Semion Shandalov

Removal of viruses from surface water and secondary effluents by sand filtration

The filtration of phi X 174, MS2, and T4 bacteriophages out of tap water and secondary effluents was performed by rapid sand filtration. The viruses were characterized, and the influence of their microscopic characteristics on filterability was examined by comparing retention values, residence times, attachment, and dispersion coefficients calculated from an advection-dispersion model and residence time variation. The only factor observed to influence retention was virus size, such that the larger the virus, the better the retention. The difference was due to the more effective transport of viruses inside the media, an observation that runs counter to currently accepted filtration theory. Cake formation on top of the filter during the initial stages of secondary effluent filtration significantly increased headloss, eventually resulting in shorter filtration cycles. However, deep filters contain buffering zones where the pressure drop is amortized, thus allowing for continued filtration. After the effluent passed through the buffer zone, regular filtration was observed, during which considerable virus retention was achieved.

Wastewater Reclamation for Agricultural Reuse in Israel: Trends and Experimental Results

Water shortage and a deterioration in the quality of water resources in Israel have made necessary a national policy recommending reuse of practically all municipal wastewater in order to supply a major part of agricultural water demand. Two pilot-scale systems were operated and studied for several years. The first one consisted of an advanced treatment scheme incorporating a sequencing batch reactor (SBR) system with further deep-bed granular filtration. The second system was an SBR unit, for the purpose of optimizing nitrogen and phosphorus removal and testing further microfiltration of SBR effluents. The SBR process has been shown to be an efficient biological treatment method producing low Biochemical Oxygen Demand (BOD) and Total Suspended Solids (TSS) effluents. SBR effluents, even if loaded with high TSS concentrations, could be further purified in the filtration stage, producing low-turbidity effluents. Granular filtration experiments were carried out using a gravitational single-medium filter composed of uniformly-sieved quartz sand. It was found that most of the suspended solids were removed in the top 10 cm of the filter bed. Influent turbidity was found to be the main parameter affecting the process, while filtration rate had only a minor effect. Microfiltration of SBR effluents showed highly efficient removal of turbidity and pathogens. Advanced mathematical models were developed and calibrated for both the biological process and for the granular filtration process.

Model calibration of deep-bed filtration based on pilot-scale treatment of secondary effluent

A mathematical model of deep-bed filtration has been calibrated and verified based on experimental results. The experimental system, used for testing of the secondary treatment quality and the tertiary filtration phase, incorporates an SBR system followed by a filtration column. The turbidity of the incoming SBR effluent was in the range of 12 to 34 NTU. The bed grain size was in the range of 1.4 to 2.0 mm. The examined filtration velocities were 11, 15, 20 and 25 m/h. The filtration process is simulated by equations of balance and kinetics. The latter includes the attachment and detachment process, characterized by rate coefficients KA and KD, respectively. These coefficients , as well as the parameters of hydrodispersivity and effective porosity, are found on the basis of nonlinear optimization, using numerical solution of the model and the experimental breakthrough curves. The method demonstrates good agreement between experimental and simulated results.

Use of MBR to sustain active biomass for treatment of low organic load grey water

The aim of this study was to test the local small-scale treatment of grey water (mainly shower water) of a sports centre to be reused for recreational irrigation. Due to the low organic load which limits the growth and aggregation of biomass, a membrane bioreactor (MBR) was selected for this purpose. A pilot-scale system was operated and studied for more than 1 year in the conduct of this task. The MBR process proved to be a very efficient biological treatment stage, producing superior effluents with low BOD5, NH4+ and TSS. Detergents and COD were degraded efficiently and the effluents did not contain total coliforms and faecal coliforms. Due to the low organic load, biomass accumulation was very slow and the system could reach and function at relatively low mixed liquid suspended solid (MLSS) levels. The MBR ultrafiltration module thus was able to produce a steady permeate flux for more than 1 year just with air scouring and without membrane backwash or chemical regenerating. Another important advantage was the minimal requirement for excess sludge wastage.