Newcastle University ePrints -eprint.ncl.ac.uk Tan DT, Poh PE, Chin SK. Microorganism preservation by convective air-drying-A review. AbstractAt present, microorganisms are mainly preserved by freeze drying. There is, however, lack of studies conducted on various cheaper yet promising convective air drying alternatives. Convective air drying has been proven to produce dried culture with comparable cell survival and final moisture content to that of freeze drying. This paper aims to draw an understanding to application and suitability of convective air drying which indludes spray-, oven, heat pump, fluidised bed, conveyor, and rotary drying to preserve microorganisms. The paper concludes that drying near ambient temperature and the addition of dehydration protectants are important to obtain satisfactory drying quality. ambient temperature and mild processing conditions [28]. Such condition is hypothesised to be favourable towards high cell survival of microorganisms [29].Majority of studies and reviews, however, largely revolve around freeze-drying and cryogenic preservation which are both costly [8,15,30,31]. Although convective air drying has been used to preserve many foodstuffs, research on its applicability for bacteria preservation is still limited [32][33][34][35][36]. This paper is aimed to critically review work on preservation of microbes; looking into the factors that will affect the cell viability in convective air drying and to suggest future directions on the use of convective air drying for microbial preservation. Methods for microorganism preservationWhile there are many means to preserve a desired culture of microorganisms, some methods might be more suitable than the other depending on the purpose of preservation. Based on applicability of the techniques, preservation methods can be distinguished into those that are limited to just laboratory scale and those that can be applied in industry, as some pilot techniques could be simple and reliable but are not scalable [15]. The key difference between laboratory and industrial scale is the amount of culture that needs to be salvaged [26]. For laboratory purposes, low cell survival is sufficient whereas large quantity (and therefore high cell survival) is required for industrial usage [15]. Typical laboratory preservation techniques include smearing and storing on agar or gelatine, cell immersion in paraffin oil, and the adsorption-desiccation of bacteria culture on filter-paper or on pre-dried plugs of starch or silica gel [15,37,38].High number of successfully preserved viable cells is particularly important to ensure possible direct inoculation to the process fluid where the bacterial culture is to be utilised [11]. The laboratory preservation methods mentioned above are unsuitable due to the complexity of the process, requirement of additives, and low recovery rate [15]. Preservation methods which are recognised to be practical for industrial use are subcultivation, freezing, and drying [39,40].
The generation of huge amount of liquid waste known as palm oil mill effluent is a major problem in oil palm industry. Meanwhile, anaerobic biodegradation of such organic effluent at thermophilic condition is a promising treatment technology due to its high efficiency. However, storage and transportation of thermophilic mixed culture sludge are challenging due to constant biogas generation and heating requirement. Hence, drying of thermophilic sludge was conducted to obtain dormant thermophiles and thus enables easier handling. In this study, thermophilic sludge was dried using heat pump at 22 and 32°C as well as hot air oven at 40, 50, 60, and 70°C. Subsequently, quality of dried sludge was examined based on most probable number enumeration, chemical oxygen demand, and methane yield. Average drying rate was found to increase from 3.21 to 17.84 g H 2 O/m 2 min as drying temperatures increases while average moisture diffusivity values ranges from 5.07 9 10-9 to 4.34 9 10-8 m 2 /s. Oven drying of thermophilic mixed culture resulted in highest chemical oxygen demand removal and lowest log reduction of anaerobes at 53.41% and 2.16, respectively, while heat pump drying resulted in the highest methane yield and lowest log reduction of methanogens at 53.4 ml CH 4 /g COD and 2.09, respectively. To conclude, heat pump at 22°C was most suitable drying technique for thermophilic mixed culture as the original methane-producing capability was largely retained after drying, at a slightly lower yet still comparable chemical oxygen demand removal when palm oil mill effluent was treated with the rehydrated culture. Keywords Biogas Á Chemical oxygen demand Á Heat pump drying Á Methane yield Á Most probable number Á Variable moisture diffusivity Editorial responsibility: M. Abbaspour.
In this research, a Coulomb force assisted heat pump (CF-HP) dryer was invented for the purpose of improving the drying characteristics and product quality of biomaterials. As compared to heat pump drying alone, the assistance of Coulomb force in heat pump dryer enhanced the drying rates and effective moisture diffusivity of lemon slices up to 26%, which eventually shortened the total drying time to 40%. This saved the total energy consumption of HP drying by 31.5%. High retention of vitamin C and TPC were also found in CF-HP dried slices due to mild drying temperature and fast drying rate. Keywords: Coulomb force; Heat pump drying; Drying rate; Vitamin C; Total Phenolic Content (TPC).
The worldwide demand for a Tire Pressure Monitoring System (TPMS) has grown due to the dangers posed by widespread tire safety abuse. The National Highway Traffic Safety Administration (NHTSA) estimates that 23,000 accidents and 535 fatalities per year involves flat tires or blowout both of which can be the result of improperly inflated tires. To further enhance vehicular safety, US government and Europe mandated the use of TPMS for all passenger cars by year 2008 and 2012 respectively. This prepare illustrates the packaging of a low cost yet complex TPMS device that involves MEMS (pressure sensing and accelerometer devices) and Controller chips integrated as one in a low cost Pre-molded Leadframe Cavity Package. Advanced solutions to resolve process challenges and material difficulties have paved the way to successfully qualify the product meeting all the intensive automotive requirements.
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