Increasing the loading rate of continuous stirred tank reactor for coffee husk and pulp: Effect of trace elements supplement

Abstract

In this study, the anaerobic performance and stability of coffee husk and pulp with and without trace element (TE) supplement was investigated, using 20 L mesophilic continuous stirred tank reactors for 140 days of experiment (DOE). The TE was cocktail of trace metals composed of Fe, Ni, Zn, Co, Mn, Mo, Se W and B. The organic loading rate (OLR) was increased stepwise from 2.5 (HRT = 40 d) to 6.0 kg VS m−3 d− 1(HRT = 16.7 d). The highest methane productivity from pulp with and without TE was 1.272 and 0.965 m3 m−3 d−1 at an OLR of 6.0 and 5.0 kg VS m−3 d−1; while the husks performed 0.895 and 0.795 m3 m−3 d−1 respectively, both at an OLR of 6.0 kg VS m−3 d−1. The specific methane yield (SMY) of pulp (at OLR = 5 kg VS m−3 d−1) with and without TEs was 217.9 ± 4.7 and 193.1 ± 8.2 L kg−1 VS; while husk yielded 149.2 ± 6.0 and 132.5 ± 4.9 L kg−1 VS, respectively. The effect of TEs on SMY was statistically significant (p < 001) at higher OLRs (5.0 ‐ 6.0 kg VS m−3 d−1). The TEs improved the anaerobic stability through an optimum alkalinity ratio (VFA/TIC < 0.3) and suppressed the accumulation of volatile fatty acids. Mono digestion of husks and pulp are prone to lack Mo, Zn, Ni and Fe in long‐term anaerobic fermentation. Further studies on co‐digestion of husk/pulp with animal manure and dry fermentation helps to efficiently use this biomass resource.

Biogas Potential of Coffee Processing Waste in Ethiopia

“…Fe, which is required in a higher amount than other trace elements, was available 29% in husk and 65% in pulp compared to the minimum requirements. Shortage of trace elements often causes a decline in biogas production due to the loss of a stable digestion process and eventually leads to a lower substrate feeding rate [36][37][38][39]. Full scale anaerobic digestion of coffee by-products thus requires supplementation of trace elements through co-digestion with animal manure or commercial formulas.…”

Novel Intelligent System Based on Automated Machine Learning for Multiobjective Prediction and Early Warning Guidance of Biogas Performance in Industrial-Scale Garage Dry Fermentation

“…46 The optimal alkalinity ratio of the system, VFA/TIC < 0.3, ensures the best stability of AD and reduces the degree of accumulation of VFA. 47 In the percolate of this study, the VFA/TIC values were only 0.08−0.24, so the stability of anaerobic wet fermentation was good. When the TIC content was too high, the VFA/TIC ratio of the system was already in the optimal alkalinity range, so the further increase of TIC had little effect on the AD environment.…”

Digestión Anaerobia De Residuales Sólidos Del Beneficio Húmedo Del Café

“…Esto corrobora el alto contenido de materia orgánica que caracteriza a estos residuales (Pandey et al 2000, Kivaisi 2002, Corro et al 2013, Shemekite et al 2014. Chala et al (2018) reportan que los sólidos volátiles constituyen el 88.3 y el 92.8 % en peso seco de la pulpa y la cáscara de café, respectivamente. Respecto a los inóculos, se observa (Cuadro II) que presentan un contenido de sólidos volátiles en base seca superior al 50 % recomendado para su empleo como fuente de biomasa al sistema (VDI 2006).…”