Cobalt toxicity in anaerobic granular sludge: influence of chemical speciation

Abstract

The influence of cobalt speciation on the toxicity of cobalt to methylotrophic methanogenesis in anaerobic granular sludge was investigated. The cobalt speciation was studied with three different media that contained varying concentrations of complexing ligands [carbonates, phosphates and ethylenediaminetetraacetic acid (EDTA)]. Three fractions (nominal added, dissolved and free) of cobalt were determined in the liquid media and were correlated with data from batch toxicity experiments. The average concentration of cobalt that was required for 50% inhibition of methanogenic activity (IC 50 ) for free Co 2? in the three sets of measurements was 13 lmol/L with a standard deviation of 22% and a similarity of 72% between the data obtained in the three different media for the range of cobalt concentrations investigated. The standard deviation of the IC 50 for the other two fractions was much higher, i.e. 85 and 144% for the added cobalt and dissolved cobalt, respectively, and the similarity was almost 0% for both fractions. Complexation (and precipitation) with EDTA, phosphates and carbonates was shown to decrease the toxicity of cobalt on methylotrophic methanogenesis. The free cobalt concentration is proposed to be the key parameter to correlate with cobalt toxicity. Thus, the toxicity of cobalt to granular sludge can be estimated based on the equilibrium-free cobalt concentration.

Effect of sorption kinetics on nickel toxicity in methanogenic granular sludge

“…The Hormesis model was used to fit the experimental data describing nickel toxicity as described by Bartacek et al [15]. The parameters of the model were calculated in accordance with Schabenberger et al [16]:…”

Effects of heavy metals as stress factors on anaerobic digestion processes and biogas production from biomass

“…It was also suspected that the precipitation-dissolution kinetics of metal sulphides might have played an important role in the bioavailability of these compounds. Bartacek et al (2008) have investigated the influence of cobalt speciation on the toxicity of cobalt to methylotrophic methanogenesis in anaerobic granular sludge. The cobalt speciation had been studied with three different media that contained varying concentrations of complexing ligands namely carbonates, phosphates and ethylenediaminetetraacetic acid (EDTA).…”

Supplementation of cobalt to UASB reactors by pulse dosing: CoCl2 versus CoEDTA2− pulses

“…This is due to the cobalt dependence of the enzymatic system of acetogenesis [25]. Alternatively, toxic effects of cobalt suppress the methylotrophic methanogenic population, the IC 50 of free cobalt amounted to 13 M for methylotrophic methanogenic anaerobic granular sludge [4]. Therefore, cobalt addition has to be done prior to the VFA accumulation in the effluent [1,3].…”

“…This leads to a decrease in the specific methanogenic activity (SMA) of the sludge, resulting in methanol accumulation, and later acidification and ultimately complete process failure of methanol-fed UASB reactors [1]. On the other hand, too high influent cobalt concentrations can result in acetate build-up due to stimulated acetogenic activity [2] or can even induce cobalt toxicity [4]. Thus, appropriate cobalt dosing strategies need to be developed that balance the nutritional requirements and the deterioration of bioreactor operation.…”