code: def frac_vol_floc_initial(ConcAluminum, ConcClay, coag, material):
      
      return ((conc_precipitate(ConcAluminum, coag).magnitude/coag.PrecipDensity)
              + (ConcClay / material.Density))
docs: Return the volume fraction of flocs initially present, accounting for both suspended particles and coagulant precipitates.
  
      :param ConcAluminum: Concentration of aluminum in solution
      :type ConcAluminum: float
      :param ConcClay: Concentration of particle in suspension
      :type ConcClay: float
      :param coag: Type of coagulant in solution
      :type coag: float
      :param material: Type of particles in suspension, e.g. floc_model.Clay
      :type material: floc_model.Material
  
      :return: Volume fraction of particles initially present
      :rtype: float