Microbial ecology of simultaneous thermophilic microbial leaching and digestion of sewage sludge

Monitoring of bacterial communities during low temperature thermal treatment of activated sludge combining DNA phylochip and respirometry techniques

Sludge reduction is one of the major challenges in biological wastewater treatment. One approach is to increase the sludge degradation yield together with the biodegradation kinetics. Among the various sludge pretreatment strategies proposed, thermal pretreatment at around 65 °C was described as promising. The enhancement in the biodegradation activity due to the selection of thermophilic hydrolytic bacteria was proposed, but further experiments are needed to demonstrate the specific role of these bacteria. In this study, concentrated activated sludge grown at 20 °C was subjected to thermal treatment at 65 °C for different periods. The originality of the work relied on a polyphasic approach based on the correlation between kinetics (chemical oxygen demand, COD; mixed liquor suspended solids, MLSS), bacterial activity (respirometry) and bacterial community structure (phylochip monitoring) in order to characterize the mechanisms involved in the thermal reduction of sludge. The bacterial activity in the aeration basin decreased to a very low level when recycling sludge was treated at 65 °C from 13 to 60 h, but then, started to increase after 60 h. In parallel to these fluctuations in activity, a drastic shift occurred in the bacterial community structure with the selection of thermophilic bacteria (mainly related to genera Paenibacillus and Bacillus), which are known for their specific hydrolases.

Metabolic and genetic diversity of mesophilic and thermophilic bacteria isolated from composted municipal sludge on poly-epsilon-caprolactones

Thirty mesophilic and thermophilic bacteria were isolated from thermobiotically digested sewage sludge in culture medium supplemented with poly-epsilon-caprolactone (PCL). The ability of each purified isolate to degrade PCL and to produce polymer-degrading extracellular enzymes was assessed. Isolates were characterized based on random amplified polymorphic DNA (RAPD), 16S rDNA sequence-based phylogenetic affiliation and carbohydrate-based nutritional versatility. Mesophilic isolates with ability to degrade PCL were attributed to the genera Acinetobacter, Burkholderia, Pseudomonas, and Staphylococcus. Thermophilic isolates were members of the genus Bacillus. Despite the restricted phylogenetic and genotypic diversity observed for thermophiles, their metabolic versatility and wide range of growth temperatures suggest an important activity of these organisms during the whole composting process.

Reclassification of Sphaerobacter thermophilus from the subclass Sphaerobacteridae in the phylum Actinobacteria to the class Thermomicrobia (emended description) in the phylum Chloroflexi (emended description)

Sphaerobacter thermophilus was originally classified as the deepest branching member of the phylum Actinobacteria (high-G+C, Gram-positive bacteria) based on 16S rRNA gene comparative analysis. However, the analysis lacked suitable outgroups, and additional 16S rRNA gene sequences indicate that it is most closely related to Thermomicrobium roseum, which it also resembles phenotypically. Furthermore, both species are reproducibly affiliated with the phylum Chloroflexi (green non-sulfur bacteria), despite T. roseum currently being classified in its own phylum, the Thermomicrobia. Transfer of Sphaerobacter to the class Thermomicrobia, and transfer of the class Thermomicrobia to the phylum Chloroflexi, are proposed. Descriptions for the phylum Chloroflexi and the class Thermomicrobia are emended to reflect the proposed changes in classification.

Bioleaching of metals from anaerobic sewage sludge: effects of total solids, leaching microorganisms, and energy source

The effects of municipal sewage sludge solids concentration, leaching microorganisms (Thiobacillus thiooxidans or Thiobacillus ferrooxidans) and the addition of energy source (S0 or Fe(II)) on the bioleaching of metals from sewage sludge has been investigated under laboratory conditions using shake flasks. The results show that metal solubilization was better accomplished if additional energy source is supplemented to the microorganisms and that T. thiooxidans furnishes, in general, more adequate conditions for the bioleaching than T. ferrooxidans. At a total solids concentration of 70 g L-1 (originally present in the sludge) pH drop and ORP increase are attenuated, so metal solubilization is negatively affected. It was also demonstrated that if lead (Pb) solubilization is to be achieved, than a special combination of microorganism/energy source must be applied.