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.

The efficiency of biological aerobic treatment of piggery wastewater to control nitrogen, phosphorus, pathogen and gas emissions.

Due to the water pollution and in order to reduce the nitrogen load applied on soils, biological nitrogen removal treatment of piggery wastewaters was developed in Brittany (France), with 250-300 units running. Four types of treatment processes were built including a biological reactor allowing to remove about 60-70% of the nitrogen content as gas by nitrification/denitrification. The addition of different mechanical separators (screw-press, centrifuge decanter ...) led to concentration of phosphorus in an exportable solid phase, allowing a reduction up to 80% of the phosphorus applied locally on soils. Moreover, a reduction of the gaseous emissions was observed using this management process as compared to conventional management (storage + land spreading) including ammonia (up to 68%) and greenhouse gases (55%). Finally, the level of enteric and pathogenic bacteria was also decreased with the treatment process as compared to conventional management systems. However, in spite of these results, the significant cost of the treatment must be underlined and alternative systems including anaerobic digestion will have to be studied.

Modelling of biological nitrogen removal during treatment of piggery wastewater.

During this study, a mathematical model simulating piggery wastewater treatment was developed, with the objective of process optimisation. To achieve this, the effect of temperature and free ammonia concentration on the nitrification rate were experimentally studied using respirometry. The maximum growth rates obtained were higher for ammonium-oxidising biomass than for nitrite-oxidising biomass for the temperatures above 20 degrees C; values at 35 degrees C were equal to 1.9 and 1.35 day(-1), respectively. No inhibition of nitrification was observed for free ammonia concentrations up to 50 mgN/L. Using these data with others experimental data obtained from a pilot-scale reactor to treat piggery wastewater, a model based on a modified version of the ASM1 was developed and calibrated. In order to model the nitrite accumulation observed, the ASM1 model was extended with a two-step nitrification and denitrification including nitrite as intermediate. Finally, the produced model called PiWaT1 demonstrated a good fit with the experimental data. In addition to the temperature, oxygen concentration was identified as an important factor influencing the nitrite accumulation during nitrification. Even if some improvements of the model are still necessary, this model can already be used for process improvement.

Modelling of biological processes during aerobic treatment of piggery wastewater aiming at process optimisation.

A dynamic mathematical model was developed for the simulation of the aerobic treatment of piggery wastewater. This model includes the carbon oxidation, the nitrification and the denitrification. According to the experimental results obtained during this study, a modified version of the activated sludge model No. 1 has been developed. The model includes (1) nitrite as intermediate of nitrification and denitrification, (2) the distinction between the anoxic heterotrophic yield and the aerobic heterotrophic yield, respectively equal to 0.53 and 0.6 and (3) the first-order hydrolysis of the slowly biodegradable fraction. The calibration and the validation of the model was performed using experimental data from three experiments with two piggery wastewaters. A set of kinetic and stoichiometric parameters emerged from these tests. Except the kinetic of hydrolysis of the slowly biodegradable organic matter varying from 6 to 25 gCOD(gCODday)(-1), all other parameters were similar for all experiments. The dissolved oxygen concentration was identified as the main variable influencing the nitrite accumulation during nitrification. In the calibrated model, the oxygen half-saturation coefficient of the ammonium oxidisers (0.3g O(2)m(-3)) was lower than for the nitrite oxidisers (1.1 gO(2)m(-3)), leading to nitrite accumulation when the dissolved oxygen concentration was low. Simulations with the proposed model could be very useful for improved design and management of biological treatment of piggery wastewaters, particularly in case of partial nitrification to nitrite directly followed by denitrification.

In situ measurement of ammonia and greenhouse gas emissions from broiler houses in France.

An experimental technique was developed for measuring gaseous emissions including ammonia (NH(3)), nitrous oxide (N(2)O) and methane (CH(4)) from broiler houses. This technique included the monitoring of the air flow rate and the gaseous concentrations. NH(3) was determined using acid trap while N(2)O and CH(4) were determined continuously by infrared gas analyser and sequentially by gas chromatography. Moreover, N(2)O and CH(4) emissions were monitored above the litter using closed flux chambers at the end of the experiment. No emissions of N(2)O and CH(4) were observed neither during the growth of the broiler nor above the litter at the end of the experiment. Ammonia concentration varied between 0.8 and 32 ppm in the building. Total ammonia emissions were estimated to 5.74 g N animal(-1) during this experiment. According to this result, ammonia emissions from broiler houses could be estimated to 5.3 kt of N per year in France.

Effect of covering pig slurry stores on the ammonia emission processes.

The aim of this study was to evaluate the effects of different covers (oil, plastic film, perforated polystyrene float, peat and zeolites) on slurry settling characteristics and ammonia emission during storage and following surface application in the field. Laboratory trials were carried out for 15 days using a pilot scale device. Samples of 5 kg slurry were used. At the end of the storage period, distributions of dry matter, pH, total ammoniacal nitrogen and total Kjeldahl nitrogen in slurry were characterized. In the field, ammonia volatilisation was measured for three days using a wind tunnel system. Oil and plastic film retained all ammoniacal nitrogen forms in the slurry, whereas the others reduced ammonia volatilisation by reducing the emitting surface or by adsorbing/absorbing ammonia. Over the whole process studied (storage plus application) ammonia emissions were reduced by 40% by oil up to 65-71% by zeolites with different particle sizes.

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.