The effects of microorganism on coffee pulp pretreatment as a source of biogas production

Chemical Engineering Department, Institut Teknologi Sepuluh Nopember, Campus ITS Sukolilo Surabaya 60111, Indonesia

^* Corresponding author: julizainul@gmail.com

Abstract

Coffee pulp waste composition consist of cellulose, hemicellulose, lignin, pectin and caffeine, tannin, and polyphenol as inhibitor substance. The high cellulose compound in coffee pulp can be used for alternative raw materials in the manufacture of biogas. This study aims to define the composition of the mixture of microorganisms of Pseudomonas putida, Trichoderma harzianum, and Aspergillus niger that are best to use in coffee pulp pretreatment to degrade inhibitor substance. The best result of pretreatment will be applied to biogas production. The first step is to do a pretreatment of the coffee pulp with variable Pseudomonas putida : Trichoderma harzianum : Aspergillus niger with a ratio of 1:1:1, 1:2:1, 1:1:2, 1:2:2, 2:1:1, 2:1:2, 2:1:1 (v:v:v), then variables that are most excellent in degrading inhibitor substance are selected. The second step, is doing anaerobic fermentation for 20 days at mesophilic temperature (30-40°C) on a reactor working volume of 4.5 L. In the making of biogas, a varied starter as much as 10% of the total are put into the reactor in the form of a mixture of cow dung : rumen fluid with a ratio of 1:0, 0:1, 1:1, 1:2, 2:1 (w/v). The parameters measured include the decreasing of the inhibitor substance, Chemical Oxygen Demand (COD), biogas (CH₄ and CO₂) and calorific value of combustion (Heating value). This study results a composition of ingredients within the pretreatment process which includes a mixture of microorganisms with a ratio of Pseudomonas putida : Trichoderma harzianum : Aspergillus niger is 1:2:1 (v:v:v). For biogas, a mixture of cow dung and rumen fluid can produce higher methane gas is the ratio of cow dung : rumen fluid is 1:2 (w/v) with the concentration of methane (CH₄) formed at 1.825%. At the concentration of methane is 1.825%, the heating value obtained is 76.032 kcal/kg with volume biogas 0.0032 m³/ kg converted of COD.