Integration of wastewater treatment into process design of lignocellulosic biorefineries for improved economic viability

Table 3 A comparison of the cost, neutralization salt characteristics and treatment methods of probable neutralizing agents for use during the bioconversion process

Neutralizing agent	Chemical cost (USD/tonne OD feedstock)	Primary salt and parameters	Downstream treatment methods
Ammonium hydroxide (NH₄OH)	18.50 [7]	(NH₄)₂SO₄ Soluble Biological nutrient [41]	Biological nitrogen removal Ion exchange Reverse osmosis Electrodialysis
Sodium hydroxide (NaOH)	14.50 [42]	Na₂SO₄ Soluble Inhibitory to anaerobic processes [12]	Ion exchange Reverse osmosis Electrodialysis
Calcium hydroxide (Ca(OH)₂)	6.90 [7]	CaSO₄ Insoluble Carbohydrate loss [7]	Precipitation Ion exchange Reverse osmosis Electrodialysis
Potassium hydroxide (KOH)	153.50 [42]	K₂SO₄ Soluble Biological nutrient [43] Inhibitory to anaerobic processes [12]	Ion exchange Reverse osmosis Electrodialysis
Calcium carbonate (CaCO₃)	28.60 [42]	CaSO₄ Insoluble Carbohydrate loss [7]	Precipitation Ion exchange Reverse osmosis Electrodialysis

The ideal neutralizing agent would be of low cost, non-inhibitory to downstream biological processes and easily treated from wastewater streams. Ammonium hydroxide and sodium hydroxide most nearly meet these requirements. Chemical cost was calculated through stoichiometric substitution of each chemical for ammonium hydroxide in the 2011 NREL Aspen Plus model [7]

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