Long-term operation of an upflow anaerobic sludge blanket reactor coupled with a two-stage constructed wetland for domestic wastewater treatment

This work investigated the long-term (>1000 days) performance of an integrated process consisting of an upflow anaerobic sludge blanket (UASB) coupled to a two-stage (saturated and unsaturated) vertical subsurface flow constructed wetland (VSSF-CW) for the treatment of up to 91.3 f 10.3 m3/d domestic wastewater. The UASB reactor operated under ambient conditions during both the winter (temperature of 13.5 f 0.7 degrees C) and the summer (temperature of 26.4 f 0.8 degrees C). The two-stage CW treated the UASB effluent to maximize the total suspended solids (TSS) and chemical oxygen demand (COD) removal of the integrated process and oxidize ammonium to nitrate. The UASB reactor was able to remove 50 % f 17 % to 83 % f 9 % of TSS and 43 % f 18 % to 76 % f 3 % of COD, producing on average 0.36 Nm3 CH4 kg CODrem-1 of biogas, which varied significantly with season. The two-stage CW contributed to the further removal of the pollutants achieving overall removal of TSS ranging from 97 % f 3 % to 99 % f 0 % and COD from 91 % f 2 % to 96 % f 1 %. The influent ammonium nitrogen removal ranged between 87 % f 4 % and 99 % f 0 % via nitrification. This operation scheme allowed nutrient retention in the final effluent as the total nitrogen and total phosphorus removal was only partial (no more than 41 % f 7 % and 44 % f 13 %, respectively). The results suggest that the UASB - CW integration is a very promising solution to produce energy and Class A reclaimed water (EU Regulation 2020/741). The robustness and effectiveness of the treatment process against loading and temperature fluctuations can prevent the quality compromise of the final effluent.