ABSTRACT

Similar mixed cultures of micro-organisms are used in the assessment of wastewater and effl uent strength by the biochemical oxygen demand (BOD) standard 5-day test (BOD 5 ), in which the oxygen demand exerted by an inoculum of microorganisms growing in the liquid sample is measured over 5 days in the dark at 20 ° C to give an estimate of the microbially oxidizible fraction in the wastewater ( Section 5.4 ). Many diseases are caused by waterborne micro-organisms, a number of which are pathogenic to humans. The danger of these diseases being transmitted via wastewater is a constant threat to public health ( Chapter 12 ). Therefore the use of microorganisms, such as Escherichia coli , as indicator organisms to assess the microbial quality of water for drinking, recreation and industrial purposes, as well as in the assessment of wastewater treatment effi ciency, is an essential tool in pollution control.