Posttreatment of Domestic Wastewater Using Green Coconut Biochar for Coriander Fertigation

Increasing water scarcity and the need for sustainable agricultural intensification have encouraged the use of treated wastewater for fertigation. However, limitations in effluent quality still restrict its safe agricultural reuse. This study evaluated green coconut biochar as a posttreatment filter for domestic wastewater and its effects on coriander (Coriandrum sativum L.) performance. Treated wastewater, with and without biochar filtration, was applied at different proportions mixed with supply water over two cultivation cycles under protected conditions. The posttreatment increased dissolved oxygen and reduced thermotolerant coliforms by more than 99%, without significantly affecting salinity. Filtered wastewater also improved plant growth, biomass accumulation, and water use efficiency, particularly at intermediate wastewater proportions. Regression analyses suggested an expanded range of wastewater application associated with optimal crop performance. These findings suggest that green coconut biochar is a promising low-cost alternative for domestic wastewater posttreatment, supporting improved effluent quality and safer agricultural reuse.