Anish Ghimire

Effects of operational parameters on dark fermentative hydrogen production from biodegradable complex waste biomass.

This work aimed to investigate the effect of the initial pH, combination of food to microorganism ratio (F/M) and initial pH, substrate pre-treatment and different inoculum sources on the dark fermentative biohydrogen (H2) yields. Three model complex waste biomasses (food waste, olive mill wastewater (OMWW) and rice straw) were used to assess the effect of the aforementioned parameters. The effect of the initial pH between 4.5 and 7.0 was investigated in batch tests carried out with food waste. The highest H2 yields were shown at initial pH 4.5 (60.6 ± 9.0 mL H2/g VS) and pH 5.0 (50.7 ± 0.8 mL H2/g VS). Furthermore, tests carried out with F/M ratios of 0.5, 1.0 and 1.5 at initial pH 5.0 and 6.5 revealed that a lower F/M ratio (0.5 and 1.0) favored the H2 production at an initial pH 5.0 compared to pH 6.5. Alkaline pre-treatment of raw rice straw using 4% and 8% NaOH at 55°C for 24h, increased the H2 yield by 26 and 57-fold, respectively. In the dark fermentation of OMWW, the H2 yield was doubled when heat-shock pre-treated activated sludge was used as inoculum in comparison to anaerobic sludge. Overall, this study shows that the application of different operating parameters to maximize the H2 yields strongly depends on the biodegradability of the substrate.

Concomitant biohydrogen and poly-β-hydroxybutyrate production from dark fermentation effluents by adapted Rhodobacter sphaeroides and mixed photofermentative cultures

This work aimed at investigating concomitant production of biohydrogen and poly-β-hydroxybutyrate (PHB) by photofermentation (PF) using dark fermentation effluents (DFE). An adapted culture of Rhodobacter sphaeroides AV1b (pH 6.5, 24±2°C) achieved H2 and PHB yields of 256 (±2) NmLH2/g Chemical Oxygen Demand (COD) and 273.8mgPHB/gCOD (32.5±3% of the dry cells weight (DCW)), respectively. When a diluted (1:2) DFE medium was applied to the adapted pure and mixed photofermentative culture, the respective H2 yields were 164.0 (±12) and 71.3 (±6) NmLH2/gCOD and the PHB yields were 212.1 (±105.2) and 50.7 (±2.7) mgPHB/gCOD added, corresponding to 24 (±0.7) and 6.3 (±0) % DCW, respectively. The concomitant H2 and PHB production from the PF process gave a good DFE post treatment achieving up to 80% COD removal from the initial DFE.

Effect of total solids content on biohydrogen production and lactic acid accumulation during dark fermentation of organic waste biomass

Production of biohydrogen and related metabolic by-products was investigated in Solid State Dark Fermentation (SSDF) of food waste (FW) and wheat straw (WS). The effect of the total solids (TS) content and H2 partial pressure (ppH2), two of the main operating factors of SSDF, were investigated. Batch tests with FW at 10, 15, 20, 25 and 30% TS showed considerable effects of the TS on metabolites distribution. H2 production was strongly inhibited for TS contents higher than 15% with a concomitant accumulation of lactic acid and a decrease in substrate conversion. Varying the ppH2 had no significant effect on the conversion products and overall degradation of FW and WS, suggesting that ppH2 was not the main limiting factor in SSDF. This study showed that the conversion of complex substrates by SSDF depends on the substrate type and is limited by the TS content.

Bioenergy Production from Waste Substrates

Remains of drainage systems to remove waste and latrines have been found in houses from the Mesopotamian Empire (3500-2500 BC); ancient Rome had its Cloaca Maxima, and there still exists a working 4000-year-old sewer system in Greece. Nevertheless, it was not until the late nineteenth century, and after a fourteenth-century long dark age, that it was recognized that municipal waste water needs to be removed from its origin and treated to prevent the outbreak of diseases (Lofrano and Brown 2010). Until then, wastewater had been discharged in surface water or so-called “night soil” (toilet waste) and collected and used for fertilization. Later, in the early twentieth century, biological oxygen demand (BOD) was introduced as a measure of pollution and the first wastewater treatment systems were installed. Recently, the recovery of nutrients, reuse of water, production of intermediates, and generation of energy have become important incentives for the treatment of wastewater from both industrial and municipal origins. This may be more feasible through separation at the source and improved design of water usage and treatment systems (Guest et al. 2009; Larsen et al. 2009). Aerobic treatment was and still is the main technology used for the treatment of municipal wastewater in the north and cold climate areas. In the twentieth century, the possible application of anaerobic systems for the treatment of industrial wastewater and municipal wastewater in warmer climates was recognized after the development of the upflow anaerobic sludge bed (UASB) system in Wageningen in the 1970s (Lettinga 2014; van Lier et al. 2015). Nowadays, with new treatment designs and the paradigm shift toward seeing wastewater as a source of valuable resources, the application of anaerobic technology may be expanded toward treating municipal sewage in cold climates as well. Anaerobic treatment has its advantages, for example, lower excess sludge production, high applicable loadings, and lower energy demands, combined with biogas production. Initially, those were the reasons for the application of anaerobic treatment. Nowadays, the fact that nutrients (N and P) are not destroyed (e.g., emitted as N2) but released as recoverable ions is considered an additional advantage, since this facilitates recovery. Therefore, anaerobic technology has a central role in existing and newly developed waste treatment systems (Figure 3.1). It is, however, important to consider that in most cases, posttreatment of anaerobic effluent is warranted to guarantee that limits for safe discharge of the effluent are met (von Sperling and de Lemos Chrenicharo 2002).