Characterization of the denitrifying bacterial community in a full-scale rockwool biofilter for compost waste-gas treatment

Effect of microbial inoculation on nitrogen transformation, nitrogen functional genes, and bacterial community during cotton straw composting

The effects of microbial agents on nitrogen (N) conversion during cotton straw composting remains unclear. In this study, inoculation increased the germination index and total nitrogen (TN) by 24-29 % and 7-10 g/kg, respectively. Inoculation enhanced the abundance of nifH, glnA, and amoA and reduced that of major denitrification genes (nirK, narG, and nirS). Inoculation not only produced high differences in the assembly process and strong community replacement but also weakened environmental constraints. Partial least squares path modelling demonstrated that enzyme activity and bacterial community were the main driving factors influencing TN. In addition, network analysis and the random forest model showed distinct changing patterns of bacterial communities after inoculation and identified keystone microorganisms in maintaining network complexity and synergy, as well as system function to promote nitrogen preservation. Findings provide a novel perspective on high-quality resource recovery of agricultural waste.

Deodorizing bacterial consortium: community analysis of biofilms and leachate water collected from an air biofiltration system in a piggery

Intensive livestock production is a source of water, soil, and air contamination. The first aspect that negatively affects the quality of life of residents in the vicinity of piggeries is malodorous aerosols, which are not only responsible for discomfort but can be an etiological factor in the development of various diseases during prolonged exposure. One of the proven and efficient ways to counteract odor emissions is the usage of air biofiltration. The purpose of this study was to qualitatively analyze the bacterial community colonizing the biofilm of a biofilter operating at an industrial piggery in Switzerland. The study material consisted of biofilm and leachate water samples. The microbiological analysis consisted of DNA isolation, amplification of the bacterial 16S rRNA gene fragment (V3-V4), preparation of a library for high-throughput sequencing, high-throughput NGS sequencing, filtering of the obtained sequencing reads, and evaluation of the species composition in the studied samples. The investigation revealed the presence of the following bacterial genera: Pseudochelatococcus, Methyloversatilis, Flexilinea, Deviosia, Chryseobacterium, Kribbia, Leadbetterella, Corynebacterium, Flavobacterium, Xantobacter, Tessaracoccus, Staphylococcus, Thiobacillus, Enhydrobacter, Proteiniclasticum, and Giesbergeria. Analysis of the microbial composition of biofilters provides the opportunity to improve the biofiltration process.

Greenhouse Gas Emissions From Biofilters for Composting Exhaust Ammonia Removal

Emissions of odorous compounds, such as ammonia (NH₃), from composting have negative agronomic and environmental impacts. A biofilter is widely used for NH₃ removal, with one of its potential detrimental by-products being nitrous oxide (N₂O), which is a higher warming potential greenhouse gas (GHG). The aim of the study was to evaluate the effect of empty bed retention time (EBRT) on GHG emissions from biofilters for removing NH₃ from composting. Composting experimental trials lasted 6 weeks, and composting materials were mixtures of dead pigs and manure. Three groups of biofilters with 1.2 m-height, 0.3 m-inner diameter, and 1.0 m media depth were conducted with EBRT of 30, 60, and 100s, respectively. Each treatment was performed in triplicate, and the gas was monitored using the dynamic emission vessel method. The Spearman’s correlation analysis showed a significantly positive correlation between inlet concentrations (ICs) of NH₃ and increased N₂O concentrations: ρ = 0.707, 0.762, and 0.607 with p ≤ 0.0001 for biofilters with EBRT of 30, 60, and 100s, respectively. The fraction of NH₃-N denitrified into N₂O-N in biofilters with EBRT of 60 and 100s was higher than that with EBRT of 30s. The total global warming potential (GWP) increased by 126%, 162%, and 144% for biofilters with EBRT of 30, 60, and 100s, respectively. These results indicated that biofilters with longer EBRT will lead to higher GWP production. Future research on odorous mitigation for composting with biofilters should focus more on greenhouse gas emissions.

Ammonium salt production in NH3-CO2-H2O system using a highly selective adsorbent, copper hexacyanoferrate

Ammonia is a beneficial material that is widely used in agriculture, but its emission into the atmosphere causes air pollution. Recently, Prussian blue (PB) and its analogs (PBA) were found to be ammonia adsorbents with high selectivity and capacity. In this study, we utilized a highly potent PBA adsorbent, copper hexacyanoferrate (CuHCF), to desorb ammonia and turn it into a reusable form. Because the reported NH₃-CO₂-H₂O system phase diagram suggests the possibility of the recovery of solid NH₄HCO₃, we examined whether adsorbed ammonia desorbs into the saturated ammonium hydrogencarbonate solution (sat. NH₄HCO₃aq). We demonstrated that 40% of adsorbed ammonia desorbed into sat. NH₄HCO₃aq. After the desorption, CO₂ was blown into the washing liquid, and NH₄HCO₃ precipitated, which was confirmed by Fourier transform infrared spectroscopy. The molar amount of solid NH₄HCO₃ was almost equal to that of desorbed ammonia. Our findings pave the way for recovery of ammonia as a valuable product from waste gas.

A review of biotechnologies for the abatement of ammonia emissions

Ammonia emissions are found in a wide range of facilities such as wastewater treatment plants, composting plants, pig houses, as well as the fertilizer, food and metallurgy industries. Effective management of these emissions is important for minimizing the detrimental effects they can have on health and the environment. Physical-chemical (thermal oxidation, absorption, catalytic oxidation, etc.) treatments are the most common techniques for the abatement of ammonia emissions. However, the requirement for more eco-friendly techniques has increased interest in biological alternatives. Accordingly, several bio-based process configurations (biofilters, biotrickling filters and bioscrubbers) have been reported for ammonia abatement in a wide spectrum of conditions. Due to ammonia is a highly soluble compound, bioscrubber seems to be the best option for ammonia abatement. However, this technology is still not widely studied. The proper managements of the ammonia bio-oxidation sub-products is a key parameter for the correct operation of the process. The aim of this review is to critically examine the biotechnologies currently used for the treatment of ammonia gas emissions highlighting the pros and cons of each technology. The key parameters for each configuration used in both full-scale and lab-scale bioreactors are analyzed and summarized according to previous publications.

Insight into the microbiology of nitrogen cycle in the dairy manure composting process revealed by combining high-throughput sequencing and quantitative PCR

Nitrogen cycling during composting process is not yet fully understood. This study explored the key genes involved in nitrogen cycling during dairy manure composting process using high-throughput sequencing and quantitative PCR technologies. Results showed that nitrogen fixation occurred mainly during the thermophilic and cooling phases, and significantly enhanced the nitrogen content of compost. Thermoclostridium stercorarium was the main diazotroph. Ammonia oxidation occurred during the maturation phase and Nitrosomonas sp. was the most abundant ammonia oxidizing bacteria. Denitrification contributed to the greatest nitrogen loss during the composting process. The nirK community was dominated by Luteimonas sp. and Achromobacter sp., while the nirS community was dominated by Alcaligenes faecalis and Pseudomonas stutzeri. The nosZ community varied in a succession of Halomonas ilicicola, Pseudomonas flexibili and Labrenzia alba dominated communities according to different composting phases. Based on these results, nitrogen cycling models for different phases of the dairy manure composting process were established.

Minimizing ammonia emissions from dairy manure composting by biofiltration using a pre-composted material as the packing media

Compost-based biofiltration is a method widely used to mitigate ammonia emissions during composting. To improve the efficiency of a composting-biofiltration system, it is necessary to determine the most effective degree of composting at which to process the packing media used in the biofiltration system. In this study, materials pre-composted for 20 and 30 d (C20 and C30, respectively), and mature compost (CM) that had been treated for 60 d, were applied as biofilter media to remove ammonia from dairy manure composting exhaust gases. A comparison of the results revealed that the C30 biofilter not only completely removed ammonia, but also produced the least nitrogen loss (1.84%). The C20 biofilter exhibited an inferior performance, indicating that enough pre-composted time is necessary for material used as the packing media. Though the CM biofilter displayed good performance with regard to ammonia removal (97.8%), it had a high nitrogen loss (6.46%). A spearman rank correlation matrix revealed that the abundance of nitrogen cycle genes including amoA, nosZ, nirK, and nirS, had a strong correlation with the physicochemical properties such as nitrate content, carbon source, moisture content, and pH of the biofilter media. C30 provided advantageous conditions and contained a relatively high abundance of nitrifiers and the lowest abundance of denitrifiers. As a result, C30 rather than CM was a more appropriate biofilter media for ammonia removal. Moreover, the occurrence of biological nitrification during the dairy manure composting process indicates the effectiveness of a material for use as biofilter media.

Microbial ecology of full-scale wastewater treatment systems in the Polar Arctic Circle: Archaea, Bacteria and Fungi

Seven full-scale biological wastewater treatment systems located in the Polar Arctic Circle region in Finland were investigated to determine their Archaea, Bacteria and Fungi community structure, and their relationship with the operational conditions of the bioreactors by the means of quantitative PCR, massive parallel sequencing and multivariate redundancy analysis. The results showed dominance of Archaea and Bacteria members in the bioreactors. The activated sludge systems showed strong selection of Bacteria but not for Archaea and Fungi, as suggested by diversity analyses. Core OTUs in influent and bioreactors were classified as Methanobrevibacter, Methanosarcina, Terrestrial Group Thaumarchaeota and unclassified Euryarchaeota member for Archaea; Trichococcus, Leptotrichiaceae and Comamonadaceae family, and Methylorosula for Bacteria and Trichosporonaceae family for Fungi. All influents shared core OTUs in all domains, but in bioreactors this did not occur for Bacteria. Oligotype structure of core OTUs showed several ubiquitous Fungi oligotypes as dominant in sewage and bioreactors. Multivariate redundancy analyses showed that the majority of core OTUs were related to organic matter and nutrients removal. Also, there was evidence of competition among Archaea and Fungi core OTUs, while all Bacteria OTUs were positively correlated among them. The results obtained highlighted interesting features of extremely cold temperature bioreactors.