Efficient sulfide bio-chemical removal by different crystalline FeOOH (α, β, γ, δ and amorphous) in sewers

H₂S corrosion in sewers causes huge economic losses. However, effective control solutions have remained lacking for decades. This study proposes FeOOH as a long-lasting and cost-effective alternative to iron salts for H₂S control in sewers. The effect of FeOOH crystalline structures, electrochemical activity, acid and thermal stability, and surface morphology on S and Fe microbial redox were investigated. δ-FeOOH exhibited nearly 100 % H₂S removal efficiency and the highest S^2- removal capacity of 369.6 mg S/g FeOOH (1.10 mol S/Fe) followed by α-, AMO-, β- and γ-FeOOH. α-FeOOH treatment showed the highest FeS-S precipitation (304.2 mg S/g) and longest duration for sulfide control. This was contributed to α-FeOOH's low surface area and high structure stability. SO₄^2--S bio-reduction inhibition was highest in δ-FeOOH (92.4 mg S/g), attributed to its highest Fe(Ⅲ)/Fe(Ⅱ), abundant sulfide oxidation genes (fccB, soxY and SUOx), and minimal electron transfer resistance. Moreover, sewer microbes enhanced the sulfide removal capacity of FeOOH by up to 6.0 times. FeOOH redirected microbial electron transfer away from SO₄^2- reduction and formed hydrogen bond with proteins that influenced SO₄^2- transport and uptake. This study provides comprehensive insights into the impact of FeOOH crystalline structure on microbial sulfur metabolism and electron transfer in sewers.