Enhancement of Biohydrogen and Biomethane Production from Wastes Using Ultrasonication

This thesis demonstrated the feasibility of using ultrasonication to solubilize the particulate matter, suppress the growth of methanogens, and enrich the biohydrogen producers, thus overcoming the main challenge of biohydrogen systems i.e. long-term stability and contamination with methanogens. Furthermore, this work emphasized the benefits of applying ultrasonication inside a bioreactor over using it as a pretreatment for biohydrogen and biomethane production from wastes. The results of this work showed that sonicating hog manure at specific energy (SE) of 500 kJ/kg TS resulted in a 20% increase in methane production and 36% increase in VSS destruction. The viability of using ultrasonication as a pretreatment method for elimination of methane producers and enrichment of hydrogen producers has been confirmed at SE of 79 kJ/g TSS. Moreover, hydrogen production in a novel sonicated biological hydrogen reactor (SBHR), which comprised a continuous stirred tank reactor (CSTR) connected with an ultrasonic probe at the bottom of the reactor, was about 85% higher than that in a conventional CSTR. On the other hand, an extensive comparative study of five different mesophilic systems (single and two-stage with and without sonicated feed, and two-stage; SBHR followed by methane reactor) was undertaken using food waste. The results showed that sonication inside the reactor in the first stage showed superior results compared to all other systems with respect to hydrogen production, methane production, and VSS destruction. The study also confirmed the advantages of two-stage mesophilic digestion of food wastes over single-stage systems, as reflected by VSS destruction efficiencies in the range of 51% - 59% versus 36% - 44% at a short SRT of 7 days

Improper Disposal of Household Hazardous Waste: Landfill/Municipal Wastewater Treatment Plant

Household hazardous waste (HHW) is not always separated for proper handling before disposal. When disposed improperly to landfills and municipal treatment plants, these products can have significant impact on the environment. Although HHW is a small portion of municipal solid waste, the presence of HHW in solid management facilities that are not equipped to handle them can have problematic effects, resulting in environmental pollution, damage to facilities, and even injury to workers. In many countries, HHW is not subject to legislation unless separated from other household waste because of its small percentage and the challenge in enforcement. In addition, there is no standard definition of HHW globally; therefore, what constitutes to HHW in one country may not be in another. Government legislation and schemes such as Extended Producer Responsibility play a vital role in encouraging proper disposal among consumers, especially when they are convenient and accessible. In this chapter, hazardous household products in different countries are considered along with common improper and acceptable disposal methods. Furthermore, the impacts of improper disposal on the environment are explored with an emphasis on landfill leachate and wastewater treatment plant effluent. Finally, current legislation and programs that encourage proper disposal are discussed

Simulation of the Impact of SRT on Anaerobic Digestability of Ultrasonicated Hog Manure

Ultrasonication at a specific energy of 500 kJ/kgTS was applied to hog manure in a continuous mode completely mixed anaerobic digestion. A process model in BioWin was developed, calibrated and tested at different solids retention times (SRTs) to evaluate the process economics. The results showed that there was a 36% increase in volatile suspended solids (VSS) removal efficiency, a 20% increase in methane production rate, a 13.5% increase in destruction of bound proteins, and a reduction from 988 to 566 ppm in H2S concentration in the digester headspace. Furthermore, a calibrated model of the process using BioWin to assess the impact of SRTs on the economics of anaerobic digestion for unsonicated and sonicated hog manure revealed that ultrasonication resulted in a net benefit of $42–46/ton dry solids at SRTs of 15–30 days

A Review on Anaerobic Co-Digestion with a Focus on the Microbial Populations and the Effect of Multi-Stage Digester Configuration

Recent studies have shown that anaerobic co-digestion (AnCoD) is superior to conventional anaerobic digestion (AD). The benefits of enhanced bioenergy production and solids reduction using co-substrates have attracted researchers to study the co-digestion technology and to better understand the effect of multi substrates on digester performance. This review will discuss the results of such studies with the main focus on: (1) generally the advantages of co-digestion over mono-digestion in terms of system stability, bioenergy, and solids reduction; (2) microbial consortia diversity and their synergistic impact on biogas improvement; (3) the effect of digester mode, i.e., multi-stage versus single stage digestion on AnCoD. It is essential to note that the studies reported improvement in the synergy and diverse microbial consortia when using co-digestion technologies, in addition to higher biomethane yield when using two-stage mode. A good example would be the co-digestion of biodiesel waste and glycerin with municipal waste sludge in a two-stage reactor resulting in 100% increase of biogas and 120% increase in the methane content of the produced biogas with microbial population dominated by Methanosaeta and Methanomicrobium

Comparing VFA Composition, Biomethane Potential, and Methane Production Kinetics of Different Substrates for Anaerobic Fermentation and Digestion

Solid waste is one of the largest sources of greenhouse gases (GHGs) today. The carbon footprint of landfills also has a large impact on global warming. Therefore, it is becoming more urgent to study the possibility of better environmentally friendly approaches for solid waste management and its safe disposal. The digestion of solid waste is a biological process that breaks down the organic content of the solid waste and thus stabilizes it. It also allows the recovery of valuable resources (such as biogas) and the utilization of stabilized waste in various industries. In this study, six substrates were studied to determine their biomethane potential (BMP) in anaerobic digestion. The substrates were fermented and digested anaerobically, and the biogas production was measured. The methane yield of food waste substrates had a higher methane yield between 354 and 347 mL/g-TCOD, and a biodegradability of 89–87%. Wastewater sludge substrates yielded between 324 and 288 mL/g-TCOD with a biodegradability of 81–73%. A kinetics analysis using first-order and Gompertz models was performed for biodegradation and methane production

Effect of Hydrothermal Pretreatment on Volatile Fatty Acids Production from Source-Separated Organics

The current study investigates the effect of hydrothermal pretreatment (HTP) on acidification of source-separated organics (SSO) in terms of volatile fatty acids (VFAs) production and solubilization. Temperature and retention time for HTP of SSO ranged from 150 to 240 °C and 5 to 30 min, respectively. The soluble substance after hydrothermal pretreatment initially increased, reaching its peak at 210 °C and then declined gradually. The highest overall chemical oxygen demand (COD) solubilization of 63% was observed at “210 °C-20 min” compared to 17% for raw SSO. The highest VFAs yield of 1536 mg VFAs/g VSS added was observed at “210 °C-20 min” compared to 768 mg VFAs/g VSS for raw SSO. Intensification of hydrothermal pretreatment temperature beyond 210 °C resulted in the mineralization of the organics and adversely affected the process