Abstract
Odour emissions from soil remediation processes are often a cause for concerns from neighboring residents, sometimes leading to community complaints and scrutiny by the overseeing authorities.At a soil remediation site in Belgium, there are frequent reports of an odour described as “fishy” in the surroundings of the site. Upon initial site inspection, the fishy odour was not immediately evident. However, subsequent air sampling above stabilized sludge heaps revealed a high concentration of trimethylamine (TMA) as confirmed by thermal desorption gas chromatography-mass spectrometry (TD-GC-MS) analysis. TMA is associated with a pungent fishy smell and a very low odour threshold of 0.076 µg.m-3. It became apparent that the fishy smell, initially masked by the smell of wet earth, began to dominate upon dilution in the environment.
Further experiments conducted focused on elucidating which process led to the formation of TMA within the remediation site. A microchamber thermal extractor (Markes µ-CTE) was used to simulate the high temperatures occurring in the sludge heaps caused by the exothermic hydration reaction of quicklime (CaO) used as a binder agent. N2-air was purged through the microchamber and collected in a Nalophan air sample bag, after which the sample was again analyzed using TD-GC-MS and a sensory odour evaluation panel. This methodology proved very powerful as it allowed for a rapid throughput of small-scale tests using only minimal amounts of sludge and chemicals.
Different combinations of sludge, drying agents, and flocculants revealed that a specific polyacrylamide (PAM) based flocculant, in conjunction with the basic conditions generated by the drying agent (CaO), facilitated the production of TMA. Subsequent efforts to identify alternative combinations of drying agents and flocculants capable of mitigating TMA emissions while remaining effective for the sludge treatment were made by systematic testing. Again, the above-described small-scale screening methodology was successfully applied.
This case study underscores the importance of proactive odour management strategies in soil remediation projects and the potential of the rapid screening of the applied chemicals. By understanding the underlying mechanisms of odour generation at soil remediation sites and employing mitigation measures, environmental impacts on the surroundings can be minimized.