Rates of liquid-solid mass transfer at horizontal single screens and an array of horizontal parallel separated screens were studied under upward cocurrent gas (N-2)-liquid bubbly Row using the electrochemical technique. Variables studied were gas and liquid flow rates, and screen characteristics (e.g., mesh number and wire diameter). Under the present conditions where relatively low solution Row rates were used the rate of mass transfer was found to be mainly determined by the gas Row rate. For a given gas flow rate, the mass transfer coefficient decreased with increasing solution Row rate. The data for single screen were correlated with a dimensionless equation. Rates of mass transfer at an array of separated horizontal screens were lower than those at the single screen by an amount ranging from 3 to 45% depending on screen mesh number and flow conditions. The importance of the present study for building continuous high space time yield catalytic, and electrochemical reactors suitable for electrochemical air pollution control is highlighted.