An Innovative Design of Media and Plant–Based Solid–Liquid Separation System for Sustainable Fecal Sludge/Septage Management

Abstract The fecal sludge treatment plant relies on effective solid–liquid separation. The present research and development integrates an innovative media and plant–based solid–liquid separation device for sustainable fecal sludge management. The study includes design, demonstration, performance evaluation, physicochemical and biological analysis of separated solids and liquids, comparison with conventional techniques, and treatment options for separated solids and liquids. The system was assessed under varied hydraulic retention time (HRT) from 1 to 7 days, with optimal results achieved at 5 to 6 days for multidirectional solid–liquid separation. The separated solids are nutrient-rich, with nitrogen, phosphorus, potassium, and carbon contents of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="75 plus or minus 6" display="inline" overflow="scroll"> <mml:mn>75</mml:mn> <mml:mo>±</mml:mo> <mml:mn>6</mml:mn> </mml:math> , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="4.0 plus or minus 0.02" display="inline" overflow="scroll"> <mml:mn>4.0</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.02</mml:mn> </mml:math> , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="1.0 plus or minus 0.01" display="inline" overflow="scroll"> <mml:mn>1.0</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.01</mml:mn> </mml:math> , and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="232 plus or minus 20 m g divided by normal g" display="inline" overflow="scroll"> <mml:mn>232</mml:mn> <mml:mo>±</mml:mo> <mml:mn>20</mml:mn> <mml:mtext> </mml:mtext> <mml:mi>mg</mml:mi> <mml:mo stretchy="false">/</mml:mo> <mml:mi mathvariant="normal">g</mml:mi> </mml:math> , corresponding to 7.5%, 0.4%, 0.1%, and 23.2% by dry mass, respectively. These values indicate strong potential for agricultural applications and resource recovery. Heavy metal concentrations were within permissible limits, ensuring environmental safety. The system demonstrated high removal of chemical oxygen demand as 97.8%, total suspended solids as 98%, and effective reductions in total nitrogen as 44.8% and total phosphorus as 66.6% in the separated liquid. Separated solid and liquid requires further treatment, including disinfection, to comply with and align with the standards for reuse of treated solid and liquid. The findings demonstrate that this system offers an energy-efficient, cost-effective, and smaller footprint solution for solid–liquid separation of fecal sludge, contributing to sustainable sanitation and environmental protection.