Beyond PHA: Stimulating intracellular accumulation of added-value compounds in mixed microbial cultures.

This review compiled and analyzed the operational conditions (dissolved oxygen, feast and famine ratio, sequential batch reactor cycle length, organic loading rate (OLR), pH, C/N, and temperature) established during the feast and famine culture strategy for the mixed microbial cultures (MMC) selection to understand how these variables could affect the synthesis of polyhydroxyalkanoates, polyglucose, triacylglycerides, levulinic acid and adipic acid from non-fermented substrates. According to the reported information, the dissolved oxygen has a greater impact on the type and amount of produced compound. In a lesser extent, the OLR and the cycle length were identified to have an impact on the accumulation of polyhydroxyalkanoates, whose accumulation was favored at lower OLR and longer cycle lengths. Thereby, the information of this work will allow the design of future strategies for the simultaneous accumulation of compounds of interest other than the polyhydroxyalkanoates or understand the operational conditions that would optimize the polyhydroxyalkanoates production.

Strategy for biological co-production of levulinic acid and polyhydroxyalkanoates by using mixed microbial cultures fed with synthetic hemicellulose hydrolysate.

Hemicellulose hydrolysates (HH), which could be an interesting carbon source to feed mixed microbial cultures (MMC) able to accumulate high value-added compounds. This research focused on the evaluation of a culture strategy to achieve the simultaneous biological production of Levulinic Acid (LA) and Polyhydroxyalcanoates (PHA) by MMC fed with a synthetic HH (SHH). The culture strategy involves the use of sequential batch reactors (SBR) to select microorganisms capable of producing LA and PHA. This work proved that the cultivation strategy used allowed the biological production of LA, reaching 37%w/w when the SHH was composed of 85% pentoses. In addition, the simultaneous biological production of LA and PHB was possible when the SHH was enriched with acetate (45% pentoses - 50% acetate). Finally, this study showed that the composition of the SHH impacts directly on the selected microorganism genus and the type and quantity of the value-added compounds obtained.

Modes of operation and pH control as enhancement factors for partial nitrification with oxygen transport limitation.

Sequencing batch (SBR) and continuous operation modes were applied using different pH control strategies to enhance partial nitrification in a biofilm rotating disk reactor. The pH control strategies were supervisory control in the range of 7.5-8.6 and fixed pH at 7.5 and 8.5, at dissolved oxygen (DO) concentrations in the range of 0.6-5.0 mg O(2)/L. Supervisory pH control enabled operation at a free ammonia concentration inhibitory to the nitrite-oxidizing bacteria (NOB) and an optimum for the ammonia-oxidizing bacteria (AOB). The results indicate that both operation modes were simultaneously controlled by oxygen transport and micro-kinetics (influenced by pH and NH(3)). The SBR mode with supervisory pH control presented more stable partial nitrification-nitrite accumulation >80% for 249 days than continuous operation. Molecular analyses showed that the SBR operation with supervisory pH control at low DO concentrations contributed to the enrichment of the AOB (>95%) over the NOB (<5%) populations. Therefore, it can be stated that a suitable pH control strategy can act as an enhancement factor of partial nitrification even under oxygen-transport-limiting conditions.

Nitrification-denitrification via nitrite accumulation for nitrogen removal from wastewaters.

The biological nitrification-denitrification process is used extensively for removal of ammonia nitrogen from wastewaters. Saves in aeration, organic matter (for denitrification) and surplus sludge are achievable if nitrite accumulation is possible in the nitrification step. In this paper, operational parameters were studied for each process for maximum nitrite accumulation in the nitrification step and nitrite adaptation in the denitrification step. Nitrite accumulation during nitrification can be controlled by the dissolved oxygen (DO) concentration, presenting a maximum of 65% at around 0.7 mg DO/L. Denitrification can be adapted to nitrite and the process is stable if nitrite in the reactor is keep low. The performance of a continuous stirred tank reactor (CSTR) and an up flow sludge blanket reactor (USB) were compared. Once the operational parameters were established, a CSTR for nitrification and an USB reactor for denitrification were operated in series for 25 days. The process was stable and a steady state was maintained for 20 days, and 93.5% of overall nitrogen removal was achieved in the nitrification-denitrification via the nitrite process.