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.

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.

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·kgTS-1 of lactic acid, 26 g·kgTS-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.

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 1.0gTVSL-1 d-1 and EOsr of 47.6mgL-1d-1. Partial inhibition of the anaerobic digestion was detected at OLR and EOsr of 1.98gTVSL-1d-1 and 88.1mgL-1 d-1, respectively and the process irreversibly stopped when OLR and EOsr reached 2.5gTVS L-1 d-1 and 111.2mgL-1 d-1, respectively. Under thermophilic conditions, the cumulative methane production (0.12LgTVS-1) was about 25% of that under mesophilic conditions (0.46LgTVS-1). The thermophilic digestion was completely inhibited at lower OLR (1.98gTVSL-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.

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 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.

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.

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.

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.