Valorization of cow manure via hydrothermal carbonization for phosphorus recovery and adsorbents for water treatment

Optimized hydrothermal carbonization of chicken manure and anaerobic digestion of its process water for better energy management

Modern poultry production is faced with the challenge of properly managing its associated wastes, in particular chicken manure (CM). There is a need to improve the management of CM through conversion processes that allow the production of value-added products, particularly for energy purposes, such as hydrothermal carbonization (HTC) and anaerobic digestion (AD). The objectives of this study were: i) to optimize the CM-HTC, using response surface methodology with simultaneous optimization of mass yield and higher heating value (HHV), and ii) to evaluate the biomethane potential of the process water generated from hydrochar production under the optimized condition. An analysis of the overall energy potential was also performed. The optimal condition for HTC was 234 °C for 30 min, resulting in hydrochar with an HHV of 14.88 ± 0.22 MJ/kg and a mass yield of 50.00 ± 3.13 wt%. The cumulative methane yield was 179.2 ± 13.1 NmL CH₄/g VSadded and 255.5 ± 14.5 NmL CH₄/g VSadded for process water at 180 °C and 234 °C, respectively. The addition of hydrochar improved the methane yield by 49.6 ± 10.8%, indicating that this is a valuable option for energy recovery from CM. Overall, the HTC-AD integration approach achieved an energy recovery potential of more than 79%, offering an efficient strategy for CM valorization.

Hydrothermal carbonization of woody waste: Changes in the physicochemical properties and the structural evolution mechanisms of hydrochar during this process

The Chinese medicine residue (CMR) is composed of wet woody waste, including licorice and ephedra, so using hydrothermal carbonization (HTC) to recover renewable energy from the CMR is a suitable treatment method. An in-depth analysis of the physicochemical properties and structural evolution mechanism of hydrochars is helpful in fundamentally promoting the energy utilization of traditional Chinese medicine waste residue. Therefore, this study analyzed the physicochemical properties and morphological structure of hydrochar produced under varying HTC conditions using multiple testing methods. The evolution of the hydrochar's structural characteristics can be categorized into three stages: component decomposition, structural rearrangement, and carbonization. During the component decomposition and carbonization stages, numerous nanoscale micropores form within the hydrochar. These micropores' specific surface area and pore volume can reach up to 113.420 m2/g and 0.01913 cm3/g, respectively. The highest fractal dimension values for D1 and D2 are 2.6354 and 2.5565, while the maximum values for the microcrystalline stacking height (Lc) and the average number of crystalline layers (Nave) are 0.3354 and 1.9968, respectively. Consequently, the hydrochar produced during these stages exhibits a rougher pore surface and a more complex structure, making it more suitable for adsorbing heavy metals from soil and sequestering CO2. During the structural rearrangement stage, the hydrochar exhibits higher contents of fixed carbon (FC), MgO, P2O5, and a higher C/N atomic ratio, with maximum values of 38.51%, 0.99%, 1.12%, and 28.49, respectively. Thus, the hydrochar produced during this stage is more suitable for soil remediation and nutrient recovery.

Comprehensive assessment of cow manure hydrothermal treatment products for land application and energy recovery

In this study, cow manure was hydrothermally treated in a 2-litre reactor for 1 h at temperatures between 100 °C and 260 °C. Both the raw manure and the solid and liquid products of the hydrothermal treatment were characterized to understand the fate of the inorganic elements and to assess the suitability of the products for land applications and energy recovery. Satisfactory elemental balances were obtained for the organic and most inorganic elements and indicated that most inorganic elements were incorporated into the solids with lower solubility, with the exception of potassium and sodium, which were mostly solubilized in the process water; calcium and chlorine were also solubilized to a lesser extent in the process water. Elemental composition and surface functional groups showed that hydrochar produced within the hydrothermal carbonization range (180-260 °C) seemed better suited for utilization as a soil amendment than raw cow manure. The potential for energy recovery lies in the anaerobic digestion of the process water, from which higher methane yields can be obtained than from raw cow manure. Lower temperatures in hydrothermal carbonization are considered a compromise for the safe land applications of cow manure, energy recovery from the process water, and enhanced dewaterability. These findings can help to eliminate bottlenecks in the upscaling of cow manure hydrothermal treatment and promote the circular bio-economy.

Carbon Sequestration Potential of Manure-Derived Hydrochar Aided by Secondary Stabilization

Hydrothermal carbonization (HTC) is a process that produces a carbon-rich solid from wet organic materials through the application of heat and pressure. Carbonized solids, previously correlated to long-term soil stability, may be considered for carbon sequestration through incorporation into soil. Chars produced by pyrolysis are known for exceptional stability in soil, but pyrolysis is expensive when applied to wet biomass, such as manure. Chars produced from manure by HTC show considerably improved potential for carbon sequestration relative to untreated manure, although not as great as that of chars produced by pyrolysis. This study focuses on producing and evaluating chars by HTC paired with pyrolysis and different methods of chemical oxidation for long-term carbon sequestration in soil. It is shown that a two-step process of pyrolysis following HTC produces a char that outperforms those produced by either individual process (HTC or pyrolysis) in carbon yield, carbon content, and, more importantly, soil carbon sequestration potential. It was found that acid-catalyzed HTC followed by pyrolysis resulted in a char with a 13% increase in carbon yield, a 51% increase in carbon content, and an atomic O/C ratio 64% smaller than the char produced by conventional pyrolysis.

Manure derived hydrochar reduced phosphorus loss risk via an alteration of phosphorus fractions and diversified microbial community in rice paddy soil

Phosphorus (P) loss caused by the irrational use of manure organic fertilizer has become a worldwide environmental problem, which has caused a potential threat to water safety and intensified agricultural non-point source pollution. Hydrothermal carbonization is method with a low-energy consumption and high efficiency to deal with environmental problems. Application of pig manure-derived hydrochar (PMH) to soil exhibited potential of sustainable development compared with the pristine pig manure (PM). However, the effects of PMH on the distribution of P among the fractions/forms and the interaction between microorganisms and P forms and its relevance to the potential loss of P in paddy fields has not been clarified. Therefore, in this study, a soil column experiment was conducted using the untreated soil (control), and the PM, PMH1 (PMH derived at 180 °C), and PMH2 (PMH derived at 260 °C) treated soils (at the dose of 0.05 %) and rice was cultivated to investigate the effects of PM and PMH on the P fractions, mobilization, ad potential loss via the induced changes on soil microbial community after a complete growing season of rice. The trend of P utilization was evaluated by P speciation via continuous extraction and 31P NMR. The addition of PMH reduced the proportion of residual P in soil by 23.8-26.3 %, and increased the proportion of HCl-P and orthophosphate by 116.2-158.6 % and 6.1-6.8 % compared to PM. The abundance of gcd gene developed after the application of PMH2, which enhanced the mobile forms of soil P utilization via secreting gluconic acid. The network diagram analysis concluded that the changes in various P forms were mainly related to Proteobacteria, Bacteroides, Firmicutes and Acidobacteria. The results illustrated that PMH mitigate the potential risk of P loss more than PM by altering P fractions and affecting soil microbial community.

Enhanced heavy metal stabilization and phosphorus retention during the hydrothermal carbonization of swine manure by in-situ formation of MgFe2O4

Hydrothermal carbonization is an efficient technique for the disposal of livestock manure, enabling its harmless treatment, quantity reduction, and resourceful utilization. Co-hydrothermal of modified materials facilitates the production of more valuable carbonaceous materials. However, further exploration is needed to understand their potential impact on the environmental risks associated with livestock manure disposal and the application of products derived from it. Therefore, the carbonization degree, heavy metals stabilization, and phosphorus retention during the hydrothermal treatment of swine manure were systematically investigated in this study under the influence of in-situ formed MgFe2O4. The results revealed that the in-situ formation of MgFe2O4 improved the dehydration and decarboxylation of organic components in swine manure, thereby improving its carbonization degree. Furthermore, both hydrothermal carbonization and MgFe2O4 modified hydrothermal carbonization resulted in an enhanced stabilization of heavy metals, leading to a significant reduction in their soluble/exchangeable fraction and reducible fraction. Phosphorus was predominantly retained in the hydrochars, with the highest retention rate reaching 88%, attributed to the significant decrease in soluble and exchangeable phosphorus fractions facilitated by the in-situ formation of MgFe2O4. Moreover, MgFe2O4 modified hydrochars exhibited remarkable adsorption capacity for Pb(II) and Cu(II) without any leaching of heavy metals. Overall, the findings indicated that the in-situ formation of MgFe2O4 positively influenced the hydrothermal of swine manure, improving certain economic benefits in its practical application.

Pyrolytic and hydrothermal carbonization affect the transformation of phosphorus fractions in the biochar and hydrochar derived from organic materials: A meta-analysis study

Carbonized organic materials are widely used to achieve soil improvement and alleviate soil pollution. The carbonization process significantly changes the total phosphorus (P) content and the P form in the solid phase derived from organic materials, which in turn has a significant impact on the P fertilizer effect in soils. In the present study, a meta-analysis with 278 observational data was conducted to detect the impact of the carbonization process (including pyrolytic carbonization and hydrothermal carbonization) on the transformation of P fractions in biochar or hydrochar derived from different organic materials. The results showed that the carbonization process significantly increased the total P content of the solid phase by 67.9%, and that the rate of P recovery from raw materials stayed high with a mean value of 86.8%. Among them, the impact of sludge-derived char was smaller when compared to the manure-derived char and biomass-derived char. The increase of total P in the biochar (or hydrochar) produced at >500 °C (or >200 °C) was more notable than that at <500 °C (or <200 °C). Simultaneously, the carbonization process significantly decreased the proportion of available P pool in the solid phase by 51.7% on average and increased the proportion of stable P pool in the solid phase by 204%. Appropriate production temperature helps to adjust the proportion of stable P pool in the solid phase. This meta-analysis pointed out that the carbonized solid phase recovers most of the P in the feedstock and that it promotes a significant transformation of available P pool in the feedstock to stable P in the carbonized solid phase. These findings provide useful information for the rational use of carbonization technology, the development of corresponding field management strategies, and the potential value of carbonized solid phase utilization.

A thematic review on livestock manure treatment strategies focusing on thermochemical conversion

Livestock manure (LSM) management is emerging as a challenge due to increasing livestock consumption. Owing to the decreased agricultural land area, it is necessary to ensure LSM utilization in non-agricultural fields. LSM can be a valuable resource if managed as a circulating resource. This study discusses research trends based on a literature review and classifies LSM treatments. The analysis of each treatment is presented according to research trends, and implications for the future LSM processing are discussed. "Biological treatment" accounted for the largest portion at 48%, "manure management," which suggests improvement in manure treatment through systematic thinking or LSM management practices, accounted for 16%, and "thermochemical conversion" accounted for 11%. In addition, "life cycle assessment (LCA) research," "solid-liquid separation approach," and "nutrient-recovery/losses" were derived. Studies on biological treatments are increasing. Although anaerobic digestion (AD) is the most used method, it has the disadvantages of long processing time and waste generation after processing. As a key supplement, thermochemical conversion (TCC) technology, which could overcome the disadvantages of AD, was reviewed.

Phosphorus recovery from aqueous product of hydrothermal carbonization of cow manure

The work studies the recovery of nutrients (phosphorus and nitrogen) from the process water of acid-assisted hydrothermal carbonization (HTC) of cow manure. Three organic acids (formic acid, oxalic acid, and citric acid) and sulfuric acid were evaluated as additives in HTC. Using 0.3 M sulfuric acid, more than 99% of phosphorus and 15.6% of nitrogen from manure are extracted and dissolved during HTC at 170 °C with 10 min reaction time in a batch reactor. Nutrients (mainly phosphorus) were recovered through precipitation from process water by raising the ionic strength of the solution by addition of salts of magnesium and ammonia, and by raising the pH to 9.5. Subsequently, phosphorus-rich solids were recovered containing almost all (greater than 95%) of the dissolved phosphorus in the sulfuric and formic acid assisted runs. Morphology and qualitative chemical analysis of the precipitates were determined. It is shown by XRD that the precipitate formed from process water generated by HTC with oxalic acid is crystalline, although the diffraction pattern could not be matched with any expected substance.

Nutrient recovery and valorisation from pig slurry liquid fraction with membrane technologies

Livestock slurry has been reported to be a potential secondary raw material as it contains macronutrients ‑nitrogen, phosphorus and potassium-, which could be valorised as high-quality fertilizers if proper separation and concentration of valuable compounds is performed. In this work, pig slurry liquid fraction was assessed for nutrient recovery and valorisation as fertilizer. Some indicators were used to evaluate the performance of proposed train of technologies within the framework of circular economy. As ammonium and potassium species are highly soluble at the whole pH range, a study based on phosphate speciation at pH from 4 to 8 was assessed to improve the macronutrients recovery from the slurry, resulting in two different treatment trains at acidic and alkaline conditions. The acidic treatment system based on centrifugation, microfiltration and forward osmosis was applied to obtain a nutrient-rich liquid organic fertilizer containing 1.3 % N, 1.3 % P₂O₅ and 1.5 % K₂O. The alkaline path of valorisation was composed by centrifugation and stripping by using membrane contactors to produce an organic solid fertilizer -7.7 % N, 8,0 % P₂O₅ and 2.3 % K₂O-, ammonium sulphate solution -1.4 % N- and irrigation water. In terms of circularity indicators, 45.8 % of the initial water content and <50 % of contained nutrients were recovered - 28.3 % N, 43.5 % P₂O₅ and 46.6 % K₂O - in the acidic treatment resulting in 68.68 g fertilizer per kg of treated slurry. 75.1 % of water was recovered as irrigation water and 80.6 % N, 99.9 % P₂O₅, 83.4 % K₂O was valorised in the alkaline treatment, as 219.60 g fertilizer per kg of treated slurry. Treatment paths at acidic and alkaline conditions yield promising results for nutrients recovery and valorisation as the obtained products (nutrient rich organic fertilizer, solid soil amendment and ammonium sulphate solution) fulfil the European Regulation for fertilizers to be potentially used in crop fields.

Addition of in situ clay catalysts at different process points in a cascaded hydrothermal carbonization-pyrolysis process for agro-industrial waste valorization

Agro-industrial wastes can be thermochemically converted to sustainable fuels and upcycled carbon products. However, processing such feedstocks through pyrolysis or hydrothermal carbonization (HTC) alone yields fuels that require significant downstream upgrading. In this work, apple pomace was treated via a cascaded HTC-pyrolysis process using inexpensive and abundant clay catalysts, montmorillonite and attapulgite. Clays were added pre-HTC to raw biomass or to hydrochar pre-pyrolysis to examine the effect of addition as a function of process insertion point. Both clays produce similar bio-oils when they are added at the same process point. However, bio-oil was affected by the point in which clay was added to the process (before or after HTC). When clay was added pre-HTC, the bio-oil had an average hydrocarbon content twice that when clay was added to the hydrochar after HTC, prior to pyrolysis.

Hydrothermal carbonization of cow dung with human urine as a solvent for hydrochar: An experimental and kinetic study

Hydrothermal carbonization (HTC) is the most cost-effective, environmentally friendly, and efficient physicochemical and biochemical process for converting biomass to products with added value. The objective and novelty of this work is to produce and investigate the qualities of hydrochar fuel (as a solid fuel) from cow manure using human urine as a solvent in order to find a suitable replacement for conventional fuel (i.e., coal). HTC based studies were conducted in batch, at three different reaction temperatures (180 °C, 200 °C, and 220 °C) and two different reaction periods (2 and 4 h). For kinetic analysis and reaction mechanism of the combustion behavior of the produced hydrochar, the model free kinetic methods and the z-master plot were used. From the model free kinetics methods, it was observed that the resultant optimum average activation energy and pre-exponential factor for the produced hydrochar at 180 °C and 2 h reaction period (HTC_180_2) were ∼120 kJ/mol and ∼5.59 × 10²⁵ sec^-1, respectively. In addition, the little variation between ΔE_α and ΔH_α (∼10 kJ/mol) suggests that the combustion of produced hydrochar (HTC_180_2) occurred with minimal energy use. Furthermore, the hydrochar exhibited its highest heating value at 200 °C for 4 h (HTC_200_4) which was 1.44 times higher than the raw dung (13.4 MJ/kg) due to the HTC process. The produced hydrochar demonstrated a significant improvement compared to the conventional solvent, i.e. water.

Rapid and Effective Lead Elimination Using Cow Manure Derived Biochar: Balance between Inherent Phosphorus Release and Pollutants Immobilization

Cow manure derived biochar (CMBC) can serve as a promising functional material, and CMBC can be regarded as an ecofriendly approach compared to conventional ones. CM bioadsorbent can be employed for heavy metal immobilization (such as for lead) as well as an amendment to increase soil fertility (e.g., phosphorus). Few studies have examined the surface interactions between pollutants and bioadsorbents when inherent nutrient release is present. In this work, CMBC was prepared and applied for Pb(II) removal, and the vital roles of released phosphorus from CMBC were comprehensively disclosed. Furthermore, CMBC could immobilize part of the Pb(II) in soil and promote plant growth. CM400 was an effective adsorbent whose calculated Q_e reached 691.34 mg·g^-1, and it rapidly adsorbed 98.36 mg·g^-1 of Pb(II) within 1 min. The adsorption mechanisms of Pb(II) by CMBC include ion exchange, physical adsorption, electrostatic attraction, chemical precipitation, surface complexation, and cation-π bond interaction. Based on the residual phosphorus content and adsorption effect, complexation rather than the chemical precipitation had a greater contribution toward adsorption. Besides, as the concentration of Pb(II) increased, the main adsorption mechanisms likely transformed from chemical precipitation to ion exchange and complexation. CMBC not only had a good effect on Pb(II) removal in the solution, but also immobilized the Pb(II) in soil to restrain plant uptake as well as promote plant growth. The main novelty of this work is providing more insights to the cow manure bio adsorbent on Pb immobilization and phosphorus release. This study is expected to serve as a basis and reference for analyzing the release effects of inherent nutrients and the interfacial behaviors with heavy metals when using CMBC and other nutrient-rich carbon-based fertilizers for pollution control.

Valorisation of agri-food waste to fertilisers is a challenge in implementing the circular economy concept in practice

The area of agricultural wastes valorisation to fertilizers is attracting growing attention because of the increasing fertilizer prices of fertilizers and the higher costs of waste utilization. Despite the scientific and political interest in the concept of circular economy, few studies have considered the practical approach towards the implementation of elaborated technologies. This article outlines innovative strategies for the valorisation of different biobased wastes into fertilizers. The present work makes a significant contribution to the field of new ideas for waste biomass management to recover significant fertilizer nutrients. These results emphasize the importance of the biomass use as a base of renewable resources, which has recently gained special importance, especially in relation to the outbreak of pandemia and war. Broken supply chains and limited access to deposits of raw materials used in fertilizer production (natural gas, potassium salts) meant that now, as never before, it has become more important and feasible to implement the idea of a circular economy and a green deal. We have obtained satisfactory results that demonstrate that appropriate management of biological waste (originating from agriculture, food processing, aquaculture, forest, pharmaceutical industry, and other branches of industry, sewage sludge) will not only reduce environmental nuisance (reducing waste heaps), but will also allow recovery of valuable materials, such as nitrogen (especially valuable amino acids), phosphorus, potassium, microelements, and biologically active substances with properties that stimulate plant growth. The results reported here provide information on production of biobased plant protection products (bioagrochemicals) from agri-food waste. This work reports an overview of biopesticides and biofertilisers production technologies and summarizes their properties and the mechanisms of action.

Hydrochar and hydrochar co-compost from OFMSW digestate for soil application: 3. Toxicological evaluation

Modern societies produce ever-increasing amounts of waste, e.g. organic fraction of municipal solid waste (OFMSW). According to the best available techniques, OFMSW should be treated through anaerobic digestion to recover biogas and subsequently composted. An innovative scheme is under investigation, where anaerobic digestion is combined with hydrothermal carbonization (HTC) and composting. The final product, referred to as hydrochar co-compost (HCO), is under study to be used as an unconventional soil improver/fertilizer. Recent studies showed that HCO is not phytotoxic. However, nothing is known about the toxicity of HCO on cells as part and organisms as a whole. This study aims to investigate in vitro genotoxicity and cytotoxicity of the HCO and its precursors in the production process. In particular, we tested water and methanolic extracts of HCO (WEHCO and MEHCO) from one side and methanolic extracts of hydrochar (MEH) and OFMSW digestate (MED) as well as liquor produced downstream HTC (HTCL) from the other side. Genotoxicity was investigated using cytokinesis-block micronucleus assay in Chinese Hamster Ovarian K1 (CHO-K1) cells. Cytotoxicity was tested in vitro against a panel of human cells line. Zebrafish embryo toxicity upon MEH treatment was also investigated. Results show that incubation of CHO-K1 cells with all the tested samples at different concentrations did not cause any induction of micronucleus formation compared to the vehicle-treated control. Treatment of cells with MEH, MED, HTCL and MEHCO, but not WEHCO, induced some degree of cytotoxicity and MEH showed to be more cytotoxic against tested cells compared to the MEHCO. Toxicity effect at the highest tested concentrations of MEH on zebrafish embryos resulted in coagulation, induction of pericardial edema and death. In conclusion, the hydrochar co-compost cytotoxicity is similar to standard compost cytotoxicity. Hence composting the hydrochar from OFMSW digestate is a good step to eliminate the cytotoxicity of hydrochar.

Hydrochars produced by hydrothermal carbonisation of seaweed, coconut shell and oak: effect of processing temperature on physicochemical adsorbent characteristics

The present study addresses the production of hydrochars from brown seaweed (Fucus serratus) (FS-HCs), coconut shell (CS-HCs), and oak (Oak-HCs) as potential adsorbents using hydrothermal carbonisation (HTC). The effect of HTC processing temperature on the physicochemical adsorbent characteristics of the hydrochars is investigated at different temperatures (200, 220, 250 °C) using a hydrothermal batch reactor. Increasing HTC temperature causes the formation of many spheres in CS-HCs and Oak-HCs, increasing their porosity, except FS-HCs. The surface area of the hydrochars increases with increasing HTC temperature; 10.93–12.78 m2/g for FS-HCs, 2.18–21.94 m2/g for CS-HCs, except for Oak-HCs which decreases from 4.89 to 3.09 m2/g. Increasing HTC temperature decreases volatile matter content in the hydrochars, increases fixed carbon content, and decreases H/C ratio (except for FS-HCs) and O/C ratio of the hydrochars. For all the hydrochars, increasing the HTC temperature results in a slight decrease in zeta potential magnitude, with negatively charged surfaces, making them potential adsorbents for cationic pollutants. The study confirms that the HTC process improves key chemical and physical characteristics of the hydrochars compared to the original biomass, and that the physicochemical adsorbent characteristics are enhanced as the processing temperature increases.