56) Cleaning is done by i)scraping and removal in filters slow sand ii)back washing in slow sand filters iii)scraping and removal in filters rapid sand iv)back washing in rapid sand filters The correct answer is

57) Disinfection of water results in

58) The disinfection efficiency of chlorine increases by i) decreasing the time of contact ii) decreasing the temperature of water iii) increasing the temperature of water The correct answer is

59) Chlorine demand of water is equal to

60) The process in which the chlorination is done beyond the break point is known as