Wastewater Treatment Facility Optimization. Imperion Can Help.
How Healthy Is Your Wastewater Treatment Facility?
A beef processing client has a 1.2 MGD onsite wastewater treatment facility. The WWTF (wastewater treatment facility) consists of primary screens, two Dissolved Air Flotation (DAF 1 & 2) units, an anaerobic digester, an aerated activated sludge lagoon, an intermediate dissolved air flotation unit (DAF 3), three polishing ponds and a belt filter press for dewatering solids.
Imperion was recruited for this project to enhance biogas production from the digester, which will be used onsite for their boiler system. Imperion identified several key opportunities for operational enhancements. These include:
Low air-to-solids ratio on the DAF units resulting in an inadequate number of air bubbles floating impurities and flocculated particles to the surface to be skimmed. Upon conferring with the DAF vendor, we were able to identify what parts were needed to increase the pressure of air sent to the DAF and get the DAF working as it was designed for the first time in its operation. This resulted in decreased levels of BOD (biochemical oxygen demand), TSS (total suspended solids), and O & G (oil and grease) in the DAF effluent. Imperion is also coordinating with a vendor to determine the feasibility of upgrading the DAFs to a suspended air floatation system (SAF).
Imperion restored the digester to a healthy biochemical state
The digester was also found to be operating sub-optimally. Following a series of unplanned high organic load dumps to the WWTF, the digester went “sour.” In other words, the alkalinity of the digester was depleted to such a point that the VFAs (volatile fatty acids) were left unchecked, and the pH in the digester dropped due to a lack of buffering capacity. This began a vicious cycle where the high acid content perpetuated itself by killing off methanogenic bacteria and favoring acidogenic bacteria, thus lowering the pH even further.
To correct the chemistry in the digester, Imperion worked closely with a chemical vendor to prescribe a tailored solution to the client that would address the issue and help future-proof the digester from the same problems. Previous chemical vendors sold lime (CaCO3) to the client in an attempt to correct the pH, which reflected a poor understanding of the chemistry within the digester, as pH is a lagging indicator of the health of the digester. We recommended magnesium hydroxide instead, which would correct the pH and restore the alkalinity so that the digester would not be susceptible to further upsets. The result was restoration of healthy pH and optimal alkalinity levels. Additionally, Imperion recommended an alkalinity testing protocol to monitor digester health.
We also determined that the digester was creating hydrogen sulfide (H2S) in such high amounts that it was prematurely depleting the scrubbing system, toxifying the methanogenic bacteria in the digester, toxifying the nitrifying bacteria in the aerated lagoon, and creating a health and safety hazard for the operators.
Imperion took a three-tiered approach to address this issue. The first was introducing micro aeration into the headspace between the tarp-covering digester and the water surface. Sulfate-oxidizing bacteria in the headspace will use H2S and O2 as an energy source. The result of this metabolic process is elemental sulfur instead of H2S.
We then collaborated with our chemical vendor to identify the best cationic polymer for neutralizing the negative charges around sulfide compounds in the wastewater. This process caused the sulfides to separate from the solution, preventing them from serving as precursors to hydrogen sulfide (H2S).
Finally, we worked with the vendor of the tarp-overlying digester to adjust the angle of the mixers so that we could agitate the sludge blanket and allow for a homogenous distribution of the coagulant. This mixing also helps remove harmful metabolic byproducts that are in contact with the methanogenic bacteria.
Imperion enhanced biological nutrient removal.
The aerated lagoon is responsible for the facility’s biological nutrient removal. The facility was found to be in violation of their permitted effluent levels of ammonia. Upon review, we found that the surface aerators in place were only aerating the first five feet of the fifteen-foot pond. This resulted in multiple anoxic layers within the pond that were not nitrifying ammonia. Imperion secured a proposal from a vendor that provided a diffused aeration system with industry-leading standard oxygen transfer efficiency (SOTE). In addition to the fine bubbles this equipment provided for diffused aeration, it also addressed the need for mixing by providing a separate outlet for coarse bubbles to disperse the fine bubbles and increase the area of influence of each aerator. Additionally, diffused aeration offers considerable energy savings compared to surface aerators, and Imperion was able to secure grants to pay for the diffused aeration system. The client is now fully compliant with their ammonia effluent limits at minimal cost and with reduced energy expenditure.
Imperion also determined that the sludge in the aerated lagoon, and thus the nitrifying bacteria, likely would not have enough residence time during the winter months to complete the nitrification cycle. During colder months, the nitrification cycle can take twice as long to complete. Imperion secured the funding necessary to upgrade the return-activated sludge (RAS) system to allow more solid retention time in the presence of aeration, thus completing the nitrification/denitrification cycle during winter months.
Realistic, Achievable Goals Based on Accurate, Verifiable Data
- Reduced energy usage.
- Reduced H2S levels.
- Viable methane is being sent to the boiler.
- Compliance with their waste discharge requirements.
- Anaerobic digester brought back to a state of health.
- DAFs finally operate as designed.
- Mixing achieved in both digester and aerated lagoon.
- RAS system upgraded.
Consulting, Compliance, Project Identification.
Let’s get your wastewater treatment facility project started!
Additional Support & Services Provided by Imperion:
- Facilitated a partnership with a firm offering onsite operational training to enhance efficiency.
- Vetted vendors and service providers for the client.
- Conducted weekly meetings to oversee and manage simultaneous projects.
- Performed monthly site visits to assess project progress and facilitate advancement.
- Coordinated with the City Water Permitting division during monthly meetings to provide ongoing assistance.
Imperion Can Help You Understand and Upgrade Your Wastewater Treatment Facility.
Identify Process Improvements
Wastewater treatment facilities are highly interconnected biochemical machines that are often difficult to troubleshoot. Imperion is well equipped to identify bottlenecks and inefficiencies within existing systems to improve contaminant removal rates and save operational expenses.
Solve Compliance Issues
As a wastewater treatment plant supervisor, there is no worse feeling than receiving a notice of violation or an order of compliance. Imperion regularly works as liaisons between municipalities and industrial users to bridge the gap in understanding and work to provide lasting compliance solutions.
Vet Chemical and Service Providers
To be able to say yes to the right solution provider typically includes saying no to several others. Imperion is experienced acting as an unbiased third-party consultant committed to selecting the correct and best options for our clients.
