In the olden days, the word "horrid" primarily meant something that was horrifying or causing Horror, but it could also describe something that was extremely bad or unpleasant. It often conveyed a sense of moral repugnance or something that was deeply offensive. Over time, its usage has evolved, and today it is more commonly used to describe something that is simply very bad or disagreeable, often in a more lighthearted context.
Discuss the purification methods used in the olden days
The adjective "olden" means "earlier" or "former" as in olden days and olden times, and is used to refer to any of several time periods, including the Middle Ages, the Renaissance, Colonial America, or as late as the late 19th century.
It all depends on what sense you are speaking of; because in the "olden days," as you say, candles were used in order to provide some light in dark places.
The moon and stars.
cotton wool
Discuss the purification methods used in the olden days
in the olden days we used smoke,light reflection and beacons
Discuss the purification methods used in the olden days
Cloth.
on the water.
In the olden days there were no banks so people used to keep their money under their heads
The adjective "olden" means "earlier" or "former" as in olden days and olden times, and is used to refer to any of several time periods, including the Middle Ages, the Renaissance, Colonial America, or as late as the late 19th century.
In the olden days it was used for entertainment.
guns and cannons
letters
It all depends on what sense you are speaking of; because in the "olden days," as you say, candles were used in order to provide some light in dark places.
the roads were used for carriges and horses to get transport in the olden days.