Ecological Processes Affecting Long-Term Eukaryote and Prokaryote Biofilm Persistence in Nitrogen Removal from Sewage.

The factors affecting long-term biofilm stability in sewage treatment remain largely unexplored. We therefore analyzed moving bed bioreactors (MBBRs) biofilm composition and function two years apart from four reactors in a nitrogen-removal sewage treatment plant. Multivariate ANOVA revealed a similar prokaryote microbiota composition on biofilm carriers from the same reactors, where reactor explained 84.6% of the variance, and year only explained 1.5%. Eukaryotes showed a less similar composition with reactor explaining 56.8% of the variance and year 9.4%. Downstream effects were also more pronounced for eukaryotes than prokaryotes. For prokaryotes, carbon source emerged as a potential factor for deterministic assembly. In the two reactors with methanol as a carbon source, the bacterial genus Methylotenera dominated, with M. versatilis as the most abundant species. M. versatilis showed large lineage diversity. The lineages mainly differed with respect to potential terminal electron acceptor usage (nitrogen oxides and oxygen). Searches in the Sequence Read Archive (SRA) database indicate a global distribution of the M. versatilis strains, with methane-containing sediments as the main habitat. Taken together, our results support long-term prokaryote biofilm persistence, while eukaryotes were less persistent.

A comparison of various bulking materials as a supporting matrix in composting blackwater solids from vacuum toilets.

This study discusses the influence of six bulking materials (peat, bark, oat husks, sawdust, food waste, and wheat bran) on the composting of blackwater solids (feces, urine and toilet paper) from low flush vacuum toilets (0.8 L/flush). The focus was on faecal indicator reduction, nutrient recycling, and carbon dioxide and methane emissions. In a composting experiment lasting 60 days, bulking materials were combined and mixed with blackwater solids, composted without stirring and with controlled aeration in a bench scale experiment. The bulking materials combination of oat husks, wheat bran and bark and of oat husks and wheat bran composted with blackwater solids showed the best results in terms of faecal indicator reduction (2.8 log10 reduction of Escherichia coli and 3.2 log10 reduction of faecal streptococci, respectively). Oat husks, bark and wheat bran combination had the smallest nutrient losses of 7.5% total nitrogen, 3.8% total phosphorus and 28% total potassium, while the highest accumulation in total phosphorus was 76.4% occurred in the mixture with oat husks and wheat bran. Peat and food waste improved the sorption of ammonia. The highest methane emissions (average 15.4%) were detected after 28 days of composting in the mixture with bran and food waste. Methane and carbon dioxide levels decreased in all the mixtures towards the end of composting indicating high organic matter degradation. Our findings show that a variety of natural and inexpensive materials can be used and adapted when composing blackwater in remote and sensitive areas.

Isovaleric acid in stool correlates with human depression.

OBJECTIVE: Human depression is a major burden, both on the individuals who suffer from the disease and on society at large. Traditionally, depression has been linked to psychological and biological causes, but there has been increasing interest in the gut-brain axis. In this regard, we have recently shown that specific bacteria are correlated with human depression, and we hypothesize that volatile fatty acids (VFAs) are mediators. METHODS: Here, we analyzed the direct correlation between VFAs, depression and cortisol in a cohort consisting of 34 depressed patients and 17 controls. RESULTS: We found statistically significant correlations between depression and the VFA isovaleric acid, as well as between isovaleric acid and cortisol. Furthermore, bacteria that previously have been identified as being correlated with depression were also correlated with isovaleric acid. Isovaleric acid showed a bimodal distribution in which the depressed patients were overrepresented in the high level group (P < 0.00005, binominal test). DISCUSSION: It has recently been shown that gut-derived VFAs can cross the blood-brain barrier, where isovaleric acid interferes with synaptic neurotransmitter release. The multiple correlation patterns, in addition to a potential mechanistic model, point towards a potential causal relationship between depression and isovaleric acid.

Methane production and energy evaluation of a farm scaled biogas plant in cold climate area.

The aim of this study was to investigate the specific methane production and the energy balance at a small farm scaled mesophilic biogas plant in a cold climate area. The main substrate was dairy cow slurry. Fish silage was used as co-substrate for two of the three test periods. Energy production, substrate volumes and thermal and electric energy consumption was monitored. Methane production depended mainly on type and amount of substrates, while energy consumption depended mainly on the ambient temperature. During summer the main thermal energy consumption was caused by heating of new substrates, while covering for thermal energy losses from digester and pipes required most thermal energy during winter. Fish silage gave a total energy production of 1623 k Wh/m(3), while the dairy cow slurry produced 79 k Wh/m(3) slurry. Total energy demand at the plant varied between 26.9% and 88.2% of the energy produced.

Bacterial removal and protozoan grazing in biological sand filters.

The objective of the study was to investigate the importance of protozoan predation as a biological removal mechanism in sand filters used for purification of bacteria from wastewater. Eleven sand filter columns were seeded with a high dose of wastewater (70 mm d(-1)) and a high concentration (10(8) colony forming units [CFU] mL(-1)) of Aeromonas hydrophila (American Type Culture Collection [ATCC] 14715) for a period of 30 d. Water samples from three filter outlets were analyzed for the concentration of A. hydrophila. In addition, one filter column was sacrificed each sampling day for the quantification of A. hydrophila, culturable bacteria (heterotrophic plate counts, HPC), total bacterial counts, and protozoa in the sand. The mean removal efficiency of A. hydrophila in the sand filter columns was 4.7 log units. The concentration of A. hydrophila in the sand filter effluent, however, had a clearly time-dependent pattern from high (log 6) and unstable concentrations to low and more stable levels (log 2). The removal efficiency of A. hydrophila correlated significantly (P = 0.0005, r2 = 0.6) with numbers of protozoa in the sand filters. Significantly higher (P < 0.05) concentrations of A. hydrophila were observed in sand filter effluents from columns treated with the protozoan inhibitor cycloheximide, compared with nontreated columns. Results from the present study show that protozoan grazing plays an important role as a bacterial removal mechanism in sand infiltration systems.

Retention and removal of pathogenic bacteria in wastewater percolating through porous media: a review.

Properly designed biological filters or infiltration systems have the capacity to significantly reduce effluent concentrations of pathogenic microorganisms in wastewater. The retention and elimination of microbial cells in biological wastewater filter systems is influenced by several factors. In this review, these factors are discussed. Immobilization of microbial cells moving through a porous media is influenced by mechanisms such as physical straining as well as adsorption to porous media. The grain size of porous media and bacterial cell size are important factors affecting the straining of bacteria, as are the hydraulic loading rate or the extent of clogging layer development in the filter. Adsorption of cells to the porous media is influenced by the content of organic matter, degree of biofilm development, and electrostatic attraction due to ion strength of the solution or electrostatic charges of cell- and particle surfaces. The rate of inactivation of pathogenic microorganisms, in adsorbed or liquid phases, has been shown to be affected by abiotic and biotic factors such as moisture content, pH, temperature, organic matter, bacterial species, predation, and antagonistic symbiosis between microorganisms in the system.

Removal of fish pathogenic bacteria in biological sand filters.

Documentation is required to evaluate the use of infiltration systems as an alternative method for removal of fish pathogenic bacteria in wastewater from fish-farms. This study was performed to investigate the removal of bacterial fish pathogens in biological sand filters. A second aim of the study was to evaluate the bacteria used in the study in order to find a suitable model organism for future experiments. Low-strength wastewater from an inland freshwater salmonid farm was intermittently loaded (70 mm/day in 24 doses) to filter columns containing either fine sand (d(10)=0.25) or coarse sand (d(10)=0.86). After a wastewater loading period of 10 weeks, separate sand columns were seeded with Yersinia ruckeri, Pseudomonas fluorescens, Aeromonas hydrophila and Aeromonas salmonicida subsp. salmonicida, respectively, for a period of 30 days. All the bacteria showed the same removal performance during the experiment, with a significantly lower removal in the beginning of the experiment (day 1-7) compared to mid- and late-phase (day 12-30). In mid- and late-phase the removal stabilized at a high level (>99.9%) for all the bacteria. The hydrophobic cell surface properties of the Aeromonads were higher than Ps. fluorescens and Y. ruckeri. This can possibly explain the significantly higher (P<0.05) removal efficiencies seen for A. hydrophila and A. salmonicida subsp. salmonicida compared to Y. ruckeri and Ps. fluorescens. Results were promising with regard to the use of low-cost infiltration systems as an alternative disinfection method for fish-farm wastewater. Following the criteria for a suitable model organism (removal efficiency, detection in filter effluent and die-off in storage tanks), Y. ruckeri was found to be a feasible model organism for use in future experiments.

Development and evaluation of a 16S ribosomal DNA array-based approach for describing complex microbial communities in ready-to-eat vegetable salads packed in a modified atmosphere.

There is a clear need for new approaches in the field of microbial community analyses, since the methods used can be severely biased. We have developed a DNA array-based method that targets 16S ribosomal DNA (rDNA), enabling the direct detection and quantification of microorganisms from complex communities without cultivation. The approach is based on the construction of specific probes from the 16S rDNA sequence data retrieved directly from the communities. The specificity of the assay is obtained through a combination of DNA array hybridization and enzymatic labeling of the constructed probes. Cultivation-dependent assays (enrichment and plating) and cultivation-independent assays (direct fluorescence microscopy and scanning electron microscopy) were used as reference methods in the development and evaluation of the method. The description of microbial communities in ready-to-eat vegetable salads in a modified atmosphere was used as the experimental model. Comparisons were made with respect to the effect of storage at different temperatures for up to 12 days and with respect to the geographic origin of the crisphead lettuce (Spanish or Norwegian), the main salad component. The conclusion drawn from the method comparison was that the DNA array-based method gave an accurate description of the microbial communities. Pseudomonas spp. dominated both of the salad batches, containing either Norwegian or Spanish lettuce, before storage and after storage at 4 degrees C. The Pseudomonas population also dominated the batch containing Norwegian lettuce after storage at 10 degrees C. On the contrary, Enterobacteriaceae and lactic acid bacteria dominated the microbial community of the batch containing Spanish lettuce after storage at 10 degrees C. In that batch, the Enterobacteriaceae also were abundant after storage at 4 degrees C as well as before storage. The practical implications of these results are that microbial communities in ready-to-eat vegetable salads can be diverse and that microbial composition is dependent both on the origin of the raw material and on the storage conditions.