On-site Anaerobic Digestion Mash Direct

Transcription

1 Final Report On-site Anaerobic Digestion Mash Direct The Driving Innovation in Anaerobic Digestion (DIAD) demonstration at Mash Direct focused on the on-site anaerobic digestion (AD) of effluent (pulped vegetable discards and other organic residues) from Mash Direct s site (Newtownards, County Down). The report remains entirely the responsibility of the author and WRAP accepts no liability for the contents of the report howsoever used. Publication of the report does not imply that WRAP endorses the views, data, opinions or other content contained herein and parties should not seek to rely on it without satisfying themselves of its accuracy. Project code: OIN Research date: Jan April 2015 Date: 17th August 2015

2 WRAP s vision is a world in which resources are used sustainably. Our mission is to accelerate the move to a sustainable resource-efficient economy through re-inventing how we design, produce and sell products; re-thinking how we use and consume products; and re-defining what is possible through re-use and recycling. Find out more at This report was commissioned and financed as part of WRAP s Driving Innovation in AD programme. The report remains entirely the responsibility of the author and WRAP accepts no liability for the contents of the report howsoever used. Publication of the report does not imply that WRAP endorses the views, data, opinions or other content contained herein and parties should not seek to rely on it without satisfying themselves of its accuracy. Document reference: Driving Innovation in Anaerobic Diegestion Written by: Richard Gueterbock Front cover photography: Mash Direct logo While we have tried to make sure this report is accurate, we cannot accept responsibility or be held legally responsible for any loss or damage arising out of or in connection with this information bein inaccurate, incomplete or misleading. This material is copyrighted. You can copy it free of charge as long as the material is accurate and not used in a misleading context. You must identify the sourc material and acknowledge our copyright. You must not use material to endorse or suggest we have endorsed a commercial product or service. For more details please see our terms and conditions o website at

3 Executive summary There are significant opportunities for the wider uptake of Anaerobic Digestion (AD) across the UK by small and medium sized enterprises (SME s), as well as rural community plants. However more needs to be done to stimulate this sector. This report is focused on the second stage of the DIAD project awarded to Clearfleau for smaller scale on-site AD and relates to an on-site demonstration at Mash Direct's manufacturing facility in Newtownards, Northern Ireland. This DIAD report describes the demonstration project undertaken by Clearfleau using their modular AD plant (Small Scale Production Plant - SSPP) that was installed and operated on the Mash Direct site from February to June The purpose of the demonstration was to showcase the on-site AD system in the vegetable processing sector, assess performance and evaluate the new membrane based solids management system retrofitted to the SSPP unit. Background Clearfleau has demonstrated the high-rate liquid AD technology with larger food and drink processors. The BV Dairy plant in Dorset, (operational since early 2011) digests processing effluent and dairy residues, supplying renewable energy to the site. It has been operational for 4 years. Further reference plants are operating in the confectionery, distillery and food sectors. The Mash Direct project is the first trial to be undertaken in Northern Ireland and also in the value added vegetable sector. The focus of this phase of the project was on-site operation of a micro-scale AD unit (using both floatation and membrane thickening options to assess the optimal configuration for a full scale project) on the factory site, treating effluents and co-products from the production process, in a system that maximises biogas output and optimise project payback. The full scale project is likely to start in Quarter and will allow Mash Direct to make use of the renewable electricity generated in the production process, replacing purchased fossil fuels and reducing treatment costs. Post treatment, the plant is also able to facilitate grey water recycling, for use on site or for watercourse discharge. The Clearfleau on-site AD plants are able to treat factory trade effluent and higher strength materials generated on-site, but unlike other high-rate AD systems, can accommodate fats and greater variability in solids content. They lower effluent treatment and energy costs by: Reducing costs of running aerobic plants or by cutting sewer discharge costs; Cutting costs of disposal of residual sludge or high strength waste materials; and Reducing energy costs, as fossil fuels are replaced by renewable energy. Operation of SSPP At Mash Direct, the mobile demonstration SSPP unit was able to process an average of 336 litres of trade effluent and other materials per day. The full scale AD plant is expected to process at least 100m 3 per day of trade effluent, plus a range of solid residues. In addition to demonstration of the membrane system, the other innovative aspect of the project was the integration of solid vegetable residues in the liquid digestion process. This demonstration at Mash Direct has applications on other projects in the added value food and vegetable processing sector. A further project at My Fresh (similar vegetable processing company) will benefit from the trials data that has been generated. 1

4 The AD process effectiveness is based on extension of the period for which bio-degradable solids are retained and re-circulated in the reactor to enable methanogenic bacteria to fully digest degradable solids and optimise biogas output. It is also a significant innovation that higher solids residues from such factories can be added to a liquid digestion system. The SSPP demonstration exercise at the Mash Direct site (at Ballyrainey Road, Newtownards) was carried out in three parts: Part 1 from commissioning to running at steady state, using factory effluent as feedstock and solids separation using the new membrane filtration unit. Part 2 using the same factory effluent as feedstock and solids separation running the alternative cavitation air flotation (CAFT) unit rather than membranes. Part 3 using factory effluent and adding increasing proportion of solid residues, as feedstock and solids separation running the CAFT to optimise performance. The project was very successful in relation to the inclusion of the degradable solids in the system. However, the initial membrane focused element of the trial was less successful and due to this Clearfleau plans further trial activity with the use of membranes linked to the Ambigas project, which has just got underway. The Ambigas project, which is funded by Innovate UK is a European project led by Southampton University that is focused on the deployment of membrane technology in a low temperature based AD system. For the Mash Direct project Clearfleau used robust hollow fibre micro-filtration membranes, from Koch Membranes. These were trialled at another site last year and fully integrated within the SSPP unit during the DIAD funded refurbishment of the SSPP unit in late A membrane based approach to degradable bio-solids recirculation will significantly reduce the chemical (polymer) consumption compared to the flotation process used at BV Dairy and on other large projects. The Ambigas project is due to take place at BV Dairy during Trial Follow-up The biogas from the full scale unit at Mash Direct will be fed to a CHP engine, to supply power to the factory. The project qualifies for Renewable Obligation certificates (ROCs) under the NIRO scheme. Anticipated capital investment for the full scale plant (to include cleansed water discharge is about 3m. The ROC revenue will be over 500,000 per annum. There were a number of visits to the demonstrations plant while it was located at the Mash Direct site and there is some interest in full scale plants from companies based in Northern Ireland and The Irish Republic. Also, My Fresh (part of the William Jackson Food Group) visited the trial unit, while assessing the technology for a possible project starting late Clearfleau will also provide information on the Mash Direct project for wider dissemination. Clearfleau is budgeting for future multiple sales due to the experience with the Mash Direct project and is confident it will supply clients both in the UK and in Ireland. The adoption of this and other on-site renewable technologies in the SME sector will provide access to on-site renewable energy, with a major impact on the carbon footprint, emissions and long term sustainability of the food processing sector in the UK, Northern Ireland and in due course the Irish republic and hopefully in other export markets in the EU and elsewhere. 2

5 Contents 1.0 INTRODUCTION AND BACKGROUND Mash Direct Project Background On-Site Digestion Technology Technology Development and Project Concept Comparison with existing process Benefits of the anaerobic digester/membrane system TECHNICAL APPRAISAL Process optimisation for smaller-scale digestion Process optimisation to ensure discharge to water course Optimisation of membrane performance and integration Optimisation to allow replicability through modular design Maximising COD removal and biogas output TECHNOLOGY and METHOD Technology Platform Demonstration Duration Plant Operation Membrane Phase CAFT Phase DEMONSTRATION EVALUATION Process Overview Project Achievements Impact of Membrane System Mash Direct Project Future Development Activity TRANSFER To MARKET Commercialisation Sales Expectations Wider environment benefits DEMONSTRATION CONCLUSIONS ANNEX 1 PROCESS FLOW DIAGRAM ANAEROBIC / AEROBIC

6 Glossary CAFT - Cavitational Air Flotation Thickener CSTR - Continuous Stirred Tank Reactor CO 2 Carbon Dioxide NO 3 Nitrate NH 4 Ammonia PO 4 -P Ortho-Phosphate S-BOD Soluble Biological Oxygen Demand S-COD Soluble Chemical Oxygen Demand SO 4 Sulphate SSPP - Small Scale Production Plant T-COD Total Chemical Oxygen Demand TKN Total Kjeldahl Nitrogen TN Total Nitrogen TSS Total Suspended Solids VSS Volatile Suspended Solids Acknowledgements Clearfleau is grateful to the engineering team at Mash Direct who supported the project and to the colleagues at WRAP for their support during this protracted project activity. 4

7 1.0 INTRODUCTION AND BACKGROUND 1.1 Mash Direct Project Background The SSPP demonstration project with Mash Direct was approved by WRAP in 2014, following issues with the planned demonstration at Hall and Woodhouse Brewery (itself a replacement for Hook Norton). This was based on concerns about the level of resources required for the demonstration at the brewery, and also the impact of the recent FIT degression which has increasingly undermined smaller scale on-site AD, particularly for low strength feedstocks. Mash Direct s feedstock offers a higher COD load but a low fat content suited to membrane based solids management. As a premium processor, the award-winning SME manufacturer is part of a family farming and food production enterprise in County Down, Northern Ireland. Mash Direct produces an innovative range of quick-serve mashed root vegetable and potato products plus other quality vegetable products. Most of the vegetables are grown close to the factory, delivered for processing within minutes of harvesting, ensuring maximum flavour and quality. Recent rapid growth has highlighted the need improve residue management and issues relating to the site s power supply. Clearfleau has demonstrated how their high-rate liquid Anaerobic Digestion (AD) technology is suited to treating residues from food and drink processors. Clearfleau's initial plant built at BV Dairy in Dorset was completed in Funded under the Environment Transformation Fund (ETF) it was a demonstration plant for the food sector. Since then plants have been built on larger sites in the distillery (on 2 Diageo sites) and food sectors (plants for Nestle and Olleco). In 2015 further plants are being built in the dairy and food processing sector. The intention for the demonstration phase of the DIAD project was to target an SME (and smaller family owned) food processing company to achieve a number of objectives: Showcase the use of membranes to enhance efficiency and reduce chemical costs within the AD process. Evaluation of the membrane system for use in the added value vegetable sector. Comparison of results from the membrane system with the existing CAFT approach. In addition to supporting Mash Direct with the SSPP s operation, the demonstration also sought to address questions specified by WRAP for the DIAD program. These include: Optimisation of the digestion process to facilitate water course discharge; Membrane integration with the AD process and solids management system; Design optimisation based on modular system and manufacturing efficiency; and Replicating process efficiency (COD removal/biogas output) with new feedstocks. The project included specific process modifications, including modularisation and the DIAD funding contributed towards the cost of running the demonstration as well as the installation of the membrane system within the SSPP demonstration unit. With respect to Mash Direct, their aim was optimise the treatment process for the site s specific production effluent and the solid residues, while maximising on-site generation of biogas. The full scale AD plant will be located on the potato factory site, close to the existing treatment facility that it will eventually replace and as a demonstration site it will include visitor access. The demonstration was designed to ensure the proposed on-site AD technology was suited to the operational needs of the Mash Direct site. In addition to cutting energy and treatment costs, on-site AD will be part of wider carbon reduction activities at Mash Direct. 5

8 Providing a technical solution for the increasing output of production residues, the full scale AD project will also provide a benefit to local farmers (product suppliers) with the supply of nutrient rich bio-solids. It will also provide a good illustration of the circular economy in practice (with a closed loop on-site treatment system delivering energy from residues), as well as helping to make the Mash Direct business more sustainable. 1.2 On-Site Digestion Technology Clearfleau Ltd, a British AD technology company, provides on-site treatment solutions for effluents and by-products. The company is currently building medium scale (mainly under 500kW electrical output) on-site projects, in the distillery, food and dairy sectors. For Mash Direct, following the demonstration, a full scale AD project is due to proceed during Q and will provide a reference for this growing food sector as well as for on-site AD in Ireland. A modular version of Clearfleau s liquid digestion system was developed for on-site trials on substrates from the food, beverage and bio-fuel sectors. Although the company is building a number of medium scale on-site AD plants, there was an opportunity to develop commercial versions of the mobile unit for sites with more limited feedstock volumes or space. However, this aspiration has not been helped by rapid and excessive degression of the sub 250kW FIT rate, which made it harder to provide an attractive payback for smaller on-site AD plants. Hence, Clearfleau is keen to enhance the efficiency of its process and is working on adoption of membranes for the solids management system. This will allow site operating costs to be reduced and build in added robustness to the process, which is vital for on-site industrial AD. Image 1: SSPP (mobile unit at Mash Direct) Clearfleau s approach has been shown to work for feedstock throughputs of over 100m 3 per day. However, interest was being shown by processors with lower throughput. Clearfleau is developing the process for under 100m 3 /day, with containerised ancillary equipment as part of the design. For Mash Direct it was hoped to specify the membrane system for the full scale plant. However, based on the experience of the demonstration on site a decision has been made to use the proven cavitation air flotation thickener (CAFT) system. The demonstration has also being monitored by My Fresh Ltd, another leading vegetable processing site in the UK, where a new project is planned for 2016 and will use the system and design that will be developed from this project. Other Northern Ireland companies are also interested having seen the trial and will follow the Mash Direct project. 6

9 1.3 Technology Development and Project Concept Based on trials that have been undertaken previously using the membrane based thickening system, further funding was sought from the DIAD program to run the on-site demonstration. The aim, to provide data to develop the detailed design for the full scale AD unit for installation on the Mash Direct site and generate confidence in the system in a fully commercial circumstances. However, based on less than satisfactory results with the membranes, further development work is required and Clearfleau is now involved in the Ambigas trial funded by Innovate UK. The Mash Direct site is located in Northern Ireland, where to date the development of AD in the region has been focused on merchant (food waste) plants and some on-farm manure plants. The success of the DIAD demonstration has ensured that the full scale project goes ahead at Mash Direct but should also facilitate development of the market for high-rate liquid AD in the added value vegetable processing sector, where existing higher solids solutions are less cost effective. It should also help raise the profile of on-site industrial AD in Ireland, where there has been limited development to date and in due course elsewhere in the EU. Image 2: Nestle on-site AD plant supplied by Clearfleau At Mash Direct, the full scale on-site AD unit will be designed to process at least 100m 3 per day of liquid trade effluent. The SSPP unit installed on the site was developed to run trials on a range of feedstocks and has undertaken 10 in the past 4 years. The unit includes full process control and monitoring equipment and a small laboratory. It has been modified to integrate the membrane unit within the 40ft container unit. A specific advantage for the food processing sector is that this is the only high-rate AD process able to digest fatty effluents. While this does not apply to the Mash Direct feedstock, for other sites this means that all bio-degradable materials generated in the production process can be accommodated in the digester. Due to the extended solids retention time, the design is able to optimise biogas output (this can be up to 20% higher than other high-rate AD systems). The process also facilitates a reduction in effluent treatment costs, due to its effectiveness which maximises the COD removal (95-99%) and hence biogas output is due to the complete mixing of the liquors in the anaerobic reactor and the sustained exposure of the active biomass to the incoming COD load. This is achieved by breaking the link between solids retention time 7

10 (of up to 50 days) and liquid retention in the digester tank (reduced to about 5 days). This limits digester tank size and hence capital and operating costs for this highly mixed system. The process enables the slow acting methanogenic bacteria to fully digest the biodegradable solids. The challenge that is being addressed is to do this on a smaller scale, based on an AD unit that can be manufactured off-site in order to minimise production costs and limit the impact of installation on busy, confined industrial sites. The pre-commissioned units will be delivered to site for connection to the on-site feedstock. Multiple SME food processors will be able to make use of smaller scale AD technology if it can be made more cost-effective. 1.4 Comparison with existing process The existing system at the Mash Direct site is an aerobic treatment process that has been upgraded on a number of occasions, as output has expanded. The changes envisaged as part of this project are intended to generate on-site energy and provide a more sustainable treatment solution for effluent and co-products from the factory. This is based on the fact that aerobic treatment has a greater energy demand and hence a higher carbon footprint. In addition to revenue from the energy generated on site, the introduction of AD technology will reduce the site s carbon footprint. The anaerobic process has a relatively low slave energy demand, whereas aerobic treatment requires significant power for the aeration. A reduction in treatment energy combined with energy use on-site and further carbon savings from the reduced need for off-site haulage and the use of residual sludge as a fertiliser on local farms. Further, at Mash Direct the AD plant will eliminate the need to install a new high voltage power supply that will otherwise be required in order to meet site expansion plans. The Clearfleau system has a valuable closed loop application (as demonstrated with larger plants on Diageo distillery sites with just three outputs: biogas, clean water and bio-solids) with local farmers that supply the processing operations being able to benefit from access to nutrients that can be applied to the land for subsequent crops. This is a valuable commercial application of the principles of the circular economy to the food industry in the SME sector. The anaerobic system is more biologically stable when compared with an aerobic system and hence offers a more robust treatment process that offers greater environmental protection to the sensitive rural area in which Mash Direct s factory is located. Also the closed loop process will minimise any odour risk from the site compared to the alternative of aerobic treatment. The proposed AD plant will limit the risk of higher COD discharge or diffuse pollution from the site. At a later date there may be an opportunity for the cleansed water to be further polished to be recycled for boiler feed and other non-food contact uses. This demonstration of how on-site AD can be deployed on rurally located food businesses has wider applications. 1.5 Benefits of the anaerobic digester/membrane system The current on-site AD system design being installed by Clearfleau on larger sites consists of a highly mixed digester tank followed by the conventional CAFT (flotation based) flocculation process that is used for solids capture and allows degradable materials to be returned to the digester, while water is removed for further treatment or sewer discharge. The membrane system replaces the flocculation based solids removal. Compared to the current CAFT solids removal process being deployed by Clearfleau on commercial sites, the membrane system is seen to have the following advantages: The regular dosage of polymer for flocculation of the biomass is not required; It operates at higher solid concentrations with subsequent higher solids discharge; Higher solid concentrations can decrease reactor volume and increase contact time; The system captures residual solids so that the effluent discharge is free of solids; 8

11 The membrane will retain all the solids without use of polymer, which can be a significant cost. However, membranes can get biologically fouled and so need cleaning. However, the power consumption of a membrane system is higher compared to a flocculation process but savings in chemical consumption can make it a more cost effective system. The membrane cleaning requirements, which are a key part of the operation process needs to be further evaluated, as this was not possible at Mash Direct due to other performance issues on this site. The membrane cleaning is automated to limit operator involvement and consumes a nominal amount of caustic and hypochlorite. The frequency of cleaning is not predictable and was not satisfactorily evaluated as part of the project. In the light of the outcome of the project and the decision to make use of the CAFT system for the full scale project, Clearfleau will be looking for additional demonstration sites in 2016 to further evaluate membrane separation. Image 3: Interior of SSPP Unit Following Refurbishment 9

12 2.0 TECHNICAL APPRAISAL Deployment of the SSPP demonstration unit at the Mash Direct site enabled the project team to follow up work undertaken in the initial feasibility phase (albeit with lower COD brewery residues and some initial work at Pure Malt's site in Haddington, Scotland, with the externally mounted membranes) to assess how the system operated in a commercial environment. In addition, we have undertaken further work on the wider efficiency of the AD process that will be fed through to the final design of the plant for Mash Direct. Project activity included: 2.1 Process optimisation for smaller-scale digestion The earlier feasibility phase of the project included design activity supported by laboratory based digestion demonstrations. This demonstration phase of the DIAD project was being undertaken to operate the membrane system on a commercial site with fully representative feedstock. It involved refitting the existing SSPP demonstrations unit with a membrane module and other adjustments to the process to accommodate the membrane package. As a small family business the demonstration needed to convince the Directors that on-site AD was a viable proposition for the business and could handle the range of residues. Image 4: SSPP unit being installed at BV Dairy 2.2 Process optimisation to ensure discharge to water course A key element being demonstrated on the Mash Direct site is the evolution of Clearfleau s innovative solids handling system in the AD plant. As indicated in 2.1 the use of membrane thickening was tried on a demonstration with malting feedstock at Pure Malt in 2014; prior to the move to Mash Direct. This was the first fully commercial demonstration with the updated SSPP unit. The membranes can replace the polymer based CAFT system that has been used in a range of dairy and other higher solids projects to enhance the operation of the system. Due to the membrane filtration pore size and extent of COD removal, the AD plant is able to achieve water course discharge standards for sensitive water systems. The permitted COD discharge concentration to the sewer at Mash Direct is 1,000mg/l (flow 150 m3/d maximum ammonia 100 mg/l NH4-N, FOG 100mg/l, SS 200mg/l). On the basis of the proposed design for the full scale plant, with feed of 165 m 3 /day (rising to 202 m3/day), the expected COD in the discharge is 650mg/l (ammonia 90 mg/l NH4-N, FOG 1> mg/l, SS 200mg/l). 10

13 Water purification can be added at the end of the full process (at a later date) to allow use of grey water on-site for boiler feed and other purposes. Also, this will facilitate discharge of cleansed post AD effluent to the local stream, delivering a further environmental benefit. 2.3 Optimisation of membrane performance and integration The in-line membrane unit will ensure capture of all biomass (but not dissolved nutrients) for return to the digester, enabling optimisation of biogas output and a potential reduction in operating costs, through limiting chemical use. This aim is to reduce on-site consumption of chemicals in two ways, by reducing existing use in the aerobic waste water treatment plant as well as requiring an overall lower chemical use in the AD plant. Furthermore the demonstration was intended to allow Clearfleau to evaluate membrane effectiveness and refine design to balance capex against operating costs. However an economic appraisal of the membrane system could not be undertaken due to the relatively poor performance in the membrane phase. Cleaning frequency (and cleaning chemical consumption) will be further evaluated in a commercial environment. This will happen with the Ambigas project, which will provide experience of extended operation at a creamery site. 2.4 Optimisation to allow replicability through modular design The DIAD contribution towards the on-site demonstration phase, as well as the cost of the refurbishment of the mobile unit, has helped progress development of the system. The use of containerised units is a key part of Clearfleau s strategy as it will not only help with the development of the SME sector (manufacture at affordable cost, ease of installation) but also with access to export markets (key components manufactured in the UK and containerised). The SSPP unit that has been operated at Mash Direct has incorporated a number of process enhancements based on the feasibility demonstrations. These included: Integration of membrane plant into the container; Redesign of the chemical storage and dosing area; Redesign of mixing and sludge pump layout. Cost effective design of the core ancillary equipment is fundamental to ensuring that the onsite AD plants can be built at a cost effective price that will ensure commercial viability. The AD rector tank will be supplied using local contractors and as with future export projects, the modular units will be manufactured off-site and wet tested prior to installation at the factory and on-site commissioning. This will enhance the efficiency of the manufacturing processes and help reduce unit costs for future export plants. 2.5 Maximising COD removal and biogas output The system is designed to optimise COD removal based on degradation of degradable solids in the digestion process. Due to the relatively consistent nature of the feedstock, operation of the plant is simpler than where flows and loads were to vary massively, as with merchant AD plants. The demonstration has shown a key attribute of the Clearfleau system - its ability to provide process stability and cope with load variations and hence optimise biogas output. The on-site process has also been proven to produce biogas with optimal methane content, regardless of the solids management system. This is due to effective mixing of liquors in the reactor, optimising exposure of biomass to the incoming load. Also biogas output volume is directly related to the level of COD load removal, which should be at least 95%. The on-site demonstration phase has allowed us to assess additional solid feedstock materials from the factory site that will enhance biogas output. However, the CAFT system has shown better performance than the Membrane system. At this stage we feel unable to recommend it for the Mash Direct project without further development work and additional trial activity. 11

14 3.0 TECHNOLOGY and METHOD 3.1 Technology Platform The SSPP refurbishment included changes to process control and monitoring equipment and installation of the membrane module in the SSPP container unit. The installation was based on the design and demonstration work that was undertaken during the feasibility phase. The on-site demonstration phase at Mash Direct, in a fully commercial environment, has allowed us to evaluate the following issues for the premium vegetable sector: Biogas production with the mobile AD plant, treating the liquid factory waste; Cost effective use of advanced membrane technology in commercial setting Modular, off-site construction to reduce costs and minimise on-site disruption; Prior to the on-site demonstration, site wastewater was sampled over 10 days with a 24 hour composite sampler and temperature logger installed on the factory - the data shown below: BOD COD (total) Nitrogen (total) Potassium (total) Ammonia as N Phosphorous Ortho as P 4,090 mg/l 40,700 mg/l 146 mg/l 918 mg/l 15.2 mg/l 30.2 mg/l 3.2 Demonstration Duration The Small Scale Production Plant (SSPP) demonstration exercise at the Mash Direct was undertaken in phases (with three work elements) post installation on site in early January: Initial set up and then commissioning of membrane unit (from 25 th Jan to 15 th Feb) Following the refurbishment of the demonstration unit some further pre commissioning and installation work had to be undertaken by the Clearfleau operations team on site. Membrane operation (15 th Feb to 20 th April) including load build up to operating levels Part 1 from commissioning of the SSPP unit to running at steady state using factory. effluent as feedstock and solids separation trial using the new membrane filtration unit. It was intended to run a second phase with increased solids residues. This could not be undertaken due to membrane performance issues but was run with the CAFT. Floatation operation with original CAFT system (for comparison 27 th April to 6 th June). Part 2 using the same factory effluent as feedstock but switching solids separation running the alternative cavitation air flotation (CAFT) unit rather than membranes. Part 3 using factory effluent and then adding increasing proportion of solid residues, to the digester feed, with solids separation using the CAFT to optimise performance. Commissioning and biomass build-up started on 25 th Jan The membrane phase of the demonstration started on 15 th Feb and due to the performance issues was extended until 20 th April (for 10 weeks). The results have been detailed in Table 2 below. This shows that the SSPP unit achieved a relatively consistent level of performance and has provided some data for the design phase of the full project but overall performance was disappointing. For the CAFT phase (initially intended to benchmark the membrane performance) was undertaken over a further 4 week period. The membrane system was shut down and the plant operated using the CAFT unit to provide some comparative data. Part 2 of the SSPP demonstration lasted for 4 weeks and was then followed by a further 2 weeks with higher solid feed being added to the digester. The CAFT out-performed the membrane system. 12

15 The entire demonstration process successfully showed that the Mash Direct residue streams are bio-degradable and digestible, although the best results were achieved in Part 2 and Part 3 of the trial, as outlined in the report. Part 1 was less successful, in part due to issues with solid material in the seed inoculant. This prevented effective operation of the membrane thickening apparatus and hindered the operational build up. This was a useful exercise in understanding operating parameters of the membranes and it took several weeks for solids to degrade to such an extent to allow successful operation of the CAFT solids separation unit. Table 1 below summarises the results achieved in Part 1, week 1 (commencing ) to week 10 (commencing ). The initial stage of this trial was intended to acclimatise the inoculant seed to the factory effluent feed stock and establish steady running conditions. The inoculant seed used came from Carrow Reagh Farm, Dundonald which operates a solids based anaerobic digester, fed with a mixture of cow slurry and silage. The seed was not ideal and contained grass fibre, which were slow to break down in the digester undermining effective solids removal. It was not until week 8 that the plant could be run effectively. 3.3 Plant Operation On 17 Feb 2015, the feed of Mash Direct s wastewater to the anaerobic reactor was started. The anaerobic sludge that was seeded into the reactor began to be adapted to the site s wastewater feed. The membrane unit was used with the AD reactor for solids management process (breaking the link between solids retention time SRT and hydraulic retention time HRT). The aim was to run this system for about 5 weeks, followed by a 4 week period when the CAF unit was put into operation (on 8 th April). Due to a number of issues, including issues with the seed quality, the duration of part 1 was extended and ran for 10 weeks. Table 1 Anaerobic digester/membrane plant results Date Digester Solids COD in COD out COD efficiency Methane Yield & % Biogas production [mg/l] [mg/l] [mg/l] [%] m 3 /day [Gas l/g COD] Week 1 46, Week 2 54, Week 3 40,900 * Week 4 15, ,280 * Week 5 15, ,753 4,084 92% ** Week 6 13,240 52,264 3,972 92% ** Week 7 11,775 44,300 2,187 95% ** Week 8 11,233 37,800 3,502 91% ** Week 9 9,950 21,708 2,440 90% ** Week 10 11,080 31,350 6,600 89% ** Average 12,600 57,997 3,797 92% ** * Unreliable performance - pump consistency issues ** inaccurate measurement of gas yield In Part 1 an average COD removal of 92% was achieved. The methane concentration was good at 53% although overall methane yield was poor. In part 2 the in-line gas flow meter was replaced with a volumetric gas meter. The increased methane yield immediately indicated that the gas flow meter was reading incorrectly and the methane yields in Part 1 hence should have been ignored. COD removal over Part 2 and Part 3 of the trial was 93%. It can be expected that the COD removal of the full scale plant will better this because even in the final stages of the trial there was still some residual solids material from the inoculant seed carrying over into the CAFT final effluent which increased the solids carryover and the COD of the final effluent. If the result for week commencing is ignored the COD removal for the final five weeks of the trial is 95%. 13

16 Also good solids capture indicates the solids recovery system will be successful and the biomass will not be flushed away with the effluent in normal operation. The average methane yield over Part 2 was 0.30 m 3 CH 4 /kg COD removed. For Part 1 the average methane yield was 0.09 m 3 CH 4 /kg COD removed and in Part 3 were 0.29 m 3 CH 4 /kg COD removed. The methane yield in Part 1 is lower than would be expected. A significant improvement in methane yield was noticed when the in-line flow meter was exchanged for an in-line volumetric gas meter. The concentration of methane averaged 52.4% over Part 2 of the trial period. Table 2 Anaerobic digester/caf based plant results Date Digester Solids COD in COD out COD efficiency Methane Yield & % Biogas production [mg/l] [mg/l] [mg/l] [%] m 3 /day [Gas l/g COD] Week 11 11,880 43, % Week 12 10,500 48, % Week 13 11,320 41,880 1,365 96% Week 14 12,680 53,100 1,493 97% Average P2 11,575 46,701 2,160 93% Week 15 13,075 23, % Week 16 13,860 24,660 1,545 94% Average P3 13,468 23,905 1,823 93% Average 2&3 12,206 39,103 2,048 93% The trial was undertaken from the 17 th February for 16 weeks until the 5 th June The trial was originally scheduled to last 12 weeks but was extended to compensate for delays in start up and to allow the solids in the inoculant seed to degrade sufficiently to allow successful use of the CAFT separation equipment. The trial data was also used to verify the final design parameters and provide Mash Direct with confidence in the performance of a full scale plant. Throughout the demonstration, the average temperature of the digester was kept at 34.4 C, with an average ph 8.2. The average retention time for the incoming wastewater feedstock within the digester/membrane plant was approximately 6.8 days at a dry solids content of 1.8%. These figures are a good indicator for design of the full scale digester and will be used for the design phase for the plant to be installed at the Mash Direct site later this year. The membrane based phase of the demonstration was completed on 20 th April. This was followed by a 6 week period using the CAFT system, which having achieved a satisfactory level of operation that has provided Mash Direct with confidence in the CAFT system rather than the membrane system as well as the data that is required to undertake detailed design and provide process guarantees for this project and for other projects in the added value vegetable sector. Although the membrane system was less successful, we will continue to develop the membrane technology as part of the Ambigas project, funded by Innovate UK. 3.4 Membrane Phase For the project Clearfleau used robust hollow fibre micro-filtration membranes, provided by Koch Membranes. This were also used in a preliminary demonstration that was run at the site of Pure Malt in Haddington, Scotland (immediately after their purchase) but were only fully installed in the SSPP unit, following the refurbishment programme at the end of The SSPP unit was fed with factory effluent, increasing the Feed to Mass ratio. This allowed anaerobic bacteria to acclimatise, allowing the reactor to mimic plant operating conditions. In order to increase the Feed to Mass ratio, a controlled increase in rate of feed was allowed. 14

17 During the first 5 days of the membrane demonstration, the COD decreased gradually and the system reached a stable level of COD removal efficiency of ~90%. However, blockages within the recirculation pump (feeding the seed) in the first week resulted in the membrane plant under-performing and hence the digester was unable to be optimised. Cavitation also inhibited the pump from pumping sludge continuously through the membrane unit and back into the digester. This situation will not occur in the full scale unit due to design changes and healthy seed (there were some initial issues with seed quality and speed of adaption). The blockages resulted in poor feed quality to the digester and lack of continuous operation of COD removal. The decision was made to extend the operational period of the membrane phase and then run the CAF for a shorter period for comparison. In the latter part of the membrane demonstration, COD efficiency increased to a maximum of 95%. The average biogas production rate during the membrane demonstration was l/g COD and a methane content in the biogas of 55%, which is comparable to what is expected on this type of material and close to the performance levels that had been indicated to Mash Direct. Overall, the membrane demonstration on the Mash Direct feedstocks has confirmed the expectation of performance based on earlier demonstrations. The addition of the membrane based thickening process was accomplished without any significant issues (once the pump issue was addressed and seed had acclimatised). Initial problems that were encountered were mechanical and had more to do with seed quality and the membrane feed mechanism. Image 5: Interior of SSPP (showing membrane unit alongside CAFT) The interruptions to the demonstration due to problems with the re-circulation pump issues persisted intermittently until the end of the demonstration. Hence it was difficult to collect consistent data from the operation of the digester. However, the overall performance of the membrane unit in producing a low COD permeate was as anticipated. In future plants will be fitted with a membrane unit with a different feeding mechanism that will avoid the issues experienced during the SSPP demonstration and operation will be much more stable. The project partners are confident in the ability of the AD system to remove up to 98% of COD from the factory waste waters and will provide process guarantees at 95%. 15

18 3.5 CAFT Phase The required level of bio-solids separation was not provided on a sustained basis, using membrane separation. For the remaining 6 weeks of the trial the switch was made to the traditional cavitation air flotation thickener (CAFT) to manage solids separation. From week 11 to week 14 (Part 2), the SSPP unit was fed with the factory effluent and the CAFT was run to separate the solids. During Part 2, COD removal ranged from 83% to 97% with an average COD removal of 93%. The CAFT thickening process worked efficiently> High COD removal efficiencies were consistently recorded for the final three weeks of Part 2. There was still some solids carry over from the initial seed which decreased the level of COD removal efficiency. Even so it is expected that in the full size plant COD removal efficiency of over 95% will be achieved. In Part 3 (week 15 and week16) the SSPP was fed factory effluent and higher solids material from the processing site. The solids were macerated using a food blender and fed directly into the digester on a batch basis using the thickened sludge return pump, replicating the system that will be used for the proposed full scale plant. COD removal efficiency was steady at 93%. Again it can be expected that COD removal efficiencies in excess of 95% will be achieved for the same reason as in Part 2. The solid feed material was not seen to be adversely affecting the thickening process. The removal efficiency is calculated from the total COD measured at the effluent discharge of the thickening equipment. This total residual COD also includes any unrecovered bacterial biomass. The COD removal figures are actually higher than presented if this contribution to the total COD measured at exit of the thickening equipment is considered. The CAFT indicates the solids recovery system will be successful and the biomass will not be flushed away with the effluent in normal operation. Capturing the solids in the CAFT had no adverse effect on the anaerobic biomass. The efficiency of the biomass in converting COD into CH 4 was unaffected by exposure to oxygen. A branched cationic polymer was used to flocculate the biomass prior to capture in the CAFT. Optimising CAFT performance a best polymer dosing rate was established of 8 kg poly/tonne dry solid (TDS). This is a relatively high dosage rate of polymer and it is expected that if a different inoculants seed is used for the start up of the full sized plant a more typical polymer usage of 4 kg poly/tonne dry solid (TDS) will be achieved. Average methane yield over Parts 2 and 3 of the trial was 0.265m 3 CH 4 per kg COD removed. An average methane yield of 0.26 m 3 CH 4 /kg COD removed was achieved in Part 2 - with a methane concentration of 53%. The methane yields and concentration in the biogas were consistent throughout this part of the trial. Methane yield was similar during Part 3 of the trial with an average of 0.29m 3 CH 4 /kg COD removed (average 53% methane concentration). This demonstrated that addition of the macerated solids did not have a marked effect upon methane yield or methane concentration. Methane yield was maintained with the addition of the solids showing clearly the added solids were contributing to the methane production. It was possible to collect data from this phase that will be helpful in the design of the full scale plant and this gave Mash Direct confidence that the system will manage all their feedstock. 16

19 4.0 DEMONSTRATION EVALUATION The demonstration project was a partial success in that it was possible to demonstrate that a new feedstock was able to be successfully degraded by the AD process. Eventually we would hope to make use of the membrane system with such substrates but it is clear that we need to do more on-site evaluation and we hope that this will be possible following the Ambigas project (see below) which will include an on-site evaluation phase in early We also want to develop the membrane system for a number of export projects that are expected to go ahead in 2016/2017. The work that was undertaken during the trial has been invaluable with respect to the operational experience gained with the membrane system on a commercial site although it is recognised that further development is required. 4.1 Process Overview By combining both the site s waste waters and the solid waste residues in the digester, Mash Direct s on-site AD plant will maximise overall energy output (and revenue) from anaerobic treatment whilst minimising the footprint of the plant. The final design for the project has been assisted by the information gained from the on-site operation of the SSPP unit. The liquid feedstock will be fed into the digester tank upstream of the chopper pumps and mixed immediately into the CSTR tank with the jetting system. All the mixing equipment is sited externally of the digester tank and the injection nozzles ensure the contents of the tank is consistently mixed, it should be noted that there are no moving parts inside the digester. Digester heating is applied through a heat exchanger, with nutrients added where necessary to maintain a healthy biomass and constant reduction in load. With a completely mixed digester, tank height can be varied to suit the location. Residual digestate is pressed and resultant liquors further treated prior to water recovery. Following anaerobic treatment the residual COD after the digester may be further reduced by an aerobic (Sequential Batch Reactor) system to obtain the reduction in COD post digestion from the anticipated level after the anaerobic treatment. This will allow cleansed water to be discharged to sewer or recycled for use in boiler feed water or for on food contact uses. Image 6: Interior of SSPP unit (showing laboratory and controls) 17

20 Biogas from the AD process is stored in the headspace of the digester tank and is expected to be above 55% methane and low in hydrogen sulphide. Ferrous salts are added as part of the AD process to fix most of the sulphide and remove it from the biogas. The biogas will be fed to a CHP unit or on-site boiler to supply energy back to the site for production processes. 4.2 Project Achievements The economic benefits of on-site AD are based on its ability to cut effluent treatment costs and also site energy costs. The anticipated energy savings (from the lower energy demand for effluent treatment and the generation of the renewable energy fed into the factory) are supplemented by revenue from renewable energy incentives The potential economic benefit of system has been highlighted to Mash Direct by the on-site SSPP (membrane/caft) demonstration. The company has seen that with onsite AD it is better able to manage the increased volume of production residues as the business expands. Mash Direct are having to replace an existing aerobic facility and although the AD plant will cost more the return on investment should exceed 25%, based on the ROC rate available for sub 500kW AD plants. This payback is supported in that they do not need to implement a proposed project to bring high voltage power to the site. The project has partially achieved a number of the objectives that were set out in the goals: Membrane efficiency: system efficiency can be enhanced and chemical costs reduced however for this feedstock it has been determined that the established CAFT system is still superior and hence is the preferred choice for the full scale plant. Membrane evaluation: the system is suited for use in the added value vegetable sector but it does not yet have the CAFT reliability and further development work is required. CAFT Comparison: results from the membrane system where inferior to the CAFT but this was in part due to issues with the quality of seed provided by the client. However use of the membrane system was sufficiently successful to justify further development. Water discharge: the operation of the SSPP and quality of the cleansed water output were sufficient to encourage Mash Direct to consider investing in grey water discharge. Membrane integration: the operation of the membrane system as an integral part of the SSPP system was a success, even if the actual performance was not as expected. Design optimisation; the deployment of the membrane in the SSPP alongside the CAFT worked well and can be replicated for future modular plant design for export projects. Process efficiency: efficiency of the system (COD removal/biogas output) with the new feedstocks was not as good as expected but still underlined the viability of the process. Overall, while the actual data produced during the on-site membrane demonstration was not as convincing as had been hoped, the system was shown to work, and we are confident that we can produce a more efficient process with the use of membranes as an alternative to the CAFT system, whereby site operating costs can be reduced (lower use of polymer) without a significant increase in overall capital costs. However, more work is required on management of the membranes and more deployment trials will be undertaken in Impact of Membrane System The membrane system will allow an easier means of automation and reduced involvement of an operator, plus lower chemical costs. The trial showed how easy it was to operate the system but also highlighted its sensitivity to non-degradable solids in the feed. It can be an easier system to operate than the CAFT (it is less sensitive to changes in quality of the feed) and the operating cost are lower, as the requirement for polymer in the CAFT is eliminated. 18