analysis of methane production by anaerobic microbiota during the co&#45;digestion of food scrap and waste&#45;activated sludge

Respirometry Protocol for Anaerobic Digestion of Food Waste and Sludge

Researchers study microbial activity at the bench scale using a variety of approaches, including batch studies, microcosms, and respirometry, amongst others. Respirometers can be used to measure cellular respiration through the growth and/or decay phases of a microbial community by observing substrate consumption and end-product production under controlled conditions1. The results from bench-scale respirometer studies can also be used to estimate biokinetic parameters for process model construction2. Respirometers have been used to examine both aerobic and anaerobic microbial activity; however, studies using respirometry to measure the biomethane potential (BMP), especially of mixed organic substrates, is an area of ongoing research3,4.
Organics in domestic wastewater are recognized as a viable renewable source of chemical energy5. Anaerobic digestion of wastewater sludges (i.e., primary sludge and waste-activated sludges, WAS) has been used to produce methane-rich biogas at wastewater treatment plants (WWTPs) for well over a century6. However, the digestion of multiple organic waste streams, such as food scrap waste with WAS, has become prevalent only in recent years and is still an active area of research. Food scrap waste is a consistent waste stream of high-density organic material in many developed countries, accounting for approximately 25% of landfill mass in the US7. Aside from diverting a portion of food scraps from disposal in landfills, the combination of food scraps and WAS in a co-digestion scenario is advantageous due to the increased volume of biogas produced (relative to a single organic waste stream). Biogas typically contains 60%-70% methane, 30%-40% carbon dioxide, and trace amounts of other gases (e.g., hydrogen sulfide)8. The biogas can be cleaned and combusted onsite at WWTPs using a combined heat and power technology to offset some of the electrical and heat energy requirements9.
Several studies have examined the biomethanation potential and biokinetic parameters of anaerobic microbiota co-digesting organic wastes1. Available studies in the literature have used batch assays in serum bottles where methane production is measured at discrete points throughout the experiment, while others have measured methane production using flowmeters connected directly to bench- or pilot-scale bioreactors2,10,11. Continuous measurement of methane production using a respirometer, such as the one described in this protocol, can provide continuous and precise methane measurements from a large number of samples run under a variety of experimental conditions1,12. While several studies have measured methane production from co-digestion of WAS coupled with other organic substrates, such as biowaste, fats, oils, grease, and agricultural wastes10,13,14, significant work remains to identify methane production rates from the large variety of co-digestion scenarios. Further, to date, no available protocol provides an in-depth, step-by-step approach using visual depictions for the measurement of methane production from the co-digestion of food scraps and WAS. Accordingly, this study presents a respirometer protocol to measure methane production and derive biokinetic parameters using a mix of dilute wastewater, WAS, and food scrap waste as substrates. Different food-to-microorganism ratios (F:M) were used to help elucidate changes in methane production. Other measurements include volatile suspended solids (VSS), chemical oxygen demand (COD), and pH of each sample. This protocol describes respirometer setup, sample creation, and critical measurements.

Author Spotlight: Advancing Anaerobic Microbiota Research Using a Novel Respirometry Protocol

Measuring Biomethane Potential of Food Scrap Waste Anaerobically Co&#45;Digested with Waste&#45;Activated Sludge Using Respirometry

The scope of our research is to use respirometry to examine the biokinetics of anaerobic microbiota co-digesting organic waste streams such as wastewater sludge and food scrap. We attempted to answer the question of how different substrate concentrations influence the rate at which these anaerobic microbiota produce methane. While several studies have measured methane production from co-digestion of waste-activated sludge coupled with other organic substrates such as a biowaste, fats, oils, grease, and agricultural waste, this research presents a respirometer protocol using a mix of dilute wastewater, waste-activated sludge, and food scrap waste as substrates.Similar studies use batch assays in serum bottles where methane production is measured at discrete points throughout the experiment, while others use flow meters connected directly to bench or pilot scale bioreactors. Our protocol uses a respirometer that provides continuous and precise methane measurements from samples run in different experimental conditions.

Analysis of Methane Production by Anaerobic Microbiota During the Co&#45;Digestion of Food Scrap and Waste&#45;Activated Sludge

Research

JoVE Journal

Environment

The use of respirometry to study the biokinetics of microbiota treating wastewater or digesting wastewater sludges has become more prevalent over the last ...