Comparison of methods for detecting protein extracted from excess activated sludge

Area of Science:

• Environmental Science
• Analytical Chemistry
• Biotechnology

Background:

• The Kjeldahl method is standard for sludge protein analysis but is inefficient.
• Alternative protein quantification methods are needed for sludge hydrolysates.

Purpose of the Study:

• To compare the precision and recovery of Lowry, bicinchoninic acid (BCA), and Bradford methods for sludge protein determination.
• To identify the most suitable method for sludge protein extraction and reclamation.

Main Methods:

• Sludge supernatants were hydrolyzed using alkaline-thermal hydrolysis (ATH), enzymatic hydrolysis (EH), and ultrasound-assisted enzymatic hydrolysis (UEH).
• Protein content was determined using Kjeldahl, Lowry, BCA, and Bradford methods.
• Precision, spiked recovery, and deviations from the Kjeldahl method were analyzed.

Main Results:

• Lowry and BCA methods showed high recovery rates (95-105%), while Bradford had significant deviations.
• The BCA method exhibited the smallest relative deviation (3-5%) compared to the Kjeldahl method.
• The BCA method was validated for analyzing protein content in residual sludge samples.

Conclusions:

• The bicinchoninic acid (BCA) method is the most appropriate for quantifying sludge proteins.
• This finding supports the development of sludge protein extraction and reclamation processes.