Agricultural Use...

Processed Sludge...

Biosolids contain the same essential nutrients that are in the foods we eat. Plants need these nutrients in order to grow, and obtain them from the surrounding soil. Animals and humans eat plants for their nutrients. Applying properly treated biosolids to the soil continues the cycle. Biosolids act as a nutrient- rich fertilizer that encourages plant growth. By this process, what we eat goes back to the earth, and nothing is wasted. Producing safe, useable biosolid from wastewater is a process that is similar to home composting on a much larger scale.

Reuse as Fertilizer...

Each of us produces about 35 kilograms of biosolids a year. As wastewater flows through a treatment plant, dissolved and solid materials are broken down and consumed by microorganisms, eventually ending up in a large tank, or digester. There they undergo anaerobic digestion, a natural process by which microorganisms digest organic matter and release energy in the form of heat. Solids remain in the digester for at least 30 days, meeting time and temperature criteria. During this time pathogens, which are disease - causing bacteria or viruses, die off from the heat and the lack of oxygen and food. The digested, concentrated solids are now called biosolids. Currently, treated biosolids are being removed and paid to truck them to farmers, who use them to fertilize pasture lands. Some biosolids are also composted by private companies. The soil manufacturing and composting facility will combine biosolids with materials such as woodchips or sawdust to produce a carbon / nitrogen ratio that is ideal for growing plants. In the composting process, biosolids are mixed with the woody materials, and then are aerated inside the facility for a number of weeks, to allow the composting process to take place. At the end of the process the compost reaches a stable state. The finished product, resembling a rich forest topsoil, is called composted biosolids, and contains nutrients for plant use.

"Use of Sludge in the US"...

Sludge Characteristics Affecting Agricultural Use...

Organic Material and Pathogens...

Degradable organic material in unstabilized sludges can lead to odor problems and attract vectors (flies, mosquitoes, and rodents) in a land application setting. Pathogens (bacteria, viruses, protozoa, and eggs of parasitic worms) are concentrated in sludges and can spread diseases if there is human exposure to the sludge. To meet the limits, organic content and pathogens must be reduced significantly prior to land application by means of preapplication treatment process. Only sludges treated by digestion or chemical stabilization to reduce pathogen levels and the potential for disease transmission can be applied to land. Land application further aids in destroying pathogens by exposing them to sunlight, the soil environment, and drastic temperature changes. Sludge - application sites are restricted to general public access for 12 months after the sludge has been applied and 30 days for grazing animals. Crops grown for human consumption have certain restrictions ranging from 14 to 38 months depending on the type of crop.

Nutrients...

Major plant nutrients (N, P, and K) are not removed substantially during sludge processing but are taken up by vegetation after application. Nitrogen is normally the nutrient of concern in land application because of the potential for nitrate contamination of groundwaters. The nitrogen uptake rate of vegetation, therefore, is a key design parameter in determining sludge loading rates.

Toxic Materials...

Wastewater sludges contain trace metals and organic compounds that are retained in the soil and pose potential toxic risks to plants, animals, and humans. The principal metal of concern is Cd because it can accumulate in plants to levels that are toxic to humans and animals but below levels that are toxic to plants.

Median Concentrations of Nutrients and Heavy Metals in Sludges
Element / Metal	ppm
Nitrogen 1	2.6
Phosphorus 1	1.6
Potassium 1	0.2
Lead	335.0
Zinc 1	1,750.0
Copper 1	475.0
Nickel	37.0
Cadmium	11.0
Chromium	380.0
Mercury	5.0
1Nutrients essential for plant growth

Water Quality...

Both surface water and groundwater must be protected in a land - application program. Nitrogen and phosphorus are the primary water contaminates from sludges. Both nutrients are necessary for plant growth and can be controlled in an environmentally sound manner. Surface waters can be protected by using conservation practices that reduce erosion and prevent the movement of sediments and accompanying nutrients from the site of application to ponds, lakes, or streams. Groundwater contamination by nitrogen may occur if the nitrogen applied in sludge is greater than the crop requires. Environmental agencies restrict sludge application to sites where surface runoff is minimized and restricted from reaching surface water bodies, drainage ditches, and other impoundments. Further, application within 30 m of wells is prohibited to reduce the potential for waste constituents to move from the soil into groundwater.

Application Criteria & Design Loading Rates...

"Sludge Application Rates"... "Soil Limitations"... "Design Based on Pollutant Loading"... "Design Based on Nitrogen Limitation"... "Design Based on Phosphorus Limitation"...

Composting...

"Compost Production for Agricultural Use"...

Incineration...

"Fluizied Bed Incineration"...

The cake residue from the filter presses is then incinerated along with the grit. Presently part of the sludge is hauled off-site to be composted, directly land applied or landfilled. The Lynn incineration system is comprised of two Oliver fluidized bed incinerators which burn the sludge at approximately 1,400 degrees Fahrenheit. The remaining ash is hauled to the off-site landfill for disposal.

On site incineration of the sludge cake occurs in two Dorr Oliver fluidized bed incinerators. A fluidized bed incinerator has sand heated to about 1,500^O F by oil or gas. The sand is blown around "fluidized" in the incinerator by a hot air blower "fluidizing blower" blowing from the bottom upwards. The sludge is metered onto a serpentex conveyor belt system then weighed on a weigh belt just prior to being feed into the incinerator via the screw feeder of the incinerator. As the sludge enters the incinerator the heated fluidized sand hits the sludge both breaking it apart like a sand blaster and burning it. The gas and ash from the burning process are carried out the top of the incinerator and through a heat exchanger, which preheats the ambient air up to 800^O F before it enters the windbox. The exhaust gas then passes through an economizer heat exchanger that recovers more heat, and supplies the solids building with hot water for the boiler and heats the entire solids building in the winter months. About 99.9 percent of the fly ash is then removed in the venturi gas scrubber. The gas stream then flows through a wet electrostatic precipitator (ESP). This device first pH adjusts the gas stream to remove sulfur dioxide. Then the gas passes by high voltage electrical coils which charge any particles of ash still in the gas stream and then removes those particles with an oppositely charged plate much like a magnet. The gas exiting the stack into the air has some water vapor with almost no particulate.

The incinerators are permitted by the states Department of Environmental Protection (DEP). There is a continuous emissions monitoring system (CEM) on each incinerator measuring Sulfur Dioxide (SO₂), Oxides of nitrogen (NO_X), and Carbon Monoxide (CO). The information from these delicate and sensitive instruments are then collected by a data logger and sent to a computer located in the incinerator control room. These results are then compiled for quarterly and semi-annual reports for both DEP and EPA. The incinerator operators use this information to operate the incinerators within the guidelines of the DEP permit as well as achieve the optimum efficiency and performance without excess emissions.