Biosolids composting mixes dewatered wastewater solids with a carbon-rich bulking agent and holds the pile at high temperature long enough to meet the federal Class A pathogen standard in 40 CFR Part 503. For an aerated static pile or in-vessel system that means 55 degrees Celsius or higher for three days, and for a windrow it means 55 degrees or higher for 15 days with at least five turnings. A utility that also meets the metal limits and a vector attraction reduction option ends up with a product it can distribute in bulk or bags instead of a cake it must haul to a field or a landfill.<\/p>\n
EPA’s use and disposal statistics<\/a> show where sewage sludge went at the facilities that report to EPA, based on 2024 annual reports: of roughly four million dry metric tons generated, about 59.5 percent was land applied, 24.5 percent was landfilled, 14 percent was incinerated and 2 percent was managed in other ways. Each of those outlets can tighten. A landfill can restrict wet loads or raise its fees, an incinerator eventually needs replacement, and Class B land application depends on willing farms, weather windows and state rules.<\/p>\n EPA’s biosolids technology fact sheet, Use of Composting for Biosolids Management<\/a>, lists the reasons composting grew: scarce landfill space, rising tipping fees, an emphasis on beneficial reuse, and a product that is easy to store, handle and use. It also notes that the added cost of reaching Class A instead of Class B can be marginal.<\/p>\n Part 503 is the federal rule for the use or disposal of sewage sludge. The requirements below are quoted from 40 CFR Part 503<\/a>. States can be stricter, so check your state biosolids program as well.<\/p>\nWhat 40 CFR Part 503 requires<\/h2>\n
Class A and Class B pathogens<\/h3>\n