Paradigms of mangroves in treatment of anthropogenic wastewater pollution

Study Number:

99

Author:

Xiaoguang Ouyang, Fen Guo

Abstract:

Mangroves have been increasingly recognized for treating wastewater from aquaculture, sewage and other sources with the overwhelming urbanization trend. This study clarified the three paradigms of mangroves in disposing wastewater contaminants: natural mangroves, constructed wetlands (including free water surface and subsurface flow) and mangrove–aquaculture coupling systems. Plant uptake is the common major mechanism for nutrient removal in all the paradigms as mangroves are generally nitrogen and phosphorus limited. Besides, sediments accrete and provide substrates for microbial activities, thereby removing organic matter and nutrients from wastewater in natural mangroves and constructed wetlands. Among the paradigms, the mangrove–aqua-culture coupling system was determined to be the optimal alternative for aquaculture wastewater treatment by multi-criterion decision making. Sensitivity analysis shows variability of alternative ranking but underpins the coupling system as the most environment-friendly and cost-efficient option. Mangrove restoration is expected to be achievable if aquaculture ponds are planted with mangrove seedlings, creating the coupling system

Main Results and Conclusions:

• Constructed mangrove wetlands are used to treat wastewater, controls floods, etc.
  • “They provide multifunctional shallow water detention and pollutant retention, and are potentially sound options for wastewater treatment to lower energy input and costs in comparison with mechanical wastewater treatment alternatives.” (972)
  • “…different mangrove genera are used to dispose wastewater in constructed wetlands, such as Avicennia, Rhizophora and Aegiceras.” (972)
• There are two kinds of constructed mangrove wetlands.
  • “Free water surface flow mangrove wetlands are constructed with the predominant water flow volume across the surface of the wetlands.” (972)
  • “Subsurface flow mangrove wetlands are designed as horizontal or vertical water flow, which is maintained below the upper surface of special media, such as gravel and sand. They are more effective in wastewater treatment compared with FSW mangrove wetlands owing to extra physical and biological mechanisms.” (972)
• Natural mangroves receive sewage or agricultural wastewater in many parts of the world.
  • “They remove contaminants primarily through tidal flushing, mangrove plant assimilation or sediment microbial metabolism.” (974)
• Mangrove-aquaculture coupling systems use mangroves and aquatic vegetation to purify aquaculture ponds and sustain the mangroves themselves.
  • “Growth of mangrove plants depends on nutrients from aquaculture ponds, and litter from mangrove plants provide food for aquatic organisms in the ponds.” (974)
  • “Existing studies have verified the sound effect of different mangrove species on removing eutrophic pollutants from aquaculture wastewater.” (974)
• It was calculated that mangrove-aquaculture coupling systems are the best paradigm for aquaculture wastewater treatment.
  • “Mangrove–aquaculture coupling systems are suggested the optimal paradigm for aquaculture wastewater treatment based on multi-criterion decision making in our study. This conforms the idea of sustainable aquaculture with the integration of mangroves as natural biofilters (Buhmann and Papenbrock, 2013). Costa-Pierce (2002) also prompted calls on developing aquaculture as the most ecologically integrated industry.” (977)