Long-term full-scale evaluation of three membrane bioreactor plants for coconut-processing wastewater treatment: Energy, cost, and pretreatment impacts

Data from three full-scale membrane bioreactor (MBR) plants treating coconut-processing wastewater in North Sumatra, Indonesia, were collected over five years and analyzed using a mass-balance, load-based framework. Energy and cost were reported as intensities (kWh/kg and USD/kg COD removed) and as volumetric indicators (kWh/m 3 and USD/m 3 of wastewater treated). All plants achieved >99.5 % removal of COD, BOD, and TSS. The electricity demand ranged from 0.37 to 0.82 kWh/m 3 , and the treatment cost ranged from 37.7 to 69.5 USD/m 3 among the three plants. On a load basis, COD removal required 0.015 to 0.182 kWh/kg and 3.19 to 11.7 USD/kg; BOD removal required 0.148 to 0.518 kWh/kg and 9.95 to 33.5 USD/kg; and TSS removal required 0.339 to 1.99 kWh/kg and 27.7 to 43.9 USD/kg. Plants with better pretreatment, including filter presses and fermentation tanks, consistently achieved lower energy use and cost. Regression analysis confirmed that each additional kilogram per day of residual TSS in wastewater increased downstream aeration and MBR electricity demand by 0.41 kWh/day (p < 0.001). This study provides the first multi-year, full-scale benchmarks for MBR treatment of high-strength coconut wastewater and demonstrates how practical solids-oil pretreatment can halve energy demand and double cost-effectiveness. The findings offer actionable guidance for engineers, operators, and regulators designing sustainable agro-industrial wastewater systems.