Characterisation and optimisation of individual wastewater treatment systems.

Onsite individual wastewater treatment systems can provide a financially attractive alternative to a sewer connection in locations far from the existing sewer network. These systems are, however, relatively new, and practical experiences, especially long-term field studies, are lacking. Therefore, a thorough study of two compact biofilm-based, aerobic onsite systems, both of five population equivalents, was started in 2001. The assessment of the treatment performance of these systems, as well as the maintenance requirements and the characterisation of the feed are of great importance for the better understanding of the systems in order to optimise their design and performance. This paper presents an evaluation and discussion of the start-up and a starvation period of the two studied systems, followed by a characterisation of the incoming wastewater using activated sludge respirometry experiments in the context of the assessment and improvement of the denitrification process. Individual wastewater treatment systems are characterised by a rather long start-up period of 70-120 days. An important characteristic during the start-up is the nitrite peak, which indicates the initiation of the nitrification process. The respirometric experiments reveal that the failing denitrification is probably caused by an insufficient amount of readily biodegradable COD in the influent.

Coupling and uncoupling of triglyceride and beta-carotene production by Dunaliella salina under nitrogen limitation and starvation.

BACKGROUND: Nitrogen starvation and limitation are known to induce important physiological changes especially in lipid metabolism of microalgae (triglycerides, membrane lipids, beta-carotene, etc.). Although little information is available for Dunaliella salina, it is a promising microalga for biofuel production and biotechnological applications due to its ability to accumulate lipid together with beta-carotene. RESULTS: Batch and chemostat experiments with various degrees of nitrogen limitation, ranging from starvation to nitrogen-replete conditions, were carried out to study carbon storage dynamics (total carbon, lipids, and beta-carotene) in steady state cultures of D. salina. A new protocol was developed in order to manage the very high beta-carotene concentrations and to more accurately separate and quantify beta-carotene and triglycerides by chromatography. Biomass evolution was appropriately described by the Droop model on the basis of the nitrogen quota dynamics. CONCLUSIONS: Triglycerides and beta-carotene were both strongly anti-correlated with nitrogen quota highlighting their carbon sink function in nitrogen depletion conditions. Moreover, these two valuable molecules were correlated each other for nitrogen replete conditions or moderated nitrogen limitations (N:C ratio higher than 0.04). Under nitrogen starvation, i.e., for very low N:C ratio, the dynamic revealed, for the first time, uncoupled part (higher triglyceride accumulation than beta-carotene), possibly because of shortage in key proteins involved in the stabilization of lipid droplets. This study motivates the accurate control of the microalgal nitrogen quota in order to optimize lipid productivity.