Granular Biochar Research Articles

Simultaneous removal of nutrients and pharmaceuticals and personal care products using two-stage woodchip bioreactor-biochar treatment systems

The co-occurrence of nutrients and pharmaceuticals and personal care products (PPCPs) in sewage effluent can degrade water quality of the receiving watersheds. This study investigated the simultaneous removal of excess nutrients and PPCP contaminants by developing a novel woodchip bioreactor and biochar (B2) treatment system. The result revealed that woodchip bioreactors could effectively remove nitrate via a denitrification process and adsorb some PPCPs. Biochar as a secondary treatment system significantly reduced the concentrations of PPCPs and dissolved reactive phosphorus (DRP) (p < 0.05), compared to the woodchip bioreactor. The removal efficiencies of all targeted contaminants by the B2 system were evaluated using various hydraulic retention times (HRTs) and biochar types (pelletized versus granular biochar). Longer HRTs and smaller biochar particles (granular biochar) could enhance the removal efficiencies of targeted contaminants. Average contaminant removals were 77.25 % for nitrate-N, 99.03 % for DRP, 69.51 % for ibuprofen, 73.65 % for naproxen, 91.09 % for sitagliptin, and 96.96 % for estrone, with woodchip bioreactor HRTs of 12 ± 1.4 h and granular biochar HRTs of 2.1 ± 0.1 h. Notably, the second-stage biochar systems effectively mitigated by-products leaching from woodchip bioreactors. The presence of PPCPs in the woodchip bioreactors enriched certain species, such as Methylophilus (69.6 %), while inhibiting other microorganisms and reducing microbial community diversity. Furthermore, a scaled-up B2 system was analyzed and assessed, indicating that the proposed engineering treatment system could provide decades of service in real-world applications. Overall, this study suggests that the B2 system has promising applications for addressing emerging and conventional contaminants.

Enhanced methane production from protein and lipid‐rich wastewater using powdered oat husk‐biochar

AbstractBACKGROUNDDue to the lower degradation and the potential inhibitory compounds present in slaughterhouse wastewater (SW), its industrial applications are often limited to methane production. This study investigated the combined effect of conductive material such as oat husk‐biochar at different concentrations (0, 5, 10, 15, 20, 25 g L−1) and particle sizes (i.e., Powder Biochar (PB) (0.05–0.08 mm) vs. Granular Biochar (GB) (0.8–1.0 mm)) in the methane production, biodegradability, kinetic parameters, methanogenic activity and digestate quality of SW, using a multilevel factorial design.RESULTSExperimental results showed that lower concentration (5, 10 g L−1) increased the methane yield up to 35% for PB and between 11 and 13% for GB compared to the control reactor. The total ammoniacal nitrogen concentrations in the digestate declined between 14% and 52% for all biochar dosages and particle sizes. PB improved the specific methanogenic activity of the biomass compared with GB, indicating that PB can support a well‐balanced methanogenic community compared with GB inside the digester. The multiple response optimization process computed that 7.5 g L−1 of PB is optimal to increase the methane yield, the COD degradation efficiency and shorten the lag phase. On the other hand, doses higher than 15 g L−1 hinder methane generation.CONCLUSIONSPB supplementation has significant potential to improve the anaerobic degradation of SW. The improvement is attributed to the higher specific surface area, contributing to better support and microbial activity. © 2024 Society of Chemical Industry (SCI).

Enhancing Anaerobic Biodegradation of Phenanthrene in Polluted Soil by Bioaugmentation and Biostimulation: Focus on the Distribution of Phenanthrene and Microbial Community Analysis

The remediation of polycyclic aromatic hydrocarbon (PAH)-contaminated soils has received much attention in recent years, and most of the contaminated sites are in anaerobic environments, such as deep soils and flooded soils. We simulated the natural flooded soil environment, selected phenanthrene (PHE) as a model PAH contaminant, and designed batch experiments run for 63 days to comprehensively investigate the effects of the combined addition of anaerobic sludge and granular biochar on microbial community and function and the anaerobic biodegradation of PHE. Firstly, the residue, distribution, and removal of PHE in the flooded soil environment were quantified for each group. Secondly, the effects of bioaugmentation of soil indigenous microorganisms by the addition of anaerobic activated sludge and biostimulation of biochar on the removal of PHE from the soil were analyzed against each other. Lastly, the changes in the structure of the microbial community under the effect of bioaugmentation and biostimulation were illustrated by sequencing analyses. The results of this study showed that the removal efficiency of PHE reached 72.0% after the addition of anaerobic activated sludge. The incorporation of anaerobic activated sludge and biochar resulted in a 25.3% increase in PHE removal compared to a single soil, suggesting that the combination of bioaugmentation and biostimulation can have a synergistic effect on the anaerobic biodegradation of PHE in contaminated soils. The results of sequencing analysis further indicated that the introduction of an exogenous microbial community changed the dominant genera associated with PHE degradation and introduced methanogenic archaea, which enriched the metabolic pathways of the carbon cycle in the system. On this basis, the addition of biochar resulted in higher anaerobic microbial community diversity, functional dominant species were enriched, and the direct interspecies electron transfer (DIET) process between electroactive bacteria (Bacteroides, f_Geobacteraceae) and Methanosaeta was facilitated, which accelerated the degradation of PHE by anaerobic microbial communities. The results of this study provide regulatory tools and basic data support for enhanced bioremediation of PAHs in flooded soils.

Overcoming methanogenesis barrier to acid inhibition and enhancing PAHs removal by granular biochar during anaerobic digestion

Alleviating acid inhibition is the most important for optimizing anaerobic digestion (AD), but the recalcitrant organic pollutants in digestates have long been ignored. In this study, we aimed to simultaneously enhance both organics bio-methanation and recalcitrant polycyclic aromatic hydrocarbons (PAHs) removal in AD system by using granule biochar and short-term ethanol stimulation. The results showed that adding biochar effectively alleviated volatile fatty acids (VFAs) accumulation and achieved 313.6 mL CH4/d•g COD average yield. Meanwhile, the efficiency of phenanthrene (PHE) biodegradation, as the model PAHs pollutant, was significantly promoted by 37.1%. Additionally, more and compact extracellular polymeric substances improved electron transfer and mass transfer among microbes, and higher enzymes (ATPase, NADH and α-Amylase) activities met the physiological demanding of efficient microbial metabolism in biochar-added reactor. Microbiological analysis revealed that biochar-mediated direct interspecies electron transfer (DIET) selectively enriched exoelectrogens (Bacteroides, Proteiniphilum, f_Christensenellaceae, etc.) and acetoclastic Methanosaeta, which contributed to increasing biomethane production. The promoted PAHs biodegradation was mainly dependent on the cooperation between fermenting f_Paludibacteraceae and hydrogenotrophic Methanolinea, and potentially related to biochar-mediated DIET. Metabolic analysis indicated that the metabolic pathways of acetogenesis and methanogenesis were significantly strengthened by biochar, thus alleviating acid inhibition. Also, biochar stimulated functional genes expression in PAHs anaerobic biodegradation. These findings were further verified by a series of short-term metabolism tests.

Size matters: Powder biochar promotes the elimination of antibiotics resistance genes and potential hosts during swine manure composting

Livestock manure faced acute environmental pollution and ecology risky caused by antibiotic resistance genes (ARGs). This study investigated the effects of biochar particle size including powder biochar (75 μm, PB), and granular biochar (2 mm, GB) on ARGs variation during the aerobic composting. The results showed that the total relative abundance (RA) of the ARGs decreased significantly in all the treatments after composting. While compared to the removal efficiency of total RA in the control (CK), PB decreased by 90.99 % and GB increased by 93.25 %, and both PB and GB removed MGEs completely. Sulfonamide antibiotic resistance genes were the main contributor of the ARGs rebounding. PB addition could hinder the rebounding of sulfonamide antibiotic resistance genes during the later stage of the composting. Co-occurrence network analysis showed that the addition of biochar (both types) increased the complexity of the microbial community the competition of inter-phylum, which was indicated by the higher number of edge and density and lower positive connection. The different ARGs removal efficiency in these two treatments might be that PB promoted the competition both inter-phylum and potential hosts-other microbes, resulted in fewer kinds and abundance of ARGs hosts, while GB increased the stability of ARGs hosts making it more resistant to environment changes. Totally, compared with the global adjustment strategy of microbial communities, more exclusive methods focusing on the controlling of ARGs hosts should be explored to decrease the ecological risk of composting products during composting process.

Biochar applications to boreal podzol improve soil hydraulic properties and control nitrogen dynamics

The study aimed to investigate the effects of biochar (BC) application on hydraulic properties and nitrogen (N) transport in a podzolic soil profile. Soil samples were collected from an agricultural research field in Pasadena, Newfoundland, Canada. The following three types of leaching columns were prepared: ( i) topsoil, ( ii) top and E-horizon soil, and ( iii) mixed soil (2:1 ratio of topsoil and E-horizon soil). Granular biochar (GBC) and powder biochar (PBC) were mixed with soils at the rate of 0%, 1% and 2% (w/w). BC’s morphological structure and pore size distribution were examined using a scanning electron microscope, and the specific surface area was assessed by the Brunauer−Emmett−Teller method. Soil physical and hydraulic properties (bulk density, porosity, field capacity (FC), permanent wilting point, plant available water (PAW)), leaching concentration of nitrate (NO3 −) and ammonium (NH4 +), and volume of leachate were measured through a total of 378 experiments under laboratory conditions. GBC and PBC showed hydrophobic and hydrophilic characteristics, respectively. With the 2% PBC amendment, porosity increased by 3%, FC by 10%, and PAW by 13% in the mixed soil and reduced NO3 − leaching by 36% in top and E-horizon soil and NH4 + leaching by 72% in mixed soil. On the other hand, NO3 − and NH4 + leaching was reduced by 26% and 33% in mixed soil when treated with 2% GBC. A 2% application rate for both BC (GBC and PBC) showed the best performance to enhance soil hydraulic properties and retain significant amounts of NO3 − and NH4 + in the boreal podzol.

Removal of bisphenol A (BPA) by fermented sludge-derived granular biochar from template-like method: From batch experiment to continuous operation

Endocrine disruptors have biological toxicity and can interfere with the endocrine system of organisms. They widely exist in natural water bodies. Here, the granular biochar was prepared from fermented sludge for the first time by using cationic polyacrylamide as template agent via a template-like method. The as prepared biochar was investigated for the removal of BPA in aqueous media by batch experiment and continuous flow experiment. The pyrolysis temperature and template concentration had a great influence on the properties of residual biochar and BPA capture. The static adsorption results show that when the template concentration was 1% with the pyrolysis temperature of 800 °C, the optimal biochar P-1%− 800 achieved the BPA adsorption value up to 84.78 mg/g. Its adsorption behavior, influencing factors, and recycling capability on BPA reduction were evaluated. Kinetics, isotherms and characterization analysis suggested that the adsorption mechanism involved pore filling, electrostatic attraction, π-π interactions and hydrogen bonding. Good regeneration performance, low concentration heavy metal leaching and lasting continuous flow stability in fixed-bed device under different water quality background demonstrated that fermented sludge-derived granular biochar P-1%− 800 is a desirable adsorbent for reducing BPA in complex water environment.

High treatment effectiveness for secondary effluent in Fe–C microelectrolysis constructed wetlands with electron donor supplementation

The deep purification of secondary effluent from wastewater treatment plants (WWTPs) is essential for protecting the receiving water environment. Recently, iron-carbon materials have attracted more and more attention for treating secondary effluent. In this study, lab-scale iron-carbon microelectrolysis constructed wetlands (Fe–C CWs) filled with iron scraps (ISs) and granular biochar were established to purify secondary effluent with C/N ratios of 0.5–5. Walnut shells or pyrite were amended as organic or inorganic electron donors to enhance nutrient removal and reduce iron consumption. The IS substrate substantially promoted nutrient removal when the C/N ratio ≤2 (20.3–36.5% for nitrogen and 10.4–21.8% for phosphorus) by supplying Fe2+/H2 for autotrophic denitrification and iron compounds for phosphorus sequestration. Walnut shell supplementation further strengthened nutrient removal, achieving excellent effluent water quality. Fe substrate consumption was alleviated by electron donor supplementation. The IS substrate decreased CO2 emissions while increasing CH4 and N2O fluxes of the biochar-based CWs, and pyrite addition mitigated the global warming potential (GWP) of the Fe–C CWs. When the C/N ratio changed from 5.0 to 0.5, the abundance of autotrophic denitrifiers and Fe cycle-related populations dominated by Dechloromonas, Ferritrophicum and Thiobacillus increased notably in ISs-amended CWs, and they were responsible for the efficient nitrogen removal. Fe–C CW supplemented with organic solid wastes presents high potential for advanced purification of low C/N nitrified effluent.

A novel approach to sorbent-based remediation of soil impacted by organic micropollutants and heavy metals using granular biochar amendment and magnetic separation

Soil remediation by sorbent amendment is a popular method to immobilize contaminants but it is limited by the fact that the sorbent cannot be retrieved from the soil, posing as a threat to its quality, due to the gradual leaching of the sorbed contaminants. To address this challenge, this work proposes the use of granular-sized, magnetically retrievable sorbents for soil remediation. Specifically, granular biochar, that offers favorable sorption sites for both organic and inorganic contaminants, was used to treat contaminated soil samples. It is demonstrated that sorbent size plays a crucial role in its separation from the soil matrix by magnetic field. Granular magnetic biochar (gMBC) of 1–2 mm was found to be the most suitable sorbent size because it does not assimilate into the soil matrix and can be quantitatively retrieved both from wet and dry soil by means of magnetism, yielding a sorbent-free matrix. In this manner, the soil is relieved from both the hazardous contaminants and the contaminant-laden sorbent. Using gMBC, the remediation of contaminated soil from both organic micropollutants and heavy metals was optimized accomplishing remediation efficiencies from 40% to 90% for organic compounds and 30–65% for heavy metals through sorption and chemical transformation of the contaminants. The results of the study show that granular magnetic sorbents can be an effective and practical solution to the remediation of soils by facilitating their retrieval directly from the solid matrix which is not possible with micro/nanoparticle sorbents.

Remediation of copper and lead contaminated sediments using iron-based granule biochar: mechanisms and enzyme activity

ABSTRACT In recent years, there has been a growing concern about heavy metal contamination in sediments. In this study, iron-based granular biochar (MGB) is prepared to remediate Cu and Pb contaminated sediments. Characterizations via scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) show that the rough surface of MGB with abundant pore structures and a large number of oxygen-containing functional groups that facilitate stabilization of Cu and Pb in sediments. Potential mobility and bioavailability of Cu and Pb are investigated using BCR sequential extraction in the 35 day remediation experiment. The XPS results indicate that FeOOH and C-OH play a crucial part in stabilizing heavy metals. Large affinity of FeOOH for Pb allows it to occupy a proportion in F2 while C–OH is attractive to Cu. Changes of pH, organic matter (OM), and available phosphorus (AP) in sediments after adding MGB as well as the relationship between changes and the stable solidification of Cu and Pb are explored. The stable solidification of heavy metals effectively reduces the available phosphorus in sediments. Magnetic and particle properties of the material are used to reduce the impact of MGB aging on sediment environment and separate it from the remediated sediment. Finally, 3% of MGB significantly enhanced the sediment catalase activity in the biological enzyme activity experiment. All findings indicate that MGB is a green and environmentally friendly sediment remediation material with satisfactory potential in synergistically stabilizing heavy metals and phosphorus. Highlights The complexation of FeOOH with Pb on the surface of MGB fixes it to the reduced state The C-OH on the surface of MGB is more attractive to Cu than Pb MGB effectively mitigates the release of bioavailable phosphorus from sediments to overlying water

Efficient treatment of mercury(Ⅱ)-containing wastewater in aerated constructed wetland microcosms packed with biochar

Effective removal of mercury (Hg) pollutants from contaminated water/wastewater to prevent severe environmental pollution is of great significance due to the extremely high toxicity of Hg. In this study, granular biochar and gravel (control) were packed into intermittently aerated constructed wetland (CW) microcosms to treat Hg(Ⅱ)-containing wastewater over 100 d. The results showed that the biochar-filled CWs exhibited notably better Hg(Ⅱ) removal than the gravel systems by facilitating chemical and microbial Hg(Ⅱ) reduction and volatilization and promoting plant growth and Hg assimilation. More than ten times more Hg was absorbed by the plants (L. salicaria) in biochar CWs than in the gravel systems, with the roots acting as the major sink. In contrast, substrate binding in a predominantly oxidizable fraction was the dominant pathway for Hg removal in the gravel CWs. Biochar substrates also exhibited higher levels of COD, N and P removal, and Hg(Ⅱ) import impacted the removal of these pollutants only slightly. Filling material played a more crucial role than Hg input in shaping the microbial communities in the CWs. The proportions of some dominant genera, including Arenimonas, Lysobacter, Micropruina and Hydrogenophaga, increased in the presence of Hg, implying their tolerance to Hg toxicity and potential roles in Hg detoxification in the CWs. Granular biochar-based CW has high potential for treating Hg(Ⅱ)-contaminated wastewater.

Fate of endosulfan in ginseng farm and effect of granular biochar treatment on endosulfan accumulation in ginseng.

Endosulfan was widely used as an insecticide in the agricultural sector before its environmental persistence was fully understood. Although its fate and transport in the environment have been studied, the effects of historic endosulfan residues in soil and its bioaccumulation in crops are not well understood. This knowledge gap was addressed by investigating the dissipation and bioaccumulation of endosulfan in ginseng as a perennial crop in fresh and aged endosulfan-contaminated fields. In addition, the effect of granular biochar (GBC) treatment on the bioaccumulation factor (BAF) of endosulfan residue in ginseng was assessed. The 50% dissipation time (DT50) of the total endosulfan was over 770days in both the fresh and aged soils under mulching conditions. This was at least twofold greater than the reported (6- > 200days) in arable soil. Among the endosulfan congeners, the main contributor to the soil residue was endosulfan sulfate, as observed from 150days after treatment. The BAF for the 2-year-old ginseng was similar in the fresh (1.682-2.055) and aged (1.372-2.570) soils, whereas the BAF for the 3-year-old ginseng in the aged soil (1.087-1.137) was lower than that in the fresh soil (1.771-2.387). The treatment with 0.3 wt% GBC extended the DT50 of endosulfan in soil; however, this could successfully suppress endosulfan uptake, and reduced the BAFs by 66.5-67.7% in the freshly contaminated soil and 32.3-41.4% in the aged soil. Thus, this adsorbent treatment could be an effective, financially viable, and sustainable option to protect human health by reducing plant uptake of endosulfan from contaminated soils.

Carbon based conductive materials mediated recalcitrant toxicity mitigation during anaerobic digestion of thermo-chemically pre-treated organic fraction of municipal solid waste

High-temperature thermal pretreatment alone or in conjugation with chemical pretreatment (highly acidic or alkaline) produced recalcitrant compounds, which inhibits the anaerobic digestion (AD) process performance. This study aims to develop a strategy to use carbon-based conductive materials to mitigate the recalcitrant toxicity and enhance the methane generation in the downstream AD. The formation of recalcitrant compounds, mainly the furan derivatives, i.e., furfural and 5-HydroxyMethyl furfurals (5-HMF) during thermo-chemical pretreatment of OFMSW at 150 °C, 175 °C, 200 °C with 3 g/L-NaOH dose, and the alleviation of their inhibitory effects by adding 25 g/L of each of granular activated carbon (GAC) and granular biochar (GBC) during mesophilic AD were studied. The addition of conductive materials resulted in the highest biogas yield of 462 mL/gVSadded (GAC) and 449 mL/gVSadded (GBC) for 175°C-3g/L-NaOH pretreatment, which was >45% higher over control. The highest improvement of >65% in biogas yield was observed for 200°C-3g/L-NaOH pretreatment despite the lower biogas yield. The conductive materials amended digester shows a significant decrease in the 5-HMF and furfurals concertation. The highest reduction in 5-HMF (44%) and furfural (51%) concentrations were observed for 200°C-3g/L-NaOH pretreatment, and 25 g/L GBC amended tests. The score plots from the principal component analysis (PCA) of the characterization of the digestate showed that the data were significant, whereas the loading plots depicted the correlation of different experimental parameters studied (like fate of recalcitrant, biogas yield and other parameters post AD of OFMSW when aided with conductive materials). Application of regression models in all the batch assays depicted that a lag phase of 2–4 days was observed in Modified Gompertz Model (MGM), 4–5 days in Logistic Model (LM) and a rapid hydrolysis was proven with the value of hydrolysis coefficient being between 0.003 and 0.029 from the first-order (FO) model.

Carbon-based conductive materials facilitated anaerobic co-digestion of agro waste under thermophilic conditions

Management of agro-waste is a major challenge globally due to inefficient disposal techniques, which concominantly leads pollution and loss of renewable bioenergy. Anaerobic digestion of agro-waste is one of the ways to tackle this problem but hindered by the recalcitrant nature of agro-waste. This study investigated the effect of granular activated carbon (GAC) and granular biochar (GBC) addition to enhance the thermophilic anaerobic co-digestion of wheat husk and sewage sludge. The conductive materials (particle size: 2–5 mm) were added separately at five different concentrations: 10, 20, 30, 40, 50 g/Linoculum. The findings revealed that samples amended with GAC and GBC at 20 g/L dosage had the highest biogas yield of 263 and 273 mL/gVSadded, respectively, corresponding to 22 and 27% higher yield than the control. Additionally, a shorter lag phase was observed in both cases compared to the Control. However, the GBC amended samples showed relatively stable biogas production compared to GAC and consistent results regarding pH, alkalinity, total volatile fatty acids, and soluble chemical oxygen demand. The preliminary techno-economic analysis indicates that addition of GAC or GBC may not be feasible and require other innovative engineered solutions for the addition of conductive materials. This study confirms that GAC and GBC amendments enhance the biogas productivity and process stability in anaerobic digestion of recalcitrant agro-waste under the high-temperature regime and calls for further research in this direction.

O-doped graphitic granular biochar enables pollutants removal via simultaneous H2O2 generation and activation in neutral Fe-free electro-Fenton process

H2O2 generation by 2-electron oxygen electroreduction reaction (2eORR) has attracted great attention as an alternative to the industry-dominant anthraquinone process. Electro-Fenton (EF) process, which relies on the H2O2 electrogeneration, is regarded as an important environmental application of H2O2 generation by 2eORR. However, its application is hindered by the relatively expensive electrode materials. Proposing cathode materials with low cost and facile synthetic procedures are the priority to advance the EF process. In this work, a composite cathode structure that uses graphitic granular bamboo-based biochar (GB) and stainless steel (SS) mesh (GBSS) is proposed, where SS mesh functions as current distributor and GB supports synergistic H2O2 electrogeneration and activation. The graphitic carbon makes GB conductive and the oxygen-containing groups serve as active sites for H2O2 production. 11.3 mg/L H2O2 was produced from 2.0 g GB at 50 mA after 50 min under neutral pH without external O2/air supply. The O-doped biochar further increased the H2O2 yield to 18.3 mg/L under same conditions. The GBSS electrode is also effective for H2O2 activation to generate OH, especially under neutral pH. Ultimately, a neutral Fe-free EF process enabled by GBSS cathode is effective for removal of various model organic pollutants (reactive blue 19, orange II, 4-nitrophenol) within 120 min, and for their partial mineralization (48.4–63.5%). Long-term stability of the GBSS electrode for H2O2 electrogeneration, H2O2 activation, and pollutants degradation were also examined and analyzed. This work offers a promising application for biomass waste for removals of organic pollutants in neutral Fe-free EF process.

Production of biochar from oil palm frond by steam pyrolysis for removal of residual contaminants in palm oil mill effluent final discharge

Advances in biochar production and modification have extended the applications of biochar to wastewater treatment. However, not all feedstocks produced porous biochar at a moderate temperature suitable for wastewater treatment. In this study, biochar was produced from oil palm frond using steam pyrolysis at 500 °C and pulverized to granular and micro-fine particles. Both biochar particles were characterized and applied as adsorbents for treating final discharge of palm oil mill effluent. The effluent was also filtered and treated to examine the effect of suspended solids on adsorption capacity. The biochar had Brunauer-Emmett-Teller surface area of 406.6 m2 g−1. Pulverization eliminated the residual macropores in granular biochar, created new external surface area, and exposed constricted nanopores, which resulted in increasing the surface area to 457.7 m2 g−1. The adsorption capacity decreased from 24.6 to 6.1 mg g−1 for chemical oxygen demand and 49.0 to 10.9 Pt–Co g−1 for color by increasing the dosage of micro-fine biochar from 5 to 30 g L−1. The total suspended solids affected the adsorption capacity of granular biochar by blocking residual macropores that provide access to adsorption sites in micropores and mesopores. At 30 g L−1, the micro-fine biochar exhibited an effective reduction of chemical oxygen demand from 224 to 41.6 mg g−1 and color from 344 to 15 Pt–Co g−1 making the wastewater suitable for reuse in palm oil mills and safe for discharge into the aquatic environment.

The 3R Principles for Applying Biochar to Improve Soil Health

Amending soil with biochar is a promising approach to persistently improve soil health and promote crop growth. The efficacy of soil biochar amendment, however, is soil specific, biochar dependent, and influenced by the biochar application programs. To maximize the benefits of biochar application, this paper proposes the 3R principles for applying biochar to soils: right biochar source, right application rate, and right placement in soil. The quality of biochar as a soil amendment varies significantly with the feedstock and the production conditions. Biochar products capable of everlastingly sustaining soil health are those with high stable organic carbon (OC) content and high water- and nutrient-holding capacities that are manufactured from uncontaminated biomass materials. Acidic, coarse-textured, highly leached soils respond remarkably more to biochar amendment than other types of soils. Soil amendment with particular biochars at as low as 0.1 mass% (equivalent to 2 Mg ha−1) may enhance the seasonal crop productivity. To achieve the evident, long-term soil health improvement effects, wood- and crop residue-derived biochars should be applied to soil at one time or cumulatively 2–5 mass% and manure-derived biochars at 1–3 mass% soil. Optimal amendment rates of particular biochar soil systems should be prescreened to ensure the pH of newly treated soils is less than 7.5 and the electrical conductivity (EC) below 2.7 dS m−1 (in 1:1 soil/water slurry). To maximize the soil health benefits while minimizing the erosion risk, biochar amendment should be implemented through broadcasting granular biochar in moistened conditions or in compost mixtures to cropland under low-wind weather followed by thorough and uniform incorporation into the 0–15 cm soil layer. Biochars are generally low in plant macronutrients and cannot serve as a major nutrient source (especially N) to plants. Combined chemical fertilization is necessary to realize the synergic beneficial effects of biochar amendment.

Powdered biochar doubled microbial growth in anaerobic digestion of oil

Oil is a desirable substrate for anaerobic digestion (AD) for its high energy recovery potential. However, low solubility of oil and long-chain fatty acids (LCFAs) inhibition hinder microbial growth and further reduce the biogas production in most cases. Biochar is a cheap but reliable additive in AD. Its functions to enrich microbial enrichment and enhance biogas production were confirmed previously. In present study, effects of biochars with different particle sizes on oil AD were investigated under thermophilic and mesophilic conditions. Results from the quantification and space distribution of microbes indicate that powdered biochar (<5 μm) aggregated more microbes than granular biochar (0.5–1 mm). Especially in the mesophilic digesters, powdered biochar doubled the number of microbes in the whole digester, which was a satisfactory result of acclimation. In addition, powdered biochar was able to adjust the microbial communities and further increased CH4 production by 13.3% in thermophilic digesters. Granular biochar enhanced the maximum CH4 potential by 32.5% under mesophilic condition, which was most promising from the perspective of energy recovery. Biochar of both particle sizes relieved propionic acid accumulation in thermophilic digesters. Hence, biochar addition might be an ideal approach to elevate energy recovery efficiency by overcoming the barriers of anaerobic microbes to utilize LCFAs.

Effects of biochar size and type on gaseous emissions during pig manure/wheat straw aerobic composting: Insights into multivariate-microscale characterization and microbial mechanism

Greenhouse gas and ammonia emissions during composting with different biochar types and particle sizes were investigated. Compared with powder-biochar, granular-biochar improved pore connectivity and was benefit to methanotrophs activities, like Methylococcaceae, reducing CH4 emissions. At the same particle size, bamboo biochar (BB) had a higher pore volume and more aerobic microenvironment within the compost than rice straw biochar (RSB), reducing GHG emissions. Bamboo biochar had high aromatic compound and NO3− concentrations and therefore surface π–π electron donor/acceptor interactions, causing low N2O emissions and inhibiting denitrifying bacteria (e.g., Bacteroidales). More CO and CO bonds in rice straw biochar than bamboo biochar caused lower NH3 emissions using rice straw than bamboo biochar. Powdered biochar had more exposed reactive functional groups and decreased NH3 production better than granular biochar. Powdered bamboo biochar controls gaseous emissions better than other biochars during aerobic pig manure/wheat straw composting.

Characteristics of biochar derived from marine macroalgae and fabrication of granular biochar by entrapment in calcium-alginate beads for phosphate removal from aqueous solution

In this work, granular biochar, Laminaria japonica-derived biochar (LB)-calcium alginate beads (LB-CAB), was successfully prepared by dropping a mixture of powder biochar and alginate solution into a calcium chloride solution for phosphate adsorption. Among different marine macroalgae derived biochars, LB exhibited the best performance, showing a phosphate removal rate of 97.02%, which was attributed to its high Ca/P and Mg/P ratios. With increasing pyrolysis temperature up to 600°C, the physicochemical properties of LB became suitable for adsorbing phosphate. Experimental results of kinetics and equilibrium isotherms at different temperatures (10–30°C) showed that the phosphate adsorption process is endothermic and is mainly controlled by external mass transfer and the intraparticle diffusion rate. The maximum adsorption capacity was found to be 157.7mgg−1 at 30°C, as fitted by the Langmuir–Freundlich model, which is higher than capacities of other powder form of biochars.