Maximizing Resource Recovery

from Biosolids

Andrew Carpenter

Organic N

Organic C(energy source)

Microbial activity

NO3-

N assimilation

N Mineralization

Organic Matter Transformations in Soil

Mature Soil Organic Matter (Soil Humus)

C assimilation

Plant-available nitrogen in a slow-release form

• Improving soil fertility through the addition of organic matter-based residuals is a primary tenet of sustainable agriculture– Healthy soil ecosystem– Long-term pool of soil nutrients– Reduced erosion– Feeding soil not just crops

The Value in Biosolids

Organic MatterIn Soil• Food for soil microbes• Builds Soil Tilth

• Erosion Resistance• Water-holding capacity

• Ability to retain nutrients

Macro-Nutrients• Nitrogen (5%)• Phosphorus (2%)• CalciumMicro-Nutrients• Zinc• Copper• Molybdenum

Nutrients

For Energy Recovery• Energy in the chemical bonds of organic

matter • 9,300,000 Btu/metric ton of biosolids

available through anaerobic digestion

Organic Matter

6.5 Million Dry Metric Tons of Municipal Wastewater Solids Generated Annually in the U.S.

Level of Treatment• 60% Class B• 40% Class A

Data excerpted from National Biosolids Regulations, Quality, End Use and Disposal Survey, 2007 (2004 data)

Overall Trends in Wastewater Solids Management

The amount being recycled to soils versus the amount going to landfills or to incineration appears to have been steady from the mid

1990s through 2004

Greater Lawrence Sanitary District, Massachusetts

Benefits• Digester Gas is used as fuel for the dryer• Solid market for the biopellets• Selling for between $15 - $25 per ton (worth closer to $50 per ton for

nitrogen and phosphorus replacement alone)• Value has increased with the recent rise in fertlizer prices• General distribution no site-specific permitting

Risk Assessment

Triclocarban: An example of a personal

care product in biosolids

InfluentEffluent

Biologically Degraded Compounds CO2 and H2O

Wastewater

Wastewater Solids

Soluble Compounds

Nutrients Organic Matter

Insoluble, non-volatile compounds

Triclocarban in anti-bacterial soap 15,000 ppm

Triclocarban

Triclocarban in biosolids 30 ppm (450 X lower concentration than in the soap)

Opportunities in the Future• Assumptions

– 30% of U.S. wastewater solids are landfilled, and half of the 15% of solids incinerated have no associated energy recovery 2.4 million dry Mg/year not utilized

– All of this would instead go to anaerobic digestion and the anaerobically digested biosolids would be land applied

– 75% volatile solids on a dry wt. basis– 60% volatile solids reduction during anaerobic digestion– 75% of nitrogen eventually available for plant uptake– 0.485 gallons of fuel oil used per kg of nitrogen fertilizer produced– 40% plant availability of phosphorus in biosolids

• 650,000,000 m3 of natural gas use avoided• 90,000 Mg/year of nitrogen fertilizer use avoided

– Additional savings of 44,000,000 gallons of fuel oil

• 42,000 Mg/year of phosphorus fertilizer (as P2O5) use avoided

Combined Scenarios(each scenario includes thickening, de-watering and

transport)

-5000

0

5000

10000

15000

20000

25000

CO

2E

quiv

alen

ce (M

g/ye

ar) transport

Energy recoveryCold wet climate

800oC25% solids

Digested solidsNo recovery

65% heat 30% elect.1% fugitive

Lan

dfill

Incin

eration 1

Incin

eration 2

900oC30% solidsundigested

Energy recoveryCement

replacement

Class A

Alk

aline

Lan

d A

pClass A using recycled lime source such as

CKD

An

aerobic d

ig. L

and

ap

Concluding Remarks

andrew@northerntilth.com

• Use It or Lose It!