Chemical Engineering Reaction Assignment
Question 1
There are numerous reasons why it is essential to study the continuous stirred tank reactor (CSTR) performance for the production of bio-hydrogen from organic waste. Firstly, CSTR is a widely utilized approach of converting reactants into valuable products in the chemical industries. Besides, the technique is commonly applied for suspension or liquid reaction. Organic waste fermentation into renewable bio-hydrogen, CSTR takes place in three stages, namely diluted water (liquid stage), total solid melon waster (solid), and CO2 and hydrogen (gas stage). However, inhibitory chemical concentration, pH, substrate reduction, and gas yield due to fermentation are challenging tasks on the three CSTR stages.
Additionally, the organic loading rate (OLR) change also plays a vital in CSTR stability performance interruption. For example, high OLR results in top inhibitory compounds and acid accumulation, thereby causing lower gas yield. On the contrary, when OLR is low, it reduces the CSTR stability as a result of a sufficient ratio between certain microorganisms’ populations and the source of the microbial substrate. Also, a low organic loading rate prevents the build-up of volatile fatty acids, thereby maintaining environmental conditions at the optimum pH level. Lastly, the application of CSTR generates renewable energy and valorize melon waste.
Question 2
- This is a complex microbial reaction that is leading to the production of hydrogen gas via dark fermentation. The reaction is simplified when the only volatile fatty acid being formed is the acetate. As a result, a maximum yield of 4 mol H2/mol glucose of hydrogen gas is achieved. In the second reaction, the production of hydrogen is less equal to half of the first reaction, forming butyric acid.
- The fermentation system’s pH at the initial stage is at optimum condition between pH 5 and pH 7. This condition is an indication that the accumulation of volatile fatty acids is not significant, especially during the first organic loading rate period 1.8 g VS/ (l.d). Nevertheless, when the organic loading rate is increased to 2.4 g VS/ (l.d), it would disturb the stability of pH value to 4.0 or lower, resulting in acidic conditions. That is, there is high volatile fatty acid accumulation generated through the degradation of the substrate. Also, it can be deduced that under this condition, the microorganisms are not capable of sustaining their degradation metabolism of melon fruit waste organic matter content.
- Eugenol accumulation is beneficial as it is one of the components of pocket melon skin that is used as an antimicrobial agent.
Question 3 Materials and Methods
Feedstock-Collecting melon and orange fruit waste from the local fruit market; then peel and cut off melon and orange fruit and subsequently grind them using a blender to form a feedstock. Store the feedstock in the freezer at -5 degrees temperature before using it as feed to CSTR.
Inoculums-microorganism that produce hydrogen is from cow dung residual sludge biogas plant. This substance is then treated over pH 5.0 for 24 hours as well as heat-shock treatment 95 for 45 minutes.
The experiment’s procedure- water, substrates, and the inoculums- is filled in the CSTR for three days before the feed at an organic loading rate of 1.2 g VS/(l.d). The feedstock is then fed to CSTR on day four per day with a quantity of 100 grams every two days. Various intervals of OLR follow this step.
Analysis-Gas Chromatography is used to analyze gas content. The Gas Chromatography is equipped with a Thermal Conductivity Detector and MS 5A column. The Helium is used to run the equipment as a gas carrier at 40 ml/minute oven temperature. The detector and injector are then set at specific intervals to enable measurements of ash, VS, and TS based on the APHA standard method.
Question 4
The ultimate choice and future of energy carrier is hydrogen, and this is because of its superior properties, such as it is renewable, produces more efficient energy with up to 50% conversion rate, and emits fewer greenhouse gases. It is also easy to produce hydrogen through electrolysis of water in the presence of enough and free electricity access to electricity, for example, the geothermal electric power. When there is limited electricity, it is challenging to use the electrolysis process; as such, dark fermentation is an alternative method of producing hydrogen using cheap raw organic waste, such as melon waste. Waste empower microbial community is used to carry out fermentative hydrogen production. Their role is to convert organic matter into volatile fatty acids through metabolism. In the process, an electron is emitted to hydrogenase that converts the proton into hydrogen gas.
Various factors influence this method, namely, inhibitors, the concentration of substrate, pH, temperature, and types of reactors. Therefore, this experiment aimed to investigate the continuous stirred tank reactor (CSTR) performance of using melon waste to produce biohydrogen via dark fermentation technique. Melon waste was collected from the local fruit market. It is then peeled and cut off and subsequently ground using a blender to form a feedstock. The feedstock is stored in a freezer at a temperature -5 degrees Celsius before it is used as feed to CSTR. Melon waste as a feedstock is fed continuously to CSTR based on the organic loading rate. To achieve optimum condition is met at OLR is highest. However, this higher OLR value also some implications; that is, it reduces the volume of total gas as a result of high acid accumulation and low removal of volatile solid substrates. The application of CSTR generates renewable energy and valorize melon waste.
References
Cahyari, K., Syamsiah, S., & Prasetya, A. (2016, November). Performance of continuous stirred tank reactor (CSTR) on fermentative biohydrogen production from melon waste. In IOP Conference Series: Materials Science and Engineering (Vol. 162, No. 1, p. 012013). IOP Publishing.