Evaluating odour control technologies using reliability and sustainability criteria--a case study for water treatment plants

Technologies for odour control have been widely reviewed and their optimal range of application and performance has been clearly established. Selection criteria, mainly driven by process economics, are usually based on the air flow volume, the inlet concentrations and the required removal efficiency. However, these criteria are shifting with social and environmental issues becoming as important as process economics. A methodology is illustrated to quantify sustainability and robustness of odour control technology in the context of odour control at wastewater treatment or water recycling plants. The most commonly used odour abatement techniques (biofiltration, biotrickling filtration, activated carbon adsorption, chemical scrubbing, activated sludge diffusion and biotrickling filtration coupled with activated carbon adsorption) are evaluated in terms of: (1) sustainability, with quantification of process economics, environmental performance and social impact using the sustainability metrics of the Institution of Chemical Engineers; (2) sensitivity towards design and operating parameters like utility prices (energy and labour), inlet odour concentration (H2S) and design safety (gas contact time); (3) robustness, quantifications of operating reliability, with recommendations to improve reliability during their lifespan of operations. The results show that the odour treatment technologies with the highest investments presented the lowest operating costs, which means that the net present value (NPV) should be used as a selection criterion rather than investment costs. Economies of scale are more important in biotechniques (biofiltration and biotrickling filtration) as, at increased airflows, their reduction in overall costs over 20 years (NPV20) is more extreme when compared to the physical/chemical technologies (chemical scrubbing and activated carbon filtration). Due to their low NPV and their low environmental impact, activated sludge diffusion and biotrickling filtration are in general the most cost-effective, and probably the technologies to be considered first for odour treatment in a wastewater treatment or water recycling plant. When, in an economical and risk evaluation, the reliability is counted to be as relevant as the overall costs, a hybrid technology (biotrickling filtration with activated carbon polishing) would be comparable to biotrickling filtration and activated sludge diffusion as the most preferred technologies, when all technologies are designed to have a 99% reduction of H2S and a 95% reduction of the odour concentration.