LIFE MAD but better. Layman s report.

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1 LIFE MAD but better Layman s report. Sewage sludge disposal is a major issue in developed countries. The EU LIFE MAD but better 1 project aimed at developing, implementing and demonstrating Enzymic Hydrolysis as a novel sludge treatment process that would meet the European Commission s aspiration for sustainable development. Blackburn was chosen as the demonstration site and since 2006 it has shown that the new technology is capable of destroying % of pathogens that posed a health risk. The treated product has low heavy metal contents and is in line with the proposed revision for Directive 86/278/EEC. The process is 2 to 3 times faster than conventional digestion processes; producing typically 24% more renewable energy and has the lowest unit cost and carbon footprint compared to the alternatives. 1 MAD refers to Mesophilic Anaerobic Digestion. 1. Introduction Every year nine million tonnes of sewage sludge are produced in Europe containing enough energy to meet the electricity and heating needs for 1.7 million homes. The residual solids could also be beneficially used to fertilise half the cereal crops in England and Wales, saving farmers over 260 million in fertiliser replacement cost. The trouble is, dealing with sludge is an environmentally sensitive issue. The application of sewage sludge to land is seen as the most sustainable solution to managing the growing quantities of sewage sludge produced across Europe (see Article 14 of the Urban Waste Water Directive 91/271/EEC) and has more recently received greater recognition for its value in agriculture as a fertiliser to improve soils. However, sludge is often perceived as a health risk due to the pathogens and heavy metals from of its faecal and industrial origins. The use of sludge as an agricultural product continues to remain an environmentally sensitive issue. There is a need to secure public acceptance and build confidence through regulatory compliance. The EU LIFE MAD but better project aimed at developing, implementing and demonstrating a novel treatment process that would meet the European Commission s aspiration for sustainable development. Specifically the project was designed to show that the process can: guarantee a safe, high quality soil conditioner and fertiliser. offer sufficient capacity to treat projected future sludge volumes, maximise biogas production as an important renewable energy source. LIFE05 ENV/UK/00124 Layman report Page 1 of 9

2 2. Background Treatment of sewage sludge presents a major issue in Europe where it has been the subject of controversy and political discussion. The need to develop and introduce advanced treatment technologies has become clear and was a major discussion point in the revision of Directive 86/278/EEC, the main regulation covering the use of sewage sludge in agriculture. In recent years sludge treatment has had a new focus aimed at improving product quality, achieving higher pathogen destruction rate and looking to treat greater quantities. A number of different techniques are currently employed across Europe for sewage sludge treatment such as drying, liming and the traditional Mesophilic Anaerobic Digestion process (MAD). However, such processes are costly, have high energy demands, and often cause public nuisance, due to odour. With respect to the health risk posed by sludge use in agriculture, in 1998 the UK Government brought the water industry, food producers and other interested parties together to address the issue. As a result the parties agreed a voluntary code of practice which came to be known as the Safe Sludge Matrix. The Safe Sludge Matrix protocol sets out the required treatment standards as follows: Conventionally treated means that sludge has undergone treatment to reduce its E. coli content by at least 99% and the final product has less than 100,000 E. coli count per g dry solid. Enhanced treated means sludge that has undergone treatment to reduce its E. coli content by at least % and the final product has less than 1000 E. coli counts per g dry solid. The product must also be free of Salmonella. Conventionally treated sludge will be used in arable farming applications where the land is ploughed, whereas for surface application the enhanced treatment standard is required. These requirements are very similar to existing regulations in North America. In an attempt to overcome the perceived risks, to address public concerns, and in anticipation of new, more stringent legislation United Utilities developed the High Rate Enzymic Hydrolysis (HREH) pre-treatment digestion technology. This was designed for retrofitting to any existing anaerobic digestion (AD) plants; AD being the preferred technology in Europe. The HREH offered the potential to provide the breakthrough in treatment technology to overcome the shortfalls of other existing technologies. 3. The Enzymic Hydrolysis process. United Utilities undertook a programme of research in the 1990 s which reviewed the characteristics and performance of the sewage sludge digestion process. Some key findings from this work were that the process was highly influenced by temperature and treatment time. At temperatures in the mesophilic range (32 o C to 42 o C), pathogens such as E. coli and Salmonella could be effectively eradicated over a period as short as two days. This compared with the traditional 30-day treatment by Mesophilic Anaerobic Digestion. Figure 1 shows the arrangements for: (a) conventional digestion (b) digestion with Enzymic Hydrolysis to achieve the conventionally treated standard and (c) digestion with Enzymic Hydrolysis to achieve the enhanced standard of the Safe Sludge Matrix. LIFE05 ENV/UK/00124 Layman report Page 2 of 9

3 Principle of Enzymic Hydrolysis Anaerobic digestion is a sludge stabilization process achieving odour, pathogen, and mass reduction. It comprises a series of complex biochemical reactions that convert organic compounds to methane and carbon dioxide. Each of the reactions requires a different temperature or acid/alkaline conditions for optimal performance. Conventional digestion typically involves the use of large single vessels that do not allow the conditions to be tailor-made for the different reactions. The United Utilities patented process makes use of of six small vessels in series allowing greater control of the reaction conditions to suit all the reactions. This enables the process to work faster and achieve greater gas production. a) Conventional digestion Raw Primary 16 o C 2ndary 14days Cake & Biogas b) Enzymic Hydrolysis Raw Heat 2 days@ 42 o C Digester 12 o C Safe Sludge Matrix conventional standard cake & biogas c) Enhanced Enzymic Hydrolysis Raw Heat Heat 1 day@ 42 o C 1 day@ 55 o C Digester 12 o C Safe Sludge Matrix enhanced standard cake & biogas Figure 1 Process flow diagrams for different digestion processes Plug Flow Reactors A multiple reactor design caters for the different component reactions since the condition in each reactor can be individually managed. By linking six completely mixed reactors in series a plug flow process is provided creating the necessary condition for natural selection of micro-organisms and optimum reactions. A plug flow design also minimises the total reactor volume necessary for digestion. Pathogen Destruction The liquors in the digestion reactors are toxic to pathogens such as E. coli and their destruction is accelerated by any increase in the reaction temperature. LIFE05 ENV/UK/00124 Layman report Page 3 of 9

4 4. Project Implementation The EU LIFE project MAD but better set out to demonstrate the benefits of the High Rate Enzymic Hydrolysis process by performing a real life, full scale test of the new technology at Blackburn. Blackburn is a major sludge centre for the Northern region. Every year the centre processes up to 13,500 tonnes sludge for 0.5M people from the Blackburn and South Lancashire area and safely recycles it to agriculture as a valuable soil conditioner and fertiliser for farmers. The introduction of the Safe Sludge Matrix at the end of 1998 provided new guidelines for the treatment of pathogens in sludge. As most of the accessible land bank within 25 miles of the works is grassland, this called for the highest standard of treatment. Since 2003 lime has been added to sludge after digestion for enhanced pathogen destruction to provide a greater safety margin. Long-term use of lime in sludge treatment is not sustainable because of its high cost, its tendency to increase product odour and soil ph as well as the greater volume at the end of treatment. The Enzymic Hydrolysis process is an ideal retrofit to the existing digesters because as well as ensuring that the required quality standard of sludge is achieved, it provides additional benefit in terms of increased biogas yield, reduced process time, reduction in weight of sludge to be transported and reduced odour. The project was part of the 7M ( 10M) investment in the Blackburn Sludge Quality Improvement Programme that commenced in March United Utilities with Engineering Services Provider, Montgomery Watson Harza undertook the design and project management. Project delivery was carried out by a partnering arrangement with an Alliance Framework Contractor; a consortium with all the resources needed to deliver a complex engineering project on a live existing operational site. The contractor was a consortium of Kier Construction, Murphy Pipelines and Interserve. Additionally United Utilities has a framework agreement with Monsal which is a specialist contractor used to supply Enzymic Hydrolysis plant and all that is required for control of the process. Construction of the plant began on 15/01/2005 and was completed by 01/08/2005. Figure 2 The Blackburn Enhanced Enzymic Hydrolysis plant The project partner was AnoxKaldnes AB, a leading research and development company based in Lund, Sweden. AnoxKaldnes brought to the project an independent high-level understanding of biochemical processes involved with sewage sludge treatment and it would be able to evaluate and report on the process performance. As a project partner AnoxKaldnes has been fully involved in the Demonstration and Monitoring programme and dissemination activities. Together LIFE05 ENV/UK/00124 Layman report Page 4 of 9

5 United Utilities and AnoxKaldnes had joint responsibility for the Demonstration and Monitoring programme. The Demonstration and Monitoring team comprised of members from both organisations. The programme was carried out over an 18 month period (January 2006 to June 2007) to assess whether the expected results have been achieved. The programme was also designed to demonstrate that the process can be easily retrofitted to an existing treatment plant. 5. Technology performance 5.1 Technical indicators By the end of the project the majority of the specific objectives had been achieved. During the demonstration period the Blackburn sludge treatment process had operated successfully with digestion time from 10.2 days to 16.8 days. Since secondary digesters were not required for extra pathogen reduction, this has resulted in digestion rates 2 to 3 times faster compared to traditional digestion processes. The project has demonstrated that for enhanced pre-treatment, the observed E. coli removal was % and Salmonella were eliminated in line with the proposed revision for Directive 86/278/EEC. E coli (cfu/gds) 7,000 6,000 5,000 4,000 3,000 2,000 1,000 0 Conventional mode Enhanced mode change over D2 D3 D4 01/01/06 02/01/06 03/01/06 04/01/06 05/01/06 06/01/06 07/01/06 08/01/06 09/01/06 Figure 3 - E. coli in digested sludge with EH and EEH pre-treatment. (Note that D refers to measures at different digesters of which there were four at Blackburn) The energy recovery efficiency of the Blackburn digestion plant was found to be in the range 57 63% which is excellent compared with the usual 30-50% range typically achieved by traditional digestion processes. The Blackburn sludge was analysed and was found to have a high level of carbohydrates with only a small amount of fats which accounted for its low Calorific Value. While fats and proteins are readily converted to biogas in the digestion process, the carbohydrate fractions which made up the bacterial cell wall were extremely resistant to enzyme attacks. Greater energy recovery can be expected for other waste streams such as food wastes which contain few bacterial cells. Overall, 8,490 tonnes of treated sludge (dry solid basis) as a cake product were produced. The final product met all the requirements of the quality assurance process designed to reduce the risk of non-compliance with regulatory compliance standards according to the Hazard Analysis Critical Control Point guidelines (HACCP). LIFE05 ENV/UK/00124 Layman report Page 5 of 9

6 The observed nutrient levels were within the normal range for a digested cake product. Heavy metal contents of sludge cake were shown to be well below the limits set by the European Council Directive 86/278/EEC Sewage Sludge Metal Level Standards (EU) and US Environmental Protection Agency (EPA) heavy metal limits in biosolids for agricultural use. The final product proved to be an excellent soil conditioner that was environmentally friendly and safe. Cake from Blackburn has been recycled mainly within the Fylde area of Lancashire. During 2006 the enhanced treated cake has been used as a seedbed fertiliser for maize and cereal crops. The product has made a significant improvement in odour performance. It has proved to be of low odour and has provided the opportunity for surface spreading on grassland, even in close proximity to residential areas. Increasingly, the ability to produce a low odour product will help to make sludge recycling more sustainable where the land bank is limited and more acceptable to the public. 5.2 Environmental indicators An Environmental Impact Assessment of the Blackburn sludge treatment scheme was carried out by WRc consultants on behalf of United Utilities. This was done by a determination of whether it was the best available technology (BAT) and best practical environmental option (BPEO). WRc used the MASTAR computer model to estimate and compare the costs and environmental impact of a number of different sludge disposal options. The study found that the Enzymic Hydrolysis was the most favourable option in terms of combined cost and environmental impact for an existing digestion facility. 2,000 1,800 1,600 1,400 1,200 1, GREEN HOUSE GAS EMISSIONS Net kgco2e per tonne DS Conventional digestion EEH digestion Liming Incineration Figure 4 A comparison of the carbon foot prints for the major sludge treatment options 5.3 Economic indicators In the UK over 65% of the total sludge quantity is recycled to agricultural land. The challenge in moving forward, however, is how to achieve even greater recycling, and to do so in an environmentally, economically and socially sustainable manner. An economic analysis of the Blackburn project has been carried out. Since Blackburn already has an existing infrastructure, where an item of equipment is already in existence, the capital cost (CAPEX) is shown as an estimated replacement cost (+/- 30% accuracy). Table 1 shows the estimated capital cost for a new sludge treatment centre at Blackburn. The estimated running costs for the sludge treatment centre are shown by Table 2. As typical for digestion projects, the digester cost (including heating) accounts for about 30% of the capital investment. The high capital cost also LIFE05 ENV/UK/00124 Layman report Page 6 of 9

7 means that the interest payment accounts for almost 50% of the revenue costs. Recycling cost (transport and spreading) only accounts for 15.7% of revenue expenditure. Interestingly, the sale of electricity with the renewable credit offset the running costs by over 25%. Overall, the unit disposal cost equates to 166 ( 240) per tonne DS. This compares very favourably with the current average landfill cost of 288 ( 418) per tonne DS (based on gate fee of 60 ( 86) per tonne cake plus the costs of cake pressing and transportation). It should be noted that in the UK it is common practice to supply sludge products to farmers free of charge. Sludge contains plant nutrients and organic matter useful in improving soil structure, drainage and water holding capacity. They are good sources of nitrogen, phosphorus, sulphur and various trace elements. The use of sewage sludge typically saves 120 ( 175) per hectare in fertiliser replacement for farmers. Table 1 Estimated capital cost for a new sludge treatment project at Blackburn (Average throughput 540m 3 /d (740m 3 /d peak) and 13,403 tds pa capacity) Items Cost basis Cost ( 000) GBT Units Replacement 1,684 EEH plant Actual 2,200 Digesters Replacement 3,006 Centrifuges Replacement 2,384 Boiler heating mixing Replacement 1,071 CHP units Actual 1,477 Sludge storage / pumping Replacement 509 Gas storage and treatment Actual 916 Flare stack Actual 57 Land purchase N/A Subtotal 13,304 Interconnecting pipework 18.5% C & M 2,114 Ground Conditions 6% C 337 Location Costs 1.6% C 90 Design & Management 7.5% subtotal 998 Installation & commission 12.5% subtotal 1,663 Total Capital cost ( 000) 18,506 Table 2 Estimated running costs for the sludge treatment process at Blackburn Items Cost basis Cost ( 000) Interest 6% capital -1,110 Depreciation Linear -420 Manpower 1.5 man -75 Polymer 8kg/tds -295 Electricity 0.05/kWhr -153 Maintenance 5%MEC&I -384 Recycling cost 10/tonne cake -348 Electricity income Include ROC credit 566 Total revenue cost -2,220 Unit cost /tds -166 LIFE05 ENV/UK/00124 Layman report Page 7 of 9

8 6. Dissemination Dissemination was a key aspect of the project both in informing regulators, water industry, energy industry and agriculturalists about the process and its capability as well as securing public confidence in the use of sewage sludge in agriculture. Those visiting the plant included water engineers and scientists from regulatory bodies and from water companies, energy technologists as well as farmers and members of the public. During the completion and implementation of the Blackburn Enhanced Enzymic Hydrolysis project some 150 visitors had been to the site. They came from 9 countries worldwide including the European countries. A visitor centre was established on the site and a brochure was provided in English, Polish and German language. Dissemination will continue beyond the LIFE project by involvement with presentation of technical papers at conferences and by hosting visits to the site. The UK has over 500 digesters which currently do not have any form of pretreatment. They suffer from ineffective pathogen reduction performance and poor energy recovery. The EU LIFE MAD but better project has demonstrated that High Rate Enzymic Hydrolysis can be easily retrofitted to an existing treatment plant. This provides the industry, both in the UK and EU as a whole, with a good opportunity to improve the safety of the treated sludge while enhancing energy recovery. The operation of Enzymic Hydrolysis will also eliminate the emissions of green house gases from secondary digesters which currently make up a significant proportion of the industry carbon foot print. During the demonstration period many visitors have come to Blackburn to see the new technology in operation. As a result five Enzymic Hydrolysis plants for sludge pre-treatment have been purchased by other water companies. The potential for further retrofit for existing treatment facilities across Europe and North America is excellent. As of August 2007 four Enzymic Hydrolysis plants had been built and commissioned by United Utilities and five other plants had been ordered by other UK water companies three of which were undergoing commissioning. Interest is also being shown from countries outside the UK. United Utilities has also looked at scaling the plant down to enable it to meet the need of small rural communities as well as for industries which produce energy rich streams that could be exploited (e.g. food, pharmaceutical, paper). Figure 5 Digested sludge cake Figure 6 Spreading cake to land LIFE05 ENV/UK/00124 Layman report Page 8 of 9

9 Figure 7 The Blackburn Combined Heat and Power plant (1MW capacity) Figure 8 Wheat grown on sewage sludge fertilised land (middle plot = control) United Utilities acknowledges the contribution of the LIFE Financial Instrument of the European Community. LIFE05 ENV/UK/00124 Layman report Page 9 of 9