Biofilter design for effective nitrogen removal from stormwater – influence of plant species, inflow hydrology and use of a saturated zone

Abstract

The use of biofilters to remove nitrogen and other pollutants from urban stormwater runoff has demonstrated varied success across laboratory and field studies. Design variables including plant species and use of a saturated zone have large impacts upon performance. A laboratory column study of 22 plant species and designs with varied outlet configuration was conducted across a 1.5-year period to further investigate the mechanisms and influences driving biofilter nitrogen processing. This paper presents outflow concentrations of total nitrogen from two sampling events across both 'wet' and 'dry' frequency dosing, and from sampling across two points in the outflow hydrograph. All plant species were effective under conditions of frequent dosing, but extended drying increased variation between species and highlighted the importance of a saturated zone in maintaining biofilter function. The saturated zone also effectively treated the volume of stormwater stored between inflow events, but this extended detention provided no additional benefit alongside the rapid processing of the highest performing species. Hence, the saturated zone reduced performance differences between plant species, and potentially acts as an 'insurance policy' against poor sub-optimal plant selection. The study shows the importance of biodiversity and inclusion of a saturated zone in protecting against climate variability.

Temporary Storage or Permanent Removal? The Division of Nitrogen between Biotic Assimilation and Denitrification in Stormwater Biofiltration Systems

“…This difference may in part reflect a design change towards media with a high sand and low nutrient content, which minimises nutrient leaching [9], [26]. However, the current results do require validation under field conditions and extension by tracing nitrogen fate over longer periods.…”

Avaliação dos dois primeiros anos de operação de um wetland construído vertical de fundo saturado aplicado no tratamento de esgoto sanitário

“…O bom desenvolvimento da macrófita provavelmente está relacionado à saturação do maciço filtrante, o qual disponibilizou maior umidade ao meio. Estudos com ensaios em colunas simulando filtros biológicos com variáveis de projeto, incluindo espécies de macrófitas e zonas saturadas, concluiu que a inclusão de uma zona saturada em filtros biológicos tem grande importância para as macrófitas, na proteção das mesmas contra a variabilidade climática, principalmente relacionada à disponibilidade hídrica [20]. Além da adaptação e do desenvolvimento, as macrófitas também se apresentaram resilientes em relação à presença de plantas invasoras e infestação de afídeos.…”

Application of denitrifying wood chip bioreactors for management of residential non-point sources of nitrogen

“…2), which promote uptake of nutrients, enhance microbial activity in the root zones and contribute DOC for denitrification [42–44]. A timeline showing the development of bioretention systems is provided in Fig.…”

“…Several studies have compared bioretention systems with and without plants and found that generally, systems with plants perform better at removing nitrogen than systems without plants [42, 44, 71, 72]. Studies have observed how plant species along with the organic content in the media of the bioreactor and the use of an IWSZ influence the variation of nitrogen removal.…”