Comparative assessment for the zero‑carbon desalination plant using nanofiltration pretreatment and membrane contactor-based carbon mineralization technology

Abstract

This study proposes a zero‑carbon desalination plant design that incorporates nanofiltration (NF) pretreatment with membrane contactor-based CO₂ mineralization to address water scarcity issue through an environmentally sustainable approach. The NF pretreatment, utilizing NF90 and NF270 membranes, effectively reduces osmotic pressure and enhances the efficiency of the subsequent reverse osmosis (RO) process. The CO₂ mineralization process, a carbon capture and utilization technology, employs silane–modified polyvinylidene fluoride (PVDF) hollow fiber membranes to capture of CO₂ and convert it into stable carbonates (${\mathrm{CaCO}}_3$ and ${\mathrm{MgCO}}_3$). The study evaluates two scenarios with different NF strategies through a 3E (energy, environmental and economic) analysis. In Scenario 1, a high-performance NF pretreatment is used to increase the capacity of the carbon mineralization process. This results in a higher levelized cost of water (LCOW) for NF but reduces the LCOW for the RO and membrane contactor (MC) processes, achieving an optimal LCOW of $1.2953/m³ at 70 % NF RE. Scenario 2, which prioritizes a more cost-effective NF pretreatment system (NF270), achieves a lower LCOW for NF due to its higher flux, reaching a minimum LCOW of 1.0403/m³ at 80 % NF RE, despite higher RO costs. Scenario 2 is deemed more feasible than Scenario 1 due to its lower overall cost at a carbon offset price of $20/tonCO₂. However, as the carbon price is projected to rise from $20 to $80 per ton by 2035, Scenario 1 is expected to become more economically viable over time. This highlights the need to adapt the NF strategy as carbon prices increase.