• Energy Research

Biochar has significant potential to improve crop performance. This study examined the effect of biochar application on the photosynthesis and yield of peanut crop grown on two soil types. The commercial peanut cultivar Middleton was grown on red ferrosol and redoxi-hydrosol (Queensland, Australia) amended with a peanut shell biochar gradient (0, 0.375, 0.750, 1.50, 3.00 and 6.00%, w/w, equivalent up to 85 t ha(-1)) in a glasshouse pot experiment. Biomass and pod yield, photosynthesis-[CO2] response parameters, leaf characteristics and soil properties (carbon, nitrogen (N) and nutrients) were quantified. Biochar significantly improved peanut biomass and pod yield up to 2- and 3-folds respectively in red ferrosol and redoxi-hydrosol. A modest (but significant) biochar-induced improvement of the maximum electron transport rate and saturating photosynthetic rate was observed for red ferrosol. This response was correlated to increased leaf N and accompanied with improved soil available N and biological N fixation. Biochar application also improved the availability of other soil nutrients, which appeared critical in improving peanut performance, especially on infertile redoxi-hydrosol. Our study suggests that application of peanut shell derived biochar has strong potential to improve peanut yield on red ferrosol and redoxi-hydrosol. Biochar soil amendment can affect leaf N status and photosynthesis, but the effect varied with soil type.

Methane (CH4) is one of the most important greenhouse gases which can be formed by methanogens and oxidized by methanotrophs, as well as ammonia oxidizers. Agricultural soils can be both a source and sink for atmospheric CH4. However, it is unclear how climate change, will affect CH4 emissions and the underlying functional guilds. In this field study, we determined the impact of simulated climate change (a warmer and drier condition) and its legacy effect on CH4 emissions and the methanogenic and methanotrophic communities, as well as their relationships with ammonia oxidizers in an acidic soil with urea application. The climate change conditions were simulated in a greenhouse, and the legacy effect was simulated by removing the greenhouse after twelve months. Simulated climate change significantly decreased the in situ CH4 emissions in the urea-treated soils while the legacy effect significantly decreased the in situ CH4 emissions in the control plots, but had very little effect in the urea-treated soils. This indicates that the impact of simulated climate change and its legacy on CH4 emissions was significantly modified by nitrogen fertilization. Methanotrophs were more sensitive than methanogens in response to simulated climate change and its legacy effect, especially in the urea treated soil. Significant negative correlations were observed between the abundances of ammonia oxidizers and methanotrophs. Additionally, results of partial least path modeling (PLS-PM) indicated that the interactions of methanogens and methanotrophs with ammonia oxidizing archaea (AOA) had significant positive relationships with in situ CH4 emissions under the simulated climate change condition. Our work highlights the important role of AOA for CH4 emissions under climate change conditions. Further research is needed to better understand this effect in other ecosystems.

Large quantities of biosolids (sewage sludge), which are produced from municipal wastewater treatment, are ever-increasing because of the commissioning of new treatment plants and continuous upgrades of the existing facilities. A large proportion of biosolids are currently landfilled. With increasing pressure from regulators and the general public, landfilling of biosolids is being phased out in many countries because of potential secondary pollution caused by leachate and the emission of methane, a potent greenhouse gas. Biosolids contain nutrients and energy that can be used beneficially. Significant efforts have been made recently to develop new technologies to manage biosolids and make useful products from them. In this paper, we provide a review of the technologies in biosolids management.A survey of literature was conducted.At present, the most common beneficial use of biosolids is agricultural land application because of inherent fertilizer values found in biosolids. Expansion of land application, however, may be limited in the future because of more stringent regulatory requirements and public concern about food chain contamination in some countries. Perceived as a green energy source, the combustion of biosolids has received renewed interest. Anaerobic digestion is generally a more effective method than incineration for energy recovery, and digested biosolids are suitable for further beneficial use through land application. Although conventional incineration systems for biosolid management generally consume more energy than they produce because of the high moisture content in the biosolids, it is expected that more combustion systems, either monocombustion or cocombustion, will be built to cope with the increasing quantity of biosolids.Under the increasingly popular low-carbon economy policy, biosolids may be recognized as a renewable fuel and be eligible for 'carbon credits'. Because ash can be used to manufacture construction materials, combustion can provide a complete management for biosolids. A number of advanced thermal conversion technologies (e.g., supercritical water oxidation process and pyrolysis) are under development for biosolids management with a goal to generate useful products, such as higher quality fuels and recovery of phosphorus. With an ever-increasing demand for renewable energy, growing bioenergy crops and forests using biosolids as a fertilizer and soil amendment can not only contribute to the low-carbon economy but also maximize the nutrient and carbon value of the biosolids.Land application of biosolids achieves a complete reuse of its nutrients and organic carbon at a relatively low cost. Therefore, land application should become a preferred management option where there is available land, the quality of biosolids meet regulatory requirements, and it is socially acceptable. Intensive energy cropping and forest production using biosolids can help us meet the ever-increasing demand for renewable energy, which can eliminate the contamination potential for food sources, a common social concern about land application of biosolids. In recent years, increasing numbers of national and local governments have adopted more stringent regulations toward biosolid management. Under such a political climate, biosolids producers will have to develop multireuse strategies for biosolids to avoid being caught because a single route management practice might be under pressure at a short notice. Conventional incineration systems for biosolids management generally consume more energy than they produce and, although by-products may be used in manufacturing, this process cannot be regarded as a beneficial use of biosolids. However, biosolids are likely to become a source of renewable energy and produce 'carbon credits' under the increasingly popular, low-carbon economy policy.To manage biosolids in a sustainable manner, there is a need for further research in the following areas: achieving a higher degree of public understanding and acceptance for the beneficial use of biosolids, developing cost-efficient and effective thermal conversions for direct energy recovery from biosolids, advancing technology for phosphorus recovery, and selecting or breeding crops for efficient biofuel production.

Globally, the valorisation of food waste into digestate through the process of anaerobic digestion is becoming increasingly popular. As a result, a large amount of food-waste digestate will need to be properly utilised. The utilisation of anaerobic digestion for fertiliser and alternative uses is essential to obtain a circular bioeconomy. The review aims to examine the environmental management of food-waste digestate, the value of digestate as a fertiliser and soil conditioner, and the emerging uses and improvements for post-anaerobic digestion reuse of digestate. Odour emissions, contaminants in food waste, emission and leaching of nutrients into the environment, and the regulations, policies, and voluntary initiatives of anaerobic digestion are evaluated in the review. Food-waste digestate can provide essential nutrients, carbon, and bio-stimulants to soils and increase yield. Recently, promising research has shown that digestates can be used in hydroponic systems and potentially replace the use of synthetic fertilisers. The integration of anaerobic digestion with emerging uses, such as extraction of value-added products, algae cultivation, biochar and hydrochar production, can further reduce inhibitory sources of digestate and provide additional economic opportunities for businesses. Moreover, the end-product digestate from these technologies can also be more suitable for use in soil application and hydroponic use.

Abstract This study explored the feasibility of simultaneously producing synthetic gases and metal-biochar catalyst from co-pyrolysis of microalgae (chlorella vulgaris, CV) and industrial waste (bauxite tailings, BT). Co-pyrolysis was conducted in two different atmospheric conditions of N2 and CO2. Real-time syngas monitoring revealed the use of CO2 substantially enhanced CO production by expediting CO2-medicated thermal cracking of CV and its impact was further pronounced when BT was incorporated in the pyrolytic process. Characterization of produced metal-biochar revealed that metal-biochar have porous structure, Fe3O4 phase, and graphitic carbon layers with defective sites. The metal-biochar removed > 72% of 5 mg L−1 methyl orange within 60 min in the presence of 2 mM peroxydisulfate at 0.1 g L−1 biochar dose. Quenching test revealed the removal of methyl orange was mainly driven by singlet oxygen (1O2) generated by persulfate activation by metal-biochar. The reusability test indicated metal-biochar maintained>80% of its catalytic capability up to five repetitive reaction cycles of methyl orange removal. Collectively, co-pyrolysis of microalgae and industrial waste containing transition metals in CO2 condition can be a viable option to harvest energy resources from biomass wastes and to produce catalytic medium applicable to remove a wide range of redox active contaminants.

Biochar is chemically more reduced and reactive than the original feedstock biomass. Graphite regions, functional groups, and redox-active metals in biochar contribute to its redox characteristics. While the functional groups such as phenolic species in biochar are the main electron donating moieties (i.e., reducers), the quinones and polycondensed aromatic functional groups are the components accepting electrons (oxidants). The redox capacity of biochar depends on feedstock properties and pyrolysis conditions. This paper aims to review and summarize the various synthesis techniques for biochars and the methods for probing their redox characteristics. We review the abiotic and microbial applications of biochars as electron donors, electron acceptors, or electron shuttles for pollutant degradation, metal(loid)s (im)mobilization, nutrient transformation, and discuss the underlying mechanisms. Furthermore, knowledge gaps that exist in the exploration and differentiation of the electron transfer mechanisms involving biochars are also identified.

Abstract The feedback of greenhouse gas emissions to climate change is vital for understanding and predicting the impact of global warming on ecosystem functions. However, the legacy effect of simulated climate change on nitrous oxide (N2O) emissions and the associated microbial guilds remain largely unknown. Using a climate change field-based mesocosm facility, we studied the impact of a warmer and drier environment and its legacy effect on in situ N2O emissions with different fertilizer types (manure and urea). The related functional guilds including N2O-producer [ammonia-oxidizing archaea and bacteria (AOA and AOB), nirS/K-type denitrifying bacteria, and nirK-type denitrifying fungi] and N2O-reducer (nosZI and nosZII) were analyzed by using high throughput and cloning sequencing. The simulated climate change significantly decreased in situ N2O emissions in the fertilized soil (urea- or manure-treated) while increasing the emissions in a non-fertilized soil. The AOA and AOB were well adapted to the simulated climate change condition in the manure- and urea-treated soil, respectively. In contrast, the fungal nirK-type N2O-producers were well adapted in non-fertilized soil. The abundance of nosZII was significantly stimulated by simulated climate change in both fertilized and non-fertilized soils. Moreover, different fertilizer types modulated the resilience of the microbial guilds. The AOA and the nirS-type denitrifying bacteria showed strong resilience, leading to a significant increase of N2O emissions in the manure-treated soil. The strong resilience was also observed in nosZII clade N2O-reducers, and the abundance of the species related to Candidatus Promineofilum breve and Gemmatirosa kalamazoonesis was stimulated by the legacy effect of simulated climate change in the urea-treated soil. The in situ N2O emissions were negatively correlated to nosZII rather than nosZI. These results highlight a significant potential of nosZII in mitigating N2O emissions under a projected climate change, especially in agroecosystems, where a large amount of fertilizers is commonly used.

Waste residues produced by agricultural and forestry industries can generate energy and are regarded as a promising source of sustainable fuels. Pyrolysis, where waste biomass is heated under low-oxygen conditions, has recently attracted attention as a means to add value to these residues. The material is carbonized and yields a solid product known as biochar. In this study, eight types of biomass were evaluated for their suitability as raw material to produce biochar. Material was pyrolyzed at either 350 °C or 500 °C and changes in ash content, volatile solids, fixed carbon, higher heating value (HHV) and yield were assessed. For pyrolysis at 350 °C, significant correlations (p < 0.01) between the biochars’ ash and fixed carbon content and their HHVs were observed. Masson pine wood and Chinese fir wood biochars pyrolyzed at 350 °C and the bamboo sawdust biochar pyrolyzed at 500 °C were suitable for direct use in fuel applications, as reflected by their higher HHVs, higher energy density, greater fixed carbon and lower ash contents. Rice straw was a poor substrate as the resultant biochar contained less than 60% fixed carbon and a relatively low HHV. Of the suitable residues, carbonization via pyrolysis is a promising technology to add value to pecan shells and Miscanthus.