A. M. Saatçi

Monitoring of population shifts in an enriched nitrifying system under gradually increased cadmium loading

The changes in nitrifying bacterial population under cadmium loading were monitored and evaluated in a laboratory scale continuous-flow enriched nitrification system. For this purpose, the following molecular microbiological methods were used: slot-blot hybridization, denaturing gradient gel electrophoresis (DGGE), real-time PCR followed by melting curve analysis, cloning and sequence analysis. The initial cadmium concentration was incrementally increased from 1 to 10mg/l which led to a drop in ammonia removal efficiency from 99 to 10%. Inhibition was recovered when cadmium loading was stopped. During the second application of cadmium, nitrifying population became more tolerant. Even at 15mg/l Cd, only a minor inhibition was observed. To investigate the variations in ammonia and nitrite oxidizing bacteria populations in a period of 483 days, ammonia monooxygenase (amoA) and 16S rRNA genes-based molecular techniques were used. An obvious shift was experienced in the diversity of ammonia oxidizers after the first application of 10mg/l Cd. Metal-tolerant ammonia oxidizing species became dominant and the microbial diversity sharply shifted from Nitrosomonas and Nitrosococcus sp. to Nitrosospira sp. which were observed to tolerate higher cadmium loadings. This result indicated that the extent of nitrification inhibition was not only related to the metal concentration and quantity of microorganisms but also depended on the type of species.

Sequential Oxidation of Humic Acids by Ozonation and Photocatalysis

In this study, humic acids, the natural polymerized organic compounds which are responsible for the formation of disinfection by-products such as haloacetic acids and trihalomethanes upon chlorination, are oxidized in a sequential system incorporating ozonation and photocatalysis. Titanium dioxide is used as photocatalyst in the photocatalytic oxidation phase. Humic acid degradation kinetics is evaluated both for ozonation and photocatalysis. The Freundlich adsorption model is used for defining the adsorption characteristics of humic acid solutions on the photocatalyst after the ozonation step. The Langmuir-Hinshelwood model is also studied for explaining the adsorptive and photocatalytic removal of humic acids.

DOMESTIC SEWAGE AS MIXING WATER IN CONCRETE

Reviews of the characteristics of domestic sewage and refinement in its composition upon biological treatment imply its suitability for use in concrete technology. A typical domestic sewage was characterized and used in this study as mixing water. Setting time, air content, specific gravity, and strength tests were performed on cement paste, mortar, and concrete specimens made with distilled water showed that untreated domestic sewage increases the initial setting time, entrains air, and reduces the strength of mortar and concrete, and therefore is not recommended for use in concrete technology. However, average biologically treated domestic wastewater is inistinguishable from distilled water when used as mixing water.

Inactivation of coliform bacteria in Black Sea waters due to solar radiation

The effects of solar radiation and temperature on bacterial die-off rates in Black Sea coastal waters using total coliform as the indicator organism were studied. Coliform die-off experiments were carried out in seawater samples collected along the coastline. The experiments were conducted in beakers filled with seawater that were kept at constant temperatures and exposed to solar radiation. The membrane filter technique was used for the coliform analysis. Temperature ranging between 9 and 26 degrees C and solar radiation between 20 and 60 cal/cm(2) h were tested. Experiments in the dark were also conducted to isolate the effect of solar radiation from the other factors and, furthermore, to determine the effect of temperature on bacterial die-off. The solar radiation was found to be the most significant factor affecting the mortality of coliform bacteria.

Effect of partial oxidation by ozonation on the photocatalytic degradation of humic acids

In this study humic acids, which are known to be a heterogeneous group of organic macro- molecules found in natural waters, were oxidized using ozonation and photocatalysis in a sequential system. Ozonation was employed for achieving partial oxidation of humic acids prior to photocatalytic oxidation. Degradation of humic acid was explained by using pseudo first order reaction rate model based on UV-vis measurements. An improvement was achieved in the photocatalytic degradation rates with respect to the degree of pre-oxidation by ozonation. Due to the surface oriented nature of photocatalysis, adsorption char- acteristics of partially oxidized humic acid samples on TiO2 photocatalyst were evaluated by the application of the Freundlich adsorption model. The photocatalytic degradation rates did not correlate well with the dark adsorption characteristics of the pre-ozonated as well as untreated humic acid samples.

Investigation of nitrogen converters in membrane bioreactor

In this study, the activity and diversity of nitrogen converters, ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB), ammonia-oxidizing archaea (AOA) and Anammox bacteria in a pilot-scale membrane bioreactor (MBR) were investigated and monitored using amoA and 16S rDNA-based molecular tools. The pilot-scale MBR (100 m3/day) was located inside the full-scale Pasakoy Advanced Wastewater Treatment Plant (WWTP), and operated for approximately 5 months without sludge purge. During 148 days of operation, volatile suspended solids (VSS) concentration increased from 2,454 mg/L to 10,855 mg/L and the average organic carbon and ammonia nitrogen removal rates were 92% and 99%, respectively. Real-time PCR results indicated that the fraction of AOB increased from 2.94% to 4.05% when VSS concentration reached to 3,750 mg/L throughout 148 days of operation. At higher VSS concentrations, the fraction of AOB declined gradually to 1.15% while the fraction of Nitrospira population was varied between 8.23 and 13.01%. However, significant change or any positive and negative correlations between VSS concentration and Nitrospira population were not observed in this period. The phylogenetic analysis revealed that MBR harbored diverse AOB community which was related to the Nitrosomonas and Nitrosospira lineage. Candidatus Nitrospira defluvii was the only detected NOB in this study.

Passive transport of solar energy downward by heat pipes

An indoor set-up is described for the passive upward pumping of condensate (acetone). A solar-operated experimental heat-pipe system is next discussed. The energy from a 1.0 m2 collector is transported passively to a 21-1. water storage tank 9 m away and located, 5 m below the collector, heating it to about 70 °C.

Temperature drops in heat pipes

The role of entrainment in limiting heat pipe power handling capacity is discussed. The effect of entrainment on the measured temperature field in the integral heat pipe of a split system solar cooker is analyzed. An experimental set-up depicting a heat loop is presented, along with test results.

Optimum pond depths for bacterial die-off

Abstract Analysis of optimum pond depths on the basis of minimum cost for the same bacterial removal efficiency were presented. The cost function depends on pond performance, C / C 0 . However, except in the case of dispersed flow ponds, the pond performance has no effect on optimum pond depths. The optimum depths are the same for plug flow, and for completely mixed flow ponds. The optimum pond depth increases with a decrease in the ratio of cost of excavation to cost of land. It also increases with increasing die-off rate constant in the dark, k d , but decreases with increasing light mortality constant, k s .

An algorithm for bank operation of declining rate filters

Abstract A mathematical theory and a computer algorithm for modeling variable declining rate filtration systems are presented. The use of harmonic mean conductivity in the calculation of laminar head loss through a filter medium is explained. It is mathematically proved that harmonic mean conductivity, as opposed to conductivity evaluated at average specific deposit, must be used if Darcys law holds. The differences between the predictions based on the two approaches to calculating average hydraulic conductivity are demonstrated. The computer algorithm presented here is capable of predicting water level variations, effluent concentrations, individual filter velocities and productions as functions of time.