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Total wastewater loads are estimated according to the GB 50101-2005 standard (the basis for the design of wastewater treatment plants in China) and the load proportion in grey- and blackwater according to Bi (2004). The specific COD and biological oxygen demand (BOD) load in blackwater is higher than reported in literature (e.g., 50 gCOD/(C·d) and 32 gBOD/(C·d) by Meinzinger & Oldenburg (2009) for excreta, or 74 gCOD/(C·d) by Todt et al. (2015)). Usually, blackwater is wastewater from toilets; in contrast, the blackwater flow to the RRC in Qingdao additionally includes kitchen wastewater. Thus, a higher specific organic load is calculated (see Table 2). An inhabitant-specific wastewater amount of 109 L/(C·d) is assumed according to Bi (2004) for the dimensioning of the RRC. This corresponds well with the water consumption of 111 L/(C·d) in 2012 in Qingdao (China Statistics Press 2013). For the hotels in the catchment area, the specific greywater production is expected to be higher (150 L/(guest·d) or 300 L/(guest·d) for 3-star and 5-star hotels), leading to a hydraulic population equivalent of 17,500 instead of 12,000, or an increase in the average inhabitant-specific amount of greywater from 41 to 60 L/(C·d). The C/N ratio in total wastewater is low, but not unusual. In China, COD often has to be dosed, because denitrification is impeded by the low C/N ratio (Xiao et al. 2014).

Table 2

Influent characteristics – comparison of data for RRC Qingdao and literature values for China

 GB 50101–2005RRC Qingdao (and reference design1)
Mean values in China2RRC Qingdao (and reference design)
WWTotalGWBWWWTotalGWBW
Load g/(C·d)Concentration mg/L
COD – 100 12.3 87.7 300–440 781 (917) 206 (300) 1,290 
BOD 25–50 50 4.9 45.1 – 391 (459) 82 (120) 663 
SS 40–65 65 10.3 54.8 – 508 (596) 171 (251) 805 
TN 5–11 11.3 0.3 11 34–40 88 (104) 5 (7) 162 
TP 0.7–1.4 1.56 0.16 1.4 4–5.4 12 (14) 3 (4) 21 
Q in L/(C·d) – 128 (109) 60 (41) 68 – – – – 
 GB 50101–2005RRC Qingdao (and reference design1)
Mean values in China2RRC Qingdao (and reference design)
WWTotalGWBWWWTotalGWBW
Load g/(C·d)Concentration mg/L
COD – 100 12.3 87.7 300–440 781 (917) 206 (300) 1,290 
BOD 25–50 50 4.9 45.1 – 391 (459) 82 (120) 663 
SS 40–65 65 10.3 54.8 – 508 (596) 171 (251) 805 
TN 5–11 11.3 0.3 11 34–40 88 (104) 5 (7) 162 
TP 0.7–1.4 1.56 0.16 1.4 4–5.4 12 (14) 3 (4) 21 
Q in L/(C·d) – 128 (109) 60 (41) 68 – – – – 

1Bi (2004); 2Qiu et al. (2010); GW – greywater; BW – blackwater; WW – wastewater; SS – suspended solids; Q – flow.

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