Removal of Hydrogen Sulfide in Septic Tanks for Treating Black Water via an Immobilized Media of Sulfur-Oxidizing Bacteria

Improving contaminant removal and inhibiting CH4 and H2S emissions from septic tanks: Nitrified human urine as a source of electron acceptor

Septic tanks are widely adopted in decentralized household wastewater treatment systems serving billions of people globally. Due to the lack of effective electron acceptors, insufficient nutrient removal and the emission of harmful gases, e. g. H2S, CH4, etc., are the common drawbacks. In the present work, we attempted to supplement nitrite into septic tanks as an electron acceptor, via nitrifying human urine source-separated from blackwater, to overcome these drawbacks. Partial or complete nitritation of source-separated urine was achieved in a sequencing batch reactor. The addition of nitrified urine into septic tanks improved organic and nitrogen removals in blackwater up to 90 % and 70 %, respectively. The emission of harmful gases from the septic tanks was stably diminished, with more than 75 % of CH4, CO2 and H2S reductions. Nitrite addition significantly reduced the abundance of hydrogenotrophic methanogens in septic tanks. Though the activity of sulfate-reducing bacteria recovered after the initial inhibition upon nitrite addition, the bio-generated H2S was retained in water since the increased wastewater pH after nitrite addition promoted the disassociation of H2S in aqueous solution.

Approaches to mitigation of hydrogen sulfide during anaerobic digestion process - A review

Anaerobic digestion (AD) is the primary technology for energy production from wet biomass under a limited oxygen supply. Various wastes rich in organic content have been renowned for enhancing the process of biogas production. However, several other intermediate unwanted products such as hydrogen sulfide, ammonia, carbon dioxide, siloxanes and halogens have been generated during the process, which tends to lower the quality and quantity of the harvested biogas. The removal of hydrogen sulfide from wastewater, a potential substrate for anaerobic digestion, using various technologies is covered in this study. It is recommended that microaeration would increase the higher removal efficiency of hydrogen sulfide based on a number of benefits for the specific method. The process is primarily accomplished by dosing smaller amounts of oxygen in the digester, which increases the system's oxidizing capacity by rendering the sulfate reducing bacteria responsible for converting sulfate ions to hydrogen sulfide inactive. This paper reviews physicochemical and biological methods that have been in place to eliminate the effects of hydrogen sulfide from wastewater treated anaerobically and future direction to remove hydrogen sulfide from biogas produced.

Partial Nitrification in a Sequencing Moving Bed Biofilm Reactor (SMBBR) with Zeolite as Biomass Carrier: Effect of Sulfide Pulses and Organic Matter Presence

This work aimed to achieve partial nitrification (PN) in a Sequencing Moving Bed Biofilm Reactor SMBBR with zeolite as a biomass carrier by using sulfide pulses in the presence of organic matter as an inhibitor. Two conditions were evaluated: sulfide (HS−) = 5 mg S/L and vvm (air volume per liquid volume per minute, L of air L−1 of liquid min−1) = 0.1 (condition 1); and a HS− = 10 mg S/L and a vvm = 0.5 (condition 2). The simultaneous effect of organic matter and sulfide was evaluated at a Chemical Oxygen Demand (COD) = 350 mg/L and HS− = 5 mg S/L, with a vvm = 0.5. As a result, using the sulfide pulse improved the nitrite accumulation in both systems. However, Total Ammonia Nitrogen (TAN) oxidation in both processes decreased by up to 60%. The simultaneous presence of COD and sulfide significantly reduced the TAN and nitrite oxidation, with a COD removal yield of 80% and sulfide oxidation close to 20%. Thus, the use of a sulfide pulse enabled PN in a SMBBR with zeolite. Organic matter, together with the sulfide pulse, almost completely inhibited the nitrification process despite using zeolite.