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BACKGROUND:The economic value of many fruit and vegetables is often linked to the ability to preserve such natural products. In the case of tomatoes, the manufacture of 1 kg of powder or concentrate requires the evaporation of about 16 kg water kg −1 dry matter. In the present work, the effectiveness and economic analysis of solar drying systems for drying of tomato paste with and without geothermal water heat exchanger (GWHE) were studied. RESULTS:The GWHE integration significantly increased the recorded drying temperature up to 53.41 °C, with an improvement of 11.5 °C compared to the conventional dryer. Moreover, the drying temperature inside the drying chamber exceeded ambient temperature after sunset and at night by 30.8 °C. GWHE ensured a continuous drying process, while drying time was 22 consecutive hours, compared to the basic dryer with 18 h in 3 days. Effective moisture diffusivity was found to be 1.617 × 10 −9 and 1.202 × 10 −9 m 2 s −1 for hybrid and basic drying systems, respectively, using the slope. Three methods were used to perform economic analysis. The cumulative present worth of savings, at 23 382.6 USD, is much higher than the capital cost of the hybrid dryer, at 467 USD. The payback period is quite acceptable, at 2.21 years as compared to dryer lifetime of 15 years. Therefore, the hybrid dryer will dry tomato paste without additional charges for 12.79 years and is recommended for a large-scale tomato paste dryer.CONCLUSION: The hybrid system with GWHE ensures a continuous drying process during night-time, in addition to reduced drying time. The economic study revealed a high feasibility for the hybrid dryer, with a short payback period.

The economic value of many fruits and vegetables is closely related to their suitability for processing and preservation. In the case of tomatoes (about 94% wet basis wb), the manufacture of 1 kg of dry basis (db) powder (5% wb) or concentrate (30% wb) requires the evaporation of 15.9 or 15.7 kg H 2 O/kg db, respectively. In the current study, mechanical dewatering and geothermal-assisted solar drying (SD) of tomato paste at 5.8 kg H 2 O/kg db allowed reaching the required final moisture level of 0.053 ± 0.002 kg H 2 O/kg wb with low-cost energy. The instant controlled pressure drop (DIC) was used for texturing the predried tomato paste using the operative parameters of absolute saturated steam-pressure P = 0.3 MPa and thermal holding-time t = 30 s. The final hot air-drying step of tomato paste was carried out at 39, 50, and 70 C with a constant velocity of 3 m s À1 . The phenomenological modeling of the drying kinetics allowed identifying the starting accessibility and the effective water diffusivity. DIC texturing reduced drying time from 7 to 1.5 hr and improved the effective water diffusivity from 1.43 Â 10 À9 to 3.67 Â 10 À9 m 2 s À1 for T = 70 C. The lowest activation energy was recorded for DIC samples with 25.69 kJ mol À1 compared with 41.87 kJ mol À1 for control samples. A comparison of visual quality revealed a huge enhancement for DIC-samples compared with the control samples (RM). Moreover, the high economic value of dewatered tomato water was noticeable. Practical ApplicationsHigh quality, low energy consumption, and processing time are decisive factors for the industrial drying operations of agro-products. Solar-geothermal drying combined with innovative treatment technology called instant controlled pressure drop (DIC)swell drying can be a good alternative to conventional drying methods such as hot air drying. Mechanical dewatering as a first step followed by solar-geothermal drying/ DIC-swell drying may greatly reduce drying time and improve the quality of the dried product on the one hand, and reduce energy consumption on the other hand. In addition to that, mechanical dewatering and separation allow us to benefit the peels and seeds, in addition to free product juice with less energy. | INTRODUCTIONToday, large quantities of tomatoes are produced in Algeria. According to FAO (2014), Algeria ranks 18th in the world tomato production with 1,065,609 tons per year. Due to their fragility and the distances between production and consumption areas, tons of harvested tomatoes are lost every year. There is therefore a considerable need for conservation and processing techniques. Drying is a remarkable way

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