Application of natural coagulant-treated greywater for sustainable interlocking paving stones production

Abstract With rapid urbanisation, demand for potable water has increased, and construction needs sustainable alternative water sources. This study aimed to assess the feasibility of using greywater (GW) with four natural coagulant treatments (NCT) from Moringa oleifera (MO) seeds, Cucumis limetta (CL) seeds, Musa sapientum (MS) peels and Carica papaya (CP) seeds for the production of interlocking paving stones (IPS). The IPS specimens were prepared in a 1:2:4 (cement:sand:stone) dust ratio and a water–cement ratio of 0.6, with dimensions of 200 × 100 × 80 mm. The experimental mixtures used greywater and NCT greywater, while the control used potable water. The Scanning Electron Microscopy-Energy Dispersive X-Ray (SEM–EDX) Spectroscopy of IPS, compressive strength, and water absorption of the IPS were determined. In addition, the physicochemical characteristics of the mixing waters, such as pH, total dissolved solids, sulphate, chloride, and turbidity were evaluated. The results indicated that the NCT water had an impact on the physicochemical properties of the greywater and resulted in different effects on the IPS performance. The compressive strength of IPS produced with CP-treated greywater was 11.20 MPa, which was about 49% higher than the control (potable water) with a value of 7.53 MPa, whereas the IPS produced with MO-treated greywater had a compressive strength of 9.70 MPa. The 28-day strengths of IPS produced with untreated greywater, CL-treated and MS-treated greywater were lower than the control. In addition, IPS produced with CP-treated greywater had relatively low water absorption (9.84%) compared to that produced with potable-water control (10.00%). The results showed that the NCT greywater can be used as an alternative mixing water for IPS production in general, and specifically, CP and MO-treated water. The approach promotes water savings, sustainable urban infrastructure and contributes towards Sustainable Development Goals 6 and 11.