Microbial and isotopomer analysis of N2O generation pathways in ammonia removal biofilters

Simultaneous removal of ammonia and sulfur odorants in biotrickling filters and N2O production

Research on the stability evaluation of biotrickling filters (BTFs) under harsh conditions and the bacterial adaptation process still needs to be improved. Herein, BTFs with polypropylene plastic (PP) and ceramic raschig rings (CRR) were investigated for a better understanding of the biodegradation of ammonia (NH3), hydrogen sulfide (H2S), and dimethyl sulfide (DMS). The results showed an excellent performance in removal efficiency (RE) for NH3 (91.6 %-99.9 %), H2S (RE: 55.3 %-99.5 %), and DMS (RE: 10.6 %-99.9 %). It was found that a more apparent positive correlation between N2O emission and pressure drop in CRR BTF (R2 = 0.92) than in PP BTF (R2 = 0.79) (P < 0.01). Low temperature promotes an increase in the abundance ofComamonasandBacillus. The polysaccharides in PP and CRR reactors decreased by 78.6 % and 68.1 % when temperature reduced from 25℃ to 8℃. This work provides a novel insight into understanding bacterial survival under harsh BTF environments.

Effects of reducing nitrogen application and adding straw on N2O emission and soil nitrogen leaching of tomato in greenhouse

Excessive input of nitrogen(N) fertilizer and improper selection of fertilizer types in the greenhouse vegetable production process will lead to a large amount of N loss. In order to relieve the environmental pollution caused by N loss, a planting experiment was carried out in a solar greenhouse in Shouguang, Shandong, China, to investigate the effects of N-reducing fertilizer and straw application on greenhouse vegetable yield and soil N loss, and to explore the fate of N after fertilizer application using the ¹⁵N isotope tracing technique. The experiment was planted for two seasons from July 2017 to June 2018 with four treatments: control (CK), conventional fertilizer (CN), reduced N topdressing (SN), and reduced N topdressing + straw (SNS). The results indicated that N reduction fertilizer and straw application resulted in a 35.25%-35.49% reduction in total N₂O emissions and 15.76%-41.77% reduction in mineral N leaching losses. ¹⁵N isotopes as tracers showed that the maximum abundance in N₂O was reduced by 58.5% and 55.68% for SN and SNS, respectively, and cumulative N₂O emissions were reduced by 80.44% and 81.67%, respectively, and mineral N leaching was reduced by 74.4% and 70.48%, respectively, after fertilization compared to CN treatment. There was no significant difference in tomato yield between the three fertilizer treatments in the two growing seasons. Therefore, in greenhouse vegetable production, the amount of N fertilizer was reduced by 40.7% and the addition of straw reduced N₂O emissions and N leaching without affecting tomato yields.

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.