Biochar pH Research Articles

Influences of chemical treatment on sludge derived biochar; Physicochemical properties and potential sorption mechanisms of lead (II) and methylene blue

Unlike agricultural biomass, sludge-derived biochar is rich in nutrients, comprising exchangeable cations and various surface oxygen functional groups with carbonaceous structures. In this study, the influence of different activating reagents such as H3PO4, H2O2, K2CO3, and NaOH on the physicochemical properties of biochar was investigated. It was found that the biochar elemental composition remains nearly the same, while the surface Fe and Si were induced for H3PO4 modification. The pH of the original biochar was varied from acidic to alkali (3.60–10.06) along the chemical treatment process. The surface-active sites of biochar and their nature were dramatically tuned based on their chemical modification. To interpret the relationship between each of the parameters obtained via chemical modification, adsorption of different pollutants, such as Pb(II), Cd(II), Cr(VI), V(V), As(III), and methylene blue (MB) were conducted. Among the biochars, NaOH-modified biochar was revealed as the optimum candidate with maximum uptake capacity for Pb(II) (195.75 mg/g) and MB (160.78 mg/g). Based on the adsorption kinetics and isotherm study, the adsorption process endorsed chemical sorption with multiple interactions along the heterogeneous surface. This study offered a comprehensive approach to manipulating the physicochemical properties of biochar.

Low-temperature straw biochar: Sustainable approach for sustaining higher survival of B. megaterium and managing phosphorus deficiency in the soil

Inoculation of phosphate-solubilizing bacteria (PSB) is a sustainable approach to increase the available P content in soils for crop production. This application, however, is constrained by the low survival rate of PSB in the field. Biochar, a carbon-rich biomaterial with a well-developed porous structure, has recently emerged as an appealing option to maintain the population size of inoculants in the soil. The efficacy of biochar as a PSB carrier is primarily determined by its physicochemical properties, which are dominated by the feedstocks and the pyrolysis temperatures. This study demonstrated a comprehensive assessment of the efficacy of straw-derived biochars prepared from different feedstocks (i.e., crop straws from cotton, peanut, maize, soybean, and wheat) and pyrolysis temperatures (i.e., 300 and 600 °C). We employed B. megaterium carrying green fluorescence protein and evaluated its survival rate and phosphate-solubilizing performance in various inoculated biochars that have distinct physicochemical properties. Our results showed that the pyrolysis temperature is more determinant of the beneficial effect of straw biochar than the feedstock species. Cotton straw biochar pyrolyzed at low temperature (i.e., 300 °C) sustained a survival rate of 6.17% for the B. megaterium and thereby entailed a significant increase in available P in soil by 30.05 mg kg−1 soil, which were nearly 18-fold and 8-fold higher than that of the no carrier treatment respectively. The performance of biochar-assisted PSB was dominant-negatively affected by the increasing pH, ash content, surface area, and total pore volume of biochar, while larger H/C ratio, water holding capacity, pore size, and surface hydrophobicity were predominantly conducive to the colonization and survival of PSB. The results of this study were expected to provide valuable guidance for biochar preparation in practice to enhance the survival and activity of PSB and maximize the utility of PSB as sustainable phosphorus fertilizer with economic applicability.

Co-pyrolysis of sewage sludge and food waste digestate to synergistically improve biochar characteristics and heavy metals immobilization

Food waste digestate (FWD) is a desirable additive in sewage sludge (SS)-based biochar preparation owing to its high contents of intrinsic inorganic minerals and lignocellulosic compounds. In this study, we investigated the co-pyrolysis of SS with FWD at different mixing ratios (4:0, 3:1, 2:2, 1:3, and 0:4; SS:FWD w/w) at 550 °C to synergistically improve the biochar characteristics and immobilize the heavy metals in the SS. The results showed that co-pyrolysis of SS with FWD greatly increased the aromaticity and pH (by 13.22–26.56%) of the blended biochar, and significantly reduced the contents of total and bioavailable heavy metals. The addition of FWD effectively enhanced the conversion of heavy metals from less stable fractions to more stable forms, but led to the transformation of Cr from the residual fraction (F4) to the oxidizable fraction (F3) when the FWD:SS ratio was ≥ 3:1. Overall, the formation of co-crystal compounds, stable kaolinite, and metal oxides together with the enhancement of biochar characteristics during co-pyrolysis significantly reduced the heavy metal-associated ecological risk (potential ecological risk index lower than 15.51) and phytotoxicity (germination index higher than 139.41%) of the blended biochar. These findings suggest that high levels of mineral components in FWD greatly immobilize more heavy metals in biochar.

Mitigation of lead (Pb) toxicity in rice cultivated with either ground water or wastewater by application of acidified carbon

Toxicity induced by a high concentration of lead (Pb) can significantly decrease plant's growth, gas exchange, and yield attributes. It can also causes cancer in humans. The use of organic amendments, especially biochar, can alleviate Pb toxicity in different crops. The application of biochar can decrease the uptake of Pb by plant roots. However, the high pH of thermo-pyrolyzed biochar makes it an unfit amendment for high pH soils. As Pb is an acute toxin and its uptake in rice is a major issue, the current experiment was conducted to explore the efficacy of chemically produced acidified carbon (AC) to mitigate Pb toxicity in rice. Lead was introduced in concentrations of 0, 15, and 30 mg kg−1 soil in combination with 0, 0.5, and 1% AC, underground water (GW) and wastewater (WW) in rice plants. The addition of 1% AC significantly improved the plant height (52 and 7%), spike length (66 and 50%), 1000 grains weight (144 and 71%) compared to 0% AC under GW and WW irrigation, respectively at 30 mg Pb kg−1 soil (30 Pb) toxicity. Similar improvements in the photosynthetic rate, transpiration rate and stomatal conductance also validated the effectiveness of 1% AC over 0% AC. A significant decrease in electrolyte leakage and plant Pb concentration by application of 0.5 and 1% AC validates the effectiveness of these treatments for mitigating 30 Pb toxicity in rice compared to 0% AC under GW or WW irrigation. In conclusion, 1% AC is an effective amendment in alleviating Pb toxicity in rice irrigated with GW or WW at 30 Pb.

Effects of Varying Rates of Nitrogen and Biochar pH on NH3 Emissions and Agronomic Performance of Chinese Cabbage (Brassica rapa ssp. pekinensis)

NH3 emitted into the atmosphere undergoes intricate chemical reactions to form fine particulate matter PM2.5. Nitrogen fertilizers are one of the major sources of gaseous ammonia. Recently, research into using biochar to lessen NH3 emissions from agricultural land has taken center stage and several studies have been executed in that regard. However, biochar’s capacity to reduce emissions of gaseous NH3 from applied nitrogen fertilizers is affected by both soil and biochar properties. While the effects of soil properties on NH3 volatilizations have been widely studied, the data concerning the effects of biochar properties on NH3 volatilizations from the soil are still scanty. It is against this backdrop that this study examined the effects of biochar pH on emissions of NH3 from the soil amended with varying quantities of nitrogen, as well as the impact on the growth and productivity of Chinese cabbage. To achieve the study objectives, acidic (pH 5.7), neutral (pH 6.7) and alkaline (pH 11.0) biochars were used and each was added to the soil at a rate of 1% (w/w). Nitrogen fertilizers were applied at three rates of 160, 320, 640 kg ha−1. In comparison with the control, the acidic, neutral and alkaline biochar amendments reduced NH3 emissions by up to 18%, 20% and 15%, respectively. However, only neutral biochar produced higher Chinese cabbage yields than the urea-only amendment and the Chinese cabbage yields increased with the increasing rates of nitrogen applied. Combined applications of neutral biochar and 640 kg/ha of nitrogen are recommended for optimal cabbage yields and low NH3 emissions.

Evaluation of NH3 emissions in accordance with the pH of biochar

Evaluation of NH3 emissions in accordance with the pH of biochar

Pyrolysis behaviors of corn stover in new two-stage rotary kiln with baffle

An instantly moving, two-stage rotary kiln reactor with baffle was proposed for the conversion of biomass to fuels and biochar. This newly configured apparatus enhanced the material particle mobility in the dead zone, but also enable ideally matched the material heating process in pilot-scale biomass pyrolysis. The thermogravimetric (TG) analysis and the distributed activation energy model (DAEM) was utilized to determine the pyrolysis kinetic of corn stover in this study. Meanwhile, the pyrolysis behaviors of corn stover were investigated in this newly designed rotary kiln, as well as the bio-oil, char and gas products. The pyrolysis experiment results indicated that this newly configured apparatus presented higher bio-oil yield and pyrolysis liquid products yield than a conventional rotary kiln. The bio-oil yield increased initially and subsequently declined with rising temperature, as did the yields of pyrolysis liquids and water, but not biochar in this newly configured apparatus. Raising the temperature from 400 °C to 700 °C increased the bio-oil yield from 14.02 wt% to 23.02 wt%, whereas increasing the temperature further to 800 °C decreased the bio-oil yield to 22.16 wt%. Bio-oil was mostly composed of ketones, phenols, furfurans, benzenes, and esters, with a large proportion of oxygen-containing compounds. The phenols compounds increase with increasing temperature, aldehydes, ketones and furans decreased in relative contents. The increased temperature raised the H2, CH4, and C2+C3 contents, but decreased the CO content. The BET surface and total volume of biochar rose first and subsequently declined with rising temperature. The proximate analysis of biochar revealed metal volatilization process, and although the pH of biochar increased with rising temperature but HHV (high heat value) of the biochar decreased.

Optimizing magnetic functionalization conditions for efficient preparation of magnetic biochar and adsorption of Pb(II) from aqueous solution

Recoverable magnetic biochar has great potential for treating wastewater contaminants such as Pb(II). However, whether magnetic modification could enhance metal adsorption efficiency is currently contradictory in the literature mainly due to the differences in selecting various magnetic functionalization conditions. Considering this gap in knowledge, the effects of magnetic functionalization method (impregnation and precipitation), concentration of precursor iron solution (0.01–1 M), and pyrolysis temperature (300–700 °C) on the characteristics and Pb(II) adsorption capacity of biochar were systematically investigated in this paper. Results indicated that Fe3O4 was the main product for magnetic biochars synthesized using the impregnation (denoted as FWFe(3)) and precipitation methods (denoted as FWFe(2)). Magnetic functionalization resulted in remarkably increased pH and more negative zeta potential for FWFe(2) samples, whereas FWFe(3) samples showed the opposite trends. The adsorption of Pb(II) on different biochars fitted the pseudo-second order model and the Langmuir model. The maximum adsorption capacity was 817.64 mg/g for FWFe(2)1M700C (precipitation by 1 M of Fe(II)/Fe(III), pyrolysis at 700 °C), outperforming FWFe(3) and pristine biochar samples by around 5–13 times. Mechanism study indicated that the adsorption mainly involved electrostatic attraction, ion exchange, co-precipitation, and complexation. Pb(II) adsorption capacity was strongly dependent on the alkali pH of biochar. However, this efficiency was less affected by biochar surface area and its morphology. The higher pH of FWFe(2) samples not only led to an increased surface charge for stronger electrostatic attraction and ion exchange but also favored the formation of co-precipitates. By contrast, FWFe(3) samples showed a decreased adsorption capacity for Pb(II) with increased concentration of embedded iron. Overall, magnetic biochar, prepared using precipitation followed by high-temperature pyrolysis (such as, FWFe(2)1M700C), can be a promising adsorbent for Pb(II) adsorption from wastewater.

Biochar derived from agricultural wastes and wood residues for sustainable agricultural and environmental applications

Lignocellulosic biomass can be circulated to produce many materials and products, including biochar. This study analyzed five different types of biochar produced from agricultural wastes and wood residues. The raw materials included three agricultural by-products: corncob, cassava rhizome, rice husk, and two types of wood residues: rain tree (Samanea saman (Jacq.) Merr.) and krachid (Streblus ilicifolius (Vidal) Corner.). The biochar were made in patented retorts with locally-appropriated technology at a temperature range of 450–500°C. This research focuses on the primary physicochemical properties and biochar components, allowing biochar to become a vital material to support sustainable agriculture and the environment. Biochar properties used for agriculture consist of specific surface area, total pore volume, average pore diameter, pH, electrical conductivity (EC), and cation exchange capacity (CEC). The properties that benefit the environmental purposes are the element: carbon (C), hydrogen (H), nitrogen (N), oxygen (O), and the molar ratio of H/C, O/C, and C/N. The study found that all five types of biochar contained suitable properties for soil amendment and carbon sequestration. However, significant differences were shown in specific surface area, average pore diameter, pH, CEC, and EC of various biochar. Based on O/C and H/C ratios, all five types of biochar persisted in soil from 100 to over 1,000 years.

Characterization of halophyte biochar and its effects on water and salt contents in saline soil.

Biochar is a beneficial soil amendment; however, biochar-based properties are mainly determined by the feedstocks and the pyrolysis temperature. Nevertheless, considering the vast biomass of halophyte, little is known about how the halophyte-derived biochar improves saline soils. In this study, we firstly produced biochars by using three different halophytes, including Tamarix chinensis (recretohalophyte), Suaeda salsa (euhalophyte), and Phragmites australis (pseudo-halophyte) at 300, 500, and 700 °C, and compared their chemical and physical properties. We applied halophyte (Tamarix chinensis and Phragmites australis) biochars (pyrolysis at 500 °C) into 0-20 cm saline soil at 2% and 4% (w/w) rates to investigate the saline soil water, salt, and pH dynamics in a 12-month column experiment. The results showed that as the pyrolytic temperature increase, biochar yield and pore diameter decreased by 37.5-44.0% and 34.6-89.7%, respectively; in contrast, biochar pH, specific surface area, and total volume increased by 24.8-47.8%, 3-37 times and 1-9 times, respectively. The halophyte types significantly controlled biochar carbon and dissolved salt content and electrical conductivity. Halophyte biochar application can increase soil water and salt content, and application of 4% of Tamarix chinensis-derived biochar can increase more soil moisture than the soil salinity, and it can maintain soil pH at a stable level, which would be a potential way to improve saline soil properties. The results are valuable for choosing halophyte types and optimizing pyrolytic temperatures for halophyte biochar production through specific environmental usage.

Suitability of rice straw for biochar production through slow pyrolysis: Product characterization and thermodynamic analysis

The main objective of the present study is to turn the wheel from waste to wealth by sustainable rice straw management practices over field burning in India. For that, slow pyrolysis of rice straw was carried out in a fixed bed reactor. The result indicated an increase in process temperature (300–600 °C) led to the decreased biochar yield, while pH (8.28–11.4), pore-volume (0.0087–0.059 cm3/g), surface area (12.78–83.06 m2/g), and HHV (17.63–20.13 MJ/kg) of biochar increased. The maximum bio-oil yield was obtained at 500 °C, and its characterization study indicated a high amount of phenol and aromatic compounds. The composition of H2 (1.9–17.72%) and CH4 (2.3–8.82%) in the gas and heating value (6.5–9.4 MJ/Nm3) of the gas increased with temperature. The energy (84.22–89.61%) and exergy efficiency (74.41–87.37%) of the pyrolysis system increased with process temperature, and the thermodynamic optimization was achieved at 600 °C.

Effects of different pretreatment methods on biochar properties from pyrolysis of corn stover

To explore the effects of pretreatment methods including drying, vacuum freezing drying (VFD), pelleting, and ultrasonic vibration-assisted pelleting (UV-AP) on corn stover and biochar properties, the physicochemical and morphological changes of biomass before and after pretreatment were examined, and the effects of different pretreatment methods on biochar properties were investigated. The results showed that different pretreatment methods have a significant effect on the surface and internal structure of biochar. The highest and lowest specific surface area, micropore area, and total pore volume of biochar were 25.84 m2/g, 9.27 m2/g, 0.53 cm3/g, and 17.33 m2/g, 4.39 m2/g, 0.29 cm3/g, respectively. FTIR analysis showed that the functional group of pretreated corn stover was similar to those of biochar. Ultimate analysis indicated that both pretreatment methods and the highest treatment temperature had a significant effect on biochar compositions. The order of carbon content of biochar derived from different pretreatment methods was drying > VFD > UV-AP > pelleting. The biochar yield, enhancement factor, and energy yield were significant affected by pretreatment methods. By contrast, the biochar pH was alkaline and not significantly affected by pretreatment methods. These findings provide a reliable route to choose pretreatment methods for producing biochar with desired properties, which could be a guide for industrial application.

Influences of soil and biochar properties and amount of biochar and fertilizer on the performance of biochar in improving plant photosynthetic rate: A meta-analysis

Most studies found the benefit of biochar in increasing plant photosynthetic rate (PR), but how experimental conditions affect PR response to biochar application remains unclear. Therefore, we performed a meta-analysis by including 965 pairwise comparisons from 135 studies. Generally, biochar application enhanced PR by 23 % on average, a statistically significant increase relative to the control. However, a large variation of percent change in PR ranging from −59 to +1267 % was also observed under different experimental conditions. Specifically, biochar properties including contents of potassium (K), phosphorus (P), sodium (Na), carbon (C) and ash and their determining factors (feedstock and pyrolysis temperature) significantly influenced PR responses to biochar addition, while biochar pH could not be used alone as an effective predictor of PR increases after biochar treatment. There was a potential match between soil pH and biochar pH, determining the performance of biochar in improving crop PR. However, the complementarity between soil pH and biochar pH was not sufficient to achieve the maximum increase in PR, appropriate biochar application rate was needed at the same time. The most suitable application rate of biochar was 10.1−20 t ha−1 or 2.01–4 %. Moreover, it is essential to take the compatibility and complementarity between biochar, soil texture and management factors such as Nitrogen (N) application rate and growing environment into consideration. Overall, adding biochar into coarse textured soils or heavy metal contaminated soils is highly recommended for increasing plant PR. Co-application of biochar with nitrogen fertilizer is also worth being advocated. When the N application rate was 101−200 kg ha−1 or ≤ 0.015 %, the maximum increase in PR was obtained. These findings can provide suggestions for biochar application in agricultural production to optimize PR benefits.

Effects of biochar application on crop productivity, soil carbon sequestration, and global warming potential controlled by biochar C:N ratio and soil pH: A global meta-analysis

Biochar application has been widely recommended as a potential solution to tackle the challenges of food security and climate change in agroecosystems, but the effect sizes of biochar application on crop yield, soil carbon sequestration, and global warming potential (GWP) shows great uncertainties. To explore the effect variation of biochar application alone (B) and biochar combined with chemical fertilizers (BF) on crop yield, soil organic carbon (SOC), and GWP, this study reviewed updated datasets with 455, 131, and 95 independent experiments globally to identify the key factors influencing the responses of crop yield, SOC, and GWP to B and BF, respectively. Overall, the effect sizes were different between B and BF in both improving crop yield (15.1 % and 48.4 %, respectively) and decreasing GWP (27.1 % and 14.3 %, respectively), whereas there were almost no differences in terms of increasing SOC (32.9 % and 34.8 %, respectively). In addition, the effect sizes of B and BF on crop yield were coupled with these on SOC. Increased biochar carbon to nitrogen ratio (C:N ratio) and soil pH decreased the impact of B and BF on crop yield, while increased SOC promoted the impact of BF on crop yield. The effect size on GWP increased with biochar pH increasing but soil pH decreasing under B and BF. The wetness index, soil properties (SOC, pH, and clay), and biochar properties (type, pH, C:N ratio, and application rate) jointly explained 70 %–79 %, 90 %–93 %, and 70 %–97 % of the effect variations in crop yield, SOC, and GWP, respectively. The biochar C:N ratio and soil pH were the most important factors determining the effect size of biochar application on crop yield, SOC, and GWP. Taken together, biochar application is a tripartite win-win solution for improving crop yield, increasing SOC, and decreasing GWP mainly depending on biochar properties and soil pH.

Miscanthus biochar value chain - A review

To complete a loop of the Miscanthus value chain including production, phytomanagement, conversion to energy, and bioproducts, the wastes accumulated from these processes have to be returned to the production cycle to provide sustainable use of the feedstock, to reduce costs, and to ensure a zero-waste approach. This can be achieved by converting Miscanthus feedstock into biogas and biochar using pyrolysis and then returning biochar to the production cycle of Miscanthus crop applications in the phytotechnology of trace elements (TEs)-contaminated/marginal lands. These processes are subjects of the current review, which focused on the peculiarities of biochar received from Miscanthus by pyrolysis, its properties, the impact on soil characteristics, the phytoremediation process, biomass yield, and the abundance of soil biodiversity. Results from the literature indicated that the pH, surface area, and porosity of Miscanthus biochar are important in determining its impact on soil characteristics. It was inferred that the most effective Miscanthus biochar was produced with a pyrolysis temperature of about 600 °C with a residence time from about 30 min to an hour. Another important factor that determined the impact of Miscanthus biochar on soil health is the application rate: with its increase, the effect became more essential, and the recommended rate is between 5% and 10%. The influence of Miscanthus biochar on the TEs phytoremediation parameters is less studied, generally Miscanthus biochar produced at higher temperatures and added with higher application rates is more likely to restrict the mobility and availability of TEs by different plants. However, some published results are contradictory to these conclusions and showed absence of significant difference in TEs reduction during application of different Miscanthus biochar doses. The future experimental studies have to focus on determining the impact of a technological pyrolysis regime on Miscanthus biochar properties on TEs-contaminated or marginal land when biochar will be obtained from contaminated rhizomes and waste after the application of phytotechnology. In addition, studies must explore the influence of this biochar on TEs phytoparameters, enhancements in biomass yield, improvements in soil parameters, and the abundance of soil diversity.

Biochar from slow pyrolysis of biological sludge from wastewater treatment: characteristics and effect as soil amendment

AbstractBiological sludge from wastewater treatment is a by‐product from the pulp and paper industry, for which several management approaches are being researched to develop added‐value applications and to decrease the disposal costs. This work studied biological sludge pyrolysis to produce biochar for further use as soil amendment. The pyrolysis was conducted in a bench‐scale fixed‐bed reactor using distinct operating conditions, namely heating rate between 2 °C min−1 and 30 °C min−1 and peak temperature between 300 °C and 600 °C. The results demonstrated that biochar yield was between 0.40 and 0.73 kg kg–1 dry sludge. A trend for biochar yield to decrease with increasing peak temperature and heating rate was observed. The carbon content of biochar was between 42.8 and 47.0 wt%. The biochar pH was between 6.9 and 11.2. The effect of the biochar produced by pyrolysis as a soil corrective was evaluated in this work. Samples of biochar produced at 450 °C and 10 °C min−1 were incubated in a selected soil and its influence on soil properties and plant growth was evaluated. It was observed that the biochar portion 2.5%, 5%, and 10% promoted an increase in soil pH and an increase in water retention. The biochar portion 2.5% and 5% promoted a higher growth of Lepidium sativum plants. The results demonstrated the potential of the pyrolysis of biological sludge from the pulp and paper industry to produce biochar to be further used as a soil amendment. This strategy is of major importance in this industrial sector, thus contributing to the European Union goals on circular economy and industrial sustainability. © 2021 Society of Industrial Chemistry and John Wiley & Sons Ltd.

Optimization of biochar production based on environmental risk and remediation performance: Take kitchen waste for example

Two major obstacles that need to be addressed for environmental application of biochar include its environmental risk and remediation performance for target pollutants. In this study, kitchen waste was taken as an example to optimize the pyrolysis temperature for biochar production based on its heavy metal risk and Cd(II) remediation performance. The results showed that the pH and ash content of kitchen waste biochar (KWB) increased; however, the yield, H/C, and N/C decreased with increasing pyrolysis temperature. Total content of heavy metals in KWB got enriched after pyrolysis, while heavy metals’ risk was reduced from moderate to low due to the transformation of directly toxic heavy metal fractions into potentially and/or non-toxic fractions. The equilibrium adsorption capacities of biochar for Cd(II) ranked as follows: 49.0 mg/g (600 °C), 46.5 mg/g (500 °C), 23.6 mg/g (400 °C), 18.2 mg/g (300 °C). KWB pyrolyzed at 500 °C was found to be the most suitable for green, efficient, and economic remediation of Cd(Ⅱ) contaminated water. SEM-EDS and XPS characterization results indicated that KWB removed Cd(II) via precipitation, complexation with carboxyl/hydroxyl, ion exchange with metal cations, and coordination with π-electrons. This study puts forward a new perspective for optimizing biochar production for environmental application.

The effect of pyrolysis temperature and feedstock on date palm waste derived biochar to remove single and multi-metals in aqueous solutions

In this study, leaf and frond date palm waste as feedstock was used to derive biochars. The effects of pyrolysis temperatures on their physical and chemical properties, and their capacity to remove copper, iron, nickel and zinc from single and multi-metal solutions at various pH values were investigated. Analytical and spectroscopic techniques such as scanning electron microscopy, energy dispersive X-ray, Fourier transform infrared spectroscopy, X-ray diffraction, carbon, hydrogen, nitrogen, sulfur elemental analysis, Brunauer Emmett Teller analysis were conducted for characterization. The pore volume, surface area, pH, and total carbon content of date palm leaf and frond biochar increased while functional groups and hydrogen, nitrogen and oxygen content of biochar decreased with increasing pyrolysis temperature compared to feedstock. The removal efficiencies and sorption capacity for single and mixed metal ions were found between 98 and close to 100% and 2.4 and 3.0 mg g− 1 by leaf and frond biochar samples at pH > 6, respectively. Biochar obtained from different feedstock at different pyrolysis temperature did not show any statistically significant improvements on the removal of single or mixed metals from aqueous solutions. The date palm leaf or frond biochar obtained at low pyrolysis temperature is as effective to remove metals as the ones obtained at high pyrolysis temperatures. Therefore, to consume less energy to produce biochar at lower temperature which exhibits same effective removal efficiency will be a win-win solution in terms of sustainability and economy. As a result, date palm waste biochar can be effectively used to remove metals in water and wastewater.

Experimental Investigation into the Effect of Pyrolysis on Chemical Forms of Heavy Metals in Sewage Sludge Biochar (SSB), with Brief Ecological Risk Assessment.

Experimental investigations were carried out to study the effect of pyrolysis temperature on the characteristics, structure and total heavy metal contents of sewage sludge biochar (SSB). The changes in chemical forms of the heavy metals (Zn, Cu, Cr, Ni, Pb and Cd) caused by pyrolysis were analyzed, and the potential ecological risk of heavy metals in biochar (SSB) was evaluated. The conversion of sewage sludge into biochar by pyrolysis reduced the H/C and O/C ratios considerably, resulting in stronger carbonization and a higher degree of aromatic condensation in biochar. Measurement results showed that the pH and specific surface area of biochar increased as the pyrolysis temperature increased. It was found that elements Zn, Cu, Cr and Ni were enriched and confined in biochar SSB with increasing pyrolysis temperature from 300–700 °C; however, the residual rates of Pb and Cd in biochar SSB decreased significantly when the temperature was increased from 600 °C to 700 °C. Measurement with the BCR sequential extraction method revealed that the pyrolysis of sewage sludge at a suitable temperature transferred its bioavailable/degradable heavy metals into a more stable oxidizable/residual form in biochar SSB. Toxicity of heavy metals in biochar SSB could be reduced about four times if sewage sludge was pyrolyzed at a proper temperature; heavy metals confined in sludge SSB pyrolyzed at about 600 °C could be assessed as being low in ecological toxicity.

Effect of Enteromorpha prolifera Biochar on the Adsorption Characteristics and Adsorption Mechanisms of Ammonia Nitrogen in Rainfall Runoff

In order to study the performance and mechanisms of bioretention pond media (Enteromorpha prolifera biochar) for NH4+-N removal in rainfall runoff, three kinds of alkali modified biochars (marked as BC1, BC2, and BC3) were prepared with various concentrations of NaOH solution (1, 2, and 3 mol·L-1) to explore their adsorption performance for NH4+-N. The results showed that:① Appropriate modifications of the NaOH concentration increased the specific surface area and surface microstructure of biochar, with the content of O and the surface functional groups being enriched. In addition, BC2 possessed the best adsorption performance. ② The adsorption capacity reached a maximum when the pH was 9.0 and the dosage of biochar was 0.5 g·L-1. Compared with BC, the adsorption capacity of BC1 and BC2 increased by 6.4% and 10.8%, respectively, while BC3 decreased by 13.7%. Moreover, BC2 had an optimal adsorption efficiency with a saturated adsorption capacity of 16.76mg·g-1. ③ The adsorption mechanism of biochar belonged to chemical adsorption with a monomolecular layer. The adsorption process was promoted by the high pH of biochar, the electrostatic attraction of biochar pores, the complexation and oxidization of the functional groups of hydroxyl (-OH), carboxyl (-COOH), and carbon-oxygen single bond (C-O). To sum up, the proper amount of NaOH to modify biochar can improve the adsorption performance of NH4+-N, and the modified biochar can be used as media of the bioretention pond to remove NH4+-N.