Sewage sludge produced by various technological treatment processes within the EU-funded project ... more Sewage sludge produced by various technological treatment processes within the EU-funded project ROUTES are assessed for their ecotoxicity with standard laboratory tests. The tests were selected among a number of test systems recommended by testing guidelines for waste. They encompass aquatic organisms (freshwater green algae and freshwater crustaceans) and terrestrial organisms (soil bacteria and earthworms). The test methods are described here and typical problems encountered with the testing of such organic material are illustrated by presenting results for one example batch of sludge samples. For this example, some evidence for a toxicity-reducing effect of the digestion treatment was observed only in the soil bacteria contact test with Arthrobacter globiformis.
The application of ultrasound to sludge is an efficient method for sludge disintegration in order... more The application of ultrasound to sludge is an efficient method for sludge disintegration in order to accelerate the anaerobic digestion process, but energy balance on the basis of lab tests is disadvantaged due to the inefficiency at this scale. In this paper the energy balance is discussed for five full scale WWTPs equipped with different devices with the aim to investigate the cost-effectiveness of the ultrasonic pre-treatment before digestion. These five experiences show positive energy gains operating at 20 kHz: best performances are attained at short sonication time and high sonication power. Moreover, sludge sonication at 200 kHz is presented as an alternative pretreatment to improve the anaerobic digestibility and to remove potentially organic micropollutants. Lab experiment results of this treatment indicated quite good disintegration effect, in terms of substrate solubilization, with consequent acceleration of the hydrolysis phase and increase of biogas production.
Questa tecnologia integra l'utilizzo di microalghe e cianobatteri per il biorimedio con la produz... more Questa tecnologia integra l'utilizzo di microalghe e cianobatteri per il biorimedio con la produzione di biocarburanti di terza generazione e di altri composti ad alto valore aggiunto (es. proteine). Questi microrganismi autotrof sono, infatti, in grado di fssare CO 2 e produrre, con un'elevata efficienza, lipidi che possono essere successivamente trasformati in biodiesel. Contestualmente, è possibile utilizzare le microalghe e i cianobatteri per un trattamento terziario delle acque reflue, o comunque di acque eutrofche, grazie alla loro capacità di rimuovere efficacemente nutrienti inorganici ed altri contaminanti, quali metalli pesanti, che vengono utilizzati per sostenere i loro veloci cicli cellulari.
Sludge microbial quality is a major issue to be assessed for the sustainable reuse of sludge in a... more Sludge microbial quality is a major issue to be assessed for the sustainable reuse of sludge in agriculture. Within the ROUTES project innovative solutions for the production of good quality sludge are evaluated and the hygienisation performances of the proposed sludge treatment systems is assessed. The paper describes the efficiency of pathogens and indicator removal by a combination of a disintegration pre-treatment, by thermal hydrolysis, and thermophilic anaerobic digestion and by a combined anaerobic and aerobic digestion process. To better address the fate of pathogens with diverse resistance capacity different indicators microorganism (E.coli, spore of sulphide reducing clostridia SSCR and somatic coliphage SOMCPH) and specific pathogens (Salmonella and enteric viruses) were monitored. An improvement of hygenization was obtained by both investigated processes. Thermal pre-treatment improved the SOMCPH removal of more than one logarithmic unit and efficiently eliminated bacter...
In the urban wastewater treatment, primary and secondary sludges are typically produced and then ... more In the urban wastewater treatment, primary and secondary sludges are typically produced and then treated in mixture before disposal. Primary sludge includes the particulate matter and colloidal material separated from the raw wastewater in the primary sedimentation; while secondary sludge is the biomass extracted from the secondary clarifier after the biological process. Separation of primary sludge from secondary one might be beneficial in a new sludge management strategy considering that secondary sludge normally poorer in pollutants but richer in nitrogen and phosphorus than primary sludge that should preferentially be used in agriculture while the typical disposal option for primary sludge should be incineration. In this perspective, lab-scale thermal tests were performed by a prototype called System for Thermal Diagnostic Studies (STDS) to verify whether the incineration of primary sludge separated from secondary one would lead to different emissions in comparison to the conven...
The IWA ADM1 model is a powerful tool to assess the anaerobic biodegradability of different typol... more The IWA ADM1 model is a powerful tool to assess the anaerobic biodegradability of different typologies of biomasses, sewage sludge and bio wastes.
The application of ultrasound to sludge is an efficient method for sludge disintegration in order... more The application of ultrasound to sludge is an efficient method for sludge disintegration in order to accelerate the anaerobic digestion process, but energy balance on the basis of lab tests is disadvantaged due to the inefficiency at this scale. In this paper the energy balance is discussed for five full scale WWTPs equipped with different devices with the aim to investigate the cost-effectiveness of the ultrasonic pre-treatment before digestion. These five experiences show positive energy gains operating at 20 kHz: best performances are attained at short sonication time and high sonication power. Moreover, sludge sonication at 200 kHz is presented as an alternative pretreatment to improve the anaerobic digestibility and to remove potentially organic micropollutants. Lab experiment results of this treatment indicated quite good disintegration effect, in terms of substrate solubilization, with consequent acceleration of the hydrolysis phase and increase of biogas production.
AN INNOVATIVE TECHNIQUE TO DECONTAMINATE ACTIVATED SLUDGE INCREASING ANAEROBIC DIGESTION PERFORMANCE
Sludge agricultural recovery mainly depends on the possibility to improve the sludge quality by m... more Sludge agricultural recovery mainly depends on the possibility to improve the sludge quality by maximizing decontamination and stabilization. Ultrasounds at 20 kHz are commonly used as pre-treatment for sludge particulate solubilisation to improve anaerobic digestion whereas high frequency ultrasounds (more than 200 kHz) are recently investigated to decontaminate wastewater via oxidation due to water sonolysis. Objective of this work is to study the effectiveness of ultrasounds at 200 kHz to remove linear alkylbenzenesulfonates (LAS) from sludge improving at the same time anaerobic digestibility. Sonolysis experiments showed that ultrasounds can remove up to 50% of the LAS content in less than 1 h at low power input. Moreover, batch anaerobic digestion tests with untreated and disintegrated sludge (20 or 200 kHz) showed improvements of volatile solid removal and of biogas production compared to untreated sludge. At 200 kHz it was possible to gain more biogas than at 20 kHz.
ROUTES is addressed to assess new routes in wastewater and sludge treatment focusing on three mai... more ROUTES is addressed to assess new routes in wastewater and sludge treatment focusing on three main objectives: 1. optimization of the sludge quality for agricultural use with the goal to produce a clean and full stabilized sludge through intensive stabilization processes with attention to a broad spectrum of parameters including micropollutants, pathogens and their indicators. 2. minimization of the sludge to be disposed by innovative technical solutions based on different approaches, either on the water or sludge treatment lines; 3. recovery of valuable resources before sludge disposal by producing a liquid fertilizer [(NH4)2SO4], biopolymers or optimizing methane production by anaerobic treatments. Technical and economic assessment of the investigated techniques on laboratory and pilot scale were carried out in a typical benchmarking study. The whole set of data is then provided to the partner involved in environmental assessment where different impact categories are considered (g...
Sewage sludge processing is a key issue in wastewater treatment plants due to the inefficacy of c... more Sewage sludge processing is a key issue in wastewater treatment plants due to the inefficacy of conventional treatments to produce high quality sludge to be safely used in agriculture. Under this framework, the performances of several enhanced stabilization processes, namely ultrasound-pretreated Mesophilic Anaerobic Digestion (US-MAD), thermophilic anaerobic digestion (TAD), thermal pretreated TAD (TH-TAD) and ultrasound-pretreated inverse Temperature Phased Anaerobic Digestion (iTPAD) have been investigated. The enhanced anaerobic processes resulted in higher specific biogas production and higher destruction of E.coli and Somatic coliphages with respect to conventional MAD process, thus confirming the feasibility of these innovative processes in full-scale implementation perspectives.
Nowadays, several technologies and management strategies are proposed for upgrading wastewater tr... more Nowadays, several technologies and management strategies are proposed for upgrading wastewater treatment plants (WWTPs) in order to improve sludge stabilization or minimize sludge production. In order to make sure that this leads to overall improvements, their techno-economic and environmental performance has to be carefully evaluated. In response to this, the techno-economic and environmental performance was assessed for a considered model reference WWTP upgraded with separate treatment and disposal for primary and secondary sludge to provide guidance to research, policy and investment efforts. This paper departs in an experimental campaign carried out within the EU project "ROUTES" and describes an assessment of an upgrade of a WWTP, involving wet oxidation of primary sludge and thermophilic anaerobic digestion (integrated with thermal hydrolysis pre-treatment) for secondary sludge. The reference plant and the upgrade implied different disposal routes for the resulting sludges: incineration for the stabilized sludge deriving from the reference WWTP; agricultural land application for the secondary stabilized sludge from the upgraded plant and landfilling for the solid residue deriving from the wet oxidation process (as non-hazardous waste).
Thermal hydrolysis pretreatment coupled with Thermophilic Anaerobic Digestion (TAD) for Waste Act... more Thermal hydrolysis pretreatment coupled with Thermophilic Anaerobic Digestion (TAD) for Waste Activated Sludge (WAS) treatment is a promising combination to improve biodegradation kinetics during stabilization. However, to date there is a limited knowledge of the anaerobic biomass composition and its impact on TAD process performances. In this study, the structure and dynamics of the microbial communities selected in two semi-continuous anaerobic digesters, fed with untreated and thermal pretreated sludge, were investigated. The systems were operated for 250 days at different organic loading rate. 16S rRNA gene clonal analysis and Fluorescence In Situ Hybridization (FISH) analyses allowed us to identify the majority of bacterial and archaeal populations. Proteolytic Coprothermobacter spp. and hydrogenotrophic Methanothermobacter spp. living in strict syntrophic association were found to dominate in TAD process. The establishment of a syntrophic proteolytic pathway was favoured by th...
Semi-continuous mesophilic and thermophilic digestion, with sludge pre-treatments. Enhanced relea... more Semi-continuous mesophilic and thermophilic digestion, with sludge pre-treatments. Enhanced release of lipids by thermal hydrolysis and proteins by ultrasounds. Pre-treatments improved organics conversion to CH 4 only at low-medium loading rate. At high organic load, TAD yield was 0.15 against 0.11 Nm 3 methane/kg COD fed of MAD. Generated charged polymers in TAD impaired filterability more rapidly than in MAD.
Proceedings of the Water Environment Federation, 2012
The legislative standards in many European countries and in the USA on sludge use in agriculture ... more The legislative standards in many European countries and in the USA on sludge use in agriculture require effective removal of pathogens during stabilization processes. Great attention is also paid nowadays to organic micropollutants like PCBs, surfactants (LAS), hydrocarbons, polynuclear aromatic hydrocarbons (PAH), halorganics (AOX) and pharmaceuticals whose removal is not effective in conventional sludge processing. Anaerobic thermophilic digestion was considered suitable for producing class A biosolids since 30 years considering that more effective removal of pathogens seems to be attained in thermophilic digestion in comparison with mesophilic conventional.
Ultrasounds pretreatment aims to convert waste activated sludge, characterized by recalcitrant pa... more Ultrasounds pretreatment aims to convert waste activated sludge, characterized by recalcitrant particulate organics, into a soluble, more biodegradable form, maximizing anaerobic stabilization and biogas recovery. Objective of this work was the assessment of the efficiency of high frequency ultrasounds, as 200 kHz, to improve sludge anaerobic digestion performances. Parallel batch anaerobic digestion tests were performed to evaluate anaerobic biodegradability of 20 or 200 kHz sonicated secondary sludge, operating at food/inoculum ratio of 0.5 and 1. Ultrasound pretreatments, independent on the frequency, accelerated the initial hydrolysis phase, and the effect was more marked working at high inoculum content. Moreover, the biogas produced by the sonicated sludge was always higher than that produced by the untreated one. This gain seemed to be independent on the F/I ratio for the digestion of the 20 kHz pretreated sludge, while, in the case of sludge treatment at 200 kHz, the biogas improvement was particularly high (about 40%) at F/I=0.5. In fact, at F/I=1, the biogas gain was only +4% due to an evident slowdown of the biogas production of the sonicated sludge, due to the accumulation of soluble organic substances, evidenced by the soluble COD pattern, suggesting discoupling between hydrolysis and methanogenesis. Fluorescence In Situ Hybridization (FISH) analysis allowed to highlight the establishment in the anaerobic biomass of different methanogens responsible for the biogas production depending on the extent of readily biodegradable substrates availability for the methanogenesis or on the amount of inoculum utilised at the start up of the anaerobic digestion process.
Proceedings of the Water Environment Federation, 2010
In the coming years, large European wastewater treatment plants (WWTPs) will need to dispose of s... more In the coming years, large European wastewater treatment plants (WWTPs) will need to dispose of sludge by transforming it into inert material by thermal processes. In fact, the present European landfill directive 99/31 has restricted this disposal route which was practically abandoned by countries, where the implementation of the directive criteria in national legislations was very stringent, either imposing a limit of the organic carbon to 4 -5 % in the wastes to be disposed (Germany) or including a leachate test with the very stringent limit of dissolved organic carbon of 80 mg/L (Italy). Moreover, guidelines for agricultural utilization, will become progressively more stringent due to increasing health concerns about the widespread diffusion of pathogenic and organic micropollutants in the environment (European Commission, 2000). Regardless, agricultural utilization involving large amounts of sludge to be spread on land does not seem feasible for the following reasons:
This paper deals with the comparison of ultrasound (mechanical) and ozone (chemical) pre-treatmen... more This paper deals with the comparison of ultrasound (mechanical) and ozone (chemical) pre-treatment on the performances of excess sludge semi-continuous digestion. Sludge solubilisation has been investigated by varying specific energy input. For each pre-treatment, long anaerobic digestion tests were carried out by two parallel digesters: one reactor, as control unit, was fed with untreated waste activated sludge, and the other one was fed with disintegrated sludge. To evaluate and compare the efficacy of both pre-treatments, the specific energy was maintained approximately the same. The digestion tests were carried out to investigate the feasibility of anaerobic digestion performance (total biogas production, volatile solids removal, sludge dewaterability) and to assess the heat balance. Results obtained from the digestion of sonicated sludge at 4% disintegration degree (w2500 kJ/kg TS) showed that the ultrasound pre-treatment may be effective both in increasing VS destruction (þ19%) and cumulative biogas production (þ26%). On the contrary, the digestion test with ozonized sludge (ozone dose of 0.05 g O 3 /g TS corresponding to w2000 kJ/kg TS) did not indicate a significant improvement on the digestion performances. By doubling the ozone dose an improvement in the organics removal and cumulative biogas production was observed. Relevant differences in terms of colloidal charge and filterability were discussed.
Sewage sludge produced by various technological treatment processes within the EU-funded project ... more Sewage sludge produced by various technological treatment processes within the EU-funded project ROUTES are assessed for their ecotoxicity with standard laboratory tests. The tests were selected among a number of test systems recommended by testing guidelines for waste. They encompass aquatic organisms (freshwater green algae and freshwater crustaceans) and terrestrial organisms (soil bacteria and earthworms). The test methods are described here and typical problems encountered with the testing of such organic material are illustrated by presenting results for one example batch of sludge samples. For this example, some evidence for a toxicity-reducing effect of the digestion treatment was observed only in the soil bacteria contact test with Arthrobacter globiformis.
The application of ultrasound to sludge is an efficient method for sludge disintegration in order... more The application of ultrasound to sludge is an efficient method for sludge disintegration in order to accelerate the anaerobic digestion process, but energy balance on the basis of lab tests is disadvantaged due to the inefficiency at this scale. In this paper the energy balance is discussed for five full scale WWTPs equipped with different devices with the aim to investigate the cost-effectiveness of the ultrasonic pre-treatment before digestion. These five experiences show positive energy gains operating at 20 kHz: best performances are attained at short sonication time and high sonication power. Moreover, sludge sonication at 200 kHz is presented as an alternative pretreatment to improve the anaerobic digestibility and to remove potentially organic micropollutants. Lab experiment results of this treatment indicated quite good disintegration effect, in terms of substrate solubilization, with consequent acceleration of the hydrolysis phase and increase of biogas production.
Questa tecnologia integra l'utilizzo di microalghe e cianobatteri per il biorimedio con la produz... more Questa tecnologia integra l'utilizzo di microalghe e cianobatteri per il biorimedio con la produzione di biocarburanti di terza generazione e di altri composti ad alto valore aggiunto (es. proteine). Questi microrganismi autotrof sono, infatti, in grado di fssare CO 2 e produrre, con un'elevata efficienza, lipidi che possono essere successivamente trasformati in biodiesel. Contestualmente, è possibile utilizzare le microalghe e i cianobatteri per un trattamento terziario delle acque reflue, o comunque di acque eutrofche, grazie alla loro capacità di rimuovere efficacemente nutrienti inorganici ed altri contaminanti, quali metalli pesanti, che vengono utilizzati per sostenere i loro veloci cicli cellulari.
Sludge microbial quality is a major issue to be assessed for the sustainable reuse of sludge in a... more Sludge microbial quality is a major issue to be assessed for the sustainable reuse of sludge in agriculture. Within the ROUTES project innovative solutions for the production of good quality sludge are evaluated and the hygienisation performances of the proposed sludge treatment systems is assessed. The paper describes the efficiency of pathogens and indicator removal by a combination of a disintegration pre-treatment, by thermal hydrolysis, and thermophilic anaerobic digestion and by a combined anaerobic and aerobic digestion process. To better address the fate of pathogens with diverse resistance capacity different indicators microorganism (E.coli, spore of sulphide reducing clostridia SSCR and somatic coliphage SOMCPH) and specific pathogens (Salmonella and enteric viruses) were monitored. An improvement of hygenization was obtained by both investigated processes. Thermal pre-treatment improved the SOMCPH removal of more than one logarithmic unit and efficiently eliminated bacter...
In the urban wastewater treatment, primary and secondary sludges are typically produced and then ... more In the urban wastewater treatment, primary and secondary sludges are typically produced and then treated in mixture before disposal. Primary sludge includes the particulate matter and colloidal material separated from the raw wastewater in the primary sedimentation; while secondary sludge is the biomass extracted from the secondary clarifier after the biological process. Separation of primary sludge from secondary one might be beneficial in a new sludge management strategy considering that secondary sludge normally poorer in pollutants but richer in nitrogen and phosphorus than primary sludge that should preferentially be used in agriculture while the typical disposal option for primary sludge should be incineration. In this perspective, lab-scale thermal tests were performed by a prototype called System for Thermal Diagnostic Studies (STDS) to verify whether the incineration of primary sludge separated from secondary one would lead to different emissions in comparison to the conven...
The IWA ADM1 model is a powerful tool to assess the anaerobic biodegradability of different typol... more The IWA ADM1 model is a powerful tool to assess the anaerobic biodegradability of different typologies of biomasses, sewage sludge and bio wastes.
The application of ultrasound to sludge is an efficient method for sludge disintegration in order... more The application of ultrasound to sludge is an efficient method for sludge disintegration in order to accelerate the anaerobic digestion process, but energy balance on the basis of lab tests is disadvantaged due to the inefficiency at this scale. In this paper the energy balance is discussed for five full scale WWTPs equipped with different devices with the aim to investigate the cost-effectiveness of the ultrasonic pre-treatment before digestion. These five experiences show positive energy gains operating at 20 kHz: best performances are attained at short sonication time and high sonication power. Moreover, sludge sonication at 200 kHz is presented as an alternative pretreatment to improve the anaerobic digestibility and to remove potentially organic micropollutants. Lab experiment results of this treatment indicated quite good disintegration effect, in terms of substrate solubilization, with consequent acceleration of the hydrolysis phase and increase of biogas production.
AN INNOVATIVE TECHNIQUE TO DECONTAMINATE ACTIVATED SLUDGE INCREASING ANAEROBIC DIGESTION PERFORMANCE
Sludge agricultural recovery mainly depends on the possibility to improve the sludge quality by m... more Sludge agricultural recovery mainly depends on the possibility to improve the sludge quality by maximizing decontamination and stabilization. Ultrasounds at 20 kHz are commonly used as pre-treatment for sludge particulate solubilisation to improve anaerobic digestion whereas high frequency ultrasounds (more than 200 kHz) are recently investigated to decontaminate wastewater via oxidation due to water sonolysis. Objective of this work is to study the effectiveness of ultrasounds at 200 kHz to remove linear alkylbenzenesulfonates (LAS) from sludge improving at the same time anaerobic digestibility. Sonolysis experiments showed that ultrasounds can remove up to 50% of the LAS content in less than 1 h at low power input. Moreover, batch anaerobic digestion tests with untreated and disintegrated sludge (20 or 200 kHz) showed improvements of volatile solid removal and of biogas production compared to untreated sludge. At 200 kHz it was possible to gain more biogas than at 20 kHz.
ROUTES is addressed to assess new routes in wastewater and sludge treatment focusing on three mai... more ROUTES is addressed to assess new routes in wastewater and sludge treatment focusing on three main objectives: 1. optimization of the sludge quality for agricultural use with the goal to produce a clean and full stabilized sludge through intensive stabilization processes with attention to a broad spectrum of parameters including micropollutants, pathogens and their indicators. 2. minimization of the sludge to be disposed by innovative technical solutions based on different approaches, either on the water or sludge treatment lines; 3. recovery of valuable resources before sludge disposal by producing a liquid fertilizer [(NH4)2SO4], biopolymers or optimizing methane production by anaerobic treatments. Technical and economic assessment of the investigated techniques on laboratory and pilot scale were carried out in a typical benchmarking study. The whole set of data is then provided to the partner involved in environmental assessment where different impact categories are considered (g...
Sewage sludge processing is a key issue in wastewater treatment plants due to the inefficacy of c... more Sewage sludge processing is a key issue in wastewater treatment plants due to the inefficacy of conventional treatments to produce high quality sludge to be safely used in agriculture. Under this framework, the performances of several enhanced stabilization processes, namely ultrasound-pretreated Mesophilic Anaerobic Digestion (US-MAD), thermophilic anaerobic digestion (TAD), thermal pretreated TAD (TH-TAD) and ultrasound-pretreated inverse Temperature Phased Anaerobic Digestion (iTPAD) have been investigated. The enhanced anaerobic processes resulted in higher specific biogas production and higher destruction of E.coli and Somatic coliphages with respect to conventional MAD process, thus confirming the feasibility of these innovative processes in full-scale implementation perspectives.
Nowadays, several technologies and management strategies are proposed for upgrading wastewater tr... more Nowadays, several technologies and management strategies are proposed for upgrading wastewater treatment plants (WWTPs) in order to improve sludge stabilization or minimize sludge production. In order to make sure that this leads to overall improvements, their techno-economic and environmental performance has to be carefully evaluated. In response to this, the techno-economic and environmental performance was assessed for a considered model reference WWTP upgraded with separate treatment and disposal for primary and secondary sludge to provide guidance to research, policy and investment efforts. This paper departs in an experimental campaign carried out within the EU project "ROUTES" and describes an assessment of an upgrade of a WWTP, involving wet oxidation of primary sludge and thermophilic anaerobic digestion (integrated with thermal hydrolysis pre-treatment) for secondary sludge. The reference plant and the upgrade implied different disposal routes for the resulting sludges: incineration for the stabilized sludge deriving from the reference WWTP; agricultural land application for the secondary stabilized sludge from the upgraded plant and landfilling for the solid residue deriving from the wet oxidation process (as non-hazardous waste).
Thermal hydrolysis pretreatment coupled with Thermophilic Anaerobic Digestion (TAD) for Waste Act... more Thermal hydrolysis pretreatment coupled with Thermophilic Anaerobic Digestion (TAD) for Waste Activated Sludge (WAS) treatment is a promising combination to improve biodegradation kinetics during stabilization. However, to date there is a limited knowledge of the anaerobic biomass composition and its impact on TAD process performances. In this study, the structure and dynamics of the microbial communities selected in two semi-continuous anaerobic digesters, fed with untreated and thermal pretreated sludge, were investigated. The systems were operated for 250 days at different organic loading rate. 16S rRNA gene clonal analysis and Fluorescence In Situ Hybridization (FISH) analyses allowed us to identify the majority of bacterial and archaeal populations. Proteolytic Coprothermobacter spp. and hydrogenotrophic Methanothermobacter spp. living in strict syntrophic association were found to dominate in TAD process. The establishment of a syntrophic proteolytic pathway was favoured by th...
Semi-continuous mesophilic and thermophilic digestion, with sludge pre-treatments. Enhanced relea... more Semi-continuous mesophilic and thermophilic digestion, with sludge pre-treatments. Enhanced release of lipids by thermal hydrolysis and proteins by ultrasounds. Pre-treatments improved organics conversion to CH 4 only at low-medium loading rate. At high organic load, TAD yield was 0.15 against 0.11 Nm 3 methane/kg COD fed of MAD. Generated charged polymers in TAD impaired filterability more rapidly than in MAD.
Proceedings of the Water Environment Federation, 2012
The legislative standards in many European countries and in the USA on sludge use in agriculture ... more The legislative standards in many European countries and in the USA on sludge use in agriculture require effective removal of pathogens during stabilization processes. Great attention is also paid nowadays to organic micropollutants like PCBs, surfactants (LAS), hydrocarbons, polynuclear aromatic hydrocarbons (PAH), halorganics (AOX) and pharmaceuticals whose removal is not effective in conventional sludge processing. Anaerobic thermophilic digestion was considered suitable for producing class A biosolids since 30 years considering that more effective removal of pathogens seems to be attained in thermophilic digestion in comparison with mesophilic conventional.
Ultrasounds pretreatment aims to convert waste activated sludge, characterized by recalcitrant pa... more Ultrasounds pretreatment aims to convert waste activated sludge, characterized by recalcitrant particulate organics, into a soluble, more biodegradable form, maximizing anaerobic stabilization and biogas recovery. Objective of this work was the assessment of the efficiency of high frequency ultrasounds, as 200 kHz, to improve sludge anaerobic digestion performances. Parallel batch anaerobic digestion tests were performed to evaluate anaerobic biodegradability of 20 or 200 kHz sonicated secondary sludge, operating at food/inoculum ratio of 0.5 and 1. Ultrasound pretreatments, independent on the frequency, accelerated the initial hydrolysis phase, and the effect was more marked working at high inoculum content. Moreover, the biogas produced by the sonicated sludge was always higher than that produced by the untreated one. This gain seemed to be independent on the F/I ratio for the digestion of the 20 kHz pretreated sludge, while, in the case of sludge treatment at 200 kHz, the biogas improvement was particularly high (about 40%) at F/I=0.5. In fact, at F/I=1, the biogas gain was only +4% due to an evident slowdown of the biogas production of the sonicated sludge, due to the accumulation of soluble organic substances, evidenced by the soluble COD pattern, suggesting discoupling between hydrolysis and methanogenesis. Fluorescence In Situ Hybridization (FISH) analysis allowed to highlight the establishment in the anaerobic biomass of different methanogens responsible for the biogas production depending on the extent of readily biodegradable substrates availability for the methanogenesis or on the amount of inoculum utilised at the start up of the anaerobic digestion process.
Proceedings of the Water Environment Federation, 2010
In the coming years, large European wastewater treatment plants (WWTPs) will need to dispose of s... more In the coming years, large European wastewater treatment plants (WWTPs) will need to dispose of sludge by transforming it into inert material by thermal processes. In fact, the present European landfill directive 99/31 has restricted this disposal route which was practically abandoned by countries, where the implementation of the directive criteria in national legislations was very stringent, either imposing a limit of the organic carbon to 4 -5 % in the wastes to be disposed (Germany) or including a leachate test with the very stringent limit of dissolved organic carbon of 80 mg/L (Italy). Moreover, guidelines for agricultural utilization, will become progressively more stringent due to increasing health concerns about the widespread diffusion of pathogenic and organic micropollutants in the environment (European Commission, 2000). Regardless, agricultural utilization involving large amounts of sludge to be spread on land does not seem feasible for the following reasons:
This paper deals with the comparison of ultrasound (mechanical) and ozone (chemical) pre-treatmen... more This paper deals with the comparison of ultrasound (mechanical) and ozone (chemical) pre-treatment on the performances of excess sludge semi-continuous digestion. Sludge solubilisation has been investigated by varying specific energy input. For each pre-treatment, long anaerobic digestion tests were carried out by two parallel digesters: one reactor, as control unit, was fed with untreated waste activated sludge, and the other one was fed with disintegrated sludge. To evaluate and compare the efficacy of both pre-treatments, the specific energy was maintained approximately the same. The digestion tests were carried out to investigate the feasibility of anaerobic digestion performance (total biogas production, volatile solids removal, sludge dewaterability) and to assess the heat balance. Results obtained from the digestion of sonicated sludge at 4% disintegration degree (w2500 kJ/kg TS) showed that the ultrasound pre-treatment may be effective both in increasing VS destruction (þ19%) and cumulative biogas production (þ26%). On the contrary, the digestion test with ozonized sludge (ozone dose of 0.05 g O 3 /g TS corresponding to w2000 kJ/kg TS) did not indicate a significant improvement on the digestion performances. By doubling the ozone dose an improvement in the organics removal and cumulative biogas production was observed. Relevant differences in terms of colloidal charge and filterability were discussed.
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Papers by Andrea Gianico