Effects of the Hydraulic Retention Time on Pig Slurry Purification by Constructed Wetlands and Stabilization Ponds

The overuse of pig slurry for fertilization purposes could involve an environmental risk. Pig slurry has been scarcely treated using constructed wetlands and stabilization ponds. Further information on hydraulic retention time comparison at fullscale in farms is desired. This survey aims to optimize a low-cost system comparing two hydraulic retention times (3 and 7 days) to purify pig slurry. Physical, chemical and microbial parameters were tested. A mechanical separator provided homogenous influent to feed the constructed wetland. Seven days of retention presented higher COD and N removal while 3 days of retention was more effective to remove TP and SO42- in the constructed wetland. However, higher removal efficiencies were registered performing 7 days of retention for Mn (148.1 %), TP (113.4 %), KN (102.6 %), COD (102.5 %), NH4+-N (94.0 %), TC (87.9 %), Cu (64.2 %), FS (47.4 %), NO3- (36.6 %), Ca2+ (32.1 %), and Br- (26.0 %) in the whole system, pointing out the positive effect of the storage pond. Though the main potential pollutants were effectively reduced, parameters such as Fe, SO42-, SS, Zn and NO2- increased after purification.