The Sensitivity of a Specific Denitrification Rate under the Dissolved Oxygen Pressure

Denitrification in hypersaline and coastal environments

As the association of denitrification with global warming and nitrogen removal from ecosystems has gained attention in recent decades, numerous studies have examined denitrification rates and the distribution of denitrifiers across different environments. In this minireview, reported studies focused on coastal saline environments, including estuaries, mangroves, and hypersaline ecosystems, have been analysed to identify the relationship between denitrification and saline gradients. The analyses of the literature and databases stated the direct effect of salinity on the distribution patterns of denitrifiers. However, few works do not support this hypothesis thus making this topic controversial. The specific mechanisms by which salinity influences denitrifier distribution are not fully understood. Nevertheless, several physical and chemical environmental parameters, in addition to salinity, have been shown to play a role in structuring the denitrifying microbial communities. The prevalence of nirS or nirK denitrifiers in ecosystems is a subject of debate in this work. In general terms, in mesohaline environments, the predominant nitrite reductase is NirS type and, NirK is found predominantly in hypersaline environments. Moreover, the approaches used by different researchers are quite different, resulting in a huge amount of unrelated information, making it difficult to establish comparative analysis. The main techniques used to analyse the distribution of denitrifying populations along salt gradients have been also discussed.

Efficient nitrogen removal from stormwater runoff by bioretention system: The construction of plant carbon source-based heterotrophic and sulfur autotrophic denitrification process

The plant carbon source and sulfur were selected as the denitrification electron donors and filled in the internal water storage zone (IWSZ) of bioretention system to establish excellent mixotrophic denitrification system, which was beneficial to waste recycling and showed very high nitrate nitrogen removal efficiency (approximately 94%). The ammonia nitrogen, total nitrogen, and chemical oxygen demand removal efficiencies could reach 79.41%, 85.89%, and 74.07%, respectively. Mechanism study revealed the synergistic degradation effect was existed between acetic acid released from plant carbon source and the generated sulfate, which improved the S/CH₃COOH mediated nitrate nitrogen removal reactions. Autotrophic denitrification occurred mainly in the upper layer of IWSZ, and the dominant bacteria were Thiobacillus. While in the lower layer, the dominant bacteria were mainly related to organic matter utilization and heterotrophic denitrification. The abundance of narG, nirK, nirS, and nosZ functional genes in the upper layer was significantly higher than the lower layers.

A Life Cycle Assessment of an Energy-Biochar Chain Involving a Gasification Plant in Italy

Life cycle assessment (LCA) is a fundamental tool for evaluating the environmental and energy load of a production cycle. Its application to renewable energy production systems offers the possibility of identifying the environmental benefits of such processes—especially those related to the by-products of production processes (i.e., digestion or biochar). Biochar has received worldwide interest because of its potential uses in bioenergy production, due to its coproducts (bio-oil and syngas), as well as in global warming mitigation, sustainable agriculture, pollutant removal, and other uses. Biochar production and use of soil is a strategy for carbon sequestration that could contribute to the reduction of emissions, providing simultaneous benefits to soil and opportunities for bioenergy generation. However, to confirm all of biochar’s benefits, it is necessary to characterize the environmental and energy loads of the production cycle. In this work, soil carbon sequestration, nitrous oxide emissions, use of fertilizers, and use of water for irrigation have been considered in the biochar’s LCA, where the latter is used as a soil conditioner. Primary data taken from experiments and prior studies, as well as open-source available databases, were combined to evaluate the environmental impacts of energy production from biomass, as well as the biochar life cycle, including pre- and post-conversion processes. From the found results, it can be deduced that the use of gasification production of energy and biochar is an attractive strategy for mitigating the environmental impacts analyzed here—especially climate change, with a net decrease of about −8.3 × 103 kg CO2 eq. Finally, this study highlighted strategic research developments that combine the specific characteristics of biochar and soil that need to be amended.

Application of Modified Spent Mushroom Compost Biochar (SMCB/Fe) for Nitrate Removal from Aqueous Solution

The public is already aware that nitrate pollution caused by nutrient runoff from farms is harmful to aquatic life and human health, and there is an urgent need for a product/technology to solve this problem. A biochar adsorbent was synthesized and used to remove nitrate ions from aqueous media based on spent mushroom compost (SMC), pre-treated with iron (III) chloride hexahydrate and pyrolyzed at 600 °C. The surface properties and morphology of SMCB/Fe were investigated using Fourier transform-infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The effect of main parameters such as the adsorbent dosages, pH of the solutions, contact times, and ion concentrations on the efficiency of nitrate removal was investigated. The validity of the experimental method was examined by the isothermal adsorption and kinetic adsorption models. The nitrate sorption kinetics were found to follow the pseudo-second-order model, with a higher determination coefficient (0.99) than the pseudo-first-order (0.86). The results showed that the maximum percentage of nitrate adsorption was achieved at equilibrium pH 5-7, after 120 min of contact time, and with an adsorbent dose of 2 g L-1. The highest nitrate adsorption capacity of the modified adsorbent was 19.88 mg g-1.