Wetland and terrestrial phytoremediation of an end-of-life municipal lagoon using cattail (Typha spp.)
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Date
2018
Authors
Jeke, Nicholson Ngoni
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Abstract
Spreading biosolids on farmland is a common biosolids management practice in western Canada. Wetland and terrestrial-based phytoremediation approaches may be viable options for remediating biosolids in end-of-life municipal lagoons. Water depth is regulated during wetland phytoremediation whereas there is no control of water regime during terrestrial phytoremediation. Studies were conducted to quantify cattail (Typha spp.) biomass and nitrogen (N) and phosphorus (P) phytoextraction from biosolids in (i) a wetland constructed in the former primary cell and (ii) a dewatered secondary cell of an end-of-life municipal lagoon. Overall, the phytoextraction of N and P by cattail was lower with a single harvest than two harvests per year. The study also examined the effects of harvest timing (August, November, and April) on nutrient removal in the harvested cattail biomass. Compared to August, harvesting cattails in the wetland in November or April reduced N and P phytoextraction by 63-85%. In the wetland study, nutrient phytoextraction was 6.2% of initial N content and 2.2% of initial P content while the terrestrial-based approach removed 5.8% and 2.3% of the initial N and P content, respectively. A greater fraction of P (~ 73%) taken up by cattail was sequestered in the rhizomes, which reduced its mobility and transport to surface waters. A study examining nutrient availability using plant root simulator (PRS) probes during wetland-based phytoremediation showed that N supply rate increased with time after July whereas phosphate supply rate remained relatively unchanged. Cumulative nutrient supply rate was positively correlated with plant uptake. The effects of flooding on P release during terrestrial phytoremediation in the secondary cell was investigated using biosolids cores. Dissolved reactive P (DRP) was the major fraction of P in floodwater. Flooding for more than 3 d resulted in the release of >0.5 mg L-1 DRP to floodwater. Our results suggest that biosolids pose a risk of P loss to surface water bodies receiving floodwater from the lagoon. Releasing floodwater closer to the start of the flooding event minimizes P release to floodwater. Overall, this research shows that phytoremediation is a viable, low-cost option for managing biosolids from end-of-life municipal lagoons.
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Keywords
Phytoremediation, Biosolids, Nitrogen, Phosphorus, Constructed wetlands