Bench-scaled nano-Fe⁰ permeable reactive barrier for nitrate removal

There are many fundamental problems with the injection of nano-zero-valent iron (NZVI) particles to create permeable reactive barrier (PRB) treatment zone. Among them the loss of medium porosity or pore blocking over time can be considered which leads to reduction of permeability and bypass of the flow and contaminant plume up-gradient of the PRB. Present study provides a solution for such problems by confining the target zone for injection to the gate in a funnel-and-gate configuration. A laboratory-scale experimental setup is used in this work. In the designed PRB gate, no additional material from porous media exists. NZVI (d₅₀ = 52 ± 5 nm) particles are synthesized in water mixed with ethanol solvent system. A steady-state condition is considered for the design of PRB size based on the concept of required contact time to obtain optimum width of PRB gate. Batch experiment is carried out and the results are used in the design of PRB gate width (~50 mm). Effect of high initial NO₃^--N concentration, NZVI concentration, and pore velocity of water in the range of laminar groundwater flow through porous media are evaluated on nitrate-N reduction in PRB system. Results of PRB indicate that increasing the initial NO₃^--N concentration and pore velocity has inhibitor effect-against the effect of NZVI concentration-on the process of NO₃^--N removal. Settlement velocity (S.V.) of injected NZVI with different concentrations in the PRB is also investigated. Results indicate that the proposed PRB can solve the low permeability of medium in down-gradient but increasing of the S.V. especially at higher concentration is one of the problems with this system that needs further investigations.