text: ###############################################################################
  # ProteusLib Copyright (c) 2021, The Regents of the University of California,
  # through Lawrence Berkeley National Laboratory, Oak Ridge National
  # Laboratory, National Renewable Energy Laboratory, and National Energy
  # Technology Laboratory (subject to receipt of any required approvals from
  # the U.S. Dept. of Energy). All rights reserved.
  #
  # Please see the files COPYRIGHT.md and LICENSE.md for full copyright and license
  # information, respectively. These files are also available online at the URL
  # "https://github.com/nawi-hub/proteuslib/"
  #
  ###############################################################################
  
  """Feed blocks for supported property packages"""
  
  from pyomo.environ import Constraint
  from idaes.generic_models.unit_models import Feed
  from proteuslib.flowsheets.full_treatment_train.model_components import property_models
  from idaes.core.util.scaling import calculate_scaling_factors
  
  
  def build_feed(m, base='TDS'):
      """
      Build a feed block for a specified property base. The state vars are fixed to the standard condition.
      Property bases include: 'TDS', 'ion', 'salt'
      """
  
      # feed block
      prop = property_models.get_prop(m, base=base)
  
      # build
      m.fs.feed = Feed(default={'property_package': prop})
  
      # specify
      property_models.specify_feed(m.fs.feed.properties[0], base=base)
      m.fs.feed.properties[0].mass_frac_phase_comp  # touch so the block can be initialized
  
  
  