Nutrient recovery from domestic wastewater using a UASB-duckweed ponds system

36 The pilot-scale wastewater treatment system used in this study comprises a 40 1 UASB reactor (6 hours HRT) followed by three duckweed ponds in series (total HRT 15 days). During the warm season, the treatment system achieved removal values of 93%, 96% and 91% for COD, BOD and TSS, respectively. Residual values of ammonia, TKN and total phosphorus were 0.41 mgN/1, 4.4 mgN/1 and 1.11 mgP/1, with removal efficiencies, 98%, 85% and 78%, respectively. The system achieved 99.998% faecal coliform removal during the warm season with final effluent containing https://www.w3.org/1998/Math/MathML" display="inline"> 4 × 10 3 cfu/100ml. During the winter, the system was efficient in the removal of COD, BOD and TSS (92%, 93% and 91%) but not for nutrients (39% for ammonia, 53% for TKN and 57% for total P). The system is deficient in the removal of faecal coliform during the winter, producing effluent with https://www.w3.org/1998/Math/MathML" display="inline"> 4 . 7 × 10 5 cfu/100ml. During the warm season, the N removal consisted of 80.5% by plant uptake, 4.7% by sedimentation and 14.8% by denitrification and volatilisation. Duckweed production rate of 33 ton dry matter per hectare per 8 months (warm season) was achieved. This amount of duckweed could replace wheat bran in commercial animal/fish feed with an equivalent value of 16,830 Egyptian Pound (US$ 4,360, March 2002) based on local price of wheat bran.