Assessing the life-cycle sustainability of algae and bacteria-based wastewater treatment systems: High-rate algae pond and sequencing batch reactor.

High Rate Algae Ponds (HRAPs) are a promising technology for the treatment of municipal wastewater in locations with sufficient space and solar radiation. Algae-based processes do not require aeration, and thus have the potential to be less energy-intensive than activated sludge processes. We used a combination of LCA and LCCA analysis to evaluate the sustainability of HRAP systems, using data from the construction and operation of two demonstration-scale systems in Almería and Cádiz, Spain.

Denitrification as an NO sink.

The strong greenhouse gas nitrous oxide (NO) can be emitted from wastewater treatment systems as a byproduct of ammonium oxidation and as the last intermediate in the stepwise reduction of nitrate to N by denitrifying organisms. A potential strategy to reduce NO emissions would be to enhance the activity of NO reductase (NOS) in the denitrifying microbial community. A survey of existing literature on denitrification in wastewater treatment systems showed that the NO reducing capacity (V) exceeded the capacity to produce NO (V) by a factor of 2-10.

O versus NO respiration in a continuous microbial enrichment.

Despite its ecological importance, essential aspects of microbial NO reduction-such as the effect of O availability on the NO sink capacity of a community-remain unclear. We studied NO vs. aerobic respiration in a chemostat culture to explore (i) the extent to which simultaneous respiration of NO and O can occur, (ii) the mechanism governing the competition for NO and O, and (iii) how the NO-reducing capacity of a community is affected by dynamic oxic/anoxic shifts such as those that may occur during nitrogen removal in wastewater treatment systems.

Growth yield and selection of nosZ clade II types in a continuous enrichment culture of N O respiring bacteria.

Nitrous oxide (N O) reducing microorganisms may be key in the mitigation of N O emissions from managed ecosystems. However, there is still no clear understanding of the physiological and bioenergetic implications of microorganisms possessing either of the two N O reductase genes (nosZ), clade I and the more recently described clade II type nosZ. It has been suggested that organisms with nosZ clade II have higher growth yields and a lower affinity constant (K ) for N O.

Life on NO: deciphering the ecophysiology of NO respiring bacterial communities in a continuous culture.

Reduction of the greenhouse gas NO to N is a trait among denitrifying and non-denitrifying microorganisms having an NO reductase, encoded by nosZ. The nosZ phylogeny has two major clades, I and II, and physiological differences among organisms within the clades may affect NO emissions from ecosystems. To increase our understanding of the ecophysiology of NO reducers, we determined the thermodynamic growth efficiency of NO reduction and the selection of NO reducers under NO- or acetate-limiting conditions in a continuous culture enriched from a natural community with NO as electron acceptor and acetate as electron donor.

Exploring microbial N O reduction: a continuous enrichment in nitrogen free medium.

N O is a potent greenhouse gas, but also a potent electron acceptor. In search of thermodynamically favourable - yet undescribed - metabolic pathways involving N O reduction, we set up a continuous microbial enrichment, inoculated with activated sludge, fed with N O as the sole electron acceptor and acetate as an electron donor. A nitrogen-free mineral medium was used with the intention of creating a selective pressure towards organisms that would use N O directly as source of nitrogen for cell synthesis.

Dark fermentation: isolation and characterization of hydrogen-producing strains from sludges.

To improve bacterial hydrogen production, ten hydrogen-producing strains belonging to Clostridium spp. were isolated from various sludges under low vacuum. Hydrogenogenesis by dark fermentation in batch cultures of these strains was optimal at about 35 degrees C and an initial pH of 6.