Application of Response Surface Methodology for H2S Removal from Biogas by a Pilot Anoxic Biotrickling Filter

Fernando Almenglo,Domingo Cantero,Martín Ramírez

doi:10.3390/chemengineering3030066

Fernando Almenglo, Domingo Cantero + Show 1 more

Open Access

https://doi.org/10.3390/chemengineering3030066

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Journal: ChemEngineering	Publication Date: Jul 13, 2019
Citations: 5	License type: CC BY 4.0

Affiliation: University of Cádiz

Abstract

In this study, a pilot biotrickling filter (BTF) was installed in a wastewater treatment plant to treat real biogas. The biogas flow rate was between 1 and 5 m3·h−1 with an H2S inlet load (IL) between 35.1 and 172.4 gS·m−3·h−1. The effects of the biogas flow rate, trickling liquid velocity (TLV) and nitrate concentration on the outlet H2S concentration and elimination capacity (EC) were studied using a full factorial design (33). Moreover, the results were adjusted using Ottengraf’s model. The most influential factors in the empirical model were the TLV and H2S IL, whereas the nitrate concentration had less influence. The statistical results showed high predictability and good correlation between models and the experimental results. The R-squared was 95.77% and 99.63% for the ‘C model’ and the ‘EC model’, respectively. The models allowed the maximum H2S IL (between 66.72 and 119.75 gS·m−3·h−1) to be determined for biogas use in a combustion engine (inlet H2S concentration between 72 and 359 ppmV). The ‘C model’ was more sensitive to TLV (–0.1579 (gS·m−3)/(m·h−1)) in the same way the ‘EC model’ was also more sensitive to TLV (4.3303 (gS·m−3)/(m·h−1)). The results were successfully fitted to Ottengraf’s model with a first-order kinetic limitation (R-squared above 0.92).

Highlights

Biogas, due to methane high combustion enthalpy, can be considered as an important renewable energy source
There are several advantages in the use of anoxic biotrickling filters (BTFs) over aerobic ones, and these include reducing the risk of explosion, no dilution of biogas, and a lower limitation in the transfer of matter for nitrate when compared to the necessary oxygen absorption [5,6]
[H2S]i where IL is the inlet load, V is the bed volume (m3), [H2S]i is the inlet H2S concentration, [H2S]o is the outlet H2S concentration, RE is the removal efficiency, EC is the elimination capacity, TLV is the trickling liquid velocity (m·h−1), EBRT is the empty bed residence time (s) and A is the cross-sectional area of the bed (m2)

Summary

Introduction

Due to methane high combustion enthalpy, can be considered as an important renewable energy source Nowadays, international laws such as the Directive of the European Parliament 2009/28/EC (April 23, 2009) recognize biogas as a source of vital energy that can reduce the European Union’s energy dependence. There are several advantages in the use of anoxic biotrickling filters (BTFs) over aerobic ones, and these include reducing the risk of explosion, no dilution of biogas, and a lower limitation in the transfer of matter for nitrate when compared to the necessary oxygen absorption [5,6]. Dynamic models provide a better understanding of the process, but their complexity means that they are seldom used for BTFs. The aim of the work described here was to study the effects of gas (FG) and liquid (FL) flow rates and nitrate concentration ([N-NO3–]) along the packed bed on the outlet H2S concentration and the EC. The H2S concentrations were measured along the bed and fitted using Ottengraf’s model [9]

Experimental Set-up

Experimental Design

Ottengraf’s Model

Findings

Conclusions