Use It Or Lose It
Andrew Carpenter, President of NEBRA, presented "Maximizing Biosolids Benefits to Soils" on May 20, 2014, at the annual WEF Residuals and Biosolids Conference in Austin, TX.
Currently, about 30% of wastewater solids produced in the U. S. are landfilled, and maybe half of the 15% of the solids that are incinerated are not managed for energy recovery. If these 2.4 million dry metric tons / year were treated with full resource recovery in mind – via anaerobic digestion and beneficial use on soils – we could annually avoid use of:
- 510 million cubic meters of natural gas (.07% of U. S. annual consumption)
- 73,000 metric tons of commercial nitrogen fertilizer
- 36,000 metric tons of commercial phosphorus fertilizer (as P2O5)
These are estimates in "Maximizing Biosolids Benefits to Soils," a presentation by NEBRA President Andrew Carpenter to the WEF Residuals & Biosolids Conference in Austin May 20, 2014. In clear and concise terms, the presentation highlighted how significant a resource biosolids are. Comparing his calculations to national data, 0.07% of U. S. consumption of natural gas and 0.7% of nitrogen fertilizer could be saved.
And there are numerous other demonstrated benefits Carpenter summarized:
- biosolids provide plant macro-nutrients: nitrogen and phosphorus
- biosolids provide micro-nutrients: copper, molybdenum, zinc, etc.
- biosolids organic matter is food for soil microbes, builds soil tilth (erosion resistance, water holding capacity), helps retain nutrients, and sequesters carbon
- biosolids organic matter can provide 22,000 Btu / kg dry solids when combusted or anaerobically digested.
Economically viable mined phosphorus is running out. Carbon has been dramatically depleted from agricultural soils, helping fuel climate change. Disruption of the natural cycle of accumulating (fossil) carbon in the earth has increased CO2 levels in the atmosphere from 280 ppm to 380+ ppm since the start of the industrial revolution, and reducing fossil fuel consumption is a widely-shared goal.
Biosolids cycling to soils is one tool that can be used in addressing these prominent environmental challenges.