Dosing Free Nitrous Acid as an Alternative Sulphide Control Technology for Pressure Sewers in Germany

Abstract

Sulphide build-up in pressure sewers has been identified as the main cause for the occurrence of odour and corrosion in sewer systems. Despite the efforts to optimize commonly used control technologies such as nitrate and iron salts to reduce sulphide emission, continuous addition of these chemicals is still required. A biocidal agent such as free nitrous acid can be added intermittently, less frequently, and in smaller quantities whilst achieving total sulphide control. So far, laboratory and field studies in Australia and the USA have successfully proven and applied the use of this control technology, exhibiting its strong biocidal effects during intermittent addition. In this study, nine trials were made to assess the application of the free nitrous acid (FNA) as an alternative sulphide control technology in Germany. The sewer pilot plant of the Berlin Water Utility Company was used to perform the trials at a technical scale using a supply of raw sewage. FNA exposure times ranging from 5 to 24 h in varying concentrations were investigated. The effectiveness of the FNA treatment was monitored using the online hydrogen sulphide (H2S) gas and dissolved-sulphide sensors installed in the sewer pilot plant. Effective sulphide control was only possible during dosing periods, with rapid resumption of sulphide production for the trials with exposure times of <12 h and concentrations ranging from 0.08 to 0.56 mg HNO2-N L−1 suggesting a slight inhibitory effect. A more pronounced biocidal effect was observed for the trials exposed to FNA treatment for 24 h at concentrations >0.29 mg HNO2-N L−1. Overall, the trials of this study demonstrated that the biofilms were FNA resistant and that the concentrations and exposure times used were inadequate to develop an effective intermittent dosing strategy.

Comparison of Online Sensors for Liquid Phase Hydrogen Sulphide Monitoring in Sewer Systems

“…In an intermittently-operated pressure sewer, sulfide production mostly occurs during and immediately following a pumping event, as the active mixing re-establishes substrate availability and enhances mass transfer at the biofilm-liquid interface [16,50]. Therefore, intermittently-operated pressure sewers with a frequent pumping activity are likely to have more sulfide problems than those with fewer and longer pumping events.…”

“…On the other hand, at lower pH (acidic range), a hyposochromic shift and hypochromic effect occur due to the prevalence of the molecular form H2S [53]. As for the micro-electrochemical sensor (SulfiLogger TM ), an increase in the sewage pH means that H2S concentration decreases to a point where the sensor is incapa- In an intermittently-operated pressure sewer, sulfide production mostly occurs during and immediately following a pumping event, as the active mixing re-establishes substrate availability and enhances mass transfer at the biofilm-liquid interface [16,50]. Therefore, intermittently-operated pressure sewers with a frequent pumping activity are likely to have more sulfide problems than those with fewer and longer pumping events.…”

“…Advances in Ultraviolet-Visible (UV/Vis) spectrophotometry have led to an increased number of spectrometers (spectral sensors) available in the market suitable for sewer sulfide monitoring. Studies using UV/Vis spectrometers developed by manufacturers such as s::can GmbH, Vienna, Austria; GO Systemelektronik GmbH, Kiel, Germany; and TriOS Mess-und Datentechnik GmbH, Oldenburg, Germany, have successfully demonstrated applications of sulfide monitoring in sewer systems [14][15][16]. More recently, using the principles of electrochemistry, SulfiLogger A/S (Aarhus, Denmark) developed a Clarke-type microelectrochemical sensor scaled for applications in the wastewater sector.…”

Biofilms in the gravity sewer interfaces: making a friend from a foe

“…To address sulfide occurrence in anaerobic gravity sewers, liquid-phase treatment targeting the biofilm-bulk phase interactions are applied by using chemicals that inhibit sulfate-reducing bacteria (SRB) activity. The administration of chemical agents such as free nitrous acid (FNA), pH shock, and iron salts are examples used to target SRB activity at the biofilmbulk interface in gravity sewers (Jiang et al 2013a;Gutierrez et al 2014;Kiilerich et al 2019;Despot et al 2021). FNA addition was shown to deactivate sewer biofilm activity when exposed for 6-24 h (Jiang et al 2011).…”