Response surface method for modeling the removal of carbon dioxide from a simulated gas using water absorption enhanced with a liquid-film-forming device

This paper presents the results from using a physical absorption process to absorb gaseous CO₂ mixed with N₂ using water by producing tiny bubbles via a liquid-film-forming device (LFFD) that improves the solubility of CO₂ in water. The influence of various parameters-pressure, initial CO₂ concentration, gas-to-liquid ratios, and temperature-on the CO₂ removal efficiency and its absorption rate in water were investigated and estimated thoroughly by statistical polynomial models obtained by the utilization of the response surface method (RSM) with a central composite design (CCD). Based on the analysis, a high efficiency of CO₂ capture can be reached in conditions such as low pressure, high CO₂ concentration at the inlet, low gas/liquid ratio, and low temperature. For instance, the highest removal efficiency in the RSM-CCD experimental matrix of nearly 80% occurred for run number 20, which was conducted at 0.30MPa, CO₂ concentration of 35%, gas/liquid ratio of 0.71, and temperature of 15°C. Furthermore, the coefficients of determination, R², were 0.996 for the removal rate and 0.982 for the absorption rate, implying that the predicted values computed by the constructed models correlate strongly and fit well with the experimental values. The results obtained provide essential information for implementing this method properly and effectively and contribute a promising approach to the problem of CO₂ capture in air pollution treatment.

Synergistic effect of pressurized carbon dioxide and sodium hypochlorite on the inactivation of Enterococcus sp. in seawater

This study investigated the effect of combined treatments using pressurized carbon dioxide (PCD) and sodium hypochlorite (NaOCl) on the inactivation of Enterococcus sp. in artificial seawater. Bacterial inactivation was conducted in a liquid-film-forming apparatus with various pressure conditions, CO₂ supply rates, and chlorine dosages. Combined PCD/chlorine treatments resulted in greater disinfection efficiency than those for the two individual treatments. Synergy values were correlated with pressure and CO₂ concentrations (p < 0.001). Combination of 0.9 MPa PCD (various CO₂ supply rates: 25% CO₂ + 75% N₂, 50% CO₂ + 50% N₂, and 100% CO₂) and chlorine (0.20 mg L^-1) yielded average synergy values of 4.9, 5.2, and 4.4 log, respectively, within 3 min. Combined treatment with PCD (100% CO₂, 0.3 MPa, and 20 °C) and chlorine (0.20-0.22 mg L^-1) achieved an average synergy value of 4.6 log and complete inactivation (5.2-5.5 log reductions) of Enterococcus sp. within 4 min. In contrast, when the two individual treatments (PCD and chlorine) were used, only 3.7 and 1.8-2.3 log reductions, respectively, were achieved after 25 min. These findings suggest that the combined PCD/chlorine treatment has synergistic benefits and provides a promising method for the disinfection of ballast water.

Potential application of high pressure carbon dioxide in treated wastewater and water disinfection: Recent overview and further trends

Recently emerging disadvantages in conventional disinfection have heightened the need for finding a new solution. Developments in the use of high pressure carbon dioxide for food preservation and sterilization have led to a renewed interest in its applicability in wastewater treatment and water disinfection. Pressurized CO2 is one of the most investigated methods of antibacterial treatment and has been used extensively for decades to inhibit pathogens in dried food and liquid products. This study reviews the literature concerning the utility of CO2 as a disinfecting agent, and the pathogen inactivation mechanism of CO2 treatment is evaluated based on all available research. In this paper, it will be argued that the successful application and high effectiveness of CO2 treatment in liquid foods open a potential opportunity for its use in wastewater treatment and water disinfection. The findings from models with different operating conditions (pressure, temperature, microorganism, water content, media …) suggest that most microorganisms are successfully inhibited under CO2 treatment. It will also be shown that the bacterial deaths under CO2 treatment can be explained by many different mechanisms. Moreover, the findings in this study can help to address the recently emerging problems in water disinfection, such as disinfection by-products (resulting from chlorination or ozone treatment).