Assessment of pre-digested piggery wastewater treatment operations with surface flow integrated constructed wetland systems

Non-point source pollution such as land-spreading of nitrogen-rich piggery wastewater poses a significantthreat to surface waters. The aim was to examine the treatment of anaerobically digested piggerywastewater using four different meso-scale integrated constructed wetland (ICW) systemsplanted with Glyceria maxima. Four replicates were used for each system to assess differences dueto nutrient loading, hydraulic loading and effluent recycling. All systems were effective in removingtotal organic nitrogen, ammonia-nitrogen, nitrate-nitrogen and molybdate reactive phosphorus. However,ammonia-nitrogen removal was the greatest challenge for high flow rates (>100 m3/ha/d). Nitrificationwas higher in summer than winter. Findings show for the first time that effluent recyclingwithin ICW was beneficial to lower ammonia-nitrogen but was associated with higher operationalcosts. The cost–benefit ratio based on ammonia-nitrogen removal for standard, recycling, high nutrientsand high flow rate treatments was 1.08:1.04:1.06:1.00. It follows that a high flow rate was onlymarginally more cost-effective