Volatile Fatty Acids Fermentation Research Articles

Effects of starch loading rate on performance of combined fed-batch fermentation of ground wheat for bio-hydrogen production

Ground wheat powder solution (10 g L −1) was subjected to combined dark and light fermentations for bio-hydrogen production by fed-batch operation. A mixture of heat treated anaerobic sludge (AN) and Rhodobacter sphaeroides-NRRL (RS-NRRL) were used as the mixed culture of dark and light fermentation bacteria with an initial dark/light biomass ratio of 1/2. Effects of wheat starch loading rate on the rate and yield of bio-hydrogen formation were investigated. The highest cumulative hydrogen formation (CHF = 3460 ml), hydrogen yield (201 ml H 2 g −1 starch) and formation rate (18.1 ml h −1) were obtained with a starch loading rate of 80.4 mg S h −1. Complete starch hydrolysis and glucose fermentation were achieved within 96 h of fed-batch operation producing volatile fatty acids (VFA) and H 2. Fermentation of VFAs by photo-fermentation for bio-hydrogen production was most effective at starch loading rate of 80.4 mg S h −1. Hydrogen formation by combined fermentation took place by a fast dark fermentation followed by a rather slow light fermentation after a lag period.

Predicting biogeochemical calcium precipitation in landfill leachate collection systems.

Clogging of leachate collection systems within municipal solid waste landfills can result in greater potential for contaminants to breach the landfill barrier system. The primary cause of clogging is calcium carbonate (CaCO3(s)) precipitation from leachate and its accumulation within the pore space of the drainage medium. CaCO3(s) precipitation is caused by the anaerobic fermentation of volatile fatty acids (VFAs), which adds carbonate to and raises the pH of the leachate. An important relationship in modeling clogging in leachate collections systems is a yield coefficient that relates microbial fermentation of VFAs to precipitation of calcium carbonate. This paper develops a new, mechanistically based yield coefficient, called the carbonic acid yield coefficient (Y(H)), which relates the carbonic acid (H2CO3) produced from microbial fermentation of acetate, propionate, and butyrate to calcium precipitation. The empirical values of Y(H) were computed from the changes in acetate, propionate, butyrate, and calcium concentrations in leachate as it permeated through gravel-size material. The theoretical and empirical results show that the primary driver of CaCO3(s) precipitation is acetate fermentation. Additionally, other non-calcium cations (e.g., iron and magnesium) precipitated with carbonate (CO3(2-)) when present in the leachate. A common yield between total cations bound to CO3(2-) and H2CO3 produced, called the calcium carbonate yield coefficient (Yc), can reconcile the empirical yield coefficient for synthetic and actual leachates.

The feeding of differently treated straw materials to piglets after various weaning times. 2. Fatty acids in the large intestine and parameters of protein, fat, carbohydrate and mineral metabolism in the blood serum during the feeding of untreated, HCl-treated and partly-hydrolysed straw meal

In feeding experiments with piglets of the country species variously treated straw materials were used in concentrate--straw meal mixtures after the traditional weaning date (49th day of life) and studies were made of the fermentation of volatile fatty acids (VFA) in the large intestine (colon) and of the concentration of selected parameters of the protein, fat, carbohydrate and mineral metabolism in the blood serum of the animals. The concentrate--straw mixtures with a 10% straw quota contained untreated (II), HCl treated (HCl treatment without steaming, without (III) and with neutralization, IV) as well as partly hydrolysed straw meal (HCl treatment with subsequent steaming, without (V) and with neutralization with CaCO3, VI) were tested in comparison with sole feeding of concentrate (I) and its combination with wheat bran (VII). With regard to the fermentation processes in the large intestine in a comparison of the feeding groups (I-VII) the highest concentration and production quota of VFA was registered in I and the lowest in II. The straw treatment variants (III, IV, V and VI) took a medium position with regard to this and did not differ from each other. After their application of a significant increase in the molar acetate quota was ascertained in comparison with the sole feeding of concentrate (I), which was also characteristic of the other crude fibre sources (II and VII) and was reflected in the extension of the C2: C3 relation. Only few of the total of 15 selected parameters in the blood serum showed reactions of the intermediary metabolism of the test groups caused by feeding. The decrease of the urea concentration in the serum after the feeding of the treated straw materials (III, IV, V and VI) is particularly remarkable. In general, the urea concentration in the serum was negatively related to growth performance of the test groups. The use of HCl treated straw materials (III-VI) proved to be advantageous in comparison to the sole feeding of concentrate (I) and the use of other crude fibre sources (untreated straw meal (II) and wheat bran, VII) in the feeding regime of the keeping stage 'weaned pigs'.

Anaerobic treatment of wastes containing methanol and higher alcohols

Experiments have been performed to ascertain the feasibility of anaerobic digestion for the treatment of an alcoholic waste (i.e. fusel oil), consisting of approx. 50% methanol and 50% higher alcohols. Batch experiments as well as continuous experiments have been conducted. The continuous experiments have been carried out using the “Upflow Anaerobic Sludge Blanket” (UASB-) process. As inoculum a sugar beet waste grown and highly settleable and active anaerobic sludge (SBA-sludge) has been used. The SBA-sludge was shown to be superior to digested sewage sludge as seed material for an anaerobic treatment process, because—although it in fact is adapted to the fermentation of volatile fatty acids (VFA)—it does not have any significant difficulty with respect to the methanogenesis of the alcohols present in the fusel oil waste. The breakdown of higher alcohols starts immediately and that of methanol within a few days, depending on the initial load applied. In the UASB-experiments sludge loads up to 0.6 kg COD·kg VSS −1·day −1 could already be well accommodated within 1 week, so that within this period a space load could be handled as high as 20 kg COD·m −3·day −1, simply by supplying the reactor with approx. 30 kg SBA-VSS·m −3 averaged over the total reactor volume. Contrary to recent findings of Smith & Mah ( Appl. envir. Microbial. 36, 870–879, 1978), which were obtained with a pure culture of Methanosarcina barkeri, the sludge is capable of fermenting VFA and methanol rapidly and simultaneously, provided the conditions for VFA and methanol fermentation are favourable. However, as in previous experiments with aqueous solutions of methanol (Lettinga et al., Water Res. 13, 725–737, 1979), we observed that the digestion process can easily become upset, especially with respect to the degradation of VFA. Once again indications have been obtained that one or more trace elements are of eminent importance with respect to the stability of the process. At present the operation of a stable anaerobic treatment process for methanolic wastes cannot be guaranteed.

Seasonal variation in diet, volatile fatty acid production and size of the cecum of rock ptarmigan

Abstract 1. Seasonal changes in the chemical and taxonomic character of the diet, the size of the cecum and cecal volatile fatty acid (VFA) production were studied in rock ptarmigan collected in interior Alaska. 2. Ptarmigan fed predominantly on buds and catkins of dwarf birch from late September through April and consumed a significant proportion of berries when available during this period, while seeds predominated in crop contents during July and leaves were preferred during August. 3. Foods selected during July and August were of higher nutritional quality than those selected during other seasons. Crude protein values were highest and lignification of the cell wall lowest in foods selected by ptarmigan during the plant growing season. 4. The length, weight of contents and tissue weight of the cecum were greatest during winter, declined to their shortest, lightest state during summer and early fall and again increased as winter approached. 5. Relative production rates of individual VFA were acetate > propionate > butyrate, whereas relative absorption rates were butyrate > propionate > acetate. 6. The proportion of propionate produced with respect to acetate was highest during summer and early fall suggesting material entering the cecum during these seasons contained the highest proportion of soluble carbohydrates. 7. Seasonal VFA fermentation rates/g of cecal contents differed significantly only during July when the rate was highest. 8. Total VFA production/day did not differ significantly among seasons and metabolizable energy available from VFA averaged 7·1 kcal/day. This energy was equivalent to about 18% of the standard metabolic rate and 7% of estimated free living energy requirements.