USE OF CONSTRUCTED WETLANDS AND SAND FILTERS TO IMPROVE THE QUALITY OF WATER IN BOMACHOGE-BORABU, KENYA

Abstract

Degradation of aquatic ecosystems resulting from pollution, poor waste disposal management practices and inadequate knowledge is of concern. Water sources in developing countries are abundantly contaminated with animal and human waste, chemicals and microbial agents, thereby causing loss of vast diversity of aquatic organisms. There is need to address this problem using efficient and affordable methods. Constructed wetlands and sand filters have been effectively used individually to improve water quality and reduce pollution levels. This study aimed at integrating constructed wetlands and sand filters to improve microbiological and physico-chemical parameters of domestic water with the hope of reducing waterborne diseases and loss of aquatic life. The study was conducted between March 2015 and March 2016 in Bomachoge Sub County, Kenya. The study sites included: Bokimonge, Magenche, Bombaba and Boochi. The study evaluated the combined effects of constructed wetlands and sand filters on selected water parameters. The experimental set up was a two level factorial design with three plant-type cultures (Colocasia esculenta and Cyperus esculentus as monocultures and a polyculture of the two plants) and 4 sand grain sizes (0, 0.5, 1.0 and 2.0 mm) as factors. The study further investigated the effects of pit latrine location, construction and designs on well and spring water quality. Data was collected using questionnaires, observations, measurements and laboratory examination of selected water parameters. The collected data was coded, scored and analyzed using SPSS program and a two-way ANOVA after appropriate transformations. Results indicated that plant-type, sand grain size and an interaction between the two factors had significant effects (P≤0.05) on the 12 microbiological and physico-chemical parameters assessed in this study. Although there were no significant differences in the removal efficiency of C. esculenta alone and with the sand filters, the addition of sand filters statistically improved the removal efficiency of C. esculenta. A combination of C. esculenta and the sand filters had the highest removal efficiency of 98% (Total coliforms (TC)), 98% (Fecal coliforms (FC)), 99% (E. coli (EC)), 99% (Fecal Streptococci (FS)), 95% (NO3) and PO4 (97%). A monoculture of C. esculentus reduced TC (21%) and FC (9%). Addition of sand filters to C.esculentus improved its reduction efficiency by an additional 64% and 60% for TC and FS respectively. A polyculture of C. esculentus and C. esculenta alone reduced TC, FC and EC by an average 26%, 36% and 31% respectively and further reduced the parameters by an average 54%, 50% and 60% for TC, FC and EC respectively on addition of the sand filters. The results revealed that water from wells and springs in this study were highly contaminated. The short horizontal and vertical separation distance between the fecal disposal point and hand dug well impacted on water pollution. However, results indicated that there were 0 cfu/100mls observed above 60 meters and vertical separation distance of 1.14 meter equally recorded 0 cfu/100mls. It was concluded that C. esculenta was efficient in improving the quality of water to almost 0 cfu/100mls as per WHO standards. It was recommended that further research be carried out on other native plant species and sand filters in others areas of Kisii county, to determine their effects on water quality. In addition, there should be good waste disposal systems with appropriate design, location and maintenance.