Experimental investigation and modelling of the effect of sulfate on anaerobic biodegradation processes in municipal solid waste

Abstract

The experimental investigations have been carried out in two parts. First, the biodegradation of the organic compounds in the municipal solid waste has been investigated with focus on different sulfate concentrations influencing the methane formation. Second, the inhibition effect of hydrogen sulfide in solution (H2S(aq)) on the acetate, and methane formation, respectively, has been studied at different pH and temperature values. In solution the equilibrium of hydrogen sulfide (H2S(aq)) and the hydrogen sulfide anion (HS-(aq)) mainly depends on pH. At pH 6.3 the favoured species is H2S(aq) whereas at pH 7.7 the HS-(aq) species is favoured. Additionally, the experiments have been carried out at two different temperatures (35 degrees C and 55 degrees C). According to the acetate and methane formation the H2S(aq) species is observed to have an inhibitory effect. All simulations based on a biodegradation model represented are in good agreement with the experimental data obtained.

Synthesis and sulfate ion-exchange properties of a hydrotalcite-like compound intercalated by chloride ions

“…[2][3][4][5][6][7][8][9][10][11][12] mM CaSO 4 with a volume of 30 ml and a prescribed amount of HT-Cl (chemical composition: [Mg 1.98 Al(OH) 5.95 ]Cl 0.71 (OH) 0.29 ·1.48H 2 O) were placed in a 50-ml screw-tube and shaken at • C for up to 60 min at 150 strokes per minute.…”

“…Current measures, such as capture-fixed methods or diffusion, are being applied to the emission of hydrogen sulfide gas, which is principally due to the reduction of sulfates by sulfate-reducing bacteria, linked to the degradation of naturally occurring and contaminant forms of organic matter under anaerobic conditions [1][2][3]. In these cases, one of the methods for controlling the emission of H 2 S gas is to remove the sulfate ions (SO 4 2− ), i.e., the source of the sulfur, thereby moderating the activity of sulfate-reducing bacteria.…”

“…Hydrotalcite-like compounds (HTs) are layered double hydroxides with anionexchange properties [4,5]. The chemical composition of a HT is Mg 1−x 2+ Al x 3+ (OH) 2 (A n− ) x/n ·mH 2 O, where A n− is an n valent anion, such as CO 3 2− , SO 4 2− , OH − , or Cl − , and 0.20 ≤ x ≤ 0.33. The crystal structure consists of positively charged brucite-like octahedral hydroxide layers, which are charge neutralized by the interlayer anion.…”

“…Water molecules occupy the remaining interlayer space inside the crystal lattice. Since CO 3 2− has an exceptionally high affinity for HTs, CO 3 2− intercalated in the interlayer (HT-CO 3 ) is a preferred solution, which can be synthesized using a coprecipitation method. An aqueous solution containing Mg 2+ and Al 3+ ions is continuously added to the appropriate aqueous solution of anions at a slow flow rate maintaining at pH from 8 to 10 by the dropwise addition of a base such as NaOH and/or Na 2 CO 3 .…”

“…The anion, which has the highest electric density, exhibits the highest electrostatic force toward the host layer. When a higher amount of Cl − is intercalated inside the HT layer, a smaller concentration of CO 3 2− and/or OH − is present in the intercalated layer; therefore, the SO 4 2− in the solution can be removed more effectively. The charge density in the interlayer is proportional to the number of Al 3+ ions, and the number of intercalated anions is determined by the charge density.…”