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A special group of microorganisms, which are called ammonia oxidizing bacteria (AOB), is capable to reduce ammonia-nitrogen from the ecosystem. However, this bacterium is slow growing and has a low yield capacity. Hence, the objective of this research was to grow the AOB using a support medium in the form of biofilters to reduce the ammonia-nitrogen. The enrichment cultures of this AOB were performed from the inoculum of common soil and effluent from fishpond. The experiment was conducted using two sets of flasks labelled Medium A and Medium B, respectively. Each medium contained three flasks of which Flasks 1 and 2 were inoculated with the common soil and effluent from a fishpond. Flask 3 was the control, which contained neither soil nor effluent from any fishpond or bio-filter. Then the ammonia-nitrogen and the formation of nitrite-nitrogen were measured. The results showed that the enrichment culture of the effluent of the fishpond had achieved a high formation of nitrite-nitrogen (450 µg/L) in comparison with the enrichment culture of the soil (360 µg/L). A high reduction of ammonia-nitrogen (50%) was obtained from the fishpond culture rather than the soil (40%). Secondly, a higher reduction of ammonia-nitrogen and production of nitrite-nitrogen were found in the bio-filter flasks against the controls (without bio-filter). In summary, it can be concluded that the bio-filter can be a reliable support to grow AOB.

Several factors have the potential to influence microalgae growth. In the present study, nitrogen concentration and light intensity were evaluated in order to obtain high biomass production and high phycoerythrin accumulation from Porphyridium purpureum. The range of nitrogen concentrations evaluated in the culture medium was 0.075−0.450 g L−1 and light intensities ranged between 30 and 100 μmol m−2 s−1. Surprisingly, low nitrogen concentration and high light intensity resulted in high biomass yield and phycoerythrin accumulation. Thus, the best biomass productivity (0.386 g L−1 d−1) and biomass yield (5.403 g L−1) were achieved with NaNO3 at 0.075 g L−1 and 100 μmol m−2 s−1. In addition, phycoerythrin production was improved to obtain a concentration of 14.66 mg L−1 (2.71 mg g−1 of phycoerythrin over dry weight). The results of the present study indicate that it is possible to significantly improve biomass and pigment production in Porphyridium purpureum by limiting nitrogen concentration and light intensity.

This work reports on the use of a bench-scale chemostat (CSTR) in continuous mode and of a pilot-scale membrane bioreactor (MBR) in fed-batch mode to intensively produce acetic and butyric acids using C. butyricum grown on synthetic media. These studies were then used to perform a cost estimation study of the MBR system to assess the potential economic impact of this proposed methodology, regarding the production of carboxylic acids. The MBR system was found to be highly productive, reaching 37.88 g L−1 h−1 of acetic and 14.44 g L−1 h−1 of volumetric cell productivity, favoring acetic acid production over butyric acid at a ratio of 3 moles to 1. The cost of preparation and production of carboxylic acid using this system was found to be 0.0062 £PS/kg with up to 99% carbon recovery.