As a promising amendment, biochar has excellent characteristics and can be used as a remediation agent for diverse types of soil pollution. Biochar is mostly made from agricultural wastes, forestry wastes, and biosolids (eg, sewage sludge), but not all the biochar has the same performance in the improvement of soil quality. There is a lack of guidelines devoted to the selection of biochar to be used for different types of soil pollution, and this can undermine the remediation efficiency. To shed light on this sensitive issue, this review focus on the following aspects, (i) how feedstocks affect biochar properties, (ii) the effects of biochar on heavy metals and organic pollutants in soil, and (iii) the impact on greenhouse gas emissions from soil. Generally, the biochars produced from crop residue and woody biomass which are composed of lignin, cellulose, and hemicellulose are more suitable for organic pollution remediation and greenhouse gas emission reduction, while biochar with high ash content are more suitable for cationic organic pollutant and heavy metal pollution (manure and sludge, etc.). Additionally, the effect of biochar on soil microorganisms shows that gram-negative bacteria in soil tend to use WB biochar with high lignin content, while biochar from OW (rich in P, K, Mg, and other nutrients) is more able to promote enzyme activity. Finally, our recommendations on feedstocks selection are presented in the form of a flow diagram, which is precisely intended to be used as a support for decisions on the crucial proportioning conditions to be selected for the preparation of biochar having specific properties and to maximize its efficiency in pollution control.

Soil fumigation continues to play an important role in soil disinfection, but tools to significantly reduce emissions while providing environmental benefits (e.g., biochar) are lacking. The objective of this study was to determine the effects of biochar products on fumigant 1,3-dichloropropene (1,3-D) and chloropicrin (CP) emissions, their distribution and persistence in soil, nematode control, and potential toxicity to plants in a field trial. Treatments included three biochar products [two derived from almond shells (ASB) at either 550 or 900 °C pyrolysis temperature and one from coconut shells (CSB) at 550 °C] at 30 and 60 t ha⁻¹, a surface covering with a low permeability film (TIF), and no surface covering (control). A mixture of 1,3-D (∼65%) and CP (∼35%) was injected to ∼60 cm soil depth at a combined rate of 640 kg ha⁻¹. All biochar treatments significantly reduced emissions by 38–100% compared to the control. The ASB (900 °C) at both rates reduced emissions as effectively as the TIF (by 99–100%). Both fumigant emission reduction and residue in surface soil were positively correlated with biochar's adsorption capacity while cucumber germination rate and dry biomass were negatively correlated with residual fumigant concentrations in surface soil. This research demonstrated the potential and benefits of using biochar produced from local orchard feedstocks to control fumigant emissions. Additional research is needed to maximize the benefits of biochar on fumigant emission reductions without impacting plant growth.

By the year 2050, it is estimated that the demand for palm oil is expected to reach an enormous amount of 240 Mt. With a huge demand in the future for palm oil, it is expected that oil palm by-products will rise with the increasing demand. This represents a golden opportunity for sustainable biohydrogen production using oil palm biomass and palm oil mill effluent (POME) as the renewable feedstock. Among the different biological methods for biohydrogen production, dark fermentation and photo-fermentation have been widely studied for their potential to produce biohydrogen by using various waste materials as feedstock, including POME and oil palm biomass. However, the complex structure of oil palm biomass and POME, such as the lignocellulosic composition, limits fermentable substrate available for conversion to biohydrogen. Therefore, proper pre-treatment and suitable process conditions are crucial for effective biohydrogen generation from these feedstocks. In this review, the characteristics of palm oil industrial waste, the process used for biohydrogen production using palm oil industrial waste, their pros and cons, and the influence of various factors have been discussed, as well as a comparison between studies in terms of types of reactors, pre-treatment strategies, the microbial culture used, and optimum operating condition have been presented. Through biological production, hydrogen production rates up to 52 L-H₂/L-medium/h and 6 L-H₂/L-medium/h for solid and liquid palm oil industrial waste, respectively, can be achieved. In short, the continuous supply of palm oil production by-product and relatively, the low cost of the biological method for hydrogen production indicates the potential source of renewable energy.

Forest fires significantly affect the wildlife, vegetation, composition and structure of the forests. This study explores the potential of partially burnt wood recovered in the aftermath of a recent Canadian forest fire incident as a feedstock for generating hydrogen-rich syngas through hydrothermal gasification. Partially burnt wood was gasified in hydrothermal conditions to study the influence of process temperature (300–500 °C), residence time (15–45 min), feed concentration (10–20 wt%) and biomass particle size (0.13 mm and 0.8 mm) using the statistical Taguchi method. Maximum hydrogen yield and total gas yield of 5.26 mmol/g and 11.88 mmol/g, respectively were obtained under optimized process conditions at 500 °C in 45 min with 10 wt% feed concentration using biomass particle size of 0.13 mm. The results from the mean of hydrogen yield show that the contribution of each experimental factors was in the order of temperature > feed concentration > residence time > biomass particle size. Other gaseous products obtained at optimum conditions include CO₂ (3.43 mmol/g), CH₄ (3.13 mmol/g) and C₂–C₄ hydrocarbons (0.06 mmol/g).

Biochar has a wide range of feedstocks, and different feedstocks often resulted in different properties, such as element distribution and heavy metal immobilization performance. In this work, batch experiments were conducted to assess the effectiveness of biochar pyrolyzed from kitchen waste (KWB), corn straw (CSB), and peanut hulls (PHB) on immobilization of Cd and Pb in contaminated soil by planting swamp cabbage (Ipomoea aquatica Forsk.) with a combination of toxicological and physiological tests. The results showed that biochar could all enhance the soil pH, and reduce extractable Pb and Cd in soil by 22.61%–71.01% (KWB), 18.54%–64.35% (CSB), and 3.28%–60.25% (PHB), respectively. The biochar led to a drop in Cd and Pb accumulation in roots, stems, and leaves by 45.43%–97.68%, 59.13%–96.64%, and 63.90%–99.28% at the dosage of 60.00 mg/kg, respectively. The root length and fresh weight of swamp cabbage were promoted, while superoxide dismutase (SOD) and peroxidase (POD) decreased after biochar treatment. The distribution of heavy metal fractions before and after biochar treatment indicated that biochar could transform Cd and Pb into a state of lower bioavailability, thus inhibiting Cd and Pb uptake by swamp cabbage. Biochar with different feedstocks could be ranked by the following order according to immobilization performance: KWB > CSB > PHB.

Proper management of waste crop residues has been an environmental concern for years. Yellow mealworms (larvae of Tenebrio molitor Linnaeus, 1758) are major insect protein source. In comparison with normal feed wheat bran (WB), we tested five common lignocellulose-rich crop residues as feedstock to rear mealworms, including wheat straw (WS), rice straw (RS), rice bran (RB), rice husk (RH), and corn straw (CS). We then used egested frass for the production of biochar in order to achieve clean production. Except for WS and RH, the crop residues supported mealworms’ life activity and growth with consumption of the residues by 90% or higher and degraded lignin, hemicellulose and cellulose over 32 day period. The sequence of degradability of the feedstocks is RS > RB > CS > WS > RH. Egested frass was converted to biochar which was tested for metal removal including Pb(II), Cd(II), Cu(II), Zn(II), and Cr(VI). Biochar via pyrolysis at 600 °C from RS fed frass (FRSBC) showed the best adsorption performance. The adsorption isotherm fits the Langmuir model, and kinetic analysis fits the Pseudo-Second Order Reaction. The heavy metal adsorption process was well-described using the Intra-Particle Diffusion model. Complexation, cation exchange, precipitation, reduction, deposition, and chelation dominated the adsorption of the metals onto FRSBC. The results indicated that crop residues (WS, RS, RB, and CS) can be utilized as supplementary feedstock along with biochar generated from egested frass to rear mealworms and achieve clean production while generating high-quality bioadsorbent for environment remediation and soil conditioning.

The effluent stream of the anaerobic digestion processes, the digestate, accommodates high residual organic content that needs to be further treated before discharge. Anaerobic treatment of digestate would not only reduce the residual organic compounds in digestate but also has a potential to capture the associated biogas. High-rate anaerobic reactor configurations can treat the waste streams using lower hydraulic retention times which requires less footprint opposed to the conventional completely stirred tank reactors. This study investigated the high-rate anaerobic treatment performance and the associated biogas capture from the digestate of a manure mixture composed of 90% laying hen and 10% cattle manures in fixed-film reactors. The results indicated that it was possible to reduce total chemical oxygen demand content of the digestate by 57–62% in 1.3–1.4 days of hydraulic retention time. The corresponding biogas yields obtained were in the range of 0.395–0.430 Lbiogas/g VSadded which were found to be comparable to many raw feedstocks. Moreover, significant total phosphorus reduction (36–47%) and greenhouse gas capture (over 14.5–18.1 tCO2e/d per m3 digestate) were also recorded in the anaerobic fixed-film reactors.

This study proposes a strategic principle to enhance the thermal efficiency of pyrolysis of municipal solid waste (MSW). An environmentally sound energy recovery platform was established by suppressing the formation of harmful organic compounds evolved from pyrolysis of MSW. Using CO2 as reaction medium/feedstock, CO generation was enhanced through the following: 1) expediting the thermal cracking of volatile organic carbons (VOCs) evolved from the thermal degradation of the MSWs and 2) directly reacting VOCs with CO2. This particular influence of CO2 on pyrolysis of the MSWs also led to the in-situ mitigation of harmful organic compounds (e.g., benzene derivatives and polycyclic aromatic hydrocarbons (PAHs)) considering that CO2 acted as a carbon scavenger to block reaction pathways toward benzenes and PAHs in pyrolysis. To understand the fundamental influence of CO2, simulated MSWs (i.e., various ratios of biomass to polymer) were used to avoid any complexities arising from the heterogeneous matrix of MSW. All experimental findings in this study suggested the foreseeable environmental application of CO2 to energy recovery from MSW together with disposal of MSW.

Aminocyclopyrachlor is a pyrimidine carboxylic acid herbicide used to control broadleaf weeds and brush. Amending soil with activated charcoal is recommended to prevent off-site transport of aminocyclopyrachlor and non-target plant damage. We used the batch-equilibrium method to determine the concentration of aminocyclopyrachlor in a pseudo-steady state with biochar, soil, and biochar-soil systems (<10% biochar by weight). We observed that aminocyclopyrachlor is mobile in soils. Soil incorporation of activated charcoal removed nearly all of the aqueous aminocyclopyrachlor thereby limiting its bioavailability to non-target flora. On the other hand, biochars were less effective than activated charcoal. Biochar produced from olive mill waste feedstock was the most effective biochar that we assessed for reducing the aqueous herbicide concentration. Although these biochars reduced the aminocyclopyrachlor concentration, they would not be practical remediation media due to the extraordinarily high application rates required to reduce the concentration by 50% (2.13 × 105 kg ha−1–7.27 × 105 kg ha−1).

Five biodiesels from different feedstocks (rapeseed, soy, sunflower, palm, and used fried oils) blended with diesel at 10% vol. ratio (B10), were tested on a Euro 3 common-rail passenger car. Limited effects (-2% to +4%) were observed on CO2 emissions. CO and HC emissions increased between 10% and 25% on average, except at high speed - high power where emissions were too low to draw conclusions. NOx emissions increased by up to 20% for two out of the five blends, decreased by up to 15% for two other blends, and remained unchanged for one blend. Particulate matter (PM) was reduced for all blends by up to 25% and the reductions were positively correlated with the extent of biodiesel saturation. PM reductions are associated with consistent reductions in non-volatile particle number. A variable behaviour in particle number is observed when volatile particles are also accounted.