The solid waste generated during leather making is significant. While the leather industry is making use of a byproduct from the meat industry, only 20% of the raw material ends up in the finished leather. This creates a huge environmental challenge for the modern tannery as the traditional options for the disposal of this waste may become cost prohibitive in the future. Waste can be viewed as a valuable resource as either a substrate for the production of value added products or as a fuel.

Adding value to waste

Research is ongoing as part of the EU collaborative project RESTORM on the utilisation of the protein-containing solid waste from tannery and beamhouse production to create value added products. The resulting products have several potential uses in both agricultural and building industries.

Chrome shavings were treated enzymatically in the presence of low molecular weight organic amines. The process is a two-stage hydrolysis and takes place using the organic amines such as isopropylamine, di-isopropylamine, cyclohexylamine and ammonia. The products are protein hydrolysate and chrome cake.

There are several possible applications for the hydrolysate produced by this process. One of the simplest applications of the hydrolysate is as an organo-nitrogeneous fertiliser in the agricultural industry. Trials have been carried out in conjunction with the Regional Department of Soil, Agrochemistry and Plant Nutrition at the Agricultural Control and Testing Institute of the Czech Republic.

The tests were carried out using prepared hydrolysate and a commercially available fertiliser, Lodovan. This product is a blend of ammonium nitrate and urea in a 1:1 ratio based on their retrospective nitrogen contents. The crop used was lettuce and both fertilisers were used keeping the mass of nitrogen constant within the dosage. A comparative control was also included using unfertilised soil.

The yield of lettuce was evaluated and the percentages of nitrates measured in the crop of each trial. Substantial differences were found in yield and particularly in the nitrate content of the lettuce. The results can be seen in Table 1In conclusion the hydrolysate showed a very positive effect on the yield of the crop with a markedly higher value as a food stuff due to a much lower nitrate content.

Another agricultural application was in the use of ‘sowing tape’. This is used to avoid the necessity for laborious thinning of seedlings. Specially treated seeds were fixed, at optimal distances, on biodegradable sowing tapes. Machine sowing requires that the tapes have good mechanical properties and meet soil conditions for optimum seed sprouting. For this reason the normal polyvinyl alcohol (PVA) tape was modified by blow moulding molten PVA with protein hydrolysate. The resulting tape shows considerable improvement in mechanical properties and has a lower cost, as the hydrolysate is 50% of the price of PVA. In addition the extra organic nitrogen added is slowly liberated into the soil and acts as a fertiliser.

The hydrolysate also has a wide range of potential applications within the building industry such as an admixture in concrete, in protective coating for buildings, in the production of thin walled surface finishes, in the manufacture of prefabricated powdered materials especially for surface finishes. Work has been carried out adding a 50% solution of the protein hydrolysate to commercially manufactured adhesives used in the wood industry. By the addition of small amounts of hydrolysate, between 1% and 5% on the weight of the adhesive, there was a great reduction in the amount of free formaldehyde liberated during the manufacture of chipboard and plywood. There was also a significant improvement in the bond strength of the wood.

Waste is energy

There are two options for the use of waste hide (protein and lipid) as a fuel. It can be dried and used as a fuel source in a thermal treatment process such as gasification or it can be converted to a fuel, referred to as biofuel, through a chemical or biochemical conversion process.

In terms of thermal processing, BLC has been engaged in an extensive programme of research and development aimed at developing a gasification process that can convert organic waste from the leather making process into energy.

While gasification technology has been in existence for a number of years, its application for the treatment of industrial biomass is relatively new and many substrates remain untested for this application. Significant research and engineering development has resulted in a system that will convert leather waste within a robust, safe and economically attractive process to a source of energy that can be converted to heat and/or power.

The process has now been evaluated commercially in conjunction with a new industrial partner, Biomass Engineering ( Biomass Engineering were established in 1996 to research and manufacture biomass-fuelled combined heat and power (CHP) systems. The company focuses on the relatively small-scale one megawatt and sub-megawatt systems for de-centralised as well as national grid power generation. Recently they won the United Utilities Low Carbon Award, distinguishing them as a company that has already been successful in reducing carbon dioxide emissions through renewable energy generation.

Biomass Engineering have developed four prototype units and supplied their first customer unit to Ballymena ECOS Millennium Centre in Northern Ireland in early 2000. Since then the company has gained a great many hours of operational experience and begun to expand their area of expertise into the global market. The result of the relationship between BLC and Biomass engineering has been a system specifically designed for the leather industry, though still adaptable to other sectors. The pilot plant is capable of treating around 75 kg/h of waste depending upon its characteristics. The scale of a full size plant would vary up to the one megawatt unit that would treat around 24 tonnes per day, so the capabilities of the system are very flexible.

With several hundred hours of operation on leather waste to demonstrate its capabilities, interest in the new gasification pilot plant has been growing. This interest has been taken one step further by one forward thinking UK leather tannery, and they have been conducting on-site trials now for several weeks. Initial results have been very encouraging. The picture opposite shows the plant in operation.

Initially the gas produced during these trials is to be flared off, though there are options to recover it in the form of heat or for use in the production of electricity in conjunction with a gas engine.

Figure 1 shows a temperature profile of the flare stack that is consistent at between 400ºC and 500ºC. Figure 2 demonstrates the profile of some of the principal product gas constituents. In particular the methane content is notably high at between 6% and 10%. This helps increase the calorific value and hence the heating or electricity production value of the gas. Both of these sets of data were gathered during runs on buffing dust. However, although wastewater effluent sludge is more difficult to treat, initial results have shown a performance that is comparable to that on buffing dust demonstrated here. Further runs will be required, but as the trial progresses further reports will be published.

Biological fuels of the future

The production of biofuels from leather waste is a new area of research. BLC is currently running two projects investigating the conversion of protein rich waste to an ethanol based transport fuel and lipid waste to a diesel type fuel.

It is reported that over 1 million tonnes per year of (protein-based) animal byproducts, hides and catering wastes are generated and disposed of each year in the UK alone. It is widely known that some 50% of an animal carcase weight on arrival at an abattoir becomes waste material, requiring specific treatment and regulatory activity.

Biofuels are a renewable source of energy. These have the potential to reduce the amount of waste generation and at the same time produce fuels (like ethanol and diesel) which can be used as a renewable energy source.

Proteinaceous waste, particularly from animal byproducts are a potential source of biomass for energy from waste or renewable energy generation. The success of projects such as this will demonstrate that protein substrates can be converted into biofuel, especially ethanol, for transportation fuel. This concept of producing fuels from waste will have a positive impact on alternative energy production worldwide.

Bioethanol is an alcohol product produced from corn, sorghum, potatoes, wheat, sugar cane, even biomass such as cornstalks and vegetable waste. When combined with gasoline, it increases octane levels while also promoting more complete fuel burning that reduces harmful exhaust pipe emissions such as carbon monoxide and hydrocarbons.

The advantages of this fuel type are

– Domestic, renewable fuel source

– Reduced reliance on foreign oil

– Cleaner fuel source

– Increases fuel octane for little cost

– Useable in virtually all vehicles

– Easily produced and stored

– Biofuels emit 40-80% less greenhouse gas emissions than fossil fuels

– Bioethanol is environmentally superior to all other major fuels

– Acid rain reduction

– Improved urban-air quality

– Less water pollution

– Less waste

The quantity of protein/animal by product waste generated in the UK, that could be used for the generation of bioethanol by the process under investigation, exceeds 1 million tonnes/year.

Current disposal routes for this material vary from composting (small and subject to increasing animal byproduct regulation), incineration (controlled eg specific risk materials (SRM materials)); or disposal to ordinary landfill – subject to increasing regulatory restrictions (Animal By-Product Regulations). The cost of disposal of this material is increasing each year in line with landfill taxation and the requirements of the EU landfill directive. This directive requires reduction in biodegradable waste disposed to <50% of the mass disposed in 1995. In real terms this is a reduction requirement to ~35% of current levels. The disposal demand from the UK industry is increasing due to the limitation in economically viable routes.

In addition to the prime wastes, other process wastes, eg greases, generated from tallow recovery or rendering, also require disposal. Some of these can be regarded as being SRM materials and as such could necessitate expensive incineration-based disposal. These waste streams may be small nationally, but are important on a site-by-site basis as the cost/ tonne is disproportionate to other waste streams.

Ethanol demand in the EU for 2003 was over 400 million litres, which represents 25% of the European Union gasoline market. Production is expected to grow over the next seven years to cover the demand derived from the targets indicated in the new European Directives, as refiners switch from (methyl tertbutyl ether) MTBE to ETBE (ethyl tertbutyl ether) production, and 5% direct blending is introduced in the market.

Future growth in demand will result from the EU’s long-term alternative fuels target of 20% substitution by 2020.

A literature review, including review of a draft report (Imperial College London) and with reference to US-based publications, illustrates that the market value of ethanol is in the region of 30p/ litre. This is in addition to latest C&E duties, at 50p/ litre taking the cost to the equivalent of gasoline. However, 100% alcohol applications are unlikely, given changes required to engine management systems.

A blend, eg 10% Ethanol + 90% gasoline, would reduce gasoline dependency and provide for cleaner burning. The cost difference between ethanol and gasoline would be favourable for this application.

Ethanol demand in the US for 2002 was 2.14 billion gallons. In 2003 ethanol production increased to 2.9 billion gallons. Production is expected to grow at an annual rate of 18% over the next five years as refiners switch from MTBE to ethanol in reformulated gasoline, and the Renewable Fuel Standard included in the Energy Bill is finally approved.

Expected ethanol demand

As MTBE is gradually replaced by ethanol, potential demand for ethanol could reach 4.2 billion gallons, ie 1.5 times the current market. The largest increases would come from the East Coast, California and the Gulf Coast.

In any of the potential scenarios, it is believed that demand will match at least the minimum required in the RFS, which will allow this industry to grow up to 5 billion gallons by 2012. The world market for ethanol cannot realistically be quantified.

Research is ongoing at BLC to demonstrate the novel conversion of protein into ethanol via hydrolysis (enzymatic and alkali), followed by application of a novel fermentation system. This system is purported to convert amino acids to alcohol as a natural byproduct. The research requires a 2m3 scale reactor plant to enable realistic and sensible results to be generated.

The aim of the project is to test the feasibility of producing ethanol from a protein waste substrate via high temperature fermentation. The ethanol will be tested for suitability as a renewable transport fuel.

The aim is primarily to test the technical innovation, then to assess the economic potential and explore opportunities for application to the market within the next few years.

The future application of this proposed technology would alleviate the regulatory burden as well as the fiscal burden on this sector, especially in the UK. Thus, assuming the process is successful, and after hydrolysis and fermentation, ~1 litre of ethanol is generated from 1kg of protein, potentially up to 1,000,000,000 litres of ethanol could be generated from this waste stream/year. At a market economic value of ~ 10p/ litre, this is equivalent to ~ £100,000,000/year of ethanol as a benefit to the current waste producers.

BLC, in association with four industrial partners, is also carrying out research aimed at investigating the feasibility of biodiesel synthesis from waste animal fat, tallow, from the leather industry. A successful outcome of the project would offer a biotechnological route to converting waste, with the associated disposal costs, to a saleable product.

The intention is to convert chemically and mechanically extracted tallow, from abattoir and tannery wastes (eg from aqueous degreasing), into a biofuel within bench scale reactor vessels via enzyme- mediated alcoholysis.

The novelty of the work lies in the use of a tallow/free fatty acid feedstock and application of suitable lipase enzymes to facilitate a biochemical rather than chemical conversion, which should require a minimal chemical input (alcohol) and produce minimal byproduct residue. The advantage of lipase-catalysed reactions are that feedstocks with high free fatty acid contents, such as tallow, are not ideally suited to the conventional chemically-mediated esterification reactions and, consequently, conversion efficiency is poor. A further advantage of the enzyme system is that the activity is site-specific, thereby reducing the potential for unwanted byproducts or incomplete conversions.

The aim of the project will be realised through a number of steps including:

l characterisation of tallow from different sources in terms of fatty acid and triglyceride composition l construction of bench-scale plants to evaluate and optimise the conditions for alcoholysis and compare chemical and lipase-mediated esterification

– screening of lipases for tallow esterification

– characterisation of the biodiesel

Currently, there is no commercially viable process for converting such animal residues (tallow/fat) into biofuel in the UK. The UK Rendering Association estimates that over 200,000 tonnes of tallow are derived from animal carcase rendering annually. This is in comparison to some 60 million tonnes of tallow/fats globally. This material is either disposed of or sold as a low grade raw material for industrial application.

Conversion of this waste substrate to a biofuel (tallodiesel) could contribute a small proportion to the current UK diesel consumption and has potential worldwide commercial applicability. Other applications for fuels derived in this manner could include replacement of domestic heating oil and application in stationary CHP generation.

Similarly acquired biodiesel, from chemically-induced transesterification of oil crops or waste oils, has previously been shown to produce lower emissions than fossil fuel derived diesel in conventional engine applications.

It also contributes to a solution for UK and EU disposal problems of animal byproducts and the fatty products of surfactant-based aqueous degreasing of hides and skins and provides, through utilisation of an existing resource, an alternative to the associated costs of ‘energy crop’ production.