Heavy metals removal from anaerobically digested sludge by chemical and microbiological methods

Area of Science:

• Environmental Science
• Biotechnology
• Chemical Engineering

Background:

• Anaerobically digested sludge contains significant levels of metals, posing environmental challenges.
• Effective metal removal is crucial for sludge management and potential resource recovery.
• Current chemical treatments can be costly and acid-intensive.

Purpose of the Study:

• To investigate and compare the efficacy of chemical treatment and microbial leaching for metal removal from sludge.
• To optimize metal removal by adjusting sludge solid concentration and pH.
• To evaluate the economic feasibility of microbial leaching versus chemical treatment.

Main Methods:

• Laboratory-scale reactors were used to conduct both chemical treatment and microbial leaching experiments.
• Sludge solid concentration and pH were systematically varied to assess their impact on metal removal.
• Metal solubilization was compared between single and mixed microbial cultures.
• Acid requirements and chemical costs were quantified for each process.

Main Results:

• Metal removal efficiency increased with decreased sludge solid concentration and lower pH.
• A pH of 1.5 was necessary for effective copper removal using acid treatment.
• Mixed microbial cultures achieved 10% greater metal solubilization than single cultures.
• Microbial leaching required less acid and resulted in an 80% cost reduction in chemicals.

Conclusions:

• Both chemical and microbial methods can remove metals from anaerobically digested sludge.
• Microbial leaching offers a more cost-effective and acid-efficient alternative to chemical treatment.
• Optimizing sludge properties and utilizing mixed microbial cultures enhance metal removal efficiency.