Stripping and Dissipation Techniques for the Removal of Dissolved Gases From Anaerobic Effluents

Abstract

-UASB reactors are a common technology for wastewater treatment. However, certain disadvantages must be considered. One of the disadvantages relates to the presence of dissolved gases, hydrogen sulfide and methane, in the effluent, which can potentially be released into the atmosphere. This can cause malodours and contribute to the greenhouse effect. In this perspective, this work investigated alternative techniques to minimize these disadvantages: air stripping inside the settling compartment; and a dissipation chamber immediately after the reactor outlet. Results achieved with the air stripping technique showed low removal efficiencies for methane, around 30%, and in the range of 40 to 60% for hydrogen sulfide. On the other hand, the removal efficiencies obtained with the dissipation chamber technique were much higher, consistently reaching 60% or more for both gases, plus a relatively lower exhaust flow. For the best operational condition tested, median removal efficiencies of 73 and 97% were observed for dissolved methane and dissolved sulfide, respectively.

Anaerobic Sewage Treatment in Latin America

“…The biogas energy recovery for more valuable purposes (e.g., a vehicular fuel, injection into the natural gas line) generally require methods that enable the selective removal of H2S and the enrichment of methane in the biogas. Different alternatives can be considered for removing the dissolved sulfide in the reactor effluent, such as stripping in a dissipation chamber, as reported by Souza et al (2012) and Glória et al (2014), followed by a treatment step (for example, using a biofilter). Additionally, important reductions of hydrogen sulfide (>80%) dissolved in the treated effluent were observed after crossing the discharge hydraulic structure of the demo-scale UASB reactor (pipeline and splitting box), largely due to high turbulence causing the emissions into the atmosphere.…”

Technological improvements in compact UASB/SBTF systems for decentralized sewage treatment in developing countries

“…If we consider the use of these biofilters to treat the CH 4 released from the effluent of full-scale UASB reactors currently in operation in Brazil, this could potentially prevent the emission of approximately 1.28 tCO 2,equiv .d -1 . This estimation was based on the following premises: i) the wastewater from approximately 22.9 million people is currently treated by anaerobic reactors in Brazil (42.8 m 3. s -1 ) (Chenicharo et al, submitted); ii) the concentration of dissolved CH 4 in the effluent of UASB reactors is close to 20 mg.L -1 (Souza et al, 2011); iii) desorption chambers can transfer around 73% of the dissolved CH 4 to the waste gas (Glória et al, 2016); iv) the biofilter can oxidise 95% of the CH 4 contained in the waste gas (best performance as shown in Figure 3).…”

“…In comparison with technologies such as membrane separation, direct combustion, catalytic oxidation, chemical scrubbers, and others listed in Estrada et al (2012) and Alfonsín et al (2015), the biofilters emerge as an attractive alternative for decentralized sewage treatment systems in developing countries. Worth to mention that to a successful CH 4 abatement with the use of biofiltration, the installation of desorption chambers for gas capture, as proposed by Glória et al (2016), is extremely relevant. The enclosed unit designed to release/strip the dissolved gases tend to increase the concentration of waste gas in a gaseous stream.…”

“…In the proposed flow-sheet ( Figure 1), after the release of waste gas from the UASB effluent in the desorption chamber (Glória et al, 2016), the gas is forwarded to biofilters consisted of columns (h = 1.2 m) packed with 60% (on a volumetric basis) of sieved composted leaves (2.0 to 6.3 mm) and 40% (on a volumetric basis) of expanded vermiculite (4.0 to 6.0 mm) completely mixed and prepared to a working bed height of 1.0 m.…”

Performance of the Catalytic Membrane Reactors of Different Pore Size With Palladium as Catalytic Phase in Hydrogenation and Oxidation Reactions

“…Regarding the amount of hydrogenation products, a lower quantity was found when the air was bubbled; apparently, the small bubbles originated by the diffusor are less efficient to produce stripping. Since gas transfer occurs through the gas-liquid interface, this operation has to be carried out so as to maximize the opportunity of interfacial contact between the two phases (Glória et al, 2016). In the reaction when iron is added, more conversion was found because iron enhances the hydroxyl radical generated from hydrogen peroxide and promoted the phenol oxidation.…”