Carbon cloth amendment for boosting high-solids anaerobic digestion with percolate recirculation: Spatial patterns of microbial communities.

The addition of conductive materials in anaerobic digestion (AD) is a promising method for boosting biomethane recovery from organic waste. However, conductive additives have rarely been investigated for the high-solids anaerobic digestion (HSAD). Here, the impact of adding carbon cloth in the solid phase of an HSAD system with percolate recirculation was investigated. Furthermore, spatial patterns of microbial communities in suspended biomass, percolate, and carbon cloth attached biofilm were assessed. Carbon cloth increased biomethane yield from source-separated organics (SSO) by 20% more than the unamended control by shortening the lag phase (by 15%) and marginally improving the methanogenesis rate constant (by ∼8%) under a batch operation for 50 days. Microbial community analysis demonstrated higher relative abundances of the archaeal population in the carbon cloth amended reactor than in unamended control (12%-21% vs. 5%-15%). Compared to percolate and suspension, carbon cloth attached microbial community showed higher enrichment of known electroactive Pseudomonas species along with Methanosarcina and Methanobacterium species, indicating the possibility of DIET-based syntrophy among these species.

Comparison of Two Process Schemes Combining Hydrothermal Treatment and Acidogenic Fermentation of Source-Separated Organics.

This study compares the effects of pre- and post-hydrothermal treatment of source- separated organics (SSO) on solubilization of particulate organics and acidogenic fermentation for volatile fatty acids (VFAs) production. The overall COD solubilization and solids removal efficiencies from both schemes were comparable. However, the pre-hydrolysis of SSO followed by acidogenic fermentation resulted in a relatively higher VFA yield of 433 mg/g VSS, which was 18% higher than that of a process scheme with a post-hydrolysis of dewatered solids from the fermentation process. Regarding the composition of VFA, the dominance of acetate and butyrate was comparable in both process schemes, while propionate concentration considerably increased in the process with pre-hydrolysis of SSO. The microbial community results showed that the relative abundance of Firmicutes increased substantially in the fermentation of pretreated SSO, indicating that there might be different metabolic pathways for production of VFAs in fermentation process operated with pre-treated SSO. The possible reason might be that the abundance of soluble organic matters due to pre-hydrolysis might stimulate the growth of more kinetically efficient fermentative bacteria as indicated by the increase in Firmicutes percentage.

Hydrothermal pretreatment of source separated organics for enhanced solubilization and biomethane recovery.

The objective of this research was to evaluate the effect of the hydrothermal pretreatment on the solubilization of source separated organics (SSO) as well as the biomethane recovery through the mesophilic batch anaerobic digestion process. For this purpose, the SSO was subjected to fifteen different pretreatment conditions within five different severity index (SI) values (3, 3.5, 4, 4.5, and 5). The pretreatment temperature, holding time, and pressure ranged from 150 to 240 °C, 5 to 30 min, and 476 to 3367 kPa, respectively. The highest solubilization improvement of ∼50% was achieved under the pretreatment condition of "220 °C-10 min-2323 kPa" corresponding to the SI value of 4.5. However, the maximum biomethane production yield of 280 mL/g TCODadded and biomethane production rate of 30 mL/g TCODadded were obtained under the less intense pretreatment conditions of "190 °C-20 min-1247 kPa" and "170 °C-30 min-786 kPa", respectively.

A systematic approach to evaluate parameter consistency in the inlet stream of source separated biowaste composting facilities: A case study in Colombia.

Biowaste is commonly the largest fraction of municipal solid waste (MSW) in developing countries. Although composting is an effective method to treat source separated biowaste (SSB), there are certain limitations in terms of operation, partly due to insufficient control to the variability of SSB quality, which affects process kinetics and product quality. This study assesses the variability of the SSB physicochemical quality in a composting facility located in a small town of Colombia, in which SSB collection was performed twice a week. Likewise, the influence of the SSB physicochemical variability on the variability of compost parameters was assessed. Parametric and non-parametric tests (i.e. Student's t-test and the Mann-Whitney test) showed no significant differences in the quality parameters of SSB among collection days, and therefore, it was unnecessary to establish specific operation and maintenance regulations for each collection day. Significant variability was found in eight of the twelve quality parameters analyzed in the inlet stream, with corresponding coefficients of variation (CV) higher than 23%. The CVs for the eight parameters analyzed in the final compost (i.e. pH, moisture, total organic carbon, total nitrogen, C/N ratio, total phosphorus, total potassium and ash) ranged from 9.6% to 49.4%, with significant variations in five of those parameters (CV>20%). The above indicate that variability in the inlet stream can affect the variability of the end-product. Results suggest the need to consider variability of the inlet stream in the performance of composting facilities to achieve a compost of consistent quality.