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.
As people get older, there are changes in an individualâs sexual response cycle, but these changes do not necessarily impact the quality of one's sex life in a negative way. Men and women have different changes to their sexual response cycles with age. As he ages, this refractory period lengthens; in his late 20s, the period maybe 15-30 minutes, while in his 40s this could take around three or four hours. 2  By the time he is in his 50s, the refractory period may take ten to twelve hours.