RESUMEN
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.
Asunto(s)
Metales Pesados/química , Aguas del Alcantarillado/química , Brasil , Fraccionamiento QuímicoRESUMEN
This research was aimed at studying oxidation processes, coliform inactivation effectiveness and disinfection byproducts (DBPs) associated with the disinfection of anaerobic sanitary wastewater effluent with ozone applied at doses of 5.0, 8.0 and 10.0mg O(3)L(-1) for contact times of 5, 10 and 15 min. The wastewater used in this research was generated by the wastewater treatment plant (WWTP), University of São Paulo - Brazil. The total coliform inactivation range was 2.00-4.06 log(10), and the inactivation range for Escherichia coli was 2.41-4.65 log(10). Mean chemical oxygen demand (COD) reductions were 37.6%, 48.8% and 42.4% for doses of 5.0, 8.0 and 10.0mg O(3)L(-1), respectively. Aldehyde formation varied with dosage only when the ozone dose was increased from 5.0 to 8.0mg O(3)L(-1) for acetaldehyde and from 5.0 to 8.0 and from 8.0 to 10.0mg O(3)L(-1) for glyoxal.