Many fresh water bodies face a great challenge of an invasive weed called water hyacinth (WH) which has great impacts on the environment, ecology, and society. Food and Agriculture Organization (FAO) estimates that over nine million tons of Fish wastes (FW) are thrown away each year. The fish waste generated poses environmental and health hazards because in most cases it is either disposed into pits or discarded onto the open grounds. Both WH and FW are potential substrates for biogas production. However, utilization of FW substrate alone has a limitation of producing a lot of amounts of volatile fatty acids (VFAs) and ammonia. Their accumulation in the digester inhibits substrate digestion. Consequently, as stand-alone it is not suitable for anaerobic digestion (AD). This can be overcome by co-digestion with a substrate like WH which has high carbon to nitrogen (C/N) ratio prior to biodigestion. Experimental variable levels for biogas were substrate ratio (WH:FW, 25–75 g), inoculum concentration (IC, 5–15 g/250 mL), and dilution (85–95 mL). Design-Expert 13 was used for optimization and results analysis. Response surface methodology (RSM) was used to examine the effects of operating parameters and identify optimum values for biogas yield. Optimum values for maximum biogas with the highest methane yield of 68% were found to be WH:FW ratio, 25:75 g, 15 g of IC, and 95 mL for dilution. The yield was 16% and 32% greater than FW and WH mono-digestion, respectively. The biogas yield was expressed as a function of operating variables using a quadratic equation. The model was significant (P < 0.05). All factors had significant linear and quadratic effects on biogas while only the interaction effects of the two factors were significant. The coefficient of determination (R2) of 99.9% confirmed the good fit of the model with experimental variables.
Rwanda's power system security is the most important in optimization of grid frequency to prevent power blackouts caused by load disturbances and power imbalances. To manually stabilize and restore network frequency, a tuned PID (Proportional, Integral, and Derivative) controller was used, but it was inefficient and unreliable. The objective of this article is to develop a system that can be used to balance generation—demand powers during power outages by alleviating grid frequency in load disturbance cascaded events. By balancing power generation and demand, the balanced steady-state approach was proposed and developed to restore and optimize grid frequency to its normal state. This technique used PID-Power System Automatic Stabilization (PID-PSAS) technique based on load frequency control. The load disturbances of ± 20%, ± 10%, and ± 5% of a 250 MW power load were considered. MATLAB/Simulink was utilized to model and simulate the Rwanda power and controller systems. The results showed that the frequency responses of single and two area western and northern grids were reduced to $${13*10}^{-5}$$ 13 ∗ 10 - 5 Hz, $${15*10}^{-6}$$ 15 ∗ 10 - 6 Hz, and 0.251 s for overshoot, steady-state error, and settling time respectively. The proposed control system performance of 99.86% success rate was achieved and compared with the current control techniques of 70.6% performance rate. A stable frequency was observed at any disturbances and more than 300 megawatt losses were mitigated. Finally, the developed control technique rapidly stabilize the frequency and balance the generation-demand powers after 0.251 s. Future works have to focus on 0 Hz of steady state errors using cyber-physical power optimization systems. Article Highlights The steadiness of connected loads and power utility supply Reduction of frequency instability and stead-state values Prevention and mitigation of power blackouts and power interruptions
Fish waste (FW) is biodegradable waste that remains underutilized and causes a problem to the environment since the existing disposal techniques result in health risks and environmental pollution. FW has significant potential for producing biogas that decrease the reliance on fossil fuels because it contains easily biodegradable organic matter. The physicochemical analysis of the fish waste such as moisture content (MC) of 61.78 %, volatile solids (VS) of 93.94 %, total solids (TS) of 38.21 %, ash content (AC) of 0.52%, total organic carbon (TOC) of 54.2%, total kjeldahl nitrogen (TKN) of 9.2% and carbon to nitrogen (C/N) ratio of 5.89 % were considered and analyzed in this research. In addition, the methane potential was determined and obtained using gas detector. The results shown that the methane (CH4) content in fish waste was 50.12 % which was the potential feedstock of fish waste for biogas production. Nevertheless, the VS of fish waste was high which was good for this feedstock to be easily digested as the sign of producing biogas and demonstrates 99.9985% of performance rate. Finally, the FW had a lower C/N ratio compared to other biogas production waste. Future work needs to consider co-digestion with higher C/N ratio feedstocks.
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