An industrial plant discharges treated effluent into the New River. The effluent becomes instantaneously and completely mixed with the New River and the BOD of the mixture is 24 mg/L, the DO is 5.5 mg/L, and the saturated DO is 9.2 mg/L. The deoxygenation rate coefficient (kd) is 0.24/day and the reaeration rate coefficient (kr) is 0.71/day (both already corrected for temperature). The river is moving with a velocity of 1 m/s and a flow of 18 m3/s. The minimum DO occurs 133 km downstream of the industrial plant effluent discharge. Find the minimum downstream DO in mg/L.

Determine the time of the day and month of the year at which the peak sensible cooling load occurs for a top floor, north-eastern corner room of an office building in durban for the following conditions: floor area: 8 x 8 x 3 m east and north walls: 115 mm face brick (outside), 20 mm air space, 115 mm ordinary brick (inside) with 15 mm plaster roof construction: suspended plasterboard ceiling, 450 mm air space, 150 mm concrete, 75mm screed, waterproofing no heat transfer across other surfaces window area 3x 1,5 m high in north wall only. ordinary glass with venetian blinds. lights and occupants : from 07: 00 to 18: 00 average light density: 25 w/m2 number of occupants : 5 seated, light office work room temperature 24°c