Highly efficient phosphorus recovery from sludge and manure biochars using potassium acetate pre-treatment

Influence of potassium addition on phosphorus availability and heavy metals immobility of biochar derived from swine manure

Pyrolysis of animal manure at high temperature is necessary to effectively immobilize heavy metals, while the available phosphorus (P) level in biochar is relatively low, rendering it unsuitable for use as fertilizer. In this study, the pretreatment of swine manure with different potassium (K) sources (KOH, K2CO3, CH3COOK and C6H5K3O7) was conducted to produce a biochar with enhanced P availability and heavy metals immobility. The addition of all K compounds lowered the peak temperature of decomposition of cellulose in swine manure. The percentage of ammonium citrate and formic acid extractable P in biochar increased with K addition compared to undoped biochar, with CH3COOK and C6H5K3O7 showing greater effectiveness than KOH and K2CO3, however, water- extractable P did not exhibit significant changes. Additionally, the available and dissolved Si increased due to the doping of K, with KOH and K2CO3 having a stronger effect than CH3COOK and C6H5K3O7. X-Ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) analysis revealed that K addition led to the formation of soluble CaKPO4 and silicate. In addition, the incorporation of K promoted the transformation of labile copper (Cu) and znic (Zn) into the stable fraction while simultaneously reducing their environmental risk. Our study suggest that the co-pyrolysis of swine manure and organic K represents an effective and valuable method for producing biochar with optimized P availability and heavy metals immobility.

Synergistic reduction of pollution and carbon mitigation in constructed wetlands-microbial fuel cell using sludge-derived biochar

Integrating microbial fuel cells (MFC) into constructed wetland systems (CW) has been an efficient wastewater treatment to improve the pollutants removal and regenerate power energy. This study fabricated a sludge biochar material (SBM) to sequestrate the carbon of residual sludge. Thereafter used SBM and modified SBM as the substrate materials to construct three groups of CW-MFC for decreasing the greenhouse gas (GHG) emission. The water quality improvement in removal efficiency achieved (2.59 %, 3.10 %, 5.21 % for COD; 3.31 %, 3.60 %, 6.71 % for TN; 1.80 %, 7.38 %, 4.93 % for TP) by the application of MFC, SBM, and modified SBM in wastewater treatment, respectively. Additionally, the reduction in global warming potential (GWP) realized 17.2 %, 42.2 %, and 64.4 % resulting from these applications. The carbon flow and fate diagrams showed MFC shifted the gas phase‑carbon flow from CH4 to CO2, and SBM promoted this shift trends. Microbial diversity indicated enrichment of electrochemically active bacteria (EAB), denitrifying bacteria, and phosphate accumulating organisms (PAOs) by SBM. Metabolic pathways analysis showed that introduction of MFC and SBM exhibited significant increases of key functional genes in metabolic pathway of anaerobic oxidation of methane (AOM). This study highlights the benefit of CW-MFC in and provides a new strategy for removing pollutants and abating GHG emissions in wastewater treatment.

Recent progress in the production and application of biochar and its composite in environmental biodegradation

Over the past few decades, extensive research has been conducted to develop cost-effective and high-quality biochar for environmental biodegradation purposes. Pyrolysis has emerged as a promising method for recovering biochar from biomass and waste materials. This study provides an overview of the current state-of-the-art biochar production technology, including the advancements and biochar applications in organic pollutants remediation, particularly wastewater treatment. Substantial progress has been made in biochar production through advanced thermochemical technologies. Moreover, the review underscores the importance of understanding the kinetics of pollutant degradation using biochar to maximize its synergies for potential environmental biodegradation. Finally, the study identifies the technological gaps and outlines future research advancements in biochar production and its applications for environmental biodegradation.

Potassium assisted pyrolysis of Chinese Baijiu distillers' grains to prepare biochar as controlled-release K fertilizer

A novel K-loaded biochar as controlled-release K fertilizer was prepared through K assisted pyrolysis of distillers' grains (DGs, typical solid-byproducts of Chinese Baijiu) under different atmospheres (N₂ and CO₂) and temperatures (400 and 800 °C). The fabricated DGs-based biochar exhibited high K loading (200.20-232.33 mg/g), and the release kinetics and column leaching experiments suggested that K-loaded biochar exhibited excellent controlled release performance in a long term. Compared with other biochar, the K-loaded biochar prepared at CO₂ and 400 °C has lower cumulative release ratio of 82.35 %, and could retain the durative K release at ~0.5 % for 25 d. The release kinetics suggested that the K release behavior was dominated by dissolution, electrostatic attraction, adsorption, confinement effect, and chemical interaction. Furthermore, pot experiments revealed that K-loaded biochar could promote the growth of Komatsuna, in which the fresh weight and chlorophyll relative content of Komatsuna cultivated with biochar prepared at CO₂ and 400 °C reached 0.146 g and 41.95 after 25 d growth, respectively. The above results suggested that the K-loaded biochar exhibited excellent utilization potential as a controlled-release K fertilizer, facilitating the sustainable development and resource valorization of Baijiu industry.