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Recycling of phosphorus (P) from pyrolysis sewage sludge is a good methodology to deal with the deficit of P resources and safely dispose the sewage sludge. However, it is essential to determine the type of sludge in sewage treatment plants (STPs) along with the most appropriate pyrolysis temperature. These factors affect the form and bioavailability of recoverable P. Thus, four kinds of sludge in a typical STP were selected, and three pyrolysis temperatures including 300, 500, and 700 °C were set to find a suitable strategy for P recovery. The results indicated that with increasing pyrolysis temperature, more organic phosphorus (OP) was transformed into inorganic phosphorus (IP) and more non-apatite inorganic phosphorus (NAIP) was converted to apatite phosphorus (AP, mainly Ca 3 (PO 4) 2 , Ca(H 2 PO 4) 2 , Mg 3 (PO 4) 2 , Ca 3 Mg 3 (PO 4) 4 , and Ca 5 (PO 4) 3 OH). Compared to other sludges, dewatered cake sludge (CS) pyrolyzed at 700 °C had the highest AP content, about 1.1–3.6 times that in other pyrolysis products, and the highest Ca 5 (PO 4) 3 OH content containing 35.8% of total phosphorus (TP). The contents of P-2% citric acid (CA) and neutral ammonium citrate (NAC) in CS obtained by pyrolysis at 500 °C reached 45.6 and 49.6 mg/g, respectively, which were 1.1–3.0 and 1.1–2.8 times that of P-CA and P-NAC in other sludges and their biochars, respectively. Moreover, the diethylenetriaminepentaacetic acid extraction analysis indicated that the good stability of heavy metals in CS-derived biochar was better than that in the feedstock. Hence, to ensure the efficiency and safety of P, CS is used as raw material in STPs to recover P resources. CS-500 can be used as the direct P source of land owing to the highest concentration of bioavailable P (P-CA and P-NAC), while CS-700 can be used to represent a slow-release P fertilizer because it contains the highest concentration of AP. [Display omitted] • High-temperature pyrolysis promoted the conversion of NAIP into AP in sludge. • The AP content of CS-700 was 29.1 mg/g about 1.1–3.6 times that in other biochars. • The fraction of hydroxylapatite in CS-700 achieved 35.8% of TP. • CS-500 had the highest level of P-CA (45.6 mg/g) and P-NAC (49.6 mg/g). • CS has the highest phosphorus recovery potential compared to other sludges in STPs. [ABSTRACT FROM AUTHOR]

Environmentally persistent free radicals (EPFRs) have attracted increasing research interest in recent years. Herein, the generation of EPFRs during the hydrothermal carbonization of sewage sludge (SS) was studied. First, the surface morphology, functional groups, constituent elements and free radicals were characterized for a holistic description of the raw SS and the selected hydrochar obtained from hydrothermal carbonization of SS (SHC). Then, the impact of hydrothermal temperature, residence time and initial pH on the formation of EPFRs was explored in detail through the investigation of g-factors and intensities of EPFRs identified in SHC. The results have shown that the formation of EPFRs was affected by the factors mentioned above, in which the impact of temperature is the greatest. Two types of EPFRs were spotted in the hydrochar, oxygen-centered (O-centered) and carbon-centered (C-centered) EPFRs, which were caught in 120–150 °C and 260–280 °C, respectively. Moreover, the intensities of Electron Paramagnetic Resonance (EPR) signals enhanced with increasing hydrothermal temperature. Whereas, residence time and initial pH only affected the amount of EPFRs in a manner. Additionally, the half-life of the O-centered EPFRs and the C-centered EPFRs was determined as long as 160.45 days and 401.10 days, respectively, indicating that EPFRs are stable in a long time. [ABSTRACT FROM AUTHOR]

In this research, a one-pot prepared modified sludge bio-hydrochar (IBHC) was prepared to activate persulfate (PS) for the degradation of tetracycline (TC) antibiotic. The obtained IBHC bearing defect structure, dispersed iron and large amounts of surface organic functional groups, acts as an outstanding modified biomass carbonaceous material for catalyzing PS to improve the removal efficiency of TC as high as 99.72%. The IBHC + PS system can remove TC effectively with a relative low IBHC dosage (0.2 g·L−1), limited PS consumption (5 mmol·L−1) and wide pH values (2–10). In addition, the degradation of TC still keep in 94.70% after 5 rounds reuse proving that IBHC possesses excellent stability and practicability. During the activation, both Image 2 and •OH were generated and the contribution of each component on the TC degradation in IBHC + PS system was explored. Furthermore, the degradation pathways of TC were proposed based on the results of LC-MS. Image 1 • An iron loaded sludge bio-hydrochar (IBHC) is synthesized by one-pot carbonization. • The IBHC acts as an outstanding catalyst for PS to degrade 99.72% of TC antibiotic. • The IBHC-catalyzed PS system removes TC effectively in a wide range of pH (2–10). • The degradation efficiency of TC reaches 94.7% in the fifth rounds reuse of IBHC. • TC is degraded due to the cleavage of aromatic ring and N-dealkylation process. [ABSTRACT FROM AUTHOR]

Application of biochar as an adsorbent for wastewater treatment has obtained a tremendous research interest owning to their low cost and surface functionality. In this research, an iron loaded sludge biochar was successfully prepared through a simple and economical one-step modification hydrothermal method. The iron loaded sludge biochar possesses large amounts of surface organic functional groups (such as hydroxy, carboxyl and aromatic ring, etc.), smaller particle size (about 10 nm) as well as relative higher surface area (82.780 m2 g−1) than of the pristine one. The selective removal of two kinds of antibiotics by the prepared products was demonstrated. Experimental data was fitted to isotherm and kinetic models, and thermodynamic parameters were also calculated. In the single antibiotic system, the maximum adsorption amount of tetracycline (TC) and doxycycline (DOX) could reach 104.86 and 128.98 mg g−1 at 293.15 K, respectively. In the binary antibiotics system, there was an antagonistic effect between TC and DOX. Furthermore, the adsorption of TC was much more inhibited than that of DOX owning to its deferent steric hindrance of molecular structure. Image 10513 • A sludge based biochar was synthesized and modified by one step hydrothermal method. • The influence of loaded iron on the characteristic of biochar was investigated. • The adsorption of antibiotics is dominant by π-π interaction and hydrogen bonds. • There is an antagonistic effect between TC and DOX in the co-adsorption of them. • The steric hindrance leads the competitiveness of TC is weaker than DOX. [ABSTRACT FROM AUTHOR]