Thermal Behavior and Pyrolysis Kinetics of Mushroom Residue with the Introduction of Waste Plastics.

Co-pyrolysis is considered a very promising technology for the treatment of solid wastes as it can rapidly realize the volume reduction of raw materials and obtain high value-added products. To realize the resource utilization of newly emerging solid wastes in relation to edible fungi residue and waste plastics, mushroom residue (MR), a representative of edible fungi residue, was co-pyrolyzed with waste plastic bags (PE), waste plastic lunch boxes (PP), and waste plastic bottles (PET). The thermal behavior and pyrolysis kinetics of the mixtures were investigated. It was found that the softening of the plastics in the mixtures led to an increase in the initial pyrolysis temperature of MR by 2-27 °C, while the pyrolytic intermediates of MR could greatly promote the decomposition of the plastics, resulting in a decrease in the initial pyrolysis temperatures of PE, PP, and PET in the mixtures by 25, 8, and 16 °C, respectively. The mixture of MR and PE (MR/PE) under different mixture ratios showed good synergies, causing the pyrolysis peaks attributed to MR and PE to both move towards the lower temperature region relative to those of individual samples. The increase in heating rate led to enhanced thermal hysteresis of the reaction between MR and PE. The strength of the interaction between plastics and MR based on mass variation was subject to the order PE > PP > PET. The pyrolysis activation energies of MR, PE, PP, and PET calculated from kinetic analysis were 6.18, 119.05, 84.30, and 74.38 kJ/mol, respectively. The activation energies assigned to MR and plastics were both reduced as plastics were introduced to co-pyrolyze with MR, indicating that MR and plastics have a good interaction in the co-pyrolysis process. This study provides theoretical and experimental guidance for the resource utilization of agricultural solid wastes via thermochemical conversion.

Effect of Adding De-Oiled Kitchen Water on the Bioconversion of Kitchen Waste Treatment Residue by Black Soldier Fly Larvae.

With the continuous development of society, the output of kitchen waste (KW) is fast increasing. De-oiled kitchen water (DKW) and kitchen waste treatment residue (KWTR), two main by-products of the KW treatment industry, are produced accordingly on a large scale. The need to develop an effective technique for the utilization of DKW and KWTR is attracting wide attention. In the present study, black soldier fly larvae (BSFL) were employed as a biological treatment method to treat KWTR with the addition of DKW. The influence of DKW (0-140 mL) on the efficiency of BSFL treatment evaluated by the growth and development of BSFL, the body composition of BSFL, the nutrient content of bioconversion residue (BR), and the bioconversion efficiency of KWTR, was investigated. The results showed that the growth and development of BSFL, the body composition of BSFL, and the conversion rate of KWTR were initially promoted and then inhibited with the addition of DKW. Notably, the amount of DKW added in the T110 group was the most suitable for the growth of BSFL and the accumulation of body composition. Compared with the blank comparison group, the content of crude protein (CP), crude ash (CA), salinity, total phosphorus (TP), and dry matter (DM) of BSFL in the T110 group increased by 3.54%, 6.85%, 0.98%, 0.07% and 2.98%, respectively. However, the addition of DKW could steadily increase the nutrient content of BR, with the highest amount at 140 mL DKW. Following DKW addition, the contents of CP, ether extract (EE), crude fiber (CF), organic matter (OM), total nitrogen (TN), TP, and total potassium (TK) were increased by 4.56%, 3.63%, 10.53%, 5.14%, 0.73%, 0.75%, and 0.52%, respectively, compared with those of the blank comparison group. The study showed that DKW could be used as a nutrient additive in the bioconversion process of KWTR by BSFL, which provided a new method for the resource utilization of DKW.

Characterization and nutritional value of hydrothermal liquid products from distillers grains.

Hydrothermal liquid products (HLPs) produced by hydrothermal treatment (HTT) contain a large amount of nitrogen, phosphorus and other substances, while the environmental problems caused by arbitrary discharge. This work explored the effects of temperature, reaction time and solid-liquid ratio on the chemistry of HLPs of two different distillers grains, with a focus on nutrient composition. Increased HTT temperature was related to increased HLPs pH, dissolved organic carbon content, and aromaticity, and decreased electrical conductivity. Maximum nutrient extraction efficiencies observed for NH4+-N, NO3--N and PO43- were 92.0, 89.9, and 94.3%, respectively. Response surface methodology showed that the release of nutrient extraction efficiency was the greatest at the hydrothermal treatment of 200 °C for 1 h, and using a solid/liquid ratio of 10%. Comparative studies, the nutritional value of HLPs are appropriate for use as an agricultural fertilizer, and its use as a substitute for synthetic fertilizers could increase the sustainability and profitability of farming.

Effective Sb(V) removal from aqueous solution using phosphogypsum-modified biochar.

Antimonate is the dominant form of antimony (Sb) in Sb mine water. The treatment of high-Sb mine water essentially reduces the discharge of antimonate oxyanions ([Sb(OH)6]-) in it. Biochar obtained from phosphogypsum-modified anaerobic digested distillers' grain (PADC) can effectively adsorb antimonate from water. In this work, using batch adsorption experiments, mathematical models, and characterization methods, the mechanism of Sb(V) adsorption by PADC was studied. Compared with pristine biochar, PADC biochar showed abundant lamellar and vesicular structures with significant calcium ion loading on the surface. The kinetics data of the adsorption of Sb(V) on the PADC biochar followed the Elovich equation (R2 = 0.992), indicating that heterogeneous adsorption had occurred. The results also showed that intraparticle diffusion played an important role in controlling Sb(V) adsorption by PADC biochar. The Redlich-Peterson model best fit the Sb(V) adsorption isotherm (R2 = 0.997), indicating that the adsorption was a combination of the Langmuir and Freundlich models. The maximum adsorption capacity of PADC biochar for Sb(V) is 8123 mg/kg, which is more than twice that of the pristine biochar (3487 mg/kg) and is sufficient for Sb(V) treatment in most mine water. Fourier transform infrared (FTIR) spectra, X-ray photoelectron spectroscopy (XPS), X-ray diffractometry (XRD), and Transmission electron microscopy with energy dispersive X-ray spectroscopy (TEM-EDS) analyses revealed that the dominant mechanism of Sb(V) removal by PADC biochar was the formation of Ca-O-Sb complexes or amorphous surface precipitation as well as electrostatic adsorption. This work demonstrated the potential of PADC biochar in the treatment of Sb-contaminated mine water.

Hydrothermal carbonization of distillers grains with clay minerals for enhanced adsorption of phosphate and methylene blue.

A novel one-pot synthesis method was developed to prepare modified hydrochar by co-hydrothermal carbonization of waste distillers grains using low-cost clay minerals (attapulgite or vermiculite). The loading of the clay minerals onto hydrochar surfaces altered the structure and surface composition of the hydrochar such that the clay-modified hydrochars showed better ability to adsorb methylene blue and phosphate in aqueous solution than the pristine hydrochar. The maximum methylene blue and phosphate adsorption capacities of the modified hydrochar reached 340.3 and 96.9 mg g-1, respectively, comparable or higher than that of many commercial sorbents. Multiple mechanisms, including electrostatic attraction, ion exchange, complexation, and physical adsorption, controlled the adsorption process. These results highlight excellent potential for distillers grains-derived hydrochar-clay composites as an environmental sorbent, capable of removing a variety of contaminants from aqueous solutions.

Adsorption of Polycyclic Aromatic Hydrocarbons from aqueous solution by Organic Montmorillonite Sodium Alginate Nanocomposites.

The adsorption method is generally considered a promising technique to remove inorganic and organic contaminants in an economically and environmentally friendly superior manner. In this study, organic montmorillonite sodium alginate composites were prepared, in which, montmorillonite and cationic surfactant (cetyltrimethylammonium bromide, CTAB) in different added amounts were coagulated with sodium alginate using CaCl2 as the crosslinking agent. The morphological properties of the composites were characterized thoroughly and employed in three typical target pollutants of polycyclic aromatic hydrocarbons (PAHs) (acenaphthene, fluorene, and phenanthrene) by batch adsorption experiments from aqueous solution. The composites provide an efficient alternative for PAHs removals. The composites could be stably separated and regenerated with methyl alcohol. Furthermore, the adsorption kinetic and isotherm data were well described by the Elovich kinetic and the Freundlich isotherm model, respectively. According to these, the adsorption process occurred via multilayer adsorption on the composite's energetically heterogeneous surface. Moreover, pore diffusion and hydrophobicity played a dominant role in the adsorption mechanism. Overall, our study offers a developed adsorbent that has the advantage of being recyclable, low cost, biodegradable and biocompatible for effectively removing PAHs from aqueous solution.

Phosphogypsum as a novel modifier for distillers grains biochar removal of phosphate from water.

A novel biochar composite was fabricated via the pyrolysis of distillers grains treated phosphogypsum for phosphate removal from water. Batch adsorption experiments were performed on the adsorption characteristics of phosphate. Effects of pyrolysis temperature, solution pH, the dosage of adsorbent, ambient temperature on phosphate adsorption were also investigated. The results demonstrated that the optimum initial solution pH for phosphate adsorption was 6.0, and high pyrolysis temperature was favorable for phosphate adsorption. The optimal dosage of biochar was 1.25 g L-1. A pseudo-second-order kinetic model can well explain the adsorption kinetics, indicative of the energetically heterogeneous solid surface of the composite. The maximum phosphate adsorption capacity of the phosphogypsum modified biochar obtained from Langmuir isotherm reached 102.4 mg g-1 which was almost five times that of distillers grains biochar alone (21.5 mg g-1). The mechanism is mainly attributed to electrostatic adsorption, surface precipitation and ligand exchange. The ideal adsorption performance indicated that biochar supported phosphogypsum can be used as high-quality adsorbent for phosphate removal in wastewater treatment.

Enhanced removal of hexavalent chromium by engineered biochar composite fabricated from phosphogypsum and distillers grains.

Two kinds of industrial wastes (distillers grains and phosphogypsum) were used as raw materials to produce a new biochar composite for Cr(VI) removal in water. The influencing factors including pyrolysis temperature, dosage, initial solution pH as well as contacting time were explored. The adsorption kinetics, isotherms, and thermodynamics of two biochars were conducted. The results show that the adsorption of Cr(VI) by biochar is related to pH. The ideal pH was 3.0 and the adsorbed Cr(VI) decreases as the pH increases. The Cr(VI) adsorption process conformed to the pseudo-second-order equation. Phosphogypsum modified (PM)-biochar is well described by the Freundlich model. The maximum adsorption capacities of distillers grains (DG)-biochar and PM-biochar on Cr(VI) were 63.1 and 157.9 mg g-1, respectively. The thermodynamic analysis indicates that the Cr(VI) adsorption occurs spontaneously which is an endothermic process. This study provided an alternative way for Cr(VI) removal from water.

Acidic leaching of potentially toxic metals cadmium, cobalt, chromium, copper, nickel, lead, and zinc from two Zn smelting slag materials incubated in an acidic soil.

A column leaching study, coupled with acid deposition simulation, was conducted to investigate the leaching of potentially toxic metals (PTM) from zinc smelting slag materials (SSM) after being incubated in an acid Alfisol for 120 days at room temperature. Two SSMs (SSM-A: acidic, 10 yrs exposure with moderate high PTM concentrations versus SSM-B: alkaline, 2 yrs exposure with extremely high PTM concentrations), were used for the incubation at 0.5, 1, 2.5, 5 wt% amendment ratios in triplicate. Five leaching events were conducted at day 1, 3, 7, 14, and 28, and the leaching of PTMs mainly occurred in the first three leaching events, with the highest PTM concentrations in leachate measured from 5 wt% SSM amendments. After leaching, 2.5, 12, 5.5, 14, 11, and 9 wt% of M3 extractable Pb, Zn, Cd, Co, Cr, and Ni could be released from 5 wt% SSM-A amended soils, being respectively 25, 12, 4, 2, 2, and 2 times more than those from 5 wt% SSM-B amended soils. In the leachates, the concentrations of PTMs were mostly affected by leachant pH and were closely correlated to the concentrations of Fe, Al, Ca, Mg and P with Cd, Pb, and Zn showing the most environmental concern. Visual MINTEQ 3.1 modeling suggested metallic ions and sulfate forms as the common chemical species of PTMs in the leachates; whereas, organic bound species showed importance for Cd, Pb, Cu, and Ni, and CdCl+ was observed for Cd. Aluminum hydroxy, phosphate, and sulfate minerals prevailed as the saturated minerals, followed by chloropyromorphite (Pb5(PO4)3Cl) and plumbogummite (PbAl3(PO4)2(OH)5·H2O) in the leachates. This study suggested that incubation of SSMs in acidic soil for a long term can enhance the release of PTMs as the forms of metallic ions and sulfate when subjected to acid deposition leaching.

Alginate-based composites for environmental applications: A critical review.

Alginate-based composites have been extensively studied for applications in energy and environmental sectors due to their biocompatible, nontoxic, and cost-effective properties. This review is designed to provide an overview of the synthesis and application of alginate-based composites. In addition to an overview of current understanding of alginate biopolymer, gelation process, and cross-linking mechanisms, this work focuses on adsorption mechanisms and performance of different alginate-based composites for the removal of various pollutants including dyes, heavy metals, and antibiotics in water and wastewater. While encapsulation in alginate gel beads confers protective benefits to engineered nanoparticles, carbonaceous materials, cells and microbes, alginate-based composites typically exhibit enhanced adsorption performance. The physical and chemical properties of alginate-based composites determine the effectiveness under different application conditions. A series of alginate-based composites and their physicochemical and sorptive properties have been summarized. This critical review not only summarizes recent advances in alginate-based composites but also presents a perspective of future work for their environmental applications.

Profile distribution and accumulation characteristics of organic carbon in a karst hillslope based on particle-size fractionation and stable isotope analysis.

Recent studies have highlighted tight coupling between soil aggregate fractions and soil organic carbon (SOC) turnover. However, large uncertainties remain and a mechanistic understanding of geomorphic and land use change effects on carbon storage in soil is still lacking. Taking typical slope of vegetation recovery in karst area as object, the present study analyzed organic carbon content and stable carbon isotope composition (δ13C value) of soil organic matter in bulk and particle size separates of soil on profiles at different topographic positions. The results showed that SOC content decreased gradually in downhill direction. Organic carbon content of sandy soil (50-2000 µm) accounted above 50% in the upper slope positions but in the middle and lower slope soil profiles, organic carbon was mainly stored in silts (2-50 µm) and clays (< 2 µm) which belonged to stable and highly humified SOC. The composition difference of δ13C values in soil profiles reflected the input of plant residues and accumulation characteristics. Organic matter was deposited in different soil particle sizes owing to different degrees of decomposition. Hence, δ13C value can help in identifying the storage and decomposition rates of soil organic matter.

Leaching of cadmium, chromium, copper, lead, and zinc from two slag dumps with different environmental exposure periods under dynamic acidic condition.

Over the past few decades, zinc smelting activities in Guizhou, China have produced numerous slag dumps, which are often dispersed on roadsides and hill slopes throughout the region. During periods of acid rain, these exposed slags release heavy metals into surface water bodies. A column leaching study was designed to test the potential release of the heavy metals cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb), and zinc (Zn) under simulated acid rain events. Two slags with varying environmental exposure periods were packed in columns and subjected to leaching solutions of pH 3.5, 5.5, or DI H2O at intervals of 1, 7, 14, 28, 56d. Pulse concentrations of Cd in leachate were found above 5µg/L, Cr, Pb, and Zn >10µg/L, whereas, Cu reached 10µg/L. After five leaching events, the leachability (percentage of cumulative heavy metal leached after five leaching events as in its respective total concentration in slags) of Cd was 0.05 percent and 0.035 percent from the old and young slag, respectively. Cr (0.035 percent and 0.05 percent) was greater than Cu (0.002 percent and 0.005 percent) and Zn (0.006 percent and 0.003 percent), while the lowest leachability was observed for Pb (0.0005 percent and 0.0002 percent) from the old and young slags, respectively. Reaction rates (release amount of heavy metals in certain period of leaching) of heavy metals in the leachates demonstrated the sequence of Zn>Cr>Cd, Cu>Pb. Leaching release of heavy metals was jointly affected by the pH of leaching solution and mineral composition of slags (including chemical forms of Cd, Cr, Cu, Pb, and Zn). Environmental exposure period of slags, resulting in the alteration of minerals, could affect the release process of heavy metals in leaching as well.

Natural and anthropogenic lead in soils and vegetables around Guiyang city, southwest China: a Pb isotopic approach.

Soils, vegetables and rainwaters from three vegetable production bases in the Guiyang area, southwest China, were analyzed for Pb concentrations and isotope compositions to trace its sources in the vegetables and soils. Lead isotopic compositions were not distinguishable between yellow soils and calcareous soils, but distinguishable among sampling sites. The highest (207)Pb/(206)Pb and (208)Pb/(206)Pb ratios were found for rainwaters (0.8547-0.8593 and 2.098-2.109, respectively), and the lowest for soils (0.7173-0.8246 and 1.766-2.048, respectively). The (207)Pb/(206)Pb and (208)Pb/(206)Pb ratios increased in vegetables in the order of roots

Lead, zinc, and cadmium in vegetable/crops in a zinc smelting region and its potential human toxicity.

Lead, Zn, and Cd in vegetables/crops were investigated in a zinc smelting region in China, and their daily dietary intake by local residents was estimated. It is observed that Pb, Zn, and Cd were in 34.7-91.1, 242-575, and 0.199-2.23 µg g(-1) dry weight in vegetables/crops with their greatest concentrations in leafy vegetable. The daily dietary intake of Pb, Zn, and Cd by adult residents reached 3, 646, 59,295, and 186 µg day, respectively, and lettuce and cabbage together contributed 75% of the Pb, 50% of the Zn, and 70% of the Cd.

[Sulfur isotopic ratios indicating sulfur cycling in slope soils of karst areas].

Sequential extraction methods for soil sulfur were used to determine delta34 S ratios and sulfur contents of total sulfur, organic sulfur, SO4(21) and FeS2 in slope soils of karst areas. In general, FeS2 has the lowest delta34 S ratios, ranging from -6.86% per hundred to -4.229% per hundred, followed in ascending order by SO4(2-) (-2.64% per hundred - -1.34% per hundred), total sulfur (-3.25% per hundred - -1.03% per hundred) and organic sulfur (-1.63% per hundred -0.50% per hundred) in surface soils of profiles, and delta34 S ratios in different sulfur forms all show increasing trend with profiles deepening. Covariations of delta34 S ratios of SO4(2-) and FeS2 with increasing depth are related to SO4(2-) dissimilatory reduction, while the increase in parallel of delta34 S ratios of total sulfur and organic sulfur could be resulted from organic sulfur cycling. delta34 S ratios have been extensively used to indicate sulfur sources, moreover, SO4(2-) dissimilatory reduction and organic sulfur mineralization result in significant sulfur isotopic fractionation, and sulfides oxidation and SO4(2-) assimilation have no isotopic fractionation occurred, the vertical variations of delta34 S ratios in different sulfur forms can therefore be good records for depth-dependant sulfur cycling processes. Furthermore, by comparing depth distributions of sulfur contents and delta34 S ratios in different sulfur forms, it is easily to discuss the migration of SO4(-1) and organic sulfur fractions in soil profiles.

Allocation and source attribution of lead and cadmium in maize (Zea mays L.) impacted by smelting emissions.

Plants grown in contaminated areas may accumulate trace metals to a toxic level via their roots and/or leaves. In the present study, we investigated the distribution and sources of Pb and Cd in maize plants (Zea mays L.) grown in a typical zinc smelting impacted area of southwestern China. Results showed that the smelting activities caused significantly elevated concentrations of Pb and Cd in the surrounding soils and maize plants. Pb isotope data revealed that the foliar uptake of atmospheric Pb was the dominant pathway for Pb to the leaf and grain tissues of maize, while Pb in the stalk and root tissues was mainly derived from root uptake. The ratio of Pb to Cd concentrations in the plants indicated that Cd had a different behavior from Pb, with most Cd in the maize plants coming from the soil via root uptake.

Heavy metals in an impacted wetland system: a typical case from southwestern China.

Historical zinc smelting in Hezhang, southwestern China, has resulted in significant heavy metal contamination of the surrounding ecosystems. The Caohai wetland system, which is an important national nature reserve close to the Hezhang zinc smelting area, was investigated in the present study. Results showed that sediments from the Caohai wetland system have been seriously contaminated by Cd, Pb and Zn with the highest concentrations in the surface sediments being up to 71, 160 and 1,200 microg g(-1), respectively. The heavy metals in the sediments were strongly associated with the organic/sulphide and residual fractions. A more oxidized condition induced by aquatic plants tended to cause the Cd, Pb and Zn bound to the Fe-Mn oxide fraction to become more dominant. Pb isotopic compositions in the sediments indicated that the inventories of Pb in the Caohai wetland sediments were mainly derived from the historical zinc smelting in the Hezhang area, although other anthropogenic sources, such as the gasoline Pb, also made a substantial contribution to the Pb in the sediments. Heavy metal contamination in aquatic plants was also studied and the results indicated that heavy metals accumulated by plants may pose a potential threat to the higher trophic-level organisms, including humans.

Environmental contamination of heavy metals from zinc smelting areas in Hezhang County, western Guizhou, China.

Total heavy metal (Cd, Cr, Cu, Pb and Zn) concentrations were evaluated in smelting waste, soil, crop and moss samples collected from the Hezhang artisanal zinc smelting areas, Guizhou, China. Soil samples from the cornfield near the smelting sites contained extremely high Cd (5.8-74 mg kg(-1)), Pb (60-14,000 mg kg(-1)) and Zn (260-16,000 mg kg(-1)) concentrations. Elevated heavy metal concentrations were also found in corn plants and total Pb (0.80-1.5 mg kg(-1)) and Cd (0.05-0.76 mg kg(-1)) concentrations in corn grain have totally or partially exceeded the national guidance limits for foodstuff. Thus, the soil-to-crop transfer of heavy metals might pose a potential health risk to the local residents. Similar to the high heavy metal levels in soil and corn, Cd, Cr, Cu, Pb and Zn concentrations in moss samples collected from the smelting sites ranged from 10 to 110, 10 to 55, 26 to 51, 400 to 1200 and 330 to 1100 mg kg(-1), respectively, exhibiting a local spatial pattern of metals deposition from the atmosphere. Based on examination of Zn/Cd and Pb/Cd ratios of the analyzed samples, we have distinguished between the flue gas dust derived and smelting waste derived metals in different environmental compartments.