Complex sentence: Fecal sludge may be treated at existing wastewater treatment plants if properly designed and sized, or stand alone treatment systems using a variety of mechanized and non-mechanized technologies.
Split into simpler sentences: Fecal sludge may be treated at existing wastewater treatment plants if they are designed and sized to take this load, or stand alone treatment systems. These may use a variety of mechanized and non-mechanized technologies.