EFFECTS OF TREATED GREYWATER IN WETLAND ON SOIL

Abstract

Declining freshwater availability has made reuse of domestic greywater for agricultural irrigation a common practice across the world. This study examined the effects of treated greywater in wetland on soil properties and yield of irrigated pepper in Akure, Nigeria. Raw Greywater (RGW) was collected from Jadesola Hostel, Federal University of Technology, Akure, Nigeria, and pretreated via a combination of gravel of diameters < 32 mm, 24 mm and 16 mm with fine sand of diameter 0.2 mm arranged, accordingly. The filtered water was then released to a plastic Constructed Wetland (CW) consisting of similar combination of layers of gravel and sand with common reed planted on it for final treatment. The RGW and Treated Greywater (TGW) were analyzed for Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD), pH, Electrical Conductivity (EC), Total Dissolved Solid (TDS) and heavy metals. Freshwater (FW) was obtained from the Central Water Reservoir located at Obanla campus of the university, and was also analyzed. The irrigation treatments consisted of RGW, TGW and FW in a Randomized Complete Block Design (RCBD) of three treatments in three replicates. Soil samples were collected before and after irrigation in order to ascertain the effect of TGW on the soil properties. Furthermore, fresh pepper were collected from each treatment plots for proximate and minerals analysis. The results showed reduction in BOD by 91.62%, 90.92% and 91.79%, COD by 92.01%, 91.46% and 90.70%; and TDS by 42.26%, 38.73% and 34.93%, in 2016, 2017 and 2018 dry seasons, respectively. In addition, TGW led to appreciable increases in yield of pepper from 1850 kg/ha to 4045 kg/ha, 2083 kg/ha to 4230 kg/ha and 1745 kg/ha to 3533 kg/ha, in 2016, 2017 and 2018 dry seasons, respectively. The results also showed reduction in Manganese (Mn) by 88.00%, 88.57% and 72.72%; Iron (Fe) by 85.70%, 85.71% and 85.71%; and Copper (Cu) by 58.33%, 79.17% and 80.56%, during the 2016, 2017 and 2018 dry seasons, respectively. Therefore, the treated greywater was suitable for irrigation purposes because their values were within the permissible limits for wastewater reuse as irrigation water. Furthermore, proximate and mineral analysis showed that pepper under TGW irrigation had 2.30%, 2.26% and 2.28% protein; 2.99%, 3.15% and 3.06% carbohydrates and 0.10 ppm, 0.10 ppm and 0.11 ppm phosphorous composition, in 2016, 2017 and 2018 dry seasons, respectively. These results showed that irrigation with TGW does not negatively affect the quality of pepper for human consumption, but rather improves the presence of food supplements needed for human growth. Moreover, soil analysis showed significant improvement in fertility status of soil with respect to macronutrients as recorded after harvest of hot pepper with Total Nitrogen (TN) ranging from 0.18 – 0.19, 0.16 – 0.17 and 0.20 – 0.21 cmol/kg; Phosphorous (P) ranging from 0.16 – 10.77, 0.18 – 10.07 and 0.14 – 11.47 mg/kg, and Potassium (K) ranging from 21 – 27, 21 – 28.5 and 21 – 26.5 cmol/kg, in 2016, 2017 and 2018 dry seasons, respectively. Findings from this study are useful for farmers in planning wastewater reuse for irrigation especially during dry seasons.