Effects of carbon-based conductive materials on semi-continuous anaerobic co-digestion of organic fraction of municipal solid waste and waste activated sludge

Organic fraction of municipal solid waste (OFMSW) and waste activated sludge (WAS) are the most produced organic waste streams in urban centres. Their anaerobic co-digestion (AcoD) allows to generate methane (CH4) and digestate employable as renewable energy source and soil amendment, respectively, fully in accordance with circular bioeconomy principles. However, the widespread adoption of such technology is limited by relatively low CH4 yields that fail to bridge the gap between benefits and costs. Among strategies to boost AcoD of OFMSW and WAS, use of conductive materials (CMs) to promote interspecies electron transfer has gained increasing attention. This paper presents one of the few experimental attempts of investigating the effects of four different carbon(C)-based CMs (i.e., granular activated carbon - GAC, graphite - GR, graphene oxide - GO, and carbon nanotubes - CNTs) separately added in semi-continuous AcoD of OFMSW and thickened WAS. The presence of C-based CMs has been observed to improve CH4 yield of the control process. Specifically, after 63 days of operation (concentrations of GAC and GR of 10.0 g/L and of GO and CNTs of 0.2 g/L), 0.186 NL/gVS, 0.191 NL/gVS, 0.203 NL/gVS, and 0.195 NL/gVS of CH4 were produced in reactors supplemented with GAC, GR, GO, and CNTs, respectively, compared to 0.177 NL/gVS produced in the control process. Likewise, at the end of the test (i.e., after 105 days at concentrations of C-based CMs half of the initial ones), CH4 yields were 0.193 NL/gVS, 0.201 NL/gVS, 0.211 NL/gVS, and 0.206 NL/gVS in reactors supplemented with GAC, GR, GO, and CNTs, respectively, compared to 0.186 NL/gVS of the control process. Especially with regard to GR, GO, and CNTs, results obtained in the present study represent a significant advance of the knowledge on the effects of such C-based CMs to realistic and scalable AD process conditions respect to previous literature.

Wastewater treatment in lagoons: A systematic review and a meta-analysis

This study has carried out a systematic review of 36 scientific papers (reporting 63 case studies) published in the last 15 years about the treatment of industrial, agri-food and municipal wastewater in lagoons. A concentration of studies from a few countries (Italy, Algeria and Iran) and about municipal wastewater (70% of papers) was revealed by the bibliographic analysis. Aeration was supplied in more than 50% of case studies; the storage capacity of lagoons (adopted as a measure of size) was extremely variable (over seven orders of magnitude), while their depth was generally lower than a few metres. The efficiency of lagoon treatments at removing COD was in a wide range (25-98%). Very few studies analysed the energy intensity of treatments in lagoons. The meta-analysis applied to a further selection of 10 papers with 29 case studies revealed significant differences in pH and dissolved oxygen concentration, due to aeration or type of treated wastewater. Treatment efficiency was higher in aerated lagoons compared to non-aerated systems, and did not depend on the type of treated wastewater. Based on the analysis of the reviewed papers, an urgent research need on this topic arises, mainly due to the oldness of most analysed studies. Practical suggestions are given to optimise the depuration performances of lagoons: (i) application of intermittent and night aeration; (ii) reduced air flow rates; (iii) adaptation of microbial biomass to high contents of inhibiting compounds in wastewater; (iv) construction of baffles to keep the planned hydraulic retention time avoiding short-circuit; (v) integration of lagoons with other treatments (e.g., constructed wetlands); (vi) ferti-irrigation of crops with lagoon effluents rather than disposal into water bodies.

A 35-year monitoring of an Italian landfill: Effect of recirculation of reverse osmosis concentrate on leachate characteristics

"Fossetto" landfill (Monsummano Terme - Tuscany, Italy) started operation in 1988 as a controlled landfill accepting mixed municipal solid waste collected without any attempt of recycling. Then, progressively, following the evolution of the state-of-the-art, it adopted biogas extraction and valorisation systems and mechanical-biological treatment for incoming waste (both since 2003). Finally, since 2006, in the plant is performed on-site reverse osmosis leachate treatment with the concentrated leachate being recirculated back into the landfill body. Recently a new landfill cell, separate from the others, was put in operation adding a capacity of 200,000 m3 to the already available 1,095,000 m3. This plant can provide long term leachate composition data to study the evolution and impact of changing landfill technology and waste composition on various parameters. The rise in leachate production (+84 % in 2018-2022 respect to the period before recirculation) cannot be totally attributable to recirculation but could be also linked to the increase in the amount of landfilled waste. The concentration of certain parameters (NH4+, Cl- and to a less extent of COD) increased (+60 %, +58 %, +17 % respectively in the last five years with respect to the period before recirculation); however, this increase did not influence the performance of the treatment plant. Nevertheless, the overall leachate management would benefit from an optimized reinjection system.

The fate of biodegradable plastic during the anaerobic co-digestion of excess sludge and organic fraction of municipal solid waste

Co-digestion of the organic fraction of municipal solid waste (OFMSW) and excess sludge has several benefits especially related to improved methane production and better process stability. In recent years, the presence of biodegradable plastics is increasingly common in OFMSW especially since, as in Italy, biodegradable bags are used for its collection. In this paper, the influence and the fate of biodegradable bags during anaerobic co-digestion of excess sludge and OFMSW are assessed. The best results in terms of methane yield (about 180 NmL/gVS) have been obtained with the 50:50 (VS basis) co-digestion of excess sludge and OFMSW with an organic loading rate of 2 kgVS/m3·d. Bioplastic degradation is very limited during the co-digestion but it does not influence methane production or digestate chemical characteristics. However, the feeding of bioplastic bags seems to induce a higher phytotoxicity and the presence of undigested fragments is anyway a problem for further treatment or direct utilization of digestate.

Integral valorization of orange peel waste through optimized ensiling: Lactic acid and bioethanol production

The management of the huge amount of orange peel waste (OPW) is a complex issue although it has a very high potential in terms of biorefining. One of the main problems in the valorisation of OPW is the seasonality of its production with the ensiling method being largely proposed as a possible solution. During the ensiling process, value added chemicals including lactic acid, acetic acid and ethanol are spontaneously produced together with a significant loss of volatile solids (VS) . In this contribution, the stimulation of lactic acid bacteria by either a biological (inoculation with leachate coming from a previous ensiling process) or chemical (MnCl₂ supplementation) methods has been tested with the aim to increase the chemicals production preventing, at the same time, the VS loss. The inoculation with the leachate improves both the VS recovery (+7%) and the concentration of lactic acid (+113%) with respect to the uninoculated one (control). The overall yields of the process are noticeable, up to about 55 g·kg_TS^-1 of lactic acid, 26 g·kg_TS^-1 of acetic acid and 120 g g·kgTS-1 of ethanol have been produced. On the other hand, the chemical stimulation enhances the production of liquid products together with a significant VS loss. The proposed preservation method, due to its simplicity, can be easily implemented at full-scale allowing the production of added-value chemicals and the concurrent storage of the OPW that can be further valorised (e.g. animal feed, pectin or biomethane production).

A standardized inspection methodology to evaluate municipal solid waste collection performance

The success of separate collection of municipal solid waste, the efficiency of the other connected services and the justification of a large cost assumed by an authority, depends on the level of service provided to customers as well as the citizens' attitude towards waste management. In this paper, a semi-qualitative inspection method to evaluate both the door-to-door collection system and the conventional curbside system is proposed. The method is based on the combined evaluation of waste collection using a set of indicators and the assessment of the perception of the citizens towards collection and street cleaning services using behavioural questionnaires. The ultimate goal was to assess potential differences between door-to-door and curbside collection systems. The standardized inspection evaluation method was applied to the city of Reggio, Calabria (Italy), since both collection systems are used there. The standardized inspection evaluation proved to be simple to implement and was effective to accurately evaluate the quality of the service delivered to the citizens. The results of the behavioural survey revealed that citizens that practised door-to-door separation had a higher recycling conscience and were more satisfied with the city waste management system than the ones that practised curbside separation. According to the results of the study, there was a qualitative agreement between the results of the standardized inspection evaluation and the behavioural survey. The door to door collection system is suggested to replace the curbside collection system.

Selective removal of heavy metals from landfill leachate by reactive granular filters

The pre-treatment of landfill leachate prior to its co-treatment in the municipal plants of waste water processing could represent an appropriate and cost-effective solution for its management. Pre-treatment is necessary especially to remove heavy metals, which may be transferred to the excess sludge preventing its valorisation. In the present paper, we propose a chemical-physical pre-treatment of leachate using four different granular reactive media able to selectively remove the contaminants present in the leachate. The efficiency of these materials was investigated using synthetic leachate through batch tests and a column test. In the latter case the four materials were placed in two columns connected in series and fed an under constant upward flow (0.5 mL/min). The first column was filled half (50 cm) with a granular mixture of zero valent iron (ZVI) and pumice and half (50 cm) with a granular mixture of ZVI and granular activated carbon (GAC). The second column, which was fed with the effluent of the first column, was filled half with zeolite (chabazite) and half with GAC. Heavy metals were mainly removed by the ZVI/pumice and ZVI/GAC steps with a removal efficiency that was higher than 98, 94 and 90% for copper, nickel and zinc, respectively, after 70 days of operation. Ammonium was removed by zeolite with a removal efficiency of 99% up to 23 days. The average reduction of the chemical oxygen demand (COD) was of 40% for 85 days, whereas chloride and sulphate removal was negligible.

Valorisation of citrus processing waste: A review

This study analyses the quantitative and qualitative characteristics of citrus peel waste and discusses the systems for its valorisation. Citrus peel waste (CPW) is the main residue of the citrus processing industries and is characterised by a seasonal production (which often requires biomass storage) as well as high water content and concentration of essential oils. The disposal of CPW has considerable constraints due to both economic and environmental factors. Currently this residue is mainly used as food for animals, thanks to its nutritional capacity. If enough agricultural land is available close to the processing industries, the use of CPW as organic soil conditioner or as substrate for compost production is also possible, thus improving the organic matter content of the soil. Recently, the possibility of its valorisation for biomethane or bioethanol production has been evaluated by several studies, but currently more research is needed to overcome the toxic effects of the essential oils on the microbial community. Considering the high added value of the compounds that can be recovered from CPW, it has promising potential uses: in the food industry (for production of pectin, dietary fibres, etc.), and in the cosmetic and pharmaceutic industries (extraction of flavonoids, flavouring agents and citric acid). However, in many cases, these uses are still not economically sustainable.

Bioplastics and waste management

Pollution of the marine environment due to plastic materials is one of the most severe environmental problems humanity has to face in the 21st century. The strategy devised until now to address this issue is mainly based on two pillars: (1) increasing the interception of discarded plastic wastes by waste management systems; and (2) substituting the traditional "petro-based" polymers with biodegradable ones. Many issues on the overall sustainability of the second option by the waste management system must still be clarified.

Anaerobic digestion of orange peel in a semi-continuous pilot plant: An environmentally sound way of citrus waste management in agro-ecosystems

The management of residues of citrus processing involves economic and environmental problems. In particular, the uncontrolled disposal of citrus processing waste near production sites can have heavy impacts on air, soil, surface water bodies and groundwater. Anaerobic digestion has been proposed as a viable alternative for citrus waste valorisation, if some problems, linked to the biochemical processes, are overcome. Although many experimental tests have studied the inhibitory effects of the high essential oil content of orange peel on biomethanisation processes, fewer experiences have been carried out in continuous or semi-continuous pilot digesters, more similar to the full-scale biogas plants, using real orange peel. This study has evaluated the methane production through anaerobic digestion of industrial orange peel using a pilot plant (84L) with semi-continuous feeding at increasing Organic Loading Rates (OLR) and essential oil (EO) supply rates (EOsr) until the complete process inhibition. Under mesophilic conditions, the highest daily specific methane yield was achieved at OLR of 1.0g_TVSL^-1 d^-1 and EOsr of 47.6mgL^-1d^-1. Partial inhibition of the anaerobic digestion was detected at OLR and EOsr of 1.98g_TVSL^-1d^-1 and 88.1mgL^-1 d^-1, respectively and the process irreversibly stopped when OLR and EOsr reached 2.5g_TVS L^-1 d^-1 and 111.2mgL^-1 d^-1, respectively. Under thermophilic conditions, the cumulative methane production (0.12Lg_TVS^-1) was about 25% of that under mesophilic conditions (0.46Lg_TVS^-1). The thermophilic digestion was completely inhibited at lower OLR (1.98g_TVSL^-1 d^-1) and EOsr (88.1mgL^-1 d^-1) compared to mesophilic conditions. This study confirmed the suitability of anaerobic digestion of orange peel for biomethane production (provided that the right management of the process is set), in view of an environmentally sound way of agricultural residues management in agro-ecosystems.

Effect of the recirculation of a reverse osmosis concentrate on leachate generation: A case study in an Italian landfill

"Fossetto" landfill has been operating in the municipality of Monsummano Terme (Pistoia Province, Italy) since 1988; the authorized volume for landfilling is about 1,000,000 m³; at the moment the plant is being mainly used to dispose of mechanically and biologically treated residual municipal solid waste. Since September 2006, an in-situ reverse osmosis leachate treatment plant has been operating to treat leachate. The treated water is being discharged into a small nearby stream while the concentrated leachate is being recirculated back into the landfill body following Italian Regulations and an authorization from the local authority (Pistoia Province). This paper presents monitoring results on leachate generation rates and composition for the past fifteen years. A moderate increase of the concentration of some of the monitored parameters occurred (e.g. ammonium, chlorides) and a decrease for most heavy metals. The increase of concentrations for Cl^- and NH₄⁺ was more evident in the leachate coming from the wells closer to reinjection area. However, the change in leachate composition did not affect the quality of the effluent from the leachate treatment plant. The annual volume of the generated leachate increased significantly right after the recirculation started.

Strategies for the sustainable management of orange peel waste through anaerobic digestion

The processing of oranges is a major industry worldwide and leads to the production of large amounts of orange peel waste (OPW). Energy production through anaerobic digestion of OPW is a promising option; however, the high content of essential oil, mainly composed of d-limonene, a well-known antioxidant, can cause the inhibition of the biological activity. In this paper, different pretreatment methods were tested (e.g. ensiling, aeration, thermal and alkaline treatments) to optimize the anaerobic digestion of OPW focusing on d-limonene removal. The raw and pretreated substrates were characterized and their biochemical methane production was measured. The results demonstrated the ability of some of the treatments to reduce d-limonene content up to 80%. A relatively high biomethane potential production of OPW (up to about 500 NmL CH₄ g^-1VS) was measured. The importance of the acclimation of inoculum and the risk connected to the accumulation of inhibiting substances in the reactor is discussed.

Effect of three pretreatment techniques on the chemical composition and on the methane yields of Opuntia ficus-indica (prickly pear) biomass

Opuntia ficus-indica (OFI) is an emerging biomass that has the potential to be used as substrate in anaerobic digestion. The goal of this work was to investigate the effect of three pretreatment techniques (thermal, alkaline, acidic) on the chemical composition and the methane yield of OFI biomass. A composite experimental design with three factors and two to three levels was implemented, and regression modelling was employed using a total of 10 biochemical methane potential (BMP) tests. The measured methane yields ranged from 289 to 604 NmL/gVS_added; according to the results, only the acidic pretreatment (HCl) was found to significantly increase methane generation. However, as the experimental values were quite high with regards to the theoretical methane yield of the substrate, this effect still needs to be confirmed via further research. The alkaline pretreatment (NaOH) did not noticeably affect methane yields (an average reduction of 8% was recorded), despite the fact that it did significantly reduce the lignin content. Thermal pretreatment had no effect on the methane yields or the chemical composition. Scanning electron microscopy images revealed changes in the chemical structure after the addition of NaOH and HCl. Modelling of the cumulated methane production by the Gompertz modified equation was successful and aided in understanding kinetic advantages linked to some of the pretreatments. For example, the alkaline treatment (at the 20% dosage) at room temperature resulted to a μ_max (maximum specific methane production rate [NmLCH₄/(gVS_added·d)]) equal to 36.3 against 18.6 for the control.

Effect of the concentration of essential oil on orange peel waste biomethanization: Preliminary batch results

The cultivation of orange (Citrus×sinensis) and its transformation is a major industry in many countries in the world, it leads to the production of about 25-30Mt of orange peel waste (OPW) per year. Until now many options have been proposed for the management of OPW but although they are technically feasible, in many cases their economic/environmental sustainability is questionable. This paper analyse at lab scale the possibility of using OPW as a substrate for anaerobic digestion. Specific objectives are testing the possible codigestion with municipal biowaste, verifying the effect on methane production of increasingly high concentration of orange essential oil (EO, that is well known to have antioxidant properties that can slower or either inhibit biomass activity) and obtaining information on the behaviour of d-limonene, the main EO component, during anaerobic digestion. The results indicate that OPW can produce up to about 370LnCH4/kgVS in mesophilic conditions and up to about 300LnCH4/kgVS in thermophilic conditions. The presence of increasingly high concentrations of EO temporary inhibits methanogenesis, but according to the results of batch tests, methane production restarts while d-limonene is partially degraded through a pathway that requires its conversion into p-cymene as the main intermediate.

Anaerobic digestion of tomato processing waste: Effect of alkaline pretreatment

The objective of the work was to assess the effect of mild alkaline pretreatment on the anaerobic biodegradability of tomato processing waste (TPW). Experiments were carried out in duplicate BMP bottles using a pretreatment contact time of 4 and 24 h and a 1% and 5% NaOH dosage. The cumulative methane production during a 30 d period was recorded and modelled. The alkaline pretreatment did not significantly affect methane production in any of the treatments in comparison to the control. The average methane production for all runs was 320 NmL/gVS. Based on first order kinetic modelling, the alkaline pretreatment was found to slow down the rate of methanogenesis, mainly in the two reactors with the highest NaOH dosage. The biodegradability of the substrates ranged from 0.75 to 0.82 and from 0.66 to 0.72 based on two different approaches.

European trends in greenhouse gases emissions from integrated solid waste management

The European Union (EU) has 28 member states, each with very different characteristics (e.g. surface, population density, per capita gross domestic product, per capita municipal solid waste (MSW) production, MSW composition, MSW management options). In this paper several integrated waste management scenarios representative of the European situation have been generated and analysed in order to evaluate possible trends in the net emission of greenhouse gases and in the required landfill volume. The results demonstrate that an integrated system with a high level of separate collection, efficient energy recovery in waste-to-energy plants and very limited landfill disposal is the most effective according to the indices adopted. Moreover, it is evident that a fully integrated system can make MSW management a carbon sink with a potentiality of up to approximately 40 Mt CO2eq year(-1).

Improving the sustainability of granular iron/pumice systems for water treatment

Metallic iron (Fe(0)) is currently used in subsurface and above-ground water filtration systems on a pragmatic basis. Recent theoretical studies have indicated that, to be sustainable, such systems should not contain more than 60% Fe(0) (vol/vol). The prediction was already validated in a Fe(0)/sand system using methylene blue as an operational tracer. The present work is the first attempt to experimentally verify the new concept using pumice particles. A well-characterized pumice sample is used as operational supporting material and is mixed with 200 g of a granular Fe(0), in volumetric proportions, varying from 0 to 100%. The resulting column systems are characterized (i) by the time dependent evolution of their hydraulic conductivity and (ii) for their efficiency for the removal of Cu(II), Ni(II), and Zn(II) from a three-contaminants-solution (about 0.3 mM of each metal). Test results showed a clear sustainability of the long term hydraulic conductivity with decreasing Fe(0)/pumice ratio. In fact, the pure Fe(0) system clogged after 17 days, while the 25% Fe(0) system could operate for 36 days. The experimental data confirmed the view that well-designed Fe(0) PRBs may be successful at removing both reducible and non-reducible metal species.

Possible interactions between recirculated landfill leachate and the stabilized organic fraction of municipal solid waste

The stabilized organic fraction of municipal solid waste (SOFMSW) is a product of the mechanical/biological treatment (MBT) of mixed municipal solid waste (MMSW). SOFMSW is considered a 'grey' compost and the presence of pollutants (particularly heavy metals) and residual glass and plastic normally prevents agricultural use, making landfills the typical final destination for SOFMSW. Recirculation of leachate in landfills can be a cost-effective management option, but the long-term sustainability of such a practice must be verified. Column tests were carried out to examine the effect of SOFMSW on leachate recirculation. The results indicate that organic matter may be biologically degraded and metals (copper and zinc) are effectively entrapped through a combination of physical (adsorption), biological (bacterial sulfate reduction), and chemical (precipitation of metal sulfides) processes, while other chemicals (i.e. ammonia nitrogen and chloride) are essentially unaffected by filtration through SOFMSW.

Estimate of the optimum weight ratio in zero-valent iron/pumice granular mixtures used in permeable reactive barriers for the remediation of nickel contaminated groundwater

This paper presents the results of laboratory column tests aimed at defining the optimum weight ratio of zero-valent iron (ZVI)/pumice granular mixtures to be used in permeable reactive barriers (PRBs) for the removal of nickel from contaminated groundwater. The tests were carried out feeding the columns with aqueous solutions of nickel nitrate at concentrations of 5 and 50 mg/l using three ZVI/pumice granular mixtures at various weight ratios (10/90, 30/70 and 50/50), for a total of six column tests; two additional tests were carried out using ZVI alone. The most successful compromise between reactivity (higher ZVI content) and long-term hydraulic performance (higher Pumice content) seems to be given by the ZVI/pumice granular mixture with a 30/70 weight ratio.

Modelling of biogas extraction at an Italian landfill accepting mechanically and biologically treated municipal solid waste

This paper presents the results of the modelling of the biogas extraction in a full-scale Italian landfill by the USEPA LandGEM model and the Andreottola-Cossu approach. The landfill chosen for this research ('Il Fossetto' plant, Monsummano Terme, Italy) had accepted mixed municipal raw waste for about 15 years. In the year 2003 a mechanical biological treatment (MBT) was implemented and starting from the end of the year 2006, the recirculation in the landfill of the concentrated leachate coming from the internal membrane leachate treatment plant was put into practice. The USEPA LandGEM model and the Andreottola-Cossu approach were chosen since they require only input data routinely acquired during landfill management (waste amount and composition) and allow a simplified calibration, therefore they are potentially useful for practical purposes such as landfill gas management. The results given by the models are compared with measured data and analysed in order to verify the impact of MBT on biogas production; moreover, the possible effects of the recirculation of the concentrated leachate are discussed. The results clearly show how both models can adequately fit measured data even after MBT implementation. Model performance was significantly reduced for the period after the beginning of recirculation of concentrated leachate when the probable inhibition of methane production, due to the competition between methanogens and sulfate-reducing bacteria, significantly influenced the biogas production and composition.

Heavy metals removal and hydraulic performance in zero-valent iron/pumice permeable reactive barriers

Long-term behaviour is a major issue related to the use of zero-valent iron (ZVI) in permeable reactive barriers for groundwater remediation; in fact, in several published cases the hydraulic conductivity and removal efficiency were progressively reduced during operation, potentially compromising the functionality of the barrier. To solve this problem, the use of granular mixtures of ZVI and natural pumice has recently been proposed. This paper reports the results of column tests using aqueous nickel and copper solutions of various concentrations. Three configurations of reactive material (ZVI only, granular mixture of ZVI and pumice, and pumice and ZVI in series) are discussed. The results clearly demonstrate that iron-pumice granular mixtures perform well both in terms of contaminant removal and in maintaining the long-term hydraulic conductivity. Comparison with previous reports concerning copper removal by ZVI/sand mixtures reveals higher performance in the case of ZVI/pumice.

Impact of mechanical street cleaning and rainfall events on the quantity and heavy metals load of street sediments

The paper presents and analyses the results of a street sediments monitoring campaign carried out during dry weather in order to quantify the impact of mechanical street cleaning and rainfall events on the quantity and heavy metals load of street sediments. The study has been carried out in an experimental catchment in a medium traffic street of a residential/commercial area in the city of Reggio Calabria (Italy). Thanks to acquired data, it was possible to assess the amount and the degree of pollution of street sediments, the efficiency of mechanical street cleaning in terms of sediments and pollutants removal, the wash-off of street sediments during rainfall events and the related potential impact on receiving water bodies. The results obtained confirm that street sweeping is generally scarcely effective as a practice for urban storm run-off quality control and that run-off is, on the contrary, quite effective in street sediments removal especially for smaller particles. Moreover, chemical analyses indicate that, although the concentration of heavy metals is higher in sediments particles having a diameter lower than 0.075 mm, the greatest part of the pollutants load is associated to larger particles.

The landfill reinjection of concentrated leachate: findings from a monitoring study at an Italian site

The membrane-based processes are among the most used techniques for leachate treatment in modern landfills but its environmental, technical and economical sustainability strongly depends on the disposal of concentrated leachate that is produced there. This paper presents the monitoring study of the landfill of the municipality of Monsummano Terme (Pistoia province, Tuscany, Italy) named "Il Fossetto" where concentrated leachate obtained during membrane treatment is recirculated. The findings resulting from the first 30 months of monitoring of concentrated leachate recirculation show that leachate production did not increase significantly and that only a few quality parameters (i.e. COD, Nickel and Zinc) presented a moderate increase. Moreover, the latest data on biogas composition seem to indicate a reduction in methane content that, if confirmed, could be related to the partial inhibition of methanogens due to the competition of sulphate reducing bacteria. The non-accumulation of other conservative pollutants such as Ammonia Nitrogen and Chloride in the leachate is still under investigation and needs to be better clarified. The overall sustainability of the reinjection as a means of disposing of the concentrated leachate produced by membrane treatment should be further analysed and evaluated in the long term.

The effect of separate collection of municipal solid waste on the lower calorific value of the residual waste

Nowadays, separate collection plays an irreplaceable role in municipal solid waste management and incineration in a waste-to-energy plant is one of the main disposal options. The objective of this study is to evaluate the effect of separate collection on the characteristics of residual municipal solid waste in terms of lower calorific value and ash production. Starting from the average Italian municipal solid waste composition, several separate collection scenarios have been considered evaluating the main characteristics of the residual waste (e.g. composition, water content, lower calorific value). Moreover, in order to have the opportunity of estimating the lower calorific value of residual waste for waste composition and separate collection scenarios different from those tested, a regression model is proposed, calibrated and partially validated.

Greenhouse gases emission from municipal waste management: The role of separate collection

The municipal solid waste management significantly contributes to the emission in the atmosphere of greenhouse gases (e.g. CO(2), CH(4), N(2)O) and therefore the management process from collection to treatment and disposal has to be optimized in order to reduce these emissions. In this paper, starting from the average composition of undifferentiated municipal solid waste in Italy, the effect of separate collection on greenhouse gases emissions from municipal waste management has been assessed. Different combinations of separate collection scenarios and disposal options (i.e. landfilling and incineration) have been considered. The effect of energy recovery from waste both in landfills and incinerators has also been addressed. The results outline how a separate collection approach can have a significant effect on the emission of greenhouse gases and how wise municipal solid waste management, implying the adoption of Best Available Technologies (i.e. biogas recovery and exploitation system in landfills and energy recovery system in Waste to Energy plants), can not only significantly reduce greenhouse gases emissions but, in certain cases, can also make the overall process a carbon sink. Moreover it has been shown that separate collection of plastic is a major issue when dealing with global warming relevant emissions from municipal solid waste management.

In sewer processes: mathematical model development and sensitivity analysis

Until now the majority of sewer networks in Italy have been built and managed considering small as well as local wastewater treatment plants (WWTPs). However, pushed by Italian and EU regulations, centralised and large WWTPs are becoming more common in Italy. One major technical aspect caused by the changing from local to centralised WWTPs is the development of significant in-sewer processes. These processes are also emphasized by the building of long interceptor sewers characterized by high hydraulic retention times and absence of tributary sewers. In this paper a model derived from the well known WATS model (Wastewater Aerobic/anaerobic Transformation in Sewers) has been set up and applied to an Italian case study located in Palermo. To assure a good degree of reliability the model needs a number of parameters that can be measured or calibrated by the combined use of field data and laboratory analyses. To support the planning of the experimental activity a sensitivity analysis to assess the influence of each model parameter has been carried out. Indeed, the sensitivity analysis allowed identifying the most significant model parameters. As a matter of the fact, by means of sensitivity analysis it was possible not only to pin down the most important model parameters but also to address the field survey towards the most sensitive model parameters in order to optimize the model application. The results are interesting and enabled to reduce the number of parameters to be calibrated from 24 to 14. More specifically, COD fractions, Y(Hw) and mu(H) showed a strong influence on the model results addressing the field campaign to an accurate evaluation of their value.

Simulation of the operation of detention tanks

The performance of detention tanks with different characteristics (volume, on-line and off-line arrangement) has been evaluated according to the results of a continuous simulation. The conceptual simplified model for sewer system simulation (COSMOSS) model has been used to simulate the operation of the tanks. The differences between the performance of on-line and off-line tanks and the influence of the characteristics of different catchments have been examined. According to the results of the simulations detention tanks demonstrated good performances in total suspended solids retention and this evenience can certainly help to prevent water pollution of receiving water bodies in urban areas, even if the differences between the catchments, especially regard to the first flush effect, influence the performance of the tanks. Anyway considerable good efficiencies can be obtained with tank volumes of about 30-50 m(3)/ha(imp), in terms of number, maximum concentrations and duration of overflows, generally not guaranteed only with overflow devices.