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Biochar is the carbon-rich organic matter that remains after heating biomass under the minimization of oxygen during a process called pyrolysis. There are a number of reasons why biochar systems may be particularly relevant in developing-country contexts. This report offers a review of what is known about opportunities and risks of biochar systems. Its aim is to provide a state-of-the-art overview of current knowledge regarding biochar science. In that sense the report also offers a reconciling view on different scientific opinions about biochar providing an overall account that shows the various perspectives of its science and application. This includes soil and agricultural impacts of biochar, climate change impacts, social impacts, and competing uses of biomass. The report aims to contextualize the current scientific knowledge in order to put it at use to address the development climate change nexus, including social and environmental sustainability. The report is organized as follows: chapter one offers some introductory comments and notes the increasing interest in biochar both from a scientific and practitioner's point of view; chapter two gives further background on biochar, describing its characteristics and outlining the way in which biochar systems function. Chapter three considers the opportunities and risks of biochar systems. Based on the results of the surveys undertaken, chapter four presents a typology of biochar systems emerging in practice, particularly in the developing world. Life-cycle assessments of the net climate change impact and the net economic profitability of three biochar systems with data collected from relatively advanced biochar projects were conducted and are presented in chapter five. Chapter six investigates various aspects of technology adoption, including barriers to implementing promising systems, focusing on economics, carbon market access, and sociocultural barriers. Finally, the status of knowledge regarding biochar systems is interpreted in chapter seven to determine potential implications for future involvement in biochar research, policy, and project formulation.

Interest in biochar production from organic waste has been growing in recent years due to its broad applicability, availability, and smoother production. Biochar production techniques are being continuously modernized to improve the production rate and quality. Though numerous methods have been reported in the recent past, a systematic classification of the same is yet to be explored. Based on the advancement of the techniques being employed for biochar production and modification of conventional methods, we have categorized all major techniques of biochar production into two primary classes. In the traditional approach, ancient methods and conventional pyrolysis techniques (Slow and Fast pyrolysis) are included, whereas, in modern approaches, several advanced technologies such as Gasification, Torrefaction, Hydrothermal carbonization, Electro-modification, along with modified traditional methods (Flash pyrolysis, Vacuum pyrolysis, and Microwave pyrolysis) are comprised. Further, the systematic review was intended to evaluate various types of feedstocks (agricultural biomass, forest/woody biomass, aquatic biomass, urban waste, and paper waste) with their potential to produce biochar. It was observed that the feedstock containing high cellulose was found to be helpful in improving the overall properties of biochar, including enhanced adsorptive action and retention of nutrients.

India, the second largest agro-based economy with year-round crop cultivation, generates a large amount of agricultural waste, including crop residues. In the absence of adequate sustainable management practices, approximately 92 seems a very small number of metric tons of crop waste is burned every year in India, causing excessive particulate matter emissions and air pollution. Crop residue burning has become a major environmental problem causing health issues as well as contributing to global warming. Composting, biochar production and mechanization are a few effective sustainable techniques that can help to curtail the issue while retaining the nutrients present in the crop residue in the soil. The government of India has attempted to curtail this problem, through numerous measures and campaigns designed to promote sustainable management methods such as converting crop residue into energy. However, the alarming rise of air pollution levels caused by crop residue burning in the city of Delhi and other northern areas in India observed in recent years, especially in and after the year of 2015, suggest that the issues is not yet under control. The solution to crop residue burning lies in the effective implementation of sustainable management practices with Government interventions and policies. This manuscript addresses the underlying technical as well as policy issues that has prevented India from achieving a long-lasting solution and also potential solutions that have been overlooked. However, effective implementation of these techniques also requires us to look at other socioeconomic aspects that had not been considered. This manuscript also discusses some of the policy considerations and functionality based on the analyses and current practices. The agricultural waste sector can benefit immensely from some of the examples from other waste sectors such as the municipal solid waste (MSW) and wastewater management where collection, segregation, recycling and disposal are institutionalized to secure an operational system. Active stakeholder involvement including education and empowerment of farmers along with technical solutions and product manufacturing can also assist tremendously. Even though the issue of crop residue burning touches many sectors, such as environment, agriculture, economy, social aspects, education, and energy, the past governmental efforts mainly revolved around agriculture and energy. This sectorial thinking is another barrier that needs to be broken. The government of India as well as governments of other developing countries can benefit from the emerging concept of nexus thinking in managing environmental resources. Nexus thinking promotes a higher-level integration and higher level of stakeholder involvement that goes beyond the disciplinary boundaries, providing a supporting platform to solve issues such as crop residue burning.

Constructed wetlands (CWs) are a cost-effective, efficient, and long-term wastewater treatment solution in various countries. The efficacy and performance of constructed wetlands are greatly influenced by the substrate. Recently, biochar as a substrate, along with sand and gravel in constructed wetlands, has gained importance due to its various physical, chemical, and biological properties. This review presents a detailed study of biochar as a substrate in CWs and the mechanism involved in efficiency enhancement in pollutant removal. Different methods for producing biochar using various types of biomasses are also addressed. The effect of biochar in removing pollutants like biological oxygen demand (BOD), chemical oxygen demand (COD), nitrogen, heavy metals, and non-conventional pollutants (microcystin, phenanthrene, antibiotics, etc.) are also discussed. Furthermore, post-harvest utilization of constructed wetland macrophytic biomass via bioenergy production, biochar formation, and biosorbent formation is explained. Various challenges and future prospects in biochar-amended constructed wetlands are also discussed. Biochar proved to be an effective substrate in the removal of pollutants and proved to be a promising technique for wastewater treatment, especially for developing countries where the cost of treatment is a constraint. Biochar is an effective substrate; further modification in biochar with the right plant combination for different wastewater needs to be explored in the future. Future researchers in the field of constructed wetlands will benefit from this review during the utilization of biochar in constructed wetlands and optimization of biochar characteristics, viz., quantity, size, preparation method, and other biochar modifications.

Municipal wastewater sludge can be pyrolyzed as biochars to better use nutrients and stabilize carbon compared with other typical technologies, such as landfill and incineration. However, sludge-derived biochars might contain large amounts of potentially toxic elements (PTEs), such as Zn, Cu, Cr, Ni, Pb, and As. The stability of PTEs in biochars might be improved by higher pyrolytic temperatures, which can be further improved by different modifications. Herein, PO 4 -modification at 300 °C and Cl-modification at 700 °C were carried out, respectively, to enhance the stability of PTEs. Various leaching tests have been performed to assess the stability of PTEs in biochars, including the synthetic precipitation leaching procedure (SPLP), toxicity characteristic leaching procedure (TCLP), diethylenetriamine pentaacetate (DTPA) extraction, and in vitro simple bioaccessibility extraction test (SBET). The morphological structure, elemental mapping, and mineral formation of the pristine and modified biochars were studied by scanning electron microscopy–energy-dispersive X-ray spectroscopy (SEM–EDS) and X-ray diffraction (XRD). Our results suggested that the leachability, mobility, plant-availability, and bioaccessibility of most PTEs were decreased by pyrolysis, yet the total contents of PTEs were elevated, especially at 700 °C. Generally, modification by phosphates and MgCl 2 enhanced the stability of PTEs in biochars. Nevertheless, it should be noted that higher bioaccessibility of PTEs was observed in biochars of P-modification than Cl-modification, which is associated with the dissolution of phosphate precipitates under acidic conditions (pH<2). Additionally, Cl-modification leads to higher plant-available Zn and Cu and bioaccessible Zn compared with the unmodified biochar produced at 700 °C.

Biochar may contribute to both agricultural productivity and atmospheric carbon dioxide removal. However, despite the many potential upsides of adding biochar to amend carbon-depleted soils in sub-Saharan Africa, deployment is largely lacking. This paper explores the socio-economic factors that can explain tendencies to avoid action. Based on a survey of 172 farming households, key informant interviews, and focus group discussions in the Mbeya and Songwe regions of Tanzania, which were targeted for a biochar aid program in 2014, several socio-economic drivers behind the continued use of biochar deployment were identified in this follow-up study. A key deployment driver was the increased crop yields, perceived to be the result of adding biochar to soils, increasing yields from 1 metric ton per hectare to 3 metric tons per hectare. Food security and family income were cited as the main reasons to engage in biochar production and use. Climate change mitigation and increased resilience were other key reasons that motivated adoption. In terms of socio-economic factors, farmers with low education and income, the majority being males aged 40–60 years, contributed to low adoption rates in the study area. Respondents often cited the alternative usage of biochar feedstocks, lack of government involvement or extension services, traditions, and farming customs as the main constraints limiting biochar deployment.

Numerous researchers have expressed concern over the emerging water scarcity issues around the globe. Economic water scarcity is severe in the developing countries; thus, the use of inexpensive wastewater treatment strategies can help minimize this issue. An abundant amount of laundry wastewater (LWW) is generated daily and various wastewater treatment researches have been performed to achieve suitable techniques. This study addressed this issue by considering the economic perspective of the treatment technique through the selection of easily available materials. The proposed technique is a combination of locally available absorbent materials such as sand, biochar, and teff straw in a media. Biochar was prepared from eucalyptus wood, teff straw was derived from teff stem, and sand was obtained from indigenous crushed stones. In this study, the range of laundry wastewater flow rate was calculated as 6.23–17.58 m 3 /day; also studied were the efficiency of the media in terms of the removal percentage of contamination and the flux rate. The performances of biochar and teff straw were assessed based on the operation parameters and the percentage removal efficiency at different flux rates; the assessment showed 0.4 L/min flux rate to exhibit the maximum removal efficiency. Chemical oxygen demand, biological oxygen demand, and total alkalinity removal rate varied from 79% to ≥83%; total solids and total suspended solids showed 92% to ≥99% removal efficiency, while dissolved oxygen, total dissolved solids, pH, and electrical conductivity showed 22% to ≥62% removal efficiency. The optimum range of pH was evaluated between 5.8–7.1. The statistical analysis for finding the correlated matrix of laundry wastewater parameters showed the following correlations: COD (r = −0.84), TS (r = −0.83), and BOD (r = −0.81), while DO exhibited highest negative correlation. This study demonstrated the prospective of LWW treatment using inexpensive materials. The proposed treatment process involved low-cost materials and exhibited efficiency in the removal of contaminants; its operation is simple and can be reproduced in different scenarios.

Open dumping of municipal solid waste is a common method of waste disposal in developing countries, thus leading to pollution by gaseous emissions and landfill leachate discharge. Biochar, a carbonaceous material produced from any biomass, is a means to transform municipal solid waste into a value-added product, which can be used for resources recovery and for contaminant mitigation. This review presents the production of biochar from municipal solid waste. Biochar from municipal solid waste has various properties depending on the production technology. We describe the use of biochar as a green adsorbent for leachate treatment and as a permeable reactive barrier material to reduce contamination. Furthermore, biochar can be used as a cover material to reduce odors.

The treatment of heavy metal-contaminated water is challenging. The use of nanomaterials from many environmental wastes is promising for removing metals and contaminants from aqueous solutions. This study is novel in using nanobiochar of water hyacinth (WH) and black tea waste (TW) as a promising approach to water decontamination owing to its unique properties that play an effective role in metal adsorption. The mono- and multi-adsorption systems of cadmium (Cd), chromium (Cr), and nickel (Ni) on biochar and nanobiochar of water hyacinths (BWH and NBWH) and black tea waste (BTW and NBTW) were investigated in this study as potential low-cost and environmentally friendly absorbents for the removal of previously mentioned heavy metals (HMs) from aqueous solutions. The WH and TW were collected from the locality, prepared, and kept until used in the experiment. Nanobiochar was prepared by grinding, characterizing, and storing in airtight containers until used. A batch experiment was designed in mono- and competitive systems to study the adsorption equilibrium behavior of HMs on biochar and nanobiochars. The Freundlich and Langmuir isotherm models were fitted to the mono- and competitive-adsorption equilibrium results. The Freundlich isotherm model provided a better fit. Furthermore, it was noticed that NBWH and NBWT efficiently removed the Cd in the mono-system by ≥99.8, especially in the smaller concentration, while NBWT and BTW removed ≥99.8 and 99.7% in the competitive system, respectively. In the mono- and competitive systems, the nanobiochars of NBTW removed more than 98.8 of Cr. The sorbents were less efficient in Ni removal compared to Cd and Cr. However, their effectiveness was very high also. The results revealed that Cd was the highest metal removed by sorbents, nanobiochars were better than biochars to remove the HMs, and the results also indicated that co-occurrence of multi-metals might fully occupy the adsorption sites on biochars and nanobiochars.