A completely mixed activated sludge process is operated without a clarifier and
ID: 92354 • Letter: A
Question
A completely mixed activated sludge process is operated without a clarifier and solids recycle. The influent soluble COD concentration is 200 mg/L and the flow is 1000 m3/day. The effluent soluble COD is 20 mg/L and the effluent biomass VSS concentration is 40 mg/L.
a) If an aerobic treatment is employed, what is the oxygen consumption rate in kg/day? Assume the net aerobic biomass yield is 0.4 g VSS/g COD.
b) If an anaerobic treatment is used, what is the methane production rate in m3/day? Assume the net anaerobic biomass yield is 0.03 g VSS/g COD, and 1 mole of methane has a volume of 25L.
c) The anaerobic process needs methanogens to produce methane. Please describe the two types of methanogens with respect you their electron donor, acceptor and energy
source. Which methanogen will produce CO2?
Explanation / Answer
The substrate utilization rate, q is
q= Q (So-Se) / V X
Vol. of aeration tank = q*Q
q= 1000 (0.2-0.02)/ .40* vol. of aeration tank
q= 1000*.18/ 0.4* q*1000
q2=.180/.40=
q=0.67g/day
a)
Specific oxygen uptake rate = oxygen uptake rate in mg per VSS
If the biomass yield or substrate yield is 0.67g per day
During the aerobic treatment, the oxygen consumption is
For 1 g of COD, 0.4g of VSS is utilized.
0.67g of substrate requires 0.67/0.4=1.675g of oxygen per day
So, 1.675g of oxygen is consumed per day or 0.001675kg of oxygen is consumed per day
b)
In anaerobic treatment, the methane production rate is
For 1 g of COD, 0.03g of VSS is utilized
0.67g of substrate requires 0.67/0.03=22.3g of COD per day
In 1 liter of tank, 40mg of methane is produced.
In 25liters, 40*25=1000mg or 1g of methane is produced.
The substrate utilization rate is 0.67g/day
If 0.67g of substrate is used per day, 1g of methane is produced
1g in 25 liters or 0.04 g/m3 per day
c)
Archae use acetate for catabolism and production of energy and hence are referred to as acetotrophic or aceticlastic. Methylotropic archae utilize methylated compounds like methanol, methylamines and methanethiol to produce carbon-di-oxide and methane gas.
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