The Missouri Department of Natural Resources describes a Biosolids Applicator business as:

An individual or business that spreads biosolids for beneficial use. Biosolids are a product of the wastewater treatment process. During wastewater treatment the liquids are separated from the solids. Those solids are then treated physically and chemically to produce a semisolid, nutrient-rich product known as biosolids. The terms ‘biosolids’ and ‘sewage sludge’ are often used interchangeably. Biosolids that are land applied must meet federal and state requirements.

You may need some or all of the following permits for a Biosolids Applicator business:

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Hazardous Waste Emergency Permit

In the event there is a situation that presents an immediate and significant threat to human health or the environment based on hazardous waste issues, the department may issue a Hazardous Waste Emergency Permit. If your business already has a hazardous waste permit, this permit would allow you to treat, store or dispose of a hazardous waste not covered by your effective permit. Non-permitted companies may also receive an emergency permit to allow them to temporarily treat, store or dispose of hazardous waste. The emergency permit clearly specifies the hazardous wastes the company intends to handle and how they are allowed to treat, store or dispose of the wastes.
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Public Drinking Water Construction Permit

If your business plans to construct a public water system that will supply drinking water to the public, you must obtain a Public Drinking Water Construction Permit. A public water system has at least 15 service connections or serves at least 25 people at least 60 days out of the year. This permit is also required if you plan to complete the following construction projects to the water system: waterline extensions, waterline replacements, drilling water supply well, construction a storage tank, adding a disinfection system, treatment changes, building a pump station or other improvements or modifications.

If your business plans to connect to a permitted public water system, then you are not required to obtain this permit.
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Sewer Extension Construction Master General Permit MO-GC00000

If your business plans to construct a gravity sewer extension, force main and lift station, you may need a site-specific Sewer Extension Construction Permit. Storage basins, considered part of the collection system, are also included. Earthen basins are not included under this permit.
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Sewer Extension Construction Master General Permit MO-GSE0000

If your business plans to construct a gravity sewer extension, force main and lift station, you may need a site-specific Sewer Extension Construction Permit. Non-earthen flow equalization storage basins at lift stations and inline storage, which flows back into the lift station or collection system, are also included.