biosolids management utilizing solar and thermal …...biosolids management utilizing solar and...

By Chris Enloe-Instrument & Supply, Inc. And Shannon Jones, P.E.-Utilities Engineer City of Fayetteville

Biosolids Management Utilizing Solar and Thermal Processes

What are biosolids? Biosolids are the treated finished product from the

wastewater treatment process. Billions of bacteria and other microbes thrive in the

wastewater facility environment where they consume the organic content from the wastewater stream and continually multiply.

To maintain optimum conditions and remove the nutrients absorbed by the microbes, a fraction of the microbial population is regularly removed. Referred to as Waste Activated Sludge (WAS).

When treated and processed, sewage sludge becomes biosolids which can be safely recycled and applied as fertilizer to sustainably improve and maintain productive soils and stimulate plant growth.

Fayetteville History In 2003, Fayetteville was forced to abandon land

application of waste sludge Landfill disposal was readily available and inexpensive By 2008, several area landfills no longer accepted AR

solids Landfill costs for those that would still take solids

skyrocketed almost 600% Fayetteville wanted a long-term, dependable, and

more sustainable solution

Why consider drying? Takes waste out of landfill Big volume reduction Beneficially useful product Self reliant If energy is managed, can be lower operating cost

AND smaller carbon footprint

Class A vs. Class B 40 CFR, Part 503 Class A biosolids contain no detectible levels of

pathogens. Class A biosolids meet strict vector attraction reduction requirements and low level metals contents, and generally have unrestricted use.

Class B biosolids are treated but still contain detectible levels of pathogens. There are buffer requirements, public access, and crop harvesting restrictions for virtually all forms of Class B biosolids.

Alternatives Considered

Specific Options Compared

Option Selected Combined application of both Solar and Thermal

Drying Results in lower capital and operating cost – long term

Combination Drying

Bound

Free

WAS

Drying Sludge Provides Big Volume Reduction

Before – 100 lbs. Wet After – 20 lbs. Dry

Beneficially Useful Product Class A Product for Distribution/Sale Stockpile storage - low cost, long life

Spreadable – bulk fertilizer

1 Air flap 2 Exhaust fans 3 Ceiling fans

4 Electric Mole 5 Inside sensor 6 Outside sensors

7 PLC

1

4

3 2 5

First Step-Solar Houses 6 7

Thermo-System Active Solar Dryer

Fayetteville, AR Biosolids Management Site

Typical Solar House Drying Cycle

De-watered biosolids are trucked to the site from either WWTP

Solids are emptied into the “Unload Basin”

Solids are then loaded into the spreader or hauled directly into the houses with the skid-steer loader

Solids are then spread as evenly as possible inside the houses

Then the ‘moles’ are turned loose to do their thing!

Mole Video

After a variable weather-dependent drying period, the final product is ready for the next step

1 Sludge goes from hopper to drying chamber. 2 Steam to condenser. 3 Dry product to silo. 4 Heated by thermal fluid from heat exchanger.

1

2

3

4

Second Step – Thermal Dryer

Inlet Conveyor

Loading product into Thermal Building

Feed Conveyor Discharges into Feed Hopper

Feed Hopper – before initial use

Feed Hopper – initial fill

Screw Conveyors Transport Solids to the Dryer

Fenton Fenix Batch Dryer - Indirect Heat

Internal Rotating Assembly

Heat Exchanger – 15,000,000 BTUs

Natural Gas - >20,000 cfh capacity

Surge Bin – allows product to cool

Finished product ready for hauling/storage

Bulk Storage Silo

Performance Solar Houses Target 50% solids before

transferring to Thermal Dryer

Initial results before thermal dryer completion (summer months)

>80% Solids (Class B) 5:1 Volume Reduction 5:1 Weight Reduction

Thermal Dryer >90% Solids (Class A) 5:1 Volume Reduction 5:1 Weight Reduction

~60% Reduction in Costs vs. Landfill

Biosolids Management Site

Project Contributors City of Fayetteville (Design & Construction Management)

CH2M HILL (Wastewater Operations)

CDM Smith (Biosolids Management Study)

McClelland Consulting Engineers (Geotech/Foundation Design)

Instrument & Supply (Manufacturer’s Representative)

Parkson / Thermo-System (Solar Equipment)

Fenton Environmental Technologies (Thermal Equipment)

Questions?