Innovative on-farm polluted river water treatment with nutrient reuse for small-scale irrigation in Addis Ababa, Ethiopia | |
| Author | Waldegabrel, Tesfalem Atnafu |
| Call Number | AIT Thesis no.ET-SUD-21-01 |
| Subject(s) | Irrigation water--Ethiopia--Addis Ababa Water quality--Ethiopia--Addis Ababa Water--Purification--Ethiopia--Addis Ababa |
| Note | A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Environmental Engineering and Management with specialization in Environmental Technology for Sustainable Development jointly offered by the Asian Institute of Technology, Thailand and UNESCO - IHE, The Netherlands |
| Publisher | Asian Institute of Technology |
| Abstract | Wastewater irrigation covers millions of hectares and has been in practice for several thousand years and continues in the future. The problem severity becomes complicated as a pollutant load is increasing over time. In contrast, the technological and economic capacity to mitigate the issues lags, especially in developing countries. This study has initiated an innovative on-farm algal pond (OAP) wastewater (polluted river water) treatment system to enhance microbial safety of vegetable irrigation that is practical, straightforward, and low tech. Two different approaches were designed to meet these objectives: first, before covering the ponds with the plastic liner (only the water budget studied), and second, after covering with liner (all other experiments). It was conducted on-farm along Little Akaki River, Ethiopia, where farmers irrigate vegetables. The OAP system was studied using mixed methods, critical desk review, conceptual analysis, experiential knowledge, and experiments. The OAP system (connected to the irrigation canal) comprised of 2 consecutives mini (50 cm depth) circular (CAP) and rectangular algal pond (RAP) and a separate algal seed pond (ASP) to culture an algal inoculum for the ponds. The system was operated as a batch reactor. Samples were collected from the river and canal (influent) at 10:00, 14:00, and 18:00 h/day; similarly, the effluent samples were collected from the algal ponds (APs) and control ponds (CPs) within 4 h/d intervals on 3 and 6 days of HRT. Algae were not filtered. The nutrients PO4 3- , NH4 + -N, NO3 - -N, and TKN in the raw or retained in treated wastewater (recovered) were determined according to APHA (2005). E. coli was analyzed based on USEPA (2002). The algal species isolated from the ponds were Euglena, Chlorella, Scenedesmus, and diatoms. At HRT of 6 days, the observed E. coli log10 removal was 3.02, 2.96, and 1.8 log units in CAP, RAP, and CP, respectively. Hence, it was possible to achieve the WHO (2006) recommended ≤4 log units E. coli/100 mL for safe use of OAP treated wastewater irrigation for leafy but not for root crops (≤3 log units). Hence, further researches are required to enhance the E. coli removal performance. In the OAP system, the mean concentration of N and P recovered in treated wastewater used for irrigation were 37% of PO4 3- (1.2 mg/L), 54% of nitrate-N (0.8 mg/L), 5% of ammonia-N (0.6 mg/L), and 75% of TKN (24.1 mg/L). Algal injection (AP/CP) significantly affects E. coli removal and nutrient recovery, but different pond geometry (RAP/CAP) did not result a fundamental (p>0.05) difference. Environmental conditions (pH and DO) might determine the OAP disinfection. Farmers can construct RAP/CAP without significant effect on the safe reuse of wastewater during the tropical dry season based on available space. The system practicality was studied through farmers’ perception, pond water budget, and irrigation water requirement (IWR). Seepage (25%) was the major OAP water loss mechanism than evaporation (5%). Five crops were selected for the IWR study: cabbage, potato, tomatoes, and small vegetables. Tomatoes IWR was the highest, and the OAP mini ponds can irrigate 30 m2 for 1d/week irrigation schedule. A structured questioner and field survey were used to study farmers’ perceptions of untreated wastewater use to irrigate vegetables. Most farmers (77%) were interested in adopting the OAP system. Empirical results from an ordered probit model show farmers’ perception on the health-related risk of untreated wastewater use on producers and consumers were dependent on years of schooling and farmer’s experience. Therefore, this study revealed the OAP system’s recommendable performance in safe nutrient recycling for small-scale untreated wastewater irrigation. Further studies and stakeholder involvement are required to realize the practicality. |
| Year | 2021 |
| Type | Thesis |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Energy and Climate Change (Former title: Department of Energy, Environment, and Climate Change (DEECC)) |
| Academic Program/FoS | Specialization in Environmental Technology for Sustainable Development (ETSUD) |
| Chairperson(s) | Shipin, Oleg V.;Van der Steen, Nico Pieter (Co-Chairperson) |
| Examination Committee(s) | Annachhatre, Ajit P.;Thammarat Koottatep |
| Scholarship Donor(s) | Netherlands Fellowship Programmes (NFP);UNESCO-IHE;Asian Institute of Technology |
| Degree | Thesis (M.Sc.) - Asian Institute of Technology - UNESCO-IHE, 2021 |