Secondary wastewater treatment, also known as biological treatment, commonly utilizes an activated sludge system that can be subjected to significant performance and reliability challenges.
This is true when used in industries whose manufacturing processes discharge variable quality wastewater to the treatment plant. Food and beverage processing and oil refining are among the industries that often have issues due to the frequent releases of varying levels of contaminants, including toxic substances, into wastewater streams by process units. These challenges are made worse at start-up, which can be a long and challenging process when the biomass has not established itself in the new system or if it was idled during a shutdown. A lack of reliable monitoring methods to catch and address these upsets can add to the performance issues of secondary wastewater treatment plants.
The activated sludge biomass contains a population of living organisms that consume, degrade and remove biodegradable organic and inorganic nutrients. This process is essentially the same as what would occur in the natural environment. The difference here is that the engineered process is designed to achieve the same objective in a much shorter period of time and without potential environmental side effects. To optimize the health, growth and processing capacity of the microbial population within the sludge, the process is ideally controlled to ensure optimal growing conditions such as pH, temperature, mixing, oxygen delivery (for aerobic processes) or suppression (for anaerobic processes), and the correct levels of macronutrients, such as nitrogen and phosphorus. Overall performance is often supported through a bio-population supplementation program known as bioaugmentation.
Bioaugmentation can either refer to the addition of specialty microorganisms to artificially strengthen the existing biomass or to the addition of specific nutrients to balance the biomass regime.
Biological wastewater treatment processes are quite stable when the incoming wastewater is of relatively consistent quality and contains the right proportion and quantity of biological nutrients, such as municipal sewage treatment processes. But when industrial processes are involved, the fluctuation in influent wastewater quality can cause upsets with little or no warning. This contributes to a higher cost of treatment and increases the risk of discharge violations and environmental impacts.
To try to prevent these upsets, treatment plant operators have a multitude of testing and monitoring tools available to them, from qualitative methods such as solids concentration and settleability to quantitative ones like respirometric or water quality analyses. Unfortunately, all these and other commonly used tests are just inferential or approximate means to relate biomass activity and often only show a noticeable change after the system has suffered from the upset conditions.
One biomass health monitoring method that has been proven as a fast and reliable means of catching secondary wastewater treatment upsets early is SUEZ’s BioHealth Monitoring. It is a field test that can be completed in less than five minutes that relies on comparing total and dissolved adenosine triphosphate (ATP) to assess biomass health so that actions can be taken before the contamination significantly deteriorates the performance and reliability of the process. Total ATP (tATP) measures all ATP contained inside a sample, including ATP from living cells plus extra cellular ATP coming from dead or dying biomass. Dissolved ATP (dATP) measures only the extra cellular quantity which is released by dead and highly stressed microorganisms. The difference between the two is referred to as Cellular ATP (cATP), providing information on the total living biomass quantity. The ratio of the two is termed the Biomass Stress Index (BSI). It indicates the relative amount of dead or stressed biomass, which is especially useful in giving an early warning of system upsets. When combined with the conventional measurement of mixed liquor suspended solids (MLSS), cATP allows the calculation of the Active Biomass Ratio, which is considered a direct proportion of living biomass in the sludge and also very useful to determine system health.
The following case studies present examples of how a bioaugmentation program combined with a BioHealth monitoring program improved the secondary wastewater treatment operation in two challenging conditions, for a food and beverage plant and an oil refining industry application.
Case study 1: New dairy secondary wastewater treatment plant start-up
The construction of a greenfield food and beverage production plant was completed in late 2020. The new 2.2 million-pound-per-year-capacity dairy plant included a new sophisticated, integrated fixed-film activated sludge (IFAS), biological nutrient removal (BNR) wastewater treatment plant. The wastewater treatment plant was designed to treat the high-strength wastewater produced by dairy operations anticipating an average daily flow of 65,000 gallons per day.
As construction neared completion, the start-up schedule was accelerated, providing less than three months to reach normal production rates. This meant that the wastewater treatment plant had to be fully commissioned and ready to treat the wastewater in compliance with permitted local discharge limits prior to discharge to the community sewer collection system on start-up day.
Importing biomass from a local municipal wastewater treatment system — a common practice for secondary treatment start-ups — would have taken months to reach the target production rate. Instead, the decision was made to use a bioaugmentation program comprising of commercially available biomass to seed the bioreactors, in combination with a nutrient supplementation program, to rapidly grow the microorganism population to full capacity. SUEZ provided two products from the BioPlus bioaugmentation portfolio as an initial source of biomass to seed the bioreactors: one a source of heterotrophic, COD-reducing microorganisms; and the other a source of autotrophic nitrifiers. As the dairy plant was not yet in operation, wastewater containing nutrients was not available to send to the bioreactors. To sustain the newly seeded biomass until start-up day, a BioPlus nutrient supplementation product was fed into the system, providing a balanced blend of carbon, nitrogen and phosphorous.
To complicate the startup of the biological wastewater plant, the laboratory facilities were not completed, and therefore, a full complement of conventional laboratory tests was impossible. The local team relied on daily COD tests from the bioreactor and SUEZ’s BioHealth Monitoring. BioHealth was used to directly measure the growth of the biomass in the bioreactors, while COD removal efficiency was monitored to determine the extent to which the organics were consumed by the biomass. Guided by the sensitive BioHealth monitoring, additional food and microorganisms were added as needed to ensure continuous growth and COD removal.
In just three short weeks, as shown in Figure 1, the biomass in the bioreactors reached acceptable levels, which allowed process wastewater to be introduced to the wastewater plant and discharged to the community sewer system. Meeting the aggressive start-up calendar would simply not have been possible using the conventional method of importing municipal sludge, which would have likely postponed production for the whole facility. Since its start-up, the wastewater plant has relied on BioHealth Monitoring and BioPlus bioaugmentation technologies, and the results are that the high-strength IFAS wastewater treatment has produced effluent to levels that have consistently met approved discharge limits.
Case study 2: Refinery prevents downtime and effluent violations
A refinery’s wastewater was characterized by high loading of organics and ammonia and high variability. Nitrifying bacteria in the wastewater biological system is essential to the degradation and removal of these high ammonia levels, but a period of high stress saw the nitrifiers’ population being depleted. During this time, the ammonia removal rate dropped significantly. The refinery’s production rates had to be reduced to prevent potential environmental impacts and discharge permit exceedances.
The onsite SUEZ team used the BioHealth monitoring technology to assess the health of the biological wastewater operation. As shown on the left-hand side of Figure 2, the BSI gradually increased, with the Active Biomass Ratio (ABR) gradually decreasing during the months when the high-stress condition took place. Nitrification became unstable and eventually was lost completely when the nitrifier population fell too low. When that happened, high effluent ammonia was observed.
The refinery required a solution to quickly regain ammonia removal capacity at the treatment plant, which was leading to a costly loss of productivity and would eventually lead to fines or other penalties from the regulator. Continued system monitoring led to the recommendation by SUEZ for the implementation of a commercially available nitrification program. Based on system conditions and feed rates, nitrification recovery using BioPlus could be expected to occur within a week. In comparison, nurturing the remaining nitrifier population back to a level that would allow full production would take many weeks, with the risk of another upset depleting the biomass further.
As seen on the right-hand side of Figure 2, with the applied bioaugmentation treatment and proper monitoring, system recovery was observed within a few days. It was estimated that the BioPlus treatment combined with the BioHealth monitoring program allowed the treatment plant to recover at least two weeks faster than the conventional method, allowing the production rate to resume that much faster and saving the refinery an estimated $850,000 in production loss. In addition, wastewater plant discharge permit compliance was maintained throughout the event.
Grégoire Poirier-Richer is marketing manager for SUEZ WTS and has over 15 years of experience in water treatment in the roles of product application specialist and technical sales executive. Gregoire is specialized in boiler treatment and pretreatment application, including chemistry, equipment design and operation, as well as automation/control. He is based in Gatineau, Quebec and manages boiler treatment training for SUEZ’s representatives in North America.