Background: Chemical fertilizers used for field crops have three main macronutrients components:
nitrogen, phosphorus and potassium. They are the limiting factor to plant growth. Effluents from treated
wastewater have appropriate concentration levels of those macronutrients to support crop production.
Aim: The main purposes of this pilot case field study were: (i) to recover the valuable nutrients from sewage
using a recirculating vertical flow constructed wetland planted on top with soybean (Glycine max, L.); (ii) to determine
the potential of growing renewable feedstock commodities irrigated with treated effluent as a phytoremediation
mechanism to clean wastewater onsite.
Method: Grab samples of effluents from both septic tank and the constructed wetland were analyzed for water
Result: Mean treatment efficiencies (removal) were high for biochemical oxygen demand (98%), ammoniumnitrogen
(97%), total suspended solids (96%), total Kjeldahl nitrogen (95%), fecal coliforms (93%), total nitrogen
(85%), and total phosphorus (77%), while it was relatively low for potassium (43%). Supplementary irrigation
or commercial fertilizers were not added during the growing season. The mean yield ± standard deviation
(seed mean weight ± standard deviation) for fresh dried weight of soybeans crop was equivalent to 2,625 ±
1,653 kg/ha (0.21 ± 0.05 g/bean).
Conclusion: These results show that soybean growing on top of a recirculating vertical flow constructed
wetland could be a sustainable alternative technology and a green mechanism to remove pollutants (nutrients)
from sewage. Also, nutrients recovery through direct reuse of treated sewage effluents as source
of fertilizers and water to grow first-generation biofuels commodities such as soybean is feasible.