High-rate volatile fatty acid (VFA) production by a granular sludge process at low pH.

Volatile fatty acids (VFA) are proposed platform molecules for the production of basic chemicals and polymers from organic waste streams. In this study we developed a granular sludge process to produce VFA at high rate, yield and purity while minimizing potential operational costs. A lab-scale anaerobic sequencing batch reactor (ASBR) was fed with 10 g l(-1) glucose as model substrate. Inclusion of a short (2 min) settling phase before effluent discharge enabled effective granulation and very high volumetric conversion rates of 150-300 gCOD l(-1) d(-1) were observed during glucose conversion. The product spectrum remained similar at the tested pH range with acetate and butyrate as the main products, and a total VFA yield of 60-70% on chemical oxygen demand (COD) basis. The requirement for base addition for pH regulation could be reduced from 1.1 to 0.6 mol OH(-) (mol glucose)(-1) by lowering the pH from 5.5 to 4.5. Solids concentrations in the effluent were 0.6 ± 0.3 g l(-1) but could be reduced to 0.02 ± 0.01 g l(-1) by introduction of an additional settling period of 5 min. The efficient production of VFA at low pH with a virtually solid-free effluent increases the economic feasibility of waste-based chemicals and polymer production. Biotechnol.

Gallionella spp. in trickling filtration of subsurface aerated and natural groundwater.

The growth of iron-oxidizing bacteria, generally regarded as obligate microaerophilic at neutral pH conditions, has been reported in a wide range of environments, including engineered systems for drinking water production. This research focused on intensively aerated trickling filters treating deep anaerobic and subsurface aerated groundwater. The two systems, each comprising groundwater abstraction and trickling filtration, were monitored over a period of 9 months. Gallionella spp. were quantified by qPCR with specifically designed 16S rRNA primers and identified directly in the environmental samples using clone libraries with the same primers. In addition, enrichments in gradient tubes were evaluated after DGGE separation with general bacterial primers. No other iron-oxidizing bacteria than Gallionella spp. were found in the gradient tubes. qPCR provided an effective method to evaluate the growth of Gallionella spp. in these filter systems. The growth of Gallionella spp. was stimulated by subsurface aeration, but these bacteria hardly grew in the trickling filter. In the uninfluenced, natural anaerobic groundwater, Gallionella spp. were only present in low numbers, but they grew extensively in the trickling filter. Identification revealed that Gallionella spp., growing in the trickling filter were phylogenetically distinct from the species found growing during subsurface aeration, indicating that the different conditions in both systems selected for niche organisms, while inhibiting other groups. The results suggest a minor direct significance for inoculation of Gallionella spp. during filtration of subsurface aerated groundwater.

Phototrophic biofilms and their potential applications.

Phototrophic biofilms occur on surfaces exposed to light in a range of terrestrial and aquatic environments. Oxygenic phototrophs like diatoms, green algae, and cyanobacteria are the major primary producers that generate energy and reduce carbon dioxide, providing the system with organic substrates and oxygen. Photosynthesis fuels processes and conversions in the total biofilm community, including the metabolism of heterotrophic organisms. A matrix of polymeric substances secreted by phototrophs and heterotrophs enhances the attachment of the biofilm community. This review discusses the actual and potential applications of phototrophic biofilms in wastewater treatment, bioremediation, fish-feed production, biohydrogen production, and soil improvement.