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Effective utilization of tapioca fiber wastes to improve methane production.

Introduction

Tapioca is a crop of great economic importance that serves as human food, animal feed and raw material for industrial products [1]. Sago is a product, prepared from the milk of "Tapioca Root" and the botanical name is Manihot Esculenta Crantz Syn.Utilissima. Methane to markets partnership reports that Tapioca is mainly cultivated in south Indian states such as Kerala, Andhra-Pradesh & Tamil Nadu [1]. The total cultivation area is nearly 3 lakh hectares, with production of 58 to 68 lakh tons of tubers. Tamil Nadu ranks second, in cultivation and production of tapioca, after Kerala, but, stands first in processing of Tapioca into Sago. This caters to approximately 80% of India's demand for Sago. Nearly 800 Sago processing units, which are located in the Salem district, use 3 [m.sup.3] of wastewater, to process one ton of tuber. This causes high amount of effluents and treatment of these to meet the envirnmental regulations of the Pollution Control Board [2]. Various anaerobic technologies, such as conventional anaerobic treatment and high rate anaerobic treatment using anaerobic filter and fluidized bed, have been used to treat Sago wastewater. However, Methane production form sago effluent offers an effective method to produce alternative energy.

Studies using fluidized bed reactor to reduce effluent concentrations showed limitations due to biofilm formation and their attachment to the carriers demonstrates Biological Oxygen Demand (BOD) removal efficiency of 90% and the methane content was determined to be 80.8% and Organic Loading Rate (OLR) of 10.1-31.1 kg COD [m.sup.-3] [day.sup.-1]. Another study showed, usage of white granite stones as filter medium for the treatment of Sago wastewater, decreased OLR to16 kg COD/[m.sup.3]/[day.sup.-1] and supported methane production [2].

It was reported below OLR of 11.6 kg COD/m3/day, biogas production decreased [3]. The tapered anaerobic fluidized bed reactor (TAFBR) was operated under steady state conditions, over a range of hydraulic retention times (HRT), and OLR of 14.4 kg COD/m3/day in order to evaluate its overall treatment capacity and efficiency [2]. The TAFBR reactor was initially operated with an OLR of 1.0 kg COD/m3/day and HRT of 26.74 hours. The chemical oxygen demand (COD) removal efficiency was shown to be 92% in the reactor and the biogas produced in the digester reached 4.49 m3/m3 of the reactor/day.

In this paper we have utilized cellulose rich, Tapioca fiber waste via anaerobic fermentation--systematic dozing of methanogen rich inoculum, to improve Tapioca fiber processing. We have studied the effectiveness of this method by measuring COD per unit volume and have developed a correlation between the COD content and the quantity of methane produced.

Materials and Methods

The tapioca tuber was processed at SPAC Tapioca Ltd. This involved cleaning freshly harvested tapioca tuber with deionized water, the roots were peeled by abrasion with paddle agitators in the holding tank and washing water was recycled in a counter current process. This was followed by a fine fiber washing using centri sieves. The crude starch slurry is then purified using nozzle centrifuge and hydro cyclones, which reduces fibre levels with minimum of fresh water. The effluent treatment involves, primary clarification using Hybrid Upward Flow Anaerobic Sludge Blanket Reactor (HUASBR), with capacity of 150 kliter. Each HUASBR consists of sensors for flow, pH, pressure, gas tantalizers, temperature, and the plant is controlled by SCADA system. Wastewater from the equalization tank is pumped into five HUASBR, which are connected in parallel.

Consistent dozing of Tapioca fiber residue in to HUASBR. Between 50 to 100 tons of wet fiber cake was fermented with methanogen rich cow dung juice and incubated for 12 to 24 hrs at room temperature. This pre treatment enhances the fiber hydrolysis to favor nutrient availability for methanogens. Tapioca fiber cake is dumped in to successive HUASBR at the rate of 10 tons per day.

Periodic dosage of Methanogen rich inoculum. The inoculum was prepared from cow dung extract. 200 lts capacity process drums were selected, each drum was packed with 50 Kg of the cow dung collected from local animal husbandry and filled with 150 lts of water and mixed with air flow for one hour with no agitation for 36 hrs. The prepared inoculum pH reaches between 5 to 6 and the inoculum is pumped to the five HUASBR. The pH in the HUASBR was maintained within the range of 6.5 to 7.5, with the regular dosing of calcium hydroxide.

Sampling and Analysis. During the operation of the HUASBR, the influent and effluent pH, COD and BOD concentrations, temperature, biogas production rate were monitored daily. The biogas produced was collected in a 20 L water displacement jar filled with 10% NaOH solution. The volume of biogas produced in the reactor was directly measured by the volume salt solution displaced from the gas. All other analytical measurements were performed according to standard methods

Results and Discussion

The routine effluent water capacity was 2150 [m.sup.3] in the anaerobic digester biogas plant and a capacity of 12,000 [meter.sup.3] biogas per day. We identified, 13000 [m.sup.3] of biogas with 60% to 65% of methane can be obtained with ~78 % reduction of COD. With, total solids in the effluent being 6450 kg, total volatile solids being 5800 kg gas potential per day was determined to be 13250 [m.sup.3] in a digester with capacity 2850 [m.sup.3] retained for 32 hrs. The methane biogas produced was found to be 5.49m3/m3. The introduction of periodic dosing of Tapioca fiber residue in to HUASBR and Methanogen rich inoculum resulted 97% reduction of chemical oxygen demand in the reactor and amount of biogas produced in the digester reached ~7.49 m3/m3 of the reactor/day. This indicates an increase of 25% in overall yields of methane.

Conclusions

With systematic and periodic dosing of methanognes rich inoculum enriched, increase in the percentage of methane produced from the tapioca effluents was identified. A systematic approach to convert tapioca-based effluents to methane has been demonstrated to be possible in large-scale plant facilities.

Acknowledgement

We express our thanks for the financial support rendered by Spac Tapioca Products (India) Ltd management and also for providing the necessary infrastructure facilities to carry out this work.

References

[1] http://www.methanetomarketsindia.com

[2] R. Parthiban, P.V.R. Iyer1* and G. Sekaran Anaerobic Tapered Fluidised Bed Reactor for Treatment of Sago Industry Effluent Indian Institute of Chemical Engineers Vol. 50 No. 4 pp. 323-333 (2008).

[3] J. Rajesh Banu,1 Sudalyandi Kaliappan and Dieter Beck Water Qual. Res. J. Canada, Treatment of Sago Wastewater Using Hybrid Anaerobic Reactor 2006 * Volume 41, No. 1, 56-62 (2006).

[4] Saravanane, R., Murthy, D.V.S. and Krishnaiah, K., "Anaerobic Treatment and Biogas Recovery for Sago Wastewater Management Using a Fluidized Bed Reactor", Water Sci. Technol., 44(6), pp. 141-147 (2001).

[5] Perez, M., Romero, L.I. and Sales, D., "Steady State Anaerobic Thermophilic Degradation of Distillery Wastewater in Fluidized Bed Bioreactors", Biotechnol. Progr., 13(1), pp. 33-38 (1997).

[6] Khageshan, P. and Govindan, V.S., "Anaerobic Filter for Treatment of Sago Wastewater", Proceedings of 4th National Symposium on Environment, Chennai, India, pp. 248-252 (1995).

[7] Hickey, R.F., Wu, W.M., Veiga, M.C. and Jones, R., "Start-up, Operation, Monitoring and Control of High-rate Anaerobic Treatment Systems", Water Sci. Technol., 24(8), pp. 207-255 (1991).

[8] Iza, J., "Fluidized Bed Bioreactors for Anaerobic Wastewater Treatment", Water Sci. Technol., 24(8), pp. 109-132 (1991).

Chandramohan Marimuthu *, Jayaramani Manickam, Sriraj Srinivasan, Ramyadevi Thangavelu, Kathiravan Veeramalai and Nandinin Kannarasan

Microcore Research Laboratories India Pvt Ltd., 9th km, 30 Feet Road, 204 A Poondurai Main Road, Checkmadu, Erode-638115, Tamil Nadu, India

* Corresponding Author: mde@microcoreresearch.com
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Article Details
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Author:Marimuthu, Chandramohan; Manickam, Jayaramani; Srinivasan, Sriraj; Thangavelu, Ramyadevi; Veeramalai
Publication:International Journal of Applied Environmental Sciences
Geographic Code:9INDI
Date:Jul 1, 2010
Words:1298
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