Optimization of Reactor Temperature for Continuous Anaerobic Digestion of Cow Manure: Bangladesh Perspective

Effect of an Electromagnetic Field on Anaerobic Digestion: Comparing an Electromagnetic System (ES), a Microbial Electrolysis System (MEC), and a Control with No External Force

This study examined the application of an electromagnetic field to anaerobic digestion by using an electromagnetic system (ES), a microbial electrolysis cell (MEC), and a control with no external force. The experimental work was performed by carrying out biochemical methane potential (BMP) tests using 1 L biodigesters. The bioelectrochemical digesters were supplied with 0.4 V for 30 days at 40 °C. The electromagnetic field of the ES was generated by coiling copper wire to form a solenoid in the BMP system, whereas the MEC consisted of zinc and copper electrodes inside the BMP system. The best performing system was the MEC, with a yield of 292.6 mL CH4/g chemical oxygen demand removed (CODremoved), methane content of 86%, a maximum current density of 23.3 mA/m2, a coulombic efficiency of 110.4%, and an electrical conductivity of 180 µS/cm. Above 75% removal of total suspended solids (TSS), total organic carbon (TOC), phosphate, and ammonia nitrogen (NH3-N) was also recorded. However, a longer exposure (>8 days) to higher magnetic intensity (6.24 mT) on the ES reduced its overall performance. In terms of energy, the MEC produced the greatest annual energy profit (327.0 ZAR/kWh or 23.36 USD/kWh). The application of an electromagnetic field in anaerobic digestion, especially a MEC, has the potential to maximize the methane production and the degradability of the wastewater organic content.

Effects of Seasonal Temperature Variation on Slurry Temperature and Biogas Composition of a Commercial Fixed-Dome Anaerobic Digester Used in Bangladesh

Biogas is produced in Bangladesh mostly through fixed-dome anaerobic digesters, which usually operate without any temperature controller. An experiment was conducted to monitor the seasonal temperature variation inside a fixed-dome type digester and its effect on biogas composition. A commercial-scale digester with a working volume of 350 m3 was used for this study. Three k-type thermocouple sensors were used to monitor the ambient, biogas, and slurry temperatures in real-time. The results showed that the average ambient temperature in the autumn, late autumn, and winter was 29.05, 22.90, and 17.64 °C, respectively. The average slurry temperature in the autumn (30.38 °C) was higher than in the late autumn (29.36 °C) and in the winter (25.76 °C). The highest and lowest slurry temperatures were found to be 31.11 and 24.47 °C, respectively, which indicated that the digester worked within a wide temperature range, establishing both psychrophilic and mesophilic operational conditions. Higher methane concentrations were observed in the autumn than in the late autumn and winter. The CO2 and H2S concentrations were higher in the winter than those of in the autumn and late autumn. The electricity generation in the winter was 47.85% and 45.15% lower than in the autumn and late autumn, respectively.

Kinetic study and optimization of total solids for anaerobic digestion of kitchen waste: Bangladesh perspective

Kitchen waste from hotels and homes is one of the major problems for urban and rural environment and could be one of the best sources of renewable energy by producing biogas through anaerobic digestion. A research work was undertaken to assess the methane potential of kitchen waste at different total solids (TS) content. Kitchen wastes such as spoiled rice, brinjal, potato, papaya, tomato, fish and poultry parts etc., which are easily decomposed, were selected for this study. Batch experiments were set up under ambient temperature. Kitchen waste was added to the batch digester at different TS content (5, 7, 10, 12 and 15%) and sealed for 146 days until the gas production stopped. Substrate characteristics were analyzed before and after the anaerobic digestion. The highest methane yield was 78.12 L/kg VS at 15% TS content followed by 12, 10, 7 and 5%. Different kinetic parameters were determined using a logistic model and the model showed a good fit with the experimental results. After modelling using Minitab^®, the optimum TS content for kitchen waste was found to be 14.90%.

Optimization of the Biomethane Production Process by Anaerobic Digestion of Wheat Straw Using Chemical Pretreatments Coupled with Ultrasonic Disintegration

Biomass is an attractive energy source that can be used for production of heat, power, and transport fuels and when produced and used on a sustainable basis, can make a large contribution to reducing greenhouse gas emissions. Anaerobic digestion (AD) is a suitable technology for reducing organic matter and generating bioenergy in the form of biogas. This study investigated the factors allowing the optimization of the process of biogas production from the digestion of wheat straw (WS). The statistical analysis of the experiments carried out showed that ultrasonic processing plays a fundamental role with the sonication density and solids concentration leading to improved characteristics of WS, reducing particle size, and increasing concentration of soluble chemical oxygen demand. The higher the sonicating power used, the more the waste particles are disrupted. The optimality obtained under mesophilic conditions for WS pretreated with 4% w/w (weight by weight) H2O2 at temperature 36 °C under 10 min of ultrasonication at 24 kHz with a power of 200 W improves the methane yield by 64%.