RESUMO
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.
Assuntos
Reatores Biológicos , Poli-HidroxialcanoatosRESUMO
This study evaluates the trace metal composition and fractionation in sludge samples from anaerobic sewage treatment plants from six cities in Brazil. Ten metals were evaluated: Ni, Mn, Se, Co, Fe, Zn, K, Cu, Pb and Cr. Specific methanogenic activity of the sludge was also evaluated using acetic acid as the substrate. Among the essential trace metals for anaerobic digestion, Se, Zn, Ni and Fe were found at a high percentage in the organic matter/sulfide fraction in all sludge samples analyzed. These metals are less available for microorganisms than other metals, i.e., Co and K, which were present in significant amounts in the exchangeable and carbonate fractions. Cu is not typically reported as an essential metal but as a possible inhibitor. One of the samples showed a total Cu concentration close to the maximal amount allowed for reuse as fertilizer. Among the non-essential trace metals, Pb was present in all sludge samples at similar low concentrations and was primarily present in the residual fraction, demonstrating very low availability. Cr was found at low concentrations in all sludge samples, except for the sludge from STP5; interestingly, this sludge presented the lowest specific methanogenic activity, indicating possible Cr toxicity.
Assuntos
Metais Pesados/química , Esgotos/química , Brasil , Fracionamento QuímicoRESUMO
Due to the low trace metals concentration in the Olive Mill Solid Waste (OMSW), a proposed strategy to improve its biomethanization is the supplementation of key metals to enhance the microorganism activity. Among essential trace metals, cobalt has been reported to have a crucial role in anaerobic degradation. This study evaluates the effect of cobalt supplementation to OMSW, focusing on the connection between fractionation of cobalt in the system and the biological response. The highest biological responses was found in a range from 0.018 to 0.035mg/L of dissolved cobalt (0.24-0.65mg total cobalt/L), reaching improvements up to 23% and 30% in the methane production rate and the methane yield coefficient, respectively. It was found that the dissolved cobalt fraction is more accurately related with the biological response than the total cobalt. The total cobalt is distorted by the contribution of dissolved and non-dissolved inert fractions.