Jean Bernier

Differences in splanchnic metabolism between late gestation and early lactation dairy cows

In the transition from the pre- to postcalving state, the demands on the cow increase from support of gestation to high rates of milk production. This extra demand is met partly by increased intake but may also involve altered metabolism of major nutrients. Six multiparous Holstein cows were used to monitor changes in net fluxes of nutrients across the portal-drained viscera and liver (splanchnic tissues) between late gestation and early lactation. Blood samples were obtained simultaneously from the portal, hepatic, and subcutaneous abdominal veins and the caudal aorta 18 d before expected calving and 21 or 42 d after calving. On the day of blood sampling and the 3 d preceding sampling, cows were fed every 2 h. The precalving (1.63 Mcal of net energy for lactation/kg and 1,326 g of metabolizable protein/d) and postcalving (1.72 Mcal of net energy for lactation/kg and 2,136 g of metabolizable protein/d) diets were based on corn silage, alfalfa hay, and corn grain. Dry matter intake increased postcalving. Net splanchnic release of glucose increased postpartum because of tendencies for both increased portal absorption and net liver release. Increased removal of lactate, rather than AA, contributed to the additional hepatic gluconeogenesis. Although portal absorption of AA increased with intake at the onset of lactation, hepatic removal of total AA-N tended to decline. This clearly indicates that liver removal of AA is not linked to portal absorption. Furthermore, net liver removal relative to total liver inflow even decreased for Gly, His, Met, Phe, and Tyr. Together, these data indicate that in early lactation, metabolic priority is given to direct AA toward milk protein production rather than gluconeogenesis, in cows fed a corn-based ration.

Modelling the nitrification in a full-scale tertiary biological aerated filter unit

A wastewater biofiltration model is used to assess its capacity to reproduce the treatment behaviour of a plant-sized tertiary nitrifying biofilter unit. It is calibrated on two different types of datasets collected at the Seine-Aval biofiltration plant (Achères, France): grab samples at several heights inside the media bed and a long-term daily plant monitoring over a 1-year period. The model parameters are first calibrated to fit the dynamics observed in the media bed, after which the model is compared to the second dataset. Further parameter changes are then made if necessary and the model is once again compared to both datasets to ensure its ability to predict the treatment behaviour on both size scales. The calibrated model provides correct predictions for most observed nutrient variables for both datasets. An overestimation of the oxygen transfer under a summer, low ammonia load period however leads to a slight underestimation of the nitrifying efficiency of the biofilters. Statistical score computation corroborates the model accuracy as the mean error scores usually remain low. They also point to a certain weakness of the model regarding the suspended solids filtration. Both datasets are overall correctly modelled using a single parameter set. Most of this parameter set is close to or contained in value ranges found in the literature. The parameters related to aeration, however, seem to be slightly higher than what is reported elsewhere.

Initial and hourly headloss modelling on a tertiary nitrifying wastewater biofiltration plant.

ABSTRACT The headloss prediction capability of a wastewater biofiltration model is evaluated on data from a full-scale tertiary nitrifying biofilter unit located in the Paris conurbation (Achères, France; 6,000,000 population equivalent). The model has been previously calibrated on nutrient conversion and TSS filtration observations. In this paper the mass of extracted biofilm during biofilter backwash and the headloss value at the start of an operation cycle are first calibrated on sludge production estimations and relative pressure measurements over the year 2009. The calibrated model is then used on two one-month periods in 2012 for which hourly headloss measurements were acquired. The observed trends are correctly predicted for 2009 but the model exhibits some heavy daily variation that is not found in measurements. Hourly predictions stay close to observations, although the model error rises slightly when the headloss does not vary much. The global model shows that both nutrient conversion and headloss build-up can be reasonably well predicted at the same time on a full-scale plant.

Early assessment of a rapid alternative method for the estimation of the biomethane potential of sewage sludge.

This short communication briefly presents a rapid method using a fluorescent redox indicator, similar to resazurin, in order to estimate the biodegradability of sewage sludge during anaerobic digestion (AD). The biodegradability and by extension the Biochemical Methane Potential (BMP) of nineteen municipal sludge samples (primary, biological and tertiary) were investigated and estimated in only 48 h. Results showed the relevance to follow the metabolic activity of anaerobic sludge by the kinetic of probe reduction. The extended lag phase of inoculum indicated an impact of pre-treatments on enzyme activity. The comparison with Automatic Methane Potential Test System II (AMPTS) confirmed the estimated values of BMP according to an uncertainty limit of 25%. These first results highlight the interest of this rapid assay as a preliminary tool of the biodegradability of sewage sludge in anaerobic digestion.