Bioreactor and wetland combinations
DOI:
https://doi.org/10.15626/Eco-Tech.2001.018Keywords:
Wastewater treatment, nutrient removal, natural treatment, biofilm, activated sludge, sustainability.Abstract
Wastewater treatment plants combining bioreactors and natural processes, designed to achieve
cost efficient treatment, are described and evaluated. The plants have a common general
layout: an anaerobic pretreatment, an aerated bioreactor, sedimentation with sludge return and
a final sub-surface flow wetland treatment. Variations in this design, adaptations to various
applications, process control strategies and sludge handling are discussed. Removal
efficiencies obtained varies in the range: 96-99 % BOO7, 72-88 % COD, 92-96 % SS, 80-99
% P, 37-91% N, where more advanced control yield higher efficiency. Thermo-tolerant fecal
coliform bacteria are typically removed by 99.9 %. Most of the nitrogen is removed in the
bioreactors. Computer controlled aeration and sludge handling is required to obtain the high
total nitrogen removal (> 80 %) Phosphorus can also be removed in the bioreactors and
exported as sludge, or, more cost effectively, mainly removed in the wetland part of the plants.
The cost efficiency of such treatment plants is good compared to alternative solutions.
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