Nutrient Transformations in a Natural Wetland Receiving Sewage Effluent and the Implications for Waste Treatment

Abstract

The processes influencing nutrient (phosphorus and nitrogen) renovation in a natural wetland which had received oxidation pond effluent for twelve years were studied, and compared with current literature perceptions. Mass transport studies showed that 30–70% of the influent P was removed from the water column, which was much greater than published values suggest could be predicted for this highly loaded (∼ 34 g P m−2 y−1) system. Sediment traps studies showed that deposition of particulate P immediately downstream of confluences with arms of the wetland not impacted by sewage effluent (natural wetlands) was the dominant cause of P removal. Separation of the deposited-P into chemically definable fractions along with studies on the water chemistry, suggested that P deposition was associated with iron-organic complexes contributed dominantly from the natural wetlands. Considerable spatial and temporal heterogeneity was also demonstrated for nitrogen transformations. During summer most of the influent-N was in nitrate form which was all transformed during passage through the wetland. Isotope (15N) dilution studies indicated that ∼ 60–70% was denitrified, 25–35% converted to ammonium (dissimilatory reduction), and 5–10% assimilated. For most of the year, however, influent N was mainly in reduced forms. Despite this, significant quantities of nitrate were exported from the wetland especially at higher flows in spring-early summer. Assays on the sediment showed that there was a marked increase in nitrification activity at the confluence with natural wetlands. It is suggested that marked changes in sediment redox potential at these confluence sites provide ideal conditions for nitrification of sorbed ammonium which is subsequently flushed from the system in ‘flood events’. The distribution and type of nutrient processing observed in this wetland are attributable to its configuration. The implication of these results to the sustainability of nutrient renovation in wetland treatment systems is discussed.

Management of Tundra Wastewater Treatment Wetlands within a Lagoon/Wetland Hybridized Treatment System Using the SubWet 2.0 Wetland Model

“…The simulations also show that designs of new systems can include shorter wetland lengths when paired with appropriately sized facultative lakes and long-term retention lagoons to avoid spring freshets laden with semi-frozen untreated wastes. Evidence from other natural wetland systems outside of the arctic demonstrates that these natural systems have an ability to treat municipal wastewater and effluents and thus corroborate our findings [42][43][44][45][46][47][48]. Even in Arctic environments where nutrient and carbon cycling proceed at a slow pace for much of the year, assimilation and even treatment through natural processes are evident.…”

Phosphorus adsorption characteristics of a constructed wetland soil receiving dairy farm wastewater

“…Phosphorus removal rates in wastewater wetland systems can be greater than that predicted by soil adsorption maxima due to Fe, Al, or Ca forming precipitates with phosphate that could remove soluble P from solution (Cooke et al 1992). Phosphorus removal in wetlands can be sustainable provided the relative supply of reactants for phosphate precipitation continues (Cooke 1994). This may be a treatment consideration of interest in the wetland due to the nature of the influent wastewater.…”

Application of Eichhornia crassipes and Pistia stratiotes for treatment of urban sewage in Israel

“…Several physical, chemical and biological processes are involved in the transformation and consumption of organic matter and plant nutrients within the wetland (Cooke, 1994;Gale et al 1993). The most important functions of the macrophytes in the treatment of wastewater relate to physical effects which they induce therein (Brix, 1997).…”