Abstract
In most of the management, treatment and environmental recovery infrastructures, anaerobic biodegradation processes of organic matter occur that lead to the generation of volatile reduced sulphur compounds (VSC), among which hydrogen sulphide (H2S) stands out, a substance that can also be generated by microbiological reduction of dissolved sulphate. The presence of H2S is especially relevant in the case of the sanitation networks and wastewater treatment plants, where the formation and subsequent accumulation of H2S occurs in the liquid phase, and from where it can be emitted into gas phase depending on factors such as: non-oxic environment, an acid-neutral pH range, moderate-high temperatures, agitation phenomena (mechanically forced or as a result of water jumps in transport) and others. The implications arising from the presence of significant concentrations of H2S in the gas phase are: a) a recognized toxicity, b) a very pronounced odour potential and c) also a notable corrosive power of both the metallic elements and even the concrete of the pipes and other structures. Consequently, it is of interest to study, prospectively and preventively, the presence and levels of dissolved H2S in wastewater (both urban and from certain industrial processes) since it constitutes the reservoir of H2S accumulation and potential transfer to later stages of the wastewater cycle where it can be released into the gas phase with possible adverse effects. In the present work, several cases are presented where the continuous measurement of dissolved H2S (H2S(d)) and temperature in elements of wastewater circuits (pumping stations, manholes, reception ponds at the entrance of WWTP) have been carried out simultaneously with the analysis of various physicochemical parameter in a series of water samples, together with measurements of H2S and other odorants in the gas phase at discrete intervals, as well as punctual samples in which odour concentration was also determined. The results obtained have allowed, among other aspects: a) determining a reservoir potential of H2S(d), b) optimize reagent injection processes for the mitigation of H2S(d) levels, c) raise alerts for possible excesses of H2S gas (H2S(g)) in the inlet stages of WWTPs and d) tentatively correlate H2S(d) / H2S(g) / odour concentration levels with events and operations carried out on the wastewater circuit.
