text: DLVO theory describes the interaction potential between charged surfaces. It is the sum of electrostatic double layer, which can be either attractive of repulsive, and attractive Van der Waals interactions of the charge surfaces. DLVO theory is applied widely in explaining the aggregation and deposition of colloidal and nano particles such as Fullerene C60 in aquatic system. Because bacteria and colloid particles both share the similarities in size and surface charge, the deposition of bacteria also can be describe by the DLVO theory. The prediction is based on sphere-plate interaction for one cell and the surface.<br /> 
  The electrostatic double layer interactions could be describes by the expression for the constant surface potential  
  Where εis the vacuum permittivity, ε is the relative dielectric permittivity of water, a is the equivalent spherical radius of the bacteria, κ is the inverse of Debye length, h is the separation distance between the bacterium and the collector surface; ψ and ψ are the surface potentials of the bacterial cell and the collector surface. Zeta potential at the surface of the bacteria and the collector were used instead of the surface potential.
  The retarded Van der Waals interaction potential was calculated using the expression from Gregory, 1981 .
  With A is Hamaker constant for bacteria-water-surface collector (quartz) = 6.5 x 10 J and λ is the characteristic wavelength of the dielectric and could be assumed 100 nm, a is the equivalent radius of the bacteria, h is the separation distance from the surface collector to the bacteria.
  Thus, the total interaction between bacteria and charged surface can be expressed as follow