Effects of hydraulic detention time, water depth, and duration of operation on nitrogen and phosphorus removal in a flow-through duckweed bioremediation system

摘要

The effects of retention time, duration of operation, and the relationship between surface area to depth ratio on nitrogen and phosphorus removal efficiencies were assessed in duckweed-populated flow-through experimental reactors. Reactors were designed so that a group of four reactors had the same surface area but each reactor in a group differed by both depth and detention times, and four sets of reactors had the same volume and detention time but differing surface areas. Removal efficiencies for nitrogen and phosphorus compounds decreased with increasing water depth and increased with increasing surface area to depth ratios. Nitrogen removal efficiency initially increased, reaching maximum removal efficiency after 6-7 days, approached approximately 100% removal efficiency for 9-10 days, and then exhibited a decrease in removal efficiency. Phosphorus removal efficiency reached a maximum after approximately 5 days, followed by reduced removal efficiencies with values approaching 0 after 12-20 days. Maximum productivity occurred at day 5 but was reduced to approximately 25% of maximum productivity by day 8. To maintain optimal productivity, duckweed harvesting should occur at 5-day intervals.