Sustainable Agricultural Use of Municipal Wastewater Sludge Eyob Habte Tesfamariam Department of Plant and Soil Science University of Pretoria 19 September 2018

How do we perceive wastewater sludge? As nuisance by product? As a product as is? As a raw material with high value with further processing?

How…? The perception of Arthur C. Clarke during the launch of Apollo 13 was different than most of us: “There is no such thing as waste, there are only resources we are too stupid to know how to use.” Quoted from a mars society convention presentation (12 August 2005)

Nutrient cycling in human food chain Non renewable nutrients K P N Renewable resources Residue Crop production Energy generation Bricks etc… ? Loss of non-renewable resources Non agricultural beneficial use ? Landfills, Incineration, Disposal (land and marine) Environmental pollution 06/04/2019

Do we perceive the role a processed municipal sludge could play Liquid & Solution Solid Source of water and crop nutrients (recycling) SDG 6 (Clean water and sanitation) SDG 1 (Zero hunger) SDG 3 (Good health and well being) SDG 15 (Life and land) Restoration of degraded lands SDG 12 (Responsible consumption and production) SDG 13 (Climate action) C sink (climate change mitigation)

Challenges and opportunities Sustainable beneficial agricultural use of sewage sludge in South Africa Challenges and opportunities

Current and Future focus Resource recovery Fertilizer recovery Water reuse Carbon sequestration Carbon footprint/ GHG emissions Reduced footprint Zero carbon footprint Carbon neutral thru offsets

Current South African sludge guideline for agricultural use Microbiological class A B C Stability class 1 2 3 Pollutant class a b c

Current South African sludge guideline regulation for agricultural use The current South African sludge guideline recommends: Sludge to be assessed if it qualifies for use in agricultural lands. Sludges to be applied according to crop nutrient requirement (upper limit: 10 t ha-1 yr-1). Assess potential environmental impacts from sludge use in agricultural lands.

SARA model development SARA model was developed to assist the implementation of SA guideline by providing: The sludge class and its suitability for use in agricultural lands, Site and crop specific sludge recommendation rates, Economic value of sludge using commercial inorganic fertilizer as bench mark, Potential trace metal accumulation from sludge application in agricultural lands.

SARA model – flow diagram SLUDGE CLASSIFICATION Does the sludge qualify for safe use in agricultural lands? No Yes Farm parameterization Location of farm: Province, nearest weather station, Sludge parametrization Crop nutrient requirements – site specific (per unit area) Nutrient availability – site specific (per unit mass of sludge) Soil parameterization Crop parameterization Sludge recommendation Economic analyses (using commercial inorganic fertilizer as bench mark) Long-term trace metal accumulation

Sludge Classification Interface Sara model

SARA Model – sludge classification interface

Site, Crop And Soil Parameterization Sara model

SARA model – Site, Crop And Soil Parameterization

Sludge Parameterization Sara model

SARA model – sludge parameterization

Sludge Recommendation Sara model

SARA model – Sludge recommendation rate per field Potassium recommendation (for optimal crop growth) Total sludge recommendation for the farm

Cost Benefit Analyzer Sara model

SARA model – Cost benefit analyser Cost benefit analyses using commercial fertilizer as bench mark

Trace Metal Accumulation Sara model

SARA model – Trace metal accumulation Years to reach threshold level

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