Question

A completely mixed high rate-activated sludge plant with recycletreats 17,500 m3/day of industrial wastewater. The influent to theactivated sludge reactor has a BOD5 of 1000 mg/L. It is desired toreduce the influent BOD5 to 120 mg/L, prior to discharge to a municipalsewer. Pilot plant analysis gave the following results: mean cellresidence time = 6 d, MLSS concentration in reactor = 5500 mg/L,Y = 0.6 kg/kg, kd = 0.03 d–1. Determine the following:________.

a. The hydraulic retention time and volume of the activated sludge
b. The wolumetric loading rate in kg BOD,/m- day to the reactor.
c. The F/M ratio in the reactor
The mass and valume of solids wasted each day, at an underflow solids concentration, Xu = 10,000 mg/L.
e. The sludge recirculation ratio

Answer 1

a) 0.488 days ≈ 11.72 hour , 8542.38 m^3

b) 2.05 kg/m^3.day

c) 0.37 day^-1

d)

i) volume of wasted solid = 783 m^3/day

ii) mass of wasted solid = 7830 kg/day

e) 1.12

Step-by-step explanation:

Given data :

Flow ( Q ) = 17500 m^3/day

BOD 5 ( influent ) = 1000 mg/L

BOD 5 ( efficient ) = 120 mg/L

mean cell residence time ( ∅ c ) = 6-day

MLSS concentration ( X ) = 5500 mg/L

a) Determine the hydraulic retention time and volume of the activated sludge

i) Hydraulic retention time ( OH ) we will use the relation below

X =
`(OcY(sin-s))/(OH(1 + Kdθc))`

5500 =
`(6*0.6(1000-120))/(OH(1 + 0.03*6))` . therefore OH = 0.488 days ≈ 11.72 hour

ii) volume of the activated sludge using the relation below

OH = V / Q

V = OH * Q

= 0.488 * 17500

= 8542.38 m^3

b) Determine the volumetric loading rate in kg BOD,/m- day to the reactor

loading rate = ( Q * Sin ) / V

= ( 17500 * 1000 ) / 8542.38

= 2.05 kg/m^3.day

c) Determine The F/M ratio in the reactor

F/M ratio : F/M = ( Q .sin ) / VX

= ( 17500 * 1000 ) / ( 8542.37 * 5500)

= 0.37 day^-1

d) Determine The mass and volume of solids wasted each day, at an underflow solids concentration

i) volume of wasted solid = 783 m^3/day

ii) mass of wasted solid = 7830 kg/day

attached below is the remaining part of the solution

e) Sludge recirculation ratio

= 1.12

attached below is the remaining part of the solution