REVIEW PAPER ON HORIZONTAL SUBSURFACE FLOW CONSTRUCTED WETLANDS: POTENTIAL FOR THEIR USE IN CLIMATE CHANGE MITIGATION AND TREATMENT OF WASTEWATER

The combination of rapid urbanization and industrialization expansion increased waste volumes. Most of the wastewaters generated from either domestic or industrial sources are still discharged without adequate treatment processes, and impact on the environment and public health. The objective of this paper was to provide a comprehensive literature review on the application of horizontal subsurface flow constructed wetlands in treating a variety of wastewaters, discussing its feasibility in pollutant removal efficiency and additional benefit in climate change mitigation through carbon sequestration. The following results were obtained: 98%, 96%, 85%, 90%, 92%, 88% for BOD5, COD, TSS, TN, NH4-N, PO(4)3- respectively in Kenya; 98.46% and 98.55% for COD and BOD5 in Indonesia; and ranges from 94-99.9%, 91.7-97.9% and 99.99% for BOD5, COD and TFC respectively in Costa Rica. Whereas in Ethiopia, the HSSFCW achieved the following abatement efficiencies: COD ranges from 58 to 80%, BOD ranges from 66 to 77%, TKN ranges from 46-61%, sulfates ranges from 53 to 82%, and NH4 - N range from 64 to 82.5% for tannery wastewater treatment. For domestic wastewater treatment; 99.3%, 89%, 855, 84.05%, 77.3%, 99% and 94.5% were achieved for BOD5, COD, TSS, TN, PO43-, TP, Sulfate, and TFC, respectively. In addition to improving water quality, CWs have a CSP. For example, CWs showed CO2 equivalent of 4119.54 g C/m(2)/yr CSP (carbon sequestration potential) which is 15118.7118 g CO2. The methane equivalent to this amount of carbon sequestration is 604.748472 g/m(2)/yr. Generally, research results indicated that constructed wetlands are efficient wastewater treatment techniques and should be encouraged for wastewater management as a strategy to reduce wastewater pollution. However, constructed wetland performance efficiency sustainability is affected by the operational conditions of HSSFCW including plant species, media/substrate types, water depth, hydraulic loading, and hydraulic retention time and feeding mode.