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.

Preliminary evaluation of the anaerobic biodegradability of three biobased materials used for the production of disposable plastics

Biodegradable plastics have been introduced to the market to substitute "traditional", non-biodegradable, petro-based plastics to alleviate plastic pollution. Biochemical methane potential tests were carried out on compostable bags made of MaterBi®, biodegradable bottle wine corks and cellulosic plates to examine the anaerobic biodegradability of those materials. The impact of four factors: type of pretreatment (predigestion, mechanical, alkaline, predigestion and alkaline), digestion duration, type of inoculum and temperature were statistically evaluated through regression modeling. Anaerobic tests on compostable and polyethylene bags (control) were carried out in mesophilic (35 °C) and thermophilic (55 °C) conditions, while tests on bottle wine corks and cellulosic plates were carried out in mesophilic conditions only. After 15 days of digestion, a dry mass reduction of 22.8 ± 6.2 % and 27.6 ± 14.0 % for mesophilic and thermophilic tests respectively was recorded for MaterBi®. Chemical pretreatment with NaOH led to a mass reduction of 78.2 ± 7.2 % and was the only statistically significant factor to affect both methane yields and dry mass loss. A higher digestion temperature led to an increased mass loss without a concurrent increase in methane production. The cellulosic plates were completely degraded (99.9 ± 0.03 % mass reduction), while the wine bottle corks weight did not change.

A systematic review on the composting of green waste: Feedstock quality and optimization strategies

Green waste (GW) is an important fraction of municipal solid waste (MSW). The composting of lignocellulosic GW is challenging due to its low decomposition rate. Recently, an increasing number of studies that include strategies to optimize GW composting appeared in the literature. This literature review focuses on the physicochemical quality of GW and on the effect of strategies used to improve the process and product quality. A systematic search was carried out, using keywords, and 447 papers published between 2002 and 2018 were identified. After a screening process, 41 papers addressing feedstock quality and 32 papers on optimization strategies were selected to be reviewed and analyzed in detail. The GW composition is highly variable due to the diversity of the source materials, the type of vegetation, and climatic conditions. This variability limits a strict categorization of the GW physicochemical characteristics. However, this research established that the predominant features of GW are a C/N ratio higher than 25, a deficit in important nutrients, namely nitrogen (0.5-1.5% db), phosphorous (0.1-0.2% db) and potassium (0.4-0.8% db) and a high content of recalcitrant organic compounds (e.g. lignin). The promising strategies to improve composting of GW were: i) GW particle size reduction (e.g. shredding and separation of GW fractions); ii) addition of energy amendments (e.g. non-refined sugar, phosphate rock, food waste, volatile ashes), bulking materials (e.g. biocarbon, wood chips), or microbial inoculum (e.g. fungal consortia); and iii) variations in operating parameters (aeration, temperature, and two-phase composting). These alternatives have successfully led to the reduction of process length and have managed to transform recalcitrant substances to a high-quality end-product.

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.

A systematic approach to evaluate parameter consistency in the inlet stream of source separated biowaste composting facilities: A case study in Colombia

Biowaste is commonly the largest fraction of municipal solid waste (MSW) in developing countries. Although composting is an effective method to treat source separated biowaste (SSB), there are certain limitations in terms of operation, partly due to insufficient control to the variability of SSB quality, which affects process kinetics and product quality. This study assesses the variability of the SSB physicochemical quality in a composting facility located in a small town of Colombia, in which SSB collection was performed twice a week. Likewise, the influence of the SSB physicochemical variability on the variability of compost parameters was assessed. Parametric and non-parametric tests (i.e. Student's t-test and the Mann-Whitney test) showed no significant differences in the quality parameters of SSB among collection days, and therefore, it was unnecessary to establish specific operation and maintenance regulations for each collection day. Significant variability was found in eight of the twelve quality parameters analyzed in the inlet stream, with corresponding coefficients of variation (CV) higher than 23%. The CVs for the eight parameters analyzed in the final compost (i.e. pH, moisture, total organic carbon, total nitrogen, C/N ratio, total phosphorus, total potassium and ash) ranged from 9.6% to 49.4%, with significant variations in five of those parameters (CV>20%). The above indicate that variability in the inlet stream can affect the variability of the end-product. Results suggest the need to consider variability of the inlet stream in the performance of composting facilities to achieve a compost of consistent quality.

Stability and maturity of biowaste composts derived by small municipalities: Correlation among physical, chemical and biological indices

Stability and maturity are important criteria to guarantee the quality of a compost that is applied to agriculture or used as amendment in degraded soils. Although different techniques exist to evaluate stability and maturity, the application of laboratory tests in municipalities in developing countries can be limited due to cost and application complexities. In the composting facilities of such places, some classical low cost on-site tests to monitor the composting process are usually implemented; however, such tests do not necessarily clearly identify conditions of stability and maturity. In this article, we have applied and compared results of stability and maturity tests that can be easily employed on site (i.e. temperature, pH, moisture, electrical conductivity [EC], odor and color), and of tests that require more complex laboratory techniques (volatile solids, C/N ratio, self-heating, respirometric index, germination index [GI]). The evaluation of the above was performed in the field scale using 2 piles of biowaste applied compost. The monitoring period was from day 70 to day 190 of the process. Results showed that the low-cost tests traditionally employed to monitor the composting process on-site, such as temperature, color and moisture, do not provide consistent determinations with the more complex laboratory tests used to assess stability (e.g. respiration index, self-heating, volatile solids). In the case of maturity tests (GI, pH, EC), both the on-site tests (pH, EC) and the laboratory test (GI) provided consistent results. Although, stability was indicated for most of the samples, the maturity tests indicated that products were consistently immature. Thus, a stable product is not necessarily mature. Conclusively, the decision on the quality of the compost in the installations located in developing countries requires the simultaneous use of a combination of tests that are performed both in the laboratory and on-site.