Plant-wide investigation of sulfur flows in a water resource recovery facility (WRRF)

International audienceEven though sulfur compounds and their transformations may strongly affect wastewater treatment processes,their importance in water resource recovery facilities (WRRF) operation remains quite unexplored, notablywhen it comes to full-scale and plant-wide characterization. This contribution presents afirst-of-a-kind, plant-wide quantification of total sulfur massflows for all water and sludge streams in a full-scale WRRF. Because ofits important impact on (post-treatment) process operation, the gaseous emission of sulfur as hydrogen sulfide(H2S) was also included, thus enabling a comprehensive evaluation of sulfurflows. Data availability and qualitywere optimized by experimental design and data reconciliation, which were applied for thefirst time to total sul-furflows. Total sulfurflows were successfully balanced over individual process treatment units as well as theplant-wide system with only minor variation to their original values, confirming that total sulfur is a conservativequantity. The two-stage anaerobic digestion with intermediate thermal hydrolysis led to a decreased sulfur con-tent of dewatered sludge (by 36%). Higher (gaseous) H2S emissions were observed in the second-stage digester(42% of total emission) than in thefirst one, suggesting an impact of thermal treatment on the production of H2S.While the majority of sulfur massflow from the influent left the plant through the treated effluent (> 95%), thesulfur discharge through dewatered sludge and gaseous emissions are critical. The latter are indeed responsiblefor odour nuisance, lower biogas quality, SO2emissions upon sludge combustion and corrosion effects