The incorporation of microbial diversity in design would ideally require predictive theory that would relate operational parameters to the numbers and distribution of taxa. Resource ratio-theory (RRT) might be one such theory. Based on Monod kinetics, it explains diversity in function of resource-ratio and richness. However, to be usable in biological engineered system, the growth parameters of all the bacteria under consideration and the resource supply and diffusion parameters for all the relevant nutrients should be determined. This is challenging, but plausible, at least for low diversity groups with simple resource requirements like the ammonia oxidizing bacteria (AOB). One of the major successes of RRT was its ability to explain the ‘paradox of enrichment’ which states that diversity first increases and then decreases with resource richness. Here, we demonstrate that this pattern can be seen in lab-scaleactivated sludge reactors and parallel simulations that incorporate the principles of RRT in a floc-based system. High and low ammonia and oxygen were supplied to continuous flow bioreactors with resource conditions correlating with the composition and diversity of resident AOB communities based on AOB 16S rDNA clone libraries. Neither the experimental work nor the simulations are definitive proof for the application of RRT in this context. However, it is sufficient evidence that such approach might work and justify a more rigorous investigation.

Interest is growing in the production of biohydrogen from algae through dark fermentation, as alternative to fossil fuels. However, one of the limiting steps of biohydrogen production is the conversion of polymeric carbohydrates into monomeric sugars. Thus, physical, chemical and biological pretreatments are usually employed in order to facilitate carbohydrates de-polymerization and enhancing biohydrogen production from algae. Considering the overall process, biohydrogen production through dark fermentation leads generally to negative net energy balances of the difference between the energy produced as biohydrogen and the direct ones (heat and electricity) consumed to produce it. Thus, to make the overall process economically feasible, dark fermentation of algae must be integrated in a biorefinery approach, where the outlets are valorized into bioenergy or value added biomolecules.The present study reviews recent findings on pretreatments and biohydrogen production through dark fermentation of algae looking at the perspectives of integrating side streams of dark fermentation from algal biomass, according to a biorefinery approach.

In this work we evaluated the effect of a perturbation on nitrification performance in a wastewater treatment plant (WWTP) treating urban and saline thermal bath wastewater, which regularly occurred during summer months. We wanted to find out if this related to changes in the ammonia oxidizing communities. The bacterial and ammonia-oxidizing bacterial (AOB) community from three different basins of the WWTP were evaluated using PCR-DGGE and cloning and sequencing of 16S rRNA gene fragments, over a six month survey. Both eubacterial and AOB communities underwent continuous change over time, with a particularly prominent shift between the third and fourth month of monitoring for eubacteria and the fourth month and fifth month for AOB. At the same time, reduction of nitrification performance was observed in the WWTP. The AOB community in the activated sludge was dominated by clones with high 16S rRNA sequence identity to halophilic-halotolerant organisms from the Nitrosomonas oligotrohpa and Nitrosomonas marina clusters. A significant correlation (R = 0.97) was detected between the structure of the AOB community and environmental parameters, indicating that the AOB community structure changed in line with the environmental changes that took place over the sampling period. This study reports a clear association of microbial community dynamics (strongly correlated to salinity, temperature, and dissolved oxygen) to nitrification performance. Particularly, ammonia-oxidizing bacteria are severely affected by drastic changes in operational conditions, with direct consequences on WWTP performance.

In order to evaluate if the reuse of food industry treated wastewater is compatible for irrigation of food crops, without increased health risk, in the present study a cropping system, in which ground water and treated wastewater were used for irrigation of tomato and broccoli, during consecutive crop seasons was monitored. Water, crop environment and final products were monitored for microbial indicators and pathogenic bacteria, by conventional and molecular methods. The microbial quality of the irrigation waters influenced sporadically the presence of microbial indicators in soil. No water sample was found positive for pathogenic bacteria, independently from the source. Salmonella spp. and Listeria monocytogenes were detected in soil samples, independently from the irrigation water source. No pathogen was found to contaminate tomato plants, while Listeria monocytogenes and E. coli O157:H7 were detected on broccoli plant, but when final produce were harvested, no pathogen was detected on edible part. The level of microbial indicators and detection of pathogenic bacteria in field and plant was not dependent upon wastewater used. Our results, suggest that reuse of food industry wastewater for irrigation of agricultural crop can be applied without significant increase of potential health risk related to microbial quality.