Monitoring the aeration efficiency and carbon footprint of a medium-sized WWTP: experimental results on oxidation tank and aerobic digester

Abstract

The efficiency of aeration systems should be monitored to guarantee suitable biological processes. Among the available tools for evaluating the aeration efficiency, the off-gas method is one of the most useful. Increasing interest towards reducing greenhouse gas (GHG) emissions from biological processes has resulted in researchers using this method to quantify NO and CO concentrations in the off-gas. Experimental measurements of direct GHG emissions from aerobic digesters (AeDs) are not available in literature yet. In this study, the floating hood technique was used for the first time to monitor AeDs. The floating hood technique was used to evaluate oxygen transfer rates in an activated sludge (AS) tank of a medium-sized municipal wastewater treatment plant located in Italy. Very low values of oxygen transfer efficiency were found, confirming that small-to-medium-sized plants are often scarcely monitored and wrongly managed. Average CO and NO emissions from the AS tank were 0.14 kg/kg and 0.007 kg/kg, respectively. For an AeD, 3 × 10 kg/kg direct CO emissions were measured, while CO emissions from NO were 4 × 10 kg/kg. The results for the AS tank and the AeD were used to estimate the net carbon and energy footprint of the entire plant.

A decade of nitrous oxide (N2O) monitoring in full-scale wastewater treatment processes: A critical review

“…0.003%, 0.065%) have been observed in reactors with diluted influent concentrations due to groundwater infiltration (Bellandi et al, 2018), nitrification efficiency less than 73% (Ahn et al, 2010b) and low TN removal (∼59%) due to COD/TN < 1.9 (Spinelli et al, 2018). Low EF in MLE reactors ranging from 0.003% to 0.065% of the NH 4 + load have been also reported in the studies of Caivano et al (2017) and Bellandi et al (2018); however, conversion of these EF to % N-load was not possible and were not included in Fig. 3.…”

Toward a New Plant-Wide Experimental and Modeling Approach for Reduction of Greenhouse Gas Emission from Wastewater Treatment Plants

“…Therefore, with a view to a plant-wide approach, RU2 has contributed in defining the experimental tests as well as the modeling approach on the sludge line, particularly on the sludge settling and aerobic digestion. In particular, considering the popularity of aerobic digestion in treating excess sludge in small-to-medium-sized WWTPs (10,000-50,000 population equivalents-PE) in Italy (Caivano et al 2017a), the interest in the contribution of aerobic digestion to the CFP and EFP of WWTPs makes the project even more integrated. According to its previous scientific experience, RU2 has started up a pilot-scale plant with the aim to analyze more effectively the processes of settling and aerobic digestion.…”

“…)Table 3. Total plant CFP (all values in kgCO 2;eq =kg bCOD ) and comparison fromCaivano et al (2017a);Gori et al (2013).…”

Life cycle assessment applied to waste management in Italy: A mini-review of characteristics and methodological perspectives for local assessment

“…Carbon and water footprints are also often used to measure waste management impacts (Fan et al, 2020). Environmental footprints are employed in many contexts, for instance to verify the efficiency of waste treatment plants (Caivano et al, 2017), to assess impacts of waste scenarios and recycling strategies (Salladini et al, 2019), to mitigate greenhouse gas emissions (Bogner et al, 2008) and to plan water and carbon regional policies (D’Ambrosio et al, 2020; Pulselli et al, 2019).…”