Effect of dissolved gas on efficacy of sonochemical reactors for microbial cell disruption: Experimental and numerical analysis.

In the present work the effect of dissolved gases on the extent of ultrasonically induced microbial cell disruption has been explored using a mathematical model and it has been validated by experimental data from literature. Degassing experiments are carried out and a degassing kinetics model for horn type ultrasonic device is presented. An overall model combining hydrodynamic and kinetics of cell disruption for horn type reactor is then proposed. The model includes several important operational parameters such as stress generated by the cavity, cell wall strength, dissolved gas concentration, degassing due to sonication, acoustic streaming generated due to sonication and attenuation of ultrasound in water. Model basically realizes in categorizing the volume of sonochemical reactor as active cavitation zone (ACZ) and inactive cavitation zone (ICZ). All the transformations are seen to occur only in ACZ. The two regions, i.e. ACZ and ICZ are assumed to behave as two mixed flow reactor arranged in closed loop. Suggestions have been also made for efficient design and scale up of ultrasonic devices for microbial cell disruption. The same model can be extended for other applications like particle size reduction, nano particle synthesis, leaching, emulsification with the knowledge of critical rate controlling parameter.

Symbiotic algal bacterial wastewater treatment: effect of food to microorganism ratio and hydraulic retention time on the process performance.

Algal incorporation into the biomass is important in an innovative wastewater treatment that exploits the symbiosis between bacterial activated sludge and microalgae (Chlorella vulgaris sp. Hamburg). It allows a good and easy algae separation by means of clarification. The effect of process parameters food to microorganisms ratio (F/M) and hydraulic retention time (HRT) on the process performance, evaluated by settleability, microalgae incorporation to biomass and nutrient removal, was studied. HRT hinted at a significant influence in the growth rate of algae, while F/M turned out to be important for stability when algae are incorporated into the biomass. This parameter also affects the total nitrogen removal of the treatment. Stable flocs with incorporated algae and supernatants with low free swimming algae concentrations were obtained at high HRT and low F/M values.

Bioflocculent algal-bacterial biomass improves low-cost wastewater treatment.

An innovative technology for the biological treatment of wastewater in regions with sufficient solar radiation based on the simultaneous growth and degradation processes of algal and bacterial biomass is presented. The aim of the work is the improvement of pond technology through the formation of stable algae-bacteria aggregates, which a) permit a simple separation of the algal biomass by gravity sedimentation, b) enable a high removal efficiency for organic carbon and nutrients, and c) are independent in terms of oxygen provision through algal photosynthesis. Algae-bacteria aggregates could be developed with a suitable algal species (Chlorella vulgaris, Strain Hamburg) as a 'model organism' in a wastewater environment. The morphology of algal-bacterial flocs is similar to activated sludge flocs. They are stable and settle quickly. Floc size ranged between 400 and 800 microm. Results of our experiments with an artificially irradiated lab-scale system, operated in continuous flow mode, revealed that even at a relatively short hydraulic detention time of two days, a high elimination capacity of 9.96 g N m(-2) d(-1) and 0.87g Pm(-2) d(-1) can be achieved. Recent investigations confirmed that floc formation of unicellular algae and wastewater bacteria also could be developed and maintained in a pilot-scale system with a water depth of 0.5 m.

Improving chlorine disinfection of wastewater by ultrasound application .

The presence of soluble organic material as well as high concentrations of suspended matter in waters and wastewaters affect the efficiency when chlorine is used as disinfection agent. The objective of our work is to explore to which extend ultrasonic treatment can facilitate wastewater disinfection with chlorine in order to bring down doses of ecologically questionable chlorine and to shorten contact times. Sewage treatment plant (STP) effluents with different concentrations of suspended solids are exposed to sonication in combination with chlorine dosage. We observed that enhancement of chlorine efficiency is better for samples with higher concentrations of suspended matter. For samples with a TSS concentration of 50 mg/L chlorination efficiency (2 mg/L) can be doubled from 0.7 to 1.4 log when treated simultaneously with 20 kHz ultrasound for 5 minutes, i.e. levels of indicator organisms can be brought down to numbers that conventionally require far higher doses of chemical disinfectants. As subsequent sonication/chlorination does not have the same significant effect as simultaneous application of these two means, ultrasound does not just have a declumping effect; it seems that ultrasound application provokes a better chlorine dispersion in the aqueous media which improves the fast chemical and bactericidal reaction.

Ultrasonic waste activated sludge disintegration for improving anaerobic stabilization.

The pretreatment of waste activated sludge by ultrasonic disintegration was studied in order to improve the anaerobic sludge stabilization. The ultrasound frequency was varied within a range from 41 to 3217 kHz. The impact of different ultrasound intensities and treatment times was examined. Sludge disintegration was most significant at low frequencies. Low-frequency ultrasound creates large cavitation bubbles which upon collapse initiate powerful jet streams exerting strong shear forces in the liquid. The decreasing sludge disintegration efficiency observed at higher frequencies was attributed to smaller cavitation bubbles which do not allow the initiation of such strong shear forces. Short sonication times resulted in sludge floc deagglomeration without the destruction of bacteria cells. Longer sonication brought about the break-up of cell walls, the sludge solids were distintegrated and dissolved organic compounds were released. The anaerobic digestion of waste activated sludge following ultrasonic pretreatment causing microbial cell lysis was significantly improved. There was an increase in the volatile solids degradation as well as an increase in the biogas production. The increase in digestion efficiency was proportional to the degree of sludge disintegration. To a lesser degree the deagglomeration of sludge flocs also augmented the anaerobic volatile solids degradation.

Removal of chlorinated pollutants by a combination of ultrasound and biodegradation.

Chlorinated organic compounds are hazardous pollutants found in waste water, surface water, and ground water. Our study shows that a combination of ultrasonic pretreatment and biodegradation effectively removes the solvent chlorobenzene and the disinfectant 2,4-dichlorophenol, also reduces Adsorbable Organic Halogens (AOX) and Chemical Oxygen Demand (COD). In our experiments, the ultrasonic dechlorination was not influenced by the presence of other soluble organic compounds like acetate or glucose. Dechlorination of chlorobenzene by ultrasound did not lead to toxic or inhibiting reaction products. More than that, the ultrasonic pretreatment significantly reduced the toxicity of 2,4-dichlorophenol and biological activity was initiated after sonication. Residual organic pollutants after ultrasonic pretreatment were eliminated by biodegradation.