Vertical flow constructed wetland treating high strength wastewater from swine slurry composting

An integral solution for the recovery of fertilizer elements contained in swine farm slurry is the joint composting of diverse solid wastes generated in the installation and surroundings, in which the composting material was watered with swine slurry. In such a system, a high percentage of the water contained in the slurry is evaporated while nutrients are, in part, retained in the compost produced. This paper presents the results of a pilot vertical flow constructed wetland (VFCW) treating the high strength leachate generated from the compost piles. The VFCW was provided with effluent recycling in order to deal with high influent concentrations of nitrogen compounds, which reached up to 459 mg NH3-N/L and 904 mg TKN/L without the need for dilution with clean water. After start-up, and operating at 10 °C with surface loading rates (SLRs) of 9.2, 17.9, 4.8 and 1.9 g/m2 d of TSS, TCOD, BOD5 and TN, respectively, the VFCW reduced the concentration of all these parameters by more than 93%. Effluent concentration of nitrate was high during the two first months of operation (178 mg NO3-N/L), but afterwards simultaneous nitrification and denitrification developed, reaching total nitrogen removal of 93% and low effluent nitrogen concentration (16 mg NH3-N/L and 10 mg NO3-N/L). Furthermore, options to avoid clogging or to facilitate the application of higher SLR are discussed.