Consultation response: PPC Technical Guidance Note 35 Anaerobic Digestion The Anaerobic Digestion and Biogas Association ( ADBA ) is the trade association that represents the range of interests and matters related to the anaerobic digestion of organic materials ( AD ) across the UK, including the collection of waste for use as feedstock. ADBA understands the complex range of skills required by developers of new AD plants, from feedstock management through technology to energy production, markets and resource to land. The organisation has over 300 members from across the AD industry, including farmers, local authorities, waste management companies, supermarkets, food processors, plant operators, energy and water companies, equipment manufacturers and suppliers, consultants, financiers and supporting service companies. Anaerobic Digestion can make a significant contribution to Climate Change, renewable energy and critical resource preservation targets, subject to the right policies being in place. ADBA is grateful for the chance to comment on SEPA s AD Technical Guidance Note and highlight any problematic issues that the industry believes could arise from the guidance or where we believe the guidance could be clearer. Scope It is recognised that a number of anaerobic digestion facilities may fall under the Waste Management Licensing Regulations 1994 (as amended) and for those sites this guidance document should also be considered what SEPA regard as best practice ADBA is concerned that the scope of this guidance could mean that many lower risk plants end up subject to the requirements. As Scotland does not operate under the environmental permitting regime for the regulation of waste sites, lower risk sites will still fall under the 1994 Waste Management Licensing Regulations. Although it is stated that this guidance will only be applied to such sites by application of best practice, care must be taken to avoid this becoming an automatic requirement for all applicants as this would be an extremely onerous task for low risk activity. Waste acceptance and biomass performance Validation monitoring should be carried out of every load for new waste streams for the first month of acceptance thereafter being relaxed to once every three months. If the process producing the waste stream changes then it may be appropriate to reassess the material on a more regular basis until satisfied that the material which is being received is consistent. This level of validation monitoring is viewed as extremely onerous and impractical. Pre-acceptance procedures should be highlighted as the key control focussing on composition and any potential for variability. In the case of an MBT site incorporating AD, it needs to be clear as to at what point this monitoring would be undertaken. Process Buildings All process buildings should be air tight, and be held under negative pressure with a minimum of three air changes per hour, vented to abatement. Assessments should be carried out annually demonstrating the integrity of the building and effectiveness of negative pressure. 1 P a g e
Specifying a minimum number of air changes regardless of location, operational conditions, waste type etc. is inappropriate. The final design of the air cleanup system, including the number of air changes should be based on a site specific risk assessment. A non-food waste facility which only receives and pre-treats waste during the day is unlikely to need this level of air extraction, particularly at night where it would result in unnecessary noise and energy consumption, compared with a food waste AD during the day in a sensitive location. The process building dealing with waste acceptance should be fitted with an airlock system. Where airlock facilities are not feasible air curtain arrangements would be considered BAT for the control of fugitive odour emissions during access and egress. Such systems should be installed on all entry points to buildings requiring negative pressure. This should again be subject to site specific risk assessment. Air lock systems for residual waste MBT facilities with AD are unlikely to require this and the location of some food waste facilities may make this an unwarranted operational constraint. Wastes should be stored no longer than 24hrs from initial acceptance onsite prior to introduction into the anaerobic digestion reactor(s) unless held in process tanks connected to abatement This is likely to be impracticable for residual waste facilities which accept large tonnages. Holding this waste for longer than 24 hours prior to the AD is unlikely to result in an unacceptable odour impact with good site controls. A site specific risk assessment would again be most appropriate, based on the waste type received, location, air extraction system installed and the system for the treatment of the extracted air. It should also be made explicit that any form of pre treatment (eg. holding in a buffering tank) should be acceptable as part of the definition of process tanks. Odour abatement and bioaerosols All odorous areas should be vented to appropriate abatement. Odour abatement systems should be designed to a minimum of 95% destruction efficiency or sufficient to meet 1.5OUE/m3 (or 1.0OUE/m3 for a hypersensitive population) standard at the site boundary. Demonstration of meeting the 1.5OUE/m3 standard should be provided within the application via full ADMS and AERMOD dispersion modelling. In addition it is considered best practice that applicants prepare and submit a method statement regarding how they intend to undertake the modelling in line with SEPAs guidance prior to actually conducting the modelling. Stipulating that 95% destruction efficiency is achieved would require monitoring both prior to and post the abatement system. Given that the key concern, and the information requiring validation for the air quality modelling, is the end of pipe emissions we do not consider that this requirement is appropriate. The requirement that ADMS and AERMOD should be used in all cases is considered unwarranted and should be based on the sensitivity of the facility location. SEPA guidance refers to either model as being acceptable. We agree that the submission of a method statement is good practice and this should consider whether the location of the facility and the sensitivity of the receptors warrants using both models. Validation of the abatement plant performance should be carried out annually via extractive odour monitoring. In addition performance indicators (such as biofilter pressure differential, liquor ph etc, scrubber liquor ph, redox and flow) should be established relevant to the abatement technology to monitor performance against design criteria. This is an unnecessary operational burden for a site which is in compliance with the odour conditions set out in the permit and where no odour complaints have been received. 2 P a g e
Containment all tanks containing liquids whose spillage could be harmful to the environment (liquid and slurries waste storage, buffer tanks, ractors, chemical and oil storage, digestate storage) should be bunded. This should not be a blanket requirement for all storage, as digestate can be stored in different forms. It should be decided through a site specific risk assessment. Modelling and impact assessment As part of the application an H1 impact assessment (carried out in accordance with the 2003 version available on SEPA s website) should be produced of emissions to air with full dispersion modelling where required All stack and flare heights shall be justified using D1 or dispersion modelling. No stack height shall be lower than the calculated D1 value without significant site specific justification. The terms stack and flare heights implies that this element refers to the emissions from CHP or flares only but the heading is confusing and conflicts with the specific requirement to model odour using AERMOD and ADMS in para 4.12. If the proposed approach is to use the H1 assessment to screen out all emissions other than odour then this should be clarified, although this highlights that a site specific risk assessment should be adopted for all emissions. Hierarchy of biogas use combustion within boilers usually acceptable as a standby arrangement only owing to reduction in efficiency. It is not clear what the implications of this statement are. The Guidance needs to clear up whether this would mean a plant would not be credited as BAT if it could have injected into the grid but has taken a different option. The guidance should also be clear that flaring is permitted where necessary, for example for safety reasons or during maintenance. The use of biomethane as a transport fuel should also be included in this hierarchy. Compared to other uses of biogas, its use for this application has unique benefits in that there are relatively few other options for decarbonising the HGV sector. The 2010 Carbon Trust report also drew out the carbon benefits of this use, stating that biomethane as a transport fuel has higher carbon savings potential compared to use for heat and electricity. Although this may be delivered through the gas grid, it could also happen through on-site upgrade and refuelling. Biogas combustion Desulphurisation plant should be provided to reduce Hydrogen Sulphide (H2S) concentration within biogas prior to combustion by a minimum of 90%. This requirement does not take into account the pre-treated concentration of H2S and it is not considered proportionate to the risk posed that desulphurisation plant is the default position. If the primary means of controlling H2S generation are adequate, e.g. controls on the input material, chemical dosing, and justifiable then the installation of desulphurisation plant should not be the default approach. 3 P a g e
Biogas engines It would be expected that an applicant would justify the levels of emission and abatement on a site specific basis. Where there is a structured argument put forward for achieving a different emission standard including all aspects including cost, efficiency, availability of technology, site specific impact at receptors etc SEPA would make a decision on BAT in the round. The following should be regarded as indicative BAT emission limits for the combustion of biogas within gas engines: Emphasising that these are only indicative limits and that ELVs should be considered on a site specific basis is crucial. Where a site specific risk assessment indicates that the existing ELV is adequate to ensure an acceptable level of impact then there should not be a default to requiring the reduced limit. NOx values of 250mg/m 3 are unlikely to be achieved without the use of specific lean burn designs (and a performance guarantee is unlikely to be forthcoming from engine manufacturers), which, given the variability of biogas methane concentrations, are likely to require derating affecting the overall efficiency of the electrical generation. This would have a negative impact both on the viability of the project and the aim of producing greater levels of renewable energy. The requirement to continuously monitor combustion efficiency will not provide significant additional benefits, and should be removed. For H2S levels, we are unclear how the 5ppm figure has been reached and, if adopted, this figure should remain subject to site specific risk assessment. The requirement to monitor inlet concentrations to CHP will also create practical difficulties. Biogas boiler For biogas boiler combustion it would be expected that an applicant should justify the levels of emission and abatement on a site specific basis. Where there is a structured argument put forward for achieving a different emission standard including all aspects including cost, efficiency, availability of technology, site specific impact at receptors etc SEPA would make a decision on BAT. The following should be regarded as indicative BAT emission limits: We again echo the sentiment in the biogas engines section to be careful to ensure the below table does not become the de facto standard regardless of location, facility design, etc. 100mg/m3 would be a more appropriate figure than 10mg/m3 for CO emissions. For H2S levels we repeat that we are unclear how the 5ppm figure has been reached and, if adopted, this figure should remain subject to site specific risk assessment. Pressure relief systems As part of any application, modelling should be conducted of any pressure relief valve systems at a credible H2S concentration to assess the odour and human health impact of any such event. As a minimum this assessment should take the form of puff modelling the methodology of which should be agreed with SEPA. This is considered an abnormal operating condition and would effectively mandate the use of ADMS as AERMOD does not contain a puff modelling capability Any application should contain a probabilistic risk assessment of the likelihood of a pressure relief event along with a hazard and operability (HAZOP) study reviewing options to reduce the risk to as low as is reasonably practicable. A HAZOP study is completed during the detailed design phase and this is unlikely to be progressed until the permit application has been made and the developer of the plant is more confident that a permit can be gained. Submission with the application is not considered appropriate but could be submitted to SEPA once completed. 4 P a g e
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