Donatella Caniani

Greenhouse gases from wastewater treatment - A review of modelling tools

Nitrous oxide, carbon dioxide and methane are greenhouse gases (GHG) emitted from wastewater treatment that contribute to its carbon footprint. As a result of the increasing awareness of GHG emissions from wastewater treatment plants (WWTPs), new modelling, design, and operational tools have been developed to address and reduce GHG emissions at the plant-wide scale and beyond. This paper reviews the state-of-the-art and the recently developed tools used to understand and manage GHG emissions from WWTPs, and discusses open problems and research gaps. The literature review reveals that knowledge on the processes related to N2O formation, especially due to autotrophic biomass, is still incomplete. The literature review shows also that a plant-wide modelling approach that includes GHG is the best option for the understanding how to reduce the carbon footprint of WWTPs. Indeed, several studies have confirmed that a wide vision of the WWPTs has to be considered in order to make them more sustainable as possible. Mechanistic dynamic models were demonstrated as the most comprehensive and reliable tools for GHG assessment. Very few plant-wide GHG modelling studies have been applied to real WWTPs due to the huge difficulties related to data availability and the model complexity. For further improvement in GHG plant-wide modelling and to favour its use at large real scale, knowledge of the mechanisms involved in GHG formation and release, and data acquisition must be enhanced.

Application of fuzzy logic and sensitivity analysis for soil contamination hazard classification.

The present article is aimed at illustrating a methodology for a rapid and effective assessment of pollution hazard connected with the presence of uncontrolled landfills. In particular, by means of a fuzzy approach, the criterion adopted allowed a comparison of the results obtained from a cross analysis of some intrinsic characteristics of the single landfills and the territory where they are located. Their identification shows the most relevant environmental problem. Therefore, we have classified each site within a hazard scale enabling us to understand which one requires to be checked more urgently, to do instrumental surveys and, if needed, to do restoration and reclamation. Moreover, the sensitivity analysis we carried out allowed us to identify which is the best membership function belonging and which is the best defuzzification method. That is, in particular, the trapezoidal function and the centroid method. The proposed fuzzy approach, supported by the sensitivity analysis, has revealed to be an important tool for supporting decisions, in order to optimise technical and economic resources.

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.

Biodegradation of carbamazepine and clarithromycin by Trichoderma harzianum and Pleurotus ostreatus investigated by liquid chromatography – high-resolution tandem mass spectrometry (FTICR MS-IRMPD)

In this study, the capability of pharmaceutical biodegradation of fungus Trichoderma harzianum was evaluated through the comparison with the well-known biodegradation capability of white-rot fungus Pleurotus ostreatus. The study was performed in aqueous phase under aerobic conditions, using two of the most frequently detected drugs in water bodies: carbamazepine and clarithromycin, with concentrations commonly found in treated wastewater (4μg/l and 0.03μg/l respectively). For the first time, we demonstrated that T. harzianum is able to remove carbamazepine and clarithromycin. The analyses were performed by reversed-phase liquid chromatography/mass spectrometry, using high-resolution Fourier-transform ion cyclotron resonance mass spectrometry upon electrospray ionization in positive ion mode. The high selectivity and mass accuracy provided by high-resolution mass spectrometry, allowed us to identify some unknown metabolites. On the basis of our study, the major metabolites detected in liquid culture treated by T. harzianum were: 14-hydroxy-descladinosyl- and descladinosyl-clarithromycin, which are pharmacologically inactive products not dangerous for the environment.

Methane oxidation in a biofilter (Part 1): Development of a mathematical model for designing and optimization.

The aim of this work is the evaluation of the efficiency of such a biofilter, through the application of a mathematical model which describes the biological oxidation process. This mathematical model is able to predict the efficiency of the system under varying operating conditions. Literature data have been used in order to build the model. The factors that mostly affect the process and which actually regulate the entire process have been highlighted in this work. Specifically, it was found that temperature, flow and methane concentration are the most important parameters that influence the system. The results obtained from the mathematical model showed also that the biofilter system is simple to implement and manage and allows the achievement of high efficiency of methane oxidation. In the optimal conditions for temperature (between 20–30°C), residence time (between 0.7–0.8 h) and methane molar fraction (between 20–25%) the efficiency of methane oxidation could be around 50%.

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.

Preliminary evaluation of Pleurotus ostreatus for the removal of selected pharmaceuticals from hospital wastewater

The fungus Pleurotus ostreatus was investigated to assess its ability to remove diclofenac, ketoprofen, and atenolol spiked at 10 mg/L each one in hospital wastewater. The degradation test was carried out in a fluidized bed bioreactor testing both the batch and the continuous mode (hydraulic retention time in the range 1.63–3 days). In batch mode, diclofenac disappeared in less than 24 h, ketoprofen was degraded up to almost 50% in 5 days while atenolol was not removed. In continuous mode, diclofenac and ketoprofen removals were about 100% and 70% respectively; atenolol degradation was negligible during the first 20 days but it increased up to 60% after a peak of laccase production and notable biomass growth. In order to identify the enzymatic system involved, further experiments were carried out in flasks. Purified laccase completely transformed atenolol and diclofenac in less than 5 h, but not ketoprofen. In vivo experiments suggested that cytochrome P450 could be involved in diclofenac and ketoprofen degradation, while partial correlation studies confirmed the role of laccase in atenolol and diclofenac degradation. Two intermediates of diclofenac and ketoprofen were detected by nuclear magnetic resonance. Moreover P. ostreatus was able to reduce chemical oxygen demand of the hospital wastewater which is an important advantage comparing to other fungi in order to develop a wastewater treatment process.

Dewaterability of CAS and MBR Sludge: Effect of Biological Stability and EPS Composition

AbstractThe dewaterability of sludge from two conventional activated sludge (CAS) and three membrane bioreactor (MBR)–based wastewater treatment plants is investigated prior to and after anaerobic ...

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.