Manure-derived hydrochar superior to manure: Reducing non-point pollution risk by altering nitrogen and phosphorus fugacity in the soil-water system

Enhanced phosphorus bioavailability and reduced water leachability in dairy manure through hydrothermal carbonization: effect of processing temperature and CaO additive

Dairy manure, a significant source of phosphorus (P), can potentially cause environmental risk due to P runoff when dairy manure is directly applied to cropland. Thus, there is an increasing interest in mitigating P loss from manure prior to land applications. This study aimed to investigate the potential of hydrochar produced by hydrothermal carbonization (HTC) for P recycling from dairy manure with and without the addition of CaO, focusing on the plant bioavailability, stabilization, and transformation of P in the resultant hydrochar. Hydrochar was prepared under different temperatures (180-240°C). The effect of CaO addition (0-10% of raw manure on dry wt. basis) was also evaluated at 220°C. Results showed that water-soluble P (WSP), a key indicator of P runoff loss, was significantly reduced in hydrochar, particularly with CaO addition. In addition, the plant available P in hydrochar increased with HTC temperature increase till 220°C, which accounted for ∼90% of total P content, then decreased with temperatures higher than 220°C. The addition of CaO slightly reduced plant bioavailability when compared to hydrochar produced at 220°C without additive. The P fractionation and speciation analyses indicated the transformation of P into Ca-associated apatite P. Hydrochar produced at 220°C with 10% CaO addition resulted in a high P recovery (∼85%) and a reduced runoff risk by 97%. The results demonstrate the efficacy of P recycling through hydrochar produced from dairy manure through HTC, which offers a sustainable approach to managing dairy waste while mitigating the potential environmental risks of P runoff.

Novel insights into released hydrochar particle derived from typical high nitrogen waste biomass: Special properties, microstructure and formation mechanism

Hydrothermal carbonization (HTC) treatment is a promising method to transforming waste biomass into valuable resources and promoting waste recycling, especially for high nitrogen feedstocks. While small-sized hydrochar particle (≥0.45 μm) released from its solid product (hydrochar) application demonstrated large knowledge gaps compared with its original hydrochar and "secondary char" from model biomass (like glucose, sucrose, and starch). Thus, hydrochar particles derived from typical high nitrogen biomass, kitchen garbage (KG), and blue-green algae mud (AM), were collected to investigate their basic properties, microstructures and corresponding formation mechanisms. The results were: 1) the micron-sized hydrochar particles with yields as 3.42-7.86 wt% presented special characteristics, i.e., poor porous structures, moderate pH value, negative surface charge and higher surface hydrophobicity (contact angles as 95.00-117.67°) relative to original hydrochar and secondary char; 2) micronuclei aromatic core and hydrophobic hydrothermal polymers (methoxyl groups/alkyl chain with ether and carboxy groups) were identified in these hydrochar microparticles (HMPs) by jointly using differential thermogravimetry (DTG) analysis, Gaussian fitting model and thermogravimetric analysis combined with Fourier transform infrared spectrometry and mass spectrometry (TG-FTIR-MS) analysis; 3) polycondensation/cyclization reactions and Maillard/Mannich reaction in the KGHMPs, as well as solid-solid conversion and Maillard/Mannich reaction, polymerization reaction in AMHMPs core and its shell were proposed as their dominated formation mechanisms. The conclusions of this study indicated strong binding of HMPs with NH4+, metals, and hydrophobic contaminants, and further reinforcing these application effects as soil fertilizer and decontaminant in soil/water for the N conversion, which also significantly depend on HTC temperature and feedstock.

Effects of biogas slurry on hydrothermal carbonization of digestate: Synergistic valorization of hydrochars and aqueous phase

In this study, livestock manure digestate (LMD) was used as feedstock for hydrothermal carbonization (HTC) at different temperature (180-260 °C) and residence time (0-4 h). Nutrient flow and distribution during the HTC process were evaluated by comparing the effects of livestock manure biogas slurry (LBS) and ultrapure water (UW) to determine the optimal reaction conditions for the synergistic production and application of hydrochars (HC) and aqueous phases (AP). Compared with UW, the HC yields derived from LBS as solvent were increased by 27.05-38.24% under the same conditions. The C content, high heating value (HHV), and energy densification of HC obtained from LMD and UW were higher than those obtained from LMD and LBS, and the ash content was lower. While, LBS circumstance improved the porosity, N content and some trace elements e.g. Ca, Fe and Mg in HC that showed excellent fertility potential. In addition, the recovery rate of K, TOC, NH4+-N, and TN concentrations in AP were significantly higher in the LBS circumstance than in UW. The results show that the addition of UW is more favorable for fuel generation, and the HC obtained from LMD and UW at 220 °C has the potential to be used as a fuel. Whereas, the addition of LBS enhanced the potential of HC and AP for agricultural applications simultaneously. It is recommended to use HC and AP obtained from LMD and LBS at 240 °C for using as fertilizer.

Enhancing C and N turnover, functional bacteria abundance, and the efficiency of biowaste conversion using Streptomyces-Bacillus inoculation

Microbial inoculation plays a significant role in promoting the efficiency of biowaste conversion. This study investigates the function of Streptomyces-Bacillus Inoculants (SBI) on carbon (C) and nitrogen (N) conversion, and microbial dynamics, during cow manure (10% and 20% addition) and corn straw co-composting. Compared to inoculant-free controls, inoculant application accelerated the compost's thermophilic stage (8 vs 15 days), and significantly increased compost total N contents (+47%) and N-reductase activities (nitrate reductase: +60%; nitrite reductase: +219%). Both bacterial and fungal community succession were significantly affected by DOC, urease, and NH4+-N, while the fungal community was also significantly affected by cellulase. The contribution rate of Cupriavidus to the physicochemical factors of compost was as high as 83.40%, but by contrast there were no significantly different contributions (∼60%) among the top 20 fungal genera. Application of SBI induced significant correlations between bacteria, compost C/N ratio, and catalase enzymes, indicative of compost maturation. We recommend SBI as a promising bio-composting additive to accelerate C and N turnover and high-quality biowaste maturation. SBI boosts organic cycling by transforming biowastes into bio-fertilizers efficiently. This highlights the potential for SBI application to improve plant growth and soil quality in multiple contexts.