| A novel wastewater microirrigation technology for plants to extract reclaimed water directly from hydrophilic, homogeneous dense membrane modules embedded in the soil was studied. The experiments were first conducted by using a sweeping air pervaporation unit to characterize hollow fiber (HF) and corrugated sheet (CS) membrane modules in terms of water permeate flux and enrichment factor, using borate, selenate, sodium chloride and glucose as model contaminants. As well, a bench soil pervaporation unit was designed and constructed to quantify the irrigation water in loamy sand and loam soils by varying feed temperature, pressure, solute concentration, soil water content and membrane configuration. The results showed that the maximum water permeate fluxes from CS and HF modules buried in saturated and unsaturated soils with less than 15% moisture content ranged from 0.2 to 1.0 L/m2/d and 0.1 to 1.0 L/m2/d, respectively. The average enrichment factors for glucose, selenate, borate and sodium chloride were 0.18, 0.08, 0.19 and 0.23, respectively, indicating that the new microirrigation technology can efficiently deliver high quality water to the crops as needed, eliminating clogging problems and potential ground and surface water contamination commonly associated with conventional irrigation systems.; Subsequently, a mathematical model was also developed by combining the solution-diffusion model for mass transport through the pervaporation membrane, the Richard's equation for soil water movement and the root-activity function for plant water uptake to predict the water permeate flux for different soil and process operating conditions. A good agreement was observed between the model predictions and the experimental measurements. Further analysis concluded that the plants will self-extract water from the membrane, as needed, depending on their evapotranspiration potential and the water potential of the soil. Thus, it can be concluded that the proposed membrane pervaporation microirrigation system holds great promise as an efficient, environmentally friendly alternative to reuse brackish or contaminated waters for plant growth. |
