Foam formation in a downstream digester of a cascade running full-scale biogas plant: Influence of fat, oil and grease addition and abundance of the filamentous bacterium Microthrix parvicella.

The microbial community composition in a full-scale biogas plant fed with sewage sludge and fat, oil and grease (FOG) was investigated over a 15-month period, including two foam formation events. Addition of FOG as a substrate in the biogas plant together with high abundances of Microthrix parvicella were found to promote foam formation in the downstream digester of a cascade of two biogas digesters. Genetic fingerprinting and quantitative PCR (qPCR) indicated a higher abundance of M. parvicella in the digester, when the digestion process was accompanied by excessive foaming relative to the reference digesters without disturbance. The creation of foam depended on the introduced proportion of FOG and the abundance of M. parvicella. Furthermore, shifts in the abundance of M. parvicella in the biogas plant were observed within the 15-month monitoring period corresponding to its seasonal abundance in the sludge of the wastewater treatment plant (WWTP).

Early warning indicators for process failure due to organic overloading by rapeseed oil in one-stage continuously stirred tank reactor, sewage sludge and waste digesters.

Early warning indicators for process failures were investigated to develop a reliable method to increase the production efficiency of biogas plants. Organic overloads by the excessive addition of rapeseed oil were used to provoke the decrease in the gas production rate. Besides typical monitoring parameters, as pH, methane and hydrogen contents, biogas production rate and concentrations of fatty acids; carbon dioxide content, concentrations of calcium and phosphate were monitored. The concentration ratio of volatile fatty acids to calcium acted as an early warning indicator (EWI-VFA/Ca). The EWI-VFA/Ca always clearly and reliably indicated a process imbalance by exhibiting a 2- to 3-fold increase 3-7days before the process failure occurred. At this time, it was still possible to take countermeasures successfully. Furthermore, increases in phosphate concentration and in the concentration ratio of phosphate to calcium also indicated a process failure, in some cases, even earlier than the EWI-VFA/Ca.

Antimicrobial mortar surfaces for the improvement of hygienic conditions.

AIMS: To evaluate the effectiveness of various antimicrobial mortar formulations in inhibiting the growth of a selection of pathogens of environmental and hygienic concern. METHODS AND RESULTS: Mortar prisms containing triclosan-incorporated fibres or different concentrations of silver copper zeolites were incubated with Escherichia coli, Listeria monocytogenes, Salmonella enterica or Staphylococcus aureus at 4 or 20 degrees C for 24 h. From plate counting, a substantial bactericidal effect (>4 log units) could only be observed for the mortar specimens containing more than 3% zeolites on cement weight base, the effect being more pronounced at 20 degrees C compared to 4 degrees C. No inhibitory effect could be observed for mortar specimens containing antimicrobial fibres. Adenosinetriphosphate (ATP) measurements allowed for a rapid indication of the occurrence of antimicrobial activity. CONCLUSIONS: In order to obtain a bactericidal effect on mortar surfaces, concentrations of silver copper zeolites of more then 3% are required. SIGNIFICANCE AND IMPACT OF THE STUDY: To our knowledge, this is the first study in which the effectiveness of various antimicrobial mortar mixtures towards the inhibition of pathogens has been evaluated in a quantitative way. Antimicrobial concrete mixtures can be used for the improvement of the hygienic conditions in a variety of environments.

Decreasing sulfide generation in sewage by dosing formaldehyde and its derivatives under anaerobic conditions.

Hydrogen sulfide emission in sewers is associated with toxicity, corrosion, odour nuisance and high costs. In this study, a new method to inhibit sulfide generation by means of formaldehyde and its derivatives has been evaluated under anaerobic conditions. The possible impact of formaldehyde on an activated sludge system and an appraisal of the economic aspects are presented as well. A dosage of 19 mg L(-1) formaldehyde resulted in a decrease of the sulfide production of 90%. Dosing of 32 mg L(-1) paraformaldehyde and addition of 111 mg L(-1) ureaformaldehyde were not sufficient to inhibit the sulfide generation in sewage to the same extent. The impacts of 19 mg L(-1) formaldehyde on activated sludge, in terms of COD removal, nitrification rate and oxygen uptake rates, were negligible. This suggests that formaldehyde dosage is a feasible technique to abate the sulfide problem in sewers.

Chemopreventive effects from prebiotic inulin towards microbial 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine bioactivation.

AIMS: Using a Simulator of the Human Intestinal Microbial Ecosystem (SHIME), we investigated the chemopreventive potential of prebiotic chicory inulin towards the in vitro bioactivation of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) by human intestinal microbiota. METHODS AND RESULTS: HPLC data revealed that inulin significantly decreased the formation of the genotoxic PhIP-M1 metabolite, with the highest inhibitory activity in the colon ascendens (87% decrease). Interestingly, this chemopreventive effect correlated with alterations of bacterial community composition and metabolism in the different colon compartments. Conventional culture-based techniques and PCR-DGGE analysis on the SHIME colon suspension revealed significant bifidogenic effects during inulin treatment, whereas the overall microbial community kept relatively unchanged. Additionally, the production of short-chain fatty acids increased with 12%, 3% and 7%, while ammonia concentrations decreased with 3%, 4% and 3% in the ascending, transverse and descending colon compartments, respectively. CONCLUSIONS: These results indicate that the prebiotic effects from inulin may also purport protective effects towards microbial PhIP bioactivation. SIGNIFICANCE AND IMPACT OF THE STUDY: As the colonic microbiota may contribute significantly to the carcinogenic potential of PhIP, the search for dietary constituents that decrease the formation of this harmful metabolite, may help in preventing its risk towards human health.

Inhibition of sulfide generation by dosing formaldehyde and its derivatives in sewage under anaerobic conditions.

Hydrogen sulfide emission in sewers is associated with toxicity, corrosion, odor nuisance and a lot of costs. The possibility to inhibit sulfide generation by formaldehyde and its derivatives (paraformaldehyde and urea formaldehyde) has been evaluated under anaerobic conditions. The impact of formaldehyde on an activated sludge system and an appraisal of the economic aspects are also presented. The optimum dosage to inhibit sulfide generation in sewage was 12-19 mg L(-1) formaldehyde. The dosages of 32 mg L(-1) paraformaldehyde or 100 mg L(-1) urea formaldehyde were not capable of inhibiting sulfide generation in sewage. The impact of 19 mg L(-1) formaldehyde on activated sludge system was negligible in terms of COD removal, nitrification rate and oxygen uptake rate.

Plant polyphenolics as anti-invasive cancer agents.

Because invasion is, either directly or via metastasis formation, the main cause of death in cancer patients, development of efficient anti-invasive agents is an important research challenge. We have established a screening program for potentially anti-invasive compounds. The assay is based on organotypic confronting cultures between human invasive cancer cells and a fragment of normal tissue in three dimensions. Anti-invasive agents appeared to be heterogeneous with regard to their chemical nature, but plant alkaloids, polyphenolics and some of their synthetic congeners were well represented. Even within this group, active compounds were quite diverse: (+)-catechin, tangeretin, xanthohumol and other prenylated chalcones, 3,7-dimethoxyflavone, a pyrazole derivative, an isoxazolylcoumarin and a prenylated desoxybenzoin. The data gathered in this system are now applied in two projects. Firstly, structure-activity relationships are explored with computer models using an artificial neural network approach, based on quantitative structural descriptors. The aim of this study is the prediction and design of optimally efficient anti-invasive compounds. Secondly, the metabolism of orally ingested plant polyphenolics by colonic bacteria is studied in a simulator of the human intestinal microbial ecosystem (SHIME) and in human intervention trials. This method should provide information on the final bioavailability of the active compounds in the human body, with regard to microbial metabolism, and the feasibility of designing pre- or probiotics that increase the generation of active principles for absorption in the gastro-intestinal tract. The final and global aim of all these studies is to predict, synthesize and apply in vivo molecules with an optimal anti-invasive, and hence an anti-metastatic activity against cancer.

Intestinal bacteria metabolize the dietary carcinogen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine following consumption of a single cooked chicken meal in humans.

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is a carcinogenic heterocyclic amine formed in meats during cooking. Although the formation of PhIP metabolites by mammalian enzymes has been extensively reported, the involvement of the intestinal bacteria remains unclear. This study examined the urinary and fecal excretion of a newly identified microbial PhIP metabolite 7-hydroxy-5-methyl-3-phenyl-6,7,8,9-tetrahydropyrido[3',2':4,5]imidazo[1,2-a]pyrimidin-5-ium chloride (PhIP-M1) in humans. The subjects were fed 150 g of cooked chicken containing 0.88-4.7 microg PhIP, and urine and feces collections were obtained during 72 h after the meal. PhIP-M1 and its trideuterated derivate were synthesized and a LC/MS/MS method was developed for their quantification. The mutagenic activity of PhIP-M1, as analyzed using the Salmonella strains TA98, TA100 and TA102, yielded no significant response. Of the ingested PhIP dose, volunteers excreted 12-21% as PhIP and 1.2-15% as PhIP-M1 in urine, and 26-42% as PhIP and 0.9-11% as PhIP-M1 in feces. The rate of PhIP-M1 excretion varied among the subjects. Yet, an increase in urinary excretion was observed for successive time increments, whereas for PhIP the majority was excreted in the first 24h. These findings suggest that besides differences in digestion, metabolism and diet, the microbial composition of the gastrointestinal tract also strongly influences individual disposition and carcinogenic risk from PhIP.

Complete lab-scale detoxification of groundwater containing 1,2-dichloroethane.

The suspected carcinogenic solvent 1,2-dichloroethane (1,2-DCA) is the most abundant chlorinated C(2) groundwater pollutant on earth. However, an efficient reductive in situ detoxification technology for this compound is not known. Detoxification results of 1,2-DCA with the recently isolated anaerobic bacterium Desulfitobacterium dichloroeliminans strain DCA1 are presented. First, it was verified that strain DCA1 could compete for nutrients in the presence of fast-growing Enterococcus faecalis; the latter was observed in the enrichment culture from which strain DCA1 was isolated. Subsequently, lab-scale bioaugmentation of the strain to groundwater containing 40 mg 1,2-DCA/l indicated that the bacterium has strong metabolic activity under prevailing environmental conditions, converting the pollutant into ethene. During exponential growth, the maximum 1,2-DCA dechlorination rate exceeded 350 nmol chloride released per min per mg total bacterial protein. Growth and dechlorination within the community with autochthonous bacteria indicated a high competitive strength of strain DCA1. Interestingly this dechlorination process does not produce any toxic byproducts, such as vinyl chloride. Furthermore, complete groundwater detoxification happens within a short time-frame (days) and is robust in terms of bacterial competition, oxygen tolerance, high ionic strength, and pH range.

Polycyclic aromatic hydrocarbons (PAHs) and estrogenic compounds in experimental flue gas streams.

The importance of combustion processes as a source of substances with estrogenic activity in the environment was investigated. Wood (nontreated and treated with wood preservatives), barbecue charcoal, meat, and kitchen waste were combusted in a laboratory-scale incinerator. Flue gas emissions (particulates and gaseous pollutants) were trapped in polyurethane foam cartridges. The cartridges were subjected to Soxhlet extraction and part of the extracts redissolved in dimethylsulfoxide (DMSO) for analyses of estrogenic activity by means of the yeast-based human estrogen receptor (hER) bioassay. A synthetic estrogen, 17-alpha-ethinylestradiol (EE2), was used as the reference estrogenic compound. Part of the extracts was analyzed for the 16 USEPA priority polycyclic aromatic hydrocarbons (PAHs). Estrogenic compounds in the flue gas (wood) were as high as 234 +/- 25 ng m(-3) EE2 equivalent compared with 27 to 81 ng m(-3) EE2 equivalent in flue gas from combustion of barbecue charcoal. Concentrations of polycyclic aromatic hydrocarbons in both flue gas streams were in the range of 21,000 +/- 2000 and 240 +/- 110 ng m(-3), respectively. In general, the concentrations of EE2 equivalent in the flue gas samples were at least a factor of 1000 lower than total PAH concentration. The EE2 levels were not related to the concentration of PAHs in any flue gas sample.

Nitrate removal in aquaria systems: use of electrochemically generated hydrogen gas as electron donor for denitrification.

Nitrate, the end product of the nitrification process, tends to accumulate in aquaria systems. Removal of nitrate in these systems by means of biological denitrification requires the addition of an external electron donor. In this study, the possibilities for using hydrogen gas in aquaria systems as a harmless alternative to other electron donors such as sulphur or reduced organic carbon was investigated. To circumvent safety issues regarding the storage of large volumes of hydrogen gas, in situ generation of hydrogen gas by means of a separate electrochemical cell was chosen. A plug flow reactor filled with polyester cotton wool as carrier material for denitrifying bacteria received hydrogen gas in the headspace. Removal rates of 15 +/- 6 mg N per day were achieved with a hydraulic residence time of 3.3 hours. During the start-up phase nitrite peaks up to 3 mg N per liter were measured in the effluent of the reactor.

Occurrence and origin of phosphine in landfill gas.

A landfill (Hooge Maey, Flanders, Belgium) was subjected to an in-depth study in order to explain the origin of phosphine detected in high amounts in landfill gas during a previous study. The spatial and temporal variability of the phosphine concentration in landfill gas was assessed. Twenty four wells were monitored and differences in phosphine concentration up to one log unit were observed (3.2-32.4 microg/m3). The phosphine concentration in each well was constant in time over a period of 4 months. No correlation was found between the phosphine concentration and methane, carbon dioxide, hydrogen sulphide, ethene or ethane concentration. In a series of laboratory tests, it was shown that phosphine was emitted during batch fermentation tests inoculated with landfill leachate when Fe0 or Al0 specimens were added. Conditions favouring corrosion of iron gave rise to higher emissions of phosphine. The phosphine concentration in the headspace of a batch test rose to 1.43 mg/m3 after 27 days of incubation. Weight loss of corroding steel coupons correlated with phosphine emission. Calculations showed that all phosphine emitted from the 0.005 km3 landfill (160 g/year) could be attributed to corrosion of metals. No evidence of de novo synthesis could be established

Assessment of the estrogenic activity of flue gases from burning processes by means of the yeast based human estrogen receptor (hER) bioassay.

Combustion processes are known to produce organic micro-pollutants in the flue gas at concentrations ranging over several orders of magnitude. Some organic micro-pollutants are suspected of being pseudo-estrogens and as such they can affect the public health. In this study, the possible application of the yeast based human estrogen receptor (hER) bioassay to screen flue gas streams for the presence of estrogenic active micro-pollutants was explored. Specifically, the protocol was modified to allow the detection and quantification of the potential estrogenic active non-polar organic micro-pollutants contained in the flue gas matrix. The modified assay was calibrated using a model estrogenic compound (17-alpha-ethinylestradiol (EE2)) dissolved in methylene chloride at concentrations ranging from 3 ng l(-1) to 3000 ng l(-1). The effective concentration to elucidate a 50% response (EC50) was 87 ng l(-1) of equivalent dissolved in methylene chloride. Samples of methylene chloride used to trap non-polar micro-pollutants in flue gas from combustion of pine wood were found to clearly register estrogenic activity by the bioassay under certain conditions. The combustion tests were performed with pinewood alone and with pine wood in the presence of both Copper-naphthenate and copper(II)chloride at 600 degrees C and 1000 degrees C. These conditions must be considered as experimental rather than practical. Overall, the results suggest that, by means of this modified assay, it is possible and warranted to screen systematically for estrogens in flue gas combustion processes.

Intestinal transport of the lactokinin Ala-Leu-Pro-Met-His-Ile-Arg through a Caco-2 Bbe monolayer.

ACE inhibitory peptides are biologically active peptides that play a role in blood pressure regulation. When derived from food proteins during food processing or gastrointestinal digestion, these peptides could function as efficient agents in treating and preventing hypertension. However, in order to exert an antihypertensive effect by inhibition of the ACE enzyme, they have to reach the bloodstream intact. The aim of this research was to assess if the known ACE inhibitory peptide Ala-Leu-Pro-Met-His-Ile-Arg, derived from a tryptic digest of beta-lactoglobulin, could be absorbed through a Caco-2 Bbe cell monolayer in an Ussing chamber and reach the serosal side undegraded. Samples of the mucosal compartment showed high ACE inhibitory activity. No or only little ACE inhibitory activity was detected in the serosal compartment. However, when the serosal sample was concentrated three-fold, a substantial ACE inhibitory activity was registered. Concomitantly, HPLC and MS clearly showed the presence of Ala-Leu-Pro-Met-His-Ile-Arg in the mucosal compartment, whereas in the serosal compartment only MS was able to detect the heptapeptide. In conclusion. under the observed experimental conditions, the ACE inhibitory peptide Ala-Leu-Pro-Met-His-Ile-Arg was transported intact through the Caco-2 Bbe monolayer, but in concentrations too low to exert an ACE inhibitory activity.

Influence of copper-alloying of austenitic stainless steel on multi-species biofilm development.

AIMS: To investigate the bactericidal influence of copper-alloying of stainless steel on microbial colonization. METHODS AND RESULTS: Inhibition of bacterial adherence was investigated by monitoring (192 h) the development of a multi-species biofilm on Cu-alloyed (3.72 wt%) stainless steel in a natural surface water. During the first 120 h of exposure, lower numbers of viable bacteria in the water in contact with copper-containing steel relative to ordinary stainless steel were observed. Moreover, during the first 48 h of exposure, lower colony counts were found in the biofilm adhering to the Cu-alloyed steel. No lower colony or viable counts were found throughout the remainder of the experimental period. CONCLUSION: The presence of Cu in the steel matrix impedes the adhesion of micro-organisms during an initial period (48 h), while this bactericidal effect disappears after longer incubation periods. SIGNIFICANCE AND IMPACT OF THE STUDY: The application of Cu-alloyed stainless steels for bactericidal purposes should be restricted to regularly-cleaned surfaces.

The use of amino compounds for binding 2,4,6-trinitrotoluene in water.

Sites polluted with 2,4,6-trinitrotoluene (TNT) constitute a worldwide problem. In this work, chemical reactions for binding TNT to amino-compounds are proposed as an initial step for developing new remediation techniques to clean-up groundwater and soils contaminated with TNT. Indeed, addition of aniline and an amino acid-like cysteine caused a decrease in free TNT of 86% and 68-100%, respectively. Using 13C-NMR spectroscopy, it was shown that TNT chemically forms a Meisenheimer complex with cysteine and aniline in 1/1 (by vol.) H2O/d6-acetone.

Protective effect of the bile salt hydrolase-active Lactobacillus reuteri against bile salt cytotoxicity.

Bacterial bile salt hydrolysis is considered a risk factor for the development of colon cancer because of the risk of forming harmful secondary bile salts after an initial deconjugation step. In this study, the influence of enhanced bacterial bile salt transformation by the bile salt hydrolase-active Lactobacillus reuteri was studied in batch culture using the microbial suspension of the Simulator of the Human Intestinal Microbial Ecosystem; (SHIME), which was supplemented with oxgall at 5 g/l or 30 g/l. Changes in the fermentative capacity of the microbial ecosystem and the (geno)toxic properties of the SHIME supernatants were investigated. Increasing concentrations of oxgall inhibited the fermentation. Transient cell toxicity was observed for samples supplemented with 5 g oxgall/l, while samples with 30 g oxgall/l exhibited toxicity. The results of the haemolysis test suggest that the detrimental effects were probably due to the membrane-damaging effects of bile salts. In all cases, the adverse effects could be counteracted by the addition of 7.5 +/- 0.5 log10 CFU L. reuteri/ml. Plausible mechanisms for the protective properties of L. reuteri could involve a precipitation of the deconjugated bile salts and a physical binding of bile salts by the bacterium, thereby making the harmful bile salts less bioavailable.