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Table 3

The clogging control technology/strategy

AimMeasurementEffect, advantage and disadvantageCountryReferences
Clogging prevention Pre-treat the wastewater Biological contact oxidation 
  • >90% SS and >33% COD were removed.

  • Ensuring long-term stable operation of the SWI system.

  • The demonstration project has been successfully operated for 11 consecutive years and no clogging has been found.

  • High pollutant removal rates but more energy consumption.

 
China Li et al. (2019)  
Oxidation and lime treatment 
  • >82% of the SS in the sewage was removed, ensuring that SAT was running normally.

  • High SS removal but the pH of wastewater will be increased.

 
Israel Wang et al. (2020)  
Biofiltration and ozonation 
  • Dissolution of manganese oxides and the presence of Mn2+ lead to clogging.

  • The combination process decreased manganese oxide dissolution, and improved DOC removal.

  • More energy consumption and complicated equipment required.

 
Israel Zucker et al. (2015)  
Unclogging technology/strategy Optimize the medium Peat and sand 
  • The pore structure of the peat allowed the biomass to distribute itself over a greater depth and delayed the formation of a biomat and eventual clogging of the filter medium.

  • Increase the construction cost.

 
Canada Mostafa & van Geel (2015)  
Sand grain 
  • Mixed and stratified mode with two different sizes (0.3 mm and 0.6 mm) of sand grains were used for column filling.

  • Clogging occurred in the mixed sand microbial column when compared with the stratified sand microbial column.

  • Stratified mode increases the complexity of system construction.

 
India Kanmani et al. (2014)  
Bioaugmentation 
  • Bioaugmentation significantly increased the relative abundance of clostridia, which have good nitrate-reducing activity.

  • The embedding strategy significantly decreased the indigenous soil microbial diversity (p < 0.05) and altered the bacterial community structure.

 
China Liu et al. (2018a, 2018b) 
Sand, quarry dust and gravel 
  • Sand substrate was observed to perform better in organic reduction compared to quarry dust and gravel, resulting in a lower risk of clogging.

  • Sand substrate will result in a lower retention time of the wastewater.

 
Kenya Mbubu et al. (2019)  
Operate alternatively 
  • Increasing the wetting–drying ratio is helpful in reducing the risk of gas clogging.

  • More land requirement.

 
China Zhang et al. (2018); Li et al. (2019)  
  • Under aerobic conditions, 35% of the accumulated solid was biodegradable at rates of 4.4–12.0 g COD/m·d.

  • More land requirement.

 
Spain Carballeira et al. (2017)  
Add oxidant 
  • The infiltration rate and porosity increased with increased dosage of NaOH, HCl, NaClO and detergent.

  • NaClO had the most obvious effects on reducing clogging and the effective porosity recovered to 69% of the original condition.

  • Disturb the microbial community structure.

 
China Hua et al. (2010)  
  • After treating wetland clogging substances with 30% concentration of H2O2, the volatile organic components were reduced by 50%.

  • Increase the operation cost.

 
India Sivasankar & Kumar (2019)  
Aerate 
  • The dissolved oxygen environment in vertical-flow constructed wetlands was improved.

  • Under the action of airflow, the biofilm is not easy to settle.

  • The removal rate of ammonia nitrogen can be as high as 89.6% while alleviating the clogging of biofilm.

  • Increase the operation cost.

 
China Li et al. (2014)  
  • Intermittent aeration achieved high removal of COD, TP, NH4+-N and TN.

  • Increase the operation cost.

 
China Pan et al. (2015) 
  • Positive correlation was found between aeration and removal efficiency of accumulated solids.

  • Increase the operation cost.

 
Italy Labella et al. (2015) 
Evaluate the clogging behavior Numerical simulation 
  • Using the equilibrium model and physical non-equilibrium model in CXTFIT, the main location and mechanism of gas clogging in SWI were initially revealed.

  • Longer time required for numerical balance.

 
China Wang et al. (2019) 
  • The two-dimensional model HYDRUS was used.

  • The rate of decline of hydraulic conductivity is likely to depend on the particle size distribution of water.

  • Few reports on its application in large-scale clogging predictions.

 
USA Sobotkova et al. (2018) 
AimMeasurementEffect, advantage and disadvantageCountryReferences
Clogging prevention Pre-treat the wastewater Biological contact oxidation 
  • >90% SS and >33% COD were removed.

  • Ensuring long-term stable operation of the SWI system.

  • The demonstration project has been successfully operated for 11 consecutive years and no clogging has been found.

  • High pollutant removal rates but more energy consumption.

 
China Li et al. (2019)  
Oxidation and lime treatment 
  • >82% of the SS in the sewage was removed, ensuring that SAT was running normally.

  • High SS removal but the pH of wastewater will be increased.

 
Israel Wang et al. (2020)  
Biofiltration and ozonation 
  • Dissolution of manganese oxides and the presence of Mn2+ lead to clogging.

  • The combination process decreased manganese oxide dissolution, and improved DOC removal.

  • More energy consumption and complicated equipment required.

 
Israel Zucker et al. (2015)  
Unclogging technology/strategy Optimize the medium Peat and sand 
  • The pore structure of the peat allowed the biomass to distribute itself over a greater depth and delayed the formation of a biomat and eventual clogging of the filter medium.

  • Increase the construction cost.

 
Canada Mostafa & van Geel (2015)  
Sand grain 
  • Mixed and stratified mode with two different sizes (0.3 mm and 0.6 mm) of sand grains were used for column filling.

  • Clogging occurred in the mixed sand microbial column when compared with the stratified sand microbial column.

  • Stratified mode increases the complexity of system construction.

 
India Kanmani et al. (2014)  
Bioaugmentation 
  • Bioaugmentation significantly increased the relative abundance of clostridia, which have good nitrate-reducing activity.

  • The embedding strategy significantly decreased the indigenous soil microbial diversity (p < 0.05) and altered the bacterial community structure.

 
China Liu et al. (2018a, 2018b) 
Sand, quarry dust and gravel 
  • Sand substrate was observed to perform better in organic reduction compared to quarry dust and gravel, resulting in a lower risk of clogging.

  • Sand substrate will result in a lower retention time of the wastewater.

 
Kenya Mbubu et al. (2019)  
Operate alternatively 
  • Increasing the wetting–drying ratio is helpful in reducing the risk of gas clogging.

  • More land requirement.

 
China Zhang et al. (2018); Li et al. (2019)  
  • Under aerobic conditions, 35% of the accumulated solid was biodegradable at rates of 4.4–12.0 g COD/m·d.

  • More land requirement.

 
Spain Carballeira et al. (2017)  
Add oxidant 
  • The infiltration rate and porosity increased with increased dosage of NaOH, HCl, NaClO and detergent.

  • NaClO had the most obvious effects on reducing clogging and the effective porosity recovered to 69% of the original condition.

  • Disturb the microbial community structure.

 
China Hua et al. (2010)  
  • After treating wetland clogging substances with 30% concentration of H2O2, the volatile organic components were reduced by 50%.

  • Increase the operation cost.

 
India Sivasankar & Kumar (2019)  
Aerate 
  • The dissolved oxygen environment in vertical-flow constructed wetlands was improved.

  • Under the action of airflow, the biofilm is not easy to settle.

  • The removal rate of ammonia nitrogen can be as high as 89.6% while alleviating the clogging of biofilm.

  • Increase the operation cost.

 
China Li et al. (2014)  
  • Intermittent aeration achieved high removal of COD, TP, NH4+-N and TN.

  • Increase the operation cost.

 
China Pan et al. (2015) 
  • Positive correlation was found between aeration and removal efficiency of accumulated solids.

  • Increase the operation cost.

 
Italy Labella et al. (2015) 
Evaluate the clogging behavior Numerical simulation 
  • Using the equilibrium model and physical non-equilibrium model in CXTFIT, the main location and mechanism of gas clogging in SWI were initially revealed.

  • Longer time required for numerical balance.

 
China Wang et al. (2019) 
  • The two-dimensional model HYDRUS was used.

  • The rate of decline of hydraulic conductivity is likely to depend on the particle size distribution of water.

  • Few reports on its application in large-scale clogging predictions.

 
USA Sobotkova et al. (2018) 
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