Comparative Study of Bio-digestion of Cassava Peelings and Efflu-ents from Gari Production in South-East Benin

Thierry Godjo^* and Albert Tchanou ^*Correspondence: Thierry Godjo, Department of Sciences, Engineering and Applied Mathematics, National University of Science Technology Engineering and Mathematics, Abomey, Benin, Email:

Author info »

Introduction

Cassava (Manihot esculenta Crantz) is one of the important sources of energy in the diet of tropical regions. It is one of the main starchy root and tuber crops grown in the world [1]. Africa is the world's leading producer of cassava with a production of more than 145 million tons in 2011 [2], almost all of which is used as a subsistence crop par excellence and is devoted to feeding the population. In Benin, cassava is one of the most important crops, with production estimated at over 3.6 million tons in 2011 [2]. The processing of this crop generates large quantities of waste. This waste is mainly peelings. Benin is one of the 20 main cassava consuming countries in the world with 1.6 million tons used in human food [3]. The waste from the processing of cassava (into gari, tapioca, Lafu in Benin) is essentially the peelings and the effluents from the pressing of the pulp. The processing of one ton of cassava generates 275 kg of cassava peelings. These peels are energetic and can be used to produce gas and biochar [4]. With a calorific value of 18 MJ/kg [5], the energy that can be generated from this biomass is approximately 32,400 MJ per year. Paradoxically, the actors of this sector are often confronted with difficulties of access to energy. The effluents are rich in organic matter [6] and very toxic due to the high cyanide content [7]. Cassava peelings and effluents are waste that is mostly dumped near urban areas, poured into the streets and constitute large piles of garbage that are often burned, cluttering up households and constituting a real problem for the environment and the health of the population. But what to do with this waste that pollutes the environment? To answer this question, we conducted a compara-tive study of bio-digestion of cassava peelings and effluent in the laboratory.

Materials and Methods

The biomasses used in this study are cassava peelings, effluents from cassava pressing and cow dung. Cassava peels and effluents were collected from the "Massavo" group in the commune of Ifangni in southern Benin. Cow dung was collected at the slaughterhouse of the Songhai Center in Porto-Novo, Benin. The bib-liographic research made it possible to collect the results of immediate analysis of the biomasses used (Table 1) [5,7,8].

Table 1: Physicochemical parameters of the biomasses used.

The setup is composed of six treatments and a control treatment. Each treatment is composed of a substrate of 800g. The first treatment (T1) is composed of 400 g of crushed cassava peels and 400 g of water. The 2^nd treatment (T2) is composed of 300 g of peels, 100 g of cow dung and 400 g of water. The 3^rd treatment (T3) consists of 200 g peelings, 200 g cow dung and 400 g water. The 4^th treatment (T4) is composed of 400 g of effluent and 400 g of water. The 5^th treatment (T5) is composed of 300 g of effluent, 100 g of cow dung and 400 g of water. The 6^th treatment (T6) is composed of 200 g of effluent, 200 g of cow dung and 400 g of water. A control device composed of 400 g of cow dung and 400 g of water was retained (T0).

Results and Discussion

Figure 1 shows the kinetics of biogas production. The maximum biogas productions of treatments T0, T1, T2, T3, T4, T5 and T6 are respectively around 100 ml at day 25, 50 ml at day 33, 55 ml at day 31, 75 ml at day 29, 75 ml at day 27, 80 ml at day 27 and 110 ml at day 21. Biogas production for treatment T1 (100% cassava peel) was nil until day 17 with an appearance on day 19 for a volume of 40 ml.

Figure 1: Daily Production of biogas.

The gas volume went through descending and ascending phases. The peak was observed on day 33 with a volume of 50 ml. From the point of view of cumulative volume (Figure 2), this treatment produced the lowest volume of biogas (270 ml) over the whole period of operation.

Figure 2: Cumulative volume of biogas.

The T2 treatment (75% peel +25% cow dung) also had a late production of biogas until the 13^th day with an appearance on the 15^th for a volume of 35 ml. As the previous one, the volume of gas knew descending and ascending phases. The peak was observed on the 31^st day with a volume of 55 ml. Concerning the T3 treatment (50% peelings +50% cow dung), the gas production occurred on the 11th day of operation with a volume of 60 ml. The volume of gas produced reached a peak of 75 ml on the 29^th day. Treatment T4 (100% cassava effluent) produced 40 ml of gas on the 5^th day of operation. Gas production in this treatment, like the others, went through ascending and descending phases. The peak was observed on the 27^th day with a volume of 75 ml. For treatment T5 (75% cassava effluent +25% cow dung), gas production was observed from day 3. The maximum volume (80 ml) of gas was observed on the 27^th day. For treatment T6 (50% cassava effluent +50% cow dung), gas production (50 ml) was recorded from the 3^rd day of its launch. The peak of this gas production was reached on the 21^st day with the highest gas volume value of 110 ml. As for the T0 treatment (100% cow dung), the gas production (100 ml) was recorded from the 3^rd day of its launching. The peak occurred on the 25^th day with a volume of 100 ml of gas.

An analysis of the results of the cumulative volumes of biogas production shows globally that the higher the percentage of cow dung addition, the higher the cumulative volume of biogas production. This is the case for treatments T0 (100% cow dung) which produced more biogas (937 ml) over the whole operating period, T6 (50% effluent +50% cow dung) which produced 785 ml and T3 (50% peel +50% cow dung) which produced 520 ml. Treatment T4 (100% effluent) produced 560 ml of cumulative biogas. Descriptive statistics of biogas volume produced by treatment

Table 2 shows the descriptive statistics of biogas obtained per biomass. It shows that 23 observations were made per treatment. Then, it is observed that the averages of biogas volume of treatments T0, T1, T3, T4, T5, and T6 are respectively 40.74 ml on the 25^th day, 11.74 ml on the 33^rd day, 13.48 ml on the 31^st day, 22.61 ml on the 29^th day, 24.35 ml on the 27^th day, 23.04 ml on the 27^th day and 34.13 ml on the 21^st day. From the results in this table, it can be stated that the volume of biogas obtained with the control treatment T0 is the highest. However, these results do not allow us to say whether there is a statistically significant relationship between the volumes of biogas obtained from the different biomasses considered. For this purpose, we had carried out an analysis of variance whose results are pre-sented in Table 3.

Table 2: Descriptive statistics of biogas volume produced per treatment.

In Table 3, we see that the test of homogeneity of variances (P=1.1592E-05) is not significant (>0.0005). We must therefore conclude that the differences in biogas volumes of the treatments are not significant.

Table 3: Analysis of variance (ANOVA).

Conclusion

In this work, we compared the bio-digestion of cassava peelings and effluents mixed with cow dung. This study showed that biogas production from co-digestion of effluent waste mixed with cow dung is more efficient than that from co-digestion of cassava peel waste mixed with cow dung.

During this study, we were able to determine the optimal conditions of bio-digestion of the bio-masses used. Also, the study indicated that the higher the percentage of cow dung addition, the higher the cumulative volume of biogas production. Finally, the analysis of variance showed that the differences in variances of biogas volumes between treatments were not significant.

Acknowledgements

The authors would like to thank the famers of cassava processing into gari of the Massavo ifangni cooperative in the South-East of Benin.

References

1. Alston J M, Beddow J M, Pardey P G. Agricultural research, productivity, and food prices in the long run. Science. 2009, 325(5945): 1209-1210.

   [Crossref] [Google Scholar]

2. Sanni L O, Onadipe O O, Ilona P, et al. Successes and challenges of cassava enterprises in West Africa: A case study of Nigeria, Benin and Sierra Leone. IITA. 2009. [Crossref]

   [Google Scholar]

3. Agbor Egbe T, Brauman A, Griffon D, et al. Transformation alimentaire du manioc. Colloques Séminaires CIRAD CTA, 1995.

   [Crossref] [Google Scholar]

4. Gurevich Messina L I, Bonelli P R, Cukierman A L. Potential uses of cassava bagasse for bioenergy generation by pyrolysis and copyrolysis with a lignocellulosic waste. Handbook on Cassava: Production, Potential Uses and Recent Advances. 2017, 335-356.

   [Crossref] [Google Scholar]

5. Godjo, T Lanmantchion, Design and performance evaluation of a Pyrolysis Reactor for vegetable biomass conversion to usable energy. Int curr eng technol. 2016, 6(5): 1865-68.

   [Crossref] [Google Scholar]

6. Ubalua AO, Cassava wastes: Treatment options and value addition alternatives. Afr J Biotechnol. 2007, 18(6): 2065-2073.

   [Crossref] [Google Scholar]

7. Kpata-Konan, N, Konan K, Kouame Kouame M, et al. Optimisation de la biométhanisation des effluents de manioc issus de la filière de fabrication de l’attiéké (semoule de manioc). Int j biol chem sci. 2012, 5(6).

   [Crossref] [Google Scholar]

8. Ognalaga M, M’Akoué DM, Mve SDM, et al. Effet de la bouse de vaches, du NPK 15 15 15 et de l’urée à 46% sur la croissance et la production du manioc (Manihot esculenta Crantz var 0018) au Sud-Est du Gabon (Franceville). J Anim Plant Sci. 2017, 31(3): 5063-5073.

   [Crossref][Google Scholar]