From Experience – Environmental, Health & Safety – Fall Issue

Key Issues with H2O2 in Wastewater

As reported in our last edition of EH&S From Experience, commercial-strength concentrations (≥ 35%) of hydrogen peroxide (H₂O₂) are more frequently being used today as a sanitizing agent in plants running Extended Shelf Life (ESL) aseptic filling systems. One of the chief benefits of the solution is its ability to sanitize equipment and the consumer packaging quickly and easily, reducing risks to the product quality.

However, these same properties can cause difficulties on the back end for those facilities that manage wastewater onsite with biological treatment. In a recent project, initial bench-scale testing found that dairy wastewater had to be diluted 10:1 in order for sufficient aerobic biological activity to occur. Initially, it was thought that the cause of this inhibition was peroxyacetic acid (PAA); however, after dilution its concentration was well below 5 ppm. Analysis revealed that the H₂O₂ concentration in the wastewater was 150-300 ppm and higher due to the use of 35% H₂O₂. Considering that H₂O₂’s natural half-life is about 11 hours, it was assumed that H₂O₂ would quickly decompose into water and oxygen in the presence of organic materials in food, beverage, and pharmaceutical wastewater. Yet during further bench-scale testing, very little H₂O₂ reduction had occurred when wastewater containing about 1,000 mg/L BOD5 was aerated for 24 hours.

Additional research found two very effective catalysts which would rapidly decompose H₂O₂ if treatment is completed before the sterilizing wash waters are discharged to process drains: catalyzed activated carbon and greensand (manganese oxide). Bench-scale testing demonstrated that these catalysts can decompose H₂O₂ to concentrations below concern within several minutes.

As H₂O₂ is increasingly used with aseptic filling, Hixson recommends that facilities evaluate its impact on on-site biological treatment, for both aerobic and anaerobic treatment. Facilities that are or will be experiencing difficulties with biological pretreatment due to H₂O₂ in their wastewater should consider capturing the hydrogen peroxide-containing rinses and either treat with catalysts or bypass these rinse waters around the biological step in their pretreatment process.

Finally, note that this may only be an issue if your facility performs biological treatment onsite. Those facilities sending wastewater to the Public-Owned Treatment Works (POTW) for biological treatment may not experience the problem.