Optimisation of small scale anaerobic digestion technology

The recent advances in anaerobic digestion (AD) technology and changes in government policies have contributed to the gradual increase in the establishment of on-site smallscale anaerobic digesters in developed regions, particularly in Europe. However, these advances have not completely eradicated some of the challenges with operating AD system. The project is aimed at investigating the potential of optimizing small-scale AD through high solid digestion (HSAD) and reduction of substrate induced inhibition (SII). The study of different inocula, changes to environmental conditions, adsorption of inhibitors and reactor modification was explored. To investigate these possibilities, an onsite mono-substrate such as citrus fruit waste (CFW) with an average dry matter of 16% was used as the substrate, biochar material (rice husk, coconut shell and wood biochar) were used as adsorbent while an operating temperature from 35 - 55 ⁰C were also investigated. Limonene is an inhibitory compound and a constituent of CFW, this was used as the inhibitor, a compartmentalized anaerobic reactor (CAR) was designed to improve HSAD while selected inocula from digested sewage sludge, compost and landfill leachate and their mixture were used as an inoculant. In the first study, the acclimation rate of different inocula to increasing concentration of limonene compound was investigated and the mixed inocula recorded the highest recovery rate and methane yield with a value of 544 ± 21 ml CH4. The mixed inocula benefited from the synergistic effect of using a broader microbial community to mitigate limonene inhibition. This was followed up with the biochar study on AD of CFW and the result showed that microbial lag phase reduced by 50% which was attributed to sorption of limonene compound and biofilm formation on the biochar material. The study on AD of CFW at a different operating temperature of 35-55 ⁰C showed that the higher temperature of 45 and 55 ⁰C outperformed the other incubation with no detectable microbial lag phase. Finally, the optimization option for HSAD was investigated using a CAR and compared against the conventional continuous stirred tank reactor and a 34%, 43.3%, 48.5% and 79.9% higher cumulative methane production for organic loading rates of 1.42, 2.85, 4.00 and 5.00 gVSL-1 day -1 , respectively was achieved. This performance was attributed to the lower compartment of the CAR which facilitated leachate treatment and distribution. The result showed that limonene a constituent of CFW and an example of SII can be counteracted by (i) inoculating with a mixture of inocula (ii) addition of biochar (iii) operation at high temperature of 45 and 55 ⁰C and (iv) the single stage compartmentalized reactor improved HSAD and reduced limonene suppression

The Impact of Enhanced and Non-Enhanced Biochars on the Catabolism of 14C-Phenanthrene in Soil

Biochar is a by-product from the pyrolysis of biomass and has a great potential in soil amendment due to its carbon and nutrient-rich properties. The aim of this study was to investigate the impact of increasing amounts (0, 0.01, 0.1, 0.2, 0.5 and 1.0%) of two types of biochar (so-called enhanced and non-enhanced) to soil on the biodegradation of 14C-phenanthrene. Enhanced biochar contains inoculants which are designed to potentially stimulate microbial activity and promote biological function in soil. After 100 d of incubation, the addition of 0.5% and 1% enhanced (EbioC) and non-enhanced biochars (NEbioC) led to longer lag phases, reduced rates and extents of 14C-phenanthrene in amended soil. However, in soils amended with 0.01%, 0.1% and 0.2% amendments, extents of mineralisation of 14C-phenanthrene increased and were found to be higher in the EBioC- as compared to the NEbioC-amended soils. Increasing soil-phenanthrene contact time also increased 14C-phenanthrene mineralisation in soil which had received smaller amounts of EBioC. Application of both EbioC and NEbioC also enriched the soil microbial populations during the incubation. However, it was found that phenanthrene-degrading microbial populations declined as soil contact time increased; this was particularly true for soils receiving larger amounts of due to reduction in the mobile/bioaccessible fraction of the phenanthrene in soil. The findings revealed the importance of the type and amount of biochar that may be added to soil to stimulate or enhance organic contaminant biodegradation

The challenges of anaerobic digestion and the role of biochar in optimizing anaerobic digestion

Biochar, like most other adsorbents, is a carbonaceous material, which is formed from the combustion of plant materials, in low-zero oxygen conditions and results in a material, which has the capacity to sorb chemicals onto its surfaces. Currently, research is being carried out to investigate the relevance of biochar in improving the soil ecosystem, digestate quality and most recently the anaerobic digestion process. Anaerobic digestion (AD) of organic substrates provides both a sustainable source of energy and a digestate with the potential to enhance plant growth and soil health. In order to ensure that these benefits are realised, the anaerobic digestion system must be optimized for process stability and high nutrient retention capacity in the digestate produced. Substrate-induced inhibition is a major issue, which can disrupt the stable functioning of the AD system reducing microbial breakdown of the organic waste and formation of methane, which in turn reduces energy output. Likewise, the spreading of digestate on land can often result in nutrient loss, surface runoff and leaching. This review will examine substrate inhibition and their impact on anaerobic digestion, nutrient leaching and their environmental implications, the properties and functionality of biochar material in counteracting these challenges

Renewable hydrogen anaerobic fermentation technology: problems and potentials

Hydrogen technology is essential to the decarbonisation of global economies because it addresses the variability and storage limitation of renewable energy. Several research literatures on hydrogen technology have focused on energy systems with minimum attention given to other fossil fuel driven sectors such as chemical and material production. For effective decarbonisation, the application of hydrogen in global economies must extend beyond the use of energy systems. Renewable hydrogen anaerobic fermentation is a suitable technology for converting the hydrogen substrate into gaseous fuel and precursors for material and green chemical production. The technology leverages on the well-established anaerobic digestion (AD) technology and can be selectively operated for a specific product. Although there are some problems associated with renewable hydrogen anaerobic fermentation, studies show different technological advancements in mitigating these challenges. This review focuses on the technological breakthroughs and limitations associated with renewable hydrogen anaerobic fermentation and provides insights on other products that could be derived from it, especially for a circular economy and the emerging market of green chemicals, sustainable agriculture, and bio-based product development.N/

The effect of substrate to inoculum ratios on the anaerobic digestion of human faecal material

The anaerobic digestion (AD) of human faecal material (HFM) was investigated to consider the effect different substrate to inoculum ratios (SIR) from 0.5 to 4on the rate and extent of methane production as well as impact on pathogen numbers. The AD process was monitored by measuring pH, total volatile fatty acid, bicarbonate alkalinity, ammonium and methane production. The results showed that the highest amounts of methane production with a value of 254.4 ±12.6 ml CH4gV S−1added and highest pathogen removal with a value of 2.7×104±40 and 2.5×103±0.5 CFU/ml, respectively, for E.coli and faecal coliform bacteria was achieved by the 0.5 SIR incubation. However, the highest organic loading found in the 4.0SIR incubation showed the lowest methane yield with a value of110 ±1.3 ml CH4gV S−1added and the lowest pathogen removal with a value of 3.2×105±19 and 3.2×104±3.5 CFU/ml, respectively for E.coli and faecal coliform bacteria. The empirical equation was used to calculate the theoretical methane and compare this with the actual values of methane production. The relatively high methane conversion efficiency between theoretical and actual values for 0.5 SIR, further suggest that this operational condition was the most effective