Fish waste management has been one of the problems having the greatest impact on the environment. Fish farming detrimental effects on the marine environment in particular have become an issue of public concern. In European Union, numerous Directives, Decisions and Regulations were voted in an attempt to minimise the environmental impact of fisheries within the frame of Integrated Coastal Management. Treated fish waste has found many applications among which the most important are animal feed, biodiesel/biogas, dietic products (chitosan), natural pigments (after extraction), food-packaging applications (chitosan), cosmetics (collagen), enzyme isolation, Cr immobilisation, soil fertiliser and moisture maintenance in foods (hydrolysates). In this review, an update of both environmental impact (inputs and outputs) and treated fish waste uses is provided by means of six comprehensive tables and seven figures.Keywords Animal feed, biogas, environmental impact, fish waste uses, input and output of fish processes.

Food industry will have to focus on waste avoidance as well as utilisation of process waste. Application of clean technologies greatly enhances the safety and quality of the product as well as reducing the energy requirements and environmental impact of the food industry. The main environmental impacts of the food sector are aquatic, atmospheric and solid waste emissions. Nowadays, the main treatment method of solid wastes is composting, while recovery and reuse of by-products and wastes as raw materials stand for another effective option (http:// www.oulu.fi/resopt/wasmin/pap.pdf). Composted olive oil waste can find applications (1) as amendment in agriculture because of its high nitrogen and phosphorus content, (2) as a biofertiliser, with a mixture of compost with Sphagnum peat or commercial substrate finding use for ornamental plants growth and (3) as a biofilter for toxic metal removal. However, there are a number of disadvantages as well, such as large decline of soil germination capability, necrosis of the leaves and slow emission of secondary stems, and enhanced phytotoxicity, because of pH neutralisation technique, which should be seriously taken into account prior to opting for composting as a promising waste treatment alternative.

Since olive oil industries were considered responsible for a great amount of pollution there has been a strong need for optimization of olive oil waste treatment systems. The currently employed systems are numerous and fall in the following large categories; bioremediation (ex-situ, in-situ), thermal processes (incineration, pyrolysis, gasification), evaporation, membrance processes, electrolysis, ozonation, digestion, coagulation/flocculation/precipitation, and distillation. Both advantages and disadvantages in conjunction with respective methodology and explicit flow diagrams were presented per waste treatment method. Furthermore, most recent studies were reported and more than twenty-five figures showing mainly the effectiveness of the current waste treatment methods versus time or temperature were displayed. The comparative presentation of the various olive oil waste treatment methodologies showed that though bioremediation stands for the most enviromentally friendly technique, its required longer treatment time in conjuction with its weakness to deal with elemental contaminants makes imperative the employment of a second alternative technique which could either be a membrance process (low energy cost, reliability, reduced capital cost) or a coagulation/flocculation method because of its low cost and high effectiveness. Biogas production appears to be another promising and energy effective waste treatment method. On the other hand, methods like distillation and ozonation (high cost) and electrolysis (experimental level) are unlikely to dominate this field unless their high cost is substantially reduced in the near future.

The ongoing stricter policy rules on environmental issues, recent changes in consumer towards the environmental effects of food production, and even stricter regulations voted by the European Union towards reduction of the use of natural resources initiated a great amount of research towards improving the thermal waste treatment methodology. The olive oil industry continues to be one of the most heavily polluting ones among the food industries. Along this line, various thermal processes, such as pyrolysis, combustion and gasification, were investigated. Another crucial issue is the fate of treated waste. This review, apart from the presentation of various thermal treatment waste methodologies summarises the uses (either currently ongoing or having potential in the future): biodiesel, activated carbon and briquette production. Ten figures and four tables illustrated in this article provide comprehensive idea of the waste treatment methodologies, their effectiveness and uses of thermally waste treated olive materials.

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