Purification of Wastewater from Biomass-Derived Syngas Scrubber Using Biochar and Activated Carbons

Abstract

Phenol is a major component in the scrubber wastewater used for syngas purification in biomass-based gasification plants. Adsorption is a common strategy for wastewater purification, and carbon materials, such as activated carbons and biochar, may be used for its remediation. In this work, we compare the adsorption behavior towards phenol of two biochar samples, produced by pyrolysis and gasification of lignocellulose biomass, with two commercial activated carbons. Obtained data were also used to assess the effect of textural properties (i.e., surface area) on phenol removal. Continuous tests in lab-scale columns were also carried out and the obtained data were processed with literature models in order to obtain design parameters for scale-up. Results clearly indicate the superiority of activated carbons due to the higher pore volume, although biomass-derived char may be more suitable from an economic and environmental point of view. The phenol adsorption capacity increases from about 65 m/g for gasification biochar to about 270 mg/g for the commercial activated carbon. Correspondingly, service time of commercial activated carbons was found to be about six times higher than that of gasification biochar. Finally, results indicate that phenol may be used as a model for characterizing the adsorption capacity of the investigated carbon materials, but in the case of real waste water the carbon usage rate should be considered at least 1.5 times higher than that calculated for phenol.

Keywords: adsorption; biochar; biomass; environmental pollution; pollutant abatement technologies; syngas scrubber wastewater.

Figure 1

Scheme of the experimental set-up used for continuous adsorption tests.

Figure 2

Pore size distribution of the investigated samples.

Figure 3

SEM images of the investigated SP1000, SP800, SPBCG and SPBCP samples. Subfigures are SEM images at higher magnification.

Figure 4

Langmuir adsorption capacity at 25 °C as a function of pore volume. Comparison with literature data [50,51,52,53,54,55].

Figure 5

UV-Vis profiles of real syngas scrubber wastewater and 5 g/L phenol solution used in this work.

Figure 6

UV-Vis profiles of scrubber wastewater as a function of carbon amount (50 mL of solution for each test) for the SPBCG sample (a) and the SP1000 sample (b).

Figure 7

Scrubber wastewater and phenol model solution purification level as a function of carbon amount for the SPBCG (a) and SP1000 (b) samples, after 24 h treatment.

Figure 8

Breakthrough curve of the SP1000 and SPBCG samples for phenol model solution. Solution initial concentration: 5000 mg/g, flowrate: 55 mL/min, carbon amount: 50 g.

Figure 9

Breakthrough curve of SP1000 as a function of carbon amount for the phenol model solution. Solution initial concentration: 5000 mg/g, flowrate: 55 mL/min.

Figure 10

Linear plot of the Thomas (a) and MDR (b) models. Dashed lines refer to the fitted linear regression model.

Figure 11

Comparison with experimental data of the Thomas (a) and MDR (b) models. Continuous lines refer to the fitted linear regression models.

Figure 12

Comparison with experimental data of the Thomas (red line) and MDR (green line) models for the biochar SPBCG sample.

Figure 13

Linear plot of the BDST model. In the linear regression model, y refers to the service time (h) and x refers to the bed height (m).

Figure 14

Breakthrough curve of the SP1000 sample for the phenol model solution and real scrubber wastewater. Solution initial phenol concentration: 5000 mg/g, flowrate: 55 mL/min, carbon amount: 50 g.