Identified factors and predicted unidentified-factors affecting ammonia emissions from a swine building

Large variabilities in ammonia (NH₃) released from animal manure and emitted from different livestock buildings were frequently reported, but the factors influencing the emissions were not sufficiently investigated. In this paper, continuously monitored data of NH₃ emissions and other relevant environmental variables under controlled conditions in a 12-room experimental swine building for a 155-d complete wean-to-finish cycle were studied. Measurement data mining was conducted at both spatial and temporal dimensions using panel data analysis with heterogeneous time trends. The pig diet, total pig weight, and the pit air temperature were identified as the major influencing factors for the variabilities by using multivariate linear regression. Two unidentified factors that imposed substantial influences on the NH₃ emission variabilities were predicted. They were most possibly related to variations in microenvironment and microbial activity inside the manure in the pit. The results suggest necessary future research to identify physical properties of the new NH₃ emissions factors in microbiological and biochemical processes.

Impacts of slurry application methods and inhibitors on gaseous emissions and N2O pathways in meadow-cinnamon soil

This study aimed to evaluate the impact of mitigation practices (slurry application methods and inhibitors applications) on gas emissions and identify the soil N₂O production pathways in cattle slurry applied soil using isotopocule mapping approach. First, we compared the NH₃ and N₂O emissions of cattle slurry applied soil in a summer maize field experiment in north China plain (NCP) with four treatments: control (CK, no fertilization), slurry application using surface (SA-S), slurry application using band application (BA-S), and chemical fertilizer application using band application (BA-C). Then, an incubation experiment was conducted to investigate the mitigation effect of nitrification inhibitors (dicyandiamide, DCD) and denitrification inhibitors (procyanidins, PC) and their combination (DCD + PC) on gaseous N emissions with slurry applied using incorporation (IA) or surface application (SA) methods. The results showed that the total gaseous N emissions (N₂O-N and NH₃-N) in field were in the order of SA-S (1534 mg m^-2) > BA-S (338 mg m^-2) > BA-C (128 mg m^-2) > CK (55 mg m^-2), and the dominant N loss contributor varied from NH₃ in SA-S (∼89%) to N₂O in BA-S (∼94%) and BA-C (∼88%). Moreover, the isotopocule mapping approach indicated that emitted N₂O of the slurry applied soil in field appeared to have lower r_N2O values and led to more N₂O + N₂ emissions at the initial fertilization period. The incubation experiment indicated that the N₂O emissions of slurry-applied soil were significantly reduced by DCD (∼45%) and DCD + PC (∼67%) application in comparison with CK (p < 0.05), and the stronger contributions of bacterial denitrification/nitrifier denitrification to N₂O production were revealed by the lower δ¹⁵N^SP in N₂O using the isotopocule mapping approach. In conclusion, in NCP the gaseous losses of the slurry applied field can be largely reduced by using incorporation method, and greater reduction could be achieved given the simultaneous application of nitrification/denitrification inhibitors.

Recovery of nitrogen and phosphorus from livestock slurry with treatment technologies: A meta-analysis

The livestock industry has developed rapidly in recent decades, but the improper treatment of livestock manure, especially slurry, causes environmental pollution. Treatment technologies are considered to be effective in alleviating nitrogen (N) and phosphorus (P) losses from livestock slurry. Here, we used published research data to conduct a meta-analysis of the recovery efficiencies of N and P of five mainstream treatment technologies, including ammonia stripping, air scrubbing, membrane filtration, microalgae cultivation and struvite crystallization. Additionally, the agronomic effects of the recovered products of these treatment technologies were evaluated. The results showed that all technologies exhibited clear recovery effects on N and P. The N recovery efficiencies ranged from 57% to 86%, and those of P ranged from 64% to 87%. Struvite crystallization was the most efficient treatment technology for both N and P recovery; moreover, the ammonia stripping and microalgae cultivation technologies were less efficient. The pH levels and temperatures are the main factors that influence ammonia stripping, struvite crystallization and microalgae cultivation, while membrane filtration and air scrubbing are mainly affected by the membrane types and properties. When the equal amount of N or P input to fields, the recovered products (ammonium sulfate and struvite crystals) may achieve a similar crop yield, relative to commercial N or P fertilizers. Our findings can provide deep suggestions and parameters for designing proper treatment technologies to reduce nutrient discharge from livestock slurry in regions with high livestock density and also for identifying the research gaps that should be paid more attention in the future.

Implications from distinct sulfate-reducing bacteria populations between cattle manure and digestate in the elucidation of H2S production during anaerobic digestion of animal slurry

Biogas produced from the anaerobic digestion of animal slurry consists mainly of methane (CH₄) and carbon dioxide (CO₂), but also includes other minor gases, such as hydrogen sulfide (H₂S). Since it can act as a potent corrosive agent and presents a health hazard even at low concentrations, H₂S is considered an undesirable by-product of anaerobic digestion. Sulfate-reducing bacteria (SRBs) have been identified as the main biological source of H₂S in a number of natural, biological, and human-made habitats, and thus represent likely candidate microorganisms responsible for the production of H₂S in anaerobic manure digesters. Phylogenetically, SRBs form a divergent group of bacteria that share a common anaerobic respiration pathway that allows them to use sulfate as a terminal electron acceptor. While the composition and activity of SRBs have been well documented in other environments, their metabolic potential remains largely uncharacterized and their populations poorly defined in anaerobic manure digesters. In this context, a combination of in vitro culture-based studies and DNA-based approaches, respectively, were used to gain further insight. Unexpectedly, only low to nondetectable levels of H₂S were produced by digestate collected from a manure biogas plant documented to have persistently high concentrations of H₂S in its biogas (2000-3000 ppm). In contrast, combining digestate with untreated manure (a substrate with comparatively lower sulfate and SRB cell densities than digestate) was found to produce elevated H₂S levels in culture. While a 16S rRNA gene-based community composition approach did not reveal likely candidate SRBs in digestate or untreated manure, the use of the dsrAB gene as a phylogenetic marker provided more insight. In digestate, the predominant SRBs were found to be uncharacterized species likely belonging to the genus Desulfosporosinus (Peptococcaceae, Clostridiales, Firmicutes), while Desulfovibrio-related SRBs (Desulfovibrionaceae, Desulfovibrionales, Proteobacteria) were the most highly represented in untreated manure. Intriguingly, the same species-level OTUs with a similar pattern of opposite relative abundance were also found in two other digesters with lower H₂S levels in their biogas. Together, our results suggest that elevated H₂S production in anaerobic digesters requires the combination of biological and nutritional factors from both untreated manure and digestate.

The oxygen isotopic composition of phosphate in river water and its potential sources in the Upper River Taw catchment, UK

The need to reduce both point and diffuse phosphorus pollution to aquatic ecosystems is widely recognised and in order to achieve this, identification of the different pollutant sources is essential. Recently, a stable isotope approach using oxygen isotopes within phosphate (δ¹⁸O_PO4) has been used in phosphorus source tracing studies. This approach was applied in a one-off survey in September 2013 to the River Taw catchment in south-west England where elevated levels of phosphate have been reported. River water δ¹⁸O_PO4 along the main channel varied little, ranging from +17.1 to +18.8‰. This was no >0.3‰ different to that of the isotopic equilibrium with water (Eδ¹⁸O_PO4). The δ¹⁸O_PO4 in the tributaries was more variable (+17.1 to +18.8‰), but only deviated from Eδ¹⁸O_PO4 by between 0.4 and 0.9‰. Several potential phosphate sources within the catchment were sampled and most had a narrow range of δ¹⁸O_PO4 values similar to that of river Eδ¹⁸O_PO4. Discharge from two waste water treatment plants had different and distinct δ¹⁸O_PO4 from one another ranging between +16.4 and +19.6‰ and similar values to that of a dairy factory final effluent (+16.5 to +17.8‰), mains tap water (+17.8 to +18.4‰), and that of the phosphate extracted from river channel bed sediment (+16.7 to +17.6‰). Inorganic fertilizers had a wide range of values (+13.3 to +25.9‰) while stored animal wastes were consistently lower (+12.0 to +15.0‰) than most other sources and Eδ¹⁸O_PO4. The distinct signals from the waste water treatment plants were lost within the river over a short distance suggesting that rapid microbial cycling of phosphate was occurring, because microbial cycling shifts the isotopic signal towards Eδ¹⁸O_PO4. This study has added to the global inventory of phosphate source δ¹⁸O_PO4 values, but also demonstrated the limitations of this approach to identifying phosphate sources, especially at times when microbial cycling is high.

Temperature response of methane production in liquid manures and co-digestates

Intensification of livestock production makes correct estimation of methanogenesis in liquid manure increasingly important for inventories of CH4 emissions. Such inventories currently rely on fixed methane conversion factors as knowledge gaps remain with respect to detailed temperature responses of CH4 emissions from liquid manure. Here, we describe the temperature response of CH4 production in liquid cattle slurry, pig slurry, and fresh and stored co-digested slurry from a thermophilic biogas plant. Subsamples of slurry were anoxically incubated at 20 temperatures from 5-52°C in a temperature gradient incubator and CH4 production was measured by gas chromatographic analysis of headspace gas after a 17-h incubation period. Methane production potentials at 5-37°C were described by the Arrhenius equation (modelling efficiencies, 79.2-98.1%), and the four materials showed a consistent activation energy (Ea) which averaged 81.0kJmol(-1) (95% confidence interval, 74.9-87.1kJmol(-1)) corresponding to a temperature sensitivity (Q10) of 3.4. In contrast, the frequency factor (A) differed among the slurry materials (30.1<ln A<33.3; mean, 31.3) reflecting that origin, age and composition of the manure affect this parameter. The Ea estimate, based on individual slurry materials, was intermediate when compared to published values of 63 and 112.7kJmol(-1) derived from composite data, but was similar to Ea estimated for CH4 production at microbial community level across aquatic ecosystems, wetlands and rice paddies (89.3kJmol(-1)). This supports that the derived temperature sensitivity parameters may be applicable to dynamic modelling of CH4 emissions from livestock manure.

Redistribution and persistence of microorganisms and steroid hormones after soil-injection of swine slurry

The redistribution and fate of contaminants in pig slurry after direct injection were investigated at two field sites, Silstrup (sandy clay loam) and Estrup (sandy loam), in Denmark. Intact soil samples were collected for up to seven weeks after slurry injection and concentrations of Salmonella Typhimurium Bacteriophage 28B (phage 28B), Escherichia coli, steroid hormones and other slurry components (water, volatile solids, chloride and mineral N) determined in and around the injection slit. The two experiments at Silstrup and Estrup differed with respect to slurry solid content (6.3 vs. 0.8%), as well as soil clay content (27 vs. 15%) and differed considerably with respect to the initial redistribution of slurry-borne contaminants in soil. The transport of microorganisms from the slurry injection slit to the surrounding soil was much lower than that of mineral N and chloride due to attachment and entrapment. The redistribution of E. coli was more affected by site-specific conditions compared to phage 28B, possibly due to the larger cell size of E. coli. The overall recovery of phage 28B was 0.8-4%, and of E. coli 0.0-1.3% in different samples, by the end of the study. Nine different steroid hormones were detected in the slurry slit, and a slow redistribution to the surrounding soil was observed. Overall recovery of estrogens was 0.0 to 6.6% in different samples. The study showed that the combination of soil and slurry properties determined the initial spreading of contaminants, and hence the potential for subsequent leaching.