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As described above, blackwater treatment in the RRC in Qingdao ShiYuan occurs in an MBR. For the reference design, the sequencing batch reactor (SBR) was chosen, because the SBR process is sufficient to meet the legal limit for discharge (Class 1A GB 18918-2002). Therefore, in contrast to the reference design, the mechanical pre-treatment is supplemented by a sieve (see Figure 1) in the RRC in Qingdao ShiYuan, to avoid problems at the membrane modules. However, this results in a further decrease of the already low C/N ratio to the biological step, because the sieve does not remove nitrogen but only COD. A by-pass of the sieve is not recommended. For this reason, the required COD dosage for denitrification is higher for the RRC in Qingdao ShiYuan, despite the fact that almost the same nitrate load has to be denitrified (see Table 3). Due to water reuse for irrigation, the discharged nutrient load can be considerably decreased (see Figure 2); depending on the recycle rate: TN down to 0.7 kg/d and TP down to 0.16 kg/d (compared to 12.2 and 0.3 kgP/d for the reference design). However, the MBR process needs considerably more energy than the SBR process (see Figure 3), mainly for cross-flow aeration, permeate and sludge recirculation pumps.

Table 3

Data from design calculation

 RRC reference design
RRC Qingdao ShiYuan
Conventional system A
Conventional system B
BWGWBWGWWWWW
Influent (incl. process water)
Q [m3/d] 885 492 868 718 1,559 3,399 
COD [mg/L] 1,271 300 1,281 206 782 359 
TN [mg/L] 161 162 89 41 
TP [mg/L] 26 27 15 
C/N ratio influent (incl. process water) 7.9 42.9 7.9 42.9 8.8 8.8 
C/N ratio influent aeration basin 38.6 5.5 38.6 6.1 6.5 
Effluent concentration (mean values according to design calculation)
COD [mg/L] <50 <50 <50 <50 <50 <50 
TN [mg/L] 14 2.1 14 1.5 14 14 
TN removal 91% 70% 91% 69% 84% 66% 
TP [mg/L] 0.33 0.33 0.33 0.33 0.33 0.33 
TP removal 99% 92% 99% 88% 98% 95% 
Dimensioning and operation parameters (according to design calculation)
Vrequired [m31,731 201 755 199 800 1,014 
SRT [d] 16.5 25 25 25 25 25 
HRT [h] 47 10 21 12 
MLSS [g/L] 3.5 10 10 10 10 10 
Net flux [L/m2/h] - (SBR) 17.5 11.3 18.7 12.5 13.1 
Elimination process (according to design calculation)
NO3-N denitrified [kg N/d] 104 – 103 – 90 61 
COD dosage [kg COD/d] 260 – 287 – 202 – 
NH4-N nitrified [kg N/d] 110 – 109 – 101 84 
Oair [Nm3/d] 647 52 638 52 627 629 
Primary sludge production [kg DS/d] 456 – 452 – 525 390 
Excess sludge production [kg DS/d] 355 80 302 80 320 405 
Electric energy demand for GW, BW, WW treatment [kWh/(C·a)]
Influent pumps 2.0 1.0 1.9 1.4 3.5 7.7 
Aeration (biol.) 13.4 1.0 13.4 1.0 13.0 13.0 
Filtration + cross-flow aeration – 9.1 23.3 10.6 38.2 79.5 
Effluent pumps – 1.7 1.6 0.9 – – 
Others 2.9 1.5 4.7 4.0 4.3 7.7 
Sum 33 63 59 108 
Electric energy production [kWh/(C·a)] 110 95 12 11 
 RRC reference design
RRC Qingdao ShiYuan
Conventional system A
Conventional system B
BWGWBWGWWWWW
Influent (incl. process water)
Q [m3/d] 885 492 868 718 1,559 3,399 
COD [mg/L] 1,271 300 1,281 206 782 359 
TN [mg/L] 161 162 89 41 
TP [mg/L] 26 27 15 
C/N ratio influent (incl. process water) 7.9 42.9 7.9 42.9 8.8 8.8 
C/N ratio influent aeration basin 38.6 5.5 38.6 6.1 6.5 
Effluent concentration (mean values according to design calculation)
COD [mg/L] <50 <50 <50 <50 <50 <50 
TN [mg/L] 14 2.1 14 1.5 14 14 
TN removal 91% 70% 91% 69% 84% 66% 
TP [mg/L] 0.33 0.33 0.33 0.33 0.33 0.33 
TP removal 99% 92% 99% 88% 98% 95% 
Dimensioning and operation parameters (according to design calculation)
Vrequired [m31,731 201 755 199 800 1,014 
SRT [d] 16.5 25 25 25 25 25 
HRT [h] 47 10 21 12 
MLSS [g/L] 3.5 10 10 10 10 10 
Net flux [L/m2/h] - (SBR) 17.5 11.3 18.7 12.5 13.1 
Elimination process (according to design calculation)
NO3-N denitrified [kg N/d] 104 – 103 – 90 61 
COD dosage [kg COD/d] 260 – 287 – 202 – 
NH4-N nitrified [kg N/d] 110 – 109 – 101 84 
Oair [Nm3/d] 647 52 638 52 627 629 
Primary sludge production [kg DS/d] 456 – 452 – 525 390 
Excess sludge production [kg DS/d] 355 80 302 80 320 405 
Electric energy demand for GW, BW, WW treatment [kWh/(C·a)]
Influent pumps 2.0 1.0 1.9 1.4 3.5 7.7 
Aeration (biol.) 13.4 1.0 13.4 1.0 13.0 13.0 
Filtration + cross-flow aeration – 9.1 23.3 10.6 38.2 79.5 
Effluent pumps – 1.7 1.6 0.9 – – 
Others 2.9 1.5 4.7 4.0 4.3 7.7 
Sum 33 63 59 108 
Electric energy production [kWh/(C·a)] 110 95 12 11 

GW – greywater; BW – blackwater; WW – wastewater; SRT – sludge retention time; MLSS – mixed liquor suspended solids.

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