The struggle to keep the right microorganisms alive: A biological reactor`s operator quest!
Sixteen months ago, and as part of the initial activities of the Work Package 1, the setting up of the Enhanced Biological Phosphorus Removal (EBPR) facility started. The installation consisted of two sequential batch reactors (SBRs) to be installed at BETA Technological Center, that would host a very specific consortium of microorganisms, known as “Phosphate Accumulating Organisms” (PAOs). The PAOs are the crucial biological part of the technology as they are the responsible for the Phosphorus recovery from, in this case, the Dairy wastewater. Therefore, the accomplishment of the ESR1 objectives within the REFLOW project were in their “hands”.
This blog entry addresses the quest of REFLOW ESR01 to build, start-up, maintain, and correct deviations in the reactor`s operation during more than one year. As the readers would probably know, biological continuous operation is a very hard topic since it requires full dedication and every little alteration on the working conditions can deteriorate (or completely ruin) the whole system’s performance. PAOs require a specific sequence of aeration conditions within the reactor as well as pH control; also, a proper and stable source of energy must be ensured. These items represent a lot of “moving items” in the operation, so it is inevitable that one (or more than one) fails!
Finally, after almost one month work, the system was finally assembled, tested and was ready to go!
The first important date (10/09/2020) represented the kick-off of the system with synthetic wastewater which mimics the real wastewater, but without any variation and without the competition with any other microorganism. The start-up is performed in this way so to give the PAOs pleasant and secure conditions to establish and replicate in the reactors. The beginning of this start-up period ran without any startle, until one of the filling peristaltic pumps failed to do its job and left one of the reactors with half the feed. This meant that the PAOs starved during one whole Saturday night. Consequence: Sunday morning was spent fixing the pump to get the reactor ready and going for the following week; First battle won!
After two weeks of the first event, one of the pH probes which reads in real time the pH value inside the reactors started providing erroneous information to the control system (PLC). The data showed the PLC that the pH in one of the reactors was extremely high, so the logic work statement was to order the acid pump to start dosing HCl until the pH recovers the desired setpoint. As the pH probe was not working properly, the signal of continued to be wrong and the acid dosing didn`t stop until it reached the alarm value of pH = 1. The result: all the microorganisms, dead! Start again! After this event, new safety and control measures were implemented so not to reach these critical values again.
A set of nice and smooth months followed the pH episode when the EBPR worked as desired, obtaining excellent results, and proving to be a trustworthy technology. Phosphorus recovery values reached 6.5% (on a dry basis) (That`s a huge value!!) in the produced sludge and the concentration of this element in the reactor throughout the cycles was in total accordance with the expected results. Increasing in the initial (Anaerobic) phase and then decreasing up to almost zero at the end of the cycle. This behavior can be beautifully appreciated in the below figure by following the blue gradient from the left to the right of the scene.
When everything was going OK, the time came to switch from synthetic wastewater to the real Dairy Processing Waste. This event triggered a new set of problems related to the nature of the feed which ended with the system losing efficacy and reaching very poor results in term of phosphorus and chemical oxygen demand removal. This situation, obliged ESR01 to search for the causes and possible solutions to face this “new reality”. The conclusion was that the real wastewater presented a much higher lipid content that the synthetic one, so the produced sludge floated. Microorganism’s cells were being lost in the emptying event at the end of each cycle thus, putting at risk the EBPR performance. After much thinking, the solution came as a result of a careful study which uncovered the new necessary feed management, and the adequate filtering and recirculation needs to overcome this problem. Back on track (again)!
Fortunately, the floating episode was the last in the series of issues which ended there. Ever since, the EBPR operation has been a complete success and allowed ESR01 to treat real dairy wastewater so to comply with the reuse and discharge limits and, at the same time, concentrate and recover phosphorus to be used as a novel Bio-based Fertilizer in the same dairy facility or to be dried and exported elsewhere. The EBPR application in dairy industries helps closing the phosphorus loop in this sector, which is one of the most economically relevant across Europe.
This story has a happy ending and shows that every problem that an operation of a continuous biological reactor, either in lab or full scale, can be overcome provided the necessary tools and knowledge are available. But the moral of the story is that the ability to maintain a biological technology working properly is a real quest, almost a love quest, you will have to start thinking about the microorganisms living inside your reactors as your beloved ones, and you will need to fully dedicate, feed them on time with quality food, and to take really good care of them exactly in the same way as you do with your kids! By doing so, the success is guaranteed!
Pablo Martin Binder (REFLOW ESR01)