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Fungi and Water
Published in Chuong Pham-Huy, Bruno Pham Huy, Food and Lifestyle in Health and Disease, 2022
Chuong Pham-Huy, Bruno Pham Huy
In the coagulation and flocculation step, chemicals with a positive charge are added to the water. The positive charge of these chemicals neutralizes the negative charge of dirt and other dissolved particles in the water. When this occurs, the particles bind with the chemicals and form larger particles, called floc (175–176).
Polymer Adsorption: Fundamentals
Published in E. Desmond Goddard, James V. Gruber, Principles of Polymer Science and Technology in Cosmetics and Personal Care, 1999
E. Desmond Goddard, James V. Gruber
The vast majority of polymeric flocculants are high-molecular-weight polyelectrolytes, which may be cationic or anionic. The charge densities of polyelectrolytes with weakly acidic or basic groups may be dependent. Some, with strongly ionized groups such as poly(styrene sulfonate), have charge densities independent of pH. Flocculation is brought about by the adsorption of a single polymer chain on more than one particle, i.e., by a bridging mechanism (9). Bridging flocculation occurs over a narrow range (of the order of several parts per million) of concentrations. The floc structures, which tend to be rather loose, sediment rapidly and are easily removed from solution by filtration. Particles and flocculants usually have opposite charges, though there is evidence of counterions facilitating the flocculation of negatively charged particles by anionic polymers. The counterions are thought to act as “bridges” to the polymer “bridges.” Charge Neutralization
Drinking water treatment *
Published in Jamie Bartram, Rachel Baum, Peter A. Coclanis, David M. Gute, David Kay, Stéphanie McFadyen, Katherine Pond, William Robertson, Michael J. Rouse, Routledge Handbook of Water and Health, 2015
In most textbooks the next unit process is described as coagulation, flocculation and sedimentation but for simplicity we have termed these linked processes as ‘clarification’. This process is the most commonly used one and is termed ‘conventional treatment’. The purpose of clarification is to remove as much of the particulate material as possible through the use of gravity (Gray, 1999a). Larger particles such as sand will settle out as their mass is sufficient to allow gravity to overcome the opposing forces in the water column. Smaller particles will not have the same gravitation forces acting on them and so resist settling. This resistance is overcome by making the smaller particles larger by allowing them to stick together. This is not a simple proposition as most particles, when immersed in water, will assume a net negative charge and when they encounter another particle each will be repelled by electrostatic forces. A way around this is to provide a particle that retains its positive charge in water allowing the negatively charged smaller particles to attach and hence increase the mass of the resulting agglomeration or ‘floc’. So coagulation is the addition and rapid mixing of a chemical (or chemicals) that acts as an aid to coagulation; flocculation is the gentle agitation of the water to ensure there is maximum interaction between particles and the coagulant to allow flocs (larger agglomerations of particles and coagulant) to occur; and the final stage, sedimentation, is when the flocs are allowed to settle out of the water column under gravity to provide a ‘clarified’ or clear water. Flocculants can include a range of aluminium and iron salts (aluminium sulphate, ferric sulphate etc.) but there are also chemicals known as ‘polyelectrolytes’ which form long strings when dissolved in water with multiple charges along their length (with positive and negative charges areas occurring on the sample molecule, hence ‘poly’ and ‘electrolyte’). Polyeletrolytes can be used in addition to flocculants to enhance the formation of the floc and hence aid with sedimentation.
Effect of aeration rate on the anti-biofouling properties of cellulose acetate nanocomposite membranes in a membrane bioreactor system for the treatment of pharmaceutical wastewater
Published in Biofouling, 2019
The probable assumption of floc breakage with increasing aeration rates was also confirmed by the particle size distribution of activated sludge in the MBR tank. The particle size distribution of activated sludge under lower and higher aeration rates are shown in Figure 6. As can be seen, there was a clear decline in floc size with the increase in aeration rates. The peak particle size was ∼43 µm and 23 µm for lower and higher aeration rates, respectively. In other words, a higher aeration rate more efficiently increases the fraction of components which resulted in the release of more EPS and SMP (see Figure 4a and b).
Membrane biofouling behaviors at cold temperatures in pilot-scale hollow fiber membrane bioreactors with quorum quenching
Published in Biofouling, 2018
Kibaek Lee, Jun-Seong Park, Tahir Iqbal, Chang Hyun Nahm, Pyung-Kyu Park, Kwang-Ho Choo
During MBR operations, mixed liquor samples were taken and centrifuged at 4,000 rpm (ie 2,951 g) for 10 min, and the resultant supernatant was filtered through a syringe filter (0.45 μm, Millipore, USA) to obtain the soluble fraction. The amounts of extracellular polymeric substances (EPSs) and soluble microbial products (SMPs) were determined as described in Weerasekara et al. (2014). EPSs were extracted via the heat extraction method (Chang and Lee 1998, Zhang et al. 2009). The sludge pellets were resuspended in 25 ml of a 0.9% NaCl solution. Subsequently, the suspension was heated to 80 °C in a water bath for 30 min and then centrifuged at 4,000 rpm (ie 2,951 g) for 10 min. Finally, EPSs were obtained by filtering the supernatant through a syringe filter (0.45 μm). Because the main constituents of EPSs and SMPs are known to be proteins and carbohydrates, the concentrations of proteins and carbohydrates present in the activated sludge extract (EPSs) and mixed liquor filtrate (SMPs) were determined using the modified Lowry (Olson and Markwell 2007, Peterson 1977) and phenol-sulfuric acid methods (DuBois et al. 1956; Nielsen 2010), respectively. The microbial floc size was measured using a laser diffraction particle size analyzer (LS 13 320, Beckman Coulter, USA). The chemical oxygen demand (COD) was determined based on the dichromate method (APHA 1998). A dichromate digestion reagent (UL, Hach, USA), which has a maximum COD detection limit of 40.0 mg l−1, was used with a COD reactor (DRB200, Hach). The initial and residual dichromate concentrations were determined using an automatic titration system (809 Titrando, Metrohm, Switzerland) with 1.0 mN ferrous ammonium sulfate solution. The total organic carbon (TOC) levels were determined using a TOC analyzer (TOC-V CPH, Shimadzu, Japan). The total nitrogen (TN) and total phosphorus (TP) were determined according to Standard Methods (APHA 1998). Error bars on the charts in this study, if applicable, indicate one standard deviation (SD) of two or more replicate experiments.
Quorum sensing: an emerging link between temperature and membrane biofouling in membrane bioreactors
Published in Biofouling, 2019
Chang Hyun Nahm, Keehong Kim, Sojin Min, Hosung Lee, Dowon Chae, Kibaek Lee, Kwang-Ho Choo, Chung-Hak Lee, Ismail Koyuncu, Pyung-Kyu Park
To determine the reason for the EPS variations at different temperatures, average floc sizes were monitored during MBR operation, as shown in Figure 6. The average floc sizes at 18 °C were higher than those at 25 °C, except at the beginning of operation. However, when the sizes at 12 and 18 °C were compared, there was a decreasing tendency in the size with a decrease in the temperature. In the activated sludge process, the floc size is in a state of equilibrium due to the reversibility of flocculation (Wilen et al. 2000), and it can change via an equilibrium shift when either flocculation or deflocculation strengthens due to any changes in the operating conditions. This is also applicable to an aerobic MBR. The increase in the floc size with a decrease in the temperature from 25 to 18 °C suggests that flocculation strengthened at 18 °C, and that the flocculation tendency is most likely associated with AHL-mediated QS activity (Tan et al. 2014). This is consistent with the increase in the C8-HSL concentration at 18 °C shown in Figure 5. However, the decrease in the floc size with the decrease in the temperature from 18 to 12 °C suggests that flocculation was inferior to deflocculation at 12 °C until a new floc size equilibrium had been reached. At a low temperature, the metabolism of many microorganisms in MBRs decreases (Krzeminski et al. 2012, Ratkowsky et al. 1982), and the AHL production rate also diminishes. Previous studies have reported that AHL production by bacteria at a temperature of 12 °C or lower was delayed or reduced (Flodgaard et al. 2003, Medina-Martinez et al. 2006a, 2006b), although these studies were not directly related to MBRs. The low concentration of C8-HSL at 12 °C in Figure 5 is in strong agreement with the scenario. This reduction in AHL production lessened the production of EPSs by bacteria inside the microbial flocs, decreased the tendency of flocculation, and finally led to difficulty in maintaining the floc structures. Hence, deflocculation occurred at 12 °C, which resulted in the release of some of the EPSs bound to microbial flocs (Jiang et al. 2005, van den Brink et al. 2011). Owing to this release of EPSs, the level of soluble EPSs in the MBR at 12 °C could increase, as shown in Figure 4.