V. Jegatheesan

Performance of suspended and attached growth MBR systems in treating high strength synthetic wastewater.

The performance of laboratory-scale attached growth (AG) and suspended growth (SG) membrane bioreactors (MBRs) was evaluated in treating synthetic wastewater simulating high strength domestic wastewater. This study investigated the influence of sponge suspended carriers in AG-MBR system, occupying 15% reactor volume, on the removal of chemical oxygen demand (COD), total nitrogen (TN) and total phosphorus (TP), and compared it to that of SG-MBR. Results showed that the removal efficiencies of COD, TN and TP in AG-MBR were 98%, 89% and 58%, respectively as compared to 98%, 74% and 38%, respectively in SG-MBR. Improved TN removal in AG-MBR systems was primarily based on simultaneous nitrification and denitrification (SND) process. These results infer that the presence of small bio-particles having higher microbial activity and the growth of complex biomass captured within the suspended sponge carriers resulted in improved TN and TP removal in AG-MBR.

Prediction of membrane fouling in MBR systems using empirically estimated specific cake resistance

The focus of this study was to empirically estimate the specific cake resistance (SCR) by the variation in shear intensity (G) in four laboratory-scale MBRs. The control reactor (MBR(0)) was operated with aeration only while other MBRs (MBR(150), MBR(300) and MBR(450)) were operated with aeration and mechanical mixing intensities of 150, 300 and 450 rpm, respectively. It was found that the SCR was strongly correlated (R(2)=0.99) with the fouling rates in the MBRs. Moreover, the contribution of cake resistance (R(c)) to the total hydraulic resistance (R(t)) was predominant compared to the irreversible fouling resistance (R(f)). On this basis, the cake filtration model was selected as a predictive tool for membrane fouling. This model was modified by replacing the SCR with its empirical shear intensity relationship. The modified model can predict the fouling rate for a given shear intensity (G) within 80 and 250 s(-1) in a MBR system.

Assessments of critical flux in a pilot-scale membrane bioreactor

In this study, the influence of various parameters such as determination methods and step height and length of incremental flux on critical flux values were investigated. Experiments were carried out on a pilot-scale membrane bioreactor (MBR) treated municipal wastewater. Three of the five critical flux determination methods, such as flux linearity, 90% permeability and flux cycling conducted in this study, indicated a decline in critical flux values as the step height of incremental flux increased. However, the hysteresis method and the two-third (2/3) flux limitation method showed an increase and independence of critical flux to the step height of incremental flux, respectively. On the other hand, the step length of incremental flux had no obvious effect on critical flux values evaluated by all critical flux determination methods. Like critical flux, sustainable flux has negative relationship with the increase of step height but no influence of step length was found in this study.

Aquaculture effluent : impacts and remedies for protecting the environment and human health

Knowledge in the field of environmental health is growing rapidly. Within the context of external factors that define its boundaries, environmental health has evolved over time into a complex, multidisciplinary and ill-defined field with uncertain solutions. Many of the key determinants and solutions to environmental health lie outside the direct realm of health and are strongly dependent on environmental changes, water and sanitation, industrial development, education, employment, trade, tourism, agriculture, urbanization, energy, housing and national security. Environmental risks, vulnerability and variability manifest themselves in different ways and at different time scales. While there are shared global and transnational problems, each community, country or region faces its own unique environmental health problems, the solution of which depends on circumstances surrounding the resources, customs, institutions, values and environmental vulnerability. This work will contain critical reviews and assessments of environmental health practices and research that have worked in places and thus can guide programs and economic development in other countries or regions.

Influence of mechanical mixing rates on sludge characteristics and membrane fouling in MBRs

Abstract The influence of shear intensity (G) induced by mechanical mixing on activated sludge characteristics as well as membrane fouling propensity in membrane bioreactors (MBRs) was investigated. Four MBRs were operated at different mechanical mixing conditions. The control reactor (MBR0) was operated with aeration only supplemented by mechanical stirring at 150, 300, and 450 rpm in MBR150, MBR300, and MBR450, respectively. It was found that the MBR300 demonstrated minimum rate of membrane fouling. The fouling potential of the MBR300 mixed liquor was lowest characterized by the specific cake resistance and the normalized capillary suction time (CSTN). Moreover, it was found that the mean particle size reduced with an increase in the shear intensity. These results reveal that membrane fouling can be significantly mitigated by appropriate shear stress on membrane fibers induced by mechanical mixing condition.

HYDROGENOTROPHIC DENITRIFICATION OF HIGHLY SALINE AQUACULTURE WASTEWATER USING HOLLOW FIBER MEMBRANE BIOREACTOR

Abstract A hydrogenotrophic denitrification system with a hollow fiber membrane was evaluated for treating and recycling synthetic aquaculture wastewater. Hollow fibers ensured bubble‐less diffusion of hydrogen and subsequent removal of nitrate from the first bioreactor. The second aerobic reactor was used for biomass filtration and removal of organic matter. Nitrate and organic matter expressed as dissolved organic carbon were 50 mgl−1 and 20 mgl−1, respectively, in the inlet. Acclimatization of hydrogenotrophic bacteria to 10, 20 and 30 ppt of salinity was also observed. Optimum hydraulic retention time and denitrification rate corresponding to these salinities were 3, 5 and 6 h and 366.8, 226.2 and 193.2 gm−3day −1, respectively.

Effect of Operating Parameters and Cleaning on the Performance of Ceramic Membranes Treating Partially Clarified Sugar Cane Juice

Abstract The performance of ceramic membranes with pore sizes of 0.05 and 0.10 µm in purifying limed and partially clarified sugar cane juice was investigated under different operating conditions. From various operating conditions and strategies, switching off the permeate for 5 seconds for every 5 minutes (S5sT5 m) by an automated control valve provided higher flux. From the three pH experiments conducted on the 0.05 µm membrane, the best performance was observed at a pH of 7.5. Amongst the four fouling models tested, the cake filtration model fitted the performance of both membranes with higher accuracy at a transmembrane pressure of 0.5 bar. Filtering the cane juice through the membrane reduced the turbidity by 99.7%, color by 15%, and the starch concentration by 80% as well as increased the purity by 1.4%. The effective cleaning chemical composition from experimental results showed that 1% NaOH and 3000 ppm NaOCl solution performed the best but only for the experiments that were treating limed and partially clarified juice at pH 7.5.