High Metal Content Research Articles

Exploitation of multi-walled carbon nanotubes/Cu(ii)-metal organic framework based glassy carbon electrode for the determination of orphenadrine citrate.

Metal organic frameworks (MOFs), with structural tunability, high metal content and large surface area have recently attracted the attention of researchers in the field of electrochemistry. In this work, an unprecedented use of multi-walled carbon nanotubes (MWCNTs)/copper-based metal-organic framework (Cu-BTC MOF) composite as an ion-to-electron transducer in a potentiometric sensor is proposed for the determination of orphenadrine citrate. A comparative study was conducted between three proposed glassy carbon electrodes, Cu-MOF, (MWCNTs) and MWCNTs/Cu-MOF composite based sensors, where Cu-MOF, MWCNTs and their composite were utilized as the ion-to-electron transducers. The sensors were developed for accurate and precise determination of orphenadrine citrate in pharmaceutical dosage form, spiked real human plasma and artificial cerebrospinal fluid (ACSF). The sensors employed β-cyclodextrin as a recognition element with the aid of potassium tetrakis(4-chlorophenyl)borate (KTpCIPB) as a lipophilic ion exchanger. The sensors that were assessed based on the guidelines recommended by IUPAC and demonstrated a linear response within the concentration range of 10-7 M to 10-3 M, 10-6 M to 10-2 M and 10-8 M to 10-2 M for Cu-MOF, MWCNTs and MWCNTs/Cu-MOF composite based sensors, respectively. MWCNTs/Cu-MOF composite based sensor showed superior performance over other sensors regarding lower limit of detection (LOD), wider linearity range and faster response. The sensors demonstrated their potential as effective options for the analysis of orphenadrine citrate in quality control laboratories and in different healthcare activities.

Exploring the characterization, liberation and flotation response of a Nigerian low-grade copper ore

This study explores the characterization, liberation and flotation response of low-grade copper ore from Anka area, Zamfara state Nigeria. The ore was crushed, milled and sieved in accordance with BS 410 standard. It was characterized with XRD, XRF, SEM-EDS and AAS. Froth flotation was carried out with varying %solids, pH, retention time and collector dosages using SEX and sodium oleate. Particle size distribution of the ore shows its economic liberation between -150 and +106 µm while 80% passing corresponds to 175.7 µm using the Gaudin Schuhmann equation. However, according to metallurgical balance calculation, 63 µm proved to have the highest metal content. Identified peaks of the copper ore by XRD revealed the presence of pyrite and chalcopyrite as the major mineral content at 47 and 36%, respectively, while other elements were present in traces. XRF shows Fe and Cu as the major elements and others in traces. Morphology, according to SEM-EDS, revealed that Fe is the major impurity while the presence of Cu and S confirmed chalcopyrite is present in the ore minerals. AAS shows an average of 25.87% Cu and 32% Fe in the ore. Optimum recoveries of copper were recorded at 30% solids, pH of 8, 30 minutes retention time. The highest recovery of 95.94% was recorded with SEX at 0.25 mol/dm3, while recoveries were lower with PAX, the highest recovery being 33% at 0.20 mol/dm3. 0.25 mol/dm3 of SEX recorded the highest yield and enrichment ratio of 40.38 and 2.38, respectively.

Surface immobilization of nitrogen-coordinated iron atoms: a facile and efficient strategy toward MNC sites with superior catalytic activities

By immobilization FeNxsites on the porous substrate surface, stable atomically dispersed iron electrocatalyst with high-performance and high-metal content was rationally produced in quantitative yield and large-scaleviaa simple two-step process.

Hyperspectral Inversion Model of Relative Heavy Metal Content in Pennisetum sinese Roxb via EEMD-db3 Algorithm

Detection rapidity and model accuracy are the keys to hyperspectral nondestructive testing technology, especially for Pennisetum sinese Roxb (PsR) due to its extremely high adsorptive heavy metal content. The study of the resolution of PsR is conducive to the analysis of the accumulated heavy metal content in its different parts. In this paper, the contents of Cd, Cu and Zn accumulated in the old leaves, young leaves, upper stem, middle stem and lower stem, as well as the hyperspectral data of the corresponding parts, were measured simultaneously in both fresh and dry states. To begin, the spectral data of PsR were preprocessed by using Ensemble Empirical Mode Decomposition-Daubechies3 (EEMD-db3), Savitzky–Golay (SG), Symlet3 (sym3), Symlet5 (sym5), and multiplicative scatter correction (MSC). The 40 samples were divided into 32 training sets and 8 validation sets. The preprocessed spectral data were transformed by the first derivative (FD) and reciprocal logarithm (log(1/R)) to highlight the singularities using binary wavelet decomposition. After screening the significant bands from the correlation curve, the competitive adaptive reweighted sampling (CARS) and successive projection algorithm (SPA) were applied to extract the spectral characteristic variables, which were used to establish the partial least-squares (PLS) regression and multiple stepwise linear regression (MSLR) inversion models of Cd, Cu, and Zn contents. Based on EEMD-db3 pretreatment, the inversion model of Zn in the dry (fresh) state had R2 values of 0.884 (0.880), NRMSE values of 0.179 (0.253) and RPD values of 3.191 (3.221), indicating excellent stability and predictive performance. The findings of this study can not only aid in the rapid nondestructive detection of heavy metal adsorption in various parts of PsR, but can also be applied to guide the development and use of animal feed.

Hydrometallurgy recovery of copper, aluminum and silver from spent solar panels

Given the daily increase in the number of spent solar panels scrapped worldwide, these materials can be recycled as value-added heavy-metal products because of their high contents of valuable metals, such as Cu, Ag. Firstly, spent solar panels were soaked in acetone solvent and then split into three parts: glass, silicon and ethyl vinyl acetate. The wafers were dissolved in nitric acid solution to produce a leachate with 16.3, 5.9 and 1.5 g/L Cu, Al and Ag, respectively. With the addition of 35 g/L oxalate, 98.9% Cu was separated from the system in the form of high-purity moolooite, whereas the loss of Al and Ag was less than 1%. In the hydrothermal process, with the addition of 3 g glucose and 30 g/L phosphate and under the reaction condition at 190 °C for 10 h, 98.7% Al can be separated efficiently from the system in the form of AlPO4, and the loss of Ag was less than 0.1%. Finally, almost all of the Ag can be recovered efficiently from the system in the form of chlorargyrite through the introduction of sodium chloride. The results of the study provide a way for the effective recycling of Cu, Al and Ag in spent solar panels.

Biochar amendment improves growth and the essential oil quality and quantity of peppermint (Mentha × piperita L.) grown under waste water and reduces environmental contamination from waste water disposal

The reuse of waste water (WW) in agriculture is challenging as a potential strategy for sustainable agriculture development. However, its high content of heavy metals may cause damage to ecosystems. The property of biochar (BC) to minimize heavy metals accumulation into the soil was studied taking as a case study peppermint (Mentha x piperita L., Lamiaceae) irrigated with WW. Application of BC and WW, separately, promoted height, shoot number, crown diameter, internode length, leaf number, leaf length, leaf width, fresh (FW) and dry aerial parts weights (DW), root FW and root DW of peppermint. Also an increment in canopy diameter was observed. BC application considerably increased N, Mg, Mn, Fe and Zn, while WW increased N, P, K and Fe levels. Irrigation of peppermint with WW led to an increase of chlorophyll (Chl) a, Chl b, Chl a+b, carotenoids, anthocyanins, photosynthetic rate, transpiration, stomatal conductance, relative water content (RWC), and crop yield. On the other hand, BC application led to a decrease of Cd and Pb accumulation in plants. BC and WW application, separately, increased the essential oil content, the total phenol content, and the antioxidant capacity. Regardless of BC levels, irrigation of plants with WW decreased the percentage of menthone, menthofuran, isomenthone and pulegone in the essential oil, and increased the percentage of menthol and carvone. Similarly, BC application raised the percentage of menthol, and decreased that of pulegone. Overall, the application of BC in the culture medium is able to decrease the heavy metal concentration and improves the essential oil quality and quantity of peppermint under WW irrigation.

RESEARCH OF A VIBRATORY ROLLER IN FIELD CONDITIONS

Post-sowing rolling is an essential operation for a good harvest, since it ensures fulfilment of basic agro-technical requirements such as soil density and structure. It should be noted that presently used soil-cultivating rollers do not ensure the fulfillment of agrotechnical requirements and, in addition, have a high specific metal content - more than 300 kg/m. Taking into account these disadvantages, a new design of the vibratory roller was developed, the metal consumption of which is 70 kg/m, which is significantly lower than the existing analogues. Moreover, it provides high-quality tillage due to vibration, and the tillage meets the basic agricultural requirements. As a result of studies of the vibratory roller on barley crops, it was revealed that the density of the soil corresponded to agrotechnical requirements and varied from 1182 kg/m3 to 1230 kg/m3, in contrast to KKZ-6, its density varied from 1098 kg/m3 to 1412 kg/m3. The studies of the structural composition of the soil showed that there were no lumps larger than 50 mm after passage of the vibratory roller, as far as KKZ-6 is concerned, there were, on average, from 10% to 20% of lumps that did not meet the agricultural requirements. As a result of high-quality tillage with a vibratory roller, it was possible to reduce the cost of fuel and lubricants as a result of weight decrease per 1 m of the working width in comparison with KKZ-6, (which was 270 kg/m), in addition it allowed to increase the yield of barley by an average of 35.7%.

Geochemical controls on mobilization of metals from a 100-year-old waste rock pile and implications for selection of cover amendments

Reclamation of mine waste rock piles typically consists of constructing a cover with amendments to improve conditions for vegetation. However, cover amendments have potential to mobilize metals in waste by introducing new chemicals and altering pH and redox conditions. This study evaluates metal phases in a 100-year-old waste rock pile with high metals content (3.5% lead by weight, 0.8% zinc, and 0.75% copper) and the potential for these metals to be mobilized by several cover materials and amendments (topsoil, spent brewery grain, biochar, compost, commercial soil media, and phosphate). Laboratory testing indicates that metals have weathered from their initial metal sulfide phases (galena, sphalerite, chalcopyrite), and are now also present as sulfates, phosphates, carbonates, and phases associated with manganese/iron oxides. Sequential extraction tests demonstrated that the largest extractable fraction of metals is associated with manganese/iron oxides (37% of lead by weight, 22% of copper, and 26% of zinc), suggesting an environmental risk should geochemically reducing conditions develop and mobilize metals in the pile after cover construction. Testing of specific cover materials demonstrated that metals mobilization also occurs from low pH (as with spent brewery grain), formation of stable aqueous metal–organic complexes (as with spent brewery grain and compost), and ligand exchange (as with phosphate amendment). Results of this study demonstrate the importance of identifying metal phases present in a waste rock pile prior to selecting cover amendments.

Environmental assessment in fine jewelry in the U.S.-Mexico's Paso del Norte region: A qualitative study via X-ray fluorescence spectroscopy

Heavy metal contamination in raw materials has spread widely in the United States. The high increased number of recalls in consumer products and the lack of stricter regulations in the raw materials to be used in the jewelry industry have raised concerns among consumers. Studies in low-cost jewelry have shown the presence and high content of heavy metals; this environmental problem led to a child's death after swallowing a charm containing elevated levels of lead (Pb). Exposure to heavy metals, through inhalation, mouth, and skin contact, causes adverse health effects in children and adults. Exposure to lead affects mainly the nervous system and brain development; exposure to cadmium (Cd) causes damage to liver, kidneys, and lungs, and potentially leads to cancer; exposure to nickel (Ni) causes severe dermatitis. Thus, the importance and impact of studies of this nature cannot be overstated. As heavy metal contamination has increased in the United States, this research fills an important knowledge gap between previous studies conducted on low-cost jewelry and fine jewelry. In this study, conducted in the Paso del Norte region, one hundred and forty-three pieces of fine jewelry were evaluated for the presence of heavy metals using X-ray fluorescence (XRF) spectroscopy. Our study showed that 61 samples (42.7 %) exhibited the presence of Ni in the metal alloy, prevailing in jewelry pieces with lower percentage of gold. Eighteen samples showed the presence of Pb in gemstones, 11 pieces of these samples (7.7 % total) had <33.3 % gold (≤10 K); however, none of the samples showed the presence of Pb in the metal alloy. Further research is needed to evaluate the bioaccessibility of Pb in these gemstones, which may pose a potential health hazard to children and adults in the US Paso del Norte region and throughout the world.

Detoxification pathways of multiple metals from intensive copper production by indigenous ureolytic microbes coupled with soil nitrogen transformation

The ubiquitous ureolytic microbes were potential to clean up toxic heavy metals from environment. Their responses and detoxification mechanisms are largely unknown for multiple metals in field soils. In this study, high-throughput sequencing of the urease-encoding genes and deep learning from bioinformatic analysis were conducted for identifying ureolytic prokaryote-related processes throughout China. The passive adsorption of heavy metals onto cell walls or cell surfaces was mainly performed by G+ ureolytic bacteria in soils located in the large-scale smelting areas with slightly high Hg and low Cu/Zn/Ni contents. For the large-scale smelting areas with the highest Cr and lowest Cu/As contents, the Cr(VI) was reduced to Cr(III) by G– ureolytic bacteria and then accumulated in their periplasmic spaces or cell surfaces. The G– ureolytic bacteria detoxified high contents of multiple metals by intracellular antioxidant defense mechanisms and extracellular urease-induced (co)precipitation in the medium-scale smelting areas, consistent with high urease activities and ureolytic microbial diversity. In addition, this large-scale field work verified that toxic metals stimulated the bacterial hydrolysis of urea as soil nitrogen fertilizers and depressed the bacterial fixation of nitrogen from air. Simultaneously, the heavy metals used nitrate-N and nitrite-N as alternative electron acceptors, driving the soil denitrification processes.

Multi-Omics Uncover the Mechanism of Wheat under Heavy Metal Stress.

Environmental pollution of heavy metals has received growing attention in recent years. Heavy metals such as cadmium, lead and mercury can cause physiological and morphological disturbances which adversely affect the growth and quality of crops. Wheat (Triticum aestivum L.) can accumulate high contents of heavy metals in its edible parts. Understanding wheat response to heavy metal stress and its management in decreasing heavy metal uptake and accumulation may help to improve its growth and grain quality. Very recently, emerging advances in heavy metal toxicity and phytoremediation methods to reduce heavy metal pollution have been made in wheat. Especially, the molecular mechanisms of wheat under heavy metal stress are increasingly being recognized. In this review, we focus on the recently described epigenomics, transcriptomics, proteomics, metabolomics, ionomics and multi-omics combination, as well as functional genes uncovering heavy metal stress in wheat. The findings in this review provide some insights into challenges and future recommendations for wheat under heavy metal stress.

Diversity, heavy metals, and antibiotic resistance in culturable heterotrophic bacteria isolated from former lead-silver-zinc mine heap in Tarnowskie Gory (Silesia, Poland).

Mine tailings represent a great environmental concern due to their high contents of heavy metals. Cultivation analysis of microbiota of Tarnowskie Góry (Poland) mine tailing showed the occurrence of bacteria with colony-forming units as low as 5.7 × 104 per one gram of dried substrate. Among 110 bacterial isolates identified by a combination of MALDI-TOF mass spectrometry and 16S rRNA gene sequencing, phylum Actinobacteria was dominant, followed by Firmicutes and Proteobacteria. Extremely high levels of heavy-metal resistance were observed in Arthrobacter spp., particularly for zinc (500mg/L), lead (1500mg/L), and cadmium (1000mg/L). On the other hand, Staphylococcus spp. showed high tolerance to several antibiotics tested, especially ampicillin, partly due to blaZ gene presence. Due to the occurrence of antibiotic-resistant bacteria, mine tailings are not the cause of heavy-metal contamination only, but also a source of antibiotic-resistant bacteria and thus may represent a serious risk for public health.

A Review of On-Line Measurement Methods of Alkali Metal Emissions from Combustion by Passive Spontaneous Emission Spectroscopy

This article reviews the principles and applications of passive spontaneous emission spectroscopy (SES) for the quantitative determination of alkali metal concentrations emitted from combustion processes. The combustion of fuels that contain a high alkali metal content (Na and/or K) is challenging, as alkali metals reduce the slag formation temperature and induce fouling, causing combustion facilities to shutdown prematurely. The in situ on-line quantification of alkali metals is, thus, a critical measure to control combustion processes, preventing slagging and fouling from occurring. This review shows that several SES systems, developed by the Huazhong University of Science and Technology (HUST), are inexpensive, portable, and useful for measuring the alkali metal content, and have been applied for biomass combustion as well as coal and municipal solid waste combustion, from laboratory-scale settings (20 kW) to industrial facilities (300 MW). Compared with other research, the SES system from HUST has successfully quantified the emitted alkali metal concentrations during combustion. This review also highlights the challenges of the SES system and recommends further work to improve it for further applications.

Soil heavy metal contamination in the vicinity of the abandoned Zeïda mine in the Upper Moulouya Basin, Morocco. Implications for airborne dust pollution under semi-arid climatic conditions

For thirteen years, the Zeïda mine was one of Morocco's biggest lead reserves. The mining activities produced a huge volume of waste stored as tailings and subjected to meteoric agents. To better understand the impact of the past mining activity on the soil ecosystem in the vicinity of the abandoned mine, several physical and chemical analysis were done to identify the level of soil contamination. A total of 27 surface soil samples were collected from a depth of about 0–20 cm from crop areas and analysed for Pb, Zn, Cu, Co, Cd, and As total concentrations (aqua regia extraction) using the ICP-MS method. Results showed that soils have high to medium levels of metal concentrations, especially close to the tailings, compared to the non-contaminated soil sample taken as a geochemical background reference. Analysis of physicochemical parameters (pH, electrical conductivity, total calcium, phosphorus, potassium, and organic matter) has shown high alkalinity levels related to carbonates, varying organic matter content, and electrical conductivity values ranging from 4.12 to 1466 μS/cm. Most of the studied soils share the same mineralogical composition that includes: carbonates (Calcite and Dolomite), Quartz, Orthoclase, and Muscovite. Lead mineral phases (cerussite and wulfenite) have been found in 3 samples (ZAM17, ZAM18, and ZAM21). The Illite and the Kaolinite are the main clay minerals. Descriptive and multivariate statistics were carried out to investigate the distribution of the studied metals. Comparing the obtained results with International Standard Limits (ISL), soils especially those close to the mine tailings show high heavy metals content. Pb, Zn, Cu, As, and Cd contents in Zeïda soils are usually linked to anthropogenic origins. Results have shown correlation values between As, Cu, and Cd and Pb and Zn indicating that they come from the same origin and react similarly throughout transport.

Elemental and boron isotopic variations in tourmaline in two-mica granite from the Cuona area, Tibet: Insights into the evolution of leucogranitic melt

Two-mica granite is the most common magmatic rock type in the Himalayan leucogranite belt, which has close relationship with rare metal mineralization. Its genesis is generally attributed to magmatic differentiation. In recent years, the mineral geochemical compositions are increasingly used to study magmatic differentiation, which are significant for deciphering the melt evolution and element migration processes. In this study, in-situ major and trace element and boron isotope compositions for tourmalines from two-mica granites in the Cuona and Cuonadong leucogranites in the Cuona area are conducted to determine microscopic changes in mineral assemblages and geochemical compositions. Analytical results show that the tourmalines in the Cuonadong leucogranite were crystallized earlier relative to the tourmalines in the Cuona leucogranite during magmatic differentiation. The volatile contents have a genetic relationship with incompatible elements in tourmaline, which is possibly responsible for the formation of tourmaline zonation and the enrichment of Sr, Zn, and Pb during magmatic differentiation. The B isotopic composition of tourmaline in the Cuona area suggests that the granitic magma was dominantly derived from the partial melting of the metasedimentary source rocks. Their B isotope variations likely resulted from fluid exsolution during B-rich melt evolution. High rare metal contents in tourmalines indicate that the two-mica granites in the Cuona area may have great mineralization potential.

High-performance pinecone-like MOF derivative electromagnetic wave-absorbing composite via in situ anisotropic-oriented growth

Designing multihierarchical electromagnetic wave-absorbing composite with multiphase, multieffective, and multidimensional properties is an effective way to improve absorption performance. Metal–organic frameworks (MOFs) have a high metal content and a stable carbon framework. By adjusting the metal type, organic ligand type, and precursor ratio during the preparation process, MOF materials with different morphologies can be synthesized and transferred into multihierarchical electromagnetic wave-absorbing composites via in situ pyrolysis. Herein, based on the Kirkendall diffusion effect, an in situ anisotropic-oriented growth strategy was advanced during the pyrolysis of Prussian blue, and a new magnetic carbon composite (γ-Fe2O3 @N-rGO/MWCNT) was prepared. The composite has a multihierarchical structure consisting of pinecone-like nanoflowers and a porous carbon framework. The nanoflowers are core-shell structures with γ-Fe2O3 magnetic nanoparticles as cores and nitrogen-doped reduced graphene oxides as shells interspersed in a porous carbon framework that includes intertwined multiwalled carbon nanotubes and amorphous carbon. The minimum reflection loss (RLmin) of the samples can reach up to − 59.2 dB at 5.51 GHz. The in situ anisotropic-oriented growth strategy used in this work shows great promise for the preparation of a variety of multihierarchical structure nanocomposite electromagnetic wave-absorbing materials with abundant absorption effects.

Use of sewage sludge biochar as a catalyst in production of biodiesel through thermally induced transesterification

Sewage sludge (SS) is a residual/semi-solid material produced from industrial and municipal wastewater treatment processes. SS contains a high content of lipids and earth alkaline metals that can be used as catalysts for various chemical applications; however, its valorization has rarely been the focus of research. This study demonstrates that SS could be a promising raw material for biodiesel production and a biochar catalyst to promote the reaction kinetics of alkylation. Thermally induced transesterification of the SS extract (SSE) was performed in comparison with the conventional homogeneous reaction. SS biochar was fabricated via pyrolysis. The highest yield (33.5 wt.% per SSE) of biodiesel production was achieved in 1 min of reaction at 305 °C via thermally induced transesterification in the presence of SS biochar, while the yield of biodiesel from (trans)esterification with 5 wt.% H2SO4 was less than 1% even after 24 h. The reaction kinetics (< 1 min) of thermally induced transesterification was extraordinarily faster than that of conventional transesterification (3–24 h). The porous structure and high content of alkaline species in the SS biochar expedited the reaction kinetics. Consequently, the integrated/hybridized process for thermally induced transesterification and pyrolysis of the solid residue of SS was experimentally proved for the valorization of SS in this study. Considering that SS is being disposed of as a waste material and generates toxic chemicals in the environment, its valorization into value-added biodiesel and a catalyst could be an environmentally benign and sustainable technique.Graphical

Results of micrometallographic analysis of metalworking tools in graves of metallurgists in Moravia/Czech Republic

AbstractThe number of finds relating to metalworking, without evidence of mining and processing facilities, is very limited. In Final Eneolith graves of specialized metallurgists that have occurred, they contain a metal‐founding or metalsmithing toolkit, whose origins were from eastern Europe (the Maykop, Yamnaya Culture). Such metallurgical tools may have reached central Europe as part of the so‐called Yamnaya Package before the onset of the Bee Beaker Culture (BBC); and unlike the Pontic region, these two types of metallurgy separated here. There are found an accumulation of metallurgists' graves in Moravia, where the complete metalworking toolkit is deposited in a predefined place in richly furnished male graves with a distinctive funerary architecture that exhibit a clear relationship to the grave goods.EDX‐analysis detected a high content of metals (Cu, Ag, Au, Au–Ag alloy) on all working surfaces of stone tools, grinders, and boar tusks used for the final treatment of their metal products. This makes us believe that the used artefacts were laid as symbolical objects in the graves of these craftsmen who perfectly knew these advanced technologies. Due to their knowledge, their social significance gradually rose and finally reached the level of social elites, who were usually buried in a spectacular manner, including the quantity of grave goods (Überausstattung) and the pars pro toto deposition in one part of the finds.

Impacts of utilizing swine lagoon sludge as a composting ingredient

Lagoon sludge, a byproduct of swine operations in the Southeast United States, poses a management challenge due to its high mineral and metal content. Composting is a low-cost, scalable technology for manure management. However, limited information is available on composting swine lagoon sludge in terms of recipes, greenhouse gas emissions and end-product quality. Moreover, due to its high Zn and Cu content, high inclusion of sludge in composting recipes can potentially inhibit the process. To address these knowledge gaps, in-vessel aerated composting (0.4 m3each) was carried out to evaluate impacts of sludge inclusion, at 10% (Low Sludge, LS-Recipe) and 20% (High sludge, HS-Recipe) wet mass-basis, on composting process and end-product quality. Comparable maximum temperatures (74 ± 2.7 °C, 74.9 ± 2.9 °C), and organic matter loss were observed in both recipes. Similarly, sludge inclusion ratio had no significant impact on cumulative GHG emissions. The global warming potential (20-year GWP) for swine lagoon sludge composting using LS and HS recipes was observed to be 241.9 (±13.3) and 229.9 (±8.7) kg CO2-e/tDM respectively. Both recipes lost 24–28% of initial carbon (C) and 4–15% of nitrogen (N) respectively. Composting and curing did not change water-extractable (WE) phosphorus (P) concentrations while WE Zn and Cu concentrations decreased by 67–74% and 55–59% respectively in both recipes. End compost was stable (respiration rates <2 mgCO2-C/g OM/day) with germination index >93 for both recipes.

Effects of lignocellulosic biomass type on the economics of hydrothermal treatment of digested sludge for solid fuel and soil amendment applications

Digested sludge is a waste stream from anaerobic digestion (AD) in wastewater treatment plants. Hydrothermal treatment (HTT) of sludge mixed with lignocellulosic biomass is an attractive approach to improve sludge dewaterability and generate value-added products. However, process economics has not been well understood. In this study, firstly, the effect of biomass type on the energy properties of hydrochars was studied. Secondly, two scenarios were simulated to evaluate the effects of biomass type on the economics (processing 50,000 tonnes of sludge per year) of HTT of digested sludge for solid fuel and soil amendment applications. The two HTT scenarios included sludge alone and sludge-biomass mixtures (four cases for four biomass feedstocks) at 180 °C for 60 min. In both scenarios, HTT liquids were returned to existing AD facilities for biomethane production to offset the energy cost of the HTT process. The results showed that the higher heating value significantly increased from 16.0–17.0 MJ kg−1 in the sludge alone case to 18.0–23.0 MJ kg−1 in sludge–biomass mixtures (except for rice husk). With the use of saved transport cost as a revenue source, HTT of sludge–biomass led to a net present value (NPV) range of AU$ 9.9–20.3 million (20 years) and an internal rate of return (IRR) range of 25.0 %–45.2 % for solid fuel application of resulting hydrochar compared to an NPV of AU$ 18.4 million and an IRR of 55.0 % from HTT of sludge alone scenario. HTT of sludge-biomass led to a NPV range of AU$ 4.5–14.5 million and an IRR range of 17.2 %–35.7 % for soil amendment application while the hydrochar from HTT of sludge alone was not recommended for soil application due to the high contents of heavy metals. This study provides useful and critical information for process scale-up and commercialization for integration into wastewater treatment plants.