Assessment of the use of mainstream iron addition for phosphorous control on H₂S content of biogas from anaerobic digestion of sludges

Abstract

A material flux analysis on sulfur (S), phosphorus (P), aluminum (Al), and iron (Fe) was conducted for two WWTPs (Galt and Kitchener) to evaluate the potential of coagulants that are employed for phosphorus control to reduce hydrogen sulfide (H2S) emissions in the biogas from anaerobic digestion. It was found that while the Galt WWTP receives higher concentrations of S in the raw wastewater than the Kitchener WWTP, this had only a modest impact on the speciation of S entering anaerobic digestion. At both plants, only 2%–4% of influent S entered the digesters. The presence of Fe in the sludge stream was found to cause S, that is released by volatile solid destruction and sulfate (SO42-SO42-) reduction, to become particulate‐bound. A dosage of 1.1 mg/L of Fe into the raw wastewater (11% of the Fe dosed for P control) was sufficient for sulfide (S2‐) control. Transitioning the Galt WWTP from Al to Fe dosing for P control had no significant impact on effluent P concentrations and resulted in a substantial reduction in the biogas H2S concentration. An additional secondary benefit was an increase in the solid content of the dewatered cake. Practitioner points Material flux analyses can be employed to gain insight into the fate of key elements contributing to biogas quality. The use of iron for phosphorous control can effectively control H2S in anaerobic biogas. Conversion from Al2(SO4)3 to FeSO4 dosing for P control resulted in increased solid content of centrifuged biosolids.

Ferric Oxide-Containing Waterworks Sludge Reduces Emissions of Hydrogen Sulfide in Biogas Plants and the Needs for Virgin Chemicals

“…For wastewater treatment plants, operators have expressed concerns that the addition of waterworks sludge could affect the drainage properties of the digestate. The opposite effect is indicated by literature data, finding that the drainage of biosolids after the addition of waterworks sludge is improved [13,18].…”

“…It has been reported that around 2-4% of influent S enters the digesters, which could be removed sufficiently by a dosage of 1.1 mg/L of Fe into the raw wastewater. A higher dry matter content was also observed in the dewatered cake as an additional secondary benefit when changing from alum dosage to iron dosage for phosphorous removal [13]. A drop in hydrogen sulfide emission from full-scale ADs at a large-scale municipal wastewater treatment plant could be achieved when dosing ferric chloride.…”

“…Often, ferric chloride solution is dosed into the reactor to achieve this removal effect on hydrogen sulfide. However, the addition of virgin ferric salts has an operational Sustainability 2021, 13, 7416 2 of 14 cost, and a water and carbon footprint. The profitability in, for instance, the Swedish biogas industry is relatively poor [2].…”

Application of Recycled Filling to Improve the Purification Performance of Confectionery Wastewater in a Vertical Anaerobic Labyrinth Flow Bioreactor

“…Industrial filters allow for the precise separation of the sulphur compounds contained in the biogas, but this is associated with considerable operating costs [78]. As far as the protection of electricity generators or CHP plants is concerned, the techniques for cleaning the biogas from H2S have a significant impact on the cost of the plants, and abandoning them or replacing them with biological filters leads to a drastic reduction in the lifetime of generators and anaerobic reactor systems [79]. In desulphurisation technology based on the use of a steel valve bed, it is possible to easily obtain a substrate for the production of this adsorber and also to easily modify existing solutions [80].…”

Mechanistic Understanding of Beneficial Aspects of Iron Salts and Waterworks Sludge Uses in Urban Wastewater System

“…sewer system and other downstream treatment units such as AS system or AD in WWTP. Direct dosing of Fe-salt in sewers (Ganigue et al, 2011b;Gutierrez et al, 2010;Zhang et al, 2009b;Zhang et al, 2010) and AD (Akgul et al, 2017;Park and Novak, 2013;Parker et al, 2019) for controlling sulfides or chemical P precipitation with Fe-salt in AS system (de Haas et al, 2000;de Haas et al, 2001;Gutierrez et al, 2010), have been established as the proven practices. Such a strategy of direct Fe-salt dosing has been reported to improve settleability (Oikonomidis et al, 2010) and dewaterability (Wei et al, 2018) of activated sludge including the dewaterability of digestate (Novak and Park, 2010;Akgul et al, 2017).…”