Volatile Fatty Acid Levels Research Articles

Anaerobic digestion of Organic Fraction of Municipal Solid Waste (OFMSW) in two-phase system

In view of recovering energy resource from the treatment of Organic Fraction of Municipal Solid Waste (OFMSW), anaerobic digestion of OFMSW prior to aerobic composting as post-treatment was considered. This study aimed to determine the operational characteristics and efficiency of a two-phase system composed of a fed-batch hydrolysis reactor (phase I) and a methanogenic Upflow Anaerobic Sludge Blanket (UASB) reactor (phase II). The effluent of the UASB reactor was recycled to the phase I reactor to avoid high levels of Volatile Fatty Acids (VFAs), which may inhibit methanogenesis and hydrolysis of solids.

Suitability of Canola Meal forAnaerobic Co-digestion with Dairy Manure

Due to the renewed interest in biogas production, co-digestion of livestock manure, especially dairy manure, and other agro-wastes has emerged as an appropriate practice in enhancing the economic viability of anaerobic digestion. In this study, various ratios of canola meal and dairy manure (100% canola meal, 10% canola meal and 90% manure, 20% canola meal and 80% manure, 40% canola meal and 60% manure, and 100% manure) by volume basis were co-digested in 0.5 L batch bioreactors at a temperature of 35°C ±1°C for 25 days and a loading of 7.5% total solids (TS). Pre- and post-digestion samples were collected and analyzed for TS, volatile solids (VS), nutrients, pH, volatile fatty acids (VFAs), fiber, and chemical oxygen demand (COD). Biogas yield was measured daily using the water displacement method, and gas composition (mainly methane, CH4) was analyzed weekly within 72 h of collection using a gas chromatograph (HP 5890 Series II) equipped with a flame ionization detector (FID). Results indicated that 0% canola meal (100% manure) and 100% canola had specific methane yields of 352 and 83 L CH4 kg-1 VS, respectively. Addition of canola meal in the dairy manure resulted in decreased cumulative biogas and specific methane yield. This is suspected to be caused by the elevated levels of VFAs of more than 4000 mg L-1 in canola meal and dairy manure mixtures. Alternative methods should be explored to alleviate the inhibition in biogas production caused by elevated VFAs.

Effect of roughage fibre content on fibrolytic activities and volatile fatty acid profiles of Neocallimastix sp. YAK11 isolated from rumen fluids of yak ( Bos grunniens)

A 10-day pure culture of Neocallimastix sp. YAK11, isolated from rumen fluids of yak ( Bos grunniens) was evaluated for fibrolytic activity, apparent dry matter disappearance (ADMD), ferulic acid, reducing sugars and volatile fatty acids (VFA). The fungus was grown on oat straw (OS), corn stalks (CS), rice straw (RS) and wheat straw (WS). Recovered activity of ferulic acid esterase peaked at day 5 in all roughages, and the lowest activity was found with low fibre OS throughout the incubation (P<0.0001). The recovered activity of acetyl esterase peaked at day 6 with WS and RS and at day 7 with CS and OS (P<0.0001). The highest acetyl esterase activity was found with high fibre WS throughout the incubation (P<0.0001). Xylanase activity increased with all roughages and was maintained at a high level throughout the incubation (P=0.0102). The lowest xylanase activity was found in WS (P<0.0001), but cultures grown on OS, CS and RS showed no differences. The highest ADMD and reducing sugar values occurred in OS and the lowest in WS (P<0.0001). Ferulic acid release did not differ between four roughages. ADMD was positively correlated with xylanase activity ( r = 0.51, P<0.01). Total VFA concentration was greatest in OS (P<0.0001) and highly correlated with fibrolytic enzyme activities ( r > 0.42, P<0.01). Molar proportions of acetate and valerate did not differ in the roughages. The lowest propionate and branch chained VFA levels occurred in WS (P=0.0115), and the highest butyrate levels occurred in OS throughout the 10-d incubation (P=0.0464). The highest ratio of non-glucogenic to glucogenic acids (NGR) occurred in WS (P=0.0481). NGR peaked for all roughages around day 3 and then slightly declined for the rest of the experiment. In general, the isolate was capable of a pronounced degradation that would depend on the fibre content of the roughages. Screening of fungi from rumen fluids of yak would appear to be a useful strategy to obtain highly active esterases and polysaccharide hydrolases.

Rapid adaptation of the bacterial community in the growing rabbit caecum after a change in dietary fibre supply

This work aimed to study the response of the growing rabbit caecal ecosystem (bacterial community and caecal environmental parameters) after a switch from a control to a low-fibre diet (LFD). A group of 160 rabbits were fed ad libitum a control diet (ADF: 20.4%) from weaning (36 days). At 49 days of age (day 0), 75 rabbits were switched to a LFD group (ADF: 10.7%), whereas 85 others (control group) remained on the control diet, for 39 days. Caecal contents were regularly sampled throughout the trial (60 rabbits per group). The bacterial community structure was characterized using CE-SSCP (capillary electrophoresis single strand conformation polymorphism) and total bacteria were quantified using real-time PCR. Redox potential (Eh), pH, NH3-N, volatile fatty acid (VFA) were measured in the caecum to characterize environmental parameters. The reduction of fibre in the diet modified the CE-SSCP profiles (P < 0.001) but not the diversity index (5.6 ± 0.8, ns). The number of 16S rRNA gene copies of total bacteria decreased (P < 0.01) in LFD rabbits compared with controls. In LFD rabbits, the caecal environment was less acid (+0.2 units; P < 0.01), more reductive (−11 mV; P < 0.05) and drier (+3.4 g 100 per g; P < 0.001), with an increase in NH3-N (+77%; P < 0.001) and a decrease in total VFA concentration (−17%; P < 0.001). We found significant correlations between the bacterial community, the quantity of bacteria and the caecal traits of the caecal ecosystem. Indeed, in both groups, the caecal traits barely constrained the total inertia of the CE-SSCP profile set (less than 14%), whereas total bacteria were positively related to total VFA, acetic acid and butyric acid levels, and Eh, and negatively related to pH. All the microbial and environmental modifications had occurred by day 2 and remained stable thereafter. These results suggest that the bacterial community in the growing rabbit caecum is able to adapt quickly after a change to in the dietary fibre supply to reach a new steady-state equilibrium.

Effect of sanitary conditions and dietary fibre on the adaptation of gut microbiota after weaning

At weaning, the intestinal microbial ecosystem has to adapt to new feeds and to a new environment. The diverse and abundant commensal microbiota and its production of volatile fatty acids (VFA), especially butyrate, are involved in the prevention of diarrhoea and defence against pathogens. This study investigated the effects of the level of dietary fibre (DF) and sanitary housing conditions on the microbiota of weaned pigs. Forty-eight piglets, weaned at 28 days of age, were housed in clean or poor conditions. They were fed during two consecutive phases, two diets containing a high level (16.9 then 21.7% total dietary fibre-TDF, mainly soluble) or a low level DF (control, 12.1 then 14.6% TDF). Five weeks after weaning, microbiota was analysed using counting techniques and VFA profiles were determined by gas chromatography in faeces collected from the rectum. When compared with the clean conditions, the faeces of piglets housed in the poor environment contained significantly more Lactobacillus and Enterobacteria and less anaerobic sulphite-reducing bacteria (+ 0.9, + 1.1, −2.1 Log 10 CFU/g faeces), 60% more total VFA, with proportionally less acetate and more butyrate (−3%, + 4%). The introduction of DF did not affect the composition of the microbiota, tended to increase total VFA (25%), and decreased the level of branched-chain VFA (−1.4%). To conclude, the degraded sanitary housing conditions and to a lesser degree DF, stimulated the bacterial ecosystem in a way that could be beneficial for digestive balance, despite their negative impact on animal performances.

INFLUENCE OF SOLID FEED INTAKE AND AGE AT WEANING ON CAECAL CONTENT CHARACTERISTICS AND POST-WEANING PERFORMANCE

This study examined the effects of the feed/milk ratio at weaning time on caecal content characteristics at weaning and on post-weaning performances. Twenty-seven primiparous New­Zealand White does were used in this study involving with standardized litters of 8 kits at birth and a mínimum of 7 kits alive at weaning. During lactation, all does were mated and fertilized 12 days after kindling. Litters were caged separately from their mother and fed according to the following scheme: Group A (n = 8), litters fed ad libitum and weaned at 35 days; Group B (n = 10) litters fed 60% ad libitum and weaned at 35 days; Group C (n = 9) litters fed ad libitum and weaned at 30 days. At weaning one animal per litter was slaughtered to study caecum characteristics, while 50 other rabbits per group were raised during 5 weeks in cages of 2 rabbits in order to evaluate post-weaning performance. At weaning, litters of Group A, besides weighing more (6141, 4693 and 4729 g in Groups A, B and C, respectively), showed as expected the highest feed/milk intake ratio (8.35, 4.05 and 1.53; P &lt; 0.01, in Groups A, B and C, respectively). At weaning, caecal content of Group A rabbits recorded a lower pH (5.67, 6.40 and 5.97, P &lt; 0.01, in Groups A, B and C, respectively), a lower concentration of ammonia (7.3, 10.1 and 9.5 mMol/I in Groups A, B and C, respectively) and a lower C3 proportion in VFA (5.8, 9.5 and 10.2% in Groups A, B and C, respectively). Group A also, had the highest levels of total volatile fatty acids (57.4, 51.2 and 46.0 mMol/I in the A, B and C Groups, respectively). During the fattening period, rabbits of Group A showed a higher feed intake (127, 115 and 100 g/d, P &lt; 0.01, in Groups A, B and C, respectively) and a poorer food conversion ratio (3.50, 3.12 and 2.78 in Groups A, B and C, respectively). Weaning age also exerted sorne specific effects, for example, on caecal content weight or post-weaning daily growth rate (36.5 g/d for C rabbits weaned at 30 days and 38.2 for B rabbits weaned with the same live weight but at 35 days; P&lt;0.05). In conclusion, the feed/milk inlake ratio al weaning influenced some characteristics of caecal contents and some post-weaning performances of rabbits.

Effects of Volatile Fatty Acids on IGF-I, IGFBP-3, GH, Insulin and Glucagon in Plasma, and IGF-I and IGFBP-3 in Different Tissues of Growing Sheep Nourished by Total Intragastric Infusions

Twelve SuffolkxSmall-tail-Han male sheep (body weight 21-26 kg), aged four months, were used to study the effects of volatile fatty acids (VFA) on IGF-I (insulin-like growth factor-I), IGFBP-3 (insulin-like growth factor binding protein-3), GH (growth hormone), insulin and glucagon in plasma, and IGF-I and IGFBP-3 in different tissues. The sheep were randomly divided into four groups with 3 sheep in each group. The sheep were sustained by total intragastric infusions and four levels of mixed VFA (the molar proportion of acetic acid, propionic acid and butyric acid was 65:25:10), which supplied 333, 378, 423 and 468 KJ energy/kg W 0.75 /d, were infused into the rumen as experimental Treatments I, II, III and IV, respectively. The experiment lasted 12 days, of which the first 8 days were for pretreatment and the last 4 days for collection of samples. At the end of the experiment, blood samples were taken and then the sheep were slaughtered and tissue samples from the rumen ventral sac, rumen dorsal sac, liver, duodenum and Longissimus dorsi muscle were obtained. IGF-I, IGFBP-3, GH, insulin and glucagon in plasma and IGF-I and IGFBP-3 in different tissues were analysed. Results showed that the concentration of IGF-I, IGFBP-3, GH, insulin or glucagon in plasma and the content of IGF-I and IGFBP-3 in the rumen dorsal sac, rumen ventral sac, liver or Longissimus dorsi muscle were increased with VFA infusion level (p 0.05). It was concluded that IGF-I, IGFBP-3, GH, insulin and glucagon in plasma and IGF-I and IGFBP-3 in rumen dorsal sac, rumen ventral sac, liver and Longissimus dorsi muscle were increased significantly with increasing level of ruminal infusion of mixed VFA.

Fecal acetone and isopropanol levels of wild sika deer (Cervus nippon yesoensis) in spring and winter

AbstractRecently, the population of Cervus nippon yesoensis, a subspecies of sika deer, has been increasing in Hokkaido, Japan. The food habits and alimentary fermentation of sika deer change dramatically with season, with food primarily composed of bark in winter, and grasses and woody leaves for the remainder of the year. To investigate the relationship of colonic fermentation in the deer with food changes, fresh fecal samples were collected in March with lingering snow, and during a verdurous period in June. Fecal alcohol, acetone, ammonia and volatile fatty acids (VFAs) were analyzed after extracting the samples with water. With the change in food from winter to spring, ethanol level decreased while acetone and isopropanol levels increased in the majority of fecal samples. In June, higher n‐butyrate levels and a lower proportion of minor VFAs containing branched acids were found, with an accompanying tendency toward higher total VFA level. Thus, alterations of colonic fermentation occurred in conjunction with the transition from winter to spring food in wild sika deer.

無動力撹拌機構を有する新規低コストメタン発酵リアクターの開発

Continuous operation treating 100 g·L-1 total solids (TS) simulated food waste was investigated using a novel methane fermentation reactor that enables the agitation of the fermentation liquid without electricity. In this study, the overall performance and reaction attributes of the reactor were evaluated. Under mesophilic condition and at different chemical oxygen demand (CODCr) loading rates (5 to 10 kg·m3·d-1), the reactor achieved 220 days of stable continuous operation. Inside the reactor, the continuous change in the liquid level and the 5 to 16 times self-agitation occurred daily, which was likely responsible for the distribution of organic load near the inlet port of the reactor. The reactor attained 0.72-0.82 m3·g-1-TS biogas production yield and 79.4-85.5% CODCr reduction on average, and a small amount of volatile fatty acid (VFA) was detected in the effluent. These results suggest that the novel reactor investigated is comparable in biogas production yield and CODCr reduction and superior in residual VFA level to the completely stirred tank reactor, in the treatment of same simulated food waste used in a previous study.

Dietary Protein and Cellulose Effects on Chemical and Microbial Characteristics of Swine Feces and Stored Manure

The objectives of this study were to investigate the effects of dietary crude protein (14.5 or 12.0%) and cellulose (8.7 or 2.5%) levels on composition of feces and manure after 8 wk of diet feeding and storage. Pigs were fed twice daily; after each feeding, urine and feces were collected and added to manure storage containers. On weeks 2 and 8 after initiation of the experiment, fresh fecal and manure samples were obtained. On Week 8, increased dietary cellulose resulted in significantly higher levels of volatile fatty acids (VFA) and phenols in feces compare to other diets. In contrast, dietary protein had the greatest effect on manure chemical composition; lower protein decreased sulfur content, ammonia, and phenolic compound concentrations. High levels of either dietary cellulose or protein tended to increase microbial community similarity in fecal samples, but only high protein increased similarity among manure sample microbial communities. Fecal and manure samples from Week 8 differed from samples taken in Week 2 both in chemical and microbiological composition. Week 2 samples had lower concentrations of many of chemical compounds and microbial diversity than samples from Week 8. The fecal results indicate that after 2 wk of feeding experimental diets the animals were not fully adapted to the diets. More importantly, after only 2 wk of urine and fecal collection, manure was not representative of stored manure, limiting its usefulness in developing standards and recommendations for on-farm management practices.

Biodegradation performance of an anaerobic hybrid reactor treating olive mill effluent under various organic loading rates

The primary objective of this study was to evaluate the performance of a 20 l lab scale anaerobic hybrid reactor (AHR) combining sludge blanket in the lower part and filter in the upper part under varying organic loading rates (OLRs) in order to study biodegradation of olive mill effluent (OME). For this purpose, some parameters, such as total phenols, effluent chemical oxygen demand (COD), suspended solids (SS), volatile fatty acids (VFAs), and pH in the influent and effluent, and removal efficiencies for those parameters (except pH) were continuously monitored throughout the experimental period of 477 days. Eleven different organic loadings between 0.45 and 32 kg COD m −3 day −1 were imposed by either varying influent COD or hydraulic retention time (HRT). The results demonstrated that the AHR reactor could tolerate high influent COD concentrations. Removal efficiencies for the studied pollution parameters were found to be as follows: COD, 50–94%; total phenol, 39–80%; color, 0–54%; and suspended solids, 19–87%. The levels of VFAs in the effluent, which was principally acetate, butyrate, iso-butyrate, and propionate, varied between 10 and 2005 mg l −1 depending upon OLRs. A COD removal efficiency of 90% could be achieved as long as OLR is kept at a level of less than 10 kg COD m −3 day −1. However, a secondary treatment unit for polishing purposes is necessary to comply with receiving media discharge standards.

Stimulation of biomethanation by Clostridium sp. PXYL1 in coculture with a Methanosarcina strain PMET1 at psychrophilic temperatures

Bioaugumentation of low temperature biogas production was attempted by addition of cold-adapted Clostridium and a methanogen. A psychrotrophic xylanolytic acetogenic strain Clostridium sp. PXYL1 growing optimally at 20 degrees C and pH 5.3 and a Methanosarcina strain, PMET1, growing optimally on acetate and producing methane at 15 degrees C were isolated from a cattle manure digester. Anaerobic conversion of xylose at 15 degrees C with the coculture of the two strains was performed, and batch culture methane production characteristics indicated that methanogenesis occurred via acetate through 'acetoclastic' pathway. Stimulation studies were also undertaken to evaluate the effect of exogenous addition of the coculture on biogas yields at 15 degrees C. Addition of 3 ml of PXYL1 at the rate of 12 x 10(2) CFU ml(-1) increased the biogas 1.7-fold (33 l per kg cowdung) when compared to control (19.3 l per kg cowdung) as well as increased the volatile fatty acid (VFA) levels to 3210 mg l(-1) when compared to 1140 mg l(-1) in controls. Exogenous of addition of 10 ml PMET1 inoculum at the rate of 6.8 + or - 10(2) CFU ml(-1) in addition to PXYL1 served to further improve the biogas yields to 46 l kg(-1) as well as significantly brought down the VFA levels to 1350 mg l(-1). Our results suggest that the rate-limiting methanogenic step at low temperatures could be overcome and that biogas yields improved by manipulating the population of the acetoclastic methanogens. Stimulation of biomethanation at low temperature by coculture.

Contribution of Lactic Acid Bacteria Esterases to the Release of Fatty Acids in Miniature Ewe’s Milk Cheese Models

The present work evaluates the contribution of esterase activities of lactic acid bacteria isolated from ewe's dairy products to the release of free fatty acids (FFA) in ewe's milk cheese models. At 60 days of ripening, single-strain cheeses Ov 409 and Ov 421 showed high levels of total FFA (3075 and 2494.62 mg/kg, respectively). Cheeses Ov 227-Ov 409 and Ov 421-Ov 409 presented high percentages of short-chain fatty acids (SCFA). The highest levels of volatile free fatty acids (VFFA) were detected in cheeses Ov 409, Ov 421-Ov 409, and Ov 421-Ov 227. Studies on esterase activities showed that these strains hydrolyzed alpha-naphthyl derivatives of fatty acids from C2 to C6, mainly associated with the wall-membrane fraction. The results showed that the strains studied contributed to the release of FFA during ripening of ewe's milk cheese models. The increase of SCFA throughout ripening involves the action of esterases of starter strains.

Effects of fermentable carbohydrates and low dietary phosphorus supply on the chemical composition of faecal bacteria and microbial metabolites in the gastrointestinal tract of pigs

The objective was to determine the effects of fermentable carbohydrates on phosphorus (P) metabolism, the chemical composition of the faecal mixed bacterial mass (MBM) and the microbial activity in the large intestine (LI) of pigs. Eight barrows (mean BW 35.9 +/- 0.9 kg), fitted with simple T-cannulas at the terminal ileum, were either fed a low-P corn-soybean meal-based control diet or 75% of the control diet supplemented with 25% cellulose, starch or pectin according to a 4 x 3 Latin Square design. Both pectin and cellulose caused higher faecal than ileal P recoveries. Ileal volatile fatty acids (VFA) levels were more pronounced for the starch (p < 0.05) rather than the cellulose and pectin treatments, whereas pectin resulted in a higher faecal VFA concentration in comparison to starch and cellulose (p < 0.05). The differences in faecal VFA concentrations corresponded to the pH values obtained in faeces. The N content of MBM was higher (p < 0.05) when cellulose was supplemented. Pectin caused a decrease in the P content of the MBM compared to the control (p < 0.05). As a result, the N:P ratio was significantly higher for the pectin (N:P = 4.33) than for the control treatment (N:P = 2.63), while the Ca:P ratio remained constant for all treatments, suggesting changes in the accumulation of N, P and Ca in MBM, probably due to changes in the species composition and activity of the microflora.

Increased Fecal Lactate and Decreased Volatile Fatty Acid (VFA), Particularly n-Butyrate Concentrations in Diarrheic Young Calves

Using 24 diarrheic dairy calves under 8 weeks old, multiple fecal samples (4-12) were collected individually during the clinical advancing (max. 10 days) to evaluate the importance of fecal ammonia, lactate and volatile fatty acid (VFA) levels. Removing 3 calves not recovered during the sampling, 21 calves were grouped into under 3 weeks (< 3 wk; n=11) and 3-8 weeks old (3-8 wk; n=10). Data were divided into diarrheic and recovered feces with averaging in individuals. Diarrheic feces showed lower VFA and n-butyrate, and higher acetate proportions than recovered feces at <3 wk, but not at 3-8 wk. Diarrhea showed higher lactate, and lower ammonia and minor VFA (i-butyrate, valerate), which might reflect insufficiency in gut flora and fermentation.

Bacterial community dynamics during reduction of odorous compounds in aerated pig manure slurry

To study the microbial community responsible for the reduction of the polluting load during aerobic digestion of pig slurry. We analysed bacterial succession by nonculture-based methods and determined the physicochemical parameters and polluting substances during 6 days of aerobic digestion. The bacterial subpopulations evolved by aeration, predominantly Bacillus spp., degraded organic matter and vigorously consumed oxygen, as indicated by low oxidation-reduction potential (ORP). In this phase, the volatile fatty acid (VFA) levels drastically decreased, and VFAs were almost depleted on day 4. Simultaneously, the ammonia concentration decreased to its lowest level on day 4; thereafter, it increased until the end of the process. After the decrease in the total organic carbon content in the supernatant of the decomposed slurry, the ORP increased (approximately 0 mV), and the microbial community showed an abundance of lineages belonging to the phylum Proteobacteria. Bacillus was the predominant member of the bacterial community driving the VFA-removal process. Their predominance was related to the presence of available carbon, including VFAs and changes in ORP. Information on the relationships among the involved microbes, polluting materials and physicochemical parameters will aid process design and retrofitting of the process.

Application of a fuzzy logic control system for continuous anaerobic digestion of low buffered, acidic energy crops as mono‐substrate

A fuzzy logic control (FLC) system was developed at the Hamburg University of Applied Sciences (HAW Hamburg) for operation of biogas reactors running on energy crops. Three commercially available measuring parameters, namely pH, the methane (CH4) content, and the specific gas production rate (spec. GPR = m(3)/kg VS/day) were included. The objective was to avoid stabilization of pH with use of buffering supplements, like lime or manure. The developed FLC system can cover most of all applications, such as a careful start-up process and a gentle recovery strategy after a severe reactor failure, also enabling a process with a high organic loading rate (OLR) and a low hydraulic retention time (HRT), that is, a high throughput anaerobic digestion process with a stable pH and CH4 content. A precondition for a high load process was the concept of interval feeding, for example, with 8 h of interval. The FLC system was proved to be reliable during the long term fermentation studies over 3 years in one-stage, completely stirred tank reactors (CSTR) with acidic beet silage as mono-input (pH 3.3-3.4). During fermentation of the fodder beet silage (FBS), a stable HRT of 6.0 days with an OLR of up to 15 kg VS/m(3)/day and a volumetric GPR of 9 m(3)/m(3)/day could be reached. The FLC enabled an automatic recovery of the digester after two induced severe reactor failures. In another attempt to prove the feasibility of the FLC, substrate FBS was changed to sugar beet silage (SBS), which had a substantially lower buffering capacity than that of the FBS. With SBS, the FLC accomplished a stable fermentation at a pH level between 6.5 and 6.6, and a volatile fatty acid level (VFA) below 500 mg/L, but the FLC had to interact and to change the substrate dosage permanently. In a further experiment, the reactor temperature was increased from 41 to 50 degrees C. Concomitantly, the specific GPR, pH and CH4 dropped down. Finally, the FLC automatically enabled a complete recovery in 16 days.

A pilot-scale comparison of mesophilic and thermophilic digestion of source segregated domestic food waste

Source segregated food waste was collected from domestic properties and its composition determined together with the average weight produced per household, which was 2.91 kg per week. The waste was fed over a trial period lasting 58 weeks to an identical pair of 1.5 m(3) anaerobic digesters, one at a mesophilic (36.5 degrees C) and the other at a thermophilic temperature (56 degrees C). The digesters were monitored daily for gas production, solids destruction and regularly for digestate characteristics including alkalinity, pH, volatile fatty acid (VFA) and ammonia concentrations. Both digesters showed high VFA and ammonia concentrations but in the mesophilic digester the pH remained stable at around 7.4, buffered by a high alkalinity of 13,000 mg l(-1); whereas in the thermophilic digester VFA levels reached 45,000 mg l(-1) causing a drop in pH and digester instability. In the mesophilic digester volatile solids (VS) destruction and specific gas yield were favourable, with 67% of the organic solids being converted to biogas at a methane content of 58% giving a biogas yield of 0.63 m(3) kg(-1) VS(added). Digestion under thermophilic conditions showed potentially better VS destruction at 70% VS and a biogas yield of 0.67 m(3) kg(-1) VS(added), but the shifts in alkalinity and the high VFA concentrations required a reduced loading to be applied. The maximum beneficial loading that could be achieved in the mesophilic digester was 4.0 kg VS m(-3) d(-1).

IMPROVEMENT OF QUALITY OF RAS CHEESE MADE FROM PASTEURIZED MILK USING A SPECIAL SLURRY FROM EWE'S MILK

The present study was carried out as an at-tempt to improve the quality of Ras cheese made from pasteurized cow's milk using ewe's milk slurry to which proteases and lipases were added. The slurry was incubated at 30oC for one week, and then added either to the cheese milk prior to coag-ulation or directly to the cheese curd before press-ing. Cheeses were analysed for chemical, microbi-ological and organoleptic properties at 0, 15, 30, 60 and 90 d of ripening. Generally, the addition of slurry affected at least four parameters of interest for the flavour development. Cheese flavour devel-opment was accelerated, the proteolysis was en-hanced and casein breakdown was stimulated. Addition of slurry increased the levels of the total volatile fatty acids at each period of ripening, par-ticularly with addition of slurry to cheese curd. Ad-dition of slurry affected the microbiological quality of cheeses. Proteolytic and lipolytic bacterial counts increased throughout ripening, while yeast and moulds were no longer detectable in slurry added cheese after 30 d of ripening. Sensory eval-uation showed that the Ras cheeses made with the slurry received higher scores for flavor and body and texture than the control cheese over 90 d of ripening. These results suggested that the addition of ewe's milk slurry was necessary for develop-ment of sensory characteristics of the cheeses.

Treatment of wastewater from red and tropical fruit wine production by zeolite anaerobic fluidized bed reactor

A study of the anaerobic treatment of wastewaters derived from red (RWWW) and tropical fruit wine (TFWWW) production was carried out in four laboratory-scale fluidized bed reactors with natural zeolite as bacterial support. These reactors operated at mesophilic temperature (35°C). Reactors R1 and R2 contained Chilean natural zeolite, while reactors R3 and R4 used Cuban natural zeolite as microorganism support. In addition, reactors R1 and R3 processed RWWW, while reactors R2 and R4 used TFWWW as substrate. The biomass concentration attached to zeolites in the four reactors studied was found to be in the range of 44–46 g volatile solids (VS)/L after 90 days of operation time. Both types of zeolites can be used indistinctly in the fluidized bed reactors achieving more than 80%–86% chemical oxygen demand (COD) removals for organic loading rates (OLR) of up to at least 20 g COD/L d. pH values remained within the optimal range for anaerobic microorganisms for OLR values of up to 20 and 22 g COD/L d for RWWW and TFWWW, respectively. Toxicity and inhibition levels were observed at an OLR of 20 g COD/L d in reactors R1 and R3 while processing RWWW, whereas the aforementioned inhibitory phenomena were not observed at an OLR of 24 g COD/L d in R2 and R4, treating TFWWW as a consequence of the lower phenolic compound content present in this substrate. The volatile fatty acid (VFA) levels were always lower in reactors processing TFWWW (R2 and R4) and these values (< 400 mg/L, as acetic acid) were lower than the suggested limits for digester failure. The specific methanogenic activity (SMA) was twice as high in reactors R2 and R4 than in R1 and R3 after 120 days of operation when all reactors operated at an OLR of 20 g COD/L d.