Part B: Advances in gas emission control techniques for anaerobic-based STPs Technical Note 6 – Energetic use and burning of waste gas

Abstract

The techniques for controlling gaseous emissions in anaerobic-based STPs studied in this collection of Technical Notes (TNs) are based on the desorption principle of dissolved gases (e.g. CH4 and H2 S) in anaerobic effuent, through their transfer to a waste gas. The waste gas must be properly managed, for example through its degradation/ oxidation in biofilters (TN 5). This TN considers other approaches to manage the waste gas: (i) its energetic use mixed with biogas; and (ii) its use as a comburent in the burning of biogas. Through mathematical models, the operating conditions of the desorption systems required for both options were established. For option (i), values of the gas / liquid ratio (QG /QL in the desorption system) in the range of 0.03-0.10 are necessary, leading to an increase in the energetic potential in the range of 18 to 58%. For option (ii), it was determined that favourable conditions of biogas production are necessary, along with QG /QL values of less than 2.5.

Dissolved methane

“…When a waste gas is too diluted and its CH 4 content is too low (as in simplified and packed desorption chambers with high Q G /Q L ratios, or in the case of gas extraction systems such as in enclosed pretreatment units or UASB reactors with enclosed settlers), the thermal oxidation (burn) of this gas is not feasible (Section 7.4.3.2) and another process for the CH 4 oxidation is required. One option that has been explored in the literature is the biological oxidation in biomass growth reactors, such as biofilters, biotrickling filters and bioscrubbers (Brandt et al, 2016(Brandt et al, , 2019(Brandt et al, , 2021a(Brandt et al, , 2021b(Brandt et al, , 2021c. These units can be used to oxidize the H 2 S and CH 4 in a waste gas.…”

“…In the biofiltration of gas mixtures containing H 2 S and CH 4 , attention should be paid to possible inhibitory effects on the activity of methanotrophic microorganisms (CH 4 oxidizers) due to the acidification of the filter bed caused by the biological oxidation of H 2 S, which can be minimized by a sequential bioreactor system, where the oxidation of H 2 S is carried out in the first Figure 7.11 Content of CH 4 in the recovered gas and gas mixture (biogas + recovered gas) derived from the recovery of dissolved methane from anaerobic reactors for a 'typical' scenario of biogas characteristics. Source: Adapted from Brandt et al (2021aBrandt et al ( , 2021bBrandt et al ( , 2021c.…”

“…Figure 7.2 Principle of dissolved methane desorption from the effluent of an anaerobic reactor. Source: Adapted fromBrandt et al (2021aBrandt et al ( , 2021bBrandt et al ( , 2021c.…”

Anaerobic Treatment of Domestic Wastewater

“…When a waste gas is too diluted and its CH 4 content is too low (as in simplified and packed desorption chambers with high Q G /Q L ratios, or in the case of gas extraction systems such as in enclosed pretreatment units or UASB reactors with enclosed settlers), the thermal oxidation (burn) of this gas is not feasible (Section 7.4.3.2) and another process for the CH 4 oxidation is required. One option that has been explored in the literature is the biological oxidation in biomass growth reactors, such as biofilters, biotrickling filters and bioscrubbers (Brandt et al, 2016(Brandt et al, , 2021a(Brandt et al, , 2021b(Brandt et al, , 2021c. These units can be used to oxidize the H 2 S and CH 4 in a waste gas.…”

“…Figure 7.2 Principle of dissolved methane desorption from the effluent of an anaerobic reactor. Source: Adapted fromBrandt et al (2021aBrandt et al ( , 2021bBrandt et al ( , 2021c.…”