Assessment of different pre-treatment methods for the removal of limonene in citrus waste and their effect on methane potential and methane production rate

The objective of this study was to assess the limonene removal efficiency of three pre-treatment methods when applied to citrus waste and to evaluate their effects on the biochemical methane potential (BMP) and the methane production rate (MPR) using batch anaerobic testsPostprint (published version

Enhancement of microalgae anaerobic digestion by thermo-alkaline pretreatment with lime (CaO)

The aim of this study was to evaluate for the first time the effect of a thermo-alkaline pretreatment with lime (CaO) on microalgae anaerobic digestion. The pretreatment was carried out by adding different CaO doses (4 and 10%) at different temperatures (room temperature (25 °C), 55 and 72 °C). The exposure time was 4 days for pretreatments at 25 °C, and 24 h for pretreatments at 55 and 72 °C. Following, a biochemical methane potential test was conducted with pretreated and untreated microalgae. According to the results, the pretreatment enhanced proteins solubilisation by 32.4% and carbohydrates solubilisation by 31.4% with the highest lime dose and temperature (10% CaO and 72 °C). Furthermore, anaerobic digestion kinetics were improved in all cases (from 0.08 to 0.14 day- 1 for untreated and pretreated microalgae, respectively). The maximum biochemical methane potential increase (25%) was achieved with 10% CaO at 72 °C, in accordance with the highest biomass solubilisation. Thus, lime pretreatment appears as a potential strategy to improve microalgae anaerobic digestion.Peer ReviewedPostprint (author's final draft

Inoculum selection influences the biochemical methane potential of agro-industrial substrates

Obtaining a reliable estimation of the methane potential of organic waste streams in anaerobic digestion, for which a biochemical methane potential (BMP) test is often used, is of high importance. Standardization of this BMP test is required to ensure inter-laboratory repeatability and accuracy of the BMP results. Therefore, guidelines were set out; yet, these do not provide sufficient information concerning origin of and the microbial community in the test inoculum. Here, the specific contribution of the methanogenic community on the BMP test results was evaluated. The biomethane potential of four different substrates (molasses, bio-refinery waste, liquid manure and high-rate activated sludge) was determined by means of four different inocula from full-scale anaerobic digestion plants. A significant effect of the selected inoculum on the BMP result was observed for two out of four substrates. This inoculum effect could be attributed to the abundance of methanogens and a potential inhibiting effect in the inoculum itself, demonstrating the importance of inoculum selection for BMP testing. We recommend the application of granular sludge as an inoculum, because of its higher methanogenic abundance and activity, and protection from bulk solutions, compared with other inocula

Polyhydroxyalkanoates in waste activated sludge enhances anaerobic methane production through improving biochemical methane potential instead of hydrolysis rate.

Anaerobic sludge digestion is the main technology for sludge reduction and stabilization prior to sludge disposal. Nevertheless, methane production from anaerobic digestion of waste activated sludge (WAS) is often restricted by the poor biochemical methane potential and slow hydrolysis rate of WAS. This work systematically investigated the effect of PHA levels of WAS on anaerobic methane production, using both experimental and mathematical modeling approaches. Biochemical methane potential tests showed that methane production increased with increased PHA levels in WAS. Model-based analysis suggested that the PHA-based method enhanced methane production by improving biochemical methane potential of WAS, with the highest enhancement being around 40% (from 192 to 274 L CH4/kg VS added; VS: volatile solid) when the PHA levels increased from 21 to 143 mg/g VS. In contrast, the hydrolysis rate (approximately 0.10 d(-1)) was not significantly affected by the PHA levels. Economic analysis suggested that the PHA-based method could save $1.2/PE/y (PE: population equivalent) in a typical wastewater treatment plant (WWTP). The PHA-based method can be easily integrated into the current WWTP to enhance methane production, thereby providing a strong support to the on-going paradigm shift in wastewater management from pollutant removal to resource recovery

Power and limitations of biochemical methane potential (BMP) tests

As energy systems transition toward renewable sources, anaerobic digestion (AD), which can be used to recover energy from organic substrates, is receiving growing attention. AD research and practice both rely on biochemical methane potential (BMP) tests to determine the methane potential of sewage sludge, energy crops and organic wastes (Pearse et al., 2018). In contrast to continuous reactor experiments, BMP tests are batch, and can be conducted without a major investment of equipment, labor and time. However, this and other differences limit the applicability of results from a BMP test to full-scale plant operation. Yet even in the peer-reviewed literature, BMP test results are not always used appropriately. An example is the determination of synergistic or antagonistic effects during anaerobic co-digestion in substrate mixtures. A BMP test is a powerful and useful tool, but it is important to recognize the type of questions that can and cannot be answered with this experimental setup. Clarification of these issues is the objective of the present contribution

Biochemical methane potential of OFMSW for City of Johannesburg

Abstract: The accumulation of Organic Fraction of Municipal Solid Waste (OFMSW) in landfills not only pose threat to the environment, it may also lead to potential health hazards. Anaerobic digestion stands a very good chance to mitigate this waste accumulation in landfills and has potential to create green jobs. BMP has been widely studied in anaerobic digestion for the production of sustainable energy. Bioprocess control Automatic Methane Potential Test System (AMPTS) II machine was used to set up the assays and run the tests. OFMSW was observed to have a low pH which affects the production process and biogas yield. Buffer solutions that were used in this study were calcium carbonate (CaCO3) and sodium hydroxide (NaOH). It was observed that CaCO3 not only stabilizes the pH but it also gives nutrients to the microbes and thus results in higher biogas yields. Inoculation also helped in stabilizing the process and improved the yield. The digester with CaCO3 resulted in a higher methane yield than the others. Though CaCO3 gave good results its use was discontinued as it has a negative impact on the environment. The BMP of OFMSW was found to be 200 ml CH4 / g VS. The methane content was found to be on average 58%

Biogas production from anaerobic digestion of fruit and vegetable waste from Johannesburg market

Abstract: Biogas production from anaerobic digestion is a promising technology for sustainable energy development. Biochemical methane potential (BMP) tests are normally run to determine the possible methane that can be obtained from each biomass. The aim of this study is to determine the biochemical potential of fruits and vegetable wastes from the Johannesburg market. The biochemical methane potential tests were carried out using the bioprocess control Automatic Methane Potential Test System (AMPTS) II machine. The initial pH of the feedstock was low during the preparation of the feed since fruits and vegetable waste (FVW) are acidic and thus buffer solutions were used to increase the pH to 6.5-7.5. The BMP for the FVW was determined to be on average 300 ml CH4 /g VS added with methane content between 50-60 % volume

Assessment of anaerobic co-digestion of food waste and wastewater solids for sustainable waste management in Yosemite National Park, USA

The growing need for sustainable municipal solid waste treatment and energy production has driven the development of new waste management methods like co-digestion. Anaerobic co-digestion of food waste (FW) and wastewater solids (WWS) has been implemented at a few wastewater treatments plants to efficiently treat organic wastes and produce methane-rich biogas as an energy source. Yosemite National Park has an opportunity to design a new co-digestion facility with an upcoming upgrade to their local wastewater treatment plant in El Portal, California. The Park annually produces approximately 5 million tons of primary WWS and 1 million tons of FW waste, with a volatile solid ratio of 70:30 FW to WWS, or 70% FW. Diverted FW is currently sent to the Mariposa County landfill’s compost facility. To measure the possible increase in biogas production associated with FW addition to WWS, a biochemical methane potential (BMP) test was done over 35 days under mesophilic conditions with treatment mixing ratios ranging from 0% to 100% FW on a volatile solids basis. Calculated annual methane production increased 3.25 times from 0% FW scenario (WWS only) versus a 70% FW scenario, translating to a potential increase in methane production at the wastewater treatment plant of 28,000 to 91,000 m3/yr. Results showed that if the wastewater treatment plant also implemented combined heat and power to combust the increased biogas from 70% FW co-digestion, potentially 920,000 kWh/yr could be produced to cover all electricity and heating needs. This research demonstrates that Yosemite National Park could combine FW and WWS to sustainably manage their organic waste in line with their Zero Landfill Initiative, as well as produce enough energy to fully power the El Portal wastewater treatment plant

Influence of a Conductive Material and Different Anaerobic Inocula on Biochemical Methane Potential of Substrates from Alcoholic Beverage Production

The impact of a conductive material as powdered activated carbon (PAC) on the biochemical methane potential of whisky pot ale (PA) and brewery spent yeast (SY) was investigated. The test was carried out with three different types of anaerobic inocula: manure inoculum (MI), sewage sludge (SS) and granular sludge (GR). Brewery spent yeast produced partial (in sewage and granular sludge) and total (in manure inoculum) methanogenesis inhibition due to the toxicity of some of its constituents (hops extract). The inhibition was overcome by the supplementation of PAC, that improved significantly the anaerobic digestion process for SY, allowing to reach biochemical methane potential values between 657-699 L CH4 kg-1 VS and it reduced redox potential from 369 to 398 mV. The activated carbon did not improve the methane yields from whisky PA since microorganisms did not have difficulties to process this substrate; in fact, the redox potential slightly increased from 355 to 330 mV