Reclamation of Degraded Land with Biosolids

Impacts of final land use,Impacts of reclamation method

GHG Consequences of Reclamation

• Final land use post-reclamation• Reclamation improvements with biosolids• Land- and biosolids use interact

Reclamation to forest

• High gains to Soil and Biomass C• Conventional and residuals reclamation

Partial Reclamation + Development

• Some soil/biomass C• But large GHG costs for construction and use

over life cycle

Field study – Soil C in Reclamation

• Soil C benefits of biosolids reclamation• Compare similar conventional and biosolids

sites up to 30 year post-reclamation

Results: Soil C sequestration

Results: Soil C sequestration

• Soil C increases with biosolids +15 Mg ha-1 (Centralia) +38 Mg ha-1 (Highland Valley)

• 0.11–1.14 Mg CO2e per Mg biosolids

Results: Soil C sequestration

• Increases and efficiency depend upon reclamation conditions and method

Centralia, 0.11 Mg CO2e per tonne: Old sites, 1 m topsoil, very high biosolids rate

Pennsylvania, 0.55 Mg CO2e per tonne: Old sites, relatively good topsoil, moderate biosolids addition

Highland Valley, 1.03 Mg CO2e per tonne: No topsoil, very poor conventional recl., low biosolids rate

Sechelt 1.14 Mg CO2e per tonne: Good response, poor topsoil moderate biosolids addition

Study conclusions

• 55–139 Mg CO2e ha-1 Soil C increase for using residuals• Increase was present even after 30 years• Specific changes related to site conditions and reclamation

history• What about other GHG shifts with reclamation?

Land use

• House or forest? Soil C Biomass C Construction/use/maintenance Operations: transport, soil N2O, fertilizer credit, etc. Competing biosolids uses

Life cycle assessment of reclamation

• What is LCA? Track all

inputs/outputs/activities required

Assign environmental impact

Assess (relative) environmental consequences

Life cycle assessment of reclamation

• Alternate post-reclamation land uses Houses vs. forest Reflects land-use pressures in Puget Sound

Life cycle assessment of reclamation

• 1 ha of degraded land • Urban margin of Puget Sound region, WA• 30 year timeline• Houses or forest

Life cycle assessment of reclamation• “Choose your own adventure”• Natural cover (forest)

Biosolids reclamation Conventional reclamation

• Development

Reclamation – Soil Carbon

• Conventional Reclamation: 110 Mg CO2e

• Biosolids reclamation: 220 Mg CO2e

• Based on C accumulation rate and Mg CO2e per tonne of biosolids

Reclamation – Biomass Carbon

• PNW forests respond to biosolids (soil low in N)

• Conventional: 183 Mg CO2e • Biosolids: 275 Mg CO2e

Conventional Reclamation

• Reclamation to Doug Fir forest

• 110 Mg CO2e soil C

• 183 Mg CO2e biomass C

• 393 Mg CO2e per ha total

Biosolids reclamation• Reclamation to D. Fir• 220 Mg CO2e soil C• 275 Mg CO2e biomass C• 18 Mg CO2e N applied as N2O• 477 Mg CO2e per ha total

Biosolids reclamation GHG emissions?

• Need to consider emissions from biosolids management

• Also alternate biosolids end-uses

Biosolids to Agriculture

• -220 Mg CO2e soil C• -275 Mg CO2e biomass C• +18 Mg CO2e N2O• +2 Mg CO2e transport (50

km)• Net: -475 Mg CO2e

• -140 Mg CO2e soil C • -28 Mg CO2e fertilizer

credit• +11 Mg CO2e transport

(300 km)• Net: -157 Mg CO2e

vs.

Biosolids to Landfill

• -220 Mg CO2e soil C• -275 Mg CO2e biomass C• +18 Mg CO2e N2O• +2 Mg CO2e transport (50

km)• Net: -475 Mg CO2e

• -29 Mg CO2e soil C • 346 Mg CO2e fugitive

GHG• +14 Mg CO2e transport

(350 km)• Net: +331 Mg CO2e

vs.

Net GHG balance of restoring vegetation

• Biosolids reclamation -475 Mg CO2e (30 years, 1 ha, 100 dt biosolids)

• Conventional reclamation -293 Mg CO2e

• What if development is chosen instead?

Suburb development

• Single-family houses• Asphalt roads• Built cover % according

to USGS• Reclaim remaining land

Suburb development: Housing

• US Census population density 3.9 houses/ha @ 243

m2 (~2,500 sq. ft)• LC GHG estimates:

Construction (incl. materials): 283 Mg CO2e

Maintenance/occupation: 989 Mg CO2e

Suburb development: Roads

• USGS % impervious cover 0.44 ha ha-1 suburb

• LC GHG estimates: Construction (incl.

materials): 93 Mg CO2e Maintenance: 42 Mg

CO2e

Net GHG balance of Suburb Development

• +1,272 Mg CO2e houses

• +135 Mg CO2e roads

• -52 Mg CO2e soil C

• -86 Mg CO2e biomass C

• Net: +1,269 Mg CO2e • Extra commuter traffic GHG?

Excluded from LCA but... ca. +1,653 Mg CO2e over 30 yr

Development or Reclamation?

• Net: -293 to -475 Mg CO2e

• Net: +1,269 Mg CO2e

vs.

• Modify and recombine scenarios to look for best and worst cases.

Worst Case

• Low density suburb, and...• Send biosolids to landfill, and...• Conventional reclamation of partial land• +1,600 Mg CO2e – largest emissions, lowest offsets

+

Optimized Case

• Housing construction in urban core, and...• Biosolids for full reclamation• -5 to +141 Mg CO2e – minimized emissions,

maximized offsets

+

Other ecosystem services

• Improved with reclamation over development: Water filtration; Biodiversity; Tourism value

++

+

Conclusions

• Land-use after reclamation has the biggest impact

• Biosolids end-use is also has an impact and is determined in part by land-use choices

• Biosolids in Puget Sound may have best end-use in reclamation but first need to not develop (degraded) land