Onwuegbunam Donatus Obiajulu

Evaluation of pollutant removal kinetics for greywater treatment in horizontal free surface flow constructed wetland

Issue 3 (203)/2025

Vivien Chikogu Ameso, Sampson Oduro-Kwarteng, Donatus Obiajulu Onwuegbunam, Ezra Lekwot Vivan, Andesikuteb Yakubu Ali, Timothy Terna Mande

DOI: https://doi.org/10.46909/alse-583189

ABSTRACT. Amidst a global freshwater shortage, reusing treated greywater is a viable option for supplementing non-potable demands. To ensure effective and sustainable treatment, understanding the kinetics of pollutant removal is essential for optimizing horizontal free surface flow constructed wetlands (HFSF). This study evaluates these kinetics for greywater in a continuous HFSF wetland planted with water hyacinth (Eichhornia crassipes) under hydraulic loading rates (HLRs). A pilot-scale HFSF wetland (12 m × 1 m × 1 m) constructed at the National Water Resources Institute, Kaduna was operated continuously at HLRs of 0.20, 0.25, and 0.30 m day-1. Greywater samples were collected biweekly and analysed for biochemical oxygen demand (BOD5), total phosphorus (TP), total suspended solids (TSS), and ammonium nitrogen (NH4–N). First-order kinetic models (k–C), a modified first-order model with background concentration (k–C*), and a Continuous Stirred Tank Reactor (CSTR) were applied to derive rate constants and assess the model’s performance. First-order rate constants increased with HLR, indicating faster reaction kinetics; however, the overall efficiency of the pollutant removal slightly declined at higher HLRs due to the reduced retention time. TSS removal declined due to resuspension and NH4–N removal was limited by oxygen deficiency at 0.30 m day-1. The models demonstrated relatively better predictive agreement for TP and NH4–N than for BOD5 and TSS, reflecting non-linear processes. The 0.20 m day-1 HLR provided the most sustainable performance through longer retention, effective biodegradation, sedimentation, and nitrification. The derived k values fall within global ranges, validating their use in wetland design.

Keywords: constructed wetland; greywater; pollutant removal; kinetics; water hyacinth.

Effect of water management strategies on two vegetable crops under a Bhungroo irrigation technology in Upper East Region, Ghana

Issue 2 (202)/2025

Henry E. Igbadun, Olufunke Cofie, Michael A. Kpakpo-Sraha, Donatus O. Onwuegbunam, Seifu Tilahun

DOI: https://doi.org/10.46909/alse-582172

ABSTRACT. Exploring options to access water for irrigation and water management strategies at the field level is pivotal for improving crop yield and water productivity. Farmer-participatory field trials were conducted in Gorogo and Sepaat communities, Upper East Region, Ghana, in the 2020/2021 and 2021/2022 irrigation seasons to evaluate the yield response of tomato and onion crops to varied levels of deficit irrigation using Bhungroo irrigation technology. The experimental factor was water application depth at four levels: 65, 85, and 100% of crop water requirement (CWR) and farmers’ discretion. Irrigation water productivity (IWP) was computed as a function of the yield and water applied. Seasonal water used in the tomato fields ranged from 232 to 502 mm, while the onion trials varied from 358 to 750 mm. The fresh fruit yield of tomato ranged from 6.0 to 17.5 t ha−1 in the two seasons, while the dry onion bulb yields ranged from 15.2 to 25.4 t ha−1. The IWP ranged from 2.11 to 3.61 kg m−3 for tomato and from 2.05 to 4.51 kg m−3 for onion. The lowest values were obtained from the least water applied, while the highest values were obtained from the highest. The deficit irrigation schedules significantly decreased both yield and IWP compared to 100% CWR in tomato and onion, while the farmers’ discretion led to over-irrigation in both study locations. It is recommended that tomato and onion crops be irrigated to meet the full crop water requirement in the study areas.

Keywords: deficit irrigation; drip irrigation; onion; tomato; water productivity.

Actual crop coefficients and yield response factors of irrigated tomato in Afaka, Northwest Nigeria

Issue 1 (201)/2025

Donatus Obiajulu Onwuegbunam, Muyideen Abubakar Oyebode, Henry Evonameh Igbadun, Habibu Ismail, Isaac John Maisamari

DOI: https://doi.org/10.46909/alse-581162

ABSTRACT. In the face of the prevailing challenges of limited water for irrigated agriculture, the knowledge of crop coefficients for use in irrigation, and the yield response to moisture stresses become pertinent for developing strategies to improve agricultural water productivity. Field experiments were conducted to evaluate the crop coefficients and yield response factors of UC 82B tomato subjected to soil moisture stresses on growth-stage basis. The irrigation treatments investigated were: a full irrigation (application of 100% ETo), and three soil moisture deficit levels (20%, 40%, 60% ETo) imposed at the vegetative, flowering and maturity growth stages, in successions. The mean crop coefficient (Kc) was highest (0.99) during the mid-season under full irrigation, and lowest (0.47) during the vegetative stage under 60% ETo soil moisture deficit, while the mean value across the entire crop growth stage was 0.88. The yield response factors (Ky) were 1.26 and 1.30 for the 2017/2018 and 2018/2019 seasons, respectively. The mean Ky of was 1.28 for the entire growth cycle, implying high sensitivity of the tomato cultivar to water deficits, and that yield reduction is proportionally larger when water used is reduced because of stress. Full irrigation at the maturity stage is recommended.

Keywords: crop coefficients; deficit irrigation; Northwest Nigeria; tomato; yield response.