Role of biochar on composting of organic wastes and remediation of contaminated soils-a review

Biochar and Water Quality

Biochar application is considered to be an emerging strategy to improve soil ecosystem services. However, implications of such application on water quality parameters have not been widely discussed. This paper synthesizes the state-of-the-art research on biochar effects on water erosion, nitrate leaching, and other sources of water pollution. Literature indicates that in general, biochar application reduces runoff by 5 to 50% and soil loss by 11 to 78%, suggesting that it can be effective at reducing water erosion, but the magnitude of erosion reduction is highly variable. Co-application of biochar with other organic amendments (i.e., animal manure, compost) appears to be more effective at reducing water erosion than biochar alone. A main mechanism by which biochar can reduce water erosion is by improving soil properties (i.e., organic C, hydraulic conductivity, aggregate stability), which affect soil erodibility. This review also indicates that biochar reduces nitrate leaching, in most cases by 2 to 88%, but has mixed effect on phosphate and dissolved C leaching. Additionally, biochar effectively filters urban runoff, adsorbs pollutants, and reduces pesticides losses. Biochar feedstock, pyrolysis temperature, application amount, time after application, and co-application with other amendments affect biochar impacts on water quality. Biochar erosion and potential reduction in nutrient and pesticide use efficiency due to the strong adsorption are concerns that deserve consideration. Overall, biochar application has the potential to reduce water erosion, nitrate leaching, pesticide losses, and other pollutant losses, but more field-scale data are needed to better discern the extent to which biochar can improve water quality.

Alginate-modified biochar derived from Ca(II)-impregnated biomass: Excellent anti-interference ability for Pb(II) removal

A novel biochar modified with sodium alginate was prepared using Ca(II)-impregnated biomass, and used to remove metals from aqueous solutions. The maximum adsorption capacity for Pb(II) was estimated to be 1.225 mmol/g (253.6 mg/g), which is far more than that of most adsorbents. Moreover, the modified biochar had a great anti-interference ability for effective removal of Pb(II) from multi-metal system. The biochar still had strong ability to adsorb Pb(II) when the initial concentrations of interfering ions were 5 times higher than that of Pb(II). Functional groups and minerals of the biochar worked for Pb(II) removal and the anti-interference ability. On the one hand, carboxyl could complex with Pb(II) through monodentate and bidentate bridging; on the other hand, Pb(II) was easier to form a precipitate with minerals than other metals. This study suggested that the novel biochar had the potential for practical application in effective removal of Pb(II) from wastewater.

Impact of percentage and particle size of sugarcane biochar on the sorption behavior of clomazone in Red Latosol

Biochar is a carbonaceous material that has excellent potential as a fertilizer and soil conditioner. However, there is a lack of information concerning the effects of the amount and particle size of this pyrogenic material on the soil sorption capacity. In this work, evaluation was made of changes in clomazone (CMZ) sorption in a Red Latosol following soil conditioning using different percentages (0.25, 0.5, and 1% w/w) of sugarcane biochar in three particle sizes (<106, 106-508, and 508-610 µm). The conditioned soils presented apparent sorption coefficients (Kd) up to 1300 times higher than that of pure soil, besides changes in the behavior of CMZ sorption. The biochar particle size and percentage influenced sorption of the herbicide as well as its retention in the amended soil during desorption processes. Both sorption and desorption Freundlich constants were linearly correlated with the external surface area of the biochar present in the soil.

Structural characteristics, analytical techniques and interactions with organic contaminants of dissolved organic matter derived from crop straw: a critical review

Dissolved organic matter (DOM) represents one of the most mobile and reactive organic compounds in an ecosystem and plays an important role in the fate and transport of soil organic pollutants, nutrient cycling and more importantly global climate change. Advances in environment geochemistry in the past two decades have improved our knowledge about the genesis, composition, and structure of DOM, and its effect on the environment. Application of analytical technology, for example UV-visible spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FTIR), Nuclear magnetic resonance (NMR) spectroscopy, and three-dimensional fluorescence spectroscopy (3D-EEM) have resulted in these advances. At present, crop straw, as a part of energy development strategy, is mainly used for soil amendment, fodder, fertilizer and industrial materials. Moreover, the fermentation and decomposition of straw should be also promoted for ecological agriculture. However, few studies have focused on the structural properties of DOM derived from crop straw in farmland soil. In this article, DOM derived from crop straw, which is abbreviated to "CDOM", presents active physicochemical properties that can affect the migration and bioavailability of organic contaminants (OCs) in terrestrial ecosystems. The objectives of this review paper are: (i) to discuss the structural characteristics, analytical techniques and interactions between CDOM and OCs in farmland soil; (ii) to present a critical analysis of the impact of CDOM on the physicochemical transformation and transport of OCs in farmland soils; (iii) to provide the perspectives in future research. Therefore, the findings obtained from this study can be utilized to evaluate the relations of interactions between CDOM and OCs in agricultural soils, in order to support some suggestions for future development in agricultural waste recycling, buffering of organic pollution, and the effect on the global carbon cycle.

Adsorption of methylene blue and tetracycline onto biomass-based material prepared by sulfuric acid reflux

The adsorptive removal of environmental pollutants is an effective method for the treatment of contaminated water. Thus, the preparation of adsorbents from low-cost, readily available, and renewable resources has garnered immense attention in recent years. In this study, a facile one-step method for the preparation of a high-capacity adsorbent is demonstrated by refluxing pine cones in concentrated sulfuric acid. With sulfuric acid reflux, the pine cones undergone carbonization as well as functionalization with sulfonic acid groups. The adsorbent demonstrated high adsorption capacity for two emerging organic pollutants, methylene blue (MB) and tetracycline (TC). Different variables such as pH, temperature, contact time, and initial concentration of the pollutants were analyzed and showed that the adsorption capacity for MB increased in a basic pH and vice versa for TC. Also, the elevated temperature favored the adsorption for both MB and TC. The maximum adsorption capacity was found to be 1666.66, and 357.14 mg g-1 for MB and TC, respectively. In comparison to the pristine pine cone, the sulfuric acid treated pine cone demonstrated an extraordinary improvement in the adsorption capacity. The adsorption of MB and TC was performed from the tap water matrix and similar adsorption capacities were found. A packed glass column was also prepared to demonstrate the adsorption of MB from tap water under flow conditions.

Effect of fermentation stillage of food waste on bioelectricity production and microbial community structure in microbial fuel cells

A single-chamber microbial fuel cell (MFC) was used in this study to treat recycled stillage obtained from food waste ethanol fermentation. Corresponding substrates inside the system were evaluated by fluorescence spectra, and microbial communities were also investigated. Results demonstrated that output voltage and current, respectively, reached 0.29 V and 1.4 mA with an external resistance of 200 Ω. Corresponding total organic carbon and chemical oxygen demand removal efficiency reached more than 50% and 70%, respectively. Results of fluorescence spectra demonstrated that tryptophan-like aromatic, soluble microbial by-product-like and humic acid-like substances accumulated and were not easily degraded. Microbial community analysis by high-throughput sequence indicated that Advenella and Moheibacter occupied the highest proportion among all genera at the anode instead of Geobacter. These results may be due to complicated accumulated stillage, and potential tetracyclines possibly influenced microbial communities. Details on how stillage affects MFC operation should be further studied, and a solution on relieving effects should be established.

The bioenergetics mechanisms and applications of sulfate-reducing bacteria in remediation of pollutants in drainage: A review

Sulfate-reducing bacteria (SRB), a group of anaerobic prokaryotes, can use sulfur species as a terminal electron acceptor for the oxidation of organic compounds. They not only have significant ecological functions, but also play an important role in bioremediation of contaminated sites. Although numerous studies on metabolism and applications of SRB have been conducted, they still remain incompletely understood and even controversial. Fully understanding the metabolism of SRB paves the way for allowing the microorganisms to provide more beneficial services in bioremediation. Here we review progress in bioenergetics mechanisms and application of SRB including: (1) electron acceptors and donors for SRB; (2) pathway for sulfate reduction; (3) electron transfer in sulfate reduction; (4) application of SRB for economical and concomitant treatment of heavy metal, organic contaminants and sulfates. Moreover, current knowledge gaps and further research needs are identified.

Changes in heavy metal bioavailability and speciation from a Pb-Zn mining soil amended with biochars from co-pyrolysis of rice straw and swine manure

Biochar has been utilized as a good amendment to immobilize heavy metals in contaminated soils. However, the effectiveness of biochar in metal immobilization depends on biochar properties and metal species. In this study, the biochars produced from co-pyrolysis of rice straw with swine manure at 400°C were investigated to evaluate their effects on bioavailability and chemical speciation of four heavy metals (Cd, Cu, Pb and Zn) in a Pb-Zn contaminated soil through incubation experiment. Results showed that co-pyrolysis process significantly change the yield, ash content, pH, and electrical conductivity (EC) of the blended biochars compared with the single straw/manure biochar. The addition of these biochars significantly increased the soil pH, EC, and dissolved organic carbon (DOC) concentrations. The addition of biochars at a rate of 3% significantly reduced the CaCl₂-extractable metal concentrations in the order of Pb>Cu>Zn>Cd. The exchangeable heavy metals decreased in all the biochar-amended soils whereas the carbonate-bound metal speciation increased. The increase in soil pH and the decrease in the CaCl₂ extractable metals indicated that these amendments can directly transform the highly availability metal speciation to the stable speciation in soils. In conclusion, biochar derived from co-pyrolysis of rice straw with swine manure at a mass ratio of 3:1 could most effectively immobilize the heavy metals in the soil.

Evaluating the effects of phytoremediation with biochar additions on soil nitrogen mineralization enzymes and fungi

Phytoremediation with biochar addition might alleviate pollutant toxicity to soil microorganism. It is uncertain to what extent biochar addition rate could affect activities of enzymes related to soil nitrogen (N) mineralization and alter fungal community under the phytoremediation. This study aimed to reveal the effects of Medicago sativa L. (alfalfa) phytoremediation, alone or with biochar additions, on soil protease and chitinase and fungal community and link the responses of microbial parameters with biochar addition rates. The alfalfa phytoremediation enhanced soil protease activities, and relative to the phytoremediation alone, biochar additions had inconsistent impacts on the corresponding functional gene abundances. Compared with the blank control, alfalfa phytoremediation, alone or with biochar additions, increased fungal biomass and community richness estimators. Moreover, relative to the phytoremediation alone, the relative abundances of phylum Zygomycota were also increased by biochar additions. The whole soil fungal community was not significantly changed by the alfalfa phytoremediation alone, but was indeed changed by alfalfa phytoremediation with 3.0% (w/w) or 6.0% biochar addition. This study suggested that alfalfa phytoremediation could enhance N mineralization enzyme activities and that biochar addition rates affected the responses of fungal community to the alfalfa phytoremediation.

The environmental characteristics and applications of biochar

The environmental deterioration is in a grave situation, and it is urgent to restore the environment. Biochar is a carbon-rich pyrolysis product of feedstock, which has aroused extensive concern due to its broad application potential for getting rid of pollutants and rehabilitating environment. This review generalizes three aspects on biochar, including production and properties, applications and mechanisms, and its modifications. Firstly, the production and characteristics have been summarized, because the practical applications of biochar are highly related to the special characteristics of biochar. Secondly, this paper outlines the latest applications of biochar for environmental remediation, and further provides a critical review on the application mechanisms in environmental restoration. Thirdly, the modification methods and applications of modified biochar are summarized, and all of the ways can be classified into two types: pretreatment of feedstock and modification of primitive biochar. Furthermore, the possible improvements and outlooks of applying biochar in environmental remediation are proposed. This review provides useful information for the application of biochar in environmental restoration.

Dynamics of labile and stable carbon and priming effects during composting of sludge and lop mixtures amended with low and high amounts of biochar

This study was performed to investigate the effects of biochar amendment on the dynamics of labile and stable carbon (C) fractions and associated priming effects during composting of sludge and lop mixtures. Furthermore, the effect of aerobic composting on biochar stable C composition was analyzed. Low amounts of activated carbon [dosage 0-1.7% w/w] and higher amounts of charcoal [dosage 0-38% w/w] were applied to the organic feedstock mixture in two separated full-scale composting trials under practical field conditions. The results demonstrated that biochar-C was substantially more stable during the composting process than compost-derived organic C resulting in a significant enrichment of the stable black C fraction in the final product. Furthermore, stability of final products were significantly increased, if more biochar has been initially added prior to composting. However, labile organic C losses were increased (positive priming) if low amounts of activated carbon have been applied, while no short-term priming effects could be observed after adding charcoal over a wider application range. Moreover, biochar stable C composition was positively affected during the composting process. Based on our results, a biochar amendment ≥10% (w/w) seems generally favorable for an accelerated composting process, while stability characteristics of the final products were improved. However, some caution seems to be required concerning the usability of activated carbon due to positive priming.

Magnetic bionanoparticles of Penicillium sp. yz11-22N2 doped with Fe3O4 and encapsulated within PVA-SA gel beads for atrazine removal

A novel magnetic bionanomaterial, Penicillium sp. yz11-22N2 doped with nano Fe₃O₄ entrapped in polyvinyl alcohol-sodium alginate gel beads (PFEPS), was successfully synthesized. The factors including nutrient substance, temperature, pH, initial concentrations of atrazine and rotational speeds were presented and discussed in detail. Results showed that the highest removal efficiency of atrazine by PFEPS was 91.2% at 8.00 mg/L atrazine. The maximum removal capacity for atrazine was 7.94 mg/g. Meanwhile, it has been found that most of atrazine were removed by metabolism and degradation of Penicillium sp. yz11-22N2, which could use atrazine as the sole source of either carbon or nitrogen. Degradation kinetics of atrazine conformed to first-order kinetics model. The intermediates indicated that the possible pathway for atrazine degradation by PFEPS mainly included hydrolysis dechlorination, dealkylation, side-chain oxidation and ring-opening.

Sorption to soil, biochar and compost: is prediction to multicomponent mixtures possible based on single sorbent measurements?

Amendment with biochar and/or compost has been proposed as a strategy to remediate soil contaminated with low levels of polycyclic aromatic hydrocarbons. The strong sorption potential of biochar can help sequestering contaminants while the compost may promote their degradation. An improved understanding of how sorption evolves upon soil amendment is an essential step towards the implementation of the approach. The present study reports on the sorption of pyrene to two soils, four biochars and one compost. Detailed isotherm analyzes across a wide range of concentration confirmed that soil amendments can significantly increase the sorption of pyrene. Comparisons of data obtained by a classical batch and a passive sampling method suggest that dissolved organic matter did not play a significant role on the sorption of pyrene. The addition of 10% compost to soil led to a moderate increase in sorption (<2-fold), which could be well predicted based on measurements of sorption to the individual components. Hence, our result suggest that the sorption of pyrene to soil and compost can be relatively well approximated by an additive process. The addition of 5% biochar to soil (with or without compost) led to a major increase in the sorption of pyrene (2.5–4.7-fold), which was, however, much smaller than that suggested based on the sorption measured on the three individual components. Results suggest that the strong sorption to the biochar was attenuated by up to 80% in the presence of soil and compost, much likely due to surface and pore blockage. Results were very similar in the two soils considered, and collectively suggest that combined amendments with compost and biochar may be a useful approach to remediate soils with low levels of contamination. Further studies carried out in more realistic settings and over longer periods of time are the next step to evaluate the long term viability of remediation approaches based on biochar amendments.

Preparation, performances and mechanisms of magnetic Saccharomyces cerevisiae bionanocomposites for atrazine removal

Saccharomyces cerevisiae and nanoparticles of iron oxide (Fe₃O₄) which were linked with chitosan (CS) through epichlorohydrin (ECH) were encapsulated in calcium alginate to prepare a novel type of bionanocomposites. Characterization results showed that the Fe₃O₄-ECH-CS nanoparticles were quasi-spherical with an average diameter of 30 nm to which chitosan was successfully attached through epichlorohydrin. The saturation magnetization value of the nanoparticles was 21.88 emu/g, and ferrous and ferric irons were simultaneously observed in the magnetic nanoparticles. Data of atrazine removal by yeasts showed that both inactivated and live yeasts could decrease the concentration of atrazine effectively. The inactivated yeasts achieved 20% removal rate, which indicated that adsorption by the yeasts also played a role in the removal. Removal efficiency of atrazine was maximized at 88% under 25 °C, pH of 7 and an initial atrazine concentration of 2 mg/L. When the magnetic bionanocomposite was recycled and reused twice, only 12% and 20% drop in removal efficiency was observed at the first time and the second time severally. So, atrazine could be used by the yeasts as the sole carbon source for growth and multiplication, and both adsorption and biodegradation by the bionanocomposite contributed to atrazine removal.

Responses of microalgae Coelastrella sp. to stress of cupric ions in treatment of anaerobically digested swine wastewater

Microalgae Coelastrella sp. could remove nutrients from anaerobically digested swine wastewater (ADSW) effectively, while its responses to the stress of Cu(II) were not well understood. In this paper, nutrients removal and growth of Coelastrella sp. were investigated at the presence of Cu(II) in ADSW. Results showed ammonium nitrogen concentration in ADSW decreased with culturing duration, while increased with an increased Cu(II) concentration. Total phosphorous concentration decreased with time, while did not drop in 4 days at Cu(II) concentration ≥1.0 mg/L. Microalgal growth was inhibited at all the Cu(II) concentrations, and ceased in about 6-8 days at Cu(II) concentration ≥1.0 mg/L. With an increased Cu(II) concentration, the contents of chlorophyll a and proteins decreased, those of malondialdehyde and superoxide dismutase, and ratios of octadecanoic acid (C18:0), hexadecanoic acid (C16:0) and octadecenoic acid (C18:1) to fatty acids in Coelastrella sp. increased, while octadecatrienoic acid (C18:3) gradually disappeared.

Effect of zinc ions on nutrient removal and growth of Lemna aequinoctialis from anaerobically digested swine wastewater

The effect of Zn²⁺ on ammonium and phosphorous removal and duckweed growth was evaluated for treatment of anaerobically digested swine wastewater (ADSW) at various initial Zn²⁺ concentrations ranging from 1.0 to 15mg/L. Lemna aequinoctialis taken from a local pond was selected for the treatment, and its fresh weight and contents of proteins, photosynthetic pigments, and vitamin E were examined. Results showed that the optimal Zn²⁺ concentration was 5.0mg/L for NH₃-N and TP removal, the duckweed growth, and the accumulation of proteins in the duckweed. A maximum content of photosynthetic pigments increased with the increase of initial Zn²⁺ concentration, and it arrived earlier for a higher concentration of Zn²⁺. Vitamin E content in the duckweed reached 4.5mg/kg at 15mg/L Zn²⁺ in 12-day cultivation, which showed the potential for producing and harvesting a high value-added product of vitamin E by culturing duckweed in ADSW.

Comparative study of modified/non-modified aluminum and silica aerogels for anionic dye adsorption performance

Developing effective and low-cost adsorbents is of great significance for controlling water contamination.

Biochar production and applications in soil fertility and carbon sequestration – a sustainable solution to crop-residue burning in India

A sustainable solution to crop residues burning by converting residues into biochars is provided.