• Energy Research

This study aims to enhance the performance of a low-buffered anaerobic co-digestion of food waste and sewage sludge using an alkaline-based additive (waste seashell). Eighteen lab-scaled reactors were performed to evaluate the synergistic effects of waste seashell on methane production at different organic load. The addition of waste seashell showed significant synergistic effects with organic load on the anaerobic co-digestion performance in reducing the inhibitory level of volatile fatty acids and ammonia by (i) increasing buffer capacity of the systems, (ii) providing various slats, and (iii) changing the methanogenic pathway for achieving higher methane production yield. The addition of waste seashell with the concentration of 8 g/L, 20 g/L, and 26 g/L declined the propionic accumulation by 55%, 54%, and 49%, respectively, compared to their peer reactor at the same organic load. The utilization of waste seashell at 26 g/L increased the methane yield up to 219 mLCH4/gVS at an organic load of 15.6 gVS/L, represented 6.44, and 7.8-times higher methane yield and organic load increment, respectively, than that of conventional anaerobic co-digestion. However, at further increase of waste seashell and organic load, the anaerobic co-digestion showed low methane generation of 89.3 mL CH4/gVS due to the inhibitory impacts of calcium concentration on the biological process.

The opportunities and challenges of applying micronutrients (MiNs) in full-scale anaerobic digestion (AD) plants has been reviewed. The review discusses the underlying mechanisms and the role of different micronutrients (Fe, Ni, Co, Mo, Zn, Cu, Se) in the enhancement of AD performance, as well as their environmental and economic implications in full-scale AD systems. Bioavailability is a key factor affecting the effectiveness of micronutrients application on the biochemical aspects of AD. Accordingly, the technical aspects of AD with a direct impact on bioavailability have been identified and critically addressed. Mono-supplementation is not the most favorable strategy to increase micronutrient bioavailability due to limited solubility, formation of insoluble compounds, interaction with other compounds, and specific microbial requirements. Nonetheless, co-supplementation can increase the bioavailability due to the simultaneous synergetic effects of co-micronutrients supplementation on the biochemical aspects of AD. However, the inconsistency of reported lab-scale results and the lack of protocols or guidelines for analyzing the bioavailability of micronutrients limit results interpretation and full-scale application. The environmental and economic implications of these micronutrients are other critical factors that need further research. The economic results showed that the mono-supplementation can be economically favorable when a methane enhancement of 20% is achieved. Co-supplementation of micronutrients is the most economically feasible option since this strategy allows reducing the total dosage of micronutrients when compared with mono-supplementation. The authors are grateful for the scholarship from the TUM SEED Center of the Technical University of Munich, which is part of the DAAD (German Academic Exchange Service) program “exceed” supported by DAAD as well as the German Federal Ministry for Economic Cooperation and Development (BMZ) and in cooperation with the hosting Chair of Urban Water System Engineering of TUM. Sergi Astals is thankful to the Spanish Ministry of Science, Innovation and Universities for his Ramon y Cajal. Peer Reviewed