title: Reduction in drying time of taro using pretreatments or posttreatment with hot air drying

authors: Thamarai Selvan, Shiva Subramani

abstract: Taro is a widely cultivated crop, primarily grown for its corm, which serves as a staple food worldwide. However, due to its high moisture content, taro is highly perishable, with an unprocessed shelf life of only 15 to 20 days. Drying has been employed as a method for extending shelf life by reducing moisture content to levels that inhibit microbial growth and prevent moisture-induced deteriorative biochemical reactions. Convective hot air drying (HAD) is the most commonly used method for food drying, but it is associated with prolonged drying times and high energy consumption. This research aimed to reduce the drying time of taro by using pretreatments and posttreatments with hot air drying. HAD without pre- or posttreatments was used as a control, and drying times were compared across four pretreatment methods (microwave, blanching, ultrasonication, and osmotic dehydration) and one posttreatment method (microwave). The results indicated that microwave post-treatment after 1 hour of hot air drying at 50°C reduced total drying time by 85% compared to the control. Similarly, microwave post-treatment after 1 hour of hot air drying at 70°C reduced drying time by 75% when moisture content decreased from 2.4 (dry basis) to 1.3 (dry basis). In contrast, blanching and osmotic dehydration pretreatments at 50°C worsened drying efficiency, increasing drying time relative to the control. Microwave pretreatments at 50°C resulted in slight reductions in drying time compared to the control.  Additionally, peeling the skin before drying reduced total drying time by approximately 36% compared to skin-on samples. However, slicing was necessary, as whole peeled samples required longer drying times than sliced ones. Taro, sliced to 8 mm thickness, dried with hot air at 70°C for 1 hour, followed by 20 minutes of microwave post-treatment, reaches 0.10 (dry basis), which is the required final moisture content for taro flour production, and is suitable for industrial scale implementation. Further research is required to assess the energy consumption of microwave post-treatment and hot air drying to determine their economic and sustainable feasibility. Quantifying energy requirements is essential for balancing efficiency with cost-effectiveness.

text: Reduction in drying time of taro using pretreatments or posttreatment with hot air drying Taro is a widely cultivated crop, primarily grown for its corm, which serves as a staple food worldwide. However, due to its high moisture content, taro is highly perishable, with an unprocessed shelf life of only 15 to 20 days. Drying has been employed as a method for extending shelf life by reducing moisture content to levels that inhibit microbial growth and prevent moisture-induced deteriorative biochemical reactions. Convective hot air drying (HAD) is the most commonly used method for food drying, but it is associated with prolonged drying times and high energy consumption. This research aimed to reduce the drying time of taro by using pretreatments and posttreatments with hot air drying. HAD without pre- or posttreatments was used as a control, and drying times were compared across four pretreatment methods (microwave, blanching, ultrasonication, and osmotic dehydration) and one posttreatment method (microwave). The results indicated that microwave post-treatment after 1 hour of hot air drying at 50°C reduced total drying time by 85% compared to the control. Similarly, microwave post-treatment after 1 hour of hot air drying at 70°C reduced drying time by 75% when moisture content decreased from 2.4 (dry basis) to 1.3 (dry basis). In contrast, blanching and osmotic dehydration pretreatments at 50°C worsened drying efficiency, increasing drying time relative to the control. Microwave pretreatments at 50°C resulted in slight reductions in drying time compared to the control.  Additionally, peeling the skin before drying reduced total drying time by approximately 36% compared to skin-on samples. However, slicing was necessary, as whole peeled samples required longer drying times than sliced ones. Taro, sliced to 8 mm thickness, dried with hot air at 70°C for 1 hour, followed by 20 minutes of microwave post-treatment, reaches 0.10 (dry basis), which is the required final moisture content for taro flour production, and is suitable for industrial scale implementation. Further research is required to assess the energy consumption of microwave post-treatment and hot air drying to determine their economic and sustainable feasibility. Quantifying energy requirements is essential for balancing efficiency with cost-effectiveness.

year: 2025

title: Accounting for stream variability in retrofit problems using Monte Carlo simulation

authors: Lal, Nathan S.

abstract: The aim of this paper is to use Monte Carlo simulation to analyse the effect of stream data variation on the economic performance of retrofit designs. The input stream data is fitted to a distribution which can be sampled from to calculate the outputs of the Heat Exchanger Network model, stochastically. A simple four-stream problem is used to demonstrate the method, comparing two retrofit designs that each reduce the hot utility by 700 kW. Monte Carlo simulation analyses how the similar designs behave differently under the variable conditions and the results show that time-average analysis can not only overestimate the Total Retrofit Profit but can also favour a different design to that favoured by the Monte Carlo results. Of the two compared designs, the Design 2 was selected with an annual Total Retrofit Profit of NZD 215,553, requiring one new exchanger and additional area on an existing one. The Monte Carlo analysis also shed light on controllability and feasibility issues in the Heat Exchanger Network.

text: Accounting for stream variability in retrofit problems using Monte Carlo simulation The aim of this paper is to use Monte Carlo simulation to analyse the effect of stream data variation on the economic performance of retrofit designs. The input stream data is fitted to a distribution which can be sampled from to calculate the outputs of the Heat Exchanger Network model, stochastically. A simple four-stream problem is used to demonstrate the method, comparing two retrofit designs that each reduce the hot utility by 700 kW. Monte Carlo simulation analyses how the similar designs behave differently under the variable conditions and the results show that time-average analysis can not only overestimate the Total Retrofit Profit but can also favour a different design to that favoured by the Monte Carlo results. Of the two compared designs, the Design 2 was selected with an annual Total Retrofit Profit of NZD 215,553, requiring one new exchanger and additional area on an existing one. The Monte Carlo analysis also shed light on controllability and feasibility issues in the Heat Exchanger Network.

year: 2018

title: Assessment of effects of proposed treated wastewater discharge to the Te Arikiroa Thermal Channel and Sulphur Bay (Lake Rotorua)

authors: Dada, Ayokunle Christopher

abstract: After 2019, irrigation operations at the Land Treatment System (LTS) in the Whakarewarewa Forest are scheduled to cease. A number of options and locations have been considered for the discharge of the treated wastewater when the current discharge consent ceases. Following consultations and technical assessments, the preferred option of Rotorua Lakes Council is to upgrade the existing plant to a full Membrane Bioreactor Plant with the addition of an Ultraviolet Disinfection System (or alternative treatment to achieve an equivalent performance in terms of treated wastewater quality). Under this arrangement, wastewater would be subjected to biological, chemical and physical treatment processes, and the treated wastewater discharged through Te Arikiroa Thermal Channel to Sulphur Bay. Rotorua Lakes Council is thus undertaking an environmental impact assessment study to determine the effects of discharging treated wastewater to the thermal channel and Puarenga Bay (Lake Rotorua), with particular reference to aesthetic, water quality and ecological considerations. These considerations include potential effects related to faecal indicator bacteria, nutrient concentrations, metals, dissolved oxygen, and taonga species (native species of cultural significance).
The assessment focused on:
(i)	The projected treated wastewater characteristics;

(ii)	Existing conditions of the receiving water;

(iii)	The sensitivity of the receiving water and the impact of the proposed discharge on water quality and taonga species (native species of cultural significance) in Te Arikiroa Thermal Channel and Sulphur Bay.

The main techniques used to inform the assessment in this study were:
1) Analysis of historical water quality data, 2011-2014;
2) Collection of additional water quality data at Te Arikiroa Thermal Channel and Sulphur Bay and along a transect to quantify spatial variability (sampling in 2016 and 2017);
3) Mass balance dilution modelling to predict water quality in the Te Arikiroa Thermal Channel and Sulphur Bay (Lake Rotorua), at a site outside of the assumed mixing zone;
4) Lake ecosystem modelling conducted by Abell et al. (2015) to assess effects related to eutrophication;
5) Background review of biological information and field investigations for taonga species at Sulphur Bay and Te Arikiroa Thermal Channel (2017).

text: Assessment of effects of proposed treated wastewater discharge to the Te Arikiroa Thermal Channel and Sulphur Bay (Lake Rotorua) After 2019, irrigation operations at the Land Treatment System (LTS) in the Whakarewarewa Forest are scheduled to cease. A number of options and locations have been considered for the discharge of the treated wastewater when the current discharge consent ceases. Following consultations and technical assessments, the preferred option of Rotorua Lakes Council is to upgrade the existing plant to a full Membrane Bioreactor Plant with the addition of an Ultraviolet Disinfection System (or alternative treatment to achieve an equivalent performance in terms of treated wastewater quality). Under this arrangement, wastewater would be subjected to biological, chemical and physical treatment processes, and the treated wastewater discharged through Te Arikiroa Thermal Channel to Sulphur Bay. Rotorua Lakes Council is thus undertaking an environmental impact assessment study to determine the effects of discharging treated wastewater to the thermal channel and Puarenga Bay (Lake Rotorua), with particular reference to aesthetic, water quality and ecological considerations. These considerations include potential effects related to faecal indicator bacteria, nutrient concentrations, metals, dissolved oxygen, and taonga species (native species of cultural significance).
The assessment focused on:
(i)	The projected treated wastewater characteristics;

(ii)	Existing conditions of the receiving water;

(iii)	The sensitivity of the receiving water and the impact of the proposed discharge on water quality and taonga species (native species of cultural significance) in Te Arikiroa Thermal Channel and Sulphur Bay.

The main techniques used to inform the assessment in this study were:
1) Analysis of historical water quality data, 2011-2014;
2) Collection of additional water quality data at Te Arikiroa Thermal Channel and Sulphur Bay and along a transect to quantify spatial variability (sampling in 2016 and 2017);
3) Mass balance dilution modelling to predict water quality in the Te Arikiroa Thermal Channel and Sulphur Bay (Lake Rotorua), at a site outside of the assumed mixing zone;
4) Lake ecosystem modelling conducted by Abell et al. (2015) to assess effects related to eutrophication;
5) Background review of biological information and field investigations for taonga species at Sulphur Bay and Te Arikiroa Thermal Channel (2017).

year: 2018