Uncoupled Metabolism Stimulated by Chemical Uncoupler and Oxic-Settling-Anaerobic Combined Process to Reduce Excess Sludge Production

Evaluation of sludge reduction by an environmentally friendly chemical uncoupler in a pilot-scale anaerobic/anoxic/oxic process

An environmentally friendly chemical, tetrakis(hydroxymethyl)phosphonium sulfate (THPS), was used as a metabolic uncoupler to reduce sludge production in a pilot-scale anaerobic/anoxic/oxic process. The results show that the addition of THPS (1.08-1.86 mL/m(3) influent) in the sludge return section could reduce waste activated sludge by about 22.5 %, and decrease the sludge yield by about 14.7 % at the end of a run. At the same time, the addition of THPS slightly lowered the removal of chemical oxygen demand (COD), soluble COD and NH4 (+)-N, and slightly improved removal of total nitrogen. The effects of THPS addition on two characteristics of activated sludge in oxic tank are discussed in detail and the results suggest that the settleability of sludge was reduced by addition of THPS, while the specific oxygen uptake rate was increased. Molecular biology analysis shows that the addition of THPS had little effect on the microbial communities of sludge.

Comparing the effects of three pre-treatment disintegration techniques on aerobic sludge digestion: biodegradability enhancement and microbial community monitoring by PCR-DGGE

The objectives of this work were to compare and investigate the effect of three activated sludge disintegration processes before aerobic sludge digestion on 1) aerobic biodegradability enhancement and 2) microbial community evolution using the polymerase chain reaction-denaturant gel gradient electrophoresis (PCR-DGGE) technique. The comparison of three disintegration processes: thermal treatment (95 degrees C, 2h), sonication (100,000 kJ/kgTS) and ozonation (0.108 g O3/gTS) showed that the disintegration processes acted differently according to the composition of the soluble phase and to the DNA damage. Thermal treatment led to significant protein solubilization and to DNA modification. Sonication and ozonation resulted in similar soluble phase compositions and did not lead to any DNA modifications. During activated sludge aerobic digestion, intrinsic biodegradability enhancement was observed for thermal and ozone activated sludge pre-treatments. The analysis of the DGGE patterns at the end of aerobic digestion showed that population diversity was affected by both the aerobic digestion and the pre-treatment. The dissimilarity percentages measured at the end of aerobic digestion in the control sample and in the treated sludge were equal to 22, 25 and 20% for thermal treatment, sonication and ozonation respectively. This study indicated that PCR-DGGE could be a useful tool for the comparison of disintegration processes before and after aerobic digestion.

Yeast protein-surfactant complexes uncouple microbial electron transfer and increase transmembrane leak of protons

AIMS

To explore the combined effect of yeast proteins and surfactants on bacterial metabolism.

METHODS AND RESULTS

Protein-rich cell-free supernatant from heat-shocked yeast Saccharomyces cerevisiae was combined with certain synthetic surfactants. These blends affected the metabolism of a Polyseed inoculum of aerobic bacteria, accelerating CO(2) production and consumption of nutrients from a sterile nutrient broth solution, without a concomitant accumulation of biomass. It is suggested that in the presence of the yeast protein-surfactant complexes, bacterial electron transport is uncoupled from biomass accumulation. The 'uncoupling hypothesis' is supported by experiments with model membranes, in which the same complexes induced proton leak similar to standard chemical uncouplers, such as dinitrophenol, indicating that uncoupling may occur at the stage of generation of the transmembrane pH gradient as the driving force for ATP production.

CONCLUSIONS

Yeast protein-surfactant complexes behave as uncouplers of oxidative metabolism in bacteria and appear to do so by increasing proton permeability of membranes.

SIGNIFICANCE AND IMPACT OF THE STUDY

Yeast proteins may be of interest as nontoxic, environmentally benign and economically sound agents accelerating oxidative bacterial metabolism while uncoupling it from biomass accumulation. There are actual and potential implications in waste water/soil decontamination, degreasing and other environmental technologies.