Synthesis and evaluation of a novel cross-linked biochar/ferric chloride hybrid material for integrated coagulation and adsorption of turbidity and humic acid from synthetic wastewater: Implications for sludge valorisation.

The deep removal of organic pollutants is challenging for coagulation technology in drinking water and wastewater treatment plants to satisfy the rising water standards. Iron (III) chloride (FeCl3) is a popular inorganic coagulant; although it has good performance in removing the turbidity (TB) in water at an alkaline medium, it cannot remove dissolved pollutants and natural organic matter such as humic acid water solution. Additionally, its hygroscopic nature complicates determining the optimal dosage for effective coagulation. Biochar (BC), a popular adsorbent with abundant functional groups, porous structure, and relatively high surface area, can adsorb adsorbates from water matrices. Therefore, combining BC with FeCl3 presents a potential solution to address the challenges associated with iron chloride. Consequently, this study focused on preparing and characterizing a novel biochar/ferric chloride-based coagulant (BC-FeCl3) for efficient removal of turbidity (TB) and natural organic matter, specifically humic acid (HA), from synthetic wastewater. The potential solution for the disposal of produced sludge was achieved by its recovering and recycling, then used in adsorption of HA from aqueous solution. The novel coagulant presented high TB and HA removal within 10 min of settling period at pH solution of 7.5. Furthermore, the recovered sludge presented a good performance in the adsorption of HA from aqueous solution. Adsorption isotherm and kinetics studies revealed that the Pseudo-second-order model best described kinetic adsorption, while the Freundlich model dominated the adsorption isotherm.

Chemical methods to remove microplastics from wastewater: A review.

Microplastics (Mps) have emerged as a pervasive environmental concern, with their presence detected not only in freshwater ecosystems but also in drinking and bottled water sources. While extensive research has centered on understanding the origins, migration patterns, detection techniques, and ecotoxicological impacts of these contaminants, there remains a notable research gap about the strategies for Mps removal. This study reviews existing literature on chemical approaches for mitigating microplastic contamination within wastewater systems, focusing on coagulation precipitation, electrocoagulation, and advanced oxidation methods. Each approach is systematically explored, encompassing their respective mechanisms and operational dynamics. Furthermore, the comparative analysis of these three techniques elucidates their strengths and limitations in the context of MPs removal. By shedding light on the intricate mechanisms underlying these removal methods, this review contributes to the theoretical foundation of microplastic elimination from wastewater and identifies future research trajectories and potential challenges.

Facile Synthesis of Magnetic Biochar Derived from Burley Tobacco Stems towards Enhanced Cr(VI) Removal: Performance and Mechanism.

In this study, ferric-loaded magnetic burley tobacco stem biochar (MBTS) was synthesized via pyrolysis to improve the removal of Cr(VI). The results showed that MBTS had an adsorption capacity of 54.92 mg Cr(VI)/g, which was about 14 times higher than raw burley tobacco stem biochar (i.e., 3.84 mg/g). According to the findings obtained, a three-step mechanism of Cr(VI) removal by MBTS was further put forward, i.e., (1) Cr(VI) exchanged with hydroxyl groups on MBTS, (2) the reduction in Cr(VI) to Cr(III) mediated by oxygen-containing groups, and (3) the chelation of produced Cr(III) with the amino groups on MBTS. FTIR spectra further revealed that C-N, C-H, and C=C groups played an important role in Cr(VI) removal. Furthermore, the adsorption equilibrium and kinetics of Cr(VI) on MBTS could better be described by the Langmuir equation and pseudo-second-order rate equation. This study clearly demonstrated that ferric-loaded biochar derived from burley tobacco stems could serve as a cost-effective magnetic adsorbent for the high-efficiency removal of soluble Cr(VI) from wastewater. Tobacco stem-adsorbed Cr(VI) realized a green path for treating waste by waste.

Investigations on the pyrolysis of microalgal-bacterial granular sludge: Products, kinetics, and potential mechanisms.

This study investigated the pyrolysis of microalgal-bacterial granular sludge for producing bio-oil and biochar. Results showed that the bio-oil productivity of pyrolyzed MBGS reached 39.5-45.4 wt%, while 23.8-41.2% for the nitrogen-containing bio-oil at the temperature of 673-1073 K. Meanwhile the biochar with a nitrogen content of 3.7-7.0 wt% could also be produced. Moreover, the Van-Krevelen diagram revealed that produced bio-oil had a H/C ratio higher than that from agroforestry biomass, but its O/C ratio was found to be similar to those of coal and biochar. It further appeared from a mass conservation analysis that the highest bio-oil production yield was achieved at a pyrolysis temperature of 773 K, while the pyrolytic kinetics of MBGS in the temperature range studied was governed by the 3-D diffusion mechanism with the activation energy of 224.96 kJ·mol-1.

Biomass enhances the reduction of oxidized pellets with carbon monoxide.

In this study, the reduction mechanism of using CO to reduce biomass-oxidized pellets (BOP) and general-oxidized pellets (GOP) was deeply analyzed. The effect of biomass addition on the reduction of oxidized pellets and the change of reduction kinetics were studied. The addition of 2 wt% biomass into pellets increases pores of the oxidized pellets, promotes the rate of CO entering the pellets and the overflow of CO2, which results in faster reduction of the oxidized pellets. The reduction reactions of BOP and GOP were controlled by internal diffusion, mixing control and interface control sequentially. Also, addition of the biomass to the pellets decreases the activation energy required for their reduction, from 87.30 to 80.65 kJ·mol-1. The addition of biomass shortens the reduction time by 3% which can reduce the energy consumption. Therefore, the biomass together with CO enhances the reduction of oxidized pellets and has real environmental benefits.

[Combined Remediation of Eutrophic Water by Phoslock® and Aerobic Denitrifying Bacteria].

Nitrogen and phosphorus are the leading causes of water eutrophication, and it is challenging to remove nitrogen and phosphorus effectively through a single water remediation method. In this study, an aerobic denitrifying bacterium (AD-19) isolated from eutrophic water was used to construct an immobilized biofilm and combined with Phoslock® to remove nitrogen and phosphorus from the water. The phosphorus control efficiency of Phoslock®, nitrogen removal performance of the denitrifying bacteria, and combined remediation performance for the eutrophic water were studied. The results demonstrated that the removal rate of PO43--P in the simulated eutrophic water reached 95% with a dosing ratio of 80 (mass ratio of Phoslock® to PO43--P), and phosphorus release from sediment was effectively inhibited at the same time. Strain AD-19, which was identified as Pseudomonas sp. Using the 16S rDNA method, had a good heterotrophic nitrification and aerobic denitrification ability, and more than 97% of the nitrogen was removed when NH4+-N or NO3--N was used as the nitrogen source. The feasibility of the combined remediation of the eutrophic water was demonstrated using a lake simulation device. Furthermore, this technique was used to restore a eutrophic pond in a park in Wuhan city. After 16 days of treatment, the water quality indices for nitrogen and phosphorus were improved from worse than Grade Ⅴ to Grade Ⅲ (GB 3838-2002, Ministry of Environmental Protection of China, 2002) and remained stable for more than 270 days, indicating that Phoslock® combined with the immobilized biofilm could quickly and effectively restore eutrophic water as well as maintain the water quality for long periods.

Microalgal-bacterial granular sludge process outperformed aerobic granular sludge process in municipal wastewater treatment with less carbon dioxide emissions.

The aerobic granular sludge (AGS) process and microalgal-bacterial granular sludge (MBGS) process were comparably applied for municipal wastewater treatment in sequencing batch reactors with a height to diameter ratio of eight. For morphological appearances, the yellow aerobic granules were strip-shaped (4.0 mm × 0.62 mm) while the green microalgal-bacterial granules were elliptical-shaped (2.0 mm × 0.75 mm). The dominated rod-shaped bacteria (e.g., Acidobacteria and Bacteroidetes) and the slender configuration might be associated with the strip shape of aerobic granules under weak acid conditions. The nutrients removal performances by MBGS process were generally slightly better than AGS process. In addition, nutrients removal mechanisms were identified to elucidate how organics, ammonia, and phosphorus were removed by AGS process and MBGS process, respectively. Mass balance calculation estimated that MBGS process appeared to achieve much less CO2 emission (5.8%) compared with AGS process (44.4%). Overall, it proved that MBGS process, with the merits of potentially low energy cost, limited CO2 emission, and excellent performance, showed more prospects in municipal wastewater treatment than AGS process.

Effect of NaCl Concentration on Microbiological Properties in NaCl Assistant Anaerobic Fermentation: Hydrolase Activity and Microbial Community Distribution.

Previous studies have demonstrated that sludge hydrolysis and short-chain fatty acids (SCFAs) production were improved through NaCl assistant anaerobic fermentation. However, the effect of NaCl concentrations on hydrolase activity and microbial community structure was rarely reported. In this study, it was found that α-glucosidase activity and some carbohydrate-degrading bacteria were inhibited in NaCl tests, owing to their vulnerability to high NaCl concentration. Correspondingly, the microbial community richness and diversity were reduced compared with the control test, while the evenness was not affected by NaCl concentration. By contrast, the protease activity was increased in the presence of NaCl and reached the highest activity at the NaCl concentration of 20 g/L. The protein-degrading and SCFAs-producing bacteria (e.g., Clostridium algidicarnis and Proteiniclasticum) were enriched in the presence of NaCl, which were salt-tolerant.

Catalytic pyrolysis of rain tree biomass with nano nickel oxide synthetized from nickel plating slag: A green path for treating waste by waste.

Catalytic pyrolysis of rain tree biomass (RTB), a typical horticultural waste, was investigated with nano-NiO as catalyst produced from hazardous nickel plating slag (NPS). It appeared from the analyses by FTIR, TGA, XRD, BET, and FESEM/EDX that nano-NiO produced had a SBET and mean particle size of 53.4 m2/g and 112.3 nm. The catalytic pyrolysis kinetics of RTB with and without catalyst were studied by Friedman method. It was found that the activation energy (Ea) was in the range of 177 to 360 kJ/mol at a conversion rate of 0.1 - 0.75. The results further revealed that the H2 increase ratio in pyrolysis above 500 °C was more than 40% in the presence of catalyst. Consequently, this study showed the great potential of nano-NiO as a high-efficiency catalyst in recovering energy from biomass.

Insight into the Ex Situ Catalytic Pyrolysis of Biomass over Char Supported Metals Catalyst: Syngas Production and Tar Decomposition.

Ex situ catalytic pyrolysis of biomass using char-supported nanoparticles metals (Fe and Ni) catalyst for syngas production and tar decomposition was investigated. The characterizations of fresh Fe-Ni/char catalysts were determined by TGA, SEM-EDS, Brunauer-Emmett-Teller (BET), and XPS. The results indicated that nanoparticles metal substances (Fe and Ni) successfully impregnated into the char support and increased the thermal stability of Fe-Ni/char. Fe-Ni/char catalyst exhibited relatively superior catalytic performance, where the syngas yield and the molar ratio of H2/CO were 0.91 Nm3/kg biomass and 1.64, respectively. Moreover, the lowest tar yield (43.21 g/kg biomass) and the highest tar catalytic conversion efficiency (84.97 wt.%) were also obtained under the condition of Ni/char. Ultimate analysis and GC-MS were employed to analyze the characterization of tar, and the results indicated that the percentage of aromatic hydrocarbons appreciably increased with the significantly decrease in oxygenated compounds and nitrogenous compounds, especially in Fe-Ni/char catalyst, when compared with no catalyst pyrolysis. After catalytic pyrolysis, XPS was employed to investigate the surface valence states of the characteristic elements in the catalysts. The results indicated that the metallic oxides (MexOy) were reduced to metallic Me0 as active sites for tar catalytic pyrolysis. The main reactions pathway involved during ex situ catalytic pyrolysis of biomass based on char-supported catalyst was proposed. These findings indicate that char has the potential to be used as an efficient and low-cost catalyst toward biomass pyrolysis for syngas production and tar decomposition.

Hydrolase activity and microbial community dynamic shift related to the lack in multivalent cations during cation exchange resin-enhanced anaerobic fermentation of waste activated sludge.

The correlation of the lack in multivalent cations with hydrolase activity and microbial community in anaerobic fermentation of waste activated sludge was investigated in this study. It was demonstrated that considerable solid phase reduction of 41 % (7.87 g/L) was achievable through a cation exchange resin-enhanced anaerobic fermentation of 4 days. The protease and α-glucosidase, especially α-glucosidase, were easily influenced by a lack in multivalent cations. Furthermore, species abundance and diversity of microbial community gradually decreased. Meanwhile, the bacteria community structure presented obvious dynamic shifts. Ruminococcaceae_UCG_009, Bacteroides and Macellibacteroides responsible for organic matter biodegradation and SCFAs production became dominant bacteria in cation exchange resin-enhanced anaerobic fermentation, which was less influenced by the lack in multivalent cations, while the SCFA consumers (e.g. methanogens) were inhibited with reduced abundances due to their susceptibility to the lack in multivalent cations. Redundancy analysis revealed that the lack in multivalent cations were responsible for the microbial community evolution, which was proved by the high Grey relational coefficients (0.747-0.820) and significant negative Spearman coefficients (-0.5798 to -0.9429) between multivalent cation and microbial community. Obviously, the cation exchange resin-induced removal of multivalent cations reduced enzyme activity and modified microbial community structure, which created a beneficial environment for enhancing anaerobic fermentation.

Cation exchange resin-induced hydrolysis for improving biodegradability of waste activated sludge: Characterization of dissolved organic matters and microbial community.

This study reported an efficient and green approach towards facilitating hydrolysis of waste activated sludge (WAS) using cation exchange resin (CER) as a recyclable additive. Through CER-mediated removal of multivalent cations, WAS flocs were disintegrated into small particles with extracellular polymeric substance (EPS) solubilization. At CER dosage of 1.75 g/g SS, SCOD increased to 2579 mg/L (SCOD/TCOD = 15.9%) after 8-h hydrolysis. Afterwards, CER displayed further sludge hydrolysis performance lasting 2 days, i.e. SCOD/TCOD = 34.2%. Meanwhile, proteins, carbohydrates and other organics in dissolved organic matters (DOMs) were major contributors for volatile fatty acids (VFAs) accumulation, with composition percentage: VFAs (58.9%) > proteins (21.8%) > other organics (8.8%) > humic acids (5.9%) > carbohydrates (4.4%). The biodegradable tryptophan-like and tyrosine-like proteins were major proteins, while other organics included amino acids, aliphatic and metabolic intermediates. More than 85.2% of DOMs were easily biodegradable. Moreover, CER-induced hydrolysis modified microbial community structure through inhibiting VFAs-utilizing microbes, while hydrolytic-acidogenic bacteria were enriched, responsible for DOMs biodegradation.

Almond Shell-Derived, Biochar-Supported, Nano-Zero-Valent Iron Composite for Aqueous Hexavalent Chromium Removal: Performance and Mechanisms.

Nano-zero-valent iron biochar derived from almond shell (nZVI-ASBC) was used for hexavalent chromium (CR) removal. Experiments showed that pH was the main factor (p < 0.01) that affected the experimental results. At a dosage of 10 mg·L-1 and pH of 2-6, in the first 60 min, nZVI-ASBC exhibited a removal efficiency of 99.8%, which was approximately 20% higher than the removal yield at pH 7-11. Fourier transform infrared spectroscopy results indicated N-H was the main functional group that influenced the chemisorption process. The pseudo second-order dynamics and Langmuir isotherm models proved to be the most suitable. Thermodynamic studies showed that the reaction was exothermic and spontaneous at low temperatures (T < 317 K). Various interaction mechanisms, including adsorption and reduction, were adopted for the removal of Cr(VI) using the nZVI-ASBC composite. The findings showed that the BC-modified nZVI prepared with almond shell exerts a good effect and could be used for the removal of Cr(VI).

Effects of biomass pyrolysis derived wood vinegar on microbial activity and communities of activated sludge.

The effects of wood vinegar (WVG) on microbial activity and communities of activated sludge were investigated in a sequencing batch reactor (SBR) process. Results showed that the optimal WVG concentration was 4 µL/L when the pollutants removal efficiency and microbial activity were promoted by a WVG dilution factor of 1000. WVG could reduce the increase in microbial species richness, which led to a more notable variety of microbial species diversity. The enhanced microbial activity and communities were addressed to the promotion of 7 main classes of microbes in Proteobacteria, Bacteroidetes, Acidobacteria, and Nitrospirae phyla. The growth of ammonia-oxidizing bacteria (AOB), nitrite-oxidizing bacteria (NOB), and main genera of denitrifying bacteria (DNB), phosphorus-accumulating organisms (PAOs), and glycogen-accumulating organisms (GAOs) could be promoted by WVG, which improved the sewage treatment effectiveness in a SBR.

Effects of biomass pyrolysis derived wood vinegar (WVG) on extracellular polymeric substances and performances of activated sludge.

The effects of wood vinegar (WVG) on extracellular polymeric substances (EPS), and flocculation, sedimentation and dewatering performances of activated sludge were investigated in sequencing batch reactor (SBR) process. Results showed that polysaccharide (PS) and DNA were accounted for the largest and smallest proportion of EPS, respectively. With WVG injection, productions of soluble EPS (S-EPS), loosely bound EPS (LB-EPS), tightly bound EPS (TB-EPS), protein (PN), PS, and DNA were significantly increased. The optimal WVG concentration was found as 4 µl/l. The effects of WVG on different types of EPS followed an order of LB-EPS > TB-EPS > S-EPS. According to batch and long-term SBR operations, WVG could increase the biomass amount of activated sludge, which was beneficial to improve sewage treatment efficiencies. However, WVG showed negative impact on flocculation, sedimentation, and dewatering performance of activated sludge.

Operation of a vertical algal biofilm enhanced raceway pond for nutrient removal and microalgae-based byproducts production under different wastewater loadings.

In this study, a vertical-algal-biofilm-enhanced raceway pond (VAB-enhanced raceway pond) was designed and assessed for wastewater treatment and algal biomass production under different nutrient loading rates. Results indicated that the maximum removal capacity of the system was accordingly 7.52, 6.76 and 0.11 g·m-2·day-1 for COD, TN and TP, under which the wastewater effluent concentration could be respectively reduced from 106.00, 92.71 and 1.48 mg/L to 43.5, 11.03 and 0.46 mg/L in continuous mode. Meanwhile, about 7.47-10.10 t·ha-1·year-1 of lipid, 14.85-23.01 t·ha-1·year-1 of protein and 10.69-14.20 t·ha-1·year-1 of carbohydrate could be produced from the algae by the system in large scale. The corresponding estimated stoichiometric-methane-potential and biodiesel production of the harvested biomass was 21,471-29,136 m3·ha-1·year-1 and 0.57-1.15 t·ha-1·year-1, respectively. The findings of this study demonstrate the feasibility of using VAB-enhanced raceway pond for economically and cost-effectively recovery of nutrients from the wastewater via algal-based byproducts production.

Studies on thermokinetic of Chlorella pyrenoidosa devolatilization via different models.

The thermokinetics of Chlorella pyrenoidosa (CP) devolatilization were investigated based on iso-conversional model and different distributed activation energy models (DAEM). Iso-conversional process result showed that CP devolatilization roughly followed a single-step with mechanism function of f(α)=(1-α)3, and kinetic parameters pair of E0=180.5kJ/mol and A0=1.5E+13s-1. Logistic distribution was the most suitable activation energy distribution function for CP devolatilization. Although reaction order n=3.3 was in accordance with iso-conversional process, Logistic DAEM could not detail the weight loss features since it presented as single-step reaction. The un-uniform feature of activation energy distribution in Miura-Maki DAEM, and weight fraction distribution in discrete DAEM reflected weight loss features. Due to the un-uniform distribution of activation and weight fraction, Miura-Maki DAEM and discreted DAEM could describe weight loss features.

Recent developments in biochar as an effective tool for agricultural soil management: a review.

In recent years biochar has been demonstrated to be a useful amendment to sequester carbon and reduce greenhouse gas emission from the soil to the atmosphere. Hence it can help to mitigate global environment change. Some studies have shown that biochar addition to agricultural soils increases crop production. The mechanisms involved are: increased soil aeration and water-holding capacity, enhanced microbial activity and plant nutrient status in soil, and alteration of some important soil chemical properties. This review provides an in-depth consideration of the production, characterization and agricultural use of different biochars. Biochar is a complex organic material and its characteristics vary with production conditions and the feedstock used. The agronomic benefits of biochar solely depend upon the use of particular types of biochar with proper field application rate under appropriate soil types and conditions. © 2016 Society of Chemical Industry.

The effect of bioleaching on sewage sludge pyrolysis.

The effects of bioleaching on sewage sludge pyrolysis were studied. Sewage sludge was treated by bioleaching with solid concentrations of 6% (w/v), 8% (w/v), 10% (w/v). Results showed that bioleaching treatment could modify the physicochemical properties of sewage sludge and enhance the metals removal. The optimum removal efficiencies of heavy metals were achieved with solid concentration of 6% (w/v) bioleaching treatment: Cu, 73.08%; Zn, 78.67%; Pb, 24.65%; Cd, 79.46%. The characterization results of thermogravimetric analysis (TGA) showed that the bioleached sewage sludge with a 6% (w/v) solid concentration treatment was the easiest to decompose. Pyrolytic experiments of bioleached sewage sludge were performed in a laboratory-scale fixed bed reactor. Results indicated that bioleaching treatment greatly influenced the product yields and gas composition.

Characteristics and kinetic studies of Hydrilla verticillata pyrolysis via thermogravimetric analysis.

The pyrolysis characteristics and kinetic of Hydrilla verticillata (HV) have been investigated using non-isothermal thermogravimetric analysis. The results showed that the pyrolysis behavior of HV can be divided into two independent stages. The kinetics of Stage I was investigated using a distributed activation energy model (DAEM) with discrete 99 first-order reactions. Stage II was an independent stage which corresponds to the decomposition of calcium oxalate, whose kinetics was studied using iso-conversional method together with compensation effect and master-plots method. The activation energies ranged from 92.39 to 506.17 and 190.42 to 222.48 kJ/mol for the first and second stages respectively. Calculated data gave very good fit to the experimental data.