We asked two regulators, Bob Holmes, Environmental Program Manager I with CalRecycle and Johnny Gonzales, Water Resources Control Engineer with the State Water Resources Control Board, about the regulations around co-digestion and the role wastewater treatment plants can play in this somewhat new waste to energy system.
Q: Has the review of co-digestion regulations changed your view of the role wastewater treatment plants can play in California’s waste and energy system?
JG: Yes. Properly regulated anaerobically digestible material(ADM) co-digestion at a publicly owned treatment works (POTW), results in enhanced generation and beneficial use of biogas and renewable energy production for co-generation at the POTW.
Co-digestion at a POTW also provides a location to discharge ADM in compliance with an approved Sewer System Management Plan, thus reducing the amount of ADM that is discharged to the sewer system and minimizing sanitary sewer overflows caused by ADM blockages. An additional benefit is that it provides a desirable outlet for the ADM waste stream, which is generated either inside or outside of a given service area.
Q: What was the greatest struggle in reviewing POTW co-digestion regulations and any lessons about how the wastewater community can partner with CalRecycle & SWRCB on future initiatives?
JG: Because co-digestion of ADM at POTWs is wide-spread in California, the State Water Resources Control Board staff initiated discussions with CalRecycle and theCalifornia Department of Food and Agriculture (CDFA) (herein after referred to as Agencies) staff with the objective of eliminating redundant cross–media regulation. The greatest struggle was in validating to CalRecycle and CDFA that POTWs are already regulated by permits issued by the Regional Water Quality Control Boards (Regional Water Boards) that sufficiently address solid waste issues.
Staff inspected several large POTWs that were co-digesting ADM to justify staff’s position. Staff found during the inspection that the ADM co-digestion process was not explicitly or clearly identified in POTW standard operating procedures (SOPs), process flow schematics, and spill contingency plans. To address the deficiency, staff from the State and Regional Water Boards, CalRecycle,CDFA, and California Association of Sanitation Agencies (CASA) worked collaboratively to resolve the cross-media issue, provide training to impacted stakeholders, and developed an SOP template for POTWs.
The group also agreed that Regional Water Board staff must have a standard provision in NPDES permits that requires POTWs proposing ADM co-digestion to develop and implement SOPs. For future initiatives, the State Water Board recommends that POTWs follow CASA’s example of early and direct communication with regulatory agencies and clearly present an issue to allow regulatory agencies to assess and resolve issues in a collaborative team process.
Q: If a POTW wants to implement co-digestion – what do you recommend they do first? And what are the basic SOPs for regulatory compliance?
JG: POTWs wishing to co-digest ADM must be a permanent facility. The POTW must submit a Notice Letter to the appropriate Regional Water Board and Local Enforcement Agency. A Notice Letter template can be found here.
The POTW’s treatment plant O&M and SOP documents must include: 1) a description of facility components (e.g., number of tanks, process configuration, enclosed structures, spill containment and piping) that will convey ADM into the existing anaerobic digestion process; and a description of the end use destination for any screenings removed, and implementation of a truck hauler certification program.
To ensure safe operation of ADM co-digestion, a POTW must develop an SOP within 90 days of initiating the co-digestion. The SOP must include a spill response and contingency plan, vector and odor control, avoidance of introduction of any materials that could cause upset and pass-through of the treatment process, and operation and maintenance procedures.
The spill response and contingency plan must outline procedures for spill containment, recovery, and cleanup procedures. O&M manuals must be updated with instructions to properly operate and maintain the system. I believe CASA has developed a SOP template and makes the template readily available to its members.
BH: Contact the RWQCB for the jurisdiction in which the POTW is located regarding SOPs and WDR and NPDES permit conditions.
Q: What should not be received at a POTW and what is the review process if a wastewater treatment plant wants to request an exemption for a specific type of high-strength organic waste?
JG: In Title 14, CCR, section 17896.2(a)(12)(A).
(D) For the purpose of exclusion, the Department, in consultation with the State Water Resources Control Board and the California Department of Food and Agriculture, will on a case-by-case basis, review and consider approval of additional types of organic materials as potential “anaerobically digestible material” beyond those specified in section 17896.6(a)(1)(C). The review process is described in full is section 17896.6(a)(1)(C). Here are the proposed regulations.
The POTW exclusion is under § 17896.6. Excluded Activities on pages 33-34.
BH: Under the POTW exclusion in the proposed CalRecycle regulations, anaerobically digestible materials must be trucked or hauled into a POTW. Once on-site, the anaerobically digestible material must be pumped or off-loaded directly into a covered, leak-proof container and then pumped, or diluted or slurried and then pumped, and co-digested in an anaerobic digester(s) at the POTW. The pumped material may be screened, otherwise separated or treated prior to anaerobic digestion, but must be conveyed in a contained system.
For the purpose of this exclusion, anaerobically digestible material means inedible kitchen grease (as defined), food material (as defined), and vegetative food material (as defined). CalRecycle, in consultation with the State Water Resources Control Board and the California Department of Food and Agriculture, will on a case-by-case basis, review and consider approval of additional types of organic materials beyond inedible kitchen grease, food material, and vegetative food material.A process for POTWs to request CalRecycle review and consider approval of additional types of organic materials is set forth in the regulations.
If a POTW wants to operate in a manner that does not qualify for the exclusion, the POTW may apply for a permit or seek other authorization through the solid waste local enforcement agency.
Q: What is on the horizon – what do you see as the future for co-digestion in California?
JG: The acceptance of hauled-in ADM for anaerobic co-digestion at POTWs is a common practice and one which is steadily increasing as a management option for this resource recoverable waste stream. Moving forward this practice will be an integral component that will play a part in achieving the dual State objectives to provide the State’s energy needs from renewable sources, and to recycle solid waste generated in the State. The State Water Board supports the CalRecycle exclusion for POTWs accepting vehicle-transported ADM, contingent on compliance with relevant provisions of the POTWs National Pollutant Discharge Elimination System (NPDES) permit or of their Waste Discharge Requirements (WDR), as applicable.
Do you have a question about codigestion regulations? Contact Johnny Gonzalez at the State Water Board or reach out to CalRecycle.