Free nitrous acid (FNA) is known for its capacity to inhibit various microorganisms in wastewater systems, significantly benefiting treatment process management
Sewer systems are essential compartments of urban life, preventing human exposure to unhygienic sewage and sewage-borne diseases. However, microbially influenced concrete corrosion (MICC) occurs in sewers globally and ultimately leads to severe structural deterioration and early failure of those concrete structures. The MICC in sewers is mainly caused by hydrogen sulfide (H2S) that occurs in the headspace gas. In sewers, H2S is produced due to the metabolism of sulfate-reducing bacteria (SRB) under anaerobic conditions in parts of sewers and is subsequently released into headspace sewer gas in the gravity sections of the sewer system. In gravity sewers, H2S in the headspace gas is further oxidized into sulfuric acid by sulfide-oxidizing microorganisms (SOMs) on concrete surfaces, leading to concrete corrosion. The remediation and replacement of corroding concrete sewers could cost billions of dollars annually, which becomes a huge financial burden worldwide. In recent years, advanced u
Recycling nutrients (nitrogen, phosphorus, and potassium) from human urine can potentially offset more than 13% of global agricultural fertilizer demand. Biological nitrification is a promising method for converting volatile ammonia in high-strength human urine into stable ammonium nitrate (a typical fertilizer), but it is usually terminated in the intermediate production of nitrite due to the inhibition of nitrite-oxidizing bacteria by free nitrous acid (FNA). This study aimed to develop a stable nitrification process in a unique two-stage bioreactor by removing critical barriers associated with FNA inhibition. Experimental results show that half of the ammonium in high-strength urine was successfully converted into nitrate, forming valuable ammonium nitrate (with a nitrogen concentration greater than 1500 mg N/L). The ammonium nitrate solution could retain most phosphorus (75% ± 3%) and potassium (96% ± 1%) in human urine, resulting in nearly full nutrient recovery. Once concentrat
Microbially influenced concrete corrosion (MICC) in sewers is caused by the activity of sulfide-oxidizing microorganisms (SOMs) on concrete surfaces, which greatly deteriorates the integrity of sewers. Surface treatment of corroded concrete by spraying chemicals is a low-cost and non-intrusive strategy. This study systematically evaluated the spray of nitrite solution in corrosion mitigation and re-establishment in a real sewer manhole. Two types of concrete were exposed at three heights within the sewer manhole for 21 months. Nitrite spray was applied at the 6th month for half of the coupons which had developed active corrosion. The corrosion development was monitored by measuring the surface pH, corrosion product composition, sulfide uptake rate, concrete corrosion loss, and the microbial community on the corrosion layer. Free nitrous acid (FNA, i.e. HNO2), formed by spraying a nitrite solution on acidic corrosion surfaces, was shown to inhibit the activity of SOMs. The nitrite spray