Biogas and Energy
HSAD is a clean, enclosed, odorless process for converting organic solid waste and sludge into biogas and a nitrogen-rich product.
Biogas results from the decomposition of organic materials in the absence of oxygen inside the HSAD bioreactor. Typically, the biogas from the HSAD
process is primarily a mixture of methane (CH4) and carbon dioxide (CO2). Although the precise composition of a biogas depends
on the waste feedstock, humidity and other process parameters, methane accounts for about 60 to 80 percent of the biogas volume and carbon dioxide
comprises the balance (20 to 40 percent).
The volume of biogas generated from an HSAD reactor depends on the proportion of degradable materials (volatile solids) present in the organic waste, which are the "food" for the anaerobic microorganisms that thrive in the HSAD bioreactor. Since the degradable fraction varies from one material to another, feedstocks introduced into an HSAD reactor decompose in different proportions. For example, the proportion of organics that degrades in food waste is generally larger than that in yard waste.
Under normal conditions (that is, one atmosphere at 131° F or 55° C), the typical yield from an HSAD bioreactor is 6 decatherms (6.3 million kilojoules) per ton of organic waste. Therefore, a 100 ton (90,718 kilogram) per day plant produces 600 Dth (633 million kilojoules) per day and around 1 million standard cubic feet (28,316 cubic meters) of biogas.
There are several ways to use the biogas, including powering an internal combustion engine to generate electricity. Biogas can also be combusted directly for heating, industrial boilers or kilns, or used to power fuel cells and gas turbines. A 120 ton per day HSAD plant processing waste feedstocks such as food waste (or the organic fraction of municipal solid waste) will have a net electrical power capacity of about 3 MW.