1 For surface waters, between 20 and 40 mm (upstream the strainer)  For municipal wastewater: for raw water, from 15 to 30 mm (but upstream from a straining and/ or lamellae settling process, fine screening is necessary); for sludge (if necessary), 10 mm or less.
Other studies. According to some studies, 18-year-old males have a refractory period of about 15 minutes, while those in their 70s take about 20 hours, with the average for all men being about a half-hour. Although rarer, some males exhibit no refractory period or a refractory period lasting less than 10 seconds.
â¢ REFRACTORY (noun) The noun REFRACTORY has 1 sense: 1. lining consisting of material with a high melting point; used to line the inside walls of a furnace. Familiarity information: REFRACTORY used as a noun is very rare. â¢ REFRACTORY (adjective) The adjective REFRACTORY has 3 senses: 1. not responding to treatment 2. temporarily unresponsive or not fully responsive to nervous or sexual stimuli 3. stubbornly resistant to authority or control Familiarity information: REFRACTORY used as an adjective is uncommon.