Table 2.

A summary of the strategies used to control sulfide inhibition by the AD system and the conditions under which they were employed.

Method/Technique	Working Principle	Appropriate condition(s)	Reference
Micro-aerobic process	The method uses oxygen as an electron acceptor during sulfide oxidation, in which excess sulfide is further transformed into elemental sulfur.	-Temperature reactor of 30 ± 1 °C -Adoption of wastewater with a higher carbon to nitrogen (C/N) ratio (1.26:1) for stimulating the growth of heterotrophic bacteria. -Aeration rate of 20 mL/min for enhanced sulfide removal -Optimal molar ratio of 0.5–1 for O2/S2-	[124,63,125,52]
Precipitation process	The method employs metals with a strong affinity for sulfur, such as iron and zinc.	-Optimum pH value (4.61–6.95) -Low-voltage electrochemical treatment (0.7–1 V) to avoid oxygen generation during anaerobic digestion. -High range of temperature (300–800 °C) for metal oxide precipitating with H2S.	[126,127,128]
Adsorption process	A material (adsorbate or sorbate) builds up on the surface of a solid (adsorbent or sorbent).	-High surface area of the adsorbent (500 m2/g) -Chemically activated adsorbent -Optimal calcination temperature of 800 °C -Pretreatment methods -Nitrogen, oxygen, and sulfur functional groups integrated with the carbon structure	[129,130,131]
Stripping	A physical system in which air and wastewater flow in opposite directions under mass transfer.	-High operating temperature (above 45 °C) -Stripping tower for volatilization of H2S	[132,133]
Wet scrubbing	The method uses water as an adsorbent since H2S is more soluble in water than methane.	-Higher Ultra Violet (UV) light intensity of about 132 μW/cm2 -Solution pH of 7.61 -Gas flow rate is about 1.5 L/min -H2O2 concentration of 0.2 mol/L -Low temperature (10 °C) -Clean air with little traces of H2S is discharged from the reactor and can be discharged into the atmosphere	[134,135]
Aerobic biological technology	The process involves using a low concentration of (DO) for microorganisms to facilitate hydrolysis acidification.	-Gas inlet load over 55 g S–H2S m−3h−1 −1:1 M ratio of N/S -Hydraulic residence time (HRT) of 36–40 h. -Gas residence time (GRT) of 41s. -Optimal pH range of 7–8.	[136,137,60]
Biofiltration	Contaminated gases are carried into the biofilm and through the biofilter, where microbes use them as carbon or energy source. The H2S is further broken down to produce sulfate or sulfuric acid.	-Maintaining a low level of oxygen, $\le$ 5%. -Low pH condition of 2–3 -Microbial community inoculation for converting H2S to SO42− or S0	[138,139,140]