Septage treatment using a combined waste stabilization ponds-vertical flow constructed wetland system

摘要

Eight vertical flow small-scale constructed wetlands were introduced in a pre-existing waste-water treatment pilot plant consisting of three interconnected waste stabilization ponds-a facultative pond followed by two maturation/aerobic ones. The wetlands were identical in couples but differed in substrate and plant presence (common reed) and were fed from the outflow of the first maturation pond. The system was monitored for two years in order to study its operation and efficiency for the treatment of septage in an open air experiment. Samples were collected twice a month and TSS, BOD_5, pH, EC, TP, N-NO_3~- and N-NH_4~+ were monitored. BOD_5 removal was greater in the summer months. The unplanted wetlands were more efficient in TSS and BOD_5 concentrations removal. Still, when estimating the BOD_5 mass in the constructed wetlands effluents using Thornthwaite model to adjust the results, it was found that the BOD_5 mass of unplanted wetlands effluents is greater than that found in planted ones. The system did not remove TP successfully, possibly due to substrate origin and stratification. N-NO_3~- concentrations in all wetlands' effluents were elevated due to nitrification. Nutrients removal was greater in the planted wetlands. Redesigning the constructed wetlands using a thicker sand layer could increase pollutants removal. The concentrations of the pollutants in the effluents from the constructed wetlands were lower than in the effluents from the waste stabilization pond that treated the same influent.