Influence of wastewater on the transport and transformation in irrigated soils

Date: 27 March 2018

Venue: Campus Drie Eiken, C1.09 - Universiteitsplein 1 - 2610 Antwerpen-Wilrijk (route: UAntwerpen, Campus Drie Eiken)

Time: 5:00 PM

Organization / co-organization: Faculty of Science

PhD candidate: Ali ERFANI AGAH

Principal investigator: Patrick Meire, Eric de Deckere

Short description: PhD defence Ali ERFANI AGAH - Faculty of Science


Irrigation by wastewater poses risks for deterioration of the hydraulic soil properties and pollution of groundwater. In order to study these concerns synthetic wastewater was used on one-dimensional aerobic sand columns and the results were analyzed. A numerical model, Hydrus-1D, was used to inversely estimate water and solute transport parameters. For the simulation studies experiments from 2 different scales were chose: lysimeter -scale, and field experiments.

At the first stage, 12 one dimensional columns were constructed in order to characterize the water flow and transport parameters. Four irrigation treatments with different levels of Chemical Oxygen Demand (COD) were applied. Regular pulse-response tracer-tests were analyzed by a transfer-function method in order to determine the dispersion coefficient and pore-water velocity. To the numerical simulation by using HYDRUS-1D, inverse modelling was first performed by using the measured water content and relative EC data from the pulse-response experiment to estimate the soil hydraulic properties and soil longitudinal dispersivity; which were then used in inverse modeling with the COD-data to find the degradation. The analysis of variance using the changes as compared to the starting values in the same columns confirmed that there was no significant difference in hydraulic transport properties. In contrast the first-order kinetics degradation constant decreased in an identical way for all COD-treatments.

At the second stage, the soil water flow, phosphorus (P) , nitrogen (N) dynamics and Electrical conductivity (EC) were simulated by Hydrus-1D in barley-crop lysimeter on three types of soil (sandy loam, loam, and clay loam) and with four types of water (wastewater, effluent, mixture of freshwater and effluent, and freshwater) during the growing period. The results of the experiments showed that the EC of leachates, being greater than the EC of the irrigated waters, was mostly a function of the soil background salts.

The effect of irrigation water and soil type on Nitrates (NO3--N) leaching was significant (p<0.05). Maximum and minimum (NO3--N) transferred were in sandy and loam soil, respectively. Except, but NO3- leaching in the treatment of wastewater was lower in clay soil comprise loam soil. The highest and lowest NO3--N leaching was in treatments wastewater and mixture of freshwater and effluent, respectively. Maximum NO3- leaching was observed at the middle of the growing season when barley needed minimum NO3--N. Soil and plant system showed high potential in filtration and removal of NO3--N. Also, the levels of NO3--N in their leachates were below the permissible limit.

Phosphorous (PO4) transfer to the depths was insignificant and amounted to 0.6 to 1.6 percent of the P in irrigation waters. The trend of charge in nutrient concentration (N+P) was a function of plant requirement. Overall, the HYDRUS-1D model overestimated the final leaching PO4 concentrations in the soil. On the basis of the results, soil with loamy texture was considered to be the most suitable type for irrigation with wastewater and effluent.

Dilute wastewater can be suitable management strategy for reducing the leaching of impurities in the wastewater and also reduce the effects of probable hazards on soil properties. The results of this research indicate that with a proper management program in regard to the types of soil to be used, crops to be cultivated, water quality and timing manure, the negative impacts of low quality water on soil/plant/groundwater systems can be minimized.

At the final stage , numerical simulation was performed to assess the accumulation and transport of Nitrate (NO3--N) in the soil profile under different irrigation and fertilizer treatments during growing season of sugarcane crop , and to simulate water and N transport in sugarcane, finally estimating potential NO3--N leaching from filed fertilized. Results showed that decreasing the potential N fertilization strongly dependent on soil factors, climate, time, method and rate of application of fertilizer. In this study amount of leaching had a close relationship with the levels of fertilizer and irrigation water .The model had under estimation of NO3- and Ammonium (NH4+) in soil depths. After calibration this issue was removed, index of agreement (d) increased to a considerable level, and the medium error (AE) has been decreased. One reason for the good estimation of model is because of the mechanisms for solute transfer, which includes mass, molecular, or ions transfers.