Application of concatenated stepped solar still system (CS₄) for RO-waste-water purification: an experimental study

This experimental study investigates the capability of a concatenated stepped solar still system (CS₄) for RO-waste-water purification by assessing its thermo-enviro-economic aspects. In order to confirm the supremacy of CS₄, a simple stepped solar still system (S5) of equivalent basin area (0.75 m²) is fabricated and tested. The experiments are conducted on CS₄ and S5 simultaneously at different flow rates for comparison. The productivity of CS₄ is observed to be 24.7 % higher than that of S5; thus, its pollutant removal efficiency is better. As compared to S5, CS₄ is found to be more sustainable, economical, and better in terms of distillate production and thermal and exergy efficiencies which are optimum at 50 ml/min. The distillate production, thermal efficiency, and exergy efficiency of CS₄ at 50 ml/min flow of RO-waste-water are 2.8 kg/day, 33.80%, and 1.93%, respectively. The second and third units in CS₄ work in active mode that increases the solar energy utilization by 34.19% at optimal flow rate. The CO₂ mitigation capability of CS₄ is 8.89 tons and its distillate production cost is $0.021. At optimum flow rate, its energy and economic payback periods are evaluated as 199 and 483 days, respectively.