Abstract
The study assessed the suitability of two effluent types, namely anaerobic filtered (AF) and horizontal flow constructed wetland (HFCW) effluent for Moistube irrigation (MTI). Secondary to this, the study determined the plugging coefficients (α) on MTI for the respective effluents. The feed water was supplied from a raised tank (3.5 m), and mass-flow rates were recorded at 15 min intervals using an electronic balance. The effluent feed water concentrations and experimental room temperature (25 °C ± 1 °C) were continuously monitored and kept constant. Hermia’s models based on the {text{R}}^{2} coefficient was used to select the best fitting fouling mechanism model and, consequently, the plugging coefficients. In addition, microbial colony analysis and scanning electron microscopy (SEM) analysis was carried out to assess the composition of the deposited sediment (DS) and adhered bacterial film (ABF) onto the MTI lateral. The study revealed that MTI pore blocking was a complex phenomenon described by complete pore-blocking model ({text{R}}^{2} ≥ 0.50). Discharge followed an exponential decay with early fouling observed on AF effluent because of a high concentration of total suspended solids (TSS) and dissolved organic matter (DOM). Discharge declined by 50% after 20 and 10 h of intermittent operation for AF and HFCW effluent, respectively. The α for each effluent (foulant) were alpha_{AF} = 0.07 and alpha_{ HFCW} = 0.05, respectively, for AF and HFCW. The microbial analysis revealed bacterial aggregation structures that contributed to pore blocking. SEM imaging revealed complete surface coverage by deposited sediment. It is concluded that water quality determines the operation life span of MTI, and the two effluents promote accelerated MTI pore fouling or blocking. Continuous use without flushing the MTI will promote membrane degradation and reduced discharge efficiency. Additional filtration can potentially mitigate the membrane degradation process.
Highlights
Agriculture consumes approximately 70% of the global blue w ater[1]
anaerobic filtered (AF) has more pronounced pore-blocking as evidenced by the high degree of clogging ( DC ) and quick decline in relative discharge qrel = 0
A high concentration of total suspended solids (TSS) and bacteria accelerate pore blocking. This was evidenced by a high DC and quick decline in qrel (AF, qrel = 0 at t = 57 h and horizontal flow constructed wetland (HFCW), qrel = 0 at t = 60 h)
Summary
Agriculture consumes approximately 70% of the global blue w ater[1]. This exacerbates water scarcity in the wake of erratic rainfall fuelled by climate variability and change. Wastewater is defined as water that has gone through anthropological change[2] Wastewater treatment plants such as the decentralised wastewater treatment system (DEWATS) produce different types of effluents; for example, there is anaerobic filtered (AF) effluent and horizontal flow constructed wetland (HFCW) effluent. The HFCW effluent is obtained by passing the AF effluent through a vertical flow constructed wetland (VFCW) which consists of planted gravel filters that aid in further filtration and removal of pathogens. A combination of wastewater usage and water use efficient irrigation technologies such as Moistube irrigation (MTI) can potentially relieve the pressure on freshwater bodies and improve water use efficiency for crop production. MTI is a new technology that uses a semi-permeable membrane (SPM) to emit water continuously in response to the soil matric potential and the applied pressure. The technology optimises irrigation field water use efficiency (fWUE) since it utilises on-demand water a pplication[12,14]
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