Vincenzo Torretta

Treatment and disposal of tyres: two EU approaches. A review

The treatment and disposal of tyres from vehicles has long been of considerable environmental importance. The main problem lies in the mixed composition of the tyres. Studies have been undertaken to modify the structure of the tyres, especially with reference to the percentage of granulated rubber incorporated, in order to improve their performance, and also to reduce their environmental impact during normal functioning (noise, particulates, etc.) and facilitate recycling and final disposal. The aim of the present study is to review and compare how used tyres are treated and disposed of in two different EU countries. The first is Italy, which has been part of the European Union since its inception, and has important industrial traditions. The second is Romania, an emerging country which recently became part of the EU, and whose economic and industrial development has had a major boost in recent years, with a strong growth in waste production, together with consumption in urban areas. The occasion was useful to consider the situation concerning the evolution of the different aspects related to the management of the end-of-life tyres. In particular, the paper considers the properties of tyre waste and their potential reuse, the enhancement of end-of-life tires and the various types of recovery, such as the reconstruction of tyres and the material recovery. The aspects related to the energy recovery and the use of the life cycle analysis, as a tool to support the choices of the best management system, were also taken into consideration, not forgetting that an adequate end-of-life planning is important when developing a sustainable product, since it can affect considerably its overall life cycle.

Recovery of different waste vegetable oils for biodiesel production: a pilot experience in Bahia State, Brazil.

In Brazil, and mainly in the State of Bahia, crude vegetable oils are widely used in the preparation of food. Street stalls, restaurants and canteens make a great use of palm oil and soybean oil. There is also some use of castor oil, which is widely cultivated in the Sertão Region (within the State of Bahia), and widely applied in industry. This massive use in food preparation leads to a huge amount of waste oil of different types, which needs either to be properly disposed of, or recovered. At the Laboratorio Energia e Gas-LEN (Energy & Gas lab.) of the Universidade Federal da Bahia, a cycle of experiments were carried out to evaluate the recovery of waste oils for biodiesel production. The experiences were carried out on a laboratory scale and, in a semi-industrial pilot plant using waste oils of different qualities. In the transesterification process, applied waste vegetable oils were reacted with methanol with the support of a basic catalyst, such as NaOH or KOH. The conversion rate settled at between 81% and 85% (in weight). The most suitable molar ratio of waste oils to alcohol was 1:6, and the amount of catalyst required was 0.5% (of the weight of the incoming oil), in the case of NaOH, and 1%, in case of KOH. The quality of the biodiesel produced was tested to determine the final product quality. The parameters analyzed were the acid value, kinematic viscosity, monoglycerides, diglycerides, triglycerides, free glycerine, total glycerine, clearness; the conversion yield of the process was also evaluated.

Effluents from MBT plants: Plasma techniques for the treatment of VOCs

Mechanical-biological treatments (MBTs) of urban waste are growing in popularity in many European countries. Recent studies pointed out that their contribution in terms of volatile organic compounds (VOCs) and other air pollutants is not negligible. Compared to classical removal technologies, non-thermal plasmas (NTP) showed better performances and low energy consumption when applied to treat lowly concentrated streams. Therefore, to study the feasibility of the application of NTP to MBTs, a Dielectric Barrier Discharge reactor was applied to treat a mixture of air and methyl ethyl ketone (MEK), to simulate emissions from MBTs. The removal efficiency of MEK was linearly dependent upon time, power and specific input energy. Only 2-4% of MEK was converted to carbon dioxide (CO2), the remaining carbon being involved in the formation of byproducts (methyl nitrate and 2,3-butanedione, especially). For future development of pilot-scale reactors, acting on residence time, power, convective flow and catalysts will help finding a compromise between energy consumption, desired abatement and selectivity to CO2.

Sewage sludge drying by energy recovery from OFMSW composting: preliminary feasibility evaluation.

In this paper an original energy recovery method from composting is analyzed. The integrated system exploits the heat available from the aerobic biochemical process in order to support the drying of sewage sludge, using a specific solar greenhouse. The aim is to tackle the problem of organic waste treatment, with specific regard to food waste. This is done by optimizing the energy consumption of the aerobic process of composting, using the heat produced to solve a second important waste management problem such as the sewage waste treatment. Energy and mass balances are presented in a preliminary feasibility study. Referring to a composting plant with a capacity of 15,000 t/y of food waste, the estimation of the power from recovered heat for the entire plant resulted about 42 kW. The results demonstrated that the energy recoverable can cover part of the heat necessary for the treatment of sludge generated by the population served by the composting plant (in terms of food waste and green waste collection). The addition of a renewable source such as solar energy could cover the residual energy demand. The approach is presented in detail in order for it to be replicated in other case studies or at full scale applications.

Treatment of slaughterhouse wastewaters using anaerobic filters

In this paper, a laboratory-scale experimentation allowed comparing the performances of two upflow anaerobic packed-bed filters filled with different packing materials and operating at mesophilic conditions (30°C) for treating slaughterhouse wastewaters. Methane production was experimentally evaluated considering different volumetric organic loading rates as well as feeding overloading conditions. Although filter performances declined with loading rates higher than 6 kg CODin m−3 d−1, the chemical oxygen demand (COD) removal efficiency remained always above 60%. The experimental results allowed for determining kinetic parameters for bacterial growth rate and methane production, following Monod and Chen–Hashimoto models, respectively. Results demonstrated that the reactors reached a cellular retention time significantly greater than the hydraulic retention time. The kinetic parameter values (Ks, μmax) revealed the low microorganisms’ affinity for the substrate and confirmed the moderate biodegradability of slaughterhouse wastewater. The kinetic analysis also allowed the comparison of the filters performances with another anaerobic system and the assessment of the parameters useful for real-scale plant design. The system design, applied to a medium-sized Argentinean slaughterhouse, demonstrated to (i) be energetically self-sufficient and (ii) contribute to the plants water heating requirements.

Laboratory-scale anaerobic sequencing batch reactor for treatment of stillage from fruit distillation

This work describes batch anaerobic digestion tests carried out on stillages, the residue of the distillation process on fruit, in order to contribute to the setting of design parameters for a planned plant. The experimental apparatus was characterized by three reactors, each with a useful volume of 5 L. The different phases of the work carried out were: determining the basic components of the chemical oxygen demand (COD) of the stillages; determining the specific production of biogas; and estimating the rapidly biodegradable COD contained in the stillages. In particular, the main goal of the anaerobic digestion tests on stillages was to measure the parameters of specific gas production (SGP) and gas production rate (GPR) in reactors in which stillages were being digested using ASBR (anaerobic sequencing batch reactor) technology. Runs were developed with increasing concentrations of the feed. The optimal loads for obtaining the maximum SGP and GPR values were 8-9 gCOD L(-1) and 0.9 gCOD g(-1) volatile solids.

Occurrence of polycyclic aromatic hydrocarbons in sludges from different stages of a wastewater treatment plant in Italy

The occurrence of polycyclic aromatic hydrocarbons (PAHs) in various sludge types from a moderate-big wastewater treatment plant in the Lombardy region, Italy, was studied. Pyrene was continuously the most abundant PAH, whereas anthracene was the PAH with the lowest concentrations. Average ΣPAH concentrations ranged between 2405 ng/g (dry weight) in the secondary sludge and 2645 ng/g (dry weight) in the final sludge. A mass balance estimation between the various sludges showed no evident degradation of PAHs. The final sludge PAH concentrations were constantly at around half of the maximum permissible limit set by the European Union for use of sewage sludge in agriculture (6 mg/kg). The highest PAH concentrations were observed during the summer periods. Finally, two approaches were used to estimate the raw wastewater concentrations based on the sludge PAH concentrations. The values obtained did not differ much from the average concentrations measured at the influent wastewaters.

An integrated wastewater treatment system using a BAS reactor with biomass attached to tubular supports

This paper describes laboratory experiments aimed to develop a new wastewater treatment system as an alternative to a conventional domestic wastewater plant. A modified Biofilm Airlift Suspension reactor (BAS), with biomass attached to tubular supports, is proposed to address low organic loads (typical of domestic sewage) and low residence time (typical of compact reactors technology). Attached and suspended biomasses, coupled to the high dissolved oxygen (DO), allow high removal efficiencies (90% and 56% for COD and N-NH(4)(+) removal respectively) and high effluent quality to be reached. The experimental activity, divided into three parts, demonstrates the good efficiency of the process, and the reduction of the removal kinetics for the high operating pressure used in the technology. The occurrence of simultaneous nitrification-denitrification (SND) was also observed. When compared with the conventional BAS system, the present treatment shows comparable removal efficiencies and higher specific removal rates (80 mg COD/g VSS and 2.60 mg N-NH(4)(+)/g VSS). The experimental results were coupled with the development of a numerical model to aid in designing a full-scale treatment plant in Italy.

PAHs in wastewater: removal efficiency in a conventional wastewater treatment plant and comparison with model predictions

Polycyclic aromatic hydrocarbons (PAHs) are very hazardous compounds and, owing to their lipophilicity, they can easily cross biological membranes and accumulate inside organisms, causing damage to the genetic material. The scientific interest in PAHs is related to their demonstrated or supposed genotoxicity (cancer-causing characteristics of B[α ]Py and dB[α, h] first suspected in the 1930s). This study tried to detect the presence of PAHs in wastewater and to estimate their removal efficiency in a conventional wastewater treatment plant (Varese Olona). The PAHs’ presence in municipal wastewater sewage system and in the WWTP effluent was determined by a specific analytical campaign, and afterwards a comparison between observed removal efficiency and FATE model (US-EPA) predictions was carried out.

Improving biotreatment efficiency of hot waste air streams: experimental upgrade of a full plant

Biological methods as bio and biotrickling filtration are an energy-efficient and economical alternative to treat biodegradable odorants and volatile organic compounds (VOCs) in order to obey stringent releases regulations that have arisen during the last few decades. In this work a plant upgrade case study, employing these techniques, is presented. It refers to a critical situation in which off air streams, characterized by medium odorous compounds loads and high temperatures, were treated using a biofilter only. In that context, sufficient removal efficiencies were not achieved. Therefore, it has been proposed to replace the existing biofilter by a biotrickling one implementing a minimal number of structural plant modifications.