Key triggering factors in the clogging process of Nyarutarama hybrid ponds treating municipal wastewater in Kigali

Abstract

Constructed wetlands are man man-made wetlands or ponds that use the natural processes involving wetland vegetation, gravel, sand and their associated microbial assemblages to treat and improve the quality of wastewater effluent. The major operational challenge faced by natural wastewater treatment systems including constructed wetlands or hybrid ponds is the clogging process of porous media resulting from the accumulation of various solids types such inorganic solids from chemical precipitation, sludge from sedimentation and biological process like plant detritus and biofilm formation. The present study was carried out to determine the level of clogging process of Nyarutarama natural ponds system treating sewage from neighboring estate. Data were collected through the key informant interview about the key triggering factors in clogging process of that treatment system. This system is made by a combination of three series of constructed ponds that were built in Kigali. The assessment results indicated the clogging level of 78%, 60%, and 75% for primary facultative pond, water lettuce covered pond and free water surface flow pond respectively. Those results indicated that the ponds system clogging was due to the accumulation of solids materials resulting from the lack of operational, monitoring and maintenance plans. The well operated and managed constructed wetlands can effectively be used for environmentally and friendly treatment of wastewater rather than using conventional treatment systems since constructed wetlands are inexpensive. The constructed wetlands and hybrid ponds can easily be operated and maintained. In addition, when they are well designed they can serve as touristic and field study areas.