Dissolved air flotation & moving-bed biofilm reactors solve compliance woes
In 2016, the egg processing facility of a leading U.S. marketer of processed egg products was given a consent order by the local government to treat its wastewater for biological oxygen demand (BOD), total Kjeldahl nitrogen (TKN) and total suspended solids (TSS) prior to discharge to the local municipal treatment facility. The processing facility itself had been around for approximately 50 years at the time of the order.
The host city limited the allowable chemical usage in the facility’s wastewater treatment process for fear of disrupting the city’s activated sludge treatment system.
“There’s a lot of politics that were going on with this,” said Justin Olson, industrial sales manager for World Water Works. “The egg processing facility discharges their wastewater to the city municipal wastewater treatment plant. The municipal plant then treats to standards that are acceptable to discharge to the lake, which is highly regulated. The municipality had a violation discharging to the lake, and therefore they blamed the egg processing facility for sending them too high of wastewater to be able to treat. That is what started the whole need for the project and forced the egg processor to install an advanced wastewater treatment system in such a short amount of time.”
Tight restrictions were put on the facility, and when it did not effectively meet those restrictions, the city ordered the processor to achieve compliance less than a year from the notice. There was lot of tension between the processor and the city, according to Olsen.
With the consent order deadline quickly approaching, a 500-gpm dissolved air flotation (DAF) rental system was provided to address and comply with the TSS limits while also significantly reducing BOD and TKN. The DAF rental system would temporarily satisfy the city and allow the facility to continue operations while a permanent system was engineered, manufactured and installed.
The city kept pressure on the facility to maintain compliance. According to Olsen, the municipality claimed that the chemical program implemented on the rental DAF system was toxic to the city’s biological wastewater treatment system. Both World Water Works and the chemical company had to prove to the city that the chemicals were not toxic to the wastewater plant. This required extensive testing.
“They had to get something in there very quickly,” Olsen said. “When the city gave them that consent order, the DAF system, as far as technology goes, is the best option. It was a very small footprint, very efficient removal.”
Many toxin tests had to be run on the chemistry so it would not kill the system. According to Olsen, the city had to approve the chemistry. It was a drawn-out process, and while the testing was being done and the approvals were going through, the egg processor was limited on the amount of use, and that resulted in high BOD and TSS, for which the city charged the egg processor.
The system efficiently removed the suspended solids and the solids inside the organics. Though challenged with high and variable loadings and a limit on the allowable chemical dosage, the DAF rental system performed well due to its design, 5-µ bubble size and a flexible onsite chemical program.
“It generates a small ‘microbubble,’ which attaches to any solids and raise it to the top of the DAF. This forms a ‘sludge blanket’ at the top of the DAF, which is basically all the solids concentrated at the top,” Olsen said. “The mechanism that removes this sludge blanket from the top of the DAF is a ‘rake and chain mechanism’ which is a chain drive with paddles that ‘scrape’ the sludge blanket off the top into a hopper for disposal.”
Olsen noted that the bubble size is important because a bubble only will be able to attach to a particle that is larger than the bubble. The smaller the bubble, the smaller the particle to which it can attach. In other words, the smaller the bubbles, the more efficient the system is at removing the solids from the water.
Following the installation of the temporary DAF system, a complete treatment process solution was provided by World Water Works to bring the facility’s wastewater discharge into compliance with city regulations. The new treatment process consists of a primary treatment DAF system, a first-stage moving-bed biofilm reactor (MBBR) for BOD removal, a second-stage MBBR for nitrogen removal and a secondary DAF for final clarification of biological solids.
This allows the facility to maintain discharge below permit limits while also handling strenuous conditions due to volatile loadings, variable flows and high doses of clean-in-place (CIP) chemicals. CIP is an industry term that food and beverage manufacturing facilities use. It means cleaning all the food production equipment according to a certain schedule set by the U.S. FDA and its quality control programs, Olsen said. The chemicals used are disinfectants such as chlorine/bleach and “quat” (quaternary ammonia), acids and caustics.
Slight adjustments were made to the DAF rental system that already had been installed so it could serve as the permanent primary DAF system. This saved a significant amount of money and allowed the company to install the permanent system without shutting down production. The DAF-MBBR process easily fit into the available footprint and is simple for non-licensed operators to manage.
The DAF-MBBR process exceeded the provided process guarantees by regularly providing TSS, BOD, TKN and NH3-N (ammonia) levels in the single-digit range. After installation, optimization and training support, the facility’s wastewater operations team can easily manage the wastewater treatment system and continue to provide safe wastewater discharge to the city.
“It was a very challenging application. There were a lot of politics involved with the local government,” Olson said. “That made it very difficult on the processor to comply. It was a very challenging application for this technology, but this technology was certainly the best available on the market. It’s putting out crystal-clear water and exceeding all expectations."