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Case Study – Chronic Inhibition at a Pulp and Paper Mill

Deflocculation and How it Affects Your SystemEnvironmental Business Specialists recently worked with a client that was experiencing TSS breakthrough at their effluent coupled with historically low MLSS values in their Reactor Basin despite having no wasting. This is a unique situation, rarely encountered under normal operation, that requires specialized testing to pinpoint the root cause. The testing includes looking at the metabolic functions of the bacteria, bacterial enumerations, exocellular polymer analysis, and chemical analysis of the water column.

Laboratory analysis revealed the bacteria were not producing exocellular polymers, the glue that allows them to produce floc, in large amounts and the net charge on these polymers was net neutral, which means the bacteria were not attracted to each other and therefore not clumping. The system showed high amounts of dispersed bacteria and low viability of the biomass. This type of deflocculation can occur for a number of reasons: chemical inhibition, chemical coating, and chemical toxicity. The key word here is chemical. All the miscellaneous chemicals that can be accidentally spilled or rinsed down the sink can have a significant impact on the bacterial population over time. Below are few groups of compounds that can have an impact on bacterial health.

Quaternary Amines: Quaternary amines are commonly used biocides and cleaning agents and therefore are commonly found in wastewater streams. The threshold for inhibition occurs at 25mg/L. These compounds degrade very slowly in aerobic systems and will accumulate in return feed systems.

Anionic Surfactants: Anionic Surfactants are culprits of foaming incidences and, in high concentrations, can coat the surface of bacterial cells causing deflocculation. These chemicals are common detergents used as cleaning agents and are difficult to degrade.

Terpenes: Terpenes are toxic to bacteria at a threshold of approximately 25mg/L. This is a commonly used chemical in most industries and proves to be difficult to break down. In our experience, terpenes tend to accumulate in the reactor biomass adding to their difficulty in treatment. Wasting is the best method to remove terpenes that have accumulated in the system.

Hydrogen Sulfide: Hydrogen sulfide has an LC50 of 1ppm at a pH of 7. Toxicity at any level will cause bacterial death and result in floc breaking apart as the bacteria die. This compound can be avoided as long as the system remains aerobic and no septicity is present upstream.

Fatty Acids: Fatty acids are often found in activated sludge plants, but rarely in levels that can cause deflocculation. More often fatty acid buildup will lead to foaming and filamentous bacterial growth. Having large amounts of fatty acids in addition to other troublesome chemical compounds can aggravate the situation and delay recovery. In addition, fatty acids are generally formed by anaerobic bacteria and therefore fatty acid build-up is an indicator compound for septicity in the system.

EBS has worked closely with Paul Klopping and Cliff Lange of Auburn University to perform the unique testing required to characterize these chemical groups and their unique impact on wastewater systems. Remediation of systems impacted in this manner is highly dependent on the type of chemical impacting the system and the layout of the system in question. As always, the best solution is to avoid putting these chemicals into the system. However, when a chemical spill occurs, EBS will be there to assist you.