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Biogas by Bioaugmentation

Centralised waste management and resource recovery complex for agricultural wastes in Landal, Portugal

Abstract: The project is an innovative concept in that agricultural effluents, wastes and residues from multiple sources are delivered to a central treatment plant, in which the design is based on the Everstech ETä principles of resource recovery and total waste management, incorporating: two stage anaerobic digestion; aerobic fermentation; anaerobic composting; solids dewatering; and filtration, leading to energy generation, organic fertiliser production and water recycling. The generation of by-products is optimised with complete odour control whilst treating the wastes by the introduction of selected microbial cultures under the principles of bio-augmentation, developed by Everstech. The resources recovered or generated will be potentially: 72 megawatts of electricity from the biogas per day; 20 tonnes of high nutrient organic fertiliser for export; and 80% of water recycled.

1. Waste Management and Resource Recovery

At every step along the overall food chain, from farm to table, every operator aims primarily to produce with maximum efficiency one or more marketable food items. Efficiency suffers, however, because each process involved—growth, manufacture, distribution, preparation—is inherently wasteful, i.e. the food passed on to each succeeding stage contains only some of the biological material received from the preceding one. Whenever an economic use can be found for this misplaced material, it is generally described as a “by-product”. Whenever an economic outlet is currently unavailable, it is a “waste.”

Organic, agricultural and food processing wastes present a twofold problem—that of disposal and that of resource losses. Large quantities of potential energy, protein/fertiliser and water are abandoned after considerable time, effort and money has been expended on their production. Recovery of these resources poses a considerable challenge.

EversTech has developed the ET treatment system, together with purpose bred range of microbial formulations, in order to meet the challenge. Accumulating experience seems to be indicating that the successful solution to any individual waste management problem is unlikely to involve just one single process, but rather a combination of processes.

2. Project Development

Landal is a small “freguesia” (parish) located in the east side of Caldas da Rainha municipality. Nearly 1.900 people live in Landal, in a total area of about 2.000 hectare. The main economic activities in this region are agriculture (fruit trees and vines) and animal production (pigs, broilers and quails). The animal production farms and other related industrial activities generate wastes in such a quantity and quality that, sometimes, an appropriate management of those residues is difficult. This results in solid wastes and liquid effluents, with high pollution loads, being inadequately disposed of or discharged into the surrounding environment.

To solve this problem, a group of animal producers in Landal, Portugal, formed APAL, the Association of Animal Producers of Landal, and later AMBILANDAL S.A., the managing company, with the purpose of building a centralised treatment plant. With the support of the Centro para a Conservação de Energia (CCE) and of the EU ALTENER programme, a project has been developed under the 5th Framework Programme (sub-programme ENERGIE) as a professional joint venture, with Everstech Consulting & Process Design of the UK, the design and engineering partner. A consortium is being set up to arrange financing of the project.

The register of potential users of the joint plant are all animal producers and industries in Landal and the surrounding regions. The operation will have the necessary means and treatment capacity to extend its action to other waste production centres in at least a 10 km radius of the treatment plant.

Users of the joint treatment and resource recovery plant will have to comply, by contract, with the specifications and regulations of the plant, providing all of their waste to AMBILANDAL, who, in exchange, will be responsible to the authorities for the adequate treatment and final destination of the treated residues. The technology to be implemented will promote maximum resource recovery through the production of biogas and organic fertiliser. The biogas will be used to produce electricity and heat (hot water), both to be used in the plant and/or sold to the grid or industrial users nearby. The biosolids material will be bagged and sold as a nutrient rich wholly organic fertiliser.

The economic value of the recovered resources will be enough to pay for the operation and management costs, thus assuring self-sufficiency of the plant. This way, the users won’t have to pay for treating their wastes. The major resource recovered will be electrical energy from the biogas, supplying the grid and the plant to an annual value of approximately 785,000 euros/year.

The discharge of the treated liquid effluents in the Rio da Sanguinheira will comply with standards set down for environmentally sensitive areas. The technical performance of the treatment system is guaranteed by Everstech, based on the quantity and quality of the input wastes.

3. Wastes in Landal

A survey was performed to assess the actual number and type of waste production centres in Landal and, at the same time, determine the characteristics of the wastes to be treated in the centralised plant. Results showed that, in a 4 km radius, a large number of small and medium size animal farms exist, as presented in Table I.

Table I—Number of farms and abattoirs, animals and waste in the Landal region

The initial design of the installation was based on the results from the field survey on the animal farms and related industries in Landal and on the amount and characteristics of the wastes produced. However, the final design parameters used in the project resulted from the incorporation of a 50% additional capacity, due to the likely reception of wastes from other users in a 10 km radius. This way, over 100,000 tonnes/year of waste can be processed in the Landal plant.

The wastes will be transported by road to the joint plant in Landal and put into appropriate reception tanks. Then, the different type of residues will be blended, together with recycled treated water, in such proportions as to enable a final mixture with suitable characteristics to be efficiently processed in the plant. The average COD of the mixture will be in excess of 100,000 mg/litre.

Table II—Average characteristics of the input to the plant from the balance tank

4. Treatment and process descriptions

The waste management and resource recovery system for Landal has innovative characteristics, particularly the use of bio-augmentation for optimised production of biogas and maximum quality of biosolids for recovery. The use of this resource recovery technology in communal waste management requires, in the first place, the availability of large amounts of suitable organic waste at the right price, and in the right place. The technology is available now, and its application is this project.

Probably the most significant contribution to economic pollution control and the justification for the current activity in this area is the relatively innovative concept of turning liabilities into assets, and maximising those assets through bio-augmentation, combined with leading edge resource recovery technology. Effectively making real and significant profits from what is considered an interminable nuisance and the accepted waste problems arising from agriculture and food production.

The innovative approach is based on three main aspects:

• thermophilic anaerobic digestion of the liquid sludges to generate biogas utilising bio-augmentation to accelerate the digestion process and give a higher quality and cleaner biogas (80 % CH4 and no H2S). The addition of selected bacterial cultures in a preliminary digestion stage increases biodegradability of the wastes and improves biogas production more than 30%, with shorter retention times (6 to 7 days).
• anaerobic composting (also using bio-augmentation) of the solid fraction, mixed with some slurry, to give an ideal compost and more biogas to increase the yield from the system. The solid fraction will be anaerobically composted in a closed reactor with biogas collection, after further addition of bio-cultures.
• aerobic treatment of the liquid effluent after separation of the digested solids, again utilising bio-augmentation to optimise the quality of the biosolids for recovery or blending, leaving a discharge complying with the most stringent standards. The surplus sludge generated (biosolids) is concentrated in nutrients and can be regarded as an organic fertiliser of the highest quality or as a protein feed.

Fig.1—Simplified schematic for the centralised plant for Landal

Finally, the three by-products of the resource recovery, incorporating bio-augmentation, will be:

• Biogas of approximately 80% methane, which will be burnt to generate electricity for on-site use and for sales to the grid.
• High quality biosolids to be bagged and sold as a fertiliser under its commercial name of "FERTILANDAL."
• Water for recycling within the treatment plant for process usage. Surplus treated water will be discharged into the nearby Rio da Sanguinheira and will comply with the Portuguese Law D.L. 152/97 in accordance with the following table:

Table III – Final effluent discharge

5. Bioaugmentation

Bio-augmentation or Bacterial Supplementation, a branch of Biotechnology, is the controlled addition of selected organisms, characterised by their unique properties, into an environment to carry out a specific objective, a technique well-known in wine making, brewing, cheese and pharmaceutical manufacturing etc. With an adequate "food supply", bacteria will grow, reproduce and manufacture the enzymes, for example, necessary for the biological stabilisation of the waste material.

A naturally occurring microbial population will consist of thousands of species of bacteria, algae, protozoa and fungi, all fighting for food and survival. The more adaptable and abundant species will metabolise and eventually dominate the system at the expense of the minor populations of micro-organisms. It is quite probable, however, that the thriving bacteria are not the most desirable strains to efficiently stabilise the particular waste products.

By the very nature of waste waters and their complex biochemical interactions, the full scientific explanation of these processes is in its infancy. Our microbiologists, in researching this field, have made considerable progress in determining some of the metabolic pathways and, in doing so, have been able to identify many of the unfavourable organisms present contributing to the problems and isolating more favourable species for substitution.

The general direct and indirect benefits of bio-augmentation are: REDUCTION OF CAPITAL AND OPERATING COSTS | REDUCTION IN EFFLUENT COD, BOD5 AND SUSPENDED SOLIDS | ELIMINATION OF OIL AND GREASE | EFFECTIVE ELIMINATION OF ODORS | ELIMINATES HYDROGEN SULPHIDE PROBLEMS | IMPROVED SETTLEABILITY OF SOLIDS | IMPROVED DIGESTION OF ORGANIC MATTER | FASTER RECOVERY FROM UPSETS.

Bio-augmentation will provide more predictable results. Being able to control the bacteria present in a waste treatment plant or substituting more desirable micro-organisms for naturally occurring ones is a step towards controlling the nature of the biomass itself, which will give greater predictability of the plant and again, knowing the organisms will not die as a result of shock loads or mechanical failures, this will give the waste treatment plant a greater working tolerance.

6. Economics of the Landal Project

The appropriate energy utility is obliged to buy all the electricity produced by any renewable energy producer. The price per kWh is independent of the installed power and will increase according to the inflation rate. A continuously working generator (24h/day) will sell electricity at an average value of 0,065 Euro/kWh. A generator operating only during the high load hours (8 to 22 h in Summer or 9 to 23 h in Winter) will be able to sell the electricity at 0,076 Euro/kWh. If operating only in the low demand hours, the average price of electricity sold will drop to 0,038 Euro, the bottom of the scale.The current price of the electricity bought from the grid is averaged at nearly the same (0,065 Euro) for a typical plant operating at medium voltage.

The market for selling organic fertilisers is yet at its early stages in Portugal However, following a 10 year marketing programme, it can be stated that the minimum price that can be considered for selling fertiliser made from the digested biomass would be, at least, 75 Euros per tonne of cake produced (65% moisture content). This is at the very bottom of the price range and is for bulk quantities only. The process plant includes a blending, pelletising/granulating and bagging unit, which will produce a commercial product as ‘FERTILANDAL’. The price of ‘FERTILANDAL’ in the UK could be anywhere between 2,000 - 1,400 Euros per tonne of product according to physical specification and packaging. The biomass (organic fertiliser) product can be exported to the UK and Europe and Ambilandal will ensure that contracts are in place to take it on a commercial scale, before the treatment plant is completed and commissioned.

Table IV—Comparison of recovered resource yields

NOTE: The higher levels of biosolids generated per kilogram of COD reduced are contrary to the normal targets of a conventional treatment plant, but this is what the ET process is all about—producing as much recoverable material that has a commercial value as possible, making the economics of the process very attractive. The higher quality biogas is as a result of the superior design of the two stage anaerobic digestion within the process, and the utilisation of selected bio-cultures in an overall bioaugmentation programme.

Table V—First year projected income and expenses for the Landal plant

Income does not include the value of heat energy recovered, which would be about 1.28 times that of the generated electricity. A Gate Fee is charged to late-comers to the scheme. The capital cost of the full plant as a turnkey contract will be approximately 5 million Euros, giving a payback period of about 3½–4 years.

NOTE: Since this paper was prepared, the design capacity of the plant has been increased by 50%, with a further 50% in reserve, due to the immense interest generated and the Government’s support in encouraging Central Waste Management facilities, eliminating small, inefficient and poorly managed individual units.

Because of the interest, further centres at other sites are now planned.

Authors: D Evers, Principal, EversTech Consulting and Process Design
P.J. Santos, Consultant, CCE Portugal