Removal of nutrients in various types of constructed wetlands

https://doi.org/10.1016/j.scitotenv.2006.09.014Get rights and content

Abstract

The processes that affect removal and retention of nitrogen during wastewater treatment in constructed wetlands (CWs) are manifold and include NH3 volatilization, nitrification, denitrification, nitrogen fixation, plant and microbial uptake, mineralization (ammonification), nitrate reduction to ammonium (nitrate-ammonification), anaerobic ammonia oxidation (ANAMMOX), fragmentation, sorption, desorption, burial, and leaching. However, only few processes ultimately remove total nitrogen from the wastewater while most processes just convert nitrogen to its various forms. Removal of total nitrogen in studied types of constructed wetlands varied between 40 and 55% with removed load ranging between 250 and 630 g N m 2 yr 1 depending on CWs type and inflow loading. However, the processes responsible for the removal differ in magnitude among systems. Single-stage constructed wetlands cannot achieve high removal of total nitrogen due to their inability to provide both aerobic and anaerobic conditions at the same time. Vertical flow constructed wetlands remove successfully ammonia-N but very limited denitrification takes place in these systems. On the other hand, horizontal-flow constructed wetlands provide good conditions for denitrification but the ability of these system to nitrify ammonia is very limited. Therefore, various types of constructed wetlands may be combined with each other in order to exploit the specific advantages of the individual systems. The soil phosphorus cycle is fundamentally different from the N cycle. There are no valency changes during biotic assimilation of inorganic P or during decomposition of organic P by microorganisms. Phosphorus transformations during wastewater treatment in CWs include adsorption, desorption, precipitation, dissolution, plant and microbial uptake, fragmentation, leaching, mineralization, sedimentation (peat accretion) and burial. The major phosphorus removal processes are sorption, precipitation, plant uptake (with subsequent harvest) and peat/soil accretion. However, the first three processes are saturable and soil accretion occurs only in FWS CWs. Removal of phosphorus in all types of constructed wetlands is low unless special substrates with high sorption capacity are used. Removal of total phosphorus varied between 40 and 60% in all types of constructed wetlands with removed load ranging between 45 and 75 g N m 2 yr 1 depending on CWs type and inflow loading. Removal of both nitrogen and phosphorus via harvesting of aboveground biomass of emergent vegetation is low but it could be substantial for lightly loaded systems (cca 100–200 g N m 2 yr 1 and 10–20 g P m 2 yr 1). Systems with free-floating plants may achieve higher removal of nitrogen via harvesting due to multiple harvesting schedule.

Introduction

Constructed wetlands are engineered systems that have been designed and constructed to utilize the natural processes involving wetland vegetation, soils, and their associated microbial assemblages to assist in treating wastewater. They are designed to take advantage of many of the processes that occur in natural wetlands, but do so within a more controlled environment (Hammer and Bastian, 1989). Synonymous terms to “constructed” include “man-made”, “engineered” or “artificial” wetlands. The basic classification is based on the type of macrophytic growth, further classification is usually based on the water flow regime (Fig. 1). The paper deals only with constructed wetlands with free-floating plants (FFP), free water surface CWs with emergent plants (FWS) and sub-surface CWs with horizontal (HSSF or HF) and vertical (VSSF or VF) flows (Fig. 2) as data on CWs with floating leaved plants and submerged plants are still not abundant, and therefore it is not possible to make sound evaluations.

Section snippets

Nitrogen

Nitrogen has a complex biogeochemical cycle with multiple biotic/abiotic transformations involving seven valence states (+ 5 to − 3). The compounds include a variety of inorganic and organic nitrogen forms that are essential for all biological life. The most important inorganic form of nitrogen in wetlands are ammonium (NH4+), nitrite (NO2) and nitrate (NO3). Gaseous nitrogen may exist as dinitrogen (N2), nitrous oxide (N2O), nitric oxide (NO2 and N2O4) and ammonia (NH3).

Phosphorus

Phosphorus in wetlands occurs as phosphate in organic and inorganic compounds. Free orthophosphate is the only form of phosphorus believed to be utilized directly by algae and macrophytes and thus represents a major link between organic and inorganic phosphorus cycling in wetlands. Another group of inorganic phosphorus compounds are polyphosphates linearly condensed and cyclic. Organically-bound phosphorus is present e.g., in phospholipids, nucleic acids, nucleoproteins, phosphorylated sugars

Conclusions

Removal of total nitrogen in studied types of constructed wetlands varied between 40 and 50% with removed load ranging between 250 and 630 g N m 2 yr 1 depending on CWs type and inflow loading. However, the processes responsible for the removal may differ in magnitude among systems. Single-stage constructed wetlands cannot achieve high removal of total nitrogen due to their inability to provide both aerobic and anaerobic conditions at the same time. Vertical-flow constructed wetlands remove

References (84)

  • C.C. Tanner et al.

    Nitrogen processing gradients in subsurface-flow treatment wetlands

    Ecol Eng

    (2002)
  • J.T.A. Verhoeven

    Nutrient dynamics in minerotrophic peat mires

    Aquat Bot

    (1986)
  • J. Vymazal

    Horizontal sub-surface flow and hybrid constructed wetlands systems for wastewater treatment

    Ecol Eng

    (2005)
  • O.K. Atkin

    Reassessing the nitrogen relations of arctic plants: a mini-review

    Plant Cell Environ

    (1996)
  • N.J. Barrow

    On the reversibility of phosphate sorption by soils

    J Soil Sci

    (1983)
  • N. Bernet et al.

    Nitrification at low oxygen concentration in biofilm reactor

    J Environ Energy

    (2001)
  • C.E. Boyd

    Production, mineral nutrient absorption, and biochemical assimilation by Justicia americana and Alternanthera philoxeroides

    Arch Hydrobiol

    (1969)
  • J.M. Bremner et al.

    Denitrification in soil. II. Factors affecting denitrification

    J Agric Sci

    (1958)
  • H. Brix

    Denmark

  • H. Brix et al.

    The use of macrophytes in water pollution control

    Ambio

    (1989)
  • H. Brix et al.

    Experiments in a two-stage constructed wetland system: nitrification capacity and effects of recycling on nitrogen removal

  • F.E. Broadbent et al.

    Denitrification

  • P.F. Cooper et al.

    Reed beds and constructed wetlands for wastewater treatment

    (1996)
  • B.C. Craft et al.

    Peat accretion and phosphorus accumulation along a eutrophication gradient in the northern Everglades

    Biogeochemistry

    (1993)
  • E.J. Dunne et al.

    Phosphorus biogeochemistry of wetlands in agricultural watersheds

  • R.M. Engler et al.

    Nitrate removal from floodwater overlying flooded soils and sediments

    J Environ Qual

    (1974)
  • D.D. Focht et al.

    Biochemical ecology of nitrification and denitrification

    Adv Microb Ecol

    (1977)
  • R. Gächter et al.

    The role of microorganisms in mobilization and fixation of phosphorus in sediments

    Hydrobiologia

    (1993)
  • T.P. Garnett et al.

    Simultaneous measurement of ammonium, nitrate and proton fluxes along the length of eucalyptus roots

    Plant Soil

    (2001)
  • B. Gopal

    Biology and ecology

  • W.D. Grant et al.

    Environmental microbiology

    (1981)
  • D.A. Hammer et al.

    Wetlands ecosystems: natural water purifiers?

  • R.D. Hauck

    Atmospheric nitrogen chemistry, nitrification, denitrification, and their relationships

  • P.G. Hunt et al.

    Nitrogen cycling in wetland systems

  • P.D. Jenssen et al.

    Design of constructed wetlands using phosphorus sorbing lightweight aggregate (LWA)

  • M.S.M. Jetten et al.

    Novel principles in the microbial conversion of nitrogen compounds

    Antonie van Leeuwenhoek

    (1997)
  • Johansen NH, Brix H. Design criteria for a two-stage constructed wetland. In: Proc. 5th Internat. Conf. Wetland Systems...
  • C.A. Johnston

    Sediments and nutrient retention by freshwater wetlands: effects on surface water quality

    CRC Crit Rev Environ Control

    (1991)
  • R.H. Kadlec et al.

    Treatment wetlands

    (1996)
  • D.R. Keeney et al.

    Denitrification and nitrate reduction in sediments: importance to the nitrogen budget in lakes

    Nature

    (1972)
  • D.R. Keeney et al.

    Effect of temperature on the gaseous nitrogen products of denitrification in a silt loam soil

    Soil Sci Soc Am J

    (1979)
  • Cited by (2216)

    View all citing articles on Scopus
    View full text