Energy-oriented optimization of an anaerobic digestion plant for the combined treatment of solid and liquid wastes in a potato chips industrial plant

Potato chips represent the main product of the snack food industry. Their processing determines the production of several kinds of wastes characterised by different physical and chemical properties that make them eligible feedstock for biological treatments. In this paper the anaerobic digestion of all the solid and liquid wastes, produced by a potato chips processing line and properly mixed, is investigated. The experiment hereby described is carried out on a pilot-scale plant and aims to reproduce the real situation of a potato chips factory by feeding all the wastes in the anaerobic reactor in a ratio suitable for an effective treatment process. A comparison between the performance of anaerobic digestion processes feed by raw potato wastes and balanced mixtures of all potato wastes deriving from potato chips processing lines is carried out. Finally, the results of the experimental investigation were used for a preliminary performance evaluation of a full-scale anaerobic digestion power plant for treating all the potato wastes produced by an industrial potato chips production plant

Biogas from anaerobic digestion of fruit and vegetable wastes: experimental results on pilot-scale and preliminary performance evaluation of a full-scale power plant

This paper presents the experimental results obtained through an anaerobic digestion pilot plant by using fruit and vegetable wastes as single substrate. The substrate materials were sampled from the wastes produced by the Fruit and Vegetable Wholesale Market of Sardinia (Italy). The experimental study was carried out over a period of about six months to evaluate the most suitable operating parameters of the process depending on the availability of different kinds of fruit and vegetable wastes over the different periods of the year. Overall, the optimum daily loading rate of wastes was 35 kg/d, with a corresponding hydraulic residence time of 27 days. The optimum organic loading rate ranged from 2.5 to 3.0 kgVS/m3d and the average specific biogas production was about 0.78 Nm3/kgVS, with a specific methane yield of about 0.43 Nm3/kgVS. The results of the experimental investigation were used for a preliminary performance evaluation of a full-scale anaerobic digestion power plant for treating all the fruit and vegetable wastes produced by the Wholesale Market of Sardinia (9 t/d). The estimate of daily methane production (290 Nm3/d) leads to a CHP unit with a power output of about 42 kW and an annual electrical production of about 300 MWh/y (about 25% of the wholesale market electrical consumption). The AD power plant also shows interesting economic features, since its energy production cost (about 150 €/MWh) is slightly lower than the energy purchase cost of the wholesale market (about 200 €/MWh) and a pay-back time of about 7.25 years can be achieved in the case of dispatching the electrical energy to the national grid. The PBT decreases to about 5.4 years if 50% of the available thermal energy is used to substitute heat production from fossil fuel boilers. Keywords Anaerobic digestion; fruit and vegetable waste; biogas production; mesophilic digestion

Energy performance assessment of mesophilic anaerobic digestion of fruit and vegetable wastes in a pilot-scale reactor

The main aim of the study presented in this paper was to evaluate the energy performance of anaerobic digestion of fruit and vegetable wastes (FVW) on a pilot scale in mesophilic conditions (35 °C), without the addition of any other kind of co-substrate. The anaerobic digestion experiment was carried out in a semi-continuous tubular horizontal reactor (1.13 m3) and lasted 6 months to take into account all the possible changes in feedstock composition during different periods of the year. Throughout the experiment the feedstock was characterized by measuring the total solid content, volatile solid content and higher heating value. The composition and energy contents of the biogas produced and the residue sludge were also evaluated. The results of the study demonstrate that fruit and vegetable wastes lead to high biogas yields and high methane contents. In particular, an average biogas yield of 0.80 Nm3 /kgvs and a specific methane yield of 0.45 Nm3 /kgvs were obtained. Since biogas is mainly used for energy production, a cumulative calculation of the energy content of feedstock, biogas and digestate during the whole experiment was carried out. At the end of the experimental period the energy content of the biogas produced was about 60% of the feedstock energy input, the residual energy content of the digestate was 15%, while the remaining 25% was the energy content of the biomass contained within the reactor. Energy conversion efficiency increases to about 80% by taking into account the biogas that would be produced by the biomass contained within the reactor. It is very interesting to note that the energy content of the reactor remains almost constant when the steady state is completely reached

Hydrothermal carbonization of hemp digestate: influence of operating parameters

In the last decade, great attention has been given to hydrothermal carbonization (HTC) as a suitable process for residual biomass valorization, able to convert organic waste into useful materials or energy carriers. However, the involved conversion reactions that biomass components undergo are influenced by the characteristics of the treated residue along with the HTC process conditions, particularly in terms of temperature and holding time. In this paper, the potential valorization of hemp digestate via HTC was investigated. The study was aimed at evaluating the effect of reaction temperature and holding time on the yield and composition of produced hydrochar and on the process water characteristics. Three temperatures (180, 200, and 220 degrees C) were investigated along with three holding times (1, 3, and 6 h) and the obtained solid and liquid phases were characterized. Results show that the investigated operating parameters affect both the solid yield and the hydrochar and process water composition. By increasing process severity conditions through an increase in temperature and/or holding time, a drop in solid yield (89-60 wt%) and an increase in carbon content (+ 15-+ 30%) and energy content (up to +22%) were achieved for the produced hydrochar compared to the feedstock, which showed suitable properties in view of its use as a fuel. Process water characteristics suggest a potential valorization in terms of nutrient recovery or biogas production by anaerobic digestion, while the feasibility of an aerobic treatment should be carefully evaluated