Phosphorus removal from agricultural tile drainage effluent

Subsurface tile drains under agricultural field crops are a major source of phosphorus
(P) discharge to aquatic ecosystems, contributing to the eutrophication of surface
waters. Adsorption reactors for P removal from drainage water (P-reactors) could
reduce P outflow from agricultural land but were rarely studied in cold, temperate
climates. In our study, four low-cost P-reactors were installed in agricultural fields
in south-central Québec, Canada. Activated alumina (AA) beads were used as Padsorptivematerial,
and the reactors were connected to tile drain outlets. Paired water
samples (39 events) from reactor inlets and outlets were analyzed for P species and
other physicochemical parameters during one calendar year to assess the P removal
from tile drain effluent in the P-reactors. Collectively, the P-reactors retained approximately
half (48%) of the total mass of P flowing through the tile drains, mostly (92%)
as particulate P. The mass of AA beads adsorbed 11% of the dissolved-P fractions.
Results are interpreted in the context of the field drainage area and will require adjustments
to the P-reactor design to accommodate larger fields. The P-reactors remained
structurally intact throughout all four seasons in a cold temperate climate, showing
the potential of simple, inexpensive P-reactors to reduce P concentration in tile drain
effluent.
Plain Language Summary
Water draining from agricultural fields contains phosphorus in dissolved and suspended
forms. As we need to minimize the phosphorus transported from agricultural
fields to rivers and lakes, the authors designed a filter system to retain the phosphorus
at the end of the field. These filters, called phosphorus adsorption reactors,
removed almost half of the phosphorus from water leaving the drainage pipe.