A further examination of heavy metal inhibition of gas production by thermophilic anaerobic sludges.
Mesophilic anaerobic digestion is a well established method for stabilising municipal sewage sludges. However, digestion in the thermophilic range is very restricted. The main reason for this has been the imbalance between the energy produced in the form of biogas and the energy required to maintain the temperature of a thermophilic system. It has been shown recently that an energy-positive process can be achieved using thickened sludges as the feedstock and, therefore, thermophilic digestion must be considered as a potentially attractive process for sludge stabilisation. However, before it can properly be offered as an alternative technology, the effect of toxic materials must be known. Currently, there is little information about the effect that known toxic agents can have on the microbial flora of a thermophilic sludge. This paper examines the toxicity (measured in terms of gas inhibition) of heavy metals, both individually and in combinations, on the sludge produced by a laboratory-scale digester (10 litres) operating at 55 degrees C with a solids retention time of 20 days. The metals used were zinc, lead, nickel, copper and cadmium and the gas inhibition studies were done in small (500 ml) flasks so that the gas production could be monitored precisely. Statistical analysis of the results showed that a model, developed previously to describe the toxicity of a range of compounds to mesophilic systems, was applicable to heavy metals and thermophilic sludges.
Tomlin
C
C
Department of Civil Engineering, University of Birmingham, Great Britain.
Forster
C F
CF
D000693:Anaerobiosis; D004734:Energy Metabolism; D006863:Hydrogen-Ion Concentration; D008670:Metals / Q000494:pharmacology*; D012722:Sewage; D012988:Soil Microbiology
D008670:Metals; D012722:Sewage