Effects of biochar on bacterial communities in a newly established landfill cover topsoil.

Recent studies revealed the benefits of applying biochar in landfill final cover soil, such as adsorbing odorous compounds and promoting microbial methane oxidation. Most of these processes are related to the soil bacterial communities. However, the effects of biochar application on the overall bacterial community in newly established landfill cover soil are not yet understood, especially in field condition. The objective of the present field study is to investigate the effects of biochar on the diversity of soil bacterial community 3 months after incubation (short-term). Landfill final cover topsoil (0.6 m) was amended with 0 (control), 5, and 10% (w/w) of biochar derived from peanut-shell and wheat straw. Soil bacterial communities were analysed using the 16S rRNA-based T-RFLP approach. Biochar application significantly (p < 0.05) increased the diversity of soil bacterial communities. The Shannon diversity index of bacterial communities in soil amended with 5 and 10% of biochar was increased from 3.34 to 3.85 and 3.92, respectively. There were four bacterial phyla recorded found at both control and amended soils, namely Actinobacteria, Bacteroidetes, Firmicutes, and Proteobacteria. In addition, Gemmatimonadetes was found only in soil amended with 10% biochar. The interactions between soil bacterial communities and measured soil parameters including moisture content, electrical conductivity, total organic matter, total nitrogen and total phosphorus were found to be statistically non-significant (p > 0.05), according to the canonical correspondence analysis (CCA). This may be due to the highly heterogeneous nature of landfill soil. Results from this study revealed that short-term biochar application already altered the soil physicochemical properties and increased the diversity of soil bacterial communities.

Arbuscular mycorrhizal fungal community in the topsoil of a subtropical landfill restored after 18 years.

Restoration of disturbed habitats (e.g., landfills and mine tailings) is important to recover ecosystem services. Arbuscular mycorrhizal (AM) fungal community is an important indicator of ecological performance of ecosystems. Rhizospheric soils were collected in two sites (A1 and A2) within the restored area of a landfill (18 yrs after restoration), and two sites (B and C, serving as control) in the adjacent natural area. Soil properties were analysed. AM fungal communities in soils were analysed by sequencing 18S small subunit rRNA gene. Results showed that genera Glomus (the most abundant, relative abundance: 10-24%), Paraglomus and Rhizophagus were commonly found at all sites. Acaulospora and Redeckera were found exclusively at natural sites, while Scutellospora only at the restored site. On average, AM fungal species richness was lower (87 operational taxonomy units, OTUs), while diversity was higher (Shannon index 3.2) in restored site, compared with control (107 OTUs, Shannon index 2.8). The structure of the AM fungal communities was influenced by soil nitrogen and cation exchange capacity. The restored sites possessed a more phylogenetically heterogeneous fungal community than that in natural sites. AM fungal community at restored sites clearly deviated from that at natural sites, indicating that current restoration practice is certainly inadequate. The trend of ecological succession could be significantly influenced by rehabilitation methods, such as adjustment of initial soil properties and selection of plant species. This study highlights the necessity of assessing AM fungal community during ecological restoration for sustainable ecosystem, in addition to plant and bacteria.

Applications of charcoal, activated charcoal, and biochar in aquaculture - A review.

Environmental pollution and poor feed quality pose potential threats to aquatic organisms and human health, representing challenges for the aquaculture industry. In light of the rising demand for aquatic organisms, there is an urgent need to improve aquacultural production and protect the products from contamination. Char, a carbonaceous material derived through pyrolysis of organic carbon-rich biomass, has proven advantages in soil, air, and water remediation. While char's performance and the associated physicochemical characteristics depend strongly on the pyrolysis temperature, residence time, and feedstock type, char generally shows advantages in pollutant removal from the environment and livestock. This enables it to enhance the health and growth performance of livestock. Given the growing attention to char application in aquaculture in recent years, this review summarises major studies on three applications: aquacultural water treatment, sediment remediation, and char-feed supplement. Most of these studies have demonstrated char's positive effects on pollutant removal from organisms and aquacultural environments. Moreover, adopting char as fish feed can improve fish growth performance and the condition of their intestinal villi. However, due to insufficient literature, further investigation is needed into the mechanistic aspects of pollutants removal in aquatic organisms by char as a feed additive, such as the transportation of char inside aquatic organisms, the positive and negative effects of char on these products, and how char alters the gut microbiota community of these products. This paper presents an overview of the current application of char in aquaculture and highlights the research areas that require further investigation to enrich future studies.

Intercropping of Pinellia ternata (herbal plant) with Sedum alfredii (Cd-hyperaccumulator) to reduce soil cadmium (Cd) absorption and improve yield.

Soil contamination by cadmium (Cd) is of global concern, threatening not only crop production, but also supply of herbal medicine. Research studies usually grow crops with Sedum alfredii (a Cd-hyperaccumulator). However, intercropping herbal plants with S. alfredii and their interactions with hydro-chemical properties of soil are rarely considered. This study examines the growth of a herbal plant, Pinellia ternata, intercropped with S. alfredii in Cd-contaminated soil. Plant characteristics were assessed, especially biomass and Cd content of bulbil (yield and quality of P. ternata). Soil hydro-chemical properties including water retention, Cd content and organic matter were determined with statistical analyses. At low soil-Cd contamination (0.6 µg/g), bulbil biomass of intercropped P. ternata (PSL) was almost double compared with monoculture of P. ternata (PL), which is barely significant (p ≈ 0.05). The corm biomass of PSL was also significantly greater than that of PL (p < 0.05). Although soil-Cd contamination became more severe by increasing to 3 µg/g, the bulbil biomass in the intercrop was not significantly different from PL (p > 0.05). That said, it is evidenced that the yield of intercropped P. ternata was improved in Cd-contaminated soil. Such improvement was mainly attributed to reduced soil-Cd content and enhanced soil-water retention which was governed by plant roots and soil organic matters. The soil-water retention was first identified as a critical parameter in promoting plant growth under intercropping. More importantly, the bulbil-Cd content of P. ternata in PSL was significantly reduced (p < 0.05). This study demonstrates that the newly proposed intercrop is feasible to improve yield of herbal plants, and at the same time reduce heavy metal absorption and accumulation in medicinal organs, especially for P. ternata. This is anticipated to reduce the human health risk imposed by ingestion of Chinese herbal plants.

Effects of biochar on hydraulic conductivity of compacted kaolin clay.

Compacted clay is widely used as capillary barriers in landfill final cover system. Recently, biochar amended clay (BAC) has been proposed as a sustainable alternative cover material. However, the effects of biochar on saturated hydraulic conductivity (ksat) of clay with high degree of compaction is not yet understood. The present study aims to investigate the effects of biochar on ksat of compacted kaolin clay. Soil specimens were prepared by amending kaolin clay with biochar derived from peanut-shell at 0, 5 and 20% (w/w). The ksat of soil specimens was measured using a flexible water permeameter. The effects of biochar on the microstructure of the compacted clay was also investigated using MIP. Adding 5% and 20% of biochar increased the ksat of compacted kaolin clay from 1.2 × 10-9 to 2.1 × 10-9 and 1.3 × 10-8 ms-1, respectively. The increase in ksat of clay was due to the shift in pore size distribution of compacted biochar-amended clay (BAC). MIP results revealed that adding 20% of biochar shifted the dominant pore diameter of clay from 0.01-0.1 µm (meso- and macropores) to 0.1-4 µm (macropores). Results reported in this communication revealed that biochar application increased the ksat of compacted clay, and the increment was positively correlated to the biochar percentage.

Effects of biochar on the ecological performance of a subtropical landfill.

Landfills commonly occupy large areas of land that may be ecologically important. Ecological restoration of landfill cover is a necessary approach to rebuild sustainable habitats. However, unfavourable soil conditions and invasion by exotic plants in certain regions hinder the restoration. In this study, the effects of biochar as a soil amendment on the restoration of a landfill cover were investigated under field condition. Topsoils of a landfill cover in the subtropical region (Shenzhen, China) were mixed with 0, 5 and 10% (v/v) of biochar. Soil pH, electronic conductivity, organic matter, total organic carbon, water content, total N and total P were enhanced by biochar amendment. After nine months of self-succession, plant productivity, species richness and diversity were enhanced by biochar. The structures of soil bacterial and arbuscular mycorrhizal (AM) fungal communities were changed, and species richness and diversity were moderately promoted. Enhanced plant growth and diversity were probably attributed to a number of enhanced bacterial functions related to nutrient cycling including aerobic ammonia oxidation, aerobic nitrite oxidation, nitrification, sulphur respiration, nitrate respiration, nitrogen respiration, ureolysis, chemoheterotrophy and fermentation. The higher abundances of bacteria Streptomyces sp. and Pseudomonas sp. in biochar treatments potentially enhanced the AM fungal diversity. The bacterial diversity was more related to the soil properties, especially pH, than AM fungi. Continuous monitoring is necessary to track the changes of species composition and ecological functions over time. This is the first comprehensive study on the effects of biochar on the ecological performance of a man-made ecosystem. In addition to agricultural application, biochar can be used for restoring degraded lands.

Comparison of plant and bacterial communities between a subtropical landfill topsoil 15years after restoration and a natural area.

Engineered sanitary landfills are becoming more and more common worldwide. Ecosystem restoration of capped sanitary landfills is essential to restore the disturbed environment. Comparing plant communities, as well as bacterial communities, in landfills and natural areas, offers an efficient way to assess the restoration status. However, such studies on the restored engineered landfills are limited. Here we present an ecological restoration case in an engineered landfill in a subtropical region. Part of the South East New Territories (SENT) landfill in Hong Kong was capped and restored, by using 16 plant species growing on top of the final cover soil, during 1997-1999. In 2014, plant survey and soil properties analyses were conducted in a restored site (AT) and a natural site (CT, an undisturbed area, serving as a control). The similarity between the biota communities (i.e., plant and soil bacteria) of the two sites was assessed. Plant and soil bacterial communities at AT were significantly different (R=1, P<0.01, ANOSIM) from those at CT. A lower plant diversity but a higher soil bacterial diversity were observed at AT. The soil bacterial community structure was potentially driven by soil pH, moisture content, cation exchange capacity (CEC), N, and P. The engineered landfill had not been restored to an ecosystem similar to the natural environment 15years after restoration. Establishing similar soil properties in the landfill topsoil would be important to achieve a bacterial community similar to the natural area. This study can also offer a quick and inexpensive method for landfill engineers to assess the bacterial restoration of man-made ecosystems using plant and soil properties rather than DNA analyzing techniques.

Gas permeability of biochar-amended clay: potential alternative landfill final cover material.

Compacted biochar-amended clay (BAC) has been proposed as an alternative landfill final cover material in this study. Biochar has long been proposed to promote crop growth, mitigate odor emission, and promote methane oxidation in field soils. However, previous studies showed that soil-gas permeability was increased upon biochar application, which will promote landfill gas emission. The objective of the present study is to investigate the possibility of using compacted BAC as an alternative material in landfill final cover by evaluating its gas permeability. BAC samples were prepared by mixing 425-µm-sieved peanut shell biochar with kaolin clay in different ratios (0, 5, 10, and 15 %, w/w) and compacting at different degrees of compactions (DOC) (80, 85, and 90 %) with an optimum water content of 35 %. The gas permeability of the BACs was measured by flexible wall gas permeameter and the microstructure of the BACs was analyzed by SEM with energy-dispersive x-ray spectroscopy (EDX). The results show that the effects of biochar content on BAC gas permeability is highly dependent on the DOC. At high DOC (90 %), the gas permeability of BAC decreases with increasing biochar content due to the combined effect of the clay aggregation and the inhibition of biochar in the gas flow. However, at low DOC (80 %), biochar incorporation has no effects on gas permeability because it no longer acts as a filling material to the retard gas flow. The results from the present study imply that compacted BAC can be used as an alternative final cover material with decreased gas permeability when compared with clay.

Feasibility of biochar application on a landfill final cover-a review on balancing ecology and shallow slope stability.

Due to the increasing concerns on global warming, scarce land for agriculture, and contamination impacts on human health, biochar application is being considered as one of the possible measures for carbon sequestration, promoting higher crop yield and contamination remediation. Significant amount of researches focusing on these three aspects have been conducted during recent years. Biochar as a soil amendment is effective in promoting plant performance and sustainability, by enhancing nutrient bioavailability, contaminants immobilization, and microbial activities. The features of biochar in changing soil physical and biochemical properties are essential in affecting the sustainability of an ecosystem. Most studies showed positive results and considered biochar application as an effective and promising measure for above-mentioned interests. Bio-engineered man-made filled slope and landfill slope increasingly draw the attention of geologists and geotechnical engineers. With increasing number of filled slopes, sustainability, low maintenance, and stability are the major concerns. Biochar as a soil amendment changes the key factors and parameters in ecology (plant development, soil microbial community, nutrient/contaminant cycling, etc.) and slope engineering (soil weight, internal friction angle and cohesion, etc.). This paper reviews the studies on the production, physical and biochemical properties of biochar and suggests the potential areas requiring study in balancing ecology and man-made filled slope and landfill cover engineering. Biochar-amended soil should be considered as a new type of soil in terms of soil mechanics. Biochar performance depends on soil and biochar type which imposes challenges to generalize the research outcomes. Aging process and ecotoxicity studies of biochar are strongly required.