ABSTRACT
An assessment of wastewater treatment efficiency of Chemirei constructed wetland (CW) at James Finlay's farm in Kericho was carried out from November 2014 to February 2015. Water samples were collected twice per month from seven sampling points (S1-S7) using acid cleaned bottles for analysis. In situ measurements of Dissolved Oxygen (DO), pH, EC and temperature were done using calibrated meters and probes. Wastewater inflow and outflow rates for each purification cell were obtained using the volumetric method. Macrophyte biomass was determined using harvest method. Hydraulic retention time (t) and loading rate (q) were determined using mean flow rate (Q), system volume (V) and wetted surface area (A). In the laboratory; SRP, TP, NH4-N, NO3-N, NO2-N, TN, TSS, BOD and COD were determined using Standard Methods for Analysis of Water and Wastewater (APHA, 2004). Data were checked for normality and homogeneity of variance prior to parametric test. Analysis was done using IBM SPSS statistics 21 (USA) and comparison of means of different wastewater variables were performed using Analysis of Variance (ANOVA). Tukey HSD post hoc test was applied to separate means between the sampling sites where all statistical tests were considered significant at p<0.05 (95% confidence interval). The mean inflow rate was 37.91 ± 9.96 m3 and outflow 12.31 ± 4.67 m3 per day with HRT of 14 days and HLR of 0.23 m per day. The results showed mean removal efficiency of NH4-N (98%), TP (93.6%), SRP (61.6%), NO3-N (88.6%), TN (88.6%), TSS (98.1%), BOD (69.5%) and COD (57.2%). Macrophyte nitrogen accumulation was highest in Fimbristylis complanata with 57.70 gm-2 and biomass of 3085 ± 99.31 gm-2 while phosphorus accumulation was highest in Cyperus alternifolius at 7.29 gm-2 with biomass of 8896 ± 195.61 gm per m2. Pistia stratiotes had the lowest nitrogen accumulation at 3.73 gm-2 with biomass of 333 ± 18.59 gm-2 while Cyperus rotundus had the lowest phosphorus at 0.58 gm-2 with biomass of 503 ± 23.99 gm-2. There was significant removal of nutrients and TSS (p<0.05) between the wetland inlet and outlet. This study found that there was no significant impact (p>0.05) on the receiving stream water at the point of effluent discharge with respect to nutrients and TSS. The constructed wetland was efficient in removing nutrients and TSS. However, it was not able to remove the COD to the required Kenyan effluent standard. The low removal rate is an indication of the presence of non-biodegradable compounds in the wastewater.
CHAPTER ONE
INTRODUCTION
Background
Rapid increase in population growth and expansion of economic activities such as urbanization, industrial and agricultural growth are frequently associated with significant wastewater (WW) generation (Nzengy'a and Wishitemi, 2001), which requires effective treatment prior to disposal into the environment. The expanding floriculture in developing countries particularly in Kenya, with an enormous and increasing application of fertilizers and pesticides poses a potential threat to the environment, including aquatic ecosystems and human health through water pollution (Kivaisi, 2001) from both non-point and point sources.
In the last two decades, Kenya has turned into a successful cut flower exporter attaining the second largest developing country exporter in the world (English et al., 2004). This industry has been valued as an economic achievement and earned an annual average of USD 141 million in foreign exchange (7 % of Kenyan export value) for the ten-year period (1996-2005) and about USD 352 million in 2005 (Mekonnen et al., 2012). Despite the economic success, flower farms have been blamed for excessive water use, pollution and impacts on aquatic biodiversity (Kimani et al., 2012; Mekonnen et al., 2012).
The polluted water is frequently discharged into the aquatic environment (rivers and lakes) partially treated or untreated fostering eutrophication and dissolved oxygen depletion, leading to the death of aquatic organisms (Chen et al., 2011; Saeed and Sun, 2012). Further, the situation is getting worse with rapid urbanization and agricultural growth coupled with continuing lack of proper sanitation in developing areas (Kivaisi, 2001). Increased use of fertilizer in agricultural activities contributes significantly to non-point source pollution through run-off. Ecological technologies such as constructed wetland (CW) for wastewater treatment (WWT) represent innovative and emerging solutions for environmental protection and restoration placing them in the overall context of the need for low cost and sustainable WWT systems in third world countries (Konnerup et al., 2009; Vymazal, 2011; Nivala et al., 2012). Constructed wetland is a potential system for treatment of agricultural wastewater due to their relatively low cost, low operation and maintenance requirements, and lack of reliance on machinery or energy inputs (Tanner et al., 1995). Constructed wetlands have been applied in wastewater purification in many parts of the world and are highly suited to tropics due to favorable climatic conditions (Diemont, 2006).
Constructed wetlands treatment efficiency is a function of environmental conditions and proper management (Akratos and Tsihrintzis, 2007). In order to establish the efficiency of CW systems, various scientists have carried out studies on removal of pathogens, organic matter and nutrients (Kouki et al., 2009; Saeed and Sun, 2012; Vymazal, 2013). Most of the research works done on CW efficiency have been carried out under temperate climate (Kaseva, 2004). To date limited research studies on the efficiencies of CW systems, particularly under tropical conditions in Africa have been reported (Kimani et al., 2012) and even adoption and application of it has been unexpectedly low (Kivaisi, 2001). The need for long term monitoring to track efficiency trends especially in CWs treating flower farm wastewater is of urgent need since information is currently lacking. This study aimed at assessing wastewater treatment efficiency of a free water surface flow CW treating floriculture wastewater at Finlays flower farm located southwest of Kericho town in Kenya. The information generated will contribute to informed decision making in the management of the CW.
Statement of the Problem
Pollution of surface water impair aquatic ecosystem processes and pose ecological and public health risks in developing countries such as Kenya. This is due to population growth estimated in 2014 to be 2.11% and economic growth of 4.7% in 2013 contributing to discharge of untreated or partially treated WW into the environment. Agro-based industries in Kenya are rapidly growing with increased generation of wastewater to the aquatic environment. The use of CW is increasingly being applied in polishing such wastewater. The Finlays flower farm in Kericho employs hydroponic techniques in flower production creating nutrient loop and uses FWS CW to treat wastewater. Despite the use of CW in treating floriculture WW, treatment efficiency data is currently lacking. Constructed wetlands are not a "built and forget" technology and efficiency may reduce depending on management. Due to continuous operation over nine years now, it is important to track performance through periodic monitoring to ensure effectiveness and hence safeguard aquatic resources and public health from water pollution
Objectives
General objective
To assess wastewater treatment efficiency of a constructed wetland at Finlays flower farm, Kericho, Kenya.
Specific objectives
1. To determine hydrological and physico-chemical characteristics of FWS CW at Finlay's flower farm and water quality characteristics upstream and downstream of the point of treated WW discharge into the river
2. To determine above-ground biomass, nutrient sequestration and WW nutrients concentration effects on selected structural characteristics of macrophytes at Finlays constructed wetland
3. To assess temporal and spatial variation in treatment efficiency of Finlay's constructed wetland
Hypotheses
1. There is no significant difference in hydrological and physico-chemical characteristics among treatment cells and water quality upstream and downstream of the recipient stream.
2. There is no significant difference between structural characteristics of the macrophytes among the purification cells, above ground biomass and nutrient sequestration between different emergent macrophytes used in treatment wetland at Finlays constructed wetland.
3. Finlays constructed wetland is not efficient in wastewater treatment
Justification
The economic and social developments anticipated by Kenya Vision 2030 require healthier aquatic ecosystems and higher quality water supplies. The Constitution of Kenya 2010 under Article 42 provides a right to clean and healthy environment for every citizen. This includes the aquatic environment and its benefits. In addition, effluent dischargers are subject to stringent regulatory standards and are expected to adopt corporate social responsibility for clean environment; assuming responsibility for the effects of their actions and reporting action taken to protect the surrounding communities from adverse impacts of pollution. The Finlays' flower farm generate WW coming from different compartments but very often there is an assumption that such generated WW is rich in nutrients due to fertilizer application. The Finlay's farm has built FWS CW to treat WW before discharging into the environment. Currently, no comprehensive study has been conducted in this CW to assess the efficiency of the FWS system in treating the WW before discharging into aquatic environment. To date, monthly monitoring exists for a few selected parameters. However, it is important to carry out a more comprehensive study on the CW's performance so as to enhance maintenance and ensure continuous efficient performance.
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Item Type: Kenyan Topic | Size: 68 pages | Chapters: 1-5
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