In-series columns adsorption performance of Kraft mill wastewater pollutants onto volcanic soil

Two in-series columns systems with volcanic soil were tested for wastewater pollutants adsorption capacity. The first system was tested with acidified volcanic soil and the second with a reactivated volcanic soil. The reactivated soil was obtained by washing the previous spent acidified soil system with an acid solution. The systems parameters were obtained using the Bohardt and Adams model for fixed-beds. The acidified soil parameters indicated an adsorption capacity q of 28 and 139 mg/g of phenolic compounds and color, respectively (for each column), compared to 12 and 39 mg/g for the reactivated soil system. The adsorption rate constant k ranged between 1.5 × 10−6 and 2.8 × 10−6 l/min mg and no significant difference was observed for each analysed column system and pollutant. Furthermore, the molecular weight distribution analysis of input and output samples of one acidified soil column indicated that the fraction >30 000 Da is the most adsorbed until the breakpoint. Moreover, the CODs and tannins and lignin removal efficiencies at the breakpoint reached values between 60% and 70% in each column and each system, indicating that lower biodegradable compounds were retained effectively. The results indicate that it is possible to compare the acidified volcanic soil adsorption capacity with natural zeolites, and a preliminary costs evaluation indicates that volcanic soil could be also competitive, even when comparing with activated carbon.