The fate of Cu and Zn along the feed-animal-excreta-effluent continuum in swine systems according to feed and effluent treatment strategies

Copper (Cu) and zinc (Zn) have negative environmental impacts as they accumulate in the soil after pig manure is spread. Cu and Zn are essential elements in pig nutrition but due to their low retention rate, more than 90% of ingested Cu and Zn are excreted. A better understanding of the behaviour of these elements throughout the animal-manure-soil continuum according to feed composition and manure management chain is thus required to propose alternative ways to reduce these environmental impacts. The aim of this study was to determine the fate of Cu and Zn throughout this continuum by studying the effect of Cu and Zn contents in animal feed and in the manure management chain based on anaerobic digestion and composting. Faeces were collected from 24 finishing pigs fed with 4 different Cu and Zn dietary levels and sources of supplementation. Samples of faeces were exposed to mesophilic anaerobic digestion or to 5-week composting with straw. Concentrations of Cu and Zn in the faeces were highly dependent on dietary supplies and ranged from 38 to 188 mg Cu/kg DM and from 191 to 728 mg Zn/kg DM. Degradation of a significant fraction of organic matter during treatment led to a significant increase in Cu and Zn concentration relative to the product's dry matter (DM) content, which. Cu and Zn concentrations relative to DM content were twice as high after treatment whatever the content and the form of Cu and Zn dietary supplementation. Otherwise, effluent treatment tended to reduce the possible availability of Cu and Zn in final organic products according to water-extractible contents. This study clearly shows that feed management is the main lever for reducing the amount of Cu and Zn amount in pig effluents and hence in the soil. Appropriate treatment could also facilitate the supply of organic fertilisers to areas with soil deficiency, but feed strategies need to be adapted to the treatment chain to enable the production of good quality organic products that respect EU regulations.

Determination of the lipid content of organic waste using time-domain nuclear magnetic resonance

Time-Domain Nuclear Magnetic Resonance (TD-NMR) was used to quantify the lipid contents of 48 different organic waste substrates. Results obtained from TD-NMR were compared to those from Soxhlet extraction, currently the prevalent method for organic waste characterization, especially in the field of anaerobic digestion. Two calibration methods were tested. The first was a self-calibration process using pure oils (NMR1) which showed good repeatability compared to Soxhlet extraction with a better coefficient of variation (5%). Analyses of volatile fatty acids (VFA) and long-chain fatty acids (LCFA) by chromatography were carried out to understand why the NMR1 method produced underestimations for some samples. Statistical analysis showed that the presence of saturated fatty acids had a significant effect on differences between the Soxhlet and NMR1 methods. The second calibration method applied chemometrics to TD-NMR raw data (NMR2), taking Soxhlet extraction values as references. It provided a good prediction of lipid content and avoided the lengthy calibration procedure usually required for this type of study. Last, the NMR2 method was shown to be highly suited to the quantification of lipids in organic waste, demonstrating better repeatability than the classic Soxhlet method.

Fate of phosphorus from biological aerobic treatment of pig slurry. By-products characterization and recovery

The fate of phosphorus distribution in the products obtained from biological aerobic treatment of pig slurry, e.g. separated solids, liquid effluent and sludge, was monitored in three different farm-scale units. Samples of raw slurry, solid products, aerated slurry, liquid effluent and sludge were characterised and analysed for their concentration in total phosphorus, nitrogen content and heavy metals (Cu and Zn). At each treatment stage, nitrogen, phosphorus and heavy metals mass balance between input and output was established. Moreover, liquid products were characterised and analysed both for their total and dissolved ortho-phosphate content. Separated solids, sludge and liquid effluent represented 5%, 15-40% and 75-83% of the mass of the raw slurry, respectively. A mechanical separation step prior to aeration allowed the export of 25-30% of total phosphorus for further use as organic fertiliser. A large amount of total phosphorus (e.g. 60-70%) was located in sludge while phosphorus remaining in liquid effluent was about 15-25%. Raw slurry separation and sufficient aeration allowed phosphorus to concentrate in the sludge. Insufficient aeration resulted in the release of phosphorus as dissolved ortho-phosphate within the liquid effluent. Finally, relevance of the agronomic use of the products was discussed and improvements of biological aerobic treatment to enhance phosphorus removal and/or recovery were considered.

Application of the 15N technique to determine the contributions of nitrification and denitrification to the flux of nitrous oxide from aerated pig slurry

In order to elucidate and quantify nitrogen transformations occurring during aerobic treatment of pig slurry, two laboratory experiments were carried out with contrasting levels of aeration, high level (experiment 1) and low level (experiment 2) of aeration. During these experiments, after reaching steady-state conditions, a single pulse of NO3(-)-15N tracer was added directly to the reactor. When nitrification conditions were prevailing (experiment 1), no transformation of added NO3(-)-15N occurred (98.7% 15N-recovery as nitrates in the liquid slurry). Moreover, the unlabelled nitrous oxide (N2O) measured (7.4% of the total nitrogen content of the raw slurry) strongly demonstrated that the source of N2O emitted was nitrification. During simultaneous nitrification and denitrification conditions (experiment 2), the added NO3(-)-15N was found in gaseous nitrogen forms (N2O-15N: 27%; N2-15N: 18%) and in the liquid (TN-15N: 54%). From this result, it was evident that N2O was mainly emitted by denitrification process. Using the decrease of the isotopic excess of the NO3(-)-15N we calculated that 92% of NO2(-)-N was directly denitrified (as gaseous forms) without any previous oxidation to nitrate.