Dynamic modeling of nutrient removal by a MBR operated at elevated temperatures.

The process performance of a MBR operated on municipal sewage at elevated temperatures was evaluated by dynamic modeling. The enhanced biological phosphorus removal (EBPR) performance varied from 40% to 95% with process temperature ranging from 24 to 38 °C. The respective maximum substrate uptake rate (qPHA) was estimated at 1.5 gCODS/gCODX.day-1 for Glycogen Accumulating Organisms (GAO) and 4.7 gCODS/gCODX.day-1 for Phosphate Accumulating Organisms (PAO) with Arrhenius coefficients (θ) for GAOs and PAOs of 1.06 and 1.04 respectively. With these parameters the effluent PO4 levels of the MBR operated for 450 days could be well described. In addition, the impact of mesophilic conditions and low influent P/VFA levels on GAO proliferation was evaluated under dynamic process conditions. Nitrification process was temporarily impaired at high temperatures around 38 °C. Simulations revealed that the contribution of the anoxic reactor to the total overall denitrification was limited to 40%The contribution of simultaneous nitrification and denitrification (SNdN) process to the denitrification was around 40-50% depending upon dissolved oxygen levels in aerobic and MBR tanks. The large contribution of SNdN was due to gas/liquid mass transfer limitation conditions mediated by high mixed liquor viscosities (20-35 mPa.S) in MBR system. The membrane flux was 43 L/m2/h corresponding to the specific permeability (K) of 413 L/m2/h/bar at 38 °C.

Long-term study on the impact of temperature on enhanced biological phosphorus and nitrogen removal in membrane bioreactor.

The study involved experimental observation and performance evaluation of a membrane bioreactor system treating municipal wastewater for nutrient removal for a period 500 days, emphasizing the impact of high temperature on enhanced biological phosphorus removal (EBPR). The MBR system was operated at relatively high temperatures (24-41 °C). During the operational period, the total phosphorus (TP) removal gradually increased from 50% up to 95% while the temperature descended from 41 to 24 °C. At high temperatures, anaerobic volatile fatty acid (VFA) uptake occurred with low phosphorus release implying the competition of glycogen accumulating organisms (GAOs) with polyphosphate accumulating organisms (PAOs). Low dissolved oxygen conditions associated with high wastewater temperatures did not appreciable affected nitrification but enhanced nitrogen removal. Dissolved oxygen levels around 1.0 mgO2/L in membrane tank provided additional denitrification capacity of 6-7 mgN/L by activating simultaneous nitrification and denitrification. As a result, nearly complete removal of nitrogen could be achieved in the MBR system, generating a permeate with no appreciable nitrogen content. The gross membrane flux was 43 LMH corresponding to the specific permeability (K) of 413 LMH/bar at 39 °C in the MBR tank. The specific permeability increased by the factor of 43% at 39 °C compared to that of 25 °C during long-term operation.

Effect of anoxic decay process on simultaneous nitrification denitrification in a membrane bioreactor operated without an anoxic tank.

This study was focused on evaluating the role and the effect of anoxic decay on the extent of simultaneous nitrification-denitrification (SNdN) process sustained in a single membrane bioreactor. The membrane bioreactor was fed with relatively strong domestic sewage and operated at steady state at a sludge age of 36 days at a corresponding suspended solids level maintained in the range of 17,500-21,000 mg/L. The SNdN could be sustained due to diffusion limitation of oxygen into the flocs. The evaluation identified an MLSS threshold level of around 17,000-18,000 mg/L below which nitrogen removal was essentially controlled by denitrification and above, the rate limiting mechanism shifted to nitrification maintaining total nitrogen removal efficiency of 85-95% for a typical domestic sewage. The contribution of anoxic decay process to the overall denitrification potential was evaluated as 60%, substantially higher than the remaining 40% associated with the anoxic growth during the SNdN process.

Modelling of long-term simultaneous nitrification and denitrification (SNDN) performance of a pilot scale membrane bioreactor.

Nutrient removal capability of the MBR process has attracted more attention than organics removal in the past few years. Apart from the conventional schemes for nitrogen removal in MBR process, simultaneous nitrification-denitrification (SNDN) requires the most attention for further research. In order to fully understand the fundemantals and mechanism of SNDN in MBRs, a pilot plant was set up. A mathematical model was adopted for investigation and calibration against the observed values. This paper reports a study focusing on evaluating major mechanisms that govern nitrogen removal from domestic wastewater in membrane bioreactors. Two items need to be emphasized in this evaluation: (i) an MBR is basically regarded as an activated sludge process-a suspended growth bioreactor with total biomass recycle and substantially higher biomass concentration; (ii) in this context an AS model, namely ASM1R modified for endogenous respiration, is used for dynamic modelling and calibration of experimental results. The impact of diffusion through biomass which obviously exerts a significant effect on system performance and denitrification is evaluated with success using the adopted model by means of switch functions that regulate nitrification-denitrification with respect to dissolved oxygen concentration in the bulk liquid.

Design procedure for carbon removal in contact stabilization activated sludge process.

The contact stabilization activated sludge process (CSASP) has been adopted and applied in full scale plants treating domestic sewage. Acquiring smaller volume thereby reducing costs and achieving the same treatment efficiency as the conventional activated sludge plants are the main advantages of the CSASP. This activated sludge modification is especially ideal for small to mid-scale plants where influent wastewater contains a high fraction of particulate COD. The simulation results reveal that the same amount of mass sludge can be retained in the system with almost 30% volume reduction compared to conventional activated sludge plants. It is also found that the CSASP treatment efficiency increases when the particulate COD fraction of an influent domestic wastewater increases. The most important process component in the design of CSASP is the sludge distribution factor (alpha) which directly affects the effluent characterization. Having most of the biomass in the stabilization reactor (meaning low alpha values) decreases the nominal hydraulic retention time (thetaHN) of the system. However the sludge distribution factor must be high enough to ensure an acceptable effluent quality.

The effectiveness of omeprazole versus lansoprazole along with amoxicillin and clarithromycin in Turkish population with duodenal ulcer.

AIM: To compare the effectiveness of omeprazole versus lansoprazole with amoxicillin and clarithromycin in the Turkish populations with duodenal ulcer. METHODS: Helicobacter pylori positive 108 patients with active duodenal ulcer randomized double blindly into 2 groups. In the group of omeprazole, amoxicillin and clarithromycin (OAC), 54 patients; 34 male, 20 female, average age (+/-SD) 43.89+/-11.77 years. Omeprazole was given 20 mg b.i.d, half an hour before meals for 14 days and then 20 mg preceeding breakfast for 6 weeks along with 1 g amoxicillin and 500 mg clarythromycin b.i.d. for both antibiotics for 14 days while lansoprazole 30 mg b.i.d. was administered half an hour preceeding food intake for 14 days and then 30 mg prebreakfast for 6 weeks with concordant 1 g b.i.d. amoxicillin and clarythromycin 500 mg, b.i.d. for 14 days in the group of lansoprazole with amoxicillin and clarithromicin (LAC) (54 patients; 31 male, 23 female, average age (+/-SD) 40.85+/-12.80 years. The patients were evaluated in clinical terms and by endoscopic parameters for healing, H. pylori eradication and drug side effects before and after 8 weeks of treatment. RESULTS: There were no significant differences in age, sex and smoking between the 2 groups (p=0.20, p=0.56, p=0.85), respectively. In the LAC group, the ulcer healing rate was 94.4% (51 out of 54 patients). H. pylori was eradicated in 49 patients out of 54 (90.7%). The H. pylori eradication rate was 89.7% (26 out of 29) among the smokers. In the OAC group the ulcer healing rate was 90.7% (49 out of 54 patients). H. pylori was eradicated in 43 patients out of 54 (79.6%). The H. pylori eradication rate was 80.0% (24 out of 30 patients) among the smokers. There was no statistical difference between the 2 groups for ulcer healing (p=0.72). There was also no statistical difference for H. pylori eradication between the LAC and OAC groups (p=0.10). Although mild side effects were observed in both groups, there was no indication for stopping the therapy. CONCLUSIONS: This study has shown that the 2 regimens (LAC and OAC) are highly effective in healing duodenal ulcers and eradicating H. pylori. Lansoprazole does not appear to have a significant advantage over omeprazole either in ulcer healing or in H. pylori eradication. Both lansoprazole and omeprazole are well tolerated, but with mild adverse effects.

Risk factors for hepatocellular carcinoma in Turkey.

The contribution of hepatitis B, hepatitis C, and excess alcohol intake to the development of hepatocellular carcinoma in Turkey was assessed. The study was conducted through a questionnaire sent to seven major medical referral centers in different regions of Turkey and is based on 207 patients seen in the period 1994-1997. Of the seven centers, two were located in West Turkey (54 patients), two were in Central Turkey (85 patients), and two were in south and southeast Turkey (68 patients). In 196 of the 207 patients (94.7%), there was a history of chronic liver disease, and in 180 patients (87%) liver cirrhosis was documented. Of the 207 patients, 116 (56%) had hepatitis B, 48 (23.2%) had hepatitis C, and 33 (15.9%) had a history of excess alcohol intake. Anti-delta testing was available in 69 of 116 patients with hepatitis B, and anti-HDV was positive in 13 of these patients (13/69, 18.8%). Of the 33 patients with a history of heavy alcohol intake, 18 had concomitant chronic viral hepatitis infection, and alcohol alone was the etiology of hepatocellular carcinoma in only 15 cases (7.2%). The distribution of etiologic factors was not homogenous in different geographical regions in Turkey. In central, south, and southeastern Turkey, the predominant etiology of hepatocellular carcinoma was hepatitis B, whereas in western Turkey the impact of hepatitis B, hepatitis C, and alcohol was similar. This study indicates that hepatitis B virus infection is the leading cause of hepatocellular carcinoma in Turkey, followed by hepatitis C infection and alcoholic liver disease.

Circulating IL-2 and IL-10 in chronic active hepatitis C with respect to the response to IFN treatment.

BACKGROUND: The importance of circulating immunoregulatory cytokines in response to IFN treatment and the change of in vivo production of these cytokines during interferon (IFN) treatment are not well known. We aimed to determine whether pretreatment serum levels of IL-2 and IL-10 are predictive of the response to IFN treatment and to investigate if treatment response or nonresponse has any effect on the circulating levels of these cytokines. PATIENTS AND METHODS: 37 patients (18 responders and 19 non-responders) with chronic hepatitis C virus (HCV) infection who received IFN-alpha2b for 6 months were studied. Responders were defined by complete alanine aminotransferase (ALT) normalization and loss of HCV RNA as detected by bDNA assay while patients who had elevated ALT levels and positive HCV RNA after 6 months were considered as nonresponders. RESULTS: Genotype distribution, ALT and HCV RNA levels were similar in responders and nonresponders. A significant number of patients with chronic hepatitis C (20/37 = 54%) had elevated IL-2 levels while IL-10 levels were not different from controls. No difference in baseline cytokine levels was observed between responders and non-responders. In the posttreatment serum samples some patients lost their detectable IL-2 or IL-10; some patients developed detectable cytokine levels after treatment irrespective of the treatment response. CONCLUSION: These results suggest that active liver injury in chronic hepatitis C is associated with increased circulating Th1 cytokine IL-2 but not with Th2 cytokine IL-10 and that circulating levels of these cytokines do not predict the response to IFN treatment. There is no constant and regular change in circulating levels of these cytokines under IFN treatment with respect to treatment response.

Circulating IL-2, IL-10 and TNF-alpha in chronic hepatitis B: their relations to HBeAg status and the activity of liver disease.

BACKGROUND/AIMS: Preferential production of immunoregulatory cytokines may play an important role in the pathogenesis of chronic hepatitis B. We aimed to determine the serum levels of IL-2, IL-10 and TNF-alpha in patients with chronic hepatitis B and to correlate these findings with the activity of liver disease, HBeAg/anti-HBe status and replication level of the virus. METHODOLOGY: Seventy-two chronic hepatitis B patients were categorized into 4 groups according to activity of liver disease and HBeAg status. Group 1 (n = 13): HBeAg and HBV DNA-positive with persistently normal ALT. Group 2 (n = 20): HBeAg and HBV DNA-positive patients with persistently elevated ALT. Group 3 (n = 19): HBeAg and HBV DNA-negative patients with persistently normal ALT. Group 4 (n = 20): HBeAg-negative patients with persistently elevated ALT and variable serum HBV DNA. IL-2, IL-10 and TNFa levels were determined in stored patient sera. RESULTS: Apart from group 1 patients, all patients groups had higher IL-2 levels compared to controls suggesting that IL-2 production is increased when liver disease becomes active in HBeAg-positive phase of HBV infection. Only group 2 patients had elevated IL-10 levels compared to controls. None of the HBeAg-negative patients had detectable TNF-alpha levels while 64% HBeAg-positive patients had elevated levels of TNF-alpha irrespective of the activity of liver disease. Except TNF-alpha, no association was found between HBV DNA status and the presence or absence of detectable cytokines in circulation. CONCLUSIONS: Our results suggest that circulating cytokine profile in chronic hepatitis B is related with the HBeAg status, replication level of the virus and the activity of liver disease.