Solar Thermophilic Anaerobic Reactor (STAR) for Renewable Energy Production

Liquid and solid cattle manures are major waste streams in Egypt . The main objective of this research was maximising the net energy production from these wastes by using a solar energy heating system. High concentration of ammonia can strongly affect the gross methane production via inhibition of methanogenesis and reduced hydrolysis. The latter is only limited addressed so far in literature and therefore taken as a second objective of this study. To be able to design a solar thermophilic anaerobic reactor (STAR) and its pumping system, the effect of temperature on the rheological properties of liquid cattle manure was measured experimentally. The effect of temperature and temperature fluctuations on the performance of completely stirred tank reactor (CSTR) systems operated at 50 o C and 60 o C treating liquid cattle manure was studied also experimentally. The temperature fluctuations of the reactor content in a STAR system, designed without extra equipment for heating during the night, shown to be in a range, which will not significantly affect the biological activity in the reactor. Simulations were carried out to study the effect of the interaction between different reactor volumes and different insulation materials on the net thermal energy production from the STAR system at Egyptian climatic conditions. Using a flat plate solar collector, with areas equal to the reactor's cross section area, improves the efficiency for large reactors only slightly, while for small reactors a large improvement is achieved. The feasibility of a non-mixed accumulation system (AC) for treatment of solid manure was studied experimentally at 40 and 50 o C and filling time of 60 days using a 10% (V/V) inoculum placed on the reactor bottom. The results showed a distinct stratification of intermediates along the reactor height. Leachate recirculation and distribution of the inoculum with the feed could improve the system performance: higher methane production with less stratification extent. The results of a mechanistic model, describing the biological process in AC system including the dispersion of intermediates and bacteria species between the system layers showed a very well agreement with the experimental data of the methane production. Finally, a design of a STAR for solid cattle wastes was studied in a model. The simulation results show that a minimum reactor temperature of 44.5 during summer and 47.6 during winter could be achieved for a well-insulated reactor with an aspect ratio of 0.6. The effect of different ammonia concentrations on the hydrolysis constant of liquid cattle manure was also studied experimentally at 50 and 60. Negative linear relations between k h and both total and free ammonia concentrations were found at each studied temperature. From a literature review it becomes clear that next to animal manure rice straw is an important waste stream from the Egyptian agriculture. Combined composting of digested manure mixed with rice straw could produce an attractive organic fertiliser. Based on emergy analysis of the system, the STAR concept can be recommended from the sustainability point of view.