Microbial examination of anaerobic sludge adaptation to animal slurry.

The objective of this study was to evaluate changes in the microbial population of anaerobic sludge digesters during the adaptation to pig slurry (PS) using quantitative real-time polymerase chain reaction (qPCR) and qualitative scanning electron microscopy (SEM). Additionally, the relationship between microbial parameters and sludge physicochemical composition and methane yield was examined. Results showed that the addition of PS to an unadapted thermophilic anaerobic digester caused an increase in volatile fatty acids (VFA) concentration, a decrease in removal efficiency and CH4 yield. Additionally, increases in total bacteria and total archaea were observed using qPCR. Scanning electron micrographs provided a general overview of the sludge's cell morphology, morphological diversity and degree of organic matter degradation. A change in microbial morphotypes from homogeneous cell morphologies to a higher morphological diversity, similar to that observed in PS, was observed with the addition of PS by SEM. Therefore, the combination of qPCR and SEM allowed expanding the knowledge about the microbial adaptation to animal slurry in thermophilic anaerobic digesters.

Process performance of anaerobic co-digestion of raw and acidified pig slurry.

The effect of incorporating different ratios of acidified pig slurry on methane yield was evaluated in two scales of anaerobic digesters: Thermophilic (50 °C) pilot scale digester (120 l), operating with an average hydraulic retention time of 20 days and thermophilic (52 °C) full-scale digesters (10 and 30 m(3)), operating with an average hydraulic retention time of 30 days. In the lab-scale digester, different inclusion levels of acidified slurry (0-60%) were tested each 15 days, to determine the maximum ratio of acidified to non-acidified slurry causing inhibition and to find process state indicators helping to prevent process failure. In the full-scale digesters, the level of inclusion of the acidified slurry was chosen from the ratio causing methane inhibition in the pilot scale experiment and was carried on in a long-term process of 100 days. The optimal inclusion level of acidified pig slurry in anaerobic co-digestion with conventional slurry was 10%, which promoted anaerobic methane yield by nearly 20%. Higher inclusion levels caused methane inhibition and volatile fatty acids accumulations in both experiments. In order to prevent process failure, the most important traits to monitor in the anaerobic digestion of acidified pig slurry were found to be: sulfate content of the slurry, alkalinity parameters (especially partial alkalinity and the ratio of alkalinity) and total volatile fatty acids (especially acetic and butyric acids).

Increasing energy and lysine in diets for growing-finishing pigs in hot environmental conditions: consequences on performance, digestibility, slurry composition, and gas emission.

The influence of dietary nutrient concentration on growth performance, manure composition, and gas emission was studied in pigs in hot environmental conditions. A total of 64 intact males and 64 females [(Landrace × Large White) × Pietrain] weighing 63.1 ± 9.7 kg were divided into 2 dietary treatments: high (HD: 14.39 MJ of DE/kg and 1.11% Lys) and low (LD: 13.97 MJ of DE/kg and 1.01% Lys) in energy and Lys contents. Pigs were allocated to 32 split-sex pens with 4 pigs/pen and 16 pens/treatment. Average productive performance was recorded for 41 d (phase 1). After phase 1, 12 females of 103.3 ± 3.15 kg (6 per treatment) were selected and housed individually, and feces and slurry were collected during 3 and 4 consecutive days, respectively, to calculate nutrient digestibility and measure gas emissions (phase 2). For gas emission measurements, slurry was pooled by treatment and stored for 76 d. Initial composition of slurry and pH were analyzed. Maximum and minimum temperatures registered in the barn throughout the growing period were 35.1 and 18.1°C, respectively. Animals fed the HD diet grew more efficiently than pigs fed the LD diet (G:F, 0.43 vs. 0.40; SEM = 0.01; P < 0.05). Fat digestibility was greater in HD compared with LD pigs (88.0 vs. 84.9%; SEM = 0.9; P < 0.05). Slurry from pigs fed the LD diet showed greater DM, OM, total N, and VFA contents than slurry from pigs fed the HD diet. Cumulative NH(3), CO(2), and especially CH(4) emissions were greater in the HD slurry compared with the LD slurry (192.4 vs. 210.g of NH(3)/m(3); 2,712 vs. 3,210 g of CO(2)/m(3); 1,502 vs. 2,647 mL of CH(4)/kg of OM). Increasing feed density in the present study led to a more efficient growth, a decreased nutrient concentration in the slurry, and a greater gas emission.