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Anaerobic Digestion of Tannery Solid Waste by Mixing with Different Substrates

S. R. Basak
Department of Civil & Environmental Engineering, Shahjalal University of Science & Technology (SUST), Sylhet, Bangladesh

M. A. Rouf
Institute of Fuel Research and Development (IFRD), BCSIR, Dr. Qudrat-I- Khuda Road, Dhanmondi, Dhaka, Bangladesh

M. D. Hossain
Department of Civil Engineering, Bangladesh University of Engineering & Technology (BUET), Dhaka, Bangladesh

M. S. Islam
Institute of Fuel Research and Development (IFRD), BCSIR, Dr. Qudrat-I- Khuda Road, Dhanmondi, Dhaka, Bangladesh

T. Rabeya
Institute of Fuel Research and Development (IFRD), BCSIR, Dr. Qudrat-I- Khuda Road, Dhanmondi, Dhaka, Bangladesh

Abstract/ Executive Summary:

The tannery solid waste (fleshing) was collected from Hazaribagh, Dhaka. It has been found that fleshing contains 82.57% volatile matter. Further characterization of fleshing showed that it contains low C/N ratio of 2.64 and high pH of 10.99. These characteristics were not suitable for using fleshing as a substrate for anaerobic digestion. The study has been carried out in different ratio of waste fleshing, domestic sewage and cow dung at total solid 6% concentration. In all the reactors fleshing and domestic sewage were mixed at 1:1 ratio. On the basis of the performance of the reactors it was evident that the reactor which contains 75% fleshing with domestic sewage and 25% cow dung showed optimum result. Under optimum condition volatile solids destruction 52%, specific gas production 0.476 L/g volatile solids feed and methane yield 73% were achieved.

Keywords: Anaerbic digestion; Tannery solid waste; Biogas

Location: Hazaribagh, Dhaka

Start Date:

End Date:

Program Area: Risk Management in Agriculture

Commodity: Contamination of soil

Objectives:

To estimate the anaerobic digestion of tannery solid waste by mixing with different substrates

Methodology:

Sample Collection: Different types of tannery waste were collected from 3 types of local tannery at different time. The waste was characterized by analyses, with Standard Methods (APHA, 1992). Substrates were collected at different time and stored at 4⁰C, before analysis and other experiments. By examining the present management practices and the characteristics of waste, the fleshing portion of tannery solid waste was chosen as a substrate for biogas generation. Preparation of substrates: The limed fleshing used as substrate was grounded to less than 6 mm diameter using a meat-grinding machine. To this, domestic sewage was added as diluent in different ratio to maintain the fleshing solids in suspension and to achieve the desired level of flowability in the feed mixture. Domestic sewage also act as a source of various microorganisms required for anaerobic digestion. The domestic sewage was collected from different locations of Elephant Road residential area. Cowdung was also used in different proportion as a substrate to maintain the C/N ratio. Sewage and Cowdung were also characterized by Standard Methods (APHA, 1992). Inoculum: Pre-digested material consisting of all the essential microbes (hydrolyzing, fermentative, acetogenic and methanogenic bacterial consortium) was chosen as an inoculum for the study. The inoculum was synthesized in the laboratory using cow dung, limed fleshing and domestic sewage in equal proportions. After cessation of gas production, the pre-digested material was tested for its activity with known quantity of sodium acetate as substrate for gas production, and later the digested residue was used as inoculum for the study. Experimental setup: In order to examine the appropriate technology for the management of solid waste from tanning industry, anaerobic digestion process has been studied using batch reactors. A simple methanogenic activity test procedure was adopted (Jawed and Tare, 1996). A known amount of substrate containing a mixture of waste was transferred into 2 L capacity wide mouth glass bottle. Different quantities of waste materials were mixed and added to the glass bottle to obtain an initial volume of 1 L in all the reactors, R1 to R4. The total gas production was measured using a water displacement method at an interval of 24 h. Contents of the glass bottle were mixed manually, after every gas measurement. Daily gas production was recorded. The entire test was conducted at a temperature of 30 ± 3⁰C for a period of 8 weeks. Analyses Carbon and Nitrogen contents of the fleshing, domestic sewage were determined by C-H-N elemental analyzer (Thermo Fischer Scientific, FLASH-2000) with TCD detector. Helium gas was used as carrier gas at 250 kpa and 140 mL/m, furnace and oven temperature were 900⁰C and 65⁰C respectively. Its moisture and ash contents were estimated by gravimetric methods by drying at 105⁰C and by complete combustion at 800⁰C respectively. The protein content was estimated from the nitrogen content by multiplying with 6.25. Total solids (TS), VS, and VFA were estimated according to the procedures recommended in the standard methods for examination of water and waste water (APHA, 1992). Assay bottles were periodically analyzed for the above-mentioned parameters for a period of 8 weeks. Gas production from the reactors was monitored by means of water displacement method on daily basis. The volume of water displaced from the bottle was equivalent to the volume of gas generated at the temperature and pressure that prevailed during the study period. Gas chromatograph (Thermo Fischer Scientific, Trace GC Ultra) with TCD detector was used to measure methane content and carbon dioxide in the biogas composition. Helium gas was used as carrier gas at 900 kpa and 10.5 mL/m, oven and detector temperature were 80⁰C and 180⁰C respectively.

Source of Information: Bangladesh J. Sci. Ind. Res. 49(2), 119-124, 2014

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The present practices of disposal of tannery waste are not environmentally friendly and cause great concern for Dhaka City. The solid waste fleshing contains about 82% VS which are amenable to biodegradation. The C/N ratio of fleshing is too low and alone is not suitable for biodegradation but mixing with other substrates with fleshing the generation of biogas is very satisfactory. The composition of reactor R2 gives the best performance for specific gas production, reduction of COD and VS reduction. In addition to this the mixing of other substrate improves the environmental condition of the biogas reactor for better anaerobic digestion. The methane content of biogas from the substrate is very satisfactory. The fleshing waste can be used as a complementary substrate part of small scale biogas plants. Use of fleshing will also reduce the cow dung requirement in a biogas plant which is also an important point, because very often cow dung scarcity turns off the biogas plants. The generation of biogas from the substrate is environmentally friendly, hygienic and it will reduce pollution.

Knowledge Management: Journal