Marianna Caivano

Validation of an analytical method for simultaneous high-precision measurements of greenhouse gas emissions from wastewater treatment plants using a gas chromatography-barrier discharge detector system.

Wastewater treatment plants (WWTPs) emit CO2 and N2O, which may lead to climate change and global warming. Over the last few years, awareness of greenhouse gas (GHG) emissions from WWTPs has increased. Moreover, the development of valid, reliable, and high-throughput analytical methods for simultaneous gas analysis is an essential requirement for environmental applications. In the present study, an analytical method based on a gas chromatograph (GC) equipped with a barrier ionization discharge (BID) detector was developed for the first time. This new method simultaneously analyses CO2 and N2O and has a precision, measured in terms of relative standard of variation RSD%, equal to or less than 6.6% and 5.1%, respectively. The methods detection limits are 5.3ppmv for CO2 and 62.0ppbv for N2O. The methods selectivity, linearity, accuracy, repeatability, intermediate precision, limit of detection and limit of quantification were good at trace concentration levels. After validation, the method was applied to a real case of N2O and CO2 emissions from a WWTP, confirming its suitability as a standard procedure for simultaneous GHG analysis in environmental samples containing CO2 levels less than 12,000mg/L.

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 N2O and CO2 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 CO2 and N2O emissions from the AS tank were 0.14 kgCO2/kgbCOD and 0.007 kgCO2,eq/kgbCOD, respectively. For an AeD, 3 × 10−10 kgCO2/kgbCOD direct CO2 emissions were measured, while CO2,eq emissions from N2O were 4 × 10−9 kgCO2,eq/kgbCOD. The results for the AS tank and the AeD were used to estimate the net carbon and energy footprint of the entire plant.

Quantification of CO2 and N2O Emissions from a Pilot-Scale Aerobic Digester, Towards the Validation and Calibration of the First Activated Sludge Model for Aerobic Digestion (AeDM1)

In this study, a pilot aerobic digester was developed and operated to monitor N2O and CO2 emissions using the off-gas technique. A 30-days monitoring campaign was carried out to evaluate the impact of aerobic digestion (AeD) in Greenhouse Gas (GHG) estimation. After the achievement of the equilibrium conditions for a conventional AeD, a monitoring campaign was performed assuming 20 days as sludge retention time. The N2O gas flux was found equal to 71.7 mgN2O m−2min−1 against 16914 mgCO2 m−2min−1 calculated for CO2, demonstrating that strong aerobic oxidation processes occur inside the digester. In terms of equivalent CO2, N2O covers the 55% of the total CO2,eq emissions and CO2 the 45%. The experimental campaigns were coupled with the development of a mathematical model for AeD, named Aerobic Digestion Model No. 1 (AeDM1). The Morris Method allowed us to carry out a sensitivity analysis on the main kinetic parameters, resulting that the maximum specific growth rate of heterotrophs is the more sensitive parameter. After the model calibration, the experimental results on the pilot digester were used to validate the model, inserting the data collected during the experimental tests as model inputs.

A New Plant Wide Modelling Approach for the Reduction of Greenhouse Gas Emission from Wastewater Treatment Plants

Recent studies about greenhouse gas (GHG) emissions show that sewer collection systems and wastewater treatment plants (WWTPs) are anthropogenic GHG potential sources. Therefore, they contribute to the climate change and air pollution. This increasing interest towards climate change has led to the development of new tools for WWTP design and management. This paper presents the first results of a research project aiming at setting-up an innovative mathematical model platform for the design and management of WWTPs. More specifically, the study presents the project’s strategy aimed at setting-up a plant-wide mathematical model which can be used as a tool for reducing/controlling GHG from WWTP. Such tool is derived from real data and mechanicistic detailed models (namely, Activated Sludge Model’s family). These latter, although are a must in WWTP modelling, hamper a comprehensive and easy application due to complexity, computational time burdens and data demanding for a robust calibration/application. This study presents a summary of the results derived from detailed mechanistic models which have been applied to both water and sludge line of a WWTP: primary treatment, biological reactor, secondary settler, membrane bioreactor, sludge digester etc. The project is organized in overall four research units (RUs) which focus each on precise WWTP units.

N2O and CO2 Emissions from Secondary Settlers in WWTPs: Experimental Results on Full and Pilot Scale Plants

Data about Greenhouse Gas (GHG) emissions from settling units in wastewater treatment plants (WWTPs) are limited, probably because of the increased difficulties in evaluating direct emissions when there is absence of an induced air stream through the liquid volume (Caivano et al. 2016). Particularly, gas samples collection is not immediate and easy due to the low off-gas flow leaving the liquid surface.

CO2 and N2O from water resource recovery facilities: Evaluation of emissions from biological treatment, settling, disinfection, and receiving water body

Water resource recovery facilities (WRRFs) contribute to climate change and air pollution, as they are anthropogenic potential sources of direct and indirect emission of greenhouse gases (GHGs). Studies concerning the monitoring and accounting for GHG emissions from WRRFs are of increasing interest. In this study, the floating hood technique for gas collection was coupled with the off-gas method to monitor and apportion nitrous oxide (N2O) and carbon dioxide (CO2) emissions from both aerated and non-aerated tanks in a municipal water resource recovery facility, in order to investigate its carbon footprint (CFP). To our knowledge, this is the first time that the chamber technique was applied to evaluate gas fluxes from the settler, where an emission factor (EF) of 4.71 ∗ 10-5 kgCO2,eq kgbCOD-1 was found. Interesting results were found in the disinfection unit, which was the major contributor to direct N2O emissions (with a specific emission factor of 0.008 kgCO2,eq kgbCOD-1), due to the chemical interaction between hydroxylamine and the disinfectant agent (hypochlorite). The specific emission factor of the biological aerated tank was 0.00112 kgCO2,eq kgbCOD-1. The average direct CO2 emission was equal to 0.068 kgCO2 kgbCOD-1 from the activated sludge tank and to 0.00017 kgCO2 kgbCOD-1 from the secondary clarifier. Therefore, taking into account the contribution of both direct N2O and CO2 emissions, values of 0.069 kgCO2,eq kgbCOD-1, 0.008 kgCO2,eq kgbCOD-1 and 0.00022 kgCO2,eq kgbCOD-1, were found for the net CFP of the aerated compartment, the disinfection unit and the clarifier, respectively. The plant energy Footprint (eFP) was also evaluated, confirming that the aeration system is the major contributor to energy consumption, as well as to indirect CO2 emission, with a specific eFP of 1.49 kWh kgbCOD-1.

Disinfection Unit of Water Resource Recovery Facilities: Critical Issue for N2O Emission

In this study, the floating hood technique for gas collection has been coupled with the off-gas method to monitor greenhouse gas emissions from the chlorination unit in a municipal water resource recovery facility located in Italy. Experimental measurements of direct nitrous oxide (N2O) from chlorination step were performed in order to investigate the contribution of this unit on the net carbon footprint. Interesting results were found on the chlorination unit which proved to be the major contributor to direct N2O emissions, due to the chemical interaction between hydroxylamine and the disinfectant agent (i.e. hypochlorite). For the first time, we measured for the chlorination unit a specific emission factor of 0.008 kgCO2,eq \( {\text{kg}}_{\text{bCOD}}^{ - 1} \), proving the innovativeness of our findings.

A Graphical User Interface as a DSS Tool for GHG Emission Estimation from Water Resource Recovery Facilities

A Grafical User Interface (GUI) for the greenhouse gas (GHG) emissions from WWTPs based on four models aimed at quantifying the gas emissions from the aerated tanks (i.e. CAS and MBR reactor), aerobic digesters, secondary clarifiers and anaerobic digesters have been englobed in a GUI in order to provide a valid decision support system (DSS) to the practitioners. The GUI allows to estimate such emissions for the different WWTP phases considered. The GUI has been developed on MATLAB platform and provides as output the GHG emissions in terms of CO2 and N2O fluxes.