State-of-the-art treatment plants utilize membrane filtration to process millions of gallons of digested dairy manure each day and reclaim between forty to sixty percent of that as clean water that can then be used in various applications that have now been made safer for the environment. Large anaerobic digesters receive manure from nearby dairy farms, for example, which is trucked to their facilities before undergoing anaerobic digestion processes that not only produce clean water, but also capture biogas which is mostly methane (CH4) and carbon dioxide (CO2), with very small amounts of water vapor and other gases. The carbon dioxide and other gases are then removed, leaving only the methane which can be injected into natural gas pipelines as Renewable Natural Gas (RNG). The material that is left after anaerobic digestion takes place is called “digestate.” Digestate is a wet mixture that is rich in nutrients and can be used as fertilizer for crops, and is usually separated into a solid and a liquid.
In general, the anaerobic digestion process is defined as a series of biological processes in which microorganisms break down biodegradable material in the absence of oxygen. The process starts with bacterial hydrolysis in order to break down insoluble organic polymers and make them available for other bacteria. Acidogenic bacteria then convert the sugars and amino acids into carbon dioxide, hydrogen, ammonia, and organic acids which are then converted into acetic acid. In the final step, methanogens convert these products to methane and carbon dioxide. Incases where membrane filtration is utilized, microfiltration and ultrafiltration membranes act as efficient solid-liquid separators that can even isolate nutrients and increase ammonia and potassium retention.
However, the typical disposal of sludge on farmland can be economically wasteful and perhaps cause serious harm to the ecosystem. Therefore, recovery of potentially hazardous materials in clarified solutions becomes an added value process. Also, removing large amounts of the digestate volume as clean water reduces the number of trucks moving digestate back to participating farms and minimizes the volume of material they are required to lagoon store and land apply each year. Since the liquid digestate that is returned to the farms is much more concentrated, money is saved on land application allowing for ferritization using a more targeted method. This helps reduce runoff and makes for a more manageable haul of material to be shared with fields located larger distances away that as a result receive less manure-based fertilizer.
Typically, a large amount of nutrients are lost during runoff which occurs during winter applications where precipitation events are common. Incorporating the water reclamation process means storing only half the volume of material which allows farmers to apply the concentrated digestate during the best weather conditions and at the best times for crop nutrient uptake. It’s believed improved anaerobic digestion processes will provide significant environmental benefits to farming communities, as well as create jobs for operators and plant staff, and represent a sustainable path forward for manure management. What’s more, advanced membrane technologies create clean water that can be discharged to produce a variety of organic fertilizer products. All good news for dairy farmers who already have plenty to digest, since their farms can produce up to one million gallons of liquid dairy manure per day. With advanced membrane technology this could mean introducing four hundred to six hundred thousand gallons of clean water back into the environment, generating 1,630 MMBTUs(Metric Million British Thermal Units) of renewable natural gas per day, and keeping hundreds of truckloads of digestate out of transport.
Graver filtration products are ideal for the separation of nutrients and other contaminants from all wastewater and process streams. Whether it’s fine solid contaminants that need to be removed using cartridge filters from Graver’s Liquid Process Filter group or Scepter crossflow technology or a process that requires the removal of arsenic, lead, and other heavy metals that can be accomplished with MetSorb adsorbent products, we’re here to assist you.
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