Infrared radiation drying of Moringa oleifera grains for use in water treatment

Vânia R. G. Nascimento,João D. Biagi,Luiz A. Rossi,Camila C. Arantes,Rafael A. de Oliveira

doi:10.1590/1807-1929/agriambi.v23n10p768-775

Abstract

ABSTRACT This study aimed to evaluate the effects of using infrared radiation in the hot-air drying of Moringa oleifera grains on the inner dryer and grain temperatures, energy consumption, and grain quality. An experiment was conducted in a factorial scheme in 2013 to identify the optimum values of the air temperature (30 to 58 ºC) and infrared radiation application time (2.0 to 4.8 min) on moisture content, drying time, drying rate, inner dryer air temperature, grain temperature, energy consumption and quality of grains used as a natural coagulant for water treatment. The results obtained were moisture content from 4.40 to 4.76% wet basis; drying time from 0.50 to 2.00 h; drying rates from 0.70 × 10-3 to 2.05 × 10-3 kgwater kg-1 dry matter min-1; inner dryer air temperatures from 42.24 to 61.82 ºC; grain temperatures from 56.32 to 76.19 ºC; energy consumptions of the fan from 0.05 to 0.20 kWh, electrical resistances from 1.41 to 4.49 kWh; resistances of the infrared heaters from 0.48 to 1.56 kWh; water turbidities from 1.36 to 5.76 NTU; grain protein contents from 34.93 to 37.93%; and peroxide value of grains from 0.009 to 0.052 meq kg-1. Both evaluated factors increased the inner dryer air temperature and grain temperature. The electrical resistances contributed the most to the energy consumption. However, the infrared radiation reduced this consumption. The drying performed with air temperature of 44 °C and infrared radiation time of 3.4 min resulted in the highest protein concentration in the Moringa oleifera L. grains and in greater removal of the water turbidity in the water treatment.

Highlights

The combined use of infrared radiation and hot-air drying is more effective than using them alone because of the synergistic effect (Puente-Díaz et al, 2013). This is because the infrared radiation directly heats the product, with little heat losses to the surrounding air, which leads to high energy efficiency and low drying time due to high heating rates
The objective of the present study was to evaluate the effects of air temperature and application time of infrared radiation on Moringa oleifera grains subjected to drying process, considering their maximum response of drying efficiency, energy consumption, and use of these grains as a natural coagulant for water treatment
Sensors were installed inside the grain layer and inside the drying chamber to evaluate the increases in the dryer and grain temperatures due to the use of infrared radiation

Summary

Introduction

The combined use of infrared radiation and hot-air drying is more effective than using them alone because of the synergistic effect (Puente-Díaz et al, 2013). This is because the infrared radiation directly heats the product, with little heat losses to the surrounding air, which leads to high energy efficiency and low drying time due to high heating rates. Studies have reported that the grains of this species are a potential alternative to chemical coagulants for water clarification (Lédo et al, 2009) This is due to their benefits, such as biodegradability, low toxicity, low rate of residue production (Madrona et al, 2012), and no significant effects on water pH and electrical conductivity after treatment (Ndabigengesere et al, 1995)

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Conclusion