Recycling Biosolids from Wastewater Treatment Facilities
Wastewater treatment results in two major outputs, effluent and biosolids. Effluent is discharged to a receiving water, typically a stream or river. The solids can be beneficially reused, incinerated, or landfilled. The specific treatment processes vary from plant to plant. Below is one.
Image provided courtesy of the Regional Municipality of Durham, Ontario Canada
Biosolids, the solid or semi-solid organic material generated by a wastewater treatment plant, result from the treatment of wastewater carried through sewer lines from homes and businesses to the treatment plant. Following treatment, the liquid (effluent) is typically discharged to a nearby stream and the solids (biosolids) or a product developed from the solids are removed from the treatment plant for disposal or beneficial use.
The characteristics of biosolids vary depending on the sources of wastewater to the treatment plant and the treatment methods used at the treatment plant, and these characteristics will determine if beneficial use is feasible.
Wastewater Treatment Capacity in New York State
As of April 1, 2014, there are currently 586 publicly-owned treatment works (POTWs) in the state of New York that are producing biosolids. The total design capacity of these POTWs is about 3,700 million gallons of wastewater per day (MGD). The operating volume of the POTWs is about 2,530 MGD. Sixty-five percent of the treatment works have a design capacity of less than 1 MGD. The total biosolids generated rate is 350,000 dry tons per year or about 1,000 dry tons per day.
Biosolids Management Options
After stabilization, composting, heat drying, or chemical fixation, biosolids can be beneficially used at appropriate application rates as soil conditioners (fertilizers, sources of organic material, etc.) on farmland, forest land, public works projects, landscaping activities, and land reclamation.
This is the firing of biosolids at high temperatures in an enclosed device. It results in an ash that must be properly disposed.
This is the placement of biosolids in a disposal facility, including monofills (sludge-only landfills) and co-disposal with mixed solid waste. Typically, landfills must have liners, groundwater monitoring, and comply with other regulatory design and operational criteria.
The biosolids generated from POTWs in New York are managed as follows:
|Biosolids Management Options||Percentage||Tons per Day|
|Beneficial Use||30%||300 dry|
There are many methods for beneficial use of biosolids including direct land application, composting, chemical stabilization, and heat drying.
Direct land application of biosolids is the placement on or in the soil to benefit the crop grown and the soil present. Application can occur on agricultural land, forest land, and for land reclamation. Biosolids are used because they provide nutrients (nitrogen and phosphorus) and organic matter to the soil and plants grown. Biosolids can be applied as either a liquid or semi-solid (dewatered) material, similar to animal manure. Biosolids are either directly injected into the soil or spread onto the soil surface and then incorporated into the soil. The application rate is determined by the crop grown and the nutrient content of the biosolids. The rate of nitrogen application must not exceed the needs of the crop grown.
Composting involves the aerobic decomposition of organic material, such as biosolids, using controlled temperature, moisture, and oxygen levels. Composting results in a humus-like material that is typically used in landscaping to enhance topsoil. All composting methods are aimed at optimizing conditions for microorganisms to efficiently degrade the material. Bulking agents such as sawdust, woodchips, or leaves are added to the biosolids to absorb moisture, increase porosity, and add carbon. The mixture is stored (in windrows, static piles, or a vessel) for a period of intense decomposition. Following this active period, the material is stored for an additional period to cure prior to use.
Heat drying is a treatment process in which almost all water is removed from biosolids by exposure to a heat source. The chemical composition of the biosolids remains essentially the same but the percent of solids of the resultant material is 90 percent or greater. Depending on the system, the end product is a powder-like material or grain-sized pellets. The heat dried
product is typically used directly as a fertilizer or blended with other material to produce a
higher grade fertilizer.
Chemical stabilization is a process in which chemicals are mixed with biosolids. Alkaline materials, such as lime or cement kiln dust, are added to dewatered biosolids. The chemicals react with the biosolids and generate heat and increase the pH of the biosolids. Due to the lime addition, the resultant product is used primarily as a lime substitute in agriculture. These facilities are relatively simple, consisting of storage facilities, mixing equipment, and an area where the material is allowed to cure.
The methods used, number of facilities, number of POTWs, and quantity are outlined below:
|Type of Applicaton||No. of Facilities||No. of POTWs||Biosolids Quantity (dry tons/day)|
|Direct Land Application||18||49||40|
Landfilling, Incineration, and Other Methods
Of the 520 dry tons of biosolids landfilled per day, 51 percent is landfilled in-state, the remainder leaves the State for disposal. In New York State, biosolids are landfilled in municipal solid waste landfills that accept primarily municipal solid waste (refuse). At present there are 27 landfills accepting biosolids in the State.
There are 12 biosolids incinerators in the State. These incinerators, located at POTWs, handle a total of 170 dry tons per day. Also, about 30 dry tons per day are incinerated at out-of-state facilities. Incineration by itself is not a disposal method. Incineration does reduce biosolids quantity by at least 70 percent but results in a residue, ash, that must be properly managed. Ash from biosolids incineration in New York State is currently landfilled.
Other management/disposal methods, used for 1 percent of the biosolids generated, include treatment lagoons and storage on-site.
New York State Regulation (6 NYCRR Part 360)
The following regulations links leave DEC's website.
The primary New York State regulations governing the beneficial use of biosolids are found in 6 NYCRR Part 360 Solid Waste Management Facilities, Subparts 360-1 (General Provisions), 360-4 (Land Application and Associated Storage Facilities), and 360-5 (Composting and Other Class A Organic Waste Processing Facilities). A Part 360 permit is required for the construction and operation of biosolids facilities.