Dynamic ammonium retention for nutrient separation from manure digestate

Area of Science:

• Environmental Science
• Chemical Engineering
• Agricultural Science

Background:

• Extensive nitrogen emissions necessitate manure valorization and nutrient fractionation for precision fertilization.
• Current methods struggle to separate ammonium (NH4+) and potassium (K+) from liquid digestate due to similar ionic properties.

Purpose of the Study:

• To develop an effective method for separating nitrogen (N) and potassium (K) from liquid manure digestate.
• To enable the production of N- and K-rich fertilizers for precision application.

Main Methods:

• Utilized a dynamic pH adjustment strategy to control the ammonia (NH3)/ammonium (NH4+) equilibrium.
• Employed membrane separation, specifically reverse osmosis (RO) membranes, with varying pH conditions.
• Tested separation efficiency using both artificial solutions and real liquid digestate.

Main Results:

• Alkaline pH conditions (pH 10) significantly enhanced N/K selectivity, with RO BW membranes achieving a selectivity of 35.
• At pH 10, over 80% of total ammonia existed as NH3, facilitating easier membrane permeation.
• A two-step RO system, involving low pH concentration, successfully produced separate N- and K-enriched fractions.

Conclusions:

• Dynamic pH control is a viable strategy for selective N/K separation from liquid digestate.
• The developed membrane process enables the recovery of valuable N and K nutrients, supporting sustainable agriculture and environmental protection.
• This approach offers a pathway to producing targeted fertilizers from manure waste.