Effect of increasing inclusion rates of tofu by-product in diets of growing pigs on nitrogen balance and ammonia emission from manure

To reduce competition with human-edible feed resources, it is of interest to incorporate by-products from the food industry in animal feeds. The current research investigated the effect of including increasing amounts of tofu by-product (TF) in practical pig diets on animal performance, nitrogen balance and ammonia emissions from manure. Two experiments were conducted including a control diet without TF, containing 160 g/kg dietary non-starch polysaccharides (NSPs) and three diets including 122, 246 and 360 g TF/kg DM (TF122, TF246 and TF360, respectively) to reach 220, 280 and 360 g/kg NSP. All diets had the same level of CP and protein digestible in the small intestine which particularly was realized by replacing rice bran with TF. Animal performance was assessed in a first experiment with 40 growing barrows with initial BW of 26.6 ± 1.80 kg (M ± SD) being allocated to the 4 treatments, during 2 growth phases (i.e. until 50 kg BW and from 50 to 80 kg BW). In the growth phase until 50 kg, feed intake and average daily gain (ADG) were linearly reduced by dietary TF inclusion, while this negative impact disappeared during the second growth phase (50 to 80 kg BW). Tofu by-product inclusion even positively affected the feed conversion ratio during this second growth phase (3.4 to 2.7 kg feed/kg ADG for 0 to 360 g/kg dietary TF). Over the entire growth period, performance and feed intake were negatively affected at the highest dietary TF level. Experiment 2 was conducted to assess digestibility, nitrogen balance and ammonia emission from manure. For this purpose, 16 pigs with BW of 62.8 ± 3.6 kg (M ± SD) were assigned to either 1 of the 4 treatments. There was no difference in total tract apparent digestibility of dietary organic matter or CP, while NDF digestibility increased with increasing TF level, suggesting increasing importance of the hindgut fermentation when digesting diets with increasing TF levels. Nevertheless, this was not reflected in increasing levels of faecal volatile fatty acids or purines, nor in reduced manure pH. As a result, ammonia emission from slurry was not reduced through dietary TF inclusion, despite the linear decrease in urinary nitrogen. In conclusion, TF can be included in pigs’ diets up to an inclusion rate of 25% without risk of impaired animal performance; however, this dietary strategy fails to mitigate ammonia emission from slurry.     

Mathematical model of anaerobic digestion in a chemostat: effects of syntrophy and inhibition

Three of the four main stages of anaerobic digestion: acidogenesis, acetogenesis, and methanogenesis are described by a system of differential equations modelling the interaction of microbial populations in a chemostat. The microbes consume and/or produce simple substrates, alcohols and fatty acids, acetic acid, and hydrogen. Acetogenic bacteria and hydrogenotrophic methanogens interact through syntrophy. The model also includes the inhibition of acetoclastic and hydrogenotrophic methanogens due to sensitivity to varying pH-levels. To examine the effects of these interactions and inhibitions, we first study an inhibition-free model and obtain results for global stability using differential inequalities together with conservation laws. For the model with inhibition, we derive conditions for existence, local stability, and bistability of equilibria and present a global stability result. A case study illustrates the effects of inhibition on the regions of stability. Inhibition introduces regions of bistability and stabilizes some equilibria.     

Residual biogas potential from the storage tanks of non-separated digestate and digested liquid fraction

Biogas plants daily produce enormous volumes of digestate that can be handled in its raw form or after mechanical separation. In Italy, effluents are usually stored within aboveground, uncovered tanks, which make them potential emitters of biogas into the atmosphere. The purpose of this study was to estimate the amount of biogas emitted to the atmosphere during the storage phase of non-separated digestate and digested liquid fraction. The trials were performed at two northwest Italy 1 MWel. biogas plants. A floating system for the residual biogas recovery, and a set of three wind tunnels for NH3 emission measurement were used. The experiment demonstrated significant loss to the atmosphere for each of the gases; specifically, on average, 19.5 and 7.90 N m3 biogas MWhel.(-1) were emitted daily from the storage tanks of non-separated digestate and digested liquid fraction, respectively.     

Modelling the change in soil organic C and N and the mineralization of N from soil in response to applications of slurry manure

A computer simulation model of the turnover of organic matter in soil was adapted to simulate the change in soil organic C and N contents of soil during several years following annual additions of farm slurry to maize fields. The model proved successful in estimating the build-up of both C and N in soil and the leaching of N to ground-water in response to applications of slurry ranging from 50 to 300 tons per hectare per year. The model was then used to estimate the build-up of organic matter in soil under crops of fodder maize that were grown using the excess of manure produced during the last 20 years in the Netherlands. The build-up of organic matter from these applications was estimated to lead to about 70 kg extra nitrogen mineralized ha^-1 yr^-1. As a result of legislation manure applications have decreased and are expected to decrease further in the immediate future. Calculations suggest that after 10 years of manure applied at rates no longer exceeding the amount needed to replace the phosphorus removed by crops, the extra mineralization of N will still be between 45 and 60 kg ha^-1 yr^-1. If manure applications cease altogether then the extra mineralization will be about 25–30 kg N ha^-1 yr^-1.     

Nitrate leaching from sandy loam soils under a double-cropping forage system estimated from suction-probe measurements

Nitrate leaching from a double-cropping forage system was measured over a 2-year period (June 1994–May 1996) in the Northwest region of Portugal using ceramic cup samplers. The crops were grown for silage making and include maize (from May to September) and a winter crop (rest of the year) consisting of a mixture of cereals and Italian ryegrass. The experiment was performed on two different sites with a history of many years under the same crop and fertiliser management, but differing in the amounts of N applied as fertiliser and by regular cattle slurry applications. The annual nitrate leaching losses measured ranged from 154 to 338 kg N ha^-1. These amounts lead to annual mean concentrations between 22 and 41 mg -N L^-1 in the drained water. The coarse textured soils (sandy loams) and the climatic conditions of the region with more than 600 mm of drainage concentrated between October and March, tended to promote the leaching of all the nitrate-N left in the soil after the maize crop plus the N released by mineralization during the winter period. On these soils, the minimum amount of drainage (necessary to provide the complete leaching of all the nitrate-N in the soil profile in the end of summer), seems to be between 300 and 400 mm. The winter crops removed important quantities of N (83–116 kg N ha^-1) but, due to their late establishment in autumn they did not succeed in taking up the nitrate-N left in the soil after the maize crop. Approaches for reducing the nitrate leaching losses in this particular system are discussed.     

Seasonal effects on the survival characteristics of Salmonella Typhimurium and Salmonella Derby in pig slurry during storage

AIMS: Studies were carried out to investigate the survival of Salmonella Typhimurium and Salmonella Derby in pig slurry during summer and winter seasons. METHODS AND RESULTS: Pig slurry samples collected from a commercial fattening house were inoculated with a broth culture of Salmonella Typhimurium and Salmonella Derby, each at a level of log(10) 5.0 CFU ml(-1) and log(10) 2.0 CFU ml(-1). At the higher inoculum level, S. Typhimurium and S. Derby survived for 34 and 23 days, respectively in the summer, and 58 and 46 days, respectively in the winter. Survival at the lower inoculum level for S. Typhimurium and S. Derby was 19 and 16 days, respectively, in the summer and 24 days for both in the winter. CONCLUSIONS: The survival of S. Typhimurium and S. Derby observed in this study indicates that a 2-month holding period of pig slurry, prior to land spreading, may be adequate if separate storage facilities are provided. SIGNIFICANCE AND IMPACT OF THE STUDY: Despite difficulties correlating laboratory studies with on-farm conditions, pig slurry may not represent a major source of transmission of Salmonella spp. in the farm environment in Ireland.     

Filtering Decanting Water in Fly-Ash Lagoons Using Geotextiles — An Experimental Study

Disposal of fly-ash at thermal power stations is carried out in the form of ash slurry by mixing the ash with water. The ash slurry is stored in an ash pond. The water in the slurry is gradually drained out, through decanting wells, earthen embankments, and over spillways, leaving the ash to be deposited in the pond. It is observed that the design of decanting wells presently used allows a considerable amount of fly-ash to flow out with the water, leading to the contamination of soil and water courses. Further, it is observed that the failure of earthen embankments of ash ponds, which results in major damage to the environment, is mainly due to ineffective functioning of filters. This article presents the details of an experimental investigation carried out to study the role of geotextiles in improving the performance of decanting wells and different drainage systems in earthen embankments. Two series of experiments were carried out. In the first series a model-decanting well was tested with two different Geotextiles linings. In the second series, a number of model earthen embankments were tested with and without geotextiles. The economics of providing geotextiles in earthen embankments was studied. The results indicated that the use of Geotextiles improve the performance of decanting wells by reducing the amount of ash flowing into the decanting well and drainage system. Further, the use of Geotextiles has shown an improvement in the performance of earthen embankment used for ash ponds. The use of Geotextiles in earthen embankment is shown to be economical compared to the conventional drainage system.     

Fate of bacterial pathogens in cattle dung slurry subjected to anaerobic digestion

The survival of certain pathogenic bacteria was studied in anaerobic batch digesters at room temperature (18–25 °C) as well as at 35 °C under laboratory conditions. The survival of Escherichia coli and Salmonella typhi at room temperature was upto 20 days whereas at 35 °C it was only upto 10 days. Shigella dysenteriae was found to be the most sensitive organism which could survive upto 10 days at room temperature and upto 5 days at 35 °C. The longest survival was observed in case of Streptococcus faecalis which could survive upto 35 days at room temperature and 15 days at 35 °C. The survival time of Salmonella typhi increased when the solid contents of the digester were elevated from 9% to 15%.     

Conversion of cereal residues into biogas in a rumen-derived process

A recently developed high-rate, two-phase process, which employs rumen microorganisms for efficient acidogenesis, was tested for anaerobic degradation of barley straw, rye straw, and maize stover. Under conditions similar to those of the rumen and loading rates varying between 9.8 and 26.0 g of organic matter/I/day in the first phase (acidogenic reactor), total fibre degradation efficiencies ranged between 42% and 57%, irrespective of the loading rate applied. Average specific production of volatile fatty acids and biogas/g volatile solid digested in the acidogenic reactor varied between 6.9 and 11.2 mmol and 0.10 and 0.25 l, respectively.The effect of varying solid retention times on the extent of degradation of barley straw was examined. Changing of retention times in the range of 60 to 156 h had no effect on degradation efficiency, but a decrease in efficiency was observed at retention times below 60 h.By connecting the acidogenic reactor in series to an Upflow Anaerobic Sludge Blanket (UASB) methanogenic reactor the volatile fatty acids were converted into biogas. Average methane contents of the gases produced in the acidogenic reactor and in the UASB reactor were 30±3% and 78±3%, respectively.