The Effect Of Biochar On Biogas Yield From Anaerobic Digestion Of Food Waste And Upgrading Of Biogas

Abstract

It has been shown that, the increase of greenhouse gases come from conversional energy resources, inadequate waste management technologies, deforestation grow rate and decrease of soil fertility are affecting worldwide environment. Therefore, anaerobic digestion technology had been integrated as one of the environmental friendly energy generation technologies and as biological techniques for waste management which use mainly organic materials (animal wastes, agriculture wastes, residential and industrial wastes) as feedstock and generate energy which is known as Biogas and fertilizer with almost zero emission of greenhouse gases. Biogas originates from mechanism of microorganism during the process of bio-degradation of organic materials under anaerobic conditions. However, anaerobic digestion still has some problems like inhibitions which affect its production. The low energy value of Biogas due to the presence of high quantity of carbon dioxide within Biogas and presence of impurities within the raw Biogas have become an obstacle for high energy application uses. There are several technologies of removing carbon dioxide and hydrogen sulphide from Biogas which have been used for many years ago. The focus of this work was to minimize inhibitory problems and maximize the production of anaerobic digester using Biochar as an additive, and upgrade produced raw Biogas using sodium scrubbing and Biochar absorption as carbon dioxide and hydrogen sulphide removal in order to enriching Biogas and enable it for high energy application uses. Biochar is the porous carbonaceous solid produced from the thermochemical conversion of biomass in the absence or limited oxygen environment at a temperature ranging from 350 to 1000oC. Recently, the use of Biochar in anaerobic digestion has been explored. However Biochar is mainly known as soil amendment or used for carbon sequestration. During the experiment, anaerobic digestion of Ethiopian food wastes was conducted and Biochars were added at different concentration(15%; 25%; 50% and 85% based on dry matter of used substrates) as an additive material after being prepared in a laboratory of AAiT. Results has indicated that, the cumulative Biogas production was extremely low and poor in terms of CH4 content where; in the 1st and 2nd experiment cumulative CH4 yield was 2.24ml/g VS from R.Control and 5.77ml/g VS from R025 respectively as the highest production value compared to 415.496ml/g VS of the theoretical cumulative CH4 yield. From the 3rd and 4th experiment where the food waste was co-digested with cow dung (for 1:2 and 1:1 ratio of cow dung to food waste) and Biochar added have produced very low cumulative Biogas and methane yield compared to the theoretical values. Upgrading of raw Biogas by removing CO2 and H2S was conducted and resulted in 81% as the highest CO2 removal efficiency with 18.93% of CH4 the lowest losses. Therefore, the effect of Biochar on anaerobic digestion of used food waste was not clear due to the quality of used food waste which has affected the system efficiency. Besides the upgrading of raw Biogas has not shown the high efficiency for CO2 and H2S removal instead high CH4 losses was presented due to the lack of appropriates equipment for upgrading of Biogas which has become an obstacle to achieve the target percentage of methane in the final product.