Performance analysis of two stage baffled anaerobic digester
Description
Data of the research conducted to analyse performance of newly designed two-stage anaerobic baffled digester comprising of analysis of substrate, analysis of digestate, biogas production during different seasons and composition of raw biogas. The values obtained were statistically analysed using Independent t-test and General Linear Model (GLM) using SPSS version 24 ® software.
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Materials and methods Two, circular fibre glass digesters of 204 cm in diameter and 100 cm in height, having a total capacity of 3000 l each were fabricated. The Single Stage Digester (SSD) had a single compartment and all the biological reactions (hydrolysis, acidogenesis, acetogenesis and methanogenesis) occurred within the same chamber. In the TS-ABD, the whole digester was divided into two halves with an opening at a particular height to optimise the flow and maximum control over the bacterial communities living within the digesters. Each chamber was again provided with vertical baffles which restrict the movement of digesta through it, at the same time increasing the surface area. The first chamber was the acidogenic chamber and the second chamber was methanogenic chamber where methanogenesis occured. The pH of methanogenic chamber of TS-ABD was maintained at 8.5 by adding sodium bicarbonate Both the digesters had a water jacket surrounding them in which hot water produced from solar energy could be circulated to optimise the digester temperature. Substrate and inocula The kitchen waste obtained from the college canteen was finely ground and homogenised with a grinder to a size less than 7 mm mixed with tap water. The finely blended kitchen waste was thoroughly mixed in 1:1 ratio with cow dung, using a mixer. The rumen liquor was collected from the nearby abattoirs to be used as inoculum. The study was carried out at the Kerala Veterinary and Animal Sciences University, Pookode, Wayanad from June 2019 to May 2020. Initially the SSD and acidic chamber of TS-ABD were filled with rumen liquor while; the alkaline chamber of TS-ABD was only filled with cow dung. After seven days of filling the digester, both SSD and TS-ABD were daily fed with substrates. During summer and winter seasons, the digester temperature was recorded. During monsoon season, the digester was heated by circulating the hot water produced by solar water heater through water jacket around the digester to optimise the digester temperature in the range of 35-37 ºC Analysis and calculations The substrates before loading and the digestate from outlet of the digesters were collected once in a week to analyse, the Total Solids (TS) and Volatile Solids (VS) according to standard methods as per AOAC (2016). Nitrogen (N) by Kjeldahl’s method and Carbon (C) by Walkley and Black method. The temperature and pH of substrate and digestate was recorded using Digital EUROLAB ST926B multi-thermometer and Eutech digital pH tutor instrument, respectively. The amount of the biogas produced per day was recorded using biogas flow meter (CLESSE CGS-4). The composition of the raw biogas obtained was weekly analysed using a biogas analyser (Model No. L-314 Precision Scientific). The values obtained were statistically analysed using Independent t-test and General Linear Model (GLM) using SPSS version 24 ® software.