient of sewage sludge content. Plant traits, soil properties, and plant and soil concentrations of N, P, K, Cd, Pb, Cu, Ni, Zn, Cr, Co, As, and Fe were recorded. The addition of sewage sludge led to a significant decrease in soil pH, and Ni, Co, and As concentrations, as well as an increase in soil organic matter and the concentrations of N, P, Cu, Zn, and Cr. Increasing sewage sludge content in the growth medium raised the total uptake of most metals by P. glandulosa plants due to higher biomass accumulation (taller plants with more leaves) and higher metal concentrations in the plant tissues. P. glandulosa concentrated more Cd, Pb, Cu, Zn, and Fe in its below-ground biomass (BGB) than in its above-ground biomass (AGB). P. glandulosa concentrated Ni, Co, and As in both BGB and AGB. P. glandulosa has potential as a biotool for the phytoremediation of sewage sludges and sewage-amended soils in arid and semi-arid environments, with a potential accumulation capability for As in plant leaves.

Syngas production and trace element emissions from microwave-assisted chemical looping gasification of heavy metal hyperaccumulators

Phytoremediation is one of the most encouraging options for the elimination of heavy metals from contaminated soil. However, the treatment and exploitation of hazardous harvested hyperaccumulator biomass is a challenge recently. In this investigation, we propose a novel microwave-assisted chemical looping gasification (MACLG) process for the disposal of hyperaccumulator biomass, and syngas fuel production and trace element emissions from MACLG over hematite is evaluated. Experimental results show that the addition of hematite as oxygen carrier (OC) favors the production of H₂ and CO. The elevated operation temperature induces a decay in CO₂ yield and an increase in H₂, CO and CH₄ yields. Meanwhile, a higher temperature causes an increased heavy metal percentage in syngas. On the other hand, the augmentation of steam flow and hematite content stimulates an uptrend for CO₂ and H₂ production and downtrend for CO generation. The percentage of each trace element in char after MACLG reduces with increasing steam flow, and its change in syngas presents the opposite trend. In addition, the proportions of trace elements in spent hematite and syngas tend to increase with an augmented hematite content whereas their portions in char reduce gradually. Moreover, our results suggest that activated carbon is capable of effective adsorption removal of heavy metals in syngas.

A mixture of cellulose production waste with municipal sewage as new material for an ecological management of wastes

Chemical contaminants present in cellulose production waste and municipal sewage sludge condition the necessity to treat these wastes before they are introduced into the environment. Environmental use of the these wastes appears to be justified owing to the content of organic substances as well as the considerable fertilising value. The aim of the study was to assess chemical composition and ecotoxicity of cellulose production waste and municipal sewage sludge in terms of their eco-friendly application. The assessment was done based on the established soil environment according to regulations in Poland. The research on the chemical composition of the wastes was conducted under laboratory conditions, determining the content of macroelements, microelements and heavy metals with respect to using these wastes in the environment. Phytotoxkit and Microtox tests were performed in order to determine the ecotoxicity of the wastes in the aspect of their environmental use. It was established that, compared to the cellulose production waste, the municipal sewage sludge used in the incubation experiment had a higher content of macroelements and microelements. The content of heavy metals in the waste did not exceed the permissible content that conditions their use in agriculture and reclamation. Based on the results of bioassays it was established that the cellulose production waste was toxic, whereas the combination of cellulose production waste and sewage sludge was found to be of low toxicity to test organisms. The applied wastes and their mixtures were ranked according to phytotoxicity in the following order: cellulose production waste > cellulose production waste + soil > cellulose production waste + sewage sludge. The research results indicate that waste mixtures qualify for environmental use. With respect to the variable chemical composition of cellulose production waste and municipal sewage sludge as well as their ecotoxicity, it was established that each batch intended for environmental use must be subjected to chemical analysis and ecotoxicological tests.

Sanitary and environmental aspects of sewage sludge management

Currently, sewage sludge management is a huge challenge in the field of environmental engineering. New effective solutions for the treatment of wastewater led to an improvement of the quality of the final effluent but considerably increased the volume of produced sewage sludge, which increases each year. Two points of view conflict regarding the recycling of those “wastes.” Primarily, dehydrated sewage sludge is considered a reservoir of nutrients and organic matter that can be used as a fertilizer in agriculture or as an organic amendment in the remediation of contaminated sites or to build “anthroposoils.” On the other hand, recycled sewage sludge is seen as a potential source of soil contamination by organic and inorganic pollutants and pathogens; potentially toxic elements (such as zinc, copper, cadmium, lead, silver, etc.); polycyclic aromatic hydrocarbons (PAH); polychlorobiphenyls (PCB); biocides and phytopharmaceuticals; pharmaceuticals, personal care products (PPCP), and residuals; synthetic hormones; microplastics; nanotechnology life cycle end products; and microorganisms such as Escherichia coli O157:H7 or Salmonella typhimurium.

This chapter will focus on these aspects, highlighting the health and ecotoxicological risks associated with the presence of such contaminants in sludge. The environmental dangers of sludge spreading on soils will be presented as well as their possible treatment scenarios to propose an acceptable reuse of sewage sludge in a circular economy.

The effect of cellulose production waste and municipal sewage sludge on biomass and heavy metal uptake by a plant mixture

Environmental management of cellulose production waste and municipal sewage sludge appears to be substantiated due to various physicochemical properties of these wastes. The aim of the conducted research was to determine the effect of cellulose production waste and sewage sludge on yielding and heavy metal uptake by a plant mixture. The research was conducted under field experiment conditions, determining the fertilizer value of these wastes in the environmental aspect. The research was carried out in the years 2013-2016. Species composition of the plant mixture was adjusted to habitat conditions. It was established that, as compared with the cellulose production waste, the municipal sewage sludge used in the experiment had a higher content of macroelements. The content of heavy metals in the studied waste did not exceed the limits that condition their use in agriculture and reclamation. Applying only the cellulose production waste did not significantly decrease the yield of the plants. Municipal sewage sludge showed the highest yield-forming effect. Mixing the above-mentioned wastes and their application to soil had a significant effect on the increase in the plant mixture yield. The waste applied to soil also increased the content of Cr, Cd, Pb, Cu, and Zn in the plant mix. The level of heavy metal content in the plant mix did not exclude this biomass from being used for fodder or reclamation purposes. The cellulose production waste and municipal sewage sludge increased the heavy metal uptake by the plant mixture. The plant biomass extracted heavy metals from the sewage sludge more intensively than from the cellulose production waste. Among the analyzed heavy metals, the highest phytoremediation was recorded for Ni (30%), followed by Cd (20%), Cr (15%), Pb (10%), and the lowest for Cu (9%) and Zn (8%). Application of the cellulose production waste and sewage sludge to soil also increased the content of the studied heavy metals in soil. However, it did not cause deterioration of soil quality standards. Heterogeneity in the chemical composition of the wastes confirms that each batch intended to be used for environmental management should be subjected to chemical control.

Phytomelatonin: Recent advances and future prospects

Melatonin (MEL) has been revealed as a phylogenetically conserved molecule with a ubiquitous distribution from primitive photosynthetic bacteria to higher plants, including algae and fungi. Since MEL is implicated in numerous plant developmental processes and stress responses, the exploration of its functions in plant has become a rapidly progressing field with the new paradigm of involvement in plants growth and development. The pleiotropic involvement of MEL in regulating the transcripts of numerous genes confirms its vital involvement as a multi-regulatory molecule that architects many aspects of plant development. However, the cumulative research in plants is still preliminary and fragmentary in terms of its established functions compared to what is known about MEL physiology in animals. This supports the need for a comprehensive review that summarizes the new aspects pertaining to its functional role in photosynthesis, phytohormonal interactions under stress, cellular redox signaling, along with other regulatory roles in plant immunity, phytoremediation, and plant microbial interactions. The present review covers the latest advances on the mechanistic roles of phytomelatonin. While phytomelatonin is a sovereign plant growth regulator that can interact with the functions of other plant growth regulators or hormones, its qualifications as a complete phytohormone are still to be established. This review also showcases the yet to be identified potentials of phytomelatonin that will surely encourage the plant scientists to uncover new functional aspects of phytomelatonin in plant growth and development, subsequently improving its status as a potential new phytohormone.