Benjamin Jurcik

Progress and perspectives of sludge ozonation as a powerful pretreatment method for minimization of excess sludge production

The treatment and disposal of excess sludge represents a bottleneck in wastewater treatment plants (WWTP) worldwide, due to environmental, economic, social and legal factors. The ideal solution to the problem of sludge disposal is to combine sludge reduction with the removal of pollution at the source. This paper presents an overview of the potential of ozonation in sludge reduction. The full-scale application of ozonation in excess sludge reduction is presented. Improvements in the biodegradability of the ozonated sludge were confirmed. The introduction of ozonation into activated sludge did not significantly influence effluent quality but improved the settling properties of the sludge. An operation with a suitable sludge wasting ratio seems to be necessary to prevent accumulation of inorganic and inert particles for long-term operation. Sludge ozonation to reduce excess sludge production may be economical in WWTP which have high sludge disposal costs and operational problems such as sludge foaming and bulking. The recommended ozone dose ranges from 0.03 to 0.05 g O(3)/g TSS, which is appropriate to achieve a balance between sludge reduction efficiency and cost. An effort to design and optimize an economic sludge reduction process is necessary.

Enhanced sludge solubilization by microbubble ozonation

A microbubble ozonation process for enhancing sludge solubilization was proposed and its performance was evaluated in comparison to a conventional ozone bubble contactor. Microbubbles are defined as bubbles with diameters less than several tens of micrometers. Previous studies have demonstrated that microbubbles could accelerate the formation of hydroxyl radicals and hence improve the ozonation of dyestuff wastewater. The results of this study showed that microbubble ozonation was effective in increasing ozone utilization and improving sludge solubilization. For a contact time of 80 min, an ozone utilization efficiency of more than 99% was obtained using the microbubble system, while it gradually decreased from 94% to 72% for the bubble contactor. The rate of microbial inactivation was obviously faster in the microbubble system. At an ozone dose of 0.02g O(3)g(-1) TSS, about 80% of microorganisms were inactivated in the microbubble system, compared with about 50% inactivation for the bubble contactor. Compared to the bubble contactor, more than two times of COD and total nitrogen, and eight times of total phosphorus content were released from the sludge into the supernatant by using the microbubble system at the same ozone dosage. The application of microbubble technology in ozonation processes may provide an effective and low cost approach for sludge reduction.

Systematic analysis of biochemical performance and the microbial community of an activated sludge process using ozone-treated sludge for sludge reduction

Two lab-scale bioreactors (reactors 1 and 2) were employed to examine the changes in biological performance and the microbial community of an activated sludge process fed with ozonated sludge for sludge reduction. During the 122 d operation, the microbial activities and community in the two reactors were evaluated. The results indicated that, when compared with the conventional reactor (reactor 1), the reactor that was fed with the ozonated sludge (reactor 2) showed good removal of COD, TN and cell debris, without formation of any excess sludge. In addition, the protease activity and intracellular ATP concentration of reactor 2 were increased when compared to reactor 1, indicating that reactor 2 had a better ability to digest proteins and cell debris. DGGE analysis revealed that the bacterial communities in the two reactors were different, and that the dissimilarity of the bacterial population was nearly 40%. Reactor 2 also contained more protozoa and metazoa, which could graze on the ozone-treated sludge debris directly.

On the shape of impactor efficiency curves

The effect of impactor stage geometry on impactor collection efficiency curves is explored numerically. It is found that the geometry of the impaction stage where the gas is accelerated does not affect the 50% cut size but has a strong effect on the sharpness and shape of the efficiency curve. This phenomenon is explained from the aerodynamic focusing effect of the particles in the nozzle (gas acceleration) section. The flat-plate orifice configuration, commonly used in cascade impactors, tends to focus particles closer to the centerline than the angled nozzle. When the real nozzle configuration is used, the prediction shows a characteristic S shape, in good agreement with the experimental results in the literature.

Changes in biomass activity and characteristics of activated sludge exposed to low ozone dose.

In this paper, the response mechanism of activated sludge exposed to low-dose ozone at less than 20mgO(3)g(-1) total suspended solids (TSS) was studied by analyzing the changes in sludge activity and the evolution of C, N, P and metals from sludge following ozonation. The intracellular ATP concentration was not affected at less than 5mgO(3)g(-1) TSS and thereafter decreased rapidly to around 60% when the ozone dose increased to 20mgO(3)g(-1) TSS. Similarly, the efficiency of sludge solubilization initially changed a little and then increased rapidly to around 30% at an ozone dose of 20mgO(3)g(-1) TSS. However, the activities of superoxide dismutase and protease decreased immediately upon exposure to ozone. These findings indicate that ozone firstly destroys the floc, leading to the disruption of the compact aggregates, which does not affect cells viability but induces a decrease in enzyme activities. Ozone then attacks the bacterial cells of the sludge, causing a decrease in cells viability. During ozonation, the content of carbon, nitrogen and phosphorus in the sludge matrix decreased, while the content of these elements in the micro-solids and supernatant gradually increased. Most of the released metals from the sludge matrix were found in the micro-solids.

The modelling of particle resuspension in turbulent flow

Abstract The resuspension of small particles by a flowing gas occurs over time periods much longer than the time required to obtain fully developed flow. In this work an analysis of particle shedding is presented and compared with experimental data. The model used here is compared with other published models (e.g. Wen and Kasper, 1989 , Reeks et al. 1988 ) The effect of the adhesion and removal force distributions on the particle shedding rate and the evolution of the adhesion force distribution through time is examined. For a wide range of adhesion and removal force distributions the experimentally observed long time behavior is found.

Improvement of multi jet low pressure impactor for high collection efficiency of UF5 in the molecular laser isotope separation of uranium

A numerical and experimental study for the collection of photo-produced UF5 particles was performed for the low pressure impactors which have different design factors at typical flow conditions (upstream pressure of the impactor = 10–15 Torr, pressure ratio of downstream to upstream of the impactor, PdownPup = 0.2–0.5) in the molecular laser isotope separation of uranium at RIKEN (RIMLIS). Smaller HW ratios (the distance between the impactor orifice exit and the impaction plate, H, divided by the orifice diameter of the impactor, W) and the smaller PdownPup were found to be preferable to obtain a higher collection efficiency from both numerical and experimental investigations. In addition it was experimentally demonstrated that the use of a 16 μm laser system for the selective reaction of 235UF6 to form 235UF5 was not relevant for the study of the collection of UF5 particles. So, we used an ultraviolet laser system (fourth harmonic YAG laser (266 nm) and an excimer laser (KrF, 248 nm)) which was more convenient to cope with various operating conditions. The collection efficiency was found to increase with the initial concentration of UF5 molecules produced. Applying the improved impactor stage, we obtained a collection efficiency which was approximately 10 times higher than that of our previous work. Higher collection efficiencies of photo-produced UF5 particles enriched in 235U reduce the enrichment cost.

Sn–Ag–Cu Soldering Reliability as Influenced by Process Atmosphere

To develop an optimal soldering process of Sn-Ag-Cu soldered joints, the influences of atmosphere and cooling speed during reflow treatment on soldering reliability have been examined through the use of Sn plated chip components and of Pd plated small outline packages (SOPs) on a printed circuit board (PCB) soldered with Sn-3wt.%Ag-0.5wt.%Cu, Sn-3.8wt.%Ag-0.75wt.%Cu and Sn-4wt.%Ag-0.9wt.%Cu solder pastes under air or N2 atmospheres. In the case of chip component joints, the solder compositions, cooling speed and atmospheres during reflow treatment slightly affect the dendritic microstructure. Those parameters rarely affect the wetting behavior and mechanical properties. In the case of SOP joints, however, the atmospheres during reflow treatment and fluxes strongly affect the appearances of fillet surfaces structure. Despite the types of solder fluxes, N2 process atmosphere obviously improved wettability of solder on lead-frame of the SOP.

Evaluation of biodegradation of soluble and particulate matter produced during sewage sludge ozonation by a combination of chemical and microbial approaches

In this study a batch aerobic reactor fed with the soluble and particulate matter produced during sludge ozonation (reactor 1) is proposed and its performance was evaluated in comparison to a reactor fed with municipal wastewater (reactor 2) to investigate the biodegradation properties of the ozone-treated sludge. During long-term operation of nearly 7 months, the efficiency of reactor 1 was preserved, although there was a 5% decrease in total COD elimination, compared with reactor 2. The released proteins and polysaccharides during sludge ozonation were effectively decomposed. The volatile suspended solid (VSS)/total suspended solid (TSS) ratio and the oxygen uptake rate in reactor 1 were lower than those in reactor 2 by 19% and 27%, respectively. However, the protease activity per gram of volatile suspended solids and the ammonium oxidation rate in reactor 1 were higher. The yields of sludge in reactor 1 fed with ozonated sludge were lower which implied that the cryptic growth using the organic autochthonous substrate might produce reduced biomass yields, which would decrease sludge production. The debris-like substances observed from scanning electron microscope (SEM) images and the functional groups associated with calcite were only found in reactor 1 by FT-IR analysis, which implies that some of the inert or inorganic substances from sludge ozonation were accumulated in the reactor.

Sn-Ag-Cu Soldering Reliability Influenced by Process Atmosphere

To develop an optimal surface mount reflow soldering process with Sn-Ag-Cu, the influences of atmosphere and cooling speed on soldering reliability have been examined by using Sn plated chip components and of Pd plated small outline packages (SOPs) on a printed circuit board (PCB). Typical three Sn-Ag-Cu alloy pastes, i.e., Sn-3.0wt%Ag-0.5wt%Cu, Sn-3.8wt%Ag-0.75wt%Cu, and Sn-4.0wt%Ag-0.9wt%Cu, were used for reflow soldering in air or N2 atmospheres. In the case of chip component joints, the solder compositions, cooling speed, and atmospheres during reflow treatment slightly affect the dendritic microstructure of the solder fillets. In contrast, these parameters rarely affect the solder wettability both on boards/components and shear strengths of the solder joints. In the case of the SOP joints, however, the atmospheres in reflow treatment and the fluxes strongly affect the appearances of solder fillet surfaces structure. Despite the types of solder fluxes, N2 process atmosphere obviously improved wettability of the solders on the lead-frames of the SOP. Moreover, the scatter in shear strengths becomes smaller and the wetting of solders on the lead-frames becomes stabler in N2 atmosphere than in air atmosphere.