Effect of Nutrient Addition during Anaerobic Digestion of Potato Peels ...

Intl' Conf. on Chemical, Integrated Waste Management & Environmental Engineering (ICCIWEE'2014) April 15-16, 2014 Johannesburg

Effect of Nutrient Addition during Anaerobic Digestion of Potato Peels and Maize Husk Ishmael Ramatsa, Noxolo Sibiya, and Roberth Huberts

Through anaerobic digestion, solar energy stored in biomass as a result of the photosynthesis reaction could be released as biogas (Yen & Brune, 2007). This study has been conducted for the purpose of investigating the effect of nutrient addition during biogas production under anaerobic conditions

Abstract--The composition of the substrate and nutrients addition plays a very significant role during the production of the biogas. For this reason this paper tries to evaluate the effect of nutrients addition during biogas production under anaerobic conditions. Potato peels wastes and maize husk were anaerobically digested in a 5 liter scale reactor at mesophilic conditions (32 o C). The characteristics of the potato peels were and maize husk are presented in Table 1. The results obtained indicated that the addition of the nutrients during anaerobic digestion has an influence on the biogas production, meanwhile methane content in biogas varied from 48 to 64%.

II. MATERIALS AND METHODS A. Digester and operating conditions A laboratory scale reactor of total volume of 5 liters was used. The reactor was made of plastic. The effective volume was maintained at 4 liters. The reactor was provided with suitable arrangement for gas collection. Biogas production from the reactor was monitored daily by water displacement method. The waster displaced from the cylinder was equivalent to the volume of gas generated. The digesting temperature was maintained at 32o Celsius

Keywords— Biogas, methane nutrients, potato peels

I. INTRODUCTION

E

NERGY is one of the most important factors to global prosperity. The dependence on fossil fuels as primary energy source has led to global climate change, environmental degradation, and human health problems. In the year 2040, the world predicted will have 9–10 billion people and must be provided with energy and materials (Okkerse & Bekkum, 1999). It is estimated that in terms of primary source used, by 2030, the structure of energy production will be based on: 75-85 % of conventional fuel combustion, 10-20 % of nuclear fission, 3-5 % of waterpower, approx. 3 % of solar and wind energy (Popescu & Mastorakis, 2010). The most common forms of renewable energy are considered the solar, geothermal energy, water, wind and finally the biomass related energy. Some of the most important benefits of using renewable energy are based on the organic composition, lack of fossil driven CO2 emission, does use mainly locally available resources and are solutions for all needs (Popescu & Mastorakis, 2010), covering best and directly the local community.

B. Characterization of wastes The type of organic substrate used for anaerobic digestion has an impact on the biogas production rate and the composition yield of the gas. The composition of the substrate in terms of total solids (TS), fixed solids (FS), volatile solids (VS), pH, C: N ratio, and soluble chemical oxygen demand (CODs) affects the digestion process, Perez et al. 1997. Table1, present characteristics of the feed material.

TABLE1 CHARACTERISTICS OF THE FEED Potato Maize Parameters peels husks VS (%) 87 54 TS (%) 7.1 14 Ash (%) 13 1.03 MC (%) 78 26 pH 6.8 6.5

Ishmael Ramatsa, Department of Chemical Engineering, Faculty of Engineering and the Built Environment, University of Johannesburg, Johannesburg, South Africa: phone 011 559 6724, email: [email protected] or [email protected] Noxolo Sibiya, University of Johannesburg, Johannesburg, South Africa email, [email protected] Roberth Huberts, Department of Chemical Engineering, Faculty of Engineering and the Built Environment, University of Johannesburg, Johannesburg, South Africa, phone: 011 559 6517, email: [email protected].

III. RESULTS AND DISCUSSION A. Biogas production Biogas yield from potato peels was investigated using 0g, 5g and 7g of nutrients ( fertilizer, N:P:K) Fig1. These results 202


demonstrate the significance of adding nutrients to the digester. The potato peels plus 5g fertilizer had the highest biogas yield compare to potato peels with and without nutrients. A total of 180ml of biogas was achieved when using 5g of nutrients in 14 days period. For 7g fertilizer it can be noted that the volume was lower than both 5g and 0g of fertilizer. This shows that biogas yield production is also affected by the amount of the nutrients added. This decrement in biogas could be attributed to the effect of K and P found in fertilizer. Yang et al. (2010) have also reported lower biogas emission on rice plot from applying N+P+K fertilizer compared to that of N-fertilizer plot.

1%yeast was used as nutrient in their study. The methane yield obtained in this study for the control tests (only potato peels) was lower than the one reported by Parawira, et al (2004) where 67% was obtained in seven days. Fig 4 shows the daily biogas production using maize husk as the substrate. In this instance about 200ml of biogas was recorded after five days of digestion, and there after it went down and peaked up again for few days. In Fig 3 more biogas was recorded wen 7g of nutrients was used. Fig 4 shows that high percentage methane composition was detected when 7g of nutrients were added, however on the seventh day methane composition of 5 and 7g were close to each other.

Fig. 3 Biogas yield from maize husks with nutrients addition Fig 1: Biogas yield from potato peels as substrate with addition

nutrients

Fig. 4 Daily cumulative methane production from maize husks with nutrient addition. Fig. 2 Daily cumulative methane production from potato peels with nutrient addition.

IV. CONCLUSION

Fig 2 shows that methane production increasing with time (days) until the end of the seventh day of digestion; however it can be noted that as more nutrients are added in the slurry the more methane is produced. The methane yield from the digesters with, 0g, 5g and 7 g of nutrients were approximately 48%, 58% and 64% respectively. These results are in agreement with what Wang et al (2004), obtained, although 203

The addition of nutrients significantly increased daily biogas production and the percentage composition of methane was also increasing daily. This shows that nutrients are influential during anaerobic digestion. The results also show that there is a maximum amount of nutrients that microorganism can tolerate.


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